Heat resistant polyethylene terephthalate and a process for the preparation of the same

A process for preparing a polyester, said process comprising the following steps:

• a. dissolving isosorbide and at least one anti-oxidizing agent in water and optionally, at least one diol to obtain an aqueous solution;
• b. reacting said aqueous solution of isosorbide with at least one aromatic dicarboxylic acid or ester thereof to obtain an oligomerized product/isosorbide oligomer via esterification or ester interchange;
• c. polymerizing said oligomerized product/isosorbide oligomer using at least one polymerization catalyst to obtain an isosorbide polymer;
• and
• d. co-polymerizing said isosorbide polymer or said oligomerized product/isosorbide oligomer with at least one alkylene aryl dicarboxylate monomer in at least one stage selected from the group consisting of before, during and after the polymerization reaction to obtain the polyester,
• wherein the polyester has at least one of the following properties:
• intrinsic viscosity greater than 0.7 dl/g at 25° C.;
• color L* ranges from 72 to 76%;
• color b* ranges from −1.5 to −2.5;
• diethylene content of less than 1.5%;
• glass transition temperature in the range of 81 to 85° C.;
• impact strength of 54 to 57 J/M;
• and
• tensile strength from 500 to 600 Kgf/cm2.