Functional Polyolefins Via Metathesis Polymerization

Polyolefins are the most widely used commodity polymeric materials.However,their inert chemical activity makes them unsuitable for those areas requiring strong hydrophilicity,polarity,biocompatibility and so on.Therefore,it is necessary to study the functionalization of polyolefins.Generally,there are several methods for the functionalization of polyolefins including post-modification,copolymerization,etc.Conducting functionalization through these methods is relatively easy and efficient,but the functional groups introduced usually were randomly distributed along the polymer backbone,rendering formation of regular chain structures really difficult.In this dissertation,metathesis polymerizations were employed to prepare functional polyolefins,aiming at precisely controlling the distribution of functional groups along the polymer backbone.Firstly,three precisely-defined polymers containing 1,3-dithiane groups were successfully synthesized by acyclic diene metathesis(ADMET)polymerization and subsequent hydrogenation.The dithiane units in the ADMET polymer with 20 methylene carbons spacing were transformed into thiol groups via reaction with Bu3SnH.This work provided a convenient route to synthesize polyethylene with pendant thiol groups that are evenly distributed in the chain.Secondly,a series of PEs containing arylene ether units as defects in the main chain were synthesized via ADMET polymerization of seven monomers containing different arylene units.NMR and GPC analysis shows that polymers with high molecular weight were obtained.According to DSC,WAXD and SAXS results,it is found that the substitution position in the arylene units has a remarkable influence on the chain stacking and ordering in the solid phase.Then,three polyethylene containing different non-planar aliphatic ring ether units were synthesized via ADMET and subsequent hydrogenation.They were compared with their counterpart polymers containing aromatic ring defects in aspects of chain structure,thermal properties and crystalline structure.It showed that non-planar aliphatic ring ether units exhibited more significant effect on the chain stacking mode and phase structures.Thirdly,a series of functional polyolefins with regularly distributed ester groups were prepared by ring-opening metathesis polymerization(ROMP)of cyclopentene-based functional monomers.At the same time,the crystallization behavior of side chains was investigated.The relationship between melting point,lamellar thickness and side chain length was clarified according to DSC and XRD results and Gibbs-Thomas equation,which provided a template for the preparation of thermosensitive polymer materials.Then,a series of PEs containing thioester pendants were successfully synthesized.According to DSC analysis,glass transition temperature and melting temperature of these polymers were higher than the counterparts containing ester pendants.TGA analysis indicated that all the thioester-containing polymers exhibited moderate thermal stability and two-stage decomposition profile,and the sulfur-containing polymers show slightly lower thermal stability than their counterparts without sulfur,meaning small modification in the main chain would substantially influence the macroscopic performance of polymers.Fourthly,ring-opening metathesis copolymerization of different cyclic monomers was explored.Some monomers during copolymerization could form alternative segments,providing a new approach for preparing precise functional polymers.Finally,by post-modification functionalization of the ROMP polymers,acidic carboxyl groups have been successfully introduced into polyolefin backbone with high density,providing an alternative method for introducing regularly distributed functional groups through post-modification.The research results offer new routes for the design and synthesis of functional polyolefins with precisely-defined chain structure,and show a better understanding of the relationship between chain structure and aggregation states of some functional polyolefins.