Publication Date:
2015-11-20
Description:
The polymerization of octamethylcyclotetrasiloxane (D4) is investigated using several five-, six- and seven-membered N-heterocyclic carbenes (NHCs). The catalysts are delivered in situ from thermally susceptible CO2 adducts. It is demonstrated that the polymerization can be triggered from a latent state by mild heating, using the highly nucleophilic 1,3,4,5-tetramethylimidazol-2-ylidene as organocatalyst. This way, high molecular weight PDMS is prepared (up to 〉400 000 g/mol, 1.6 〈 Ð M 〈 2.5) in yields 〉95%, using low catalyst loadings (0.2–0.1 mol %). Furthermore, the results suggest that a nucleophilic, zwitterionic mechanism is in operation, in preference to purely anionic polymerization.
Print ISSN:
2195-951X
Electronic ISSN:
1860-5397
Topics:
Chemistry and Pharmacology