Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.langmuir.4c01584

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s10965-024-04059-4

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.polymer.2024.126906

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.polymer.2023.126558

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Scientific Reports  

The effect of thermal and shear histories on the crystallization rate of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) was studied. As with other crystalline polymers, the shear history greatly affected the crystallization rate when the shear rate was beyond a critical value, i.e., the inverse of the Rouse relaxation time. Even after the formation of extended chain crystals, spherulite texture was clearly discernable. It grew from certain points on the extended chain crystals. Consequently, a row of spherulites appeared along the flow direction. The resin temperature in the molten state was also significant. When the sample was heated to 170 °C, which is beyond the main melting peak in the differential scanning calorimetry curve, unmolten crystals did not affect the linear viscoelastic properties. They acted as effective nucleating agents for the rest of the polymer during cooling. Therefore, the shear history hardly affected the crystallization rate and the number of spherulites.

DOI： 10.1038/s41598-023-27595-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.polymer.2023.126590

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s10924-023-03104-5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.polymer.2023.126330

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.reactfunctpolym.2023.105682

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

Abstract

α‐form crystalline isotactic polypropylene (PP) was prepared by two methods: quenching from the melt state at slow or high crystallization rates. The mechanical properties of the resulting PP samples were evaluated using tensile and stress–relaxation tests to investigate the influence of nodular or spherulite morphologies. PP samples with different morphologies had almost the same crystallinity after annealing at 100°C for 5 h. The yielding stress, strain‐hardening modulus, and strength of the nodular PP were higher than those of the spherulite PP, although the crystallinity was almost the same for both PP samples. Furthermore, the relaxation time during the stress–relaxation process at ε = 4.0 was longer for the nodular PP than for the spherulite PP. The lamellar structure of a spherulite morphology comprises parent and daughter lamellar crystals, whereas that of a nodular morphology prepared via a mesophase structure comprises only parent lamellar crystals. The formation of the daughter lamellae reduces the number of tie chains. Therefore, the nodular PP has more tie chains than the spherulite PP. This transformation from a spherulite to a nodular morphology improved the mechanical properties of the PP.

Highlights

Influences of morphology on mechanical properties of polypropylene (PP).

Tensile properties were higher for nodular PP than spherulite PP.

Relaxation time of nodular PP was longer than spherulite PP.

Nodular PP has more tie chains, resulting in improvements of tensile properties.

DOI： 10.1002/pen.26504

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsomega.3c03280

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1038/s41428-023-00821-5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s00396-023-05143-9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACS Applied Polymer Materials  

The present study revealed that an injection-molded product comprising poly(lactic acid) (PLA) and poly(vinyl alcohol) (PVAL) exhibited an anomalous dimensional change, i.e., expansion in the flow direction, after postprocessing annealing (around 2.9% expansion by annealing at 80-100 °C for 3 h). Although the crystallization of the PLA during cooling was not accelerated by the addition of PVAL, the PLA showed transcrystallization from the dispersed PVAL droplets, which were deformed in the flow direction, during postprocessing annealing. Therefore, after annealing, the injection-molded products exhibited a high degree of molecular orientation, in contrast to the original unannealed products, which were not oriented. This anomalous behavior should be noted as a means of controlling dimensional change after processing.

DOI： 10.1021/acsapm.2c02155

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Polymers  

The effect of shear history on structure development during post-processing annealing was studied using poly(lactic acid) PLA. Since PLA shows a low crystallization rate, quenched films had no crystallinity. Moreover, molecular orientation was not detected in the films. During the annealing procedure beyond its glass transition temperature, however, molecular orientation to the flow direction occurred with the crystallization growth in the films having an appropriate shear history. This peculiar crystal growth during the annealing was most probably attributed to the crystallization from extended chain crystals generated during the applied shear history, although the amount of extended chain crystals was low. The results obtained in this study should be noted because the molecular orientation proceeded due to the annealing history applied. Furthermore, this phenomenon will be used to suppress dimensional change and increase product rigidity.

DOI： 10.3390/polym15030693

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Applied Polymer Science  

Exposure to shear flow produced by a pressure-driven capillary rheometer provides a concentration gradient without phase separation in miscible polymer blends of bisphenol-A polycarbonate containing low-molecular-weight poly(methyl methacrylate) (PMMA). The strand surface extruded from the rheometer contains a large amount of PMMA. However, the strand is transparent because there is no light scattering due to phase separation. The segregation behavior, that is, enrichment of the PMMA content at the strand surface, is enhanced when the molecular weight of PMMA is low. Furthermore, the segregation is also enhanced at high temperatures and at high shear rates. By contrast, the die length barely affects the degree of segregation. The segregation phenomenon should be noted because it may facilitate the modification of the surface properties of various products.

DOI： 10.1002/app.53258

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Materials  

The rheological properties and processability at injection molding were studied for bisphenol-A polycarbonate (PC) that was modified by low-density polyethylene (LDPE) having a low shear viscosity. The LDPE addition significantly decreased the steady-state shear viscosity, especially in the high shear rate region. The decrease did not originate from slippage on the die wall but due to interfacial slippage between the PC and dispersed LDPE droplets that deformed to the flow direction to a great extent. As a result of the viscosity decrease, injection pressure largely decreased from 150 to 110 MPa with the addition only 5 wt.% of LDPE. The enhanced flowability also reduced the warpage of the molded product significantly, demonstrating that the processability at injection molding was improved by the addition of LDPE.

DOI： 10.3390/ma16020866

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Macromolecules  

We investigated the effects of molecular components of different molecular weights on the tensile properties of polyethylene (PE) by measuring the microscopic deformation of deuterated molecular chains of various molecular weights and narrow molecular weight distributions using rheo-Raman spectroscopy. The strain-hardening modulus increased by adding the high-molecular-weight chains connecting more than four to six lamellar crystalline layers. These high-molecular-weight molecular chains showed large peak shifts and orientation parameter values during strain hardening. In contrast, almost no stretching load was applied to the low-molecular-weight molecular chains that connected only two or three lamellar crystals in the strain-hardening region, and the strain-hardening modulus was unchanged by adding these low-molecular-weight chains. These results suggest that the high-molecular-weight molecular chains connecting more than four to six lamellar crystals act as stress transmitters throughout the crystal structure in the strain-hardening region.

DOI： 10.1021/acs.macromol.3c00197

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Polymers  

Mechanical responses after the uniaxial deformation of graded styrene–butadiene rubber (SBR) with a gradient in the crosslink points in the thickness direction were investigated as compared with those of homogenously vulcanized SBR samples. The elongational residual strain of a graded sample was found to depend on the part with a high crosslink density. Therefore, it showed good rubber elasticity. After stress removal, moreover, the graded sample showed a marked warpage. This suggested that shrinking stress acted on the surface with a high crosslink density, which would avoid a crack growth on the surface. The sample shape was then recovered to be flat very slowly, indicating that the shrinking stress worked for a long time. This unique rubber elasticity, i.e., slow strain recovery with an excellent strain recovery, makes graded rubber highly significant.

DOI： 10.3390/polym14245477

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Polymers  

In this paper, the structure and properties of transparent films composed of bisphenol-A polycarbonate (PC) and a commercially available copolyester, poly(1,4-cyclohexanedimethanol-co-2,2,4,4-tetramethyl-1,3-cyclobutanediol-co-terephthalate) (CPE), were studied. Both PC and CPE films are known to be transparent with good mechanical toughness. It was found that PC/CPE (50/50) showed miscibility in both the molten and solid states, indicating that there is a high possibility for the blend system to be miscible in the whole blend ratios. Because of the miscibility, the blend films showed no light scattering originating from phase separation. The mechanical properties of the films, such as Young’s modulus, yield stress, and strain at break, were determined by the blend ratio, and the glass transition temperature increased with the PC content, which corresponded well with the values predicted by the Fox equation. These results demonstrate that the thermal and mechanical properties of the films can only be controlled by the blend ratio. Since these transparent films showed excellent mechanical toughness irrespective of the blend ratios, they can be employed in various applications.

DOI： 10.3390/polym14194146

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACS Applied Polymer Materials  

Cross orientation between lamellae and amorphous chains was generated by forming residual crystals during extrusion and melt stretching under temperature-controlled processing conditions in a thermoplastic polyester elastomer (TPEE). Some crystals were not completely melted at a certain temperature slightly higher than the melting temperature of the sample during a heating process, and the survived crystals are called residual crystals. The TPEE exhibited prolonged relaxation at the temperature slightly higher than the melting temperature owing to the formation of the network structure composed of the residual crystals. The formation of the weak network affected the processability during extrusion, such as the swell ratio and the drawdown force. Although polarized microscopy images apparently showed that the average molecular orientation was along the drawing direction, it was found that the lamellar crystals oriented orthogonal to the fiber axis to reduce the hydrodynamic force during extrusion according to the results of multiple structural analyses. The orthogonal orientation of the lamellar crystals should be caused by the high aspect ratio of the lamellar crystals grown from the residual crystals. The orthogonal orientation resulted in a high Young's modulus and yield stress. The method for generating cross orientation of crystalline and amorphous chains will be applied to the preparation of high-performance fibers with high strength and modulus.

DOI： 10.1021/acsapm.2c00508

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Polymer  

The present paper describes a novel method for reinforcing isotactic polypropylene (PP) by adding poly(vinyl alcohol) (PVA) fibers prepared by melt-stretching. Low-viscosity PVA droplets were deformed into fibers in the molten PP by melt-stretching them beyond the melting point of PVA. When the obtained composite was extruded below the melting point of PVA, the fibers became oriented toward the flow direction. The PVA demonstrated marked nucleating activity with regard to PP crystallization, which was further promoted by enlargement of the surface area by fibrillization. As a result, there was virtually no orientation relaxation of the PP chains with an increase in crystallinity, which explains the improvement in rigidity of the reinforced composite.

DOI： 10.1016/j.polymer.2022.125043

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Polymer  

We have examined the mechanism of strain hardening of polyethylene (PE) using a step-cycle test with in situ Raman spectroscopy, small-angle X-ray scattering, and wide-angle X-ray diffraction measurements. A stable fibrillar structure was formed at the onset of strain hardening. The fraction of the long-consecutive trans chains increased and decreased with increasing and decreasing strain during the stretching and unloading steps, respectively. The peak shift of the C–C stretching mode showed a red shift by applying the stretching stress to the specimen, accompanied by the broadening of the peak width. The broadening of the Raman band is interpreted as the strong stretching load becoming concentrated on the taut-tie chains. According to these results, we concluded that the strain hardening was caused by the increment of the modulus resulting from the increase in the number of taut-tie chains caused by chain pull-out from the crystalline structure.

DOI： 10.1016/j.polymer.2022.124869

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Polymer  

We evaluated the rigid–amorphous (RA) fraction of isotactic polypropylene (iPP) samples by various measurement techniques and investigated the role of the RA chains on the mechanical properties of iPP. The RA fraction was increased by annealing above the α-relaxation temperature, although the RA fraction was almost independent of the molecular weight. The RA fraction obtained by differential scanning calorimetry increased linearly with the number of consecutive helical chains with 12–14 monomer units, suggesting that the RA chains are attributable to crystalline defects. Moreover, the α-relaxation temperature varied linearly with the RA fraction; the RA chains present as crystalline defects were removed from the crystalline structure by α relaxation. The yielding region of the stress–strain curve became broad by increasing the RA fraction; the fragmentation strength of the lamellar crystals was widely distributed owing to the large number of crystalline defects.

DOI： 10.1016/j.polymer.2022.124834

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Polymer  

Cyclic olefin copolymers (COCs), among which ethylene (E)/norbornene (NB) copolymer have been commercialized, are novel optical plastics but their brittleness narrows their application fields. In this research, star polymers with NB/1-octene (O) gradient copolymer arms and cross-linked cores were synthesized by adding norbornadiene (NBD)/E or 1,11-dodecadiene (DOD) after NB/O copolymerization using a (tBuNSiMe2Flu)TiMe2 (I)-[Ph3C][B(C6F5)4] catalyst system with 2,6-di-tert-butyl-4-methylphenol-treated tri-n-octylaluminum (Oct3Al/BHT) as a scavenger. The obtained star polymers possessed the O-rich soft segments close to the core and the NB-rich hard segments in the outer layer. The DOD-cored star polymers had a larger number of arms (15) and a higher star polymer content (68 wt%) than the NBD/E-cored ones (6 and 58 wt%, respectively). The films of the mixtures of the star and the corresponding arm polymers were molded by a melt-pressing procedure. The tensile properties of the films of the DOD-cored star polymer mixtures were significantly improved compared to those of the arm polymers. The Young's modulus, yield stress, strength, and strain at break were controlled by the NB content, the arm length, and the gradient structure of the arms. These results clarified the novelty of the star-shaped NB/α-olefin copolymers and would expand the application fields of COCs.

DOI： 10.1016/j.polymer.2022.124844

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Materials  

Miscible blends composed of bisphenol-A polycarbonate (PC) and poly(methyl methacrylate) (PMMA), in which one of them has low molecular weight, were employed to study the surface segregation behavior during flow. The blend samples showed typical rheological behaviors, such as simple polymer melts without a long-time relaxation mechanism ascribed to phase separation, demonstrating that they were miscible. After injection molding, the amounts of a low molecular weight component on the blend surface were found to be larger than the actual blend ratio. Because the injection-molded products were transparent despite a huge difference in refractive indices between PC and PMMA, they showed no phase separation. This result demonstrated that surface segregation of a low molecular weight component occurred under flow field, which expands the material design such as tough plastics with good scratch resistance and optical fibers with tapered refractive index.

DOI： 10.3390/ma15092994

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Materials  

Viscoelastic properties including melt processability were evaluated for a fully biomass-based glassy plastic comprising cellulose acetate (CA) and triethyl citrate (TEC). The TEC exerted an excellent plasticizing effect without dissolving the CA crystals. Pure CA has poor melt processability. In contrast, the TEC-plasticized CA had good melt-processability at 205◦C, which is lower than the degradation temperature of CA. Extrusion was possible even at 1000 s−1 without any flow instabilities, similar to conventional plastics showing good processability at extrusion. Furthermore, there was marked strain-hardening behavior in the transient elongational viscosity, suggesting that various processing operations are possible, such as a long-chain branched polymer. This biomass-based plastic can be used as a substitute for conventional glassy plastics because it is highly transparent and its softening temperature is above 100◦C.

DOI： 10.3390/ma15093038

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Materials  

The effects of pressure and shear rate on the miscibility of binary blends comprising bisphenol-A polycarbonate (PC) and low molecular weight poly(methyl methacrylate) (PMMA) were investigated using a capillary rheometer. Both pressure and shear rate affected the miscibility. The examination of an extruded strand of the blend provided information about the cause of the phase change. Under high pressure, pressure-induced demixing occurred at temperatures below the lower critical solution temperature (LCST) of the blend. Consequently, the extruded strand became opaque throughout. During shear-induced mixing/demixing, a part of the strand became opaque because of the distribution of the shear rate in the strand. For example, during shear-induced demixing, only the exterior of the strand, i.e., the high shear rate region, became opaque. Above the LCST, shear-induced mixing occurred, and only the center region of the strand became opaque.

DOI： 10.3390/ma15082783

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Polymer Journal  

The crystallization behavior of isotactic polypropylene containing a fibrous nucleating agent in a flow field was investigated using a polarized optical microscope equipped with a parallel-plate shear device. The addition of the fibrous nucleating agent greatly enhanced the crystallization rate, although isotactic polypropylene crystallization without the nucleating agent was enhanced after exposure to shear flow at a high shear rate. The sample with the nucleating agent demonstrated high molecular orientation to the flow direction after shear flow, even at a low shear rate. This was attributed to the formation of a pseudo shish-kebab structure, in which the fibrous nucleating agent acts as the shish. Moreover, the high level of molecular orientation without spherulitic morphology was responsible for the reduced light scattering, which resulted in good transparency.

DOI： 10.1038/s41428-021-00596-7

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Macromolecules  

Copolymerization of norbornene (NB) and fluorene-containing alkene comonomers using the Me2Si(Flu)(NtBu)TiMe2 complex as a catalyst was investigated. The copolymerization successfully proceeded at any monomer feed ratio in high activity and gave copolymers with various comonomer contents. The structure of these copolymers would be gradient because NB was preferentially consumed in a quasi-living polymerization system. Two relaxation processes at 100-150 and 270-300 °C in dynamic mechanical analysis, which show phase-separation of the copolymer, supported the formation of the gradient structure. The obtained copolymers showed a high refractive index as hydrocarbons and extremely low photoelasticity (<10-11 Pa-1). For reducing the photoelasticity, a monomer design free from reactive tertiary carbons would be important.

DOI： 10.1021/acs.macromol.1c02101

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Polymer  

An appropriate processing protocol was proposed to improve the rubber elasticity of a thermoplastic polyester elastomer (TPEE). Rheology measurements at the processing temperature and thermal measurements determined the critical temperature at which small numbers of crystals exist. It was found from dynamic mechanical analyses, wide- and small-angle X-ray measurements, and electron microscope observations that cooling from the critical temperature markedly promoted the crystallization of hard segments. Moreover, tensile tests revealed that the modulus and yield stress increased. Most importantly, compared with films obtained by cooling from high temperatures, the residual strain at a fixed stress was low—i.e., the rubber elasticity was improved owing to its well-developed crystalline structure. These effects were accelerated by a more optimized process—i.e., subsequent heating at slightly below the critical temperature. The technique is noteworthy because a TPEE with high modulus generally shows poor elasticity.

DOI： 10.1016/j.polymer.2021.124376

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Macromolecular Science, Part B: Physics  

The repeating cycle of freezing and thawing brings about a physical gelation for the solutions of polyacrylonitrile (PAN) in N, N-dimethylacetamide (DMA) for appropriate concentrations. It was revealed from wide-angle-X-ray diffraction that the PAN molecules were cross-linked by the crystallization to form a network through the freezing and thawing steps. The profiles of small-angle-X-ray scattering for the gels showed the excess scattering from the network structure formed through gelation, which could not be observed for the pure PAN solution. A reversible swelling and shrinking were observable for the PAN gel as a function of the relative content of DMA and benzene by varying the mixing ratio. The degree of swelling measured by weight, for the swollen and shrunk gels, was in a range from 0.7 to 8. A scaling relation appeared for the gel swelling between the PAN volume fraction (ϕ) and the shear moduli (G) which was measured by tensile and indentation tests, as G = G s ×(ϕ)s; G s= 1200 kPa and s = 2.26 ± 0.23. A discussion is given on the value of the scaling exponent, s, on the basis of the conformation of flexible chain molecules in solution and the analogy in the microscopic and macroscopic properties between semidilute polymer solutions and gels.

DOI： 10.1080/00222348.2022.2127264

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Nihon Reoroji Gakkaishi  

The microscopic deformation behaviors of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) under uniaxial stretching were investigated using rheo-Raman spectroscopy. The crystalline chains of LDPE were oriented uniaxially into the stretching direction beyond the first yielding point, which was accompanied by applying stretching load to the crystalline chains. In contrast, at the first yielding point of HDPE, the orientation of crystalline chains was suppressed and compression load was applied to the amorphous and crystalline chains owing to lateral shrinkage of the specimen. Additionally, the orthorhombic crystalline regularity was significantly disordered at the first yielding point for HDPE, concomitant with the fragmentation of the rigid lamellar crystals. In comparison, the disordering of the crystalline regularity of LDPE was induced at the second yielding point, when the orientation of the crystalline chains was nearly complete, owing to the application of a strong stretching load to the highly oriented crystalline chains.

DOI： 10.1678/rheology.50.287

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Nihon Reoroji Gakkaishi  

Raman spectroscopy is a vibrational spectroscopic technique that is widely used for analyses of the chemical structures and morphologies of polymeric materials. The peak position and peak area of each Raman band are influenced by microscopic deformations of molecular chain e.g. load-sharing, orientation, and conformational state. In particular, Raman spectroscopic analysis has been used to investigate the structure–mechanical properties relationship of semi-crystalline polyolefins (POs) because the C–C stretching mode, which is the main chain vibration of POs, is strongly Raman-active. The present review summarizes recent Raman spectroscopic analyses of the structure–mechanical properties relationship of POs.

DOI： 10.1678/rheology.50.21

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Macromolecular Chemistry and Physics  

Polystyrenes (PStX, X = -H, -OMe, -Me, or -Cl at 4-position) are synthesized by the use of anilinonaphthoquinone-ligated nickel complexes [Ni(C10H5O2NAr)(Ph)(PPh3): 1a, Ar = C6H3-2,6-iPr; 1b, Ar = C6H2-2,4,6-Me; 1c, Ar = C6H5] activated with modified methylaluminoxane (MMAO) in toluene. The polymer yield is dependent on the substituent X and decreases in the following order: -OMe > -Me > -H >> -Cl. The highest weight-average molecular weight (Mw) of 107 000 with polydispersity (Ð) of 1.4 is achieved for PStOMe by the 1a-MMAO catalytic system. 13C NMR analysis indicated that the polymers obtained at 70 °C are atactic but those obtained at 0 °C are isotactoid (isotactic triad ≈ 74 ̶ 82 %), which depended on X. The linear viscoelasticity measurement is also performed to investigate the influences of the substituent on the rheological properties. The critical molecular weight of the chain entanglement of PStOMe is higher than that of PStMe, which should be due to the suppression of the chain entanglement by the methoxy group.

DOI： 10.1002/macp.202100402

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

The effects of the ultra-high-molecular-weight (UHMW) component of polypropylene (PP) on its rheological properties, crystallization behavior, and solid-state mechanical properties were investigated using various measurement techniques. The terminal relaxation time—determined by measuring the linear viscoelasticity—was increased by adding the UHMW component. The increase in the melt elasticity produced by adding the UHMW component was observed by measuring the steady-state shear flow, although the shear viscosity was not greatly affected. Owing to the long characteristic time of the Rouse relaxation of the UHMW component, PP with the UHMW component formed highly oriented structures through a shear-induced crystallization process. The addition of the UHMW component enhanced the orientation and regularity of crystalline structure for extruded films. Therefore, the Young′s modulus, yield stress, and strength were higher in the PP film containing the UHMW component than in one without the UHMW component, irrespective of the direction of tensile deformation.

DOI： 10.3390/polym13234222

PubMed

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

The effects of magnesium salts with various anion species on the structure and properties of a poly(vinyl alcohol) (PVA) film were studied. The glass transition temperature of the PVA film increased following the addition of a magnesium salt. Furthermore, the salt greatly enhanced the modulus and yield stress and reduced the crystallinity of the film. These effects were attributed to the strong ion–dipole interactions between the magnesium salts and the PVA chains. The strength of interaction, i.e., the reduction of segmental motions, depended on the anion species in the following order: Mg(ClO4)2, MgBr2, MgCl2, Mg(CH3COO)2, and MgSO4. The order corresponded to the Hofmeister series, which predicts the ability to break the structure of water.

DOI： 10.3390/polym13213760

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s00397-021-01286-0

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Other Link： https://link.springer.com/article/10.1007/s00397-021-01286-0/fulltext.html

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

We prepared model polyethylene (PE) samples that contain the controlled-amounts of the high-molecular-weight component by blending a monodispersed PE into a polydispersed PE, to elucidate the influence of the high-molecular-weight component of a polymer on its mechanical properties. The strength and strain-hardening modulus were significantly enhanced by the addition of a monodispersed PE of sufficiently high molecular weight, and the critical value of M was determined to be ~3.0 × 10 . The improved strength and strain-hardening modulus are attributed to higher amounts of inter-cluster links that bridge adjacent lamellar cluster units because these links act as stress transmitters between these units. w 5

DOI： 10.1016/j.polymer.2021.123526

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.macromol.0c02686

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

As a promising biodegradable and biorenewable alternative to ubiquitous petrochemical plastics, poly(L-lactide) (PLLA) can be widely employed in biomedical and pharmaceutical fields. In this work, triblock copolymers, poly(L-lactide)-b-poly(2-methyl-1,3-propanediyl adipate)-b-poly(L-lactide) (PLLA-b-PMPA-b-PLLA)s, were synthesized by two-step polymerization from 2-methyl-1,3-propanediol (MP), adipic acid (AA) and L-lactide (LLA) as new biodegradable thermoplastic elastomers. The copolymers exhibited glass-transition temperature at below -40 degrees C and melting temperature at 140-160 degrees C. These copolymers showed much higher elongation at break and lower tensile modulus than those of PLLA. Enzymatic degradation tests of the obtained copolymers were performed using proteinase K and lipase PS as catalysts in hydrolysis reaction to demonstrate rapid degradation for these copolymers. Seawater biodegradability test was conducted for 28 days for each sample. The triblock copolymer and PMPA homopolymer were found to show about 50% biodegradation within 28 days representing very high biodegradable property in sea-water. (C) 2020 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.polymdegradstab.2020.109467

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

An innovative type of biodegradable thermoplastic elastomers with improved mechanical properties from very common and potentially renewable sources, poly(L-lactide)-b-poly(2-methyl-1,3-propylene glutarate)-b-poly(L-lactide) (PLA-b-PMPG-b-PLA)s, has been developed for the first time. PLA-b-PMPG-b-PLAs were synthesized by polycondensation of 2-methyl-1,3-propanediol and glutaric acid and successive ring-opening polymerization of L-lactide, where PMPG is an amorphous central block with low glass transition temperature and PLA is hard semicrystalline terminal blocks. The copolymers showed glass transition temperature at lower than −40 °C and melting temperature at 130–152 °C. The tensile tests of these copolymers were also performed to evaluate their mechanical properties. The degradation of the copolymers and PMPG by enzymes proteinase K and lipase PS were investigated. Microbial biodegradation in seawater was also performed at 27 °C. The triblock copolymers and PMPG homopolymer were found to show 9–15% biodegradation within 28 days, representing their relatively high biodegradability in seawater. The macromolecular structure of the triblock copolymers of PLA and PMPG can be controlled to tune their mechanical and biodegradation properties, demonstrating their potential use in various applications.

DOI： 10.3390/life11010043

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.macromol.0c02124

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

<p>A series of di- and triblock copolymers composed of gradient norbornene (NB)/α-olefin segments were synthesized by a (<italic>t</italic>-BuNSiMe₂Flu)TiMe₂-based catalyst and their physical and mechanical properties were investigated.</p>

DOI： 10.1039/d0py01370f

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC RHEOLOGY, JAPAN  

Although the entanglement network among polymers has been widely investigated, the spatial distribution of entanglement nodes has been rarely discussed. In this study, we obtained the radial distribution functions (RDFs) for the entanglement nodes from the snapshots of multi-chain slip-link simulations. The model employed in this study is the primitive chain network (PCN) model, which has been validated to reproduce the entangled polymer dynamics semi-quantitatively. The statistics of captured entanglement networks were compared to those reported for the primitive path network extracted by the CReTA procedure from the full-atomistic molecular model of a polyethylene melt. In the range of distance longer than the average strand length, the network structure from PCN does not show any structural correlation, and the intra-chain correlation is close to that for Gaussian chains with non-interacting slip-links. These features are consistent with the CReTA network and the conventional assumptions made for single-chain models. Meanwhile, in the short-range, the structural correlation in PCN is much weaker than that in CReTA. This discrepancy is because the short-range structure in PCN is realized as a result of imposed fluctuations, whereas it is determined by the minimization of the primitive path in CReTA.

DOI： 10.1678/rheology.49.337

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Triblock copolymers, poly(L-lactide)-b-poly(2-methyl-1,3-propanediyl succinate)-b-poly(L-lactide) (PLLA-b-PMPS-b-PLLA), were synthesized as new biodegradable thermoplastic elastomers by two-step polymerization. In the first step, hydroxy-telechelic poly(2-methyl-1,3-propanediyl succinate) (PMPS) was synthesized from 2-methyl-1,3-propanediol (MP, small excess) and succinic acid (SA) using two-stage reaction of esterification and simple polycondensation processes. In the second step, plant derived L-lactide (LLA) was polymerized using the bifunctional PMPS as a macroinitiator to synthesize PLLA-b-PMPS-b-PLLA triblock copolymers. The structures of the triblock copolymers as well as the PMPS macroinitiator were characterized by NMR and GPC analysis. PMPS is an amorphous polymer with T-g at lower than -24 degrees C. The triblock copolymers also exhibited low T-g for the PMPS segment at lower than -20 degrees C as well as T-m, at around 150 degrees C for the PLLA segment. The tensile tests of the triblock copolymers demonstrated their low modulus and high elongation. The biodegradation tests of these polymers were also performed using enzymes and seawater to reveal their biodegradability. (C) 2020 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.polymdegradstab.2020.109353

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Society of Rheology Japan  

DOI： 10.1678/rheology.48.153

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

The copolymerization of norbornene (NB) and various alpha-olefins [1-octene (O), 1-decene (De), and 1-dodecene (Do)] was achieved with high activity using ((t)BuNSiMe(2)Flu)TiMe2 (1)-[Ph3C][B(C6F5)(4)] and 2,6-bis(1,1-dimethylethyl)-4-methylphenol (BHT)-treated tri-i-butylaluminum ((Bu3Al)-Bu-i) or tri-n-octylaluminum (Oct(3)Al) as a scavenger. The catalytic systems gave NB/alpha-olefin copolymers with number-average molecular weights over 100,000 and polydispersity indices below 1.3. The copolymers possessed the gradient structure starting from the NB-rich segment to the alpha-olefin-rich terminal because of the difference of the monomer reactivity ratios between NB and alpha-olefins. Films of the copolymers were successfully molded using a melt-pressing procedure. The strain at the break of the copolymer films increased with the length of the alkyl group of the alpha-olefin accompanied by a decrease in strength. The tensile properties of the copolymers are controlled by the NB content and the M-n value. The copolymer films showed transmittance of up to 80% in the visible-light range.

DOI： 10.1021/acs.macromol.0c00431

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Language：English   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

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Publisher：Royal Society of Chemistry ({RSC})  

DOI： 10.1039/C9PY01186B

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Publisher：American Chemical Society ({ACS})  

DOI： 10.1021/acs.macromol.8b02740

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Ltd  

Raman spectroscopy has been used to reveal the microscopic structural changes of low-density polyethylene under ultraviolet irradiation. The fraction of non-crystalline consecutive trans chains (the molecular chains in the trans conformation separate from the orthorhombic crystalline phase) drastically decreases at ∼600 h, together with a decrement in the molecular weight and an increment in the crystallinity owing to chemicrystallization. This suggests that short trans chains are prolonged to form consecutive trans chains before chemicrystallization. Moreover, gradual increases of the stretching and compression stresses are observed on the trans and amorphous chains, respectively. These conformational changes are detected by Raman spectroscopy even in the early stage of photodegradation. Chemicrystallization at ∼600 h is accompanied by structural changes, such as shortening of the interchain distance of the lamellar crystals and thinning of the amorphous layer, which induce formation of surface cracks on the macroscopic specimen.

DOI： 10.1016/j.polymdegradstab.2018.02.010

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Other Link： http://orcid.org/0000-0002-9494-3004

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley-VCH Verlag  

In situ polarized Raman spectroscopy is applied for the tensile deformation of high- and low-density polyethylenes (HDPE and LDPE), and the orientation parameters as well as the orientation distribution function (ODF) are determined. While random orientation is maintained in the elastic region, the orientation of the polymer chains begins after the first yield point. The ODF for LDPE shows a peak at the stretching direction throughout the elongation process, and the maximum value of the ODF monotonously increases with the strain. For HDPE, the ODF in the yielding region has a broad peak at an intermediate angle of 30–70° from the stretching direction, while the orientation at the stretching direction is restored in the strain-hardening region. The tilted orientation is explained with the concept of the lamellar cluster units formed in the yielding region after the collapse of the spherulites. The HDPE with lower molecular weight and that with wider molecular weight distribution show high orientation, which is explained with the smaller size of the lamellar cluster units and the higher network density in the amorphous phase, respectively.

DOI： 10.1002/masy.201700020

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Other Link： http://orcid.org/0000-0002-9494-3004

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley-VCH Verlag  

The microscopic deformation behaviors such as the load sharing and the molecular orientation of the crystalline chains of isotactic polypropylene under tensile stretching are examined by using rheo-Raman spectroscopy. The Raman bands assigned to the skeletal CC stretching modes show blue shifts after the yielding, indicating that the stretching stress is applied to the main chain. The CH3 rocking band shows red shift in the yielding region, suggesting that the compression stress is applied in the interchain direction of the crystalline chains. While the molecular orientation of the crystalline chains begins after the first yield point, the crystalline orientation is hindered due to the existence of the rigid and bulky lamellar cluster units. Beyond the yielding region, the orientation toward the stretching direction proceeds rapidly, and the crystalline chains simply orient in the stretching direction in the highly strained region.

DOI： 10.1002/masy.201700019

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Other Link： http://orcid.org/0000-0002-9494-3004

Publisher：Wiley-Blackwell  

DOI： 10.1002/pi.5533

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Society of Plastics Engineers  

Raman spectroscopy is applied to elucidate microscopic structural changes in low-density polyethylene under ultraviolet irradiation. The crystallinity estimated with the 1418 cm-1 band shows a stepwise increase at ~600 h accompanied by sharp decrease of the molecular weight, suggesting chemicrystallization. The increase of crystallinity and the thinning of amorphous layer at ~600 h lead to macroscopic shrinkage of the specimen, inducing the formation of surface cracks. It is also suggested that contraction of interchain distance and conformational changes take place gradually during photodegradation. In this work we demonstrate Raman spectroscopy can be utilized for non-destructive diagnosis of degradation and deterioration of polyolefin solids.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：EDP Sciences  

The microscopic deformation behaviors such as the load sharing and the molecular orientation of high-density polyethylene under uniaxial stretching at various strain rates were investigated by using in-situ Raman spectroscopy. The chains within crystalline phase began to orient toward the stretching direction beyond the yielding region and the orientation behavior was not affected by the strain rate. While the stretching stress along the crystalline chains was also not affected by the strain rate, the peak shifts of the Raman bands at 1130, 1418, 1440 and 1460 cm-1, which are sensitive to the interchain interactions obviously, depended on the strain rate
the higher strain rates lead to the stronger stretching stress or negative pressure on the crystalline and amorphous chains. These effects of the strain rate on the microscopic deformation was associated with the cavitation and the void formation leading to the release of the internal pressure.

DOI： 10.1051/matecconf/201713005001

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Other Link： http://orcid.org/0000-0002-9494-3004

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Other Link： http://orcid.org/0000-0002-9494-3004

Language：English   Publishing type：Research paper (scientific journal)   Publisher：BUDAPEST UNIV TECHNOL & ECON  

The molecular orientation behavior of isotactic polypropylene (iPP) is investigated by using in situ Raman spectroscopy under tensile tests. A versatile method of the tilt-angle correction for the orientation parameters is newly developed, where the molecular orientation in highly oriented specimens is assumed to be entropically favorable. The real-time changes of orientation parameters and orientation distribution functions are determined for the molecular chain axis of iPP during uniaxial stretching. The molecular orientation remains random in the elastic region, and increases after the first yield point. In the yielding region, a broad distribution of orientation toward an intermediate angle of 30-70 degrees from the stretching direction is observed. This is interpreted as reorientation of the crystalline chains being hindered by rigid, bulky lamellar cluster units. After the yielding region, orientation toward the stretching direction proceeds rapidly, approaching highly oriented states.

DOI： 10.3144/expresspolymlett.2016.63

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Other Link： http://orcid.org/0000-0002-9494-3004

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

In situ observation of the microscopic structural changes in high-density polyethylene during hot drawing was performed by incorporating a temperature-controlled tensile machine into a Raman spectroscopy apparatus. It was found that the load sharing and molecular orientation during elongation drastically changed at 50 degrees C. The microscopic stress of the crystalline chains decreased with increasing temperature and diminished around 50 degrees C. Moreover, the orientation of the crystalline chains was greatly promoted above 50 degrees C. These microscopic structural changes were caused by the thermal activation of the molecular motion within lamellar crystalline chains owing to the onset of relaxation of the crystalline phase. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymertesting.2015.03.018

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Other Link： http://orcid.org/0000-0002-9494-3004

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

The microscopic mechanism of high-density polyethylene under uniaxial drawing is investigated using in situ Raman spectroscopy. From the peak shifts of the symmetric and anti-symmetric C-C stretching modes, it is found that the load sharing on the polymer chain in the yielding region is anisotropic with stretching along the chain and compression perpendicular to the chain. The orientation functions (&lt; P2 &gt; and &lt; P4 &gt;) as well as the orientation distribution function (N(theta)) are determined from the polarized Raman spectra. The molecular orientation with cold drawing is found to proceed more effectively for lower crystallinity specimens. In the yielding region, it is also found that N(theta) has a maximum at the polar angle theta = 30-70 degrees. This peculiar behavior in the microscopic scale is explained by the preferential collapse of spherulites and the existence of lamellar clusters as the bulky mobile units. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymer.2014.12.030

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Other Link： http://orcid.org/0000-0002-9494-3004

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Other Link： http://orcid.org/0000-0002-9494-3004

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

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Language：Japanese   Publisher：Society of Rheology Japan  

DOI： 10.1678/rheology.49.49

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)   Publisher：大阪工研協会  

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)   Publisher：化学工業  

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)   Publisher：加工技術研究会  

Award type：Honored in official journal of a scientific society, scientific journal 

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Country：Japan

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Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

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Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

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