SJnOpeifJRubber-reinforced thermoplastics are produced commercially by diseolvmg a rubber in the monomer of a glessy polymer and commencing polymerization with a free-radical initiator. Beyond a few per cent conversion, the incompatibility of the two polymers c a w a phase geparation, with each phase containing one nearly pure polymer. Subsequent polymerization o c c m in each phase. The heterogeneous nature of the reaction can influence both the kinetics of the reaction and the amount of grafting in the product. The fact that only monomer which polymerizes in the rubber phase can possibly graft establishes an upper limit to the amount of grafting and hence influences the mechanical properties of the product. It is shown theoretically how unequal partitioning of monomer and initiator between the phases can influence the extent of grafting, and can also explain the kinetic rate reductions which have been observed in such systems. The distributions of monomer and benzoyl peroxide and azobisisobutyronite initiators between the phases have been determined experimentally for 8 styrene-polystyrenepolybutadiene system. They cannot account for the rate reduction observed in such systems.
SynopsisThe effect of dissolved polybutadiene on the initial rate of polymerization of styrene was investigated by using high-precision dilatometric techniques. The dissolved polymer reduced the rate of polymerization by amounts greater than can be accounted for by a reduction in monomer concentration. Rate reductions' increased with the amount of dissolved polybutadiene and with its molecular weight and were greater for benzoyl peroxide initiator than for equal concentrations of azobisisobutyronitrile. Surprisingly, analogous rate reductions were observed when polystyrenes were substituted for the polybutadienes, except that at high polystyrene concentrations, the expected autoacceleration was observed. These rate reductions showed no correlation with the viscosity of the reaction mass, nor did the dissolved polymer affect initiator efficiency. At a given level of a particular dissolved polybutadiene, rate reductions were diminished by increasing levels of each initiator, and by adding a chain-transfer agent. Good quantitative agreement was obtained with the number-average length of the growing polymer chains, whether varied by using different initiators, changing initiator level, or adding chain-transfer agent. These results are inconsistent with a chemical mechanism, but they are explained by a proposal originated .by North and Reed whereby the dissolved polymer makes the reaction mass a "poorer" solvent for the growing polymer chains, reducing their overall coil dimensions and enhancing their rate of diffusion together for termination.
Pressure losses at the sharp edged entrance to a cylindrical tube were investigated for glycerine-water solutions over a Reynolds number range of 6 to 2,000.For the experimental area contraction ratio of 0.0156, the Hagenbach ( K ) and Couette ( K ) coefficients are 2.4 and 295, respectively. Comparison with limited previous work shows that both coefficients increase with the area contraction ratio p over range O
Two‐phase polymer systems have achieved commercial importance due mainly to the improvement in impact strength brought about by the addition of dispersed rubber particles to a normally brittle glassy polymer. Rubber‐reinforced polystyrene and ABS plastics are two familiar examples. An important drawback of this class of materials is their lack of transparency, caused by the scattering of light at the interface between the phases. The theory of light scattering by spherical particles indicates that the degree of scattering (turbidity) is a function of the amount of dispersed phase present, its particle size, the ratio of refractive indices of the phases, and the wavelength of light. Quantitative predictions of the effects of the above parameters on the transparency of two‐phase systems can be made, providing answers to the questions “How close must the refractive indices be?” and “What size must the dispersed‐phase particles be?” for a given level of transparency. Calculations for typical polymer pairs reveal that at a given dispersed‐phase level, a maximum in turbidity is obtained roughly in the range of particle sizes thought to be necessary for good impact strength. Also, if the refractive indices are matched at a particular temperature, small particle sizes greatly increase the temperature range over which scattering is minimized.
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