Noritaka Kimura

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.

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.

Conformational analysis of 1,2-dimethoxyethane and 1,2-diphenyloxyethane incorporated in nematic liquid crystals

Abstract The conformations of flexible chain molecules incorporated in a nematic environment have been investigated. The phase behaviours and orientational characteristics of 1,2-dimethoxyethane (DME) dissolved in 4′-methoxybenzylidene-4-n-butylaniline at low solute mol fraction have been reported in our previous paper. In this work, proton–proton and carbon–carbon dipolar coupling constant measurements were attempted in addition to 2H NMR observations of quadrupolar splittings. These conformation-dependent properties were analysed according to the rotational isometric state (RIS) simulation scheme previously proposed. Our treatment rests on the assumption that the molecular axis of the chain should tend to align along the nematic field. Studies were further extended to a mixture of 1,2-diphenyloxyethane (DPE) with a nematic liquid crystal, 4,4′-azoxyanisole. Replacement of the terminal methyl groups in DME by phenyl groups leads to DPE. The results of the analysis indicate that the fraction of elongated ...

On the correlation of the glass transition temperature of a copolymer with its comonomer sequences

The glass transition temperature of a copolymer depends not only on chemical composition but also on its comonomer sequences. This experimental fact is explained by Bartons and Johnstons equations. Their equations, though complicated, become simple, if a suitable parameter is used to describe the comonomer sequences. It is shown that with these new expressions, their equations can be used to understand glass transition temperatures of two additional types of copolymers, compatible multiblock copolymers and homopolymers with various tacticities treated as steric copolymers.

A note on analysis of glass transition temperature data of steric copolymers

The tacticity dependence of the glass transition temperature ( T g ) of a steric copolymer, such as poly(methyl methacrylate), composed of meso and racemic dyads, is discussed using T g equations which is useful for ordinary copolymers. With the T g values of isotactic and syndiotactic forms together with that of the heterotactic form newly determined therefrom, it was shown to predict satisfactorily the T g value of a given steric copolymer from its triad data. In addition, it turned out that in a plot of T g against dyad or (syndiotactic) triad fraction, a linear correlation can be expected only for steric copolymers containing negligible amounts of the heterotactic triad and, in general, the data are scattered due to different polymerization kinetics.

Effects of sequence length distribution on heat capacity and glass transition temperature of styrene—methyl methacrylate copolymers

Abstract Heat capacities of alternating, statistical and diblock copolymers of styrene and methyl methacrylate were measured with a differential scanning calorimeter from 200 to 450 K to examine the additivity of heat capacity. In both solid and liquid regions, the heat capacity was found to be additive, in most cases within ± 2% error irrespective of sequence length distribution. The glass transition temperatures, determined from enthalpy—temperature plots, depended on sequence length distribution as well as composition. This behaviour, although theoretically expected, was found to be complicated by another factor, tacticity.