A DSC study of the miscibility of poly(ethylene oxide)-block-poly(DL-lactide) copolymers with poly(DL-lactide)

The purpose of this study was to examine the miscibility of poly(ethylene o xide)-block-poly(DL-lactide) copolymers with poly (DL-lactide). The copolym ers L7E73L7 and L17E78L17 (L = carbonyloxymethylmethylene unit, OCOCH(CH3); E = oxyethylene unit, OCH,CH,) were synthesised by non-catalysed anionic p olymerisation and characterised by gel permeation chromatography and C-13 N MR. Blends of each of the copolymers with poly(DL-lactide) with composition s over the range from 10 to 90 wt% copolymer were cast as thin films and ex amined by differential scanning calorimetry (DSC) to determine glass transi tion temperatures (T-g) and melting temperatures (T-m). The phase diagram s howed a region of miscibility above the melting point of the copolymer in t he system (approx. 35-40 degrees C). Within this region the system was glas sy at low mass fractions of oxyethylene in the copolymer (w(E) less than or equal to 0.1) and rubbery at higher mass fractions. Below T-m a mechanical ly compatible glassy blend existed at low w(E) whilst quenching of systems of higher w(E) led to phase separation, the biphasic region consisting of c rystalline E-m-sequences of copolymer separated from non-crystalline poly(D L-lactide). The phase diagram resulting from this study provides the means for the design of drug delivery systems based on blends of poly(DL-lactide) and poly(ethylene oxide)-containing components. The crystal melt boundary can be lowered by the use of block copolymers with short poly(ethylene oxid e) blocks permitting the preparation of blends which are miscible at room t emperature and rubbery or glassy according to composition. (C) 1999 Elsevie r Science Ltd. All rights reserved.