Patent ID: 7244792

Claim:
Process for making a modified thermoplastic polyester by reacting a thermoplastic polyester with a nitrogen-containing compound, comprising the steps of: (a) contacting the thermoplastic polyester in the solid state with an inert gas atmosphere containing at least one amino-compound of formula H 2 N—R—(X) n , wherein n is an integer≧0, R=a linear, branched or cyclo-aliphatic or aromatic residue comprising 1–24 C-atoms and optionally containing hetero atoms, X═—NH 2 or another functional group reactive with the thermoplastic polyester, at a temperature T(a) between room temperature and the melting point Tm of the thermoplastic polyester, during at least 1 s; (b) heating the thermoplastic polyester obtained in step (a) to a temperature T(b) between T(a) and T m , during up to 10 hours; (c) solid state polymerising the thermoplastic polyester obtained in step (b) at a temperature T(c) between (T m −50) and T m , during up to 100 hours, with T(a)<T(b)<T(c).