1993 рік

Copolyesters of poly(1,4-phenylene terephthalate) and poly(t-butyl-l,4-phenylene terephthalate) are synthesized by melt polycondensation using an acetolysis route. The products are characterized by solution viscometry, wide-angle X-ray scattering, hot-stage polarizing microscopy and thermal analysis (d.s.c., t.g.a. and t.m.a.). The copolymers are semicrystalline throughout the range, exhibit a minimum melting temperature at approximately equimolar proportions of the two components, and are melt-processable in the middle of the range.

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Miscibility, phase separation and curing behaviour have been studied in blends of poly (methyl methacrylate ) (PM MA ) with diglycidyl ether of bisphenol A (DGEBA) resin and 4,4'-diamino-3,3'-dimethyidicyclohexylmethane (3DCM) hardener. Quasi-binary mixtures of PMMA with the resin monomer show complete miscibility over the whole composition range, at all temperatures studied (-25 to 200°C). However, PMMA is much less miscible with the hardener, and cast films show two T~ values. Several techniques have been used to monitor phase separation and curing characteristics in PMMA blends, including viscometry, size exclusion chromatography, turbidity and optical microscopy. The morphologies and the thermal and dynamic mechanical properties of the cured blends, including non-stoichiometric compositions, are related to these observations.

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The thermodynamic properties of s-type trans-l,4-polyisoprene crystals grown from solution were investigated by differential scanning calorimetry and X-ray diffraction. The equilibrium melting temperature estimated from the plot of melting temperature against crystallization temperature was found to be 101.5°C. The surface free energy calculated from the slope of the plot of melting temperature against reciprocal lamellar thickness was found to be 9.6 kJ mol- 1, in good agreement with Keller and Martuscelli's work. The lamellar thickness of ~t-TPI crystals grown at high crystallization temperatures (10-35°C) increased with the increase of crystallization temperature. At low crystallization temperatures, e.g. - 10 and -20°C, the lamellar thickness was greater than the expected value. This may be caused by the occurrence of isothermal thickening. At such low temperatures, the lamellar thickness was independent of crystallization temperature. The chain-folded lamellae of ~-TPI crystals grown from hexane were estimated to have looser and longer surface folds than those grown from amyl acetate at the same crystallization temperature. Based on the crystallinity data, the stem lengths of lamellae grown from hexane were found to be slightly shorter than those of lamellae grown from amyl acetate. These findings are in agreement with the results determined by ozonolysis-g.p.c, measurements.

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A filled epoxy resin used as a structural adhesive and based on the diglycidyl ether of bisphenol A cured with dicyandiamide has been subjected, in its bulk form, to ageing at 40, 55 and 70°C and ca. 100% relative humidity. Gravimetric, viscoelastometric and FTi.r. studies have been effected after various times of exposure. Water absorption in the polymer is essentially Fickian, although closer inspection reveals the finer behaviour to be sigmoidal. The activation energy for diffusion is of the order of 80 kJ mol- 1, but there appears to be no clear relationship between equilibrium absorption values and temperature. Viscoelastometry has shown that T~ diminishes from ca. 115°C before ageing to ca. 90°C at saturation, 1% of water uptake corresponding to ca. 8°C reduction in T r Reductions in Young's modulus were observed both in the glassy and rubbery states after ageing and the latter is associated with molecular chain scission. FTi.r. analysis has shown several modifications occurring due to water absorption, the main one being an increase in intensity of the band at 1740cm -1. It is concluded that water absorption leads both to plasticization effects and chemical modification of the epoxy resin

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A novel diethylaminoethyl chitosan was synthesized via Schiff-base intermediates. The C2 amino group in chitosan was protected from the reaction between benzaidehyde and chitosan to form N-benzylidene chitosan. After reaction with diethylaminoethyl chloride, the Schiff base was removed by reacting O-diethylaminoethyl-N-benzylidene chitosan and dilute ethanolic hydrochloride solution. The tensile strength of diethylaminoethyl chitosan was improved by incorporation of the diethylaminoethyl group in the C6 position of chitosan. Diethylaminoethyl chitosan showed pH-dependent swelling characteristics

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The glass transition of natural rubber (NR) in a mixture with polystyrene (PS) was investigated by global thermally stimulated depolarization current (t.s.d.c.) measurements and by the partial polarization technique. The experiments were carried out on samples with different NR/PS ratios and different PS particle dispersion. The activation energy (E=) and the approximate number of dipoles (N) which take part in ~ relaxation were determined. A simple method for approximating the N(E~) distribution was proposed. The results show that the presence of PS significantly decreases N as well as the width of the distribution. The agglomeration of PS particles reduces their activity. The specific influence of PS is expressed most at low PS concentrations. The results confirm the existence of attractive interactions at the NR-PS interfaces.

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Miscibility and morphology in blends of poly(e-caprolactone) (PCL) and poly(styrene-ran-acrylonitrile) (SAN) were examined by light scattering and optical microscopy. The blends display miscibility in the amorphous state in a limited range of copolymer composition. Morphologies, formed as a combined effect of liquid-liquid phase separation and crystallization of PC L, are discussed. Crystallization leads to spherulite structure in the blends. Upon crystallization, PCL segregates from the amorphous state resulting in the observation of ring patterns in miscible blends. Its periodicity decreases with increasing fraction of SAN in the blend. Ring-banded spherulites have not been observed in neat PCL or in immiscible blends. These effects are discussed in terms of twisted crystallizatio

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Highly plasticized poly(vinyl chloride) membranes (200 parts per hundred resin, phr) form the basis of ion-selective electrodes. The effects that five different plasticizers with different chemical structures, polarities and molecular weights /~, have on modified mechanical properties such as strength, secant stiffness, toughness and ductility were examined by puncture testing. As a function of membrane thickness, strength, toughness, and secant stiffness increase, while ductility remains constant. For maximal membrane strength and toughness, plasticizer M, should be roughly 1000, The optimal ratio of experimental plasticization level (phr=~p = 200) to the minimal level required for complete plasticization (phrmin) was found to be ~ 2. A 'tube'-like model for plasticizer interaction with polymer chains is proposed to explain the vast differences in the mechanical properties of membranes

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The metallocene catalyst system Cp2ZrCl2-methylaluminoxane showed surprisingly high activity for 1-hexadecene, and high concentrations of comonomer could be incorporated into the copolymer compared with a heterogeneous titanium catalyst. A temperature rising elution fractionation (TREF) fractogram of the copolymer revealed it to have narrow branching distribution, much narrower than in commercial linear low density polyethylene, and to have features in common with a commercial low density polyethylene

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The effect of equilibrium moisture content (M~o) on the glass transition region of a cured unsaturated polyester resin has been studied. Variation of the accelerator content has been shown to result in different values of Mo~. The moisture sensitivity has been studied by comparing the rate of change of the glass transition temperature with equilibrium moisture concentration [dTf/dMool over a range of accelerator concentrations. Following the arguments in Part 11, it is demonstrated that variations in moisture sensitivity arise from differences in average crosslink density. The moisture dependence of the expansion coefficient can also be interpreted on the basis of a heterogeneous crosslink density, which results from the statistics of the addition copolymerization responsible for cure

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