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ABSTRACT:Deviation from nonlinear first order polymerization kinetic models is usually observed for cases where steric effects are dominant. A kinetic model was developed for the homo-oligomerization of bulky maleic anhydride units. Factors affecting the kinetics of homo-oligomerization of maleic anhydride have also been studied using two different initiators, azoisobutyronitrile (AIBN) and benzoyl peroxide , at 10 mol % concentrations in two different solvents o-xylene and toluene. Maleic anhydride polymers having a number average molecular weight by SEC, between 300 and 900, and a polydispersity of between 1.0 and 2.0 were observed, and data were justified by the model. The molecular weight of the polymers increased with the conversion, and steric effects dominated at higher molecular weight as observed from the decrease in magnitude in the corresponding termination rate constants. The model values of conversion were compared with experimental data and cross verification of the model was done using molecular weight calculations. The present model represents the data with an average error of less than 5% over the entire experimental range.

A class of maleic anhydride copolymers (YMR-A series) with a narrow molecular weight distribution between 500-1500 and a polydispersity of 1.0-1.11 was obtained from n-alkylacrylamide and maleic anhydride monomers via atom transfer radical polymerization. The monomer conversion reached about 71% corresponding to 1:4 [FeCl 2 ] to [SA] molar ratios for (AAH/MA) copolymer initiated by CPN whereas for the polymerization initiated by MCPN the conversion reached 51.9% under similar condition showing better performance of CPN initiator. Resultant polymers were characterized by means of 1 H-NMR and 13 C-NMR. The inhibition behavior of these YMR-A polymers against CaCO 3 and CaSO 4 was evaluated using static scale inhibition method. The inhibition efficiency on the calcium carbonate scale is much higher and even with 5 ppm dosage level the efficiency is around 99.33 % at pH 10.45 and temperature 70 C, where as for calcium sulfate scales the inhibition efficiency, is lower and 99.9% inhibition is observed at 7-9 ppm level.

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Calcium sulfate is one of the dominant scales which, unlike carbonate scale, are not easily removable by acid. To inhibit CaSO scale formation in artificial cooling water systems, well-defined low molecular weight maleic anhydride and n-alkylacrylamide copolymers (YMR-S series) were synthesized via nitroxide-mediated radical polymerization initiated by benzoyl peroxide in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy at varying concentrations. These polymerizations exhibit living polymerization characteristics; that is, they show linear growth in chain length as a function of monomer conversion, and have narrow molecular weight distributions. Resultant polymers were characterized by means of H-NMR andC-NMR. The inhibition behavior of these YMR-S series polymers against CaSO was evaluated using the static scale inhibition method and a dynamic tube block test. The inhibition ability on the CaSO scale is 99.5% with 9 ppm dosage level at pH 10.45 and temperature 70°C. Scanning electronic microscope analysis proved the morphological changes of the CaSO scales due to the strong inhibition action of YMR-S polymers. It is also observed that the antiscaling effect of the copolymers greatly depends on the molecular weight, and the optimum range is below 20,000 and approximately in the range 500-2000.

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