Preparation And Properties Of Liquid Crystal Polymer Materials With Controllable Sequence

Liquid crystal polymer(LCP)materials have attracted tremendous scientific attention since the first discovery in the middle of the 20 th century.Benefited from their excellent thermal stability and mechanical property,LCPs have wide applications in many fields,such as organic photoelectric materials,engineering plastics,high modulus fibers,tunable diffraction gratings and thermal-isolation materials,etc.Preparation and research of novel LCP materials have become the basis for designing further viable applications,and one of hotspots in recent years.Among these researches,LCPs with controllable sequence have gained popularity for their potential applications in optoelectronic device materials.The molecular chains of LCPs can be oriented by a certain level of external stimulus such as mechanical friction,electric field and magnetic field,and the thermal conductivity along oriented direction can be greatly improved correspondingly.This type of ordered LCPs may has wide application value in high thermal conductivity insulating materials.Novel sequence-determined side-on liquid crystal polymers(SCLCPs)can be prepared via sequence-controlled synthesis,and the mesogenic units with different lengths and distributions can form various ordered sequences,which further endow LCP materials with diverse functions.Herein,the main work of this paper can be divided into the following two aspects:(1)A new type of LCP film material was prepared.Mesogenic unit(MU)was induced to homeotropic align via simple mechanical action to enhance thermal conductivities along normal directions of the film.For this purpose,two techniques,polymerizer heat-pressing and monomer cross-linking,were used in this work.In the way of polymerizer heat-pressing,we designed and synthesized an end-on acrylate-containing LC monomer LC1,which was easy to homopolymerize.The mesomorphic behaviors of LC1 were studied by POM and DSC.Solution polymerization,bulk polymerization and photopolymerization were tried respectively to select suitable film-forming and oriented polymers.In the way of monomer cross-linking,we designed and synthesized a novel liquid crystal monomer LC2 which was easy to cross-link.Simultaneously,crosslinker 11 UB and N2 was synthesized.Then,by using PMHS as the framework,LC2 was crosslinked into liquid crystal elastomer(LCE)film with Pt catalyst.Finally,we attempted to realize the MU homeotropic alignment by applying dynamic mechanical pressure.(2)A new alternating SCLCP Poly(Y1801-alt-Y1802)embedded with side-on mesogen Y1801 and end-on mesogen Y1802 was designed and synthesized via styrene-maleimide alternative copolymerization.Two homopolymers PY1801 and PY1802 were prepared consecutively for comparison.The GPC and NMR experiments of SCLCP Poly(Y1801-alt-Y1802)proved the success of alterative copolymerization.The mesomorphic properties of LCPs are characterized by DSC,POM and WAXS.Both the side-on SCLCP PY1801 and the end-on SCLCP PY1802 exhibited nematic phase,in contrast,the alternating copolymer Poly(Y1801-alt-Y1802)showed an interdigitated SmA phase,a compromised molecular arrangement instead.Additionally,UV-vis and FS spectra of the alternating SCLCP Poly(Y1801-alt-Y1802)were measured and the FS emission of the alternating copolymer Poly(Y1801-alt-Y1802)in the DMF solution was observed.The findings indicate novel potential applications of alternating copolymers in thermodynamics,optical-physics and other fields.