Design,Synthesis And Application Of Side Chain Crystalline Comb-like Polymer

The comb-like polymer with crystalline side chain was a unique type of polymer molecule.Due to the difference between the main chain and the side chain,it show diversity and special performance and wide application prospects,such as responsiveness,improving the melt processability and solubility of rigid polymers.Therefore,researchers have applied it in the fields of pour point depressants,phase change energy storage materials,hydrogels,and shape memory materials,et al.At present,it was still a research focus to design and prepare side chain crystalline comb-like polymers with special functions and expand their applications.Therefore,in this article,comb-like polymers was designed and applied in the fields of phase change energy storage,gas barrier,and high dielectric.The main contents were as follows:Chapter 2,a series of side chain crystalline comb-like polymers with hydrogen bond network were synthesized and the long alkyl side chain can form a eutectic with paraffin.It was used as supporting materials to prepare phase change energy storage materials with stable shape and high heat storage value.First,a series of poly(styrene-co-acrylic acid)n(P(S-AA)n,wherein "n" denoted AA feed ratio;n=20,30,and 40)was prepared by free radical polymerization.Subsequently,the comb-like polymer material P(SAA)n-C18 was constructed through the amidation reaction between the carboxyl group of AA and the amino group of octadecylamine.Then,novel PW@P(S-AA)n-C18 nanocomposie form-stable phase change materials(FSPCMs)were obtained by package P(S-AA)n-C18 into paraffin(PW),where cocrystal structure formed by interaction between P(S-AA)n-C18 and paraffin was as heat storage component.We have studied the chemical structure,crystalline structure and thermal properties by means of FTIR,GPC,XPS,XRD,DSC,TGA,etc.XRD analysis demonstrated the presence of cocrystal structure.Moreover,the as-prepared polymer exhibited desirable packaging liquid paraffin properties with low concentration(>90 wt%paraffin in FSPCMs without obvious leakage)above the melting point and thermal cycling performance due to the collective contributions from hydrogen-bonding,?-? stacking interactions and solvophilic interaction.Interestingly,it was worth nothing that the melting and freezing enthalpies of the composites can reach 124.4 and 126.3 J g-1,respectively,which was higher than that of pure paraffin.The composite system composed of as-prepared comb-like polymer and paraffin offered an avenue for developing the high-efficient thermal energy storage materials.Chapter 3,adjusting the grafting density and the length of the side chain,a comb-like polymer composed of an amorphous layer and a layered crystal layer was designed and synthesized,and hydrogen bonds were introduced into the amorphous layer to improve the order of the polymer backone.The comb-like polymer was used as the gas barrier film and then achieved low gas permeability and excellent permeability jump.By "grafting from"method,a series of comb-like polymers with crystallizable long alkyl side chains,P(S-AA)-g(p)(wherein "p" denoted the number of side chain carbon atoms;n=30,40,50,60,70),have been synthesized.Through DSC analysis,it was found that the crystallinity of the comb-like polymer was affected by the length of the side chain,the graft density,and especially the hydrogen bond.Through XRD,AFM analysis,it was found that the formation of restricted crystalline nanolayers strongly depend on the length of the side chain.For example,P(S-AA)50-g(14)showed a disordered crystalline arrangement,while P(S-AA)30-g(18)had a nanolayer structure.More interestingly,the hydrogen bonds between the amide groups could confine the main chain to a narrow amorphous domain,thereby making it more orderly and reducing the interlayer spacing.Based on the above findings,comb-like polymer materials were applied in the field of gas barrier.The results showed that P(S-AA)n-g(p)showed good gas barrier properties and temperature-sensitive properties.For P(S-AA)70-g(18),the nitrogen permeability was 1.78×10-14 cm3·cm/cm2·s·Pa,and the permeation switches reached 500 times traversing the melting point.Chapter 4,a comb-like polymer with a layered structure(amorphous layer and crystalline layer)was designed and synthesized.It was used as a template to induce modified carbon nanotubes(MWCNT)to selectively enter the crystalline layer of the polymer,and thus the nanocomposite materials with a low permeability threshold(Pc)and good dielectric properties were obtained.First,butyl methacrylate-octadecyl acrylate copolymer(P(BMA-OA)40;40 represents the molar ratio of OA to monomer)was synthesized.Then,octadecylamine was grafted onto MWCNT(MWCNT-ODA).Finally,P(BMA-OA)40@MWCNT-ODA nanocomposite was obtained by solution mixing method.After characterization,it was found that the straightened MWCNT-ODA was distributed heterogeneously near the lamellar-structured crystallization but homogeneously in the planar directions.Therefore,we use it as an efficient flexible polymer-based nanocomposite dielectric material.Contributed by such special topological structure,the good dielectric performance of P(BMA-OA)40@MWCNT-ODA was achieved,and the results showed a low percolation threshold of approximately 1.5wt%.The dielectric constant of the nanocomposite with 8wt%MWCNT-ODA reached up to?315 at 1 kHz,which was approximately 137 times the dielectric constant(?2.3)of pure P(BMA-OA)40.Moreover,AC conductivity still continued to exhibit a correlation with the frequency and the dielectric loss was only about 0.6.Thereby,a wide processing window(>6.5 wt%)was realized so that dielectric properties of nanocomposite can be adjusted near the Pc.