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A. Duda

Aggregation of initiators and active species in the polymerization of ε-caprolactone initiated with aluminum alkoxides

Polimery 1995, No 7-8, 393

DOI: dx.doi.org/10.14314/polimery.1995.393


The effect of aggregation of initiators and active species involved in the polymerization of ε-caprolactone (εCL) initiated with Et2AlOEt and Al(OiPr)3, on the polymerization kinetics and on the molecular structure of the resulting poly(ε-caprolactone) [poly(ε CL)] was studied. It was show that the initiation with Et2AlOEt, known to exist as the trimeric aggregate, is fast and quantitative. However, only the non-aggregated active species Et2AlO—poly(ε CL), being in a dynamic equilibrium with the inactive trimers [Et2AlO—poly(εCL)]3, are the actual propagating species. Thus, the aggregation of the dialkyl monoalkoxide active species led to the decrease of propagation rate and to the fractional kinetics orders with respect to initiator. The pertinent kinetic scheme was analyzed and solved. Al(OiPr)3, existing mosty in the form of the slowly interconverting trimers (A3) and/or tetramers (A4), gives results depending on the A3/A4 concentrations ratio. Initiation with A3 is also fast and quantitative, but the rate of initiation with A4 is approximately 1000 times lower, under the otherwise comparable conditions. When the A3/A4 mixture as initiator is used, A3 is consumed quantitatively, whereas A4 remains unreacted at least during the time required for the complete εCL polymerization. The slow initiation with A4 alone does not allow the molar masses of the resulting poly(eCL) to be controlled and gives polymers with a broad molar mass distribution. Active species derived from Al(OiPr)3 (both from A3 and A4) form exclusively the non-aggregated three arm structures, in which three poly(εCL) chains grow from one Al atom: Al[O—poly(εCL)]3. Thus, the first order of propagation with respect to A3 was observed.

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