Ring-opening polymerisation of l- and rac-lactide using group 4 permethylpentalene aryloxides and alkoxides.

A new family of group 4 permethylpentalene (CMe; Pn*) aryloxide and alkoxide complexes have been synthesised and fully characterised by multinuclear NMR spectroscopy and single-crystal X-ray diffraction; (η-CMe)Zr(OR) (R = Bu (1), 2,6-Me-CH (2), 2,6-Pr-CH (3) and 4-OMe-CH (4)), (η-CMe)Zr (OR) (R = 2,6-Bu-CH (5) and 2,6-Bu-4-Me-CH (6)), (η-CMe)ZrCp(OR) (R = Bu (7), 2,6-Me-CH (8) and 2,6-Pr-CH (9)), (η-CMe)TiCp(O-2,6-Me-CH) (10) and (η-CMe)ZrCp(OR) (R = 2,6-Me-CH (11), 2,6-Pr-CH (12) and 2,4-Bu-CH (13)). 2, 3, 6, 7, 9, 10 and 12 were studied as initiators for the ring-opening polymerisation (ROP) of l-lactide, and 2, 3, 6, 7 and 10 were studied as initiators for the ROP of rac-lactide. 3 was found to be the most active initiator for the ROP of l-lactide (k = 0.35 h) and 2 for the ROP of rac-lactide (k = 0.21 h). These initiators produced isotactic PLA for the ROP of l-lactide and moderately heterotactic enriched (maximum P of 0.69) or atactic PLA for the ROP of rac-lactide with polymer chains consisting of polylactic acid repeat units with -OR and -OH end groups.