IN-VITRO DEGRADATION OF NANOSPHERES FROM POLY(D,L-LACTIDES) OF DIFFERENT MOLECULAR-WEIGHTS AND POLYDISPERSITIES

The aim of this work was to study the stability of nanospheres from po ly(D,L-lactide) in aqueous media. The influence of the poly(D,L-lactid e) molecular weight and polydispersity, pH of the medium and temperatu re, was investigated. The degree of DL PLA degradation was estimated b y monitoring the total acidity of the medium, the lactic acid producti on, the molecular weight of the polymer, the mean diameter of the nano spheres and the amount of polymer remaining insoluble. Poly(D,L-lactid e) degradation rate depended on polymer molecular weight and polydispe rsity. The data suggested that it resulted from a hydrolysis which is much more catalysed at acidic and alkaline pH than at neutral pH. Two main hydrolysis mechanisms can be proposed: a random scission at acidi c pH and a sequential cleavage from the chain end in alkaline medium. Higher temperature accelerated the degradation process. The best stora ge conditions for an aqueous dispersion of poly(D,L-lactide) nanospher es were deduced(temperature: 4 degrees C, pH close to neutrality).