Yoshiharu Miyashita

Thermal and viscoelastic properties of alginate/poly(vinyl alcohol) blends cross-linked with calcium tetraborate

Abstract Binary blends of alginate (Alg) with poly(vinyl alcohol) (PVA) were cast in film form from mixed aqueous polymer solutions by solvent evaporation. The thermal transition and viscoelastic behavior of the Alg/PVA blends were investigated by differential scanning calorimetry and dynamic mechanical analysis. Irrespective of composition, blend samples gave a single glass transition temperature (Tg) situated between the Tgs of PVA and alginate per se. The melting point of the PVA component was depressed systematically with increasing alginate content in the blends. These observations indicate that the polymer blend of Alg/PVA is capable of forming a thermodynamically miscible phase in the amorphous state. An additional treatment of as-cast samples with calcium tetraborate solution gave rise to a marked elevation of their Tgs. This may be ascribed to the possible, simultaneous occurrence of a chelate complexation of alginates with Ca2+ cation and a borate ion-aided cross-links between PVA chains, resulting in the formation of an ‘IPN’ structure.

Blends of poly(∈-caprolactone) with cellulose alkyl esters: effect of the alkyl side-chain length and degree of substitu tion on miscibility

Cellulose alkyl esters, CELL- OCOCnH2n+1(n = 1 ∼ 6), were synthesized by a homogeneous reaction of cotton cellulose with different acyl chlorides in N,N-dimethylacetamide--lithium chloride solution. The miscibility of the esterified celluloses with poly(∈-caprolactone) (PCL) was investigated, mainly through thermal analysis by differential scanning calorimetry (DSC). A polymer pair, cellulose butyrate (CB)/PCL, showed the highest miscibility of all the binary blends examined here; this is usual when relatively high-substituted esters (DS ≥ 2.0) are used as the respective component. The butyl ester derivatives with DS ≤ 1.5 showed poor miscibility with PCL

Transition behavior and phase structure of chitin/ poly(2-hydroxyethyl methacrylate) composites synthesized by a solution coagulation/bulk polymerization method

Abstract Chitin/poly(2-hydroxyethyl methacrylate) (PHEMA) composites were synthesized via photo-polymerization in a gel state of chitin swollen with HEMA monomer as reactive impregnant. The transition behavior and phase structure of the chitin/PHEMA composites were characterized by differential scanning calorimetry, dynamic viscoelastic analysis, and solid-state 13C NMR spectroscopy. For compositions containing ≲ 20wt% chitin, it was reasonably assumed that an original network structure of chitin gels was sufficiently perpetuated into the cross-linked PHEMA matrix, resulting in the formation of an interpenetrating polymer network (IPN) type organization. Owing to this IPN effect, the lowering of the dynamic modulus E of the composites in the glass transition temperature region was extremely suppressed, compared with the corresponding E-drop observed for plain PHEMA samples. From measurements of the proton spin-lattice relaxation times t1ρh in the NMR study, the IPN-like composites were estimated to be homogeneous on a scale of less than ~2.4nm.

Transition behaviour of cellulose/poly(N-vinylpyrrolidone-co-glycidyl methacrylate) composites synthesized by a solution coagulation/bulk polymerization method

Abstract Cellulose/poly( N -vinylpyrrolidone- co -glycidyl methacrylate) (CELL/P(VP- co -GMA)) composites were synthesized via photopolymerization in the gel state of cellulose swollen in a mixture of VP and GMA monomers as reactive impregnant. The cellulose gels were formed from homogeneous solutions in N,N-dimethylacetamide/lithium chloride by coagulation in ethanol, followed by exchange of the coagulant for the monomer mixture. The thermal transition behaviour and phase construction of the (CELL/P(VP- co -GMA) composites obtained in film form over a wide composition range were investigated. For compositions containing less than 20 wt% CELL, it was reasonably assumed that the original network structure of cellulose gels was sufficiently perpetuated into the polymerized bulk. Dynamic mechanical analysis revealed that the lowering of the storage modulus ( E ′) of the copolymer-rich composites in the glass transition temperature ( T g ) region was extremely suppressed, compared with the corresponding E ′ drop observed for plain P(VP- co -GMA) samples. The additional treatment of as-polymerized composites with aqueous formic acid or sodium hydroxide solution gave rise to a marked elevation of their T g values, due to a certain crosslinking reaction in the copolymer constituent. A similar T g elevation phenomenon was noted in the case where CELL/P(VP- co -GMA) samples were subjected to a prolonged heat treatment at temperatures higher than ca. 175°C. This may be ascribed to the prominence of crosslinking between the cellulose and copolymer components through reaction of GMA epoxides with cellulose hydroxyls.

End-Crosslinking Gelation of Poly(amide acid) Gels studied with Scanning Microscopic Light Scattering

Network formation in the gelation process of end-crosslinked poly(amide acid) gels, which are the precursor of end-crosslinked polyimide gels, was studied by scanning dynamic light scattering. The gelation process is essentially non-reversible due to the formation of covalent bonds. The molecular structure formed in the gelation process is controlled by varying the equivalence ratio of end-crosslinker to oligomer during the preparation. It was found that a couple of relaxation modes are observed in the gelation point even for semi-rigid poly(amide acid) solutions. This is similar to flexible polymer solutions and convenient to characterize the molecular structure in the gelation processes. The fast mode is related to the cooperative diffusion process of the network structure formed by over lapped macromolecules, i.e., gel mode, which determines the averaged mesh-size of the network structure. The slow mode is related to the relaxation time of the formation of the transient network structure, which shows a slowing down close to the gelation point and disappears after gelation due to the formation of the permanent network structure.

Cellulose/poly(acryloyl morpholine) composites: synthesis by solution coagulation/bulk polymerization and analysis of phase structure

Cellulose/poly(acryloyl morpholine) (CELL/PACMO) compo sites were synthesized by bulk polymerization in the gel state of cellulose impregnated with reactive ACMO monomer. The thermal transition behaviour and phase structure of the CELL/PACMO composites obtained in film form were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and solid-state 13C NMR spectroscopy. For compositions rich in PACMO (CELL ≤ 30 wt %), it was revealed by DSC and DMA that the synthesized samples gave a composition-dependent Tg value higher than that of PACMO homopolymer, and the magnitude of the lowering of their dynamic modulus E′ in the glass transition region became extremely small in comparison with the corresponding drop in E′ noted for plain PACMO samples. These observations were interpreted as being due to the development of an interpenetrating polymer network (IPN)-type organization, resulting from successful fixation of an original netw ork structure of cellulose gels into the polymerized bulks. From the measurements of proton spin-lattice relaxation times in the NMR study, the IPN-like composites were estimated to be substantially homogeneous on a scale of a few nanometers. 0969--0239

Phase structure of chitin/poly(glycidyl methacrylate) composites synthesized by a solution coagulation/bulk polymerization method

Abstract Chitin/poly(glycidyl methacrylate) (PGMA) composites were synthesized via bulk polymerization in a gel state of chitin impregnated with reactive GMA monomer. The thermal transition behaviour and phase structure of the chitin/PGMA composites were characterized by differential scanning calorimetry (d.s.c.), dynamic mechanical analysis (d.m.a.), and solid-state 13C n.m.r. spectroscopy. For compositions rich in PGMA (chitin ⪅ 20 wt%), it was revealed by d.s.c. and d.m.a. that the polymerized samples gave a Tg value higher than that of PGMA homopolymer, and the magnitude of lowering of their modulus E′ in the glass transition region became extremely small, compared with the corresponding E′-drop noted for PGMA alone. To interpret these observations, it was reasonably assumed that an original network structure of chitin gels was sufficiently perpetuated into the polymerized bulks, accompanied by the formation of an IPN-like organization. Through the measurements of proton spin-lattice relaxation times in the n.m.r. study, the scale of homogeneous mixing in the IPN type of polymer composites was evaluated. The result suggested that the chitin and PGMA components were mixed mutually on a scale of a few nanometres in those composites.

Nanoincorporation of layered double hydroxides into a miscible blend system of cellulose acetate with poly(acryloyl morpholine).

Blend miscibility of cellulose acetate (CA) with poly(acryloyl morpholine) (PACMO) was examined by thermal transition measurements and solid-state (13)C NMR spectroscopy, in which CA materials of acetyl DS=1.80-2.95 were used. All the blends prepared gave a single Tg and formed an amorphous monophase homogeneous within a distance of ∼2.0nm. An Al/Mg-based, layered double hydroxide (LDH) was modified with different ionic oligomers, and an attempt was made to incorporate the respective organophilic LDHs (3-3.5wt%) into blend films of the miscible PACMO/CA pair, via bulk polymerization of an ACMO monomer/organo-LDH mixture and then blending CA with the polymer/inorganic hybrid precursor. Particularly, 12-hydroxystearic acid-modified LDH was well exfoliated and ultimately dispersed in the PACMO/CA matrix on a scale of less than a few tens of nanometers in thickness. This gave rise to a successful reinforcement effect leading to the improvement in thermo-mechanical property of the polymer blends.

Enthalpy Relaxation Behavior of Liquid-Crystalline Glasses of an Esterified Cholesterol Derivative and its Complex Salts with Aliphatic Amines

Abstract A cholesteryl hydrogen phthalate (CHP) and its complex salts with normal aliphatic amines (Cn-amines) are capable of forming a glassy liquid-crystalline phase, where an anisotropic organization of their fluid mesophase is frozen in an uncrystallized solid state. Differential scanning calorimetry (DSC) measurements were conducted for these glassy materials to examine an enthalpy relxation phenomenon, occurring when they were annealed adequately at temperatures lower than the glass transition temperature. The enthalpy relaxation behavior, monitored as evolution of a DSC endothermic peak, was analyzed in terms of a Kohlrausch-Williams-Watts type of stretched exponential equation, and the overall relaxation time τ and a parameter β chracterizing the distribution of the relaxation mode were evaluated. It turned out that the τ values obtained for CHP/Cn-amine salts were rather smaller than those for CHP per se, and β became close to unity when CHP was complexed with the Cn-amines through ionic interaction, the latter component employed having 12, 16, and 18 carbons. The activation energy for the relaxation process of the CHP/Cn-amine samples was considerably small, compared with that in the case of CHP alone, and tended to decrease with an increase in the carbon number of the amine component. An attempt was also made to estimate the fragility of these samples as glass.

High-Strength Network Structure of Jungle-Gym Type Polyimide Gels Studied with Scanning Microscopic Light Scattering

Latest high-strength gels overcome brittleness due to the inhomogeneities built in their network structure. However, the inhomogeneities still prevent precise characterization of their network structures by scattering methods. A new concept is to take advantage of the ensemble-averaged structure characterization with scanning microscopic light scattering (SMILS), in order to study the network structure and properties of inhomogeneous high-strength gels nondestructively in wide spatio-temporal ranges. In this study, two kinds of the jungle-gym type polyimide gels that have semi-rigid main-chains or rigid main-chains were synthesized in varying the preparing concentration and studied with SMILS. The optimal concentration of polyimide achieved ten times higher Young modulus than before.