Polymer composition comprising an impact modifier and method of making the same

A polymer composition comprising a polymeric matrix and particles of an impact modifier within the polymeric matrix, wherein the impact modifier comprises at least one urethane group and is obtained by reacting in situ within the polymeric matrix:

• a) a polyester polyol comprising a dimer fatty diacid;
• and
• b) an aromatic or aliphatic polyisocyanate,
• wherein:
• the polymeric matrix comprises polylactic acid (PLA),
• the impact modifier is obtained by forming phase-separated particles of the polyol within a continuous phase of the polymeric matrix and then reacting the polyol with the polyisocyanate,
• the polyisocyanate reacts with the polyol and with the polymeric matrix,
• the polymer composition has an unnotched impact strength of at least 40 kJ/m2 as measured by ISO 179 and an elongation at break of at least 10% as measured by ISO 527, and
• the polymer composition comprises 1 to 25 wt % of the polyol and 0.1 to 10 wt % of the polyisocyanate.