Quasi-Living Copolymerization of Aryl Isocyanates and Epoxides

Abstract

Nontraditional polyurethane (PU) has been successfully synthesized by anionic copolymerization of some typical aryl isocyanates and epoxides with ammonium halide onium salt (Lewis base) as the initiator and triisobutylaluminum (Lewis acid) as the activator and the synergistic coordinator. In contrast to the traditional step-growth approach, this chain-growth copolymerization can maintain the anionic propagation site and exhibit some living features with a high activity, by which the copolymers synthesized have narrow molecular weight distributions and discrete end groups. The copolymer is primarily constituted by a urethane linkage, and the byproducts of isocyanurate trimer and oxazolidinone can be effectively suppressed as the polymerization proceeds. Density functional theory (DFT) calculations were also performed to support the proposed reaction mechanism.

Heterocycle/Heteroallene Ring‐Opening Copolymerization: Selective Catalysis Delivering Alternating Copolymers

“…In related work Oct4NBr/(iBu)3Al was investigated for ArNCO/butylene oxide ROCOP, albeit with poor polymer and linkage selectivity. [219] Using n BuLi as the initiator, resulted in successful RNCS/ES ROCOP to produce semicrystalline poly(imino dithioacetal), [-CH2CH2-S-C(=NR)-S-]n (Tm = 63 -128 °C depending on R; Mn = 25 -60 kg/mol). [220] Polymerisation rates were increased using -142 kg/mol).…”

“…By changing the epoxide, it was feasible to control T g in the resulting polyurethanes to give values as low as −24 °C; it was also noted that TsNCO/EO yields a semi‐crystalline polyurethane, with T m =61 °C ( T c =44 °C). In related study, Oct 4 NBr/( i Bu) 3 Al was investigated for ArNCO/butylene oxide ROCOP, but gave poor polymer and linkage selectivity [219] …”

Heterocycle/Heteroallene Ring‐Opening Copolymerization: Selective Catalysis Delivering Alternating Copolymers

“…In related study, Oct 4 NBr/(iBu) 3 Al was investigated for ArNCO/butylene oxide ROCOP,b ut gave poor polymer and linkage selectivity. [219] Using n BuLi as the initiator resulted in successful RNCS/ ES ROCOP to produce semi-crystalline poly(imino dithioacetal), [-CH 2 CH 2 -S-C(=NR)-S-] n (T m = 63-128 8 8Cdepending on R; M n = 25-60 kg mol À1 ). [220] Polymerisation rates were increased when using coordinating solvents,f or example, THF or (Me 2 N) 3 P = O, which enhance the nucleophilicity of the dithiocarbamate chain end through its coordination to lithium.…”

Alternating Chain Growth Copolymerization of Isothiocyanates and Epoxides

“…Previously, anionic copolymerization of aryl isocyanates with epoxides has been accomplished by employing Lewis pairs, in which ammonium halide onium salt serves as an initiator and triisobutylaluminum as an activator and a synergistic coordinator. 18 Unfortunately, we found that this approach could not be applied to synthesize copolymers of isothiocyanate and epoxide. Herein, we reported another strategy to achieve perfectly alternating copolymerization of isothiocyanates and epoxides with t-BuOLi, as shown in Scheme 1.…”