PREPARATION OF A THIOPHENOL FORMALDEHYDE RESIN - ITS STRUCTURE AND THE MECHANISM OF ITS PYROLYSIS

A thiophenol/formaldehyde resin (TPFR) was synthesized under basic (Na OH) conditions, and its structure was thermally investigated by isothe rmal pyrolysis, under fluidized-bed conditions, at various temperature s. The pyro-products, volatilized during pyrolysis, were trapped and m ost of them were identified by GC and GC/MS to be sulfur-containing co mpounds, i.e. thiophenol, methylthiobenzene, benzothiophenes, diphenyl sulfide, diphenyl disulfide, thioxanthene, thianthrene and p-mercapto benzyl phenyl sulfide (MBPS). The relative distribution of the condens ed pyro-products was temperature dependent. The kinetic profiles of th e pyrolysis were evaluated in relation to the spatial structure. The t hermal behavior of a structurally similar monomer, benzyl phenyl sulfi de (BPS), was studied under the same pyrolytic conditions. The similar ities and the differences between the thermal behaviors of BPS and TPF R are discussed and decomposition mechanisms are proposed. The main co nclusions of this work are: (i) TPFR is a highly branched polymer buil t from BPS units; (ii) cleavage of the benzylic C-S bond, which is the weakest bond in the resin, is the key step in the formation of most o f the pyro-products; (iii) the structure of TPFR indicates that the po lymerizations mechanism of thiophenol and formaldehyde differs conside rably from that of phenol/formaldehyde resins. The proposed mechanisms for polymerization and for thermal decomposition are discussed in rel ation to our previous studies on phenol/formaldehyde resins.