1999 рік

Crosslinkable liquid crystalline co-polyesters based on substituted terephthalic acid moiety have been synthesised and their phase behaviour characterised. The network formation by thermally activated radical reaction has been examined on polymers with different amounts of monomer units bearing reactive acryloyloxy substituents at the terephthalic group. The relatively low melting temperatures allow fibre extrusion to be performed from a polymer matrix containing the crosslink reaction activator. Successive thermal curing produces a stabilisation of the macroscopic orientation of the liquid crystalline network.

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The mechanical properties of crosslinked polystyrene-block-polybutadiene-block-polystyrene (SBS) triblock copolymer films were examined by dynamic viscoelastic measurements and tensile stress–strain tests. The lamellar forming SBS sample was used in this study. The sample was chemically crosslinked in the disordered state in the presence of solvent and then was subjected to microphase separation by extracting the solvent. It was found that the degree of completion of the microphase separation is suppressed due to the chemical crosslinks. It was also revealed that crosslinking in the disordered state is a useful method to improve mechanical properties of the SBS thermoplastic elastomers.

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A series of flame-retardant wholly aromatic polyesters was synthesized by high temperature solution polycondensation of 2-(6-oxido-6Hdibenz 具c,e典具1,2典 oxaphosphorin-6-yl)-1,4-dihydroxy phenylene (I) with various aromatic acid chlorides in o-dichlorobenzene. These polyesters have good mechanical properties (G’:10 8 –10 9Pa) up to 180°C and good thermal and flame retardant properties. The glass transition temperatures of these polyesters are in the range of 198.1°C–220.3°C. The degradation temperatures (Td 5%) in nitrogen ranged from 460°C to 495°C and char yields at 800°C are 34%–47%. The degradation temperatures (Td 5%) in air ranged from 450°C to 472°C and char yields at 800°C are 21%–32%. The activation energies of degradation ranged from 177.4 KJ/mol to 238.8 KJ/mol. The limiting oxygen indexes (LOIs) of these polyesters are in the range of 37–48.

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We developed a new model based on the lattice cluster theory to describe phase behaviors of binary hyperbranched polymer solution systems. To account for highly oriented interactions between segments, the proposed model requires an additional parameter (d1 /k) related to the energy of the oriented interaction. A thermo-optical analysis (TOA) technique was used to determine cloud-points for the given systems. Hyperbranched polyol/water systems exhibit an upper critical solution temperature (UCST) behavior.

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The influence of glass beads on the phase transition of syndiotactic polypropene has been investigated. The glass transition at 4°C, detected by means of dynamic mechanical analysis, and multiple melt behaviour, detected by means of differential scanning calorimetry (DSC), does not depend upon the presence of glass bead fillers. However, dynamic mechanical analysis shows an unexpected phase transition at 55°C. This transition, which is not found for neat syndiotactic polypropene, can be also detected by DSC and pressure–volume–temperature (PVT) measurements. The signal detected by PVT appears at higher temperatures, due to higher pressure during measurement. Wide angle X-ray scattering (WAXS) measurements reveal that neat syndiotactic polypropene crystallizes in unit cell II, whereas glass bead-filled syndiotactic polypropene crystallizes in unit cells I and II. Glass bead-filled syndiotactic polypropene, heated up above 60°C, shows a WAXS pattern corresponding to unit cell II. From these results, it can be concluded, that glass beads can nucleate the formation of unit cell type I, which transforms into unit cell type II upon heating at 55°C.

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Several stable structures of the 1:1 complexes of a lithium ion with tetra-, penta- and hexaglyme [CH3O(CH2CH2O)nCH3, n ˆ 4–6] have been obtained with ab initio calculations at the Hartree–Fock level of theory employing the 3-21G* basis set. Twenty-three different stable complexes were found with coordination numbers of lithium ranging from four to six; i.e., no stable heptacoordinated complexes emerged. The total energies and the binding energies were evaluated by using density functional theory (DFT) calculations (B3LYP/6-31G*//HF/321G*) and showed the total binding energy to increase with the glyme length. The average binding energy for the different glymes reaches a maximum of ⬃620 kJ mol ⫺1 for the hexaglyme complexes, with an absolute maximum of 631 kJ mol ⫺1 obtained for a hexacoordinated Li ⫹ – hexaglyme complex. The average binding energy per bond for a specific coordination number for lithium shows only minor changes when extending the oligomer (<5 kJ mol ⫺1 bond ⫺1). The large number of complexes obtained with clearly different geometry within a small energy range — six different complexes within 15 kJ mol ⫺1 for lithium–tetraglyme — clearly reflects the flexibility of the oligomer chains.

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Diblock copolymers composed of poly(g-benzyl l-glutamate) (PBLG) as the hydrophobic component and poly(ethylene oxide) (PEO) as the hydrophilic component were obtained by the polymerization of g-benzyl l-glutamate N-carboxyanhydride, initiated by the primary amino end group of the a-methoxy-v-amino PEO. Nanoparticles are formed from an organic solution of the block copolymers by the diafiltration method. From the NMR measurement of the nanoparticle in water, the PEO segments in the copolymer extend out as the shell from the nanoparticle core into the aqueous environment. From circular dichroism measurements in ethylene dichloride solution, it was found that the polypeptide block exists in the a-helical conformation and adopts right-handed helix sense, as in PBLG homopolymer. However, the helix sense of PBLG in the copolymer nanoparticles prepared from organic solvent depends on the PEO content in the copolymer and the nature of solvent.

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Isotactic polypropylene (iPP) was doped with pimelic acid/calcium stearate to promote the formation of the hexagonal (b) crystals during melt crystallisation. The conversion of growth pattern from the b- to the a-phase due to lowering of the crystallisation temperature was studied by a two-step crystallisation process in a DSC. The polymer melt was first allowed to crystallise isothermally at 130°C to produce almost pure b-phase and then the crystallising polymer was cooled to different temperatures between 115 and 25°C for a second-step crystallisation. It was found that the amount of a-phase was negligible after the second-step crystallisation process at 85°C or above. When the secondstep crystallisation process was below 85°C, however, the amount of a-PP increased abruptly with a corresponding drop in the b-phase. This indicated that a major conversion of the b-growth to a-growth occurred near 85°C. Recrystallisation of the b-phase during heating was dependent upon the heating rate as well as the crystallisation condition of the samples.

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Montmorillonite (MMT)/Organo-soluble polyimide (PI) hybrids were prepared using a monomer solution intercalation polymerization method. The organo-soluble polyimide was based on pyromellitic dianhydride and 4,4 0 -diamino-3,3 0 -dimethyldiphenylmethane. The MMT was organo-modified with three types of intercalation agents: amino acids, primary aliphatic amines and quaternary ammonium salt. The dispersion behavior of MMT in organic solvents and polyimide depends on the type of the functional group and the bulky group of the intercalation agent. The MMT modified with 1-hexadecylamine is observed to possess the best dispersion behavior. The properties of a MMT/PI hybrid are also greatly dependent upon the dispersion behavior of MMT particles. When the MMT is well dispersed, a MMT/PI hybrid would possess desired properties such as strengthening and toughening at the same time, improved thermal stability, decreased thermal expansion coefficient, retaining of the solubility of the polyimide matrix and high optical transparency.

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Composites of a biodegradable thermoplastic aliphatic polyester, polybutylene succinate adipate (PBSA), with granular corn starch were investigated for processability, mechanical and thermal properties, and biodegradability. The PBSA/starch films were prepared with starch contents of 5%–30% by weight and processed by blown film extrusion. Increasing the starch content led to an increase in modulus and decreases in tensile strength, elongation to break and toughness. The rate of biodegradation in soil, as measured by respirometry, increased significantly as the starch content was increased to 20% and then plateaued. Scanning electron microscopy revealed that the starch granules were embedded in the continuous-phase PBSA and that starch promotes the biodegradation of PBSA. Gel permeation chromatography indicated a molecular weight decrease for the PBSA after soil exposure and confirmed that biodegradation was enhanced by the presence of starch. The results demonstrated that the biodegradable PBSA/starch system has mechanical properties useful for blown film applications.

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