Liquid Crystalline Behavior, Fiber Shape Memory Effect And Application Of PBPCS Based On Mesogen-jacketed Liquid Crystalline Polymer

Mesogen-jacketed liquid crystalline polymer (MJLCP) that the rigid mesogens directly attach to the backbone chain only through a covalent bond, is considered as the third classic novel liquid crystalline polymer (LCP) after main chain liquid crystalline polymers (MCLCP) and side chain liquid crystalline polymer (SCLCP). Because of its special macromolecular chain structure and the "Jacketed effect", macromolecular chain demonstrates special "linear" columnar chain characteristics not the usual "random coil" chain. As well known, the performance is determined by the structure, the physical properties of MJLCP, such as liquid crystalline (LC) behavior, molecular orientation, rheological properties, fiber formation, and the unique shape memory effect, are important and significant for academic research. In this paper, Poly-{2,5-bis[(4-butoxyphenyl)oxycarbonyl]styrene}, PBPCS, has been investigated as the research model of MJLCP for the above questions.In section for the in-depth investigation of PBPCS LC behavior, PBPCS was macro-prepared and characterized with IR, NMR, element analysis, PBPCS thermotropic LC behavior was investigated through POM, WAXD, ARES. On the basis of thermodynamics and kinetics, hexagonal columnar liquid crystalline phase was formed by entropy change and self-assembly. Because of the complete "coupling effect", PBPCS demonstrated various types of meta-stable phase in phase transition by the cooperation and competition between flexible backbone chain and side mesogens. The stability of liquid crystalline phase was determined by intermolecular condensed force, the greater condensed force, the more stable liquid crystalline phase. Due to the crosslinked structure formation at high-temperature LC phase, PBPCS showed abnormal rheology and viscoelasticity. At the same time, PBPCS Lyotropic LC behavior was also investigated.In section for the PBPCS fiber formation, firstly, the molecular orientation of PBPCS melt-spinning in LC phase was investigated according to Baleo TIF model in theory. The orientation varieties of the original PBPCS fiber, drawn fibers (draw ratioλ=300%,λ=500%) were investigated by two-dimensional X-ray diffraction (2D WAXD), orientation degree (F), the average orientation angleθ, the draw direction vector nz.were enhanced with the draw ratio increasing. During the drawing upon applied load, the segment orientation will be occurred firstly, then the cooperation between the flexible backbone chain and mesogens drives the orientation of the macromolecular chain and self-assembly unit. Further orientation of the macromolecular chain and self-assembly unit were completed by the conformation change through covalent bands rotation of the flexible backbone chain, and the deformation occurred at the same time. During the steady shear flow of melt spinning, Dewitt model and ARES experiments both showed shear-thinning behavior and "structural viscous" characteristics, therefore, spinning at low shear rate was performed in order not to destroy the self-assembly structure of PBPCS. During the uniaxial elongation flow of melt spinning, according to the Lodge network model and long relaxation time of PBPCS, spinning was performed at slow stretching rate. At the same time, DMA,2D WAXD, SEM were applied to investigate the post-drawing of PBPCS original fiber, after 5 times drawing treatment, the orientation degree increased from 64% to 85%, the tensile strength and elongation at break were improved from lOMpa to 35Mpa and from 6% to 15%, respectively. However, due to the limitation of maximum draw ratio,2D WAXD experiments demonstrated molecule chain slippage of self-assembly PBPCS as the draw ratio was 7, so the fiber formation of PBPCS was performed under low shear rate and slow stretching rate, the suitable post-drawing ratio is 5In section for the shape memory effect of PBPCS fiber, self-assembly PBPCS fiber is novel shape memory material in molecular level. PBPCS fiber belonged to heat-triggered SMP that the thermo-responsive temperature was about 108℃near glass transition temperature (Tg), the recovery depended not only on the temperature but also the time, recovery rate was slow and recovery plots were similar under different cases, a viscoelastic model based on two Maxwell models in parallel was discussed for the shape memory behavior, recovery stress was about 1.6Mpa determined by DMA. In order to verify the repeatability of shape memory effect, cyclic thermo-mechanical tests for 5 times were performed, the results indicated that PBPCS fiber exhibited excellent shape memory effect, shape fixing ratio was above 99.5%, shape recovery ratio was near 100%. A reasonable mechanism was proposed, flexible backbone chains acted as switch structure, mesogens as fixing structure, and the self-assembly cross-linked network structure formed in LC phase lead to shape memory effect of PBPCS fiber.Finally, PBPCS in high-performance damping materials application was investigated, the ternary blend damping materials with MJLCP and IPN polyacrylate were prepared by situ composite through dispersing PBPCS into polyacrylate core-shell structure. MJLCP was wrapped in IPN polyacrylate according to IR and TEM experiments, however the adding PBPCS affected the normal morphology of core-shell particle. The dissipation damping factor was determined by DMA, results revealed ternary blends’maximum dissipation factor increased above 0.9 at high temperatures region because of PBPCS adding, it indicated that MJLCP can promote the damping ability of IPN polyacrylate to some extent.