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Issue 30, 2013
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Structural and kinetic studies of the polymerization reactions of ε-caprolactone catalyzed by (pyrazol-1-ylmethyl)pyridine Cu(II) and Zn(II) complexes

Stephen O. Ojwach,*a  Teddy T. Okemwa,b  Nelson W. Attandoha  and  Bernard Omondic 
Author affiliations

* Corresponding authors

a School of Chemistry and Physics, University of KwaZulu-Natal, Pietermaritzburg Campus, Private Bag X01 Scottsville, 3209, South Africa
E-mail: ojwach@ukzn.ac.za
Fax: +27 (33) 260 5009
Tel: +27 (33) 260 5239

b Department of Chemistry, Maseno University, P. O. Box 333, Maseno, Kenya

c School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Private Bag X54001, Durban, South Africa

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

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Publication details

The article was received on 22 May 2013, accepted on 04 Jun 2013 and first published on 17 Jun 2013


Article type: Paper
DOI: 10.1039/C3DT51338F
Citation: Dalton Trans., 2013,42, 10735-10745
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    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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