F. Cser

Investigations in the field of radiation-induced solid-state polymerization—XXIV The polymerization of cetyl vinyl ether

Abstract According to our investigations, cetyl vinyl ether has a smectic liquid crystalline state between its m.p. (16·5°) and −2·5°. Below this temperature range, it has two different solid crystalline states with a phase transition point at −16°. Solid-state polymerizations carried out in the latter two systems gave kinetic curves with linear character but those curves obtained in the liquid crystal line phase were accelerating types. This observation can be explained by the formed polymer not destroying the crystal lattice but actually stabilizing the regular smectic structure. The transition from the liquid crystalline into the three-dimensional structure takes a few hours, therefore it is possible to carry out even below −2·5° an accellerating type of polymerization corresponding to the liquid crystalline structure. The mechanism of the polymerization is probably cationic. The polymers obtained show an optical birefringence and melt sharply at 36°. The structure of the polymer reflects that of the monomer matrix. This feature disappears only after having melted the system. The DP of the polymers does not depend on the polymerization parameters (temperature, dose rate), but is governed by the size of those “crystal sections” which are perfect from the viewpoint of polymerization linkage.

Polymerization in liquid crystal. XVIII: Effect of the polyethyleneoxide main chain on the properties of polymers containing mesogenic groups in the side chain

Abstract The effect of the main chain on the mesomorphic properties was studied on the basis of the three-component thermodynamic model of polymers containing mesogenic groups in the side chain. Poly(ethylene oxide) oligomers substituted with mesogenic groups were prepared by reacting epichlorohydrin with mesogenic molecules. It was established that the glass transition temperatures of these oligomeric products were markedly reduced in comparison to polyacrylates containing the same rigid core. The relatively flexible main chain increases the clearing point relative to that of the monomer. Clearing point rises with length of the main chain. A flexible main chain suppresses the vibration of the rigid cores thus increasing the thermal stability of the mesomorphic structure. No explanation was found for the exothermic latent heat of 170 J/g observed during the first melting of the cholesteryl succinyl epoxypropionate oligomers and polymers.

Polymerization in liquid crystal — XVII. Effect of flexible substituents in the mesogenic side-chain on the behaviour of mesogenic polymers☆

Nine monomers, derivatives of the phenyl ester of acryloyloxybenzoic acid with general were synthesized; X was -(CH2)6O-, -(CH2)2O- or nothing; R was -O(CH2)4H, -OCH3, or -H. Polymers from all the monomers were studied by polarization microscopy, differential scanning calorimetry and mechanical relaxation spectroscopy. It was established that transition temperatures of the polymers, as plotted against the chain length of the spacer as well as of the p-alkoxy substituent, were monotonous functions tending to limiting values. A nematic state was found only for the polymer from p-butoxyphenyl-p′-acryloyloxy hexoxybenzoate.

Investigation of the mesomorphic structure of p-alkoxy-phenyl-p-acryloyloxy benzoate polymers

Abstract Polymers were prepared from the phenyl and p-alkoxy-phenyl esters of p-acryloyloxy benzoic acid. These polymers resulted in anisotropic systems during the cooling of their melt or on concentrating their solutions. The anisotropic polymers had a Schlieren texture. On the basis of small- and wide-angle X-ray scattering the polymers are identified as non-crystalline, the diffuse reflections are related to their molecular dimensions. By GPC in sym-trichloro benzene a broad distribution of molecular dimensions was observed where the number average molecular dimension corresponded to that measured in bulk. The average degree of polymerization is about the same for the five polymers. The polymer molecules are cylinders of 8–10 nm length and 2.5-3.9 nm diameter, which form the anisotropic state by close packing. The polymer molecule cylinders are made up of aperiodic helices, therefore the nematic state becomes glassy on cooling without formation of any crystalline polymer.

Polymerizations in liquid crystals—II [1] copolymerization of P-methyl-P-acryloyloxy-azoxybenzene and cholesteryl vinyl succinate in the meso phase

Abstract Phase diagram of p -methyl- p ′-acryloxy azoxy-benzene (MAAB) and cholesteryl vinyl succinate (CVS) was determined. The two crystalline materials form a cutectic mixture at a CVS content of 0.56 mole fraction. In the isotropic and mesomorphous states, however, they form a totally miscible series. The total heat of mixing is −704.5 cal/mole; melting heats of pure MAAB and CVS are 5369.3 and 5665.3 cal/mole while those of the mesophases are 101.5 and 97.4 cal/mole respectively. In the mesophase, copolymerization follows the same composition regularities as in the liquid phase but has a lower rate. Melting point of the copolymer decreases as the CVS content increases up to M cvs = 0.6; above this value, it is constant.

Polymerizations in liquid crystals—III [1]. Studies on the structures of some polymeric azoxyacrylates

Abstract The structures of some azoxy-acrylate polymers were studied by small-angle and wide angle X-ray diffraction methods. The phase diagram of the p -methyl- p ′-acryloyloxy-azoxybenzene monomer/polymer system was determined by DSC. X-ray diffractometry, thermomechanical measurements and polarization microscopy. The monomer and polymer form a complete miscible series both in the nematic phase and in the isotropic liquid state. At room-temperature, the polymers were found to be in the glassy nematic phase.

INVESTIGATIONS IN THE FIELD OF RADIATION-INDUCED SOLID-STATE POLYMERIZATION. XIII. INHIBITION OF THE SOLID-STATE POLYMERIZATION

Abstract The solid system of n -vinylsuccinimide with benzoquinone is characterized by the formation of an eutectic. Up to the composition of the eutectic, the rate of the solid-state polymerization decreases regularly with an increase in the BQ concentration. Beyond the eutectic composition the polymerization rate is constant even at very high concentrations of benzoquinone. This is explained by the development of a system (as shown by the X-ray patterns) with maximum heterogeneous interfaces and of a very fine structure in which the inhibitor interfaces and the inhibitor molecules are able to exert their inhibiting action on the surfaces of the monomer crystals. The phase diagram of the n -vinylsuccinimide -phthalic anhydride system shows a eutectic also. In this case, polymerization rate increases with increasing phthalic anhydride concentration, and no energy transfer effect can be observed in the heterogeneous system containing an aromatic component.

Polymerization in liquid crystals—IX: Structural investigations of copolymers containing p-methyl-p′-acryloyloxy azoxybenzene and cholesterylvinyl succinate☆

Abstract Structure of copolymers of p-methyl-p′-acryloyloxy azoxybenzene (MAAB) with cholesterylvinyl succinate (CVS) was studied by small- and wide-angle X-ray diffractometry, DSC, polarizing microscopy, and thermomechanical methods. The copolymers were found to be anisotropic non-crystalline substances in which the radial distribution of the radius of gyration of inhomogeneities corresponds to that of the diameter of the molecules determined by GPC. Both phase transition temperatures and clearing points of copolymers show a minimum as functions of the composition. On both sides of this minimum, the copolymers have different structures. At higher MAAB contents, the copolymer structure is similar to that of polyMAAB; at lower MAAB concentrations, alternating copolymer is formed similar in structure to polyCVS. For identification of the structures, copolymer/comonomer phase diagrams were also investigated.

Investigations in the field of solid-state polymerizations—XXXIII: Molecular motion studies on acenaphthylene-poly-(acenaphthylene) systems

Abstract Spin-lattice relaxation measurements of composite systems with different monomer-to polymer ratios are consistent with the phase diagram described previously. Relaxation curve of the system with monomer content higher than Mcr shows behaviour different from those for systems of higher polymer content. Below Mcr, all composites have the same slope and similar T1 values in the glassy state. Infra-red spectra confirm the similarity between the molecular arrangement in the monomerpolymer system and in the crystalline monomer. X-Ray diffraction measurements show a diffusion of monomer molecules from their crystalline particles into the glassy polymer. According to the new diffusion scheme proposed, an interface layer (δ) is formed between the crystalline monomer and the glassy polymer in which a diffusion, controlled polymerization can proceed.

Polymerization in liquid crystals—XI: Copolymerization of N-acryloyl piperidine with cholesteryl acrylate and phenyl-p-acryloyloxy benzoate☆

Abstract N-acryloyl piperidine (AP) was copolymerized with mesogenic monomers [such as cholesteryl acrylate (CA) and phenyl-p-acryloyloxy benzoate (PAB)] in isotropic solution using radical initiation (AAP = 1.1, rCA = 0.16, and rAP = 0.81, rPAB = 0.16. The copolymers are anisotropic having minimum values of transition and clearing points with composition. The composition corresponding to the minimum is a boundary between two structures as indicated by wide-angle X-ray scattering. Distribution of the gyration radii determined by GPC in tetrahydrofuran is identical to that of solid polymers measured by small-angle X-ray scattering, except that the average value of the latter is about 10−6 cm less than that of the former. It was established that AP as a non-mesogenic comonomer did not suppress the mesomorphism of the copolymer and in fact formed mesomorphic homopolymers. In the solid polymer, the macromolecule which is anisotropic in geometry was found to form the structural unit having a minimum of the melting and clearing point with composition, as for a eutectic system.