Shape Memory Properties And Modification Of Mesogen-jacketed Liquid Crystalline Polymers Based On Vinyl Terephthalate

Shape memory polymers are intelligent polymers that can be recovered to the original shape under external stimuli(such as heat,electricity,magnetic fields,light,solvents,and pH etc.).The shape memory polymers have the advantages of light weight,low cost,easy shaping,high deformation and quick recovery,Which are widely used in the fields of aerospace,bio medicine,sports equipment,sensors and military weapons.Developing shape memory polymers with low cost,simple structure,stable deformation and high recovery efficiency is of great significance.Mesogen jacketed liquid crystal polymer is a kind of liquid crystalline polymer with a large side group,which is linked to the polymer flexible backbone via a short spacer at the waist,mesogen jacketed liquid crystal polymers have unique performance due to its special structure.Most of mesogen jacketed liquid crystal polymers are thermotropic liquid crystalline materials.It is of great significance to develop novel shape memory materials based on mesogen jacketed liquid crystal polymers and their composite materials with shape memory effect.According to the previous studies,the shape memory properties of mesogen jacketed liquid crystal polymers based on vinyl terephthalate have been further investigated in this paper.The modification of mesogen jacketed liquid crystal polymers has been carried out by blending technology,and the specific contents are as follows:(1)Four kinds of mesogen jacketed liquid crystal polymers based on vinyl terephthalate,that is PBPCS,PMPCS,PDCHVT and PbiPCS,have been synthesized,which have different rigidity end groups in side chain,these four kinds of mesogen jacketed liquid crystal polymers have good heat resistance,and the higher rigidity of the end group,the greater rigidity of the corresponding polymer sheet in the temperature range of 30~80 ?.Through shape memory angle recovery tests,the results indicate that all mesogen-jacketed liquid crystalline polymers have good shape memory fixation ratios,and they are close to 100%,The shape memory recovery effect is related to the end group of polymer side chain,When the end group of side chain is P-butoxy phenyl and cyclohexyl(corresponding polymers are PBPCS and PDCHVT),the polymer sheets show good shape memory properties,shape memoryrecovery ratios are 87% and 100%,respectively.PDCHVT fiber have been prepared by melt spinning,The shape memory properties of PDCHVT fiber have been measured by DMA shape memory cycle test,the results show that the fibers exhibit stable and excellent shape memory effect.(2)SBS have been mixed with four kinds of mesogen jacketed liquid crystal polymers(PBPCS,PMPCS,PDCHVT,PbiPCS)at different ratios,and then their films were prepared.With the increase of SBS component,the storage modulus of the blend film at room temperature are decreased significantly,however the toughness,the fracture tensile stress and tensile strength are all increased.The change of the film's Tg with the increase of SBS content have been tested by DSC.The results show that the mesogen jacketed liquid crystal polymers and SBS are incompatible components.DMA shape memory test results show that,after the SBS is added,shape memory fixing ratios of thin films are decreased,SBS/PBPCS and SBS/PDCHVT blend films have better shape memory properties than SBS/PMPCS and SBS/PbiPCS blend films.(3)MWCNT and PDCHVT composites have been prepared by solution blending,and MWCNT/PDCHVT are made into sheets and fibers through heat pressing and melt spinning respectively.The storage modulus,breaking tensile stress and tensile strength of PDCHVT are improved because of the addition of MWCNT.The material has maximum tensile stress and fracture strain when the content of MWCNT is 3%,The surface morphology of the composite was observed by SEM,and it is found that the agglomeration of MWCNT is occurred with the increasing content of MWCNT,and the micropores are appeared on the surface of the material.The addition of MWCNT improves the shape memory recovery speed and shape memory recovery force of PDCHVT.At the MWCNT content of 3%,the obtained composites demonstrate the best shape memory effect and tensile properties.