Abstract
The sulphonated phenol novolac (PNBS) which was used as a curing agent of epoxy was synthesised from phenol novolac (PN) and 1, 4‐butane sultone and confirmed by FTIR and ^1^H NMR. The degree of sulphonation (DS) in PNBS was calculated by ^1^H NMR. The semi‐IPN membranes composed of sulphonated tetramethyl poly(ether ether ketone) (STMPEEK) (the value of ion exchange capacity is 2.01 meq g^–1^), epoxy (TMBP) and PNBS were successfully prepared. The semi‐IPN membranes showed high thermal properties which were measured by differential scanning calorimeter (DSC) and thermogravimetric analyses (TGA). With the introduction of the cross‐linked TMBP/PNBS, the mechanical properties, dimensional stability, methanol resistance and oxidative stability of the membranes were improved in comparison to the pristine STMPEEK membrane. Although the proton conductivities of the semi‐IPN membranes were lower than those of the pristine STMPEEK membrane, the higher selectivity defined as the ratio of the proton conductivity to methanol permeability was obtained from the STMPEEK/TMBP/PNBS‐14 semi‐IPN membrane. The results indicated that the semi‐IPN membranes could be promising candidates for usage as proton exchange membranes in direct methanol fuel cells (DMFCs).