The synthesis of crosslinkable P(VDF-CTFE) copolymer with controllable structure, molecular weight and terminal and side chain silane groups was developed. The chemistry of the synthesis was centered on a specifically designed functional borane initiator containing silane groups. Polymer electrolyte composite membranes were fabricated by dispersion of additive particles in the polymer solution and film casting, followed by thermocompression, which allowed for formation of crosslinking sites in 3-D polymer network. Two types of membranes were investigated: P(VDF-CTFE)/Nafion/ Inorganic and P(VDF-CTFE) with incorporated sulfonated units. Different types of inorganic proton conductors were synthesized and tested in P(VDF-CTFE)/Nafion/ Inorganic membranes. The highest conductivity was obtained using H 3OZr2PO4)3 particles. Optimization of the P(VDF-CTFE)/Nafion/H3OZr2(PO4) 3 membrane composition allowed to substantially increase the membrane conductivity. Two avenues were explored to add sulfonic acid groups to P(VDF-CTFE) to obtain a desirable membrane conductivity without an addition of Nation: introduction of sulfonated silicon dioxide and sulfonated SPETMS.