Issue 30, 2013

Structural and kinetic studies of the polymerization reactions of ε-caprolactone catalyzed by (pyrazol-1-ylmethyl)pyridine Cu(ii) and Zn(ii) complexes

Abstract

The structural and kinetic studies of polymerization reactions of ε-caprolactone (ε-CL) using (pyrazolylmethyl)pyridine Cu(II) and Zn(II) complexes as initiators is described. Reactions of 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L1) and 2-(3,5-diphenylpyrazol-1-ylmethyl)pyridine (L2) with Zn(Ac)2·2H2O or Cu(Ac)2·2H2O produced the corresponding complexes [Zn(Ac)2(L1)] (1), [Cu(Ac)2(L1)] (2), [Zn(Ac)2(L2)] (3) and [Cu2(Ac)4(L2)2] (4) respectively. Solid state structures of 1 and 4 confirmed that complexes 1 and 4 are monomeric and dimeric respectively and that L1 is bidentate in 1 while L2 is monodentate in 4. X-band EPR spectra of 2 and 4 revealed that complex 2 is monomeric both in solid and solution state, while the paddle-wheel structure of 4 is retained in solution. Complexes 1–4 formed active initiators in the ring opening polymerization of ε-CL. Zn(II) complexes 1 and 3 exhibited higher rate constants of 0.044 h−1 and 0.096 h−1 respectively compared to rate constants of 0.017 h−1 and 0.031 h−1 observed for the corresponding Cu(II) complexes 2 and 4 respectively at 110 °C. All the polymerization reactions follow pseudo first-order kinetic with respect to ε-CL monomer. Initiator 1 showed first-order dependency on the polymerization reactions and utilizes only one active site as the initiating group. The molecular weights of the polymers produced range from 1982 g mol−1 to 14 568 g mol−1 and exhibited relatively broad molecular weight distributions associated with transesterification reactions.

Graphical abstract: Structural and kinetic studies of the polymerization reactions of ε-caprolactone catalyzed by (pyrazol-1-ylmethyl)pyridine Cu(ii) and Zn(ii) complexes

Supplementary files

Article information

Article type
Paper
Submitted
22 May 2013
Accepted
04 Jun 2013
First published
17 Jun 2013

Dalton Trans., 2013,42, 10735-10745

Structural and kinetic studies of the polymerization reactions of ε-caprolactone catalyzed by (pyrazol-1-ylmethyl)pyridine Cu(II) and Zn(II) complexes

S. O. Ojwach, T. T. Okemwa, N. W. Attandoh and B. Omondi, Dalton Trans., 2013, 42, 10735 DOI: 10.1039/C3DT51338F

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