Poly(methyl glyoxylate) (PMG) is a biodegradable polyacetal. Its low ceiling temperature requires endcapping extremities. Until now, esterification and etherification were the main ending reactions used, but the results were inconclusive. Using functional isocyanates having alkoxysilane, methacrylic, styrenic or isocyanate functions, the end-capping is complete and no depolymerization occurs. Thermal stability of these new end-capped PMGs has been performed. Whereas, degradation begins at 67 degrees C for non-terminated PMG, stabilized PMG can be stable up to 177 degrees C. Physicochemical characteristics of the chains are given according to the chemical nature of the extremities. In particular, we can notice an important effect on glass transition temperature at low molecular weight with a discrepancy of about 20 degrees C between the silane and methacrylic extremities.