Process for the preparation of a vinylidene chloride polymer composite comprising a solid particulate encapsulated in the vinylidene chloride polymer. The process comprises providing a dispersion of a solid particulate material in a liquid phase, said dispersion comprising a RAFT/MADIX agent; providing vinylidene chloride and optionally one or more ethylenically unsaturated monomer copolymerisable therewith to said dispersion; and polymerising vinylidene chloride and said optionally present one or more ethylenically unsaturated monomer under the control of said RAFT/MADIX agent to form polymer at the surface of said solid particulate material.