Polyester composition and process for producing the same

A polyester composition comprising the following two components (a) and (b):

• (a) a polyester;
• and
• (b) a modified first block copolymer (b-1) having chain-terminating hydroxyl groups, said first block copolymer comprising:
• at least one block A selected from the group consisting of a polymer block consisting essentially of an aromatic vinyl compound and a hydrogenated polybutadiene block obtained by hydrogenating a polybutadiene block having not more than 20% of a 1,2-bond and
• at least one block B selected from the group consisting of a hydrogenated polyisoprene block, and a hydrogenated isoprene-butadiene random copolymer block;
• and/or
• a modified second block copolymer (b-2) having chain-terminating hydroxyl groups, said second block copolymer comprising:
• at least one polymer block C principally comprising an aromatic vinyl compound and
• at least one polyisobutylene block D;
• the ratio by weight between said component (a) and said component (b) being (a)/(b)=98/2 to 40/60.