Preparation Methods Of PMAA Standards For Gel Permeation Chromatography Calibration

Due to the presenced of non-volume effect, when used monodisperse non-polyelectrolyte as standards, the method of determination of molecular weight and distribution of the polyelectrolyte by GPC presenced errors. To solve this problem, we prepared polymethylacrylic acid standard samples for GPC calibration through series of methods. The research including the following:(1) Proposed an method of ester hydrolysis, the results showed that dubbed poly (methyl methacrylate)(PMMA) standard samples in10%dioxane solution, reflux hydrolyzed24hours in KOH methanol solution under the protection of nitrogen atmosphere, evaporated solvent and continued to reflux hydrolysis24hours in1mol/L NaOH aqueous solution, the degree of hydrolysis could be reached99%.(2) Uesed toluene as good solvent, petroleum ether as the precipitant, through isothermal precipitation grading, PMMA crude products were graded into six narrow distribution standard samples with molecular weight in3.1X103～4.3X104. The obtained PMMA standard samples molecular weight distributed evenly and had good grade efficiency. Individually hydrolyzed self-made PMMA standard samples to PMAA samples, GPC analysis showed the self-made PMAA sample peak shape and symmetry, the dispersion coefficients were small, they could be applied to determinate the molecular weight and distribution of PMAA and its derivatives.(3) Used methanol as good solvent, ethyl ether as precipitating agent, the PMAA crude products were graded into five narrow distribution standards by isothermal precipitation grading.With self-made narrow distribution PMAA as raw materials for esterification, using thionyl chlorided and alcohol decomposed to get narrow distribution of PMMA. The molecular weight of obtained PMMA samples were in the range of2.97x103-3.63x104, molecular weight distribution coefficient were less than2, GPC analysis showed the peak of self-made PMAA and PMMA standard samples were symmetrical and narrow, molecular weight distribution were evenly. The viscosity average molecular weight values by calculating were tested by Ubbelohde viscometer,the relative error did not exceed10%, proved that the method preparing PMAA samples in this paper was feasible, and the molecular weight values were accurate and reliable.(4) The study found that,when used polyacrylic acid (PAA) and PMAA respectively to determinate molecular weight and distribution of four different types of polycarboxylate superplasticizers, the error were less than20%, but the determination results of non-electrolyte standard polyethylene glycol (PEG) and PMAA samples falls far short, which indicating non-polyelectrolyte standards will bring significant errors in the determination of molecular weight and distribution of the polyelectrolyte. The error between the determination results by light scattering and GPC measurements results by self-made PMAA as standards were less than20%, proved that determination of molecular weight and distribution of polycarboxylate superplasticizer by self-made polyelectrolyte standards was reliable.