Morphology And Properties Of Cinnamic Acid Copolymerization Modified Polystyrene(SCA) And Its Zn Salt Ionomer

Although polystyrene?PS?has been one of the five general-purpose resins due to its good transparency,dyeability,and excellent electrical insulation,processability;the shortcomings such as high brittleness and unsatisfied heat resistance owing to the presence of bulky,rigid pendant phenyl groups as well as weak,nonpolar chain-segmental interactions,restrict the engineering application of PS.In this work,the green comonomer,cinnamic acid?CA?,was copolymerized into PS main chain by traditional emulsion free radical copolymerization,a styrene-cinnamic acid random copolymer?SCA?with commercial molecular weight????_w?217,000?and 6.8 mol%of carboxylic acid was succesfully synthesized,which was confirmed by a gel permeation chromatography,Fourier transform infrared?FTIR?spectrum of the occurrence of 1744 and 1703 cm^-1 stretches,respectively,characteristic of the free and dimeric carboxyl C=O bands,and acid-base titration;followed by its melt neutralization with ZnO and solution neutralization with Zn?CH₃COO?₂,respectively.And confirmed by their FTIR spectrum with the antisymmetric and/or symmetrical stretching vibration absorption peaks of COO^-(1640 cm^-1 and 1554,1415 cm^-1,respectively)in the bridging bidentate ligand and chelating ligand between-COO^-and Zn²⁺and/or their inductively coupled plasma emission spectra,three theoretical effective ion contents of 0.54,1.4,3.4 mol%and five actual ion contents of 0.23,0.55,1.3,3.0,5.5 mol%of SCA Zn salt ionomers?SCA-Zn's?were successfully synthesized,respectively;after that,the mechanical,heat resistance,processing,and other properties of the SCA,melt-neutralized SCA-Zn's,and the ionic aggregation,thermal behavior of the solution-neutralized SCA-Zn's were characterized,respectively.Firstly,upon the interchain hydrogen bond cross-linking by CA,the impact toughness(?_cN)of the SCA was considerably improved by 47.2%against a commercial PS resin,the glass transition?T_g?,heat deflection?HDT?,and Vicat softening temperatures?VST?were significantly enhanced until 117.0,108.0,and 118.3 ?,respectively,compared with the PS?95.2,87.6 and 96.0 ??,and the melt strength of the SCA was near an order of magnitude higher than the PS?especially the widening of the temperature range corresponding to the actual foaming viscosity?;while the other properties of the SCA were not significantly deteriorated.The three kinds of SCA-Zn's neutralized by ZnO could also significantly increase the?_cN of the SCA under the synergistic effects of reversible hydrogen bonding and-ionic crosslinking,without reducing the mechanical strength and processability of the SCA,especially only adding1.6 and 4 parts of ZnO?i.e.,the theoretical ion contents of the SCA-Zn's are 1.4 and 3.4mol%,respectively?increased the?_cN by?11.4% and 68.6%,respectively.Compared with the commercial PS,SCA-Zn's could also significantly improve the heat resistance of PS?both the T_g and VST were increased by 20 ??and impact toughness without significantly deteriorating the processability of PS,especially the content of 1.4 and 3.4mol%of the SCA-Zn's increased the?_cN of the PS by 69.6%and 156.5%,respectively.Compared with the modification methods such as filling and blending,which cannot take into account both heat resistance and toughness,hydrogen bonding cross-linking and ion cross-linking improve both the brittleness and heat resistance of PS efficiently,which provides an efficient way of expanding the market application of styrenic resins.In addition,the results of ionic aggregation morphology and thermal behavior of the SCA-Zn's with five different ion contents showed that,consistent with a large number of reports about ionomers,the T_g of the SCA-Zn matrix was raised linearly at a rate of 0.8 ? mol^-1 and no cluster phase appeared;however,it seems that due to the steric hindrance effect of the groups,i.e.,rigid and large benzene rings,adjacent to the-COO-ions in the SCA,even if the ion content reached 5.5 mol%,the isolated ion pairs failed to aggregate to form considerable concentration of ion aggregates,which indicates that there is a critical ion content,significantly higher than that reported in the literature,for isolated ion pairs clustering into ion clusters for the SCA Zn salt ionomer.