The polymerisation of styrene by trifluoroacetic acid

The polymerisation of styrene (St) by trifluoroacetic acid (TFA) in methylene chloride was studied by high‐vacuum dilatometry at 40°C with specially purified reagents. Drying increases rates, changes the internal orders, and changes the MWD in that with undried TFA the MWD is bimodal, with the driest TFA it is unimodal. For undried TFA, the whole reaction cannot be represented by a single, simple equation; with dried TFA, —d[St]/dt = kv [St]2[TFA]3. When polymerisation is complete the solutions contain free TFA and polystyryl trifluoroacetates. 1‐Phenylethyl trifluoroacetate itself is not an initiator, it yields oligostyrene if treated with TFA, and if present in a reaction mix of St + TFA it retards the polymerisation, is consumed, and causes a distinctly bimodal MWD. The relation of our results to those of Sawamoto et al is discussed.