Cyclodextrins Initiated Ring-Opening Polymerization of Lactide Using 4-Dimethylaminopyridine (DMAP) as Catalyst: Study of DMAP/ß-CD Inclusion Complex and Access to New Structures.

Cyclodextrins (CDs) are cyclic oligosaccharides used in many fields. Grafting polymers onto CDs enables new structures and applications to be obtained. Polylactide (PLA) is a biobased, biocompatible aliphatic polyester that can be grafted onto CDs by -OH-initiated ring-opening polymerization. Using 4-dimethylaminopyridine (DMAP) as an organocatalyst, a quantitative functionalization is reached on native α-, ß-, γ- and 2,3-dimethyl- ß-cyclodextrins. Narrow molecular weight distributions are obtained with the native CDs (dispersity < 1.1). The DMAP/ß-CD combination is used as a case study, and the formation of an inclusion complex (1/1) is shown for the first time in the literature, which is fully characterized by NMR. The inclusion of DMAP into the cavity occurs via the secondary rim of the ß-CD and the association constant (Ka) is estimated to be 88.2 M-1. Its use as an initiator for ring-opening polymerization leads to a partial functionalization efficiency, and thus a more hydrophilic ß-CD-PLA conjugate than that obtained starting from native ß-CD. Polymerization results including also the use of the adamantane/ß-CD inclusion complex as an initiator suggest that inclusion of the DMAP catalyst into the CD may not occur during polymerization reactions. Rac-lactide does not form an inclusion complex with ß-CD.

Isoprene polymerization mediated by vanadium-[ONNO] complexes.

A series of vanadium complexes bearing dianionic tetradentate amine-bisphenolate [ONNO] ligands, V([double bond, length as m-dash]O)X[ONNO(Me)] (X = Cl (1); O(i)Pr (2)), VCl2[ONNO(Me)] (3) and V(O(i)Pr)2[ONNO(R)] (R = Me (4), (t)Bu (5), Cl (6)), displaying various electronic and steric properties have been prepared. The molecular structures of two of these complexes, namely V[ONNO(R)](O(i)Pr)2 with R = (t)Bu (5) or Cl (6), are reported. Activated with dialkylmagnesium, all complexes lead to modest isoprene homo-polymerization activities at 50 °C. Quantitative polymerizations were observed using 4 and 6 as pre-catalysts combined with Al(i)Bu3. The resulting polyisoprene microstructure was composed of ca. 70% 3,4 enchainments, the remaining 30% 1,4 enchainments being a mixture of cis and trans stereoisomers. 6 leads to a more active catalyst than 4. ß-Hydride abstraction occurs during the reaction.