Evidence for in situ graft copolymer formation and compatibilization of PC and PMMA during reactive extrusion processing in the presence of the novel organometallic transesterification catalyst tin(ii) 2-ethylhexanoate

Abstract

In this work, we have investigated the role of an organometallic catalyst, tin(II) 2-ethylhexanoate, for the first time for developing compatibilized PC/PMMA blends by a reactive extrusion process. This catalyst is found to be very efficient, as even 0.5% (w/w) of the catalyst is sufficient to develop blends with a single Tg in the second run DSC and a single degradation step in TGA thermograms up to 40% PMMA content. We have shown that the carbonyl peak of PMMA is present in the FTIR spectra of the acetone insoluble portion of the blends, after the extraction of acetone soluble (free/unreacted) PMMA, if there is any, suggesting the development of strong chemical bonding between the PC and PMMA chains during the reactive extrusion process. Furthermore, 1H NMR studies show that the methyl ester proton peak of PMMA is shifted from 3.547 to 3.624 ppm in the blends, revealing a change in the proton environment. We have proposed that the exchange reaction between the carbonate and ester groups of PC and PMMA leads to PC-g-PMMA graft copolymer formation, which is responsible for the observed chemical shift of the methyl ester proton. This graft copolymer, formed in situ during the reactive extrusion process, compatibilizes the PC and PMMA phases. A significant improvement in optical transparency over the otherwise opaque nature of the uncompatibilized blends confirms the compatibilization of PC and PMMA in the blends.