[Bis(guanidine)]zinc complexes and their application in lactide polymerisation

The bis(guanidine)-stabilised zinc complexes [N-1,N-2-bis(1,3-dimethylimidazolidin-2-ylidene) ethane- 1, 2-diamine] dichloridozinc(II), [Zn(DMEG(2)e)Cl-2] (C1), diacetato[N-1,N-2-bis(1,3-dimethylimidazolidin- 2-ylidene)ethane -1, 2-diamine]zinc (II), [Zn(DMEG(2)e)(CH3COO)(2)] (C2), and bis[N-1,N-2-bis(1,3-dimethylimidazolidin-2-ylidene) ethane- 1, 2 -diamine]zinc(II) bis(trifluoromethanesulfonate), [Zn(DMEG(2)e)(2)](CF3SO3)(2) (C3), have been synthesised and completely characterised by means of X-ray structure analysis, NMR spectroscopy and mass spectrometry. These [bis(guanidine)]zinc complexes were investigated regarding their activity in the bulk polymerisation of D,L-lactide. If could be shown that these compounds are able to act as initiators for lactide polymerisation, and polylactides with molecular weights (M-W) of around 18000-59000 g/mol could be obtained. Variation of the reaction temperature revealed that the molecular weights decrease with increasing temperature. Additionally, the correlation of the intrinsic viscosity with the molecular weight demonstrates that the obtained polymers are linear and structurally homogeneous. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).