Search

This paper describes the ring-opening methathesis polymerization of homopolymers and copolymers of exo- and endo-2-cyanobicyclo[2.2.1]hept-5-ene (norbornenenitrile) in solution. Polymerization kinetics were followed via 1H NMR spectroscopy in real time while the final polymer microstructure was determined via 13C NMR. While pure endo monomer does not polymerize readily, it copolymerizes with exo monomer, rapidly and to high conversions. The structure of the copolymer appears to be quite similar to that of exo homopolymer. We conclude that exo monomer adds directly to either exo or endo, while endo-endo addition is sterically hindered.

A RIM polymerization process for nonpolar cycloolefins is described. WCl6 catalyst was modified with the diethyl acetal of acetaldehyde to increase its solubility and activity, thereby reducing residual volatiles m the RIM polymerization. The catalyst was activated with aluminum alkyls, and norbornene nitrile (NN) was used to control polymerization rates. Methyltetracyclododecene (MTD) copolymerizes easily with NN, but at high MTD levels there appears to be phase separation, indicating block copolymer formation. NN controls polymerization rate and participates in the polymerization, yielding copolymers with high Tg. Polymer properties were analyzed by dynamic mechanical analysis and DSC. The monomer and polymer compositions were analysed by NMR spectroscopy. Two-dimensional NMR determined that MTD was a mixture of two isomers, and high resolution 13C NMR of the copolymers showed high conversions in all cases.

It is shown by means of x-ray diffraction and PMR broad line spectroscopy, that the structure of the flexible spacer drastically influences the order within the nematic phase of thermotropic polyesters based on the 4,4′ - dioxy- 2, 2′-dimethyl azoxybenzene moiety. The existence of two distinct molecular arrangements is proposed: one is characterized by an unusually high degree alignment of macromolecules, the other by a lower degree of alignment. The former is displayed by spacers with an even number of methylene units in the alkanedioic acid moiety of the spacer (odd number of bonds); the latter by a certain number of flexible spacer moieties with an odd number of methylene groups (even number of bonds), as well as in mixed spacers irregularly alternating along the macromolecular chain (copolyesters).

The homologous series of 4, 41 -dialkanoyloxydiphenyldiacetylenes with n ranging from zero to ten have been prepared. Optical microscopy, differential scanning calorimetry and X-ray diffraction have been used to study the mesomorphic behavior of these compounds. All homologs with n=1-7 are liquid crystals having nematic phases. In addition to nematic phases, these esters have extensive solid-state polymorphism. The transition enthalpies and entropies have also been calculated.

Etude de poly(dioxy-4,4' dimethyl-2,2' azoxybenzene alcanedioyl): il existe un arrangement cybotactique et une phase nematique «ordinaire»

A novel extension of the Yamazaki reaction is used to prepare block copolymers having rigid blocks of poly-(p-benzamide) (PBA) and semiflexible blocks of polyamide-hydrazide. A PBA prepolymer having M ≅ 10,000 was synthesized by the usual Yamazaki reaction using triphenylphosphite. As previously reported, higher-molecular-weight PBA could be obtained using 4-N-(4′-aminobenzamido)benzoic acid containing a preformed amide linkage. Addition of p-aminobenzhydrazide and terephthalic acid then led to formation of the polyamide-hydrazide blocks using as the active reactant the diphenylphosphite formed as a by-product in the first polymerization. Evidence that a block copolymer is produced includes an increase in inherent viscosity during the second step, differences in the solubility of the copolymer compared to the homopolymers, and comparison of the phase diagram of the block copolymer in N-methylpyrrolidone having 4% added LiCl with those of a random copolymer, and of mixtures of the two homopolymers. The critical concentration required to form a nematic phase in solutions of the block copolymers is correlated with the length (or axial ratio) of the rigid block, and with its proportion in the copolymer.

Unsaturated polyesters based on maleic and phthalic anhydrides have been modified by 1,3,4-oxadiazole derivatives, viz. 2,5-bis-(m- or p-carboxyphenyl)-1,3,4-oxadiazole and 5,5-bis-(m- or p-carboxyphenyl)-1,3,4-oxadiazolyl-2,2. A study has been made of the influence of the modifying additives on the formation of polyethylene glycol maleatophthalates and on curing of the latter by oligoester acrylates, as well as the effect of these additives on the properties of the cured products. It is shown that the additives have an accelerating influence on the polycondensation reaction. The modified polyesters have in the oxadiazole ring structure a tertiary nitrogen atom, which accelerates peroxide decay during copolymerization with the unsaturated monomers, and plays the role of an accelerator. The modifying additives enhance mechanical properties of the cured polyesters, giving better heat stability, increased hardness and higher breaking stress levels under compression. Changes in the foregoing properties stem from the influence of 1,3,4-oxadiazole derivatives on cis-trans-isomerization of the maleate units into fumarate ones. An 85% degree of isomerization is attained, mainly in the initial period of the reaction.

A homologous series of polyesters was prepared from 4,4′-dihydroxybiphenyl and dibasic acids having 5-12 methylene units. The mesophases formed at elevated temperatures were studied by differential scanning calorimetry and polarized light microscopy. This family exhibits an unusual odd-even effect when the transition temperatures are plotted as a function of the number of methylene units in the dibasic acid. Not only do the points for odd and even members fall on different curves, but the odd members exhibit a nematic phase over a very short temperature interval, while the even members form a highly ordered smectic phase. For both the odd and even series, the transition temperatures are significantly depressed when the inherent viscosity falls below 0.2 dL/g. The largest depression occurs for the crystal melting transition, so that polymers of low ηinh show anisotropic and biphasic regions over wider temperature ranges. A copolymer formed from an equimolar mixture of sebacic and chiral (+)-3-methyl adipic acid forms a cholesteric phase. Evidently copolymerization destabilizes the smectic phase which would have been expected. The results are discussed in terms of existing theory.

Mesomorphic polyesters were synthesized from 4, 4′-dihydroxy-α-methylstilbene and adipic acid (P-6) or (+)-3-methyl adipic acid (P-6M). P-6 forms a thermotropic nematic phase and P6-M a thermotropi...

The temperature dependence of phase structure in 5,6-dioxycarbonyl [2.2.1] bicyclohept-2-ene was investigated by Dsc, X-ray diffraction, optical microscopy and 1H NMR. The existence of an endotherm in DSC, loss of optical anisotropy, formation of diffuse diffraction patterns and drastic changes in 1H Nmr relaxations indicated the formation of a ‘plastic crystal’ phase, well below the melting point. NMR relaxation rates were measured as a function of temperature. There are sharp changes in relaxation rates at the plastic crystal transition. The transition introduces rapid molecular rotation, without translation. TIH relaxations show a change in magnitude for the rate, but no change in relaxation mechanism.

4,4′-Diaminobenzanilide (DAB) was reacted with diacids via the Yamazaki phosphorylation reaction to yield simple polyamides and random copolyamides. The use of DAB was found to promote polycondensation because DAB contains a preformed amide linkage which minimizes the amounts of by-products formed. It also maximizes polymer solubility since the monomer is unsymmetrical. The order of the inherent viscosity values of the polymers obtained from DAB by reaction with different diacids, isophthalic > aliphatic > terephthalic, was found to parallel polymer solubility in the reaction medium. The inherent viscosity of the polyamide based on terephthalic acid, DAB-T, was increased greatly by copolymerization, isophthalic acid being more effective than an aliphatic diacid in this regard. None of the polymers formed a thermotropic nematic phase, but the copolymer having an equimolar ratio of terephthalic and adipic acid formed anisotropic solutions in 100% sulfuric acid at polymer concentrations exceeding 40%. Strong films were cast from such solutions.

Phase transitions in thermotropic nematic and cholesteric main chain polyesters were investigated by polarizing microscopy and differential scanning calorimetry. The polymers were formed by condensation of 4, 4′-dihydroxybenzene and 2, 2′-dimethy1–4, 4′dihydroxyazoxybenzene with various diacid chlorides acting as flexible spacer groups. Polydisperse homopolymers and copolymers, sharp fractions of homopolymers and mixtures of polydisperse polymers with a low mass mesogen were investigated. Supercooling at the mesophase-isotropic and solid-mesophase transitions, sharpness of the nematic-isotropic transition (range of N+I biphase), polymer crystallization from the mesophase melt, and enhancement of crystallinity upon addition of a low mass nematic, were studied.

Polymers displaying liquid crystalline behavior have been known since 1933 (1,2) and the theoretical foundation for solutions of long rods was established by Onsager (3) and Flory (4) over 25 years ago. Thermotropic mesomorphism in polymers, however, was largely ignored until the recent development of ultra-high strength, ultrahigh modulus fibers spun from nematic solutions of rigid aromatic polyamides. It was then soon realized that synthetic polymers have a strong tendency to promote the formation of liquid-crystalline phases in solution or in melt, provided that mesogenic moieties be incorporated either into side groups or into the backbone itself (5). The field of liquid-crystalline polymers, originally confined mainly to helical rodlike macromolecules, has recently expanded into the realm of semi-flexible and flexible synthetic macromolecules and is now at the forefront of industrial and academic research.