A new functionalized and crosslinkable P(VDF-CTFE) (vinylidene fluoride/chlorotrifluoroethylene copolymer) was synthesized using functional borane/oxygen initiator. and grafted with styrene (St) via atom transfer radical polymerization followed by partial or the whole sulfonation of phenyl groups. Materials with different composition and level of sulfonation were prepared and tested to balance proton conductivity, water swelling, and flexibility. The addition of hexafluoropropylene (HFP) to copolymer improved plasticity and swelling without compromising the conductivity. To understand the effect of different membrane components on its properties, thermal properties of composites have been investigated. It was found that the content of CTFE units, St and sulfonic groups effected membrane flexibility and swelling. Several classes of inorganic proton conductors with high water retention capability, including mesoporous materials (sulfonated alumina, zirconia, titania) were synthesized and tested for conductivity to introduce into polymeric material to improve membrane mechanical properties and conductivity.