Self-crosslinkable and modifiable polysiloxanes possessing Meldrum's acid groups

Abstract

Meldrum's acid (MA) groups are incorporated into polydimethylsiloxane (PDMS) chains as reactive units to impart self-crosslinkable and modifiable features to PDMS. The synthesis of MA-functionalized PDMS (MA-PDMS) has been performed through hydrosilylation reactions using an MA-functionalized bifunctional styrenic compound and Si–H terminated dimethylsiloxane compounds as monomers. The MA-PDMS samples exhibit number-averaged molecular weights of about 5000–10 000 Da and have been spectrally characterized with Fourier transform infrared and ¹H and ²⁹Si nuclear magnetic spectroscopies. Thermolysis of the MA groups of MA-PDMS is traced with thermal analysis (differential scanning calorimetry and thermogravimetric analysis) to demonstrate the reactivity of MA-PDMS. Self-crosslinking and post-modification reactions of MA-PDMS are carried out with the ketene groups generated from the MA thermolysis reaction through ketene dimerization and nucleophilic addition reactions, respectively. A phosphorus compound (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, DOPO) is utilized as the modifier for MA-PDMS post modification so as to result in DOPO-functionalized PDMS (DOPO-PDMS). Based on the developed reaction routes, this work also demonstrates a convenient and effective approach for preparing DOPO-functionalized-PDMS compounds, which are potential flame retardants for polymeric materials exhibiting Si/P synergistic effects on flame retardation.