Solution properties and branching of styrene‐butadiene rubber

Abstract

AbstractA number of polydisperse samples of styrene‐butadiene rubber differing in the preparation conditions were investigated by the methods of light scattering, viscometry and sedimentation analysis. The molar masses were measured by light scattering in cyclohexane solutions (25°C, thermodynamically good solvent) and by the Archibald approach to equilibrium method in methyl‐n‐propyl ketone (21°C, θ‐solvent); the intrinsic viscosity was determined in both solvents. The log [η] vs. log Mw dependence was curved in all cases, departures from linearity due to branching increased with increasing molar mass. The degree of branching was estimated using the viscometric method consisting in the determination of the intrinsic viscosity in two solvents with sufficiently different values of the MARK‐HOUWINK exponent. The degree of branching of macromolecules under the conditions used is essentially determined by the length of the primary chain given by the regulator concentration in the polymerization mixture and by conversion. In the emulsion system used the degree of branching does not depend significantly on the polymerization conversion if the latter is lower than 50%, but increases considerably at higher conversions.