FACTORS AFFECTING PROPAGATING FRONTS OF ADDITION POLYMERIZATION - VELOCITY, FRONT CURVATURE, TEMPERATURE PROFILE, CONVERSION, AND MOLECULAR-WEIGHT DISTRIBUTION

Several properties of propagating fronts of addition polymerization we re studied. A power function could be fit to the velocity dependence o n initiator concentration, but not with the exponents predicted by cur rent models or in agreement with other published work. Bubbles from th e volatile by-products of initiator decomposition were found to depend linearly on temperature over a moderate range. The conversion of meth acrylic acid in fronts varied greatly with initiator type and concentr ation. Benzoyl peroxide produced much lower conversion than t-butyl pe roxide, but fronts with tBPO propagated slower. A dual initiator syste m of BPO and tBPO produced rapidly propagating fronts with good conver sion but the contribution of each initiator to the velocity was not ad ditive. The possibility of chain branching was considered. The apparen t molecular weight distributions were very broad, often trimodal, and found to depend on initiator type and concentration as well as the tub e diameter. The temperature profiles were measured and found to be ver y sharp for BPO and broader for tBPO but both had front temperatures i n excess of 200 degrees C, indicating a high ceiling temperature. (C) 1995 John Wiley & Sons, Inc.