Fabrication Of Polyurethane Elastomers And Study Of Their Relationships Between Microstructure And Dielectric,Electromechanical Properties

Dielectric elastomer is a kind of electroactive polymer that has a wide range of applications in sensors,actuators,artificial muscles and energy harvesters.In order to improve dielectric and electromechanical properties of polyurethane dielectric elastomers,a series of hydroxyl-terminated butadiene-acrylonitrile copolymer?HTBN?based polyurethane elastomers?PUs?and poly?urethane urea?elastomers?PUUs?were fabricated.The main works in the thesis are consist of following five parts.1)In part 1,effects of different hard segment contents on microphase separated structure and properties of PUs were investigated.The results indicated that the crystallinity of hard segment,Young's modulus and breakdown field strength were increased significately with increase of HS content,whereas,the dielectric constant and actuated area strain were decreased slightly.2)In part 2,effects of chain length of diol chain extenders on microphase separated structure and properties of PUs were investigated.The resuls showed that the crystalline structure and degree of hydrogen bonding of HS were significantly influenced by the length of chain extenders,results in influencing their dielectric constant,Young's modulus and actuated strain perfomance.Among the ethylene glycol?EG?,propylene glycol?PG?,butanediol?BDO?and hexadiol?HDO?,the PU with EG showed higher dielectric constant?9.6@1 k Hz?and actuated strain(6.1%@70 kV mm^-1).3)In part 3,effects of different contents of urea groups in HSs on microphase separated structure and properties of PUUs were investigated.The results showed that degree of hydrogen bonding,crystallinity of HS,hard domain size and Young's modulus of PUUs were significantly increased with increase of HS content,whereas,the dielectric constant and actuated strain were decreased.4)In part 4,effects of the chemical structure of amine chain extenders on microphase separated structure and properties of PUUs were investigated.The results showed that PUU with 4,4'-diamino dicyclohexyl methane?PACM?chain extender exhibited higher elastic recovery and lower Young's modulus among the chain extender of 4,4'-diamino dicyclohexyl methane?PACM?,3,3'-dimethyl-4,4'-diaminodicyclohexylmethane?DMDC?and methyl cyclohexanediamine?HTDA?.And,the PUU with DMDC chain extender can be reached 27%of actuated area strain.However,the crystallinity and dielectric property were less affected by the volume effect of chain extender.5)In part 5,effects of crosslinking agent?trifunctional chain extender?content on microphase separated structure and properties of PUs were investigated.The results showed that the crystallinity,hard domain content and Young's modulus of the PUs were significantly reduced with increase of crosslinkable chain extender content,whereas,the dielectric constant was slightly increased.However,the actuated strain under a certain electric field was almost independent on crosslinkable chain extender content.Those results showed that the microphase separated structure,dielectric and electromechnical properties of PUs and PUUs could be controlled by adjusting the HS content and chemical structure,and the electromechnical properties of PUs and PUUs can be improved via balancing the dielectric and and mechanical properties.