Study On Synthesis Of Poly{2, 5-Bis[(4-Butoxyphenyl) Oxycarbonyl] Styrenes} (PBPCS) And Its Fiber Strurcture And Property

Poly{2,5-bis[(4-butoxyphenyl)oxycarbonyl]styrenes}(PBPCS) is a classical Mesogen Jacketed Liquid Crystal Polymers(MJLCPs),in which the bulky and rigid mesogenic units are laterally bonded to the flexible polyethylene backbone through their centre of gravity without spacers.From the chemical structure,MJLCPs belong to the side chain type liquid crystal polymers.MJLCPs can be synthesised from vinyl monomer by the chain polymerization.So it is easy to get a product which has high molecular weight,controllable chain structure and molecular weight.The main chains of MJLCPs have to take the relatively extended conformation because of the spatial requirement of the bulky and density mesogenic units.Therefore MJLCPs show properties of main chain liquid crystal polymers of rigid or semi rigid chains,which have higher glass transition temperature(T_g) and operating temperature,and can easily orientate under the shear field and the stretching field,etc.In this dissertation,PBPCS were synthesised by the ordinary radical polymerization using benzoyl peroxide(BPO) as initiator.Three samples with different molecular weight have been obtained by changing the ratio of initiator and monomer.One of them has the highest molecular weight so far,M_n= 63.79×10~4g/mol.The research results showed that the phase behaviour and rheological behaviour of PBPCS is unusual.With the increasing of temperature,PBPCS forms very stable liquid crystal phase above the T_g.However,the LC phase has been destroyed during the process of the cooling and the LC phase formed at higher temperature disappeared upon subsequent cooling.The viscosity and modulus of PBPCS in LC phase are obviously higher than they are in isotropic.These results are the same with the research of Peking University.Furthermore,the original fibres of PBPCS were made by micro extruder through melt spinning method.The mechanical properties of the original PBPCS fibres extruded from the LC phase are the same as those from isotropic phase because of the unusual phase behaviour.The original fibres are brittle and weak,the broken elongation is 3%and the tensile strength is 18MPa.When the original PBPCS fibres were stretched under appropriate conditions,the mechanical properties of PBPCS fibres can be significantly improved.The highest broken strength can reach 32.3Mpa after the original PBPCS fibres were stretched 5 times and its elongation at break reach 37.1%.2D WAXD results show that the orientation index of the original PBPCS fibres was only about 60%.And the orientation index of the stretched fibres with 5 times can reach 78.3%,which increases 32.8%.Therefore the molecular chains have orientated along the stretching direction during the stretching process,which causes the improvement of the mechanical properties of PBPCS fibres.Finally,the phase memory effect of PBPCS fibre was studied by Dynamic Mechanical Analysis (DMA).According to the research results,the outstanding shape recovery ability of PBPCS fibre is found. Above 145℃,the rate of shape recovery is the best.The time recover from 400%draw ratio to origin length is about 9 minutes.The repeatability of shape memory is good in 5 repeated times.2D WAXD experiments showed the diameter of helical cylindrical block changed from 2.2nm to 2.1nm after deformation and this result indicated PBPCS helical main-chain in a more straight conformation.So,there would be a certain inner stress in molecular chain,namely shape memory force(Fsm).There were not the stable and memory phase structure of traditional SMP in PBPCS because it is an amorphous polymer.The reason of PBPCS fibre with the shape memory effect is its special helical molecular chain structure just as a spring,say,flexible polystyrene main chain makes PBPCS fibre present good strain reversion ability and the mesogenic effect of side chain makes fibre keep the origin dimension.