A method is described for the preparation of well-defined four-star polystyrenes involving coupling of polystyryllithium with l,2-bis(methyldichlorosilyl)ethane. Nine samples were prepared over a 30-fold range of molecular weight.Osmotic and light-scattering techniques were used to measure number-and weight-average molecular weights where possible. Intrinsic viscosity and sedimentation coefficients were measured in cyclohexane at 35 and 50°and in toluene at 35°. The ratio g' ([z?](branched)/[T7](linear)) was found to be 0.76 under 6 conditions and slightly lower in better solvents. The value falls between theoretical estimates. The corresponding ratio of sedimentation coefficients (/z) was found to be 0.93-0.94 compared with a theoretical value of 0.89.

X study of the kinetics of the initiation and propagation reactions in the polynlerization oE styrene by butyllithium in benzene solution has been made. The initiation has been shown to be first order in styrene and 0.155 order in butyllithium, the propagation to be first order ill styrene and half order with respect to active chain ends. The apparent activation energies oE the two reactions have been shown to be 18,000 calories and 14,300 calories respectively. The ultraviolet absorption spectra oE colored species produced has been measured and compared with others found in similar systems.

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A series of polydimethylsiloxanes and two-block copolymers with styrene of reasonably narrow molecular weight distribution has been prepared using the monomer hexamethylcyclotrisiloxane. The initiator was sec-butyllithium. Evidence was found for a low level of side reactions which results in the molecular weight distributions becoming broader at very high molecular weights. Similarly block copolymers with > 2 X 10s were contaminated with both homopolymers. Purification methods to remove the homopolymers are described. The solution properties of polydimethylsiloxane agreed in general with earlier studies which used fractions produced by polymerization of octamethylcyclotetrasiloxane. The intrinsic viscosities of the block copolymers are, unlike those of styrene-isoprene two-block copolymers, greater than the average of those of the homopolymers. This suggests greater segregation of the two types of segment. The optical properties of the block copolymers are rather unusual. Refractive index increments of the two types of segment are markedly different and in toluene opposite in sign. The overall refractive index increment can therefore be rather small and the Pe function under these conditions greater than unity at finite angles. Zimm plots of unusual form are then observed. These effects are explained in terms of the Benoit theory of light scattering from block copolymers.

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