1992 рік

A new approach to thermally stable elastomers for use between temperatures of 180°C and 275°C has been developed. Wholly aromatic poly(aryl ether ketone)s of various molecular weights have been synthesized with maleimide end groups. These structures have glass transition temperatures (Tzs) in the 150°C range, and when thermally crosslinked, they exhibited elastomeric characteristics ~30-50°C above their Tss (~200°C). The moduli of the networks at 200°C were comparable to those of unreinforced poly (dimethylsiloxane) elastomers ( 1-2 MPa) and the elongations ranged from 200 to 300%. The poly.(aryl ether ketone) elastomers showed exceptional thermal stability with little weight loss up to 490°C. The results from the chemorheology and stress relaxation measurements are discussed and compared to poly (dimethylsiloxane) networks.

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The structures of three poly(4-methyl-l-pentene) samples prepared with an AIC13 catalyst in C2HsC1 solvent at - 78, - 50 and + 5°C were studied by 13 C nuclear magnetic resonance spectroscopy. Surprisingly, no detectable amount of the 1,2-unit was observed in these three polymers, meaning that the isomerization reaction takes place much faster than the propagation reaction even at + 5°C. The four structural units previously known were confirmed in this work. In addition, a new structural unit, which implies successive hydride, methide and hydride shifts, was found.

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By defining a total correction factor Fa for the WAXS curves of amorphous homopolymers, a new method for the resolution between overlapping WAXS curves is proposed and used to evaluate the apparent crystallinity relative to the entire sample and the substantial crystallinity relative to the poly(ethylene oxide) grafts alone in polystyrene-graft-poly(ethylene oxide) binary copolymers. By introducing the concept of ‘amorphous matrix’, the same method is also used to evaluate the two kinds of crystallinities in poly(n-butyl acrylate-acrylic acid)-graft-poly(ethylene oxide) ternary copolymers. Both apparent crystallinity and substantial crystallinity increase with increasing poly(ethylene oxide) content, but the substantial crystallinity can characterize the effects of the backbone chains on the crystallization of the poly(ethylene oxide) grafts more distinctly and more reasonably than the apparent crystallinity

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Non-reactive polyamides were prepared by reacting a mixture comprising polymeric fatty acids, diamines such as ethylenediamine and hexamethylenediamine and an aliphatic monobasic acid or amine, to obtain a product of the desired extent of reaction, degree of polymerization, number average molecular weight, viscosity and softening point. The polymeric fatty acids used were of four types : imported acids ; 97/3, 83/17 and 75/25 dimer/trimer mixtures, Empol 1010, 1018 and 1024 respectively and indigenous dimer acids. The indigenous acids were prepared in the authors' institute and comprised mixtures of monomer, dimer and trimer acids. In all the polyamides prepared, the extent of reaction was ~96%, the degree of polymerization ranged from 5-14, the number average molecular weight ranged from 1423-11 848, the viscosity of 35% solution in butanol/toluene 1:1, v/v, 19-147 s at 25°C (Ford Cup No. 4) and the softening point was 94.5-115°C. Most of these polyamides have properties comparable to the commercially available polyamides used in flexographic inks, adhesives and over-print varnishes.

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Calorimetric studies of the diacetylene monomer bis-isopropylurethane of 5,7-dodecadiyn-l,12-diol, synthesized by a new method, and the polydiacetylene (PDA) from this monomer (PDA-IPUDO) rule out the possibility that monomer melting plays a significant role in the thermochromic phase transition of this polymer. X-ray powder diffraction studies at room temperature and 150 + 5°C reveal that the structural changes which occur in the course of the endothermic thermochromic phase transition are analogous to those of a related PDA.

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High resolution x3C n.m.r, spectra were obtained from two ethylene-propylene copolymers containing 23% (EP23) and 36% (EP36) propylene swollen with CDC13 after v-irradiation, although the line widths increased and the intensities of the original resonances decreased with increasing radiation dose. A resonance at 42 ppm after low doses (0.02-0.14 MGy) was attributed to methine carbons in H-crosslinks. New resonances at 11.3, 14.1, 14.5, 22.7 and 23.1 ppm were assigned to methyl and methylene groups on various chain-end structures arising from main chain scission, and yields (G values) were derived for doses up to 2 MGy. G(scission) values of 0.16 and 0.37 for EP23 and EP36, respectively, were in good agreement with values derived previously from soluble fraction measurements and from solid-state n.m.r, spectra after much higher radiation doses. The proportions of different chain-end structures suggested that scission was favoured by a factor of 1.6 at C-C bonds adjacent to the methyl substituents compared with other main-chain C-C bonds.

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Extended X-ray absorption fine structure (EXAFS) experiments were performed at 25 and 105°C for Zn (II) salts of ethylene-methacrylic acid (5.4 mol% ) copolymer and their complexes with 1,3-bis (aminomethyl) cyclohexane (BAC) (EMAA-Zn-BAC). The zinc carboxylate in EMAA-Zn-BAC systems was in a four-fold coordination at room temperature. The Zn-0 distance increased with increasing BAC content, and became smaller at 105°C than at room temperature for EMAA-06OZn and EMAA-06OZn-04OBAC but scarcely changed with temperature for EMAA-0.60Zn-0.97BAC. The fluctuation factor (a) was larger at 105°C than at room temperature for all the samples, due to thermal vibration. In this paper, it is pointed out that these EXAFS results support the presence of an order-disorder transition in ionic clusters

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E.s.r. studies on N-methyl-N-allylmethacrylamide (MAMA) and allyl crotonate (AC) were undertaken in order to obtain information on the mechanism of their cyclopolymerization and reactivities of the double bonds involved in these dienes. Amino, hydroxyl and phenyl radicals were used as initiating species. The radicals detected revealed that the rate of intramolecular cyclization of MAMA is faster than that of AC and the methacryloyl group of MAMA has even lower reactivity than allyl and crotonyl groups. The extremely low reactivity of the former is considered to be mainly due to steric hindrance and partly due to the unconjugative nature of its C=C and C=O double bonds.

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Values of the polymer/solvent interaction energy parameter were obtained within the Flory and Fujisawa-Hamada-Nakajima (FHN) corresponding states frameworks for the system carbon tetrachloride/poly(vinyl methyl ether). The FHN theory follows more closely the free-volume variation with temperature and accordingly, one is better able to correct for these free volume effects, obtaining a polymer/solvent interaction energy parameter independent of temperature. The scaling is also such, with FHN, that it results in lower, i.e. more negative, interaction energy parameters.

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Crosslinked networks displaying both thermotropic and lyotropic liquid crystalline phases have been prepared from hydroxypropyl cellulose. The phase transitions from the liquid crystal to isotropic state are reversible for materials with moderate levels of crosslinking. These materials show characteristic optical textures similar to uncrosslinked cellulose-based liquid crystal polymers although well defined patterns typical of cholesteric structures were not observed. The samples were insoluble in water, but high levels of swelling with acetone and benzene were observed and in the steady state condition a lyotropic phase was present even though the level of swelling was in excess of 500%. A reversible liquid crystalline to isotropic phase was observed with the swollen materials as the fraction of sweUant was adjusted. The elastomers show marked global orientation effects when mechanically deformed but surprisingly the response was less dramatic than in some side-chain liquid crystal elastomers.

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