Organocatalytic Living Ring-Opening Polymerization of Cyclic Carbosiloxanes

Abstract

[reaction: see text] An organocatalytic route to narrowly dispersed poly(carbosiloxanes) of predictable molecular weight and end group fidelity is described. N-Heterocyclic carbenes (NHC) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) catalyze the ring opening of cyclic carbosiloxanes. The pK(b) of the catalyst is important in preventing adverse transetherification reactions and obtaining well-defined polymers. Mechanistic studies indicate that hydrogen bonding to TBD or the NHC activates alcohols or silanols for ring-opening reactions.

N-Heterocyclic carbene-catalyzed dehydration of α,ω-disilanol oligomers

“…The high catalytic activity of 1a suggests that the carbene behaves as a base in the polycondensation of dihydroxysiloxanes. In fact, the interaction of NHCs with relatively acidic proton has already been reported [7,13]. Therefore, the polycondensation reaction proceeds with the NHC bearing very bulky mesityl groups (1c) which is completely inactive for the ROP of cyclosiloxanes [8], suggesting that the role of the NHC catalyst is different in each case (ROP/polycondensation).…”

“…In contrast, NHC catalysts have only been involved in a few polymerization reactions [4], such as polymerization of isocyanates [5], ring-opening polymerization (ROP) of cyclic esters [6], and cyclic siloxanes [7]. Recently we have also reported that NHCs are efficient catalysts for the ROP of cyclotetrasiloxane (D 4 ), which is one of the rare examples of the transformation of non-carbonyl compounds catalyzed by NHCs [8].…”

Organophosphate-catalyzed bulk ring-opening polymerization as an environmentally benign route leading to block copolyesters, end-functionalized polyesters, and polyester-based polyurethane

“…In order to avoid metal contamination without any special purification steps, the organocatalytic approach has emerged as a powerful metal-free polymerization process in recent years. 7 Considerable effort has been directed toward the evaluation of various types of both organic acids/bases for the ROP of cyclic esters, 7-37 cyclic carbonates, [38][39][40][41][42][43] epoxides, [44][45][46][47] lactams, 48 cyclic (carbo)siloxanes, 49 cyclic phosphates, [50][51][52][53][54] etc. Regarding the ROP of cyclic esters, organic Brønsted acids, e.g., methane sulfonic acid (MSA) and triflimide, were found to be suited for the polymerization of lactones, [8][9][10][11][12][13][14][15][16][17][18][19] whereas organic bases, e.g., 1,8-diazadicyclo [5.4.0]undec-7-ene (DBU) and 4-dimethylaminopyridine (DMAP), were effective for the ROP of the lactide (LA).…”

Synthesis and trans-ureation of N,N’-diphenyl-4,4′-methylenediphenylene biscarbamate with diamines: a non-isocyanate route (NIR) to polyureas

“…In fact, several attempts have tried to use carbamates, or biscarbamates directly as precursors for polyurethane (PU) and polyurea synthesis bypassing isolation of diisocyanate completely [26]. In 2000, ring-opening isomerization of cyclic-urethane [27][28][29] and trans-esterification [30,31] to make PU are notable examples. However, both produce low molecular weight polymers.…”