GRAFT-POLYMERIZATION OF METHYL ACRYLATE ONTO GRANULAR STARCH - COMPARISON OF THE FE+2 H2O2 AND CERIC INITIATING SYSTEMS/

Graft polymerizations of methyl acrylate (MA) onto granular cornstarch were carried out in water with both ferrous ammonium sulfate/hydrogen peroxide (FAS/H2O2) and eerie ammonium nitrate (CAN) initiation. Star ch concentrations were 10, 20, and 30% in water, and the amount of MA used was either 0.5, 1, or 2 mol per AGU of starch. Two concentrations of FAS/H2O2 were used: 1 mol each of FAS and H2O2 per 100 AGU of star ch, and 1 mol per 1000 AGU. Significant amounts of acetone-extractable PMA homopolymer were produced, and homopolymer formation was especial ly high at the 1 : 100 ratio. Sharp exotherms were observed, and react ion mixtures reached maximum temperature within 2 min or less. Total c onversions of MA to PMA were higher at the 1 : 100 ratio, and conversi ons in some polymerizations were nearly quantitative. CAN-initiated po lymerizations were run under the same conditions used for FAS/H2O2; ho wever, the amount of CAN used was limited to 1 mol per 100 AGU because of low conversions at the 1 : 1000 ratio. Compared with FAS/H2O2, CAN gave more moderate exotherms; and longer time periods were required f or reaction mixtures to reach maximum temperature. CAN gave quantitati ve conversions of MA to PMA, but only low percentages of PMA homopolym er were observed. Differences between FAS/H2O2 and CAN initiation are consistent with differences in the two initiation mechanisms. High lev els of homopolymer produced on starch granule surfaces with FAS/H2O2 c ould be seen in scanning electron micrographs and were also apparent i n infrared spectra obtained with an attenuated total reflectance (ATR) cell. ATR spectra of acetone-extracted products indicated that the am ount of PMA actually grafted to starch granule surfaces was similar wi th both initiating systems. Tensile properties of extruded ribbons pre pared from these polymers did not vary greatly with the initiator used . (C) 1996 John Wiley & Sons, Inc.(dagger)