Crystallization behavior of a novel ether ketone polymer containing meta-phenylene linkage: PEKEKK (T/I)

Nonisothermal and isothermal melt crystallization kinetics of a novel aryl ether ketone polymer containing meta-phenylene linkages, PEKEKK (T/I), were studied by differential scanning calorimetry (DSC). The Avrami equation modified by Jeziorny and a new approach by combining the Avrami equation with the Ozawa equation could describe the nonisothermal crystallization. Isothermal crystallization could also be described by the Avrami equation. The activation energies were 187 and 159 kJ/mol for nonisothermal and isothermal crystallization, respectively. Using the Hoffman-Weeks method, the equilibrium melting point T-m(o) was estimated as 353 degrees C. From the spherulitic growth equation proposed by Hoffman and Lauritzen, the nucleation parameter K-g of the isothermal melt crystallization was estimated as 5.49 x 10(5) K-2. The crystallization characteristics of PEKEKK (T/I) were compared with those of all-para PEKEKK. The differences were explained by differences in the chain flexibility of the two polymers.

Shear induced mixing/demixing: Blends of homopolymers, of homopolymers plus copolymers, and blends in solution

Shear may shift the phase boundary towards the homogeneous state (shear induced mixing, SIM), or in the opposite direction (shear induced demixing, SID). SIM is the typical behavior of mixtures of components of low molar mass and polymer solutions, SID can be observed with solutions of high molar mass polymers and polymer blends at higher shear rates. The typical sequence with increasing shear rate is SIM, then occurrence of an isolated additional immiscible area (SLD), melting of this island into the main miscibility gap, and finally SIM again. A three phase line originates and ends in two critical end points. Raising pressure increases the shear effects. For copolymer containing systems SID is sometimes observed at very low shear rates, preceding the just mentioned sequence of shear influences.

Synthesis and thermotropic liquid crystalline behaviour of novel poly(aryl ether ketone)s with a lateral methoxy group

Novel poly(aryl ether ketone)s containing a lateral methoxy group were synthesized by nucleophilic substitution reactions of 4,4'-biphenol and methoxyhydroquinone with 1,4-bis(4-fluorobenzoyl)benzene in a sulfolane solvent in the presence of anhydrous potassium carbonate. Their thermotropic liquid crystalline properties were characterized by a variety of experimental techniques, e.g. differential scanning calorimetry (DSC), polarized light microscopy and temperature-dependent FTIR. Thermotropic liquid crystalline behaviour was observed in the copolymers containing 30-80 mol-% mexthoxyhydroquinone. Both melting (T-m) and isotropization (T-i) transitions appeared in the DSC curves. The polarized light microscopy study of the liquid crystalline copolymers suggested their ordered smectic structures. As expected, the copolymers had lower melting transitions than the biphenol-based homopoly(aryl ether ketone)s because of the copolymerization effect of the crystal-disrupting monomer methoxyhydroquinone.

Molecular heterogeneity and crystal morphology in metallocene short chain branch polyethylene (SCBPE)

Metallocene, a newer generation of commercial polymerization catalysts for polyolefins, is best known for its "single sitednss", and the intermolecular structural homogeneity of metallocene polyethylene copolymer is a very interesting research issue. The molecular segregation effects on the crystallization, melting and crystal morphologies of metallocene SCBPE have been investigated with DSC and TEM. The multiple endothermic peaks were observed in the DSC thermograms during heating experiments. The heterogeneity increases as branching content increases, the lamellae becomes thinner, and lamellae distribution becomes broader. Both macroscopic segregation (between two crystal aggregates) and microscopic segreation (between two lamellae) have been observed when SCBPE crystallized from phase separated melt.

Phase behavior of polymer blends

The present report deals with some results on phase behavior, miscibility and phase separation for several polymer blends casting from solutions. These blends are grouped as the amorphous polymer blends, blends containing a crystalline polymer or two crystalline polymers. The blends of PMMA/PVAc were miscible and underwent phase separation at elevated temperature, exhibited LCST behavior. The benzoylated PPO has both UCST and LCST nature. For the systems composed of crystalline polymer poly(ethylene oxide) and amorphous polyurethane, of two crystalline polymers poly(epsilon-caprolactone) and poly[3,3,-bis-(chloromethyl) oxetane], appear a single T-g, indicating these blends are miscible. The interaction parameter B's were determined to be -14 J cm(-3), -15 J cm(-3) respectively. Phase separation of phenolphthalein poly(ether ether sulfone)/PEO blends were discussed in terms of thermal properties, such as their melting and crystallization behavior.

Radiation effects on the immiscible polymer blend of nylon1010 and high-impact polystyrene (HIPS) I: Gel/dose curves, mathematical expectation theorem and thermal behaviour

This paper studies the radiation properties of the immiscible blend of nylon1010 and HIPS. The gel fraction increased with increasing radiation dose. The network was found mostly in nylon1010, the networks were also found in both nylon1010 and HIPS when the dose reaches 0.85 MGy or more. We used the Charleby-Pinner equation and the modified Zhang-Sun-Qian equation to simulate the relationship with the dose and the sol fraction. The latter equation fits well with these polymer blends and the relationship used by it showed better linearity than the one by the Charleby-Pinner equation. We also studied the conditions of formation of the network by the mathematical expectation theorem for the binary system. Thermal properties of polymer blend were observed by DSC curves. The crystallization temperature decreases with increasing dose because the cross-linking reaction inhibited the crystallization procession and destroyed the crystals. The melting temperature also reduced with increasing radiation dose. The dual melting peak gradually shifted to single peak and the high melting peak disappeared at high radiation dose. However, the radiation-induced crystallization was observed by the heat of fusion increasing at low radiation dose. On the other hand, the crystal will be damaged by radiation. A similar conclusion may be drawn by the DSC traces when the polymer blends were crystallized. When the radiation dose increases, the heat of fusion reduces dramatically and so does the heat of crystallization. (C) 1999 Elsevier Science Ltd. All rights reserved.

Confined crystallization behavior of PEO in silica networks

Poly(ethylene oxide) (PEO) and silica (SiO2) organic-inorganic hybrid materials have been synthesized by sol-gel approach. The crystallization behavior of PEO in silica networks has been investigated by differential scanning calorimeter (DSC) and scanning electron micrograph (SEM). The degree of PEO crystallinity in PEO/SiO2 hybrid networks reduces with the increase of SiO2. PEO is in amorphous state when the concentration of PEO is lower than 50 wt% in the hybrid materials. The melting points of PEO in the networks are lower than that of pure PEG, but the melting point of PEO in the networks almost has the same melting point. WAXD and SEM results show that the crystalline behavior of PEO in PEO/SiO2 hybrid system is sternly confined. (C) 1999 Elsevier Science Ltd. All rights reserved.

Radiation crosslinking of biodegradable poly(butylene succinate) at high temperature

Poly(butylene succinate), (PBS) with different molecular weight was gamma -irradiated at different temperatures and various doses. PBS with high molecular weight and smaller peak area of crystal melting gave the highest gel content at the same temperatures and dose. A two-step irradiation (irradiation in molten state after irradiation at room temperature) gave the highest gel content in different conditions. This is due to the formation of network structure by pre-irradiation at room temperature that leads to less degradation. PBS prepared by two step irradiation was effective for improvement of heat stability because of high gel content formation. Unirradiated PBS sheets broke immediately at 110 degrees, while the irradiated sample (gel fraction, 50%) by a two step-method did not break even up to 200 minutes at 130 degreesC. The PBS sheets are biodegradable even after crosslinking.

The effect of chain flexibility and chain mobility on radiation crosslinking of polymers

Radiation crosslinking of polymers mainly depends on the structure of polymer chain. The flexibility and mobility of chain directly influence the possibility of the reactive radicals recombination. Flexible chain is easier to crosslink than rigid-chain polymer. The latter must be crosslinked at high temperature, as most polymers can only crosslink above their melting point. Structural effect also influences the mechanism of radiation crosslinking of polymers. We find from the results in literature and in our laboratory that, the flexibility chain polymer mainly crosslinked with H type, but the rigid chain polymer mainly crosslinked with Y type. (C) 2001 Published by Elsevier Science Ltd.

Confined crystallization behavior of PEO in organic networks

Poly (ethylene oxide) (PEO) and poly (trimethopropane trimethacrylate) (PTMPTMA) interpenetrate networks have been synthesized. The confined crystallization behavior of PEO in the PTMTYTMA networks has been investigated by a differential scanning calorimeter and scanning electron microscope. The degree of PEO crystallinity in PEO/PTMPTMA interpenetrate networks reduces with the increase of PTMPTMA. PEO is in an amorphous state when the concentration of PEO is lower than 50% in the interpenetrate networks system. The melting points of crystalline PEO in the networks are lower than that of pure PEG, and the melting point of PEO in the networks is higher and increases with the increase of PEO in the interpenetrate networks. Wide-angle X-ray diffraction results show that the PEO crystallite size perpendicular to the (120) plane is not affected as much as PEO in silica networks. (C) 2001 Elsevier Science Ltd. All rights reserved.

Studies on the structure and properties of thermotropic liquid crystalline poly(aryl ether ketone)s

Series of thermotropic liquid crystalline poly (aryl ether ketone) s were synthesized by mucleophilic substitution reactions of 4,4'-biphenol and substituted hydroquinone with different difluoromonomers, The relationship between structure and properties of the novel copolymers was investigated. For the copolymers with liquid crystalline properties, their melting transition temperatures show no great change with increase the content of the crystal-disrupting unit. The reason is that the crystal phase is directly transformed from the ordered liquid crystal phase. Side-groups have important effect on mesophase stability, The temperature range of mesophase stability for the chloro-polymers is smaller than those of other series of copolymers (P-phenyl, t-butyl, methoxy, 3-trifluoromethylbenzene). This behavior indicates that the effect of geometric repulsive factor on the thermodynamic stability of the mesophase is much larger than that of the polarizability attractive factor. Different ordered liquid crystal phases are observed in the polymers with different molecular weights. At low molecular weight, highly ordered smectic liquid crystal phases form. With increasing the molecular weight, the ordered degree of the liquid crystals decreases, and only the nematic liquid crystal phase is observed in the polymer with higher molecular weight.

The effects of different alkyl substitution on the structures and properties of poly(3-alkylthiophenes)

In order to investigate the influence of different alkyl side chain substitution on the structures and properties of P3ATs, X-ray diffraction, differential scanning calorimetry (DSC), thermal gravity analysis (TGA), Fourier transform infrared spectra (FTIR) and ultraviolet-visible spectra (W-VIS) were applied to characterizing the samples of ploy(3-octylthiophene) (P3OT), poly(3-dodecylthiophene) (P3DDT) and poly(3-octadecylthiophene) (P3ODT). It is found that the different length of alkyl group substitution leads to great difference in molecular chain packings, according to the room temperature X-ray diffraction results. The temperature dependence of X-ray diffraction experiments were also performed to study the melting processes of P3ATs. With the increase in the number of carbon atoms in alkyl side chains, the melting point decreases, and the thermal stability decreases too. The results of both FTIR and W-VIS spectra indicate that the conjugation length of P3DDT is the longest. among the three P3ATs. (C) 2001 Elsevier Science B.V. All rights reserved.

Size-affected crystallization of trans-1,4-polybutadiene

By using different catalyst systems, two trans-1,4-polybutadiene (TPBD) samples with different tr trans-content and molecular weight were synthesized. The phase transition of two samples from monoclinic form to hexagonal phase was revealed by differential calorimeter scanning and X-ray, respectively. The small-angle X-ray scattering measurements showed the remarkable discrepancy of phase transition and melting point between the two samples was attributed to the different lamellar thickness of crystals: The crystals with different crystalline morphology and lamellar thickness were developed by casting different concentration TPBD solutions. Transmission electron microscopy morphology observations proved that annealing the specimen at the temperature above the phase transition point for different times resulted in the different lamellae thickening of monoclinic form. It means that annealing the TPBD in its hexagonal phase will also slightly favor the increase of both the phase transition temperature and melting point of hexagonal phase. (C) 2001 Elsevier Science Ltd. All rights reserved.

Crystallization behavior of PCL in hybrid confined environment

Poly(epsilon -caprolactone) (PCL) and silica (SiO2) organic-inorganic hybrid materials have been synthesized by the sol-gel method. The crystallization behavior of PCL in silica networks has been investigated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The degree of PCL crystallinity in PCL/SiO2 hybrid networks reduces with increase of SiO2. PCL is in an amorphous state when the concentration of PCL is lower than 40wt% in the hybrid system. The melting point of PCL in the networks is lower than, but close to that of pure PCL. WAXD and SEM results show that the crystalline behavior of PCL in PCL/SiO2 hybrid system is strictly confined. (C) 2001 Elsevier Science Ltd. All rights reserved.

Syntheses and properties of thermotropic copolyesters of p-hydroxybenzoic acid

Two series of thermotropic copolyesters of p-hydroxybenzoic acid (HBA) were synthesized by direct thermal polycondensation. One comprised aromatic copolyesters from HBA, terephthalic acid, bis(4-hydroxyphenyl) ketone (BHP) and resorcinol. The other comprised semi-aromatic copolyesters from HBA, terephthalic acid, BHP and alpha,-diols with carbon atom number of 4, 6, 8, 10. The properties of the two series were characterized by polarized light microscopy, differential scanning calorimetry and wide angle X-ray diffraction. Most of the resulting copolyesters could form a nematic phase over a wide temperature range above their melting points. The effects of Variation in composition and monomer structure on the properties of copolyesters were discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.