Polystyrenes of known structure: Part 3. Polymers with long-chain branching

Abstract

The melt- and solution viscosity behaviour of some polystyrenes with long-chain branching is described. These polymers, which were prepared by reacting chloromethylated polystyrene with potassium polystyryl, are distinguishable from the comb-shaped polystyrenes previously described in having longer branches and lower branching frequencies. (The number-average molecular weight of the branches is greater than 4.6 × 10 4 and in some cases greater than that of the backbone.) Their low shear melt viscosities and intrinsic viscosities in tetrahydrofuran and cyclohexane are above those of the backbone polymer and increase as the branch length increases for a given branching frequency, the rate of increase being greater the lower the branching frequency. In each solvent the intrinsic viscosities of the branched polymers are below those of linear polymers of comparable molecular weights. The melt viscosities of the majority of the branched polymers are also below those of linear polymers of the same molecular weights, but for a few, those with the longest branches in the series with the lowest branching frequency, the opposite is true. Another outcome of this work is the finding that for these branched polymers the low-shear melt viscosities and the intrinsic viscosities in solution are given by: viscosity ∝〈S 2 0〉 a where 〈S 2 0〉 is the theoretical mean square unperturbed radius of gyration. The exponents a for the branched polymers in the melt and in tetrahydrofuran differ from those for linear polystyrenes for which a similar relation holds, but are about equal for branched and linear polystyrenes in cyclohexane. The behaviour shown by the branched polystyrenes described here is considered in relation to the behaviour of the comb-shaped polystyrenes reported earlier and that of the branched polystyrenes studied by Decker and by Fujimoto et al.