ACYCLIC DIENE METATHESIS (ADMET) POLYMERIZATION - DESIGN AND SYNTHESIS OF UNSATURATED POLY(CARBOSILOXANE)S

The synthesis of unsaturated poly(carbosiloxane)s, a new class of siloxane polymers possessing a perfectly alternating siloxane and alkenylene main chain, is presented. 1,5-Bis(allyl)-1,1,3,3,5,5-hexamethyltrisiloxane (4), 1,3-bis(4-pentenyl)tetramethyldisiloxane (6), 1,4-bis(3-allyl-1,1,3,3-tetramethyl-disiloxanyl)benzene (8), and telechelic alpha,omega-di-4-pentenylpoly(1,1,3,3-tetramethyldisiloxanylpentylene) (10) undergo acyclic diene metathesis (ADMET) polymerization catalyzed by [(CF3)2CH3CO]2(N-2,6-C6H3-i-Pr2)Mo=CHC(CH3)2Ph (1). These polymerizations, which are performed under bulk conditions and at low temperatures, continuously release ethylene to give poly(1,1,3,3,5,5-hexamethyltrisiloxanyl-2-butenylene) (5), poly(1,1,3,3-tetramethyldisiloxanyl-4-octenylene) (7), poly(1,1,3,3-tetramethyldisiloxanyl-p-phenylene-1,1,3,3-tetramethyldisiloxanyl-2-butenylene) (9), and poly(1,1,3,3-tetramethyldisiloxanylpentylene-co-1,1,3,3-tetramethyldisiloxanyl-4-octenylene) (11), respectively. Bis(vinyl)tetramethyldisloxane fails to homopolymerize under ADMET conditions, and bis(allyl)tetramethyldisiloxane (2) releases ethylene when catalyzed by 1 in the absence of solvent, to give, exclusively, the ring-closed product, 1, 1,3,3-tetramethyldisiloxacyclohept-5-ene (3). Extending the methylene units or the siloxane linkage in the monomer results in facile ADMET polycondensation, in essentially quantitative conversions, affording well-defined, low-T(g), linear polymers with known vinylic end groups. The polymerizations are void of competing reactions except when back-biting reactions are favorable. Polymer 5 undergoes back-biting to generate the nine-membered cyclic silaoxalkene 13, when active polymer is diluted or, to a lesser extent, when in the bulk. All monomers and polymers were characterized by infrared spectroscopy and H-1, C-13, and Si-29 NMR spectroscopy. Number average molecular weights were determined by gel permeation chromatography and quantitative C-13 NMR end group analysis when possible. Synthesis, characterization, thermal analysis, and the current scope of this polymerization are discussed.