A low molecular weight linear unsaturated precursor, poly [(dimethyldichlorosilane)-alt-(fumaric acid/sebacic acid)], PDFS with active dimethylchlorosilyl terminal groups, has been synthesized by polycondensation of fumaric acid and sebacic acid with the aid of dimethyldichlorosilane as coupling agent. PDFS has been used to prepare poly [(dimethyldichlorosilane)-alt-(fumaric acid/sebacic acid)]-co-PEG, P(DFS-co-EG) block copolymer. Each of the compounds, PDFS or P(DFS-co-EG), has been cross-linked with a vinyl monomer like methyl methacrylate or styrene. Products thus obtained have been investigated in terms of molecular weight, composition, structure, and thermal properties. Hydrolytic degradation of P(DFS-co-EG) block copolymer in aqueous media (pH 7.3, 37 degreesC) in a 28-day period is also investigated.