Synthesis and characterization of multiblock copolymers poly[poly(L-lactide)-block-polydimethylsiloxane]

✍ Scribed by Abdelkrim Bachari; Georges Bélorgey; Gérard Hélary; Georges Sauvet

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Weight: 813 KB
• Volume: 196
• Category: Article
• ISSN: 1022-1352
• DOI: 10.1002/macp.1995.021960130

✦ Synopsis

The preparation of multiblock copolymers poly[poly(~-lactide)-block-polydimethylsiloxane]

by polycondensation of bifunctional oligomers via hydrosilylation is described. The procedure consists first to synthesize the two bifunctional oligomers a,wdisilyl-polydimethylsiloxane and a,wdiallyl-poly(L-lactide). The former is prepared in one step by cationic polymerization of octamethylcyclotetrasiloxane in the presence of 1,1,3,3-tetramethyldisiloxane as end-blocker. Two steps are necessary to prepare a,wdiallyl-poly(L-lactide). The first one is the polymerization of L-lactide initiated by the system ethylene glycol/tin 2-ethylhexanoate. In a second step, the hydroxyl end-groups of the resulting a,wdihydroxy-poly(L-lactide) are transformed, by reaction with ally1 isocyanate, into terminal allylic functions. Different multiblock copolymers were prepared by hydrosilylation (catalyzed by hexachloroplatinic acid) using the same a,wdiallylpoly(L-lactide) (M, = 2000 g . mol and various a,w-disilyl-polydimethylsiloxanes (& from 1 750 to 9000 g * mol-'). The influence of parameters such as temperature, stoichiometry of reactive end-groups and catalyst concentration on the molecular weight of the copolymers was studied. High molecular weight copolymers were obtained (DP, > 12 by SEC). In addition to the biodegradability of the lactic acid units, the immiscibility of the polydimethylsiloxane and poly(L4actide) blocks imparts thermoplastic elastomer properties to these copolymers. The crystallinity of the poly(L-lactide) phase is dependent on the molecular weight of the polydimethylsiloxane blocks.