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, io nic strength, and temperature were successfully prepared by direct pol ycondensation of L-lactic acid (LA), D,L-mandelic acid (MA), and 3-(p- hydroxyphenyl)propionic acid (HPPA) without the use of a catalyst at 2 00-degrees-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 w eight M(n)BAR less-than-or-equal-to 2100 and weight-average molecular weight M(w)BAR less-than-or-equal-to 4100. Poly{(L-lactic acid)-CO-(D, L-mandelic acid)-co-[3-(p-hydroxyphenyl)propionic acid]} (poly(LA/MA/H PPA)) 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-degrees-C. With increasing pH and temperature, the rate of de gradation was markedly accelerated.