Towards the synthesis of polythiazolines: a post-polymerization approach

The synthesis of novel tertiary polythioamide copolymers, analogues of poly(2-ethyl-2-oxazoline) (PEtOx), is reported. Firstly, the direct synthesis of poly(2-methyl-2-thiazoline) was attempted via the cationic ring-opening polymerization of 2-methyl-2-thiazoline, in analogy to the well-known 2-alkyl-2-oxazoline monomers. Since no conversion was monitored under several conditions - which was investigated in parallel by density functional theory calculations - the post-polymerization modification of PEtOx using Lawesson's reagent was successfully achieved, yielding poly(2-ethyl-2-thiazoline)-co-(2-ethyl-2-oxazoline) copolymers with up to 95 mol% of the thioamide unit. The newly synthesized copolymers exhibited significantly lower water solubility and thermal stability than the pristine PEtOx, as demonstrated during cloud point temperature determination and thermal gravimetric analysis, respectively. Moreover, the glass transition temperature of the copolymers increases linearly with increasing oxygen-sulfur exchange.