Copolymerization of ethylene and vinyl acetate at low pressure. Determination of the kinetics by sequential sampling

Monomer reactivity ratios in ethylene-vinyl acetate copolymn. at 62.deg. and 33.9 atm were detd. to be 0.746 +- 0.005 and 1.515 +- 0.007, resp., by sequential sampling of monomer feed, quant. gas chromatog., and computer calcn. based on nonlinear least-squares metho

Dilatometric investigation of deformation mechanisms in polystyrene-polyethylene block copolymer blends. Correlation between Poisson ratio and adhesion

The deformation behavior of blends contg. polystyrene (I) [9003-53-6], low-d. polyethylene (II) [9002-88-4], and a hydrogenated butadiene-styrene diblock copolymer (III) was examd. by tensile testing with simultaneous vol. measurements. Assuming that shearing causes no vol. changes, crazing, after yielding, was the only deformation mechanism in blends with low I and III contents. Shearing became important in blends with high I concns. due to formation of a semicontinuous low modulus phase. The decrease in the Poisson ratio with increasing II content in I-II blends, as opposed to an increase in the presence of III, shows the Poisson ratio to be very sensitive to adhesion between the components. The toughness of I-II blends is discussed in terms of concns. of craze nuclei. Too few craze nuclei give rise to brittle failure because the resulting low no. of crazes cannot accommodate much deformation of the matrix whereas too many craze nuclei also cause brittle failure because of the high probability of combination of the crazes to form a crack. The concn. of craze nuclei depends on the no. of dispersed particles and their adhesion to the matrix. [on SciFinder (R)

Determination of the kinetics by sequential sampling

synopsis In behalf of a detailed study on the course of copolymerization reactions, this paper describes an improved and generally applicable experimental method and an efficient computational procedure to match. The experimental method is based on quantitative gas chromatography, and permits frequent measurement of the monomer feed composition throughout (co)polymerization processes a t pressures up to 40 kgf/cm2 ( = 38.7 atm). The given method is applied to the study of the radical copolymerization of ethylene with vinyl acetate in a series of kinetic experiments, a t 62OC and 35 kgf/cm2 (= 33.9 atm) in tert-butyl alcohol, in which 20-40q7, conversion is reached. Monomer feed composition and degree of conversion are entered into a computational procedure based on nonlinear least-sqnares methods applied to the integrated version of the copolymer equation. The experimental data, covering a region of ethylene molar feed frartions between 0.24 and 0.74 and copolymer concentrations up to 8 wt-%, are precisely consistent with the usual model. The respective reactivity ratios are Fe = 0.743 f 0.00<5 and P, = 1.515 f 0.007