Aggregation of poly(γ‐benzyl‐α, L ‐glutamate)

The aggregation of poly(γ‐benzyl‐α,L‐glutamate) and its enantiomer in toluene has been investigated by following the viscosity as a function of temperature, concentration, molecular weight, molecular‐weight distribution, helix chirality, and shear rate. The temperature and concentration data for a 138,000‐molecular‐weight sample was fitted to an open, reversible end‐to‐end aggregation model. The aggregation numbers resulting from this fit were consistent with the sudden onset in non‐Newtonian flow resulting from only a 0.2‐wt% increase in concentration. The association equilibrium constant was then used to predict viscosity for comparison with other data, in particular, the effect of molecular weight and molecular‐weight distribution. A mixture of right‐and left‐handed helices showed the aggregation was not chiral selective. The stiffness of end‐to‐end aggregated (hydrogen‐bonded) molecules differed little from their covalent counterparts, at least below a molecular weight of ∼106. We conclude that polybenzylglutamate aggregation in toluene can be described by an open end‐to‐end aggregation model.