Selective synthesis of cyclic-polymer-free poly(ether sulfone)s with OH ends or F ends by non-stoichiometric, reversible polycondensation

Abstract

Reversible polycondensation of bis(phenol) silyl ether 1 and bis(4-fluorophenyl) sulfone 2 with an excess of one monomer in the presence of base was investigated for the synthesis of telechelic poly(ether sulfone) (PES) end-capped with the excess monomer, without the formation of cyclic polymer. In the polycondensation of an excess of bisphenol A bis(trimethylsilyl ether) (1a) and 2 in the presence of K₂CO₃ in N-methyl-2-pyrrolidone (NMP) ([2]₀ = 1.0 M) at 145 °C, PES having a phenol moiety derived from 1a at both ends (designated as HO/OH) was obtained. The molecular weight increased up to M_n = 8380 as the excess ratio of 1a was decreased, but the product was contaminated with cyclic polymer; this issue was overcome by increasing the monomer concentration ([2]₀ = 4.0 M). On the other hand, in the polycondensation using an excess of 2, CsF was an effective base to obtain PES with a fluorophenyl sulfone moiety at both ends (designated as F/F). The polycondensation using 1.05 equivalents of 2 in N,N-dimethylacetamide (DMAc) ([1a]₀ = 4.0 M) at 165 °C afforded high-molecular-weight PES with F/F ends (M_n = 11 200), free from cyclic polymer. Furthermore, other compounds 1 were polymerized with 2 under the optimized conditions established for the polycondensation of 1a with 2. The polycondensation of 1.1 equivalents of 1c, having a bis(trifluoromethyl) group, with 1.0 equivalent of 2 afforded PES with HO/OH ends, whereas the polycondensation of 1.0 equivalent of 1b, bearing a cyclohexylidene group, with 1.1 equivalents of 2 afforded PES with F/F ends. In the polycondensation of unsubstituted bisphenol silyl ether 1d with 2, gelation occurred when an excess of either 1d or 2 was used.