Cationic Copolymerization Of Isobutylene With 4-Vinylbenzenecyclobutulene:Characteristics And Mechanisms

Polyisobutylene(PIB)is widely used for its excellent chemical stability,air tightness,and non-toxicity and harmlessness to the human body.At present,various polyisobutylene-based multifunctional elastomers have been developed.With the continuous advancement of medical technology,the use of polymers as implants in vivo has become a routine operation.Among them,the outstanding biological stability of polyisobutylene groups is receiving increasing attention.The development of polyisobutylene-based biomedical materials has great significance.Significance and application value.Two cationic initiators 2,4,4-trimethylpentane(TMPCl)and 5-tert-butyl-1,3-bis(1-methyl-1-methoxyethyl)benzene(HDCE),using a co-initiator TiC14 and two main initiators respectively to initiate the polymerization of isobutylene(IB),and the addition of proton trapping agent 2,6-di-tert-butylpyridine(DTBP)to ensure the activity of the reaction.The polymerization law and activity characteristics of isobutene during cationic polymerization initiated by the initiation system;the random copolymerization and block copolymerization reaction rules of isobutylene and 4-vinylbenzocyclobutene were investigated,and isobutylene and 4-vinylbenzocyclobutene were proposed.Reaction mechanism during random copolymerization of olefins;characterizes the structural changes after thermal cross-linking of 4-vinylbenzocyclobutene and the thermal and mechanical properties of isobutene and 4-vinylbenzocyclobutene copolymers after thermal crosslinking Performance changes.The results show that:① The conversion rate of isobutene polymerization initiated by TMPCl/DTBP/TiCl4 system can reach 96%at 90 min.The molecular weight of polyisobutylene increases linearly with the monomer conversion rate and the molecular weight distribution is between 1.20 and 1.35;random copolymerization of isobutene and 4-vinylbenzocyclobutene has no activity.The molecular weight of the random copolymer gradually decreases as the feed ratio of 4-VBCB increases,and the molecular weight distribution increases with the feed amount of 4-VBCB.Larger and larger;calculated the monomer reactivity ratios of IB and 4-VBCB random copolymerization,respectively,r1=0.47,r2=2.08;proposed the reaction mechanism of IB and 4-VBCB random copolymerization,namely Compared with IB,VBCB is more prone to get protons from living polymer chains to become a new active species core,which causes chain transfer.The 4-VBCB segment in polymer chains also undergoes self-coupling and causes chain transfer.②HDCE/DTBP/TiCl4 Isobutene polymerization initiated by the system can be 96%at 50min.The molecular weight of polyisobutylene also increases linearly with the conversion of monomers,and the molecular weight distribution is between 1.10～1.20;both initiation systems have achieved cationic controlled polymerization,HDCE/DTBP/TiCl4 has higher efficiency than TMPCl/DTBP/TiC14.The block copolymer p(4-VBCB-b-IB-b-4-VBCB)of IB and 4-VBCB was successfully synthesized using HDCE/DTBP/TiCl4 as the initiation system;Based on the introduction of styrene,the p(styrene-block-4-VBCB)-PIB-P(styrene-block-4-VBCB)terpolymer was successfully synthesized.The copolymerization can be increased by increasing the amount of styrene.The molecular weight of the polymer indirectly regulates the glass transition temperature of the copolymer.③The polymer was heated in a solid form at 250℃ to achieve the cross-linking of the copolymer.The cross-linked copolymer was characterized by nuclear magnetic resonance,carbon,and infrared spectroscopy.Cross-linked formation was found in all three spectra.8-membered ring structure;Through DSC and TGA characterization analysis,the copolymer will increase its glass transition temperature and thermal decomposition temperature after heat treatment cross-linking;the cross-linking strength of the copolymer will increase with the extension of heat treatment time,After the heat treatment for about 30 minutes,the cross-linking strength no longer changes greatly;the strength of the copolymer is greatly improved after the cross-linking and curing.