1999 рік

The random and block copolyesters of poly(ethylene 2,6 naphthalate) (PEN) and poly(ethylene terephthalate) (PET) are synthesized and studied by 1 H-n.m.r., DSC, X-ray. The block length decreases and the degree of transesterification increases at a similar composition ratio. The melting point depressions occur with increasing the content of the other component, and melting peaks disappear at a similar composition ratio. The results of X-ray diffractograms match well with those of dyads fraction, block length, and DSC. It can be seen that a critical block length is needed for components in order to crystallize.

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Thermal analysis, optical and scanning electron microscopy were performed to characterize solution-blended poly(4-methyl styrene) (P4MS)/poly(cyclohexyl methacrylate) (PCHMA) of full compositions. It is concluded that the true state of blend phase structure is miscibility with non-specific intermolecular interactions. To probe molecular interactions between the polymer pairs, FT-IR analysis was also used to assess possible evidence. The FT-IR results for the P4MS/PCHMA suggest that the intermolecular interactions between the pairs are likely non-specific and only comparable with those among the homopolymer molecules. Casting temperature did not seem to have any effect on the miscible phase structure of P4MS/PCHMA. Both optical microscopy and SEM characterization revealed that solution casting of P4MS/PCHMA at either temperature yielded equally homogeneous phase structure. The cloud point phenomenon is attributed to a thermodynamic lower critical solution temperature (LCST) but is kinetically irreversible at normally accessible time scales. The observed LCST could be made to be reversible in an appropriate environment where the molecules were given enough molecular mobility.

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A scaling model is proposed for A–B diblock copolymers in homopolymer melts based on the minimization of free energy. Competition between the migration of block copolymer to the A and B homopolymer interface and formation of micelles in the B phase has been modeled. Sample calculations done for polystyrene (PS), polybutadiene (PB), and PS–PB diblock copolymers support experimental observation for the onset of micellization and for the aggregation number of a micelle. The model is relatively simple and testable. It can be used as a predictive tool, once knowledge of three scaling factors is obtained. This would allow a priori calculation of the block copolymer concentration needed for full coverage of the homopolymer interface.

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The dynamic yield stress for polycarbonate, polystyrene and poly(methyl methacrylate) was measured by an instrumented Charpy impact tester in a wide temperature range. The dynamic yield stress is interpreted as being proportional to a negative pressure. The temperature dependence can be described by a Williams–Landel–Ferry type of equation. The extrapolation to ambient pressure leads to the main a transition and is used to connect the dynamic yield stress to the pressure dependence of the a dispersion zone.

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A novel dianhydride, 3,3 0 -dioxo-[1,1 0 ]-spirodiphthalan-5,5 0 ,6,6 0 -tetracarboxylic dianhydride, was synthesized and used as a monomer to prepare polyimides with several diamines via a conventional two-stage procedure. The intermediate poly(amic-acid)s had inherent viscosities of 0.84–1.71 dL/g and could be thermally converted into lightly yellow, transparent, flexible and tough films. Films cast from chemically imidized polyimides were transparent and colorless. The glass transition temperatures (Tg) were > 400°C, and the 5% weight-loss temperatures were > 420°C in N2 and in air. The solubilities of these polyimides in various solvents were evaluated. The mechanical properties of some polyimides were also tested.

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Novel cross-linked urethane/urea polymers with two soft segments, polypropylene oxide and polybutadiene, were prepared by extending polypropylene oxide-based isocyanate-terminated triol prepolymer with polybutadiene diol. Infra-red spectra indicated that with increasing polybutadiene content in the polymers, the hydrogen bonding of urethane/urea groups among hard segments became weaker. This was interpreted as an improvement of freedom of urethane/urea groups and their mixing with polypropylene oxide. The dynamic mechanical thermal analysis indicated that the two soft segments were highly dispersed, and could lead to a molecularly mixed phase. The swelling experiments with ethanol aqueous solutions indicated a preferential sorption of ethanol and a decrease of the swelling degree with increase of polybutadiene content in the polymer films. The preferential permeation of ethanol is confirmed by the pervaporation results.

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An ionomeric blend of maleated ethylene–propylene–diene monomers (mEPDM) and maleated high-density polyethylene (mHDPE) exhibits higher melt viscosity than the corresponding non-ionomeric polyblend. The addition of zinc stearate decreases the melt viscosity of the ionomeric polyblend. The ionomeric polyblend shows superior physical properties to the corresponding non-ionomeric polyblend. The addition of zinc stearate causes an increase in tensile strength of the ionomeric polyblend. Infra-red studies show that an interionic interaction exists between the zinc stearate and ionomeric polyblend. Reprocessability studies reveal the thermoplastic elastomeric nature of the blend.

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Toluene vapour sorption behaviours in syndiotactic polystyrene (SPS) film were measured at 25°C by the quartz crystal microbalance method. The sorption isotherm of this system was concave toward the pressure axis below the activity of toluene vapour (p/p0 ˆ 0.3), indicating a strong interaction between toluene vapour and sorption sites in the mesophase consisting of TTGG conformation. On the other hand, the sorption isotherm of toluene vapour in atactic polystyrene film showed a normal good solvent type and could be described by Flory–Huggins thermodynamics. In addition, the structural changes in SPS film by toluene vapour sorption were characterized by Infrared spectroscopy. The absorbance at 933 cm ⫺1, which is assigned to TTGG conformation, was found to be constant below p/p0 ˆ 0.3; however, it increased above p/p0 ˆ 0.3 and was saturated above p/p0 ˆ 0.6. These results showed that toluene vapours penetrated into the pre-existing sorption sites composed of TTGG conformation to form the clathrate structure (d form) below p/p0 ˆ 0.3. Furthermore, in the range of p/p0 ˆ 0.3–0.6, the sorption of toluene vapour could induce a large increase in the ordered structure (d form), i.e., TTGG confirmation. The changes in the non-clathrate structure with toluene (a form) composed of TT conformation, could be characterized by the absorbance at 1222 cm ⫺1. It was confirmed that the a form could be also increased by toluene vapour sorption above p/p0 ˆ 0.4. The sorption enthalpy of toluene vapour (DHs), estimated from sorption isotherms showed a negative value below p/p0 ˆ 0.6, but showed a positive value above p/p0 ˆ 0.6, even though the polymer–good solvent pair. This result also supports the structural organization in SPS film by toluene vapour sorption.

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Thermal, wide angle X-ray scattering and light microscopy studies have been carried out on sulphonated poly(butylene terephthalate) (SPBT) and its blends with polycarbonate (PC). A better understanding of the morphology and behaviour of the ionomer SPBT as well as initial information on the miscibility and level of crystallinity of the new family of ionomer blends, SPBT/PC, has been obtained. The samples with a degree of sulphonation above 7 mol.% showed the partial miscibility as well as improved optical clarity with respect to blends of non-sulphonated PBT/PC.

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The dynamic mechanical properties of polymethyl methacrylate reinforced with different amounts of aluminum filler were investigated. The internal friction and the shear storage modulus were measured with an automated damped torsional pendulum in the temperature range between 200 and 375 K in an argon atmosphere. An increase in the glass transition temperature occurred at higher filler contents. The amount of filler in the matrix seems to modify the b relaxation of the composite. The dynamic modulus increases with the aluminum percentages for low filler content. These results were explained in terms of a model presented in the literature for the elastic modulus.

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