Rhodium-Mediated Stereospecific Carbene Polymerization: From Homopolymers to Random and Block Copolymers

Abstract

New stereoregular homo- and copolymers with an ester group at every backbone carbon atom were prepared from ethyl, benzyl and tert-butyl diazoacetate (Mw of homopolymers up to 690 kDa and copolymers up to 430 kDa). With polarizing optical microscopy we found that the homopolymers poly(ethyl 2-ylideneacetate) and poly(benzyl 2-ylideneacetate) are able to form stable and accessible thermotropic and lyotropic nematic phases. Both two polymers show relatively high storage moduli up to the glass transition temperature (Tg), as evidenced by dynamic mechanical thermal analysis. The materials retain quite decent storage moduli in a broad elevated temperature range between Tg and Tm. The formation of (block) copolymers was confirmed by a combination of NMR spectroscopy, differential scanning calorimetry and size-exclusion chromatography. 2D-solubility−gradient chromatography−SEC as well as pyrolysis-gas chromatography−mass spectrometry (Py−GC−MS) showed a clear difference in the composition of the random and block copolymers with benzyl and ethyl ester groups. Thermal analysis showed that the homopolymers and block copolymers are semicrystalline, while the random copolymers are completely amorphous. The polymers are thermally stable toward decomposition up to 300 °C (and polymers containing tert-butyl ester groups up to 200 °C). The formation of cross-linked polymer was achieved by heating copolymers containing tert-butyl ester groups.