Gas-free initiators for high-temperature free-radical polymerization
Quaternary ammonium persulfates as free-radical initiators for high-temperature polymerization are synthesized and their shelf-life stability investigated. These initiators do not have gaseous byproducts and are therefore ideal for frontal polymerization, a process in which polymeric materials are produced via a thermal front that propagates through the unreacted monomer/initiator solution. Quaternary ammonium persulfate initiators offer additional qualities such as high solubility in organic media and low volatility, which are desirable for frontal polymerization. The initiators are synthesized using two procedures, and the initiating efficacy of the respective products is compared to a peroxide initiator in the frontal polymerization of 1,6-hexanediol diacrylate. Of all the quartenary ammonium persulfates synthesized, tricaprylmethylammonium (Aliquat) persulfate (APSO) is the best initiator for frontal polymerization because it is soluble in organic media, is very reactive, and does not produce volatile byproducts under decomposition. A study of the decomposition kinetics of APSO is performed, and frontal polymerization is proposed as a quicker analytical technique to assay the purity. (C) 2000 John Wiley & Sons, Inc.