Multinuclear NMR Characterization of Co-cross-linking of Ethylene-co-vinylacetate and Ethylene-co-methylacrylate Polymer Blends in the Presence of Dibutyltin Oxide

The co-cross-linking reaction of ethylene-co-vinylacetate (EVA) and ethylene-co-methylacrylate (EMA) polymer blends in the presence of dibutyltin oxide in the molten state is an interchain redistributive transesterification (ester-ester interchange reaction). It is shown with model esters, namely n-octyl acetate (1) and methyl nonanoate (2) in solution, that the efficientcatalytic species are 1,3-acyl, alkoxy distannoxane from the reaction of esters with dibutyltin oxide. An intermolecular dimeric rearrangement between acyl and alkoxy dimeric distannoxanes from (1) and (2) esters occurs at ambient temperature without ligand exchange. Ligand exchange on tin atoms by reactions between free ester (1) and dimeric distannoxane occurs at higher temperature at both acyloxy and alkoxy tin sites. Reactions are characterized by multinuclear NMR spectroscopy ( 1 H, 13 C, 119 Sn). Tetra acyloxy or tetra alkoxy distannoxanes are also efficientcatalysts for this redistributive transesterification.