Al（C₆F₅）₃-based Frustrated Lewis Pairs Mediated Polymerization Of Polar Olefin Monomers

Polar olefin polymers, including poly(methyl methacrylate)(PMMA), can effectively improve the viscosity, toughness, and interfacial properity of polyolefins, owing to the introduction of polar group in the main chain of polymers, significantly broadening their commerical applictions.The development of a simplified, and efficient polymerization catalyst systems is highly desirable. Extraodinary advancements have been achieved in the employment of frustrated Lewis pairs (FLPs) or classical Lewis pairs (CLPs) in polymerization of polar olefin monomers, such as methyl methacrylate (MMA) and a-methylene-y-butyrolactone (MBL). However, this polymerization catalysis also suffers from some problems:1) Though some catalyst systems peformed high polymerization activity, the initiator efficiency is very low (<5%), and also the polymerization is uncontrollable.2) The block complymer can not be synthesized for the polymerization terminates at end.3) The reported application of the catalyst systems is very limited.In this dissertation, Lewis pair composed of N-Heterocyclic olefin (NHO), and a strong Lewis acid such as Al(C6F5)3in polymerizing of polar olefin monomers was studied. This disseretation primarily covers the following three aspects:1. Three NHOs with different structures as Lewis base were used in polymerizing polar olefin monomers in the presence of Al(C6F5)3. First, the interaction of NHOs and Al(C6F5)3was studied. Crystal data and19F NMR spectrum of Al(C6F5)3-NHO adducts proved that NHO shows a strong tendency of interaction with Al(C6F5)3, so the latter can hardly be used in this polymerization directly. The monomers should be premixed with with Al(C6Fs)3before the addition of NHO. High molecular weight (Mn=7.50×105g/mol) and narrow molecular weight distribution (PDI<1.5) were achieved with Al(C6F5)3-NHO Lewis pair. The highest TOF of is up to15480h-1. The catalyst system was also found to be active in copolymerizing of MMA and BMA with high activity. Reactivity ratio shows that the copolymerization is irregular. Electrospray ionization time-of-flight mass spectrometry (ESI-TOF MS) study provides a straightforward approach to insight into details of polymerization of MMA mediatied by Al(C6F5)3/NHO Lewis pairs, and therefore the possible polymerization mechanism was proposed.2. Al(C6F5)3-based Lewis pair polymerization provides a practical and feasible method in polymerizing asymmetric divinyl monomers such as4-vinylbenzyl methacrylate in high reactivity under mild conditions, producing soluble polymers with high molecular weight (up to6.4×105g/mol) and narrow polydispersity (PDI～1.3). ESI-TOF MS study demonstrated that the polymerization took place exclusively on the methacrylic double bond, and the pendant allylic or styrene C=C bond remained intact. The Lewis pair also performed good activity and regioselectivity in copolymerizing AMA and VMA, affording the corresponding polymers with high molecular weight and narrow PDI.3. The diblock copolymer composed of polar monomer and lactide was successfully synthesized. PMMA with vinyl group at chain end was prepared by Lewis pair polymerization. The vinyl group was transferred to hydroxy group by the click reaction with PhCH2SH. The resulted PMMA with-OH end group can be directly used as macroinitiators to succeedingly initiate ring-opening polymerization of lactide with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) to synthesize the PMMA/PLA diblock copolymers. ESI-TOF MS analysis demonstrated the PLA was increased on the PMMA chain. The thermoledynamics properity of block copolymer can be adjusted by changing the length of two polymer chain segments.