Synthesis And Property Studies Of Conjugated Polymers/Liquid Crystalline Elastomer Composites

Liquid crystalline elastomers(LCEs)are anisotropic,elastic,crosslinked polymeric materials,possessing a unique shape memory function that can perform reversible shape transformations under the external stimulus(such as heat,light,electric,magnetic,etc.).Recently,NIR-stimulus-responsive LCEs have become an important research topic due to its prospective applications in the biotechnology field.NIR-responsive LCEs can be prepared by doping inorganic photothermal conversion fillers.The poor dispersion of inorganic nanoparticles will inevitably weaken materials' mechanical properties and the photo-actuation rates.In this work,we report the first example of monodomain polysiloxane-based LCE composite material by doping polyaniline nanoparticles.This material has excellent stability and photo-actuation rates.The most widely used method to prepare monodomain LCEs is a one-pot,two-stage hydrosilylation process invented by Finkelmann.But this traditional method towards monodomain LCEs requires complicated procedures,elevated reaction temperatures,and a prolonged preparation time ranging from several hours to even several days.Herein,we report an ultrafast one-pot,two-stage thiol-ene photoaddition method to synthesize monodomain polysiloxane-based LCE films.Starting from mesogenic monomers,the whole preparation process can be finished in less than 30 minutes,and all the preparation experiments are performed at room temperature,in an open air environment..This thesis can be divided into two parts:1.We first synthesize polyaniline nanoparticles which show excellent photothermal conversion efficiency.We choose polymethylhydrosiloxanes(PMHS)as the main chain,MBB as monomer,11UB as crosslinker,Pt as the catalyst to produce conjugated polymer/liquid crystalline elastomers by doping polyaniline nanoparticles and using Finkelmann two-stage crosslinking protocol.Their properties are characterized in detail by a combination of NMR,Fourier transform infrared spectra(FTIR),ultraviolet and visible spectrophotometry(UV-Vis),differential scanning calorimetry(DSC),polarized optical microscope(POM)and scanning electron microscope(SEM).A series of comparative experiments are performed to investigate the photo-responsive properties of these polyaniline/LCE samples in correspondence to the two different conjugation forms(emeralidine salt(ES)or emeralidine base(EB))and the varied doping concentrations(0.5 wt%or 1.0 wt%)of the incorporated polyaniline nanoparticles.In summary,these conjugated polymer/LCE composite materials show excellent photothermal conversion efficiency and mechanical property.Also,these LCEs can lift up materials which are ca.200 times weights compared to their own weights under the NIR illumination driving force,and such a photo-stimulated muscle-like actuation behavior is fully reversible after NIR light is removed.2.We choose poly(3-mercaptopropylmethylsiloxanes)(PMMS)as the main chain,MBB as monomer,11UB as crosslinker,benzoin dimethyl ether(DMPA)as the catalyst,using a two-step photocrosslinking method by thiol-ene click chemistry to prepare polysiloxane-based liquid crystalline polymers and elastomers.By controlling the time of the mixture under the UV irradiation,we get the pre-crosslinked polymer.The polymer main chain is aligned unixially.After a second UV irradiation for 15 minutes,the desired monodomain LCE film is prepared.We study their properties in detail by a combination of NMR,Fourier transform infrared spectra(FTIR),differential scanning calorimetry(DSC),polarized optical microscope(POM),dynamic mechanical analyzer(DMA)and small angle X-ray scattering(SAXS).The results suggest that this monodomain LCE material exhibits excellent thermoelasticity,anisotropic property and mechanical property.In comparison with the traditional hydrosilylation method which takes more than 24 hours to prepare LCEs and requires using noble metal catalyst platinum,this two-step photocrosslinking method can produce polysiloxane-based monodomain LCEs in less than 30 minutes,and all the preparation experiments are performed at room temperature,in open air.