Synthesis of polylactides by new aluminium schoff's base complexes

The kinetics of DL-lactide polymerization was studied in CH2Cl2 and dioxane at 25 degreesC and in toluene at 70 degreesC with different aluminium Schi ff's base initiators namely HAPENAlOMe, HAPENAlO(i)Pr, 5-ClSALENAlO(i)Pr an d 5-ClSALOPHENAlO(i)Pr. It was observed that HAPEN-type complexes derived f rom 2-hydroxyacetophenone lead to much faster polymerization as compared to SALEN- or 5-CISALEN-type initiators derived from salicylaldehyde. Moreover , substitution of the methoxide group coordinated to the central aluminium by an isopropoxide group brings about an increase in the polymerization rat e but leads to transesterification reactions at much lower percentage conve rsion. On the other hand, replacement of the flexible ethylene diamino grou p by the more rigid phenylenediamino substituent slows down considerably th e polymerization reaction. Analysis of the microstructure of all poly(DL-la ctides) obtained revealed the presence of isotactic sequences in agreement with a first order Markovian statistics.