No abstract

Simultaneous interpenetrating polymer networks (IPNs) based on polyether polyurethane (PUR) and poly(methyl methacrylate-co-trimethylolpropane trimethacrylate) (PMMA) were prepared in bulk at 60 °C. The gelation time of the individual PMMA network was found to be faster when using azobis(isobutyronitrile) (AIBN) in the presence of stannous octoate (SnOc2) as activating system, compared to pure AIBN. Kinetic measurements have shown that the synergistic SnOc2 role concerns the initiation of the free-radical polymerization. The results were explained by assuming the formation of a cyclic complex between the nitrile groups of AIBN and the tin(II) atom of SnOc2.

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Simultaneous interpenetrating polymer networks (IPNs) based on polyether polyurethane (PUR) and poly(methyl methacrylate‐co‐trimethylol‐propane trimethacrylate) (PMMA) were prepared in bulk at 60°C, using tin(II) octoate and azobisisobutyronitrile (AIBN) as pur polymerization catalyst and free‐radical initiator, respectively. The kinetics of the PUR network formation, PMMA network formation as well as PUR/PMMA IPN formation were studied independently by Fourier transform infra‐red spectroscopy. The simultaneous formation of the two networks interfered with each other, although they follow different polymerization mechanisms. Mainly two effects concerning the free‐radical polymerization have been seen: a decrease of the initiation period and an earlier appearance of the Trommsdorff effect when increasing the concentration of the catalyst. On the other hand, the presence of AIBN in the reaction medium drastically reduced the catalytic efficiency of the organotin compound. An explanation of these results for this particular activating system could be the formation of a cyclic equimolar complex by coordination of the nitrile groups of AIBN with the Sn(II) atom. Complexation both reduces the effective catalyst concentration and induces steric constraints in the azo bond of AIBN, rendering this linkage weaker and more easily cleavable and allowing an early decomposition into radicals of the complexed AIBN. The maximum rate corresponds to a 1:1 complex. Further, decomposition into radicals leads to tin oxidation and formation of a new tetravalent organotin compound, the catalytic activity of which is lower than that of pure tin(II) octoate for the isocyanate‐alcohol reaction.