Synthesis, structure and thermogravimetric analysis of alpha,omega-telechelic polydimethylsiloxanes of low molecular weight

Abstract

A series of alpha,omega-telechelic polydimethylsiloxanes (PDMS), with predetermined molecular weights of about 2500 g mol(-1), was synthesized by siloxane equilibration reaction. Syntheses were performed using octamethylcyclotetrasiloxane (D-4) and various disiloxanes: hexamethyldisiloxane (HMDS), 1,1,3,3-tetramethyldisiloxane (TMDS), 1,3-divinyltetramethyldisiloxane (DVTMDS), 1,3-bis(3-carboxypropyl) tetramethyldisiloxane (DCPTMDS) and 1,3-bis(3-aminopropyl) tetramethyldisiloxane (DAPTMDS). The role of the disiloxane was to introduce terminal functional groups at the end of the polymer chains and to control the molecular weight of the polymers. Polymers with trimethyl, hydrido, vinyl, carboxypropyl and aminopropyl end-groups were obtained in this way. The structure of the alpha,omega-telechelic PDMSs was confirmed by NMR and IR spectroscopy. The molecular weights of the polymers were determined by H-1-NMR, gel permeation chromatography (GPC) and dilute solution viscometry. Thermogravimetric analysis (TGA) under nitrogen and air showed that the type of the terminal groups significantly influenced the thermal and thermo-oxidative stability, as well as the degradation mechanism of the alpha,omega-telechelic PDMSs.