Modeling And Kinetic Study On Semi-batch Aqueous Solution Copolymerization Of Acrylic Acid And Maleic Anhydride

Poly(acrylic acid (AA)-co-maleic acid (MA))(PAAMA) owns high density of carboxyl groups on carbon chains, which can be used as a kind of formaldehyde-free thermoset binders for natural or artificial fibers by combining with polyol, and substitutes traditional formaldehyde resins for same applications. PAAMA was synthesized via an aqueous solution free radical copolymerization of AA and maleic anhydride at high temperature. As there is substantial difference between reactivity ratios of AA and MA, unreacted maleic acid accumulates in the products and byproduct malic acid and fumaric acid form during the polymerization. How to reach high MA conversion and minimize the formation of malic acid and fumaric acid is therefore crucial in producing PAAMA products. The understanding of kinetics and mechanism of the copolymerization of AA and MA and the side reactions of MA is therefore highly required. But there is no such study reported in the literature at the moment.The kinetic and mechanism study of a semi-batch aqueous solution copolymerization of AA and MA at120℃with hydrogen peroxide as an initiator has been conducted in this work. A mathematic model on polymerization kinetics has been developed. It showed that MA had low activity and was very difficult to be polymerized in absent of AA. Low MA ratio in the monomers, long semi-batch feeding time, and high amount of the initiator were effective to increase the conversion of MA and reduce the by-product formation. Neutralization of the monomer solution could change the reactivity ratio of the monomers, increase the conversion of MA, and lower down the hydration rate. Hydrogen peroxide could decompose and generate oxygen while forming radicals during the polymerization, resulting in the increase of the polymerization pressure in the reactor. But the inhibition of oxygen was minor. The isomerization and hydration rate constants were obtained by fitting the experimental date with the kinetic equations of side reactions.A terminal model was used to develop a kinetic model of the semi-batch aqueous solution copolymerization of AA and MA. The side-reactions of isomerization and hydration, release of oxygen from the decomposition of hydrogen peroxide, inhibition effect by dissolved oxygen, and the change of pressure in reactor were considered. Kinetic equations were established by using a moment method. The conversions, copolymer compositions, average molecular weights and polydispersities of polymers, and amount of byproducts were estimated using the model. The model prediction results are in good agreement with the experimental results.The innovations in this work comprise:understanding the kinetics and mechanism of the semi-batch aqueous solution copolymerization of AA and MA at120℃with hydrogen peroxide as an initiator, investigating the mechanisms of side reactions of maleic acid, using a combined mathematic model and kinetic study to find out the suitable polymerization conditions to promote the MA conversion, to minimize the side reactions, and to fulfill high efficient manufacture of PAAMA.