Controllable Synthesis Of Carboxyl-Terminated Polyolefins Via Olefin Metathesis And Hydrogenation

Polyolefins with excellent properties are one type of the most widely used and commercialized polymers.However,the non-polarity of their structures limits the improvement of material performance and expansion of application range in some extent.The introduction of polar groups into the molecular chain of polyolefins not only keeps the original excellent properties of polyolefins,but also endows them with reactivity,thus improving their properties and expanding their application fields.Among them,carboxyl-terminated polyolefins can be used as electrical insulation,solid rocket propellant,sealant and so on,having a good application prospect The coordina-tion polymerization of olefins usually afforded the formation of single carboxyl-terminated polyolefins.In recent years,via olefin metathesis-hydrogenation strategy provided a new method for the synthesis of terminal-functionalized polyolefins with mild conditions and controllable products.This thesis aimed at the controllable synthesis of carboxyl-terminated polyolefins via olefin metathesis-hydrogenation.The major achievements of this thesis are as follows:(1)Taking diene rubbers as starting materials,the carboxyl-terminated poly dienes were synthesized via olefin metathesis degradation of diene rubbers catalyzed by Grubbs Ⅱ catalyst(G2)in the presence of maleic acid as a chain transfer agent(CTA).The influences of reaction conditions on the molecular weight and molecular structure of products,including reaction time,reaction temperature,molar ratios of C=C/catalyst and C=C/chain transfer agent,were investigated.The carboxyl-terminated polyolefins were further prepared by the subsequent chemical hydrogenation with p-toluene-sulfonyl hydrazide/tri-n-propyl amine reagents.The results indicated that the catalyst was highly active for the metathesis degradation of diene rubbers even if there was no existence of chain transfer agents.The molecular weight of products could be controlled by varying the molar ratio of C=C/catalyst or C=C/chain transfer agent.It’s worth noting that the trans-1,4 content of carboxyl-terminated polybutadiene via metathesis degradation greatly increased and the corresponding cis-1,4 content decreased and this change in the microstructure further affected the properties of polymers.After hydrogenation,the carboxyl-terminated polyolefins had better thermal stability than the carboxyl-terminated polydienes.(2)The carboxyl-terminated polynorbornene and its copolymers with cyclooctene were synthesized via ring-opening metathesis(co)polymerization of norbornene cataly-zed by Grubbs Ⅱ catalyst(G2)in the presence of maleic acid as a chain transfer agent(CTA).Similarly,the molecular weight of products could be effectively controlled by changing the molar ratio of monomer/catalyst or monomer/chain transfer agent.With-out a chain transfer agent,polynorbornene with high molecular weight were obtained.The addition of chain transfer agent caused the homopolymer to metathesize and degrade,resulting in a low molecular-weight carboxyl-terminated polynorbornene.The molecular structure of copolymers changed with the variation of norbornene/cyclooct-ene ratio,which led to different thermal stability.The product with 1:1 ratio of NB and COE had the worst thermal stability and the lowest melting point due to the highest chemical irregularities.