Study On The Size Effect Of Long Side-Chain Of Comb-Like Polyelectrolyte In Gel Permeation Chromatography

Four kinds of polyacrylic acid-g-methoxyl polyethylene glycol acrylate (PAA-g-MPEGA) with different length and density of side-chain and two kinds of polyacrylic acid-g-TPEG (PAA-g-TPEG) with different density of side-chain, composed of three polymerization degrees, were respectively synthesized by copolymerization of methoxyl polyethylene glycol acrylate (MPEGA), TPEG and acrylic acid (AA). Molecular weight and shape of those comb-like polyelectrolyte samples were studied by Gel Permeation Chromatography (GPC) and focused on effect of long side-chain on PAA molecular size. Experimental results and conclusion are as follows:(1) Four kinds of PAA-g-MPEGA with different polymerization degrees were determined by direct calibration and hydrolysis method. Side-chains of PAA-g-MPEGA samples were hydrolyzed by optimized situation. Molecular weight of backbone was determined by GPC and calibrated by PAA standards. The molecular weight of each sample was calculated and accorded with light scattering testing results. Results showed that molecular weight and molecular weight distribution which were attained by GPC and calibrated by PAA standards were far from true value and still needed to be calibrated.(2) Based on molecular weight obtained by hydrolysis method, linear relationship of molecular weight and retention volume of PAA-g-MPEGA of four compositions were obtained by asymptotic calibration. When molecular weight of side-chain increased, molecular size of polymerization products with same monomer composition decreased, while the molecular weight of polymerization products became significant different from each other with the same molecular size. Besides, when grafting density of side-chain increased, the molecular size of polymerization products with same molecular weight decreased. While the molecular weight of polymerization products with same molecular size increased. Relationship of molecular size and molecular weight was almost the same for polymerization products with the same proportion of polyethylene side-chain. As molecular weight and grafting density rose, molecular size increased with the same polymerization degree of backbone. Meanwhile, when the proportion of carboxyl in molecular increased, the molecular size of polymerization product first increased and then kept constant.(3) Intrinsic viscosity of polymerization products and parameters K and a of Mark-Houwink Equation were obtained by viscosity method. The value of a rose when mass fraction of polyethylene side-chain increased. Conformation of chain tended to be bent and tangled. Increasing steric effect of side-chain groups inhibited extension of polymer chains. Therefore, flexibility of polymer chains and slack degree of coil decreased.(4) By comparison of asymptotic calibration equation of PAA-g-MPEGA and calibration equations of PAA and PEG, relationship of the second calibration parameter of comb-like polyelectrolyte and PEG side-chain mass fraction was obtained. According to the fitting linear equation, molecular weight of PAA-g-TPEG could be directly calculated by simply linear standards and well accorded with testing results of light scattering. It was proved that the research of molecular shape and molecular weight calibration based on PAA-g-TPEG could be promoted to other aqueous system of comb-like polyelectrolyte with the similar structure and a good reference to further study of comb-like polyelectrolyte.