Stereospecific polymerization of alkyl thiolacrylates. Part II‐1. Infrared spectra of polyethyl and polypropyl thiolacrylates

The infrared spectra of amorphous and crystalline polypropyl thiolacrylates and of amorphous polyethyl thiolacrylate were examined in the range from 3500 to 700 cm −1 . A polymorphism was observed in the crystalline poly‐ n ‐propyl thiolacrylate. A film prepared by drying a cloroform solution of the polymer under air was transparent (Type 2), whereas, a film dried in the current of cloroform vapour was resinous and opaque (Type 1). Type 2 structure was unstable, and it turned into Type 1 structure by stretching in a stream of hot air. Type 1 polymer chains occurred as helices with three monomer units per turn. Type 2 polymer showed non three‐fold screw helices. The infrared spectrum of Type 1 polymer was different from that of Type 2 polymer in many absorption bands, viz., the methylene twisting bands in the vicinity of 1200 cm −1 , the CC stretching bands near 1130 cm −1 , the asymmetrical CSC stretching and methyl rocking bands in the vicinity of 960 cm −1 and the symmetrical CSC stretching bands near 730 cm −1 . In these regions, the spectrum of the crystalline polyisopropyl thiolacrylate was similar to that of Type 2 polymer.