1993 рік

The spherulitic growth rate ofisotactic polypropylene in dotriacontane was studied using optical microscopy. Polymer concentration was varied from 100 to 10 wt% iPP in 10 wt% intervals. Crystallization temperature was varied from 372 to 429 K in 1 K intervals. The influence of these variables on polymer spherulitic growth rate and regime transitions was analysed using the Lauritzen-Hoffman and Toda nucleation theories

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Post-polymerization crosslinking of polystyrene solutions followed by sulfonation has been studied for the preparation and characterization of macronet crosslinked sulfonated polystyrene. A bifunctional benzene derivative (1,4-dichloromethyl-2,5-dimethyl benzene) was used as the crosslinking agent for the main crosslinking reaction. Extensive sulfone-type bridging was found to occur during sulfonation. In addition, the ion-exchange resins that were achieved by this process show increased network density at high sulfonating agent molar ratios. Determination of the porosity and the degree of swelling of the polymers in water was also performed in order to demonstrate the effects of the nominal sulfonating agent concentration on network properties.

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Two copolymers of acrylamide/N-4-ethylphenylacrylamide have been prepared by an aqueous micellar copolymerization technique with two different amounts of an anionic surfactant (sodium dodecyl sulphate). Such changes in the polymerization medium give copolymers with different microstructures. Samples of each copolymer were subsequently hydrolysed to 10, 20 and 40% completion. Hydrophobic interactions of all the samples in aqueous solution were then studied in the semi-dilute concentration range near to and above the chain overlap concentration, c*, via rheological and fluorescence techniques. The samples were each studied as a function of concentration, salt concentration, surfactant concentration and temperature. In all cases, the rheological and the fluorescence data were consistent and directly related to the number of interchain liaisons in solution. The number of interchain liaisons increased with increase in the copolymer hydrophobicity and were hence related to the hydrolysis level and the blockiness of the copolymer

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Bulk crystallization rates, nucleation density, general morphological features, equilibrium melting point and absolute crystalline percentage of linear and star-branched nylon-6 have been studied as a function of branch-point functionality and temperature. Overall bulk crystallization rates were described in terms of the Avrami equation and crystallization half-times. No significant differences in bulk crystallization rates as a function of crystallization temperature or absolute crystalline percentage were observed between linear, three-arm and six-arm samples with identical thermal history. Equilibrium melting points obtained by Hoffman Weeks analysis were reduced in star-branched nylon-6 compared to the linear polymer of comparable molecular weight. In order to deconvolute the effects of a decreased thermodynamic driving force for formation of crystals of branched polymers, crystallization half-times were measured as a function of supercooling. The crystallization half-times of star-branched nylon-6 as a function of supercoolin9 were reduced compared to those of linear nylon-6 of comparable molecular weight. The general spherulitic superstructure appeared unaffected by increasing branch-point functionality up to six. However, irregularities in lamellar structure were implied by SAXS experiments on samples with branch-point functionality as low as three.

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Simultaneous g.p.c, and cyclic voltammetry measurements were carried out in the course of the electrocatalysed polymerization of various 3,6-dibromo(N-alkylcarbazole)s. The evolution of the molar mass population distribution as a function of the electrolysis time reveals a step polymerization process, while showing a termination of the chain growth due to the occurrence of monobrominated species. The consumption of the catalytic species corresponds in a first step to an increase in the chain length, while after given periods there is no more chain growth related to the continuous consumption of the catalytic precursor. The study of the effect of the initial [monomer]/[catalyst] ratio on the molar mass population evolution indicates that the coupling of Ni(0)-activated species is responsible for the chain growth.

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An equation suggested by Fedors for application to intrinsic viscosity determination of dilute to moderately concentrated solutions is re-examined taking into account polymer swelling behaviour and polymer-solvent interactions. For a given polymer-solvent system, the observed variation of the constant of the equation (defined as the maximum volume fraction to which polymer particles can pack), q~m, and its estimated values beyond its theoretical limit of unity are the main difficulties in its application. These problems are solved by a suggested modification to the equation, and ~b m is shown to be less than or equal to unity and constant for many polymer-solvent systems. This modification facilitates the use of the Fedors equation for dilute to concentrated polymer solutions for determining the intrinsic viscosity at a single polymer concentration.

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A dynamic mechanical analysis has been performed on three thermotropic polydibenzoates, designated PDEB, PTEB and PTTB, synthesized from p,p'-dibenzoic acid and di-, tri- or tetraethylene glycol, respectively. The isotropization temperature decreases greatly as the length of the spacer increases, and the mesophase of PTTB is not detected at all. Three dynamic mechanical relaxations are found for each polymer in the temperature range from - 150 to 100°C. The a relaxation corresponds to the glass transition of the polydibenzoates, the fl relaxation is typical of polyesters and the 7 relaxation has its origins in the crankshaft motions of the oxyethylene units in the spacer, i.e. the oxygen atom can cooperate in this movement when substituting for a methylenic unit.

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This paper describes the influence of an external continuous magnetic field on the radical bulk polymerization of methyl, ethyl and butyl methacrylates. The variation in the effect of the field on the ester's alkylic substituent length is described. The processes were compared with the classical bulk method. Some properties of the synthesized poly(methyl methacrylate), poly(ethyl methacrylate) and poly(butyl methacrylate) are also presented.

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Water vapour was used as a diffusional probe to study segmental mobility in hydrogen-bonded polymer blends. Modified polystyrenes containing 4-hydroxystyrene as comonomer units were blended with poly(methyl methacrylate). The diffusion coefficient of water decreased with increasing concentration of the diffusant. Clustering of water molecules in the polymer rendered a fraction of the sorbed water comparatively immobile. A partial immobilization model was used to estimate the diffusion coefficient of the clusters. Interpolymer hydrogen bonding acted as physical crosslinks, which decreased the diffusivity of clusters. However, the positive excess volume of mixing for one blend composition seemed to have nullified the restrictive effect of hydrogen bonding on cluster diffusivity

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A linear correlation function is found for cloudpoint composition curves of ternary systems consisting of one polymer, one solvent and one non-solvent. The conditions for validity of this correlation function appear to be that the polymer is strongly incompatible with the non-solvent, and that only liquid-liquid demixing occurs. The linearized cloudpoint (LCP) curve is interpreted in terms of the various parameters occurring in the Flory-Huggins theory. The slope of the LCP line appears to be only dependent on the molar volumes of the components. Information about the binary Flory-Huggins interaction parameters and their concentration dependence can be obtained from the intercept of the linearized curve. Cloudpoints induced by crystallization do not follow the correlation. This gives an opportunity to distinguish between crystallization and liquid-liquid demixing without any additional experiments.

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