Synthesis of degradable terpolymers responding to external stimuli such as pH, ionic strength and temperature

Degradable copolymers which respond to external stimuli such as pH, ionic strength, and temperature were successfully prepared by direct polycondensation of L ‐lactic acid (LA), D , L ‐mandelic acid (MA), and 3‐( p ‐hydroxyphenyl)propionic acid (HPPA) without the use of a catalyst at 200°C by bubbling nitrogen through the solution. The molecular weights of the copolymers obtained were relatively low because of the low polymerizability of MA and HPPA, e. g., number‐average molecular weight M̄ n ≦ 2100 and weight‐average molecular weight M̄ w ≦ 4100. Poly{( L ‐lactic acid)‐ co ‐( D , L ‐mandelic acid)‐ co ‐[3‐( p ‐hydroxyphenyl)propionic acid]} (poly(LA/MA/HPPA)) with a composition of the monomeric units (in mol‐%) LA:MA:HPPA = 80:10:10 showed rapid degradation after a lag time of 5 h within 48 h from the start of the test, in M/15 phosphate buffer solution (pH 7,2) at 37°C. With increasing pH and temperature, the rate of degradation was markedly accelerated.