Mass spectrometric monitoring of change of resole structures by compounding and curing of EPDM compound

Change of resole structures in a rubber compound by compounding and curing processes were investigated using ethylene-propylene-diene terpolymer (EPDM) compound and atmospheric pressure chemical ionization-mass spectrometry (APCI-MS). Resole structures were divided into three groups of reactive, pendent, and unreactive species to examine in detail the structural changes. Reasonable resole species of the major resole species having two possible structures were determined using variations of the relative abundances by compounding and curing. Of the major resole species, there was no resole species having both terminals of methylol. It was found that resole was not simply mixed in a rubber matrix and reactive resole species were diversified and activated through the compounding process. Almost all reactive resole species participated in crosslinking reactions, but some reactive resole species still remained in the vulcanizate.