E. M. Antipov

First observation of a columnar mesophase in a carborane-containing main-chain semiflexible copolymer

A comparison of the structure and phase composition of a recently synthesized carborane-containing copolymer and its wholly organic analogue was carried out by DSC and X-ray analysis in a wide temperature range between 20–300°C. It is found that the incorporation of 10 mol-% of m-carboranedicarboxylic units in the polymer prepared from 4,4′-dihydroxybiphenyl and sebacic acid, acting as mesogen and flexible spacer, respectively, leads to the formation of a columnar mesophase at elevated temperatures. This newly observed phase occurs in addition to the crystalline and liquid crystalline smectic phases known for the wholly organic analogue.

Structure of trans-1,4-polybutadiene synthesized with a new catalyst system

Abstract The structure, phase composition, and temperature behavior of two trans-1,4-polybutadienes (TPBs) were studied by means of x-ray scattering and differential scanning calorimetry (DSC) techniques. The two samples examined were (1) PB synthesized using an immobilized titanium-magnesium catalyst and (2) a random copolymer based on PB prepared with a homogeneous vanadium-containing catalyst used as a reference material. It was found that the nascent structure of the first PB involves three phases: crystalline, mesomorphic (low-temperature form), and amorphous. In the vicinity of 65°C, a first-order phase transition occurs. The system becomes biphasic and contains the high-temperature form of the mesophase, as well as the amorphous phase, component. Above 165°C, the polymer melts to form a single-phase isotropic melt with a structure typical of liquids. The lateral dimension of crystallites reversibly changes at the crystal-mesophase transition. It is suggested that during annealing of the mesophase f...

Structure of Polybutadienes Synthesized with a New Catalyst System, 2 - Blends of trans- and cis-1,4-polybutadiene

The structure, composition and temperature behaviour of polybutadienes prepared with binuclear metal complex catalysts immobilized on a solid carrier are investigated by differential scanning calorimetry, infra-red spectroscopy and X-ray scattering. Polybutadienes of nascent structure are blends of trans-1,4- and cis-1,4-homopolymers, whereas 1,2-units are randomly distributed in both macromolecules. The blends exhibit two-step melting characteristics for the crystalline trans-1,4-polybutadiene: the low-temperature transition from the monoclinic crystal form to the pseudohexagonal mesophase and the high-temperature transition from mesophase to the melt. A bimodal character of the endothermic maximum in DSC traces was observed for the former transition. In addition, it was shown that the nascent blend treated by hot toluene posseses a three-phase structure and contains, besides the well-known trans-1,4-polybutadiene crystalline and amorphous phases, an additional phase component of unknown structure.

Structure of Polybutadienes synthesised with a New Catalyst System, 3 - Random Copolymers of trans-1,4- and 1,2-polybutadiene

The structure and phase composition of random copolymers based on mesomorphic trans-1,4-polybutadiene containing a different amount of vinyl units (2-41 mol-%) were studied at various temperatures by X-ray analysis and differential scanning calorimetry. As the amount of 1,2-units in the polymer increases, temperatures of the phase transitions crystal-mesophase and mesophase-melt decrease, thus leading to a more narrow temperature range corresponding to an existence of the mesomorphic state. At a concentration of alien units of about 30 mol-%, the copolymer loses the ability to form a mesophase. Upon a further increase of 1,2-unit content (35-40 mol-%), the copolymer no longer crystallizes. The phase diagram of the copolymer is discussed in relation of temperature of phase transitions versus composition. It was shown that the destruction of the regular structure of the mesophase polymer by incorporation of alien units in its main chain leads to substantial decrease of the tendency of the material to mesomorphism, even more strongly than its ability to crystallize.

Comparative analysis of the structure of two thermotropic LC copolyesters

A comparative study of the structures of two thermotropic liquid crystal copolyesters (LCP) was carried out. The first copolymer, LCP-1, comprises three different monomer units of equal length, whereas the second copolymer, LCP-2, contains two monomer units which differ significantly in length. Both copolymers exhibit random structure. It was established that despite the irregular structure both copolymers have the ability to crystallize. Moreover, during crystallization of LCP-1 microphase separation into two phases occurs. Each phase has an orthorhombic crystal structure but with slightly different parameters of the unit cell. The reason for this difference is probably associated with configuration isomerism because of possible head-to-head or head-to-tail additions during synthesis of the copolyester. Upon annealing, the maximum degrees of crystallinity are 35% and 25% for LCP-1 and LCP-2, respectively. The noncrystalline fraction of the material, whose content exceeds appreciably the content of the crystalline phase, shows a LC smectic structure. However, the fundamental difference between the two copolymers is that, in the case of LCP-1, the periodic layer structure is observed, whereas for LCP-2 the layer structure is aperiodic. The above phenomena are universal, and this makes it possible to predict the structure and character of temperature behavior of any representative of the class of fully aromatic rigid-chain copolyesters only from the chemical formula of the copolymer.

THE EFFECT OF MOLECULAR-WEIGHT ON THE STRUCTURE AND TEMPERATURE BEHAVIOR OF A THERMOTROPIC MAIN-CHAIN LIQUID-CRYSTALLINE COPOLYESTER

The structure of a fully aromatic thermotropic liquid crystalline (LC) copolyester poly-[(phenyl-p-phenylene)-co-(terephthalate)-co-(p-hydroxybenzoate)] (PES) prepared from terephthalic acid, phenylhydroquinone, andp-hydroxybenzoic acid at a molar ratio of 45/45/10, respectively, was studied at ambient and elevated temperatures by means of x-ray diffraction and differential scanning calorimetry as a function of molecular weight. On heating of PES fibers with fixed ends an irreversible phase separation process takes place above the glass transition point and two different crystalline phases are formed. A model is proposed where the phases are assumed to contain the constituents of the statistical copolymer in different amounts. The relative volume fraction of the two crystalline modifications depends on the molecular weight of the investigated fibers. At higher temperatures the melting of the two crystalline phases and their transition to a LC nematic mesophase is observed.

Some unusual structures in thermotropic mesophase polymers

Random copolymers of polyester type have been shown to exhibit simultaneous crystallization into two different crystalline forms which are transformed into different hexagonal mesophase structures on heating. Some of these polymers have been found to form LC aperiodic smectic structures. Liquid Crystal elastomers, H-bonded networks and grafted LC materials are discussed. Mechanical field creates the director reorientation in monodomain elastomers and H-bond networks which is discussed in terms of soft elasticity. Grafting of particular LC polymer on fluorine containing polymer support results in the formation of composite sandwich-type material. Mechanical deformation leads to the macroscopic alignment of the LC grafted layer. There is a pronounced memory effect, which is manifested in the macroscopic alignment of the grafted layer under cooling from an isotropic to a LC state. The phenomenon observed results from the strong influence of the polymer support on the LC director orientation. The optical and mechanical properties of sandwiched samples can be regulated in wide limits.

Temperature Evolution of the Structure of the Thermotropic Co-Polyester: Poly[(Phenyl-P-Phenylene)-Co-(Terephtalate)-Co-(P-Hydroxybenzoate)]

The crystalline structure and phase behaviour of the thermotropio main-chain liquid-crystalline random copolyester (PES) prepared from terephthalic acid, phenylhydroquinon and p-hydrobenzoic acid (molar ratio 45/45/10) is determined by X-ray diffraction and differential scanning calorimetry in a wide temperature range.