A first insight into the thermal degradation mechanism of silylated methacrylic homopolymers synthesized via the RAFT process

The mechanism of thermal degradation of two series of methacrylic-based polymers was investigated. Unconventional methacrylic homopolymers bearing a tert-butyldimethylsilyl ester group were synthesized by Reversible Addition-Fragmentation chain Transfer (RAFT) and conventional free radical polymerizations using 2,2-azobis(isobutyronitrile) as initiator. 2-Cyanoprop-2-yl dithiobenzoate (CPDB) was used as chain transfer agent (CTA) in the RAFT process. The thermal stability of this polymer family was compared to the well-known thermal behavior of poly(methyl methacrylate) PMMA under nitrogen atmosphere. RAFT- and free radically-synthesized polymers were studied by non-isothermal thermogravimetric experiments (TGA). TGA data revealed two main degradation stages for all polymers. The chain transfer agent was shown to limit the production of unsaturated polymer end-groups during polymerization and consequently the thermal stability of the resulting RAFT-polymers was enhanced. Depolymerization was the main thermal degradation mechanism of silylated polymers associated with a side-group elimination for RAFT-synthesized polymers. Pyrolysis-Gas chromatography-Mass spectrometry (Py-GC/MS) experiments clearly demonstrated the formation of volatile tert-butyldimethylsilanol and bis(tert-butyldimethylsiloxane) side-products.