| Unsaturated polyester resin (UPR) is one of the most important thermosettingpolymer because of its high performance and low cost. The most common usedinitiating system for the ambient temperature curing of UPR is methyl ethyl ketoneperoxide (MEKP) accelerated by metal ion. Further research on the decompositionand initiating mechanism of MEKP-metal-ion system is of great importance to thedevelopment of new initiating system and UPR. MEKP for industry use is mainlycomposed of hydrogen peroxide,2,2-dihydroperoxybutane (T4) and2,2’-dihydro-peroxy-2,2’-dibutyl peroxide (T3).The decomposition and initiation reactions of initiator MEKP accelerated byCo2+or Cu2+metal ion were studied by radical trapping technique and high resolutionHPLC-ESI/MS with4-benzyloxy-2,2,6,6-tetramethyl-1-piperidinyloxy (T) as radicalscavenger. T4and T3were separated from MEKP and used as initiators in this studyto avoid the difficult in understanding the reaction mechanism, due to the complexcomposition of MEKP. The ESI/MS analysis of trapping products indicated that ethyl,methyl and hydroxyl were the major radicals initiating monmer, and the products ofalkoxyl radical initiating monomer directly were not detected.Based on these data, the reaction pathways of the decomposition of MEKP andMEKP-cobalt initiated polymerization were proposed. Alkoxyl radicals, generatedfrom the decomposition of MEKP, could not initiate monomer in our research. Instead,alkoxy radicals goes β-scission to form ethyl radical and peroxyacetic acid (majorpath) or methyl radical and perpropionic acid (minor). Methyl and ethyl radicals canbe trapped by radical scavenger directly or be trapped after added to monomer.Peroxyacetic acid may decompose to generate acetyl radical and hydroxyl ion oracetic ion and hydroxyl radical. As for the initiation of styrene and diethyl fumarate,methyl radical is more prone to initiate styrene than diethyl fumarate, while ethylradical is more prone to initiate diethyl fumarate. At the same time, hydrogenabstraction from the solvent was also detected in the reaction. |
