LACTIC ACID COPOLYMER

FIGURE 12 Control of the rate of release of methadone from microspheres by the use of blends of a e-caprolactone-lactic acid copolymer and polylactic acid. (From Ref. 63.)... 

Montaudo, M.S. Sequence Constraints in a Glycine-Lactic Acid Copolymer Determined by MALDI-MS. Rapid Commun. Mass Spectrom. 1999, 13, 639-644. 

Helder, J., Dijkstra, P., and Feijen, F. J. In vitro degradation of glycine/DL-lactic acid copolymers. J. Biomed. Mater. Res. 24 1005-1020, 1990. 

Zhong, S.P., Doherty, P.J., and Williams, D.E, 1994. A preliminary study on the free radical degradation of glycolic acid/lactic acid copolymer. Lastics, Rubber and Composites Processing and Application, 21 89. 

Montaudo, M.S., Sequence Constraints in Glycine-Lactic acid Copolymer Determined by MALDl-MS analysis, Rapid Comm Mass Spectrom, 13, 639 (1999). 

Lactic acid reacts with diacid or diol to form telechelic polylactic acid, then through further a linking reaction it forms high-molecular-weight lactic acid copolymers [33, 44, 45]. Polymerization of a racemic mixture of L- and D-lactides usually leads to the synthesis of poly-DL-lactide (PDLLA)which is amorphous. Use of stereospecific catalysts can result in heterotactic PLA which is found to show crystallinity [46, 47]. The degree of crystallinity and many associated properties are greatly controlled by the ratio of D to l enantiomers in the polymer [48]. 

Whereas most medical uses of polymeric materials require biostability, applications that use the biodegradable nature of some macromolecules have been developed. An example is the use of poly(glycolic acid) and glycolic acid/lactic acid copolymers as absorbable sutures, which go under the trade name Lactomer. 

A small hydrophilic prodrug (PROLI/NO) to be delivered to the alveolar region of the lungs was encapsulated with microparticles of a biodegradable, hydrophilic lactic acid-glycolic acid copolymer and an ethylene oxide-lactic acid copolymer and the kinetics of release of nitric oxide characterised using three parameters. These parameters were maximum concentration of nitric oxide per unit weight of microparticles, window of time over which the concentration exceeded 50% of the maximum concentration and the initial rate of release. 18 refs. 

The copolymerization approach has successfully been applied for poly(ester-urethane)s by equipping the prepolymers with elastomeric properties by copolymerization. e-Ca-prolactone-lactic acid copolymers have been reported to result in a significant increase in the strain and the flexibility [62]. Table 3.2 shows the changes in the material properties that have been achieved by varying the prepolymer composition [50, 62]. 

A series of papers has been published on the direct degradation of a variety of polyesters in the ion source of a mass spectrometer. Polymers examined were poly(/3-propiolactone), poly(/S-pivalolactone), poly(y-valerolactone) poly-lactide, polyglycolide, and a glycolic acid-lactic acid copolymer poly(oxysuc-cinyloxy-1,4-phenylene) and poly(oxyterephthaloyloxy-l,4-phenylene). ... 

DSC has been used to measure T on a variety of polymers including naphthalate copolymers [111,112], polyethylene terephthalate-5-nitrosophthalic acid copolymers [113], propene-pentene copolymers [114], 4-hydroxy benzoic acid-2-hydroxy-6-naphthoic acid copolymers [115], fluorinated perfluorocyclo butylenes [116], PET [117], polythioether ether ketones [14,104], polyvanillylidiene, alkyl/aryl phosphate esters [118], poly(L-lactic acid-poly(e-caprolactone) [119], benzylated waste pulp-L-lactic acid copolymers [120], PET - poly-1,4 butylene succinate [121], polyarylate-polytrimethylene terephthalate [122], polyimines [77], PVOH [123, 124], various Nylons [125]. 

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