Abstract The solid phase cationic polymerization of p-benzoquinone using tin (II) chloride as catalyst has been investigated by isolation and identification of the reaction products. The polymerization reaction leads to formation of polymeric chains of hydroquinone nuclei linked together by SnOSn bonds and free from combined chlorine. The tin content of the polymer is increased by increasing the molar ratio of the catalyst and ranges from 4·7 to 55·6% tin. It is probable that the tin atoms are involved in the reaction products as a result of the interaction between polymeric chains having terminal catalyst residues. The resulting polymeric products are characterized by high thermal stability with a decomposition temperature in the region of 400°C. A mechanism which can account for the polymerization products has been developed. In view of the expected high potency of these products, together with their high thermal stability, they will be investigated as radical scavengers in the stabilization of polymeric material against radical degradation processes.