Synthesis and characterization of new ring opening polymerization（ROP）catalysts based on aluminium or tungsten complexes

Cyclic esters provide versatile biocompatible and biodegradable polymers possessing good mechanical properties. These polymers are also models for studying the kinetics, thermodynamics, and mechanisms of many elementary reactions in polymerization. Both organoaluminium and tungsten complexes for ring opening polymerization have received increasing attention over the last few years. The aim of this study is to investigate a series of new complexes incorporating aluminium and tungsten metals in combination of various ligands, and assess their ability as catalysts for the ring opening polymerization of ε−caprolactone and rac-lactide.Reaction of Me₃Al (two equivalents) with anisidines formed a family of organoaluminium complexes, viz {[1,2-(OMe),N-C₆H₄(μ-Me₂Al)](μ-e2Al)}₂ (1), [1,3-(Me₃AlOMe),NHC₆H₄(μ-Me₂Al)]₂ (2) and [1,4-(Me₃AlOMe),NHC₆H₄(μ-Me₂Al)]₂ (3). Complexes 1 - 3 were found to be highly active for the ring opening polymerization (ROP) of ε-caprolactone either with or without benzyl alcohol present; at various temperatures, the activity order 1 > 2 ≈ 3 was observed. For the ROP of rac-lactide results for 1 – 3 were poor (Chapter 2).By varying the reaction conditions, the reaction of [W(eg)3] (eg = 1,2-ethanediolato) with p-tert-butylcalix[n]areneHn (n = 6 or 8) in refluxing toluene affords different tungstocalixarene complexes. Complexes {[W(eg)]₂(μ-O)p-tert-butylcalix[6]arene} (1), {[W(eg)]₂p-tert-butylcalix[8]arene}·MeCN (3), {1,2-[W(eg)2]2p-tert-butyl calix[8]areneH₄}/{1,3-[W(eg)₂]₂p-tert-butylcalix[8]areneH₄} (4a)/(4b)• 3.5MeCN and {[WO(eg)]₂p-tert- butyltetrahomodioxacalix[6]areneH₂} (5) have been screened for their ability to ring open polymerize (ROP) ε-caprolactone; conversion rates were poor at temperatures below 110 oC. All tungsten complexes have similar conversion rates, yet ROP using complex 3 has outstanding polymerization weight compared with other co-catalysts (Chapter 3)