Ethylene‐co‐vinyl acetate copolymer crosslinking through ester–alkoxysilane exchange reaction catalyzed by dibutyltin oxide: mechanistic aspects investigated through model compounds by multinuclear NMR spectroscopy

Abstract

It was shown that the crosslinking of ethylene‐co‐vinyl acetate (EVA) copolymer by a tetraalkoxysilane in molten state, in the temperature range 100–250 °C, was obtained only in the presence of dibutyltin oxide. At this temperature EVA pendant ester groups readily react with dibutyltin oxide to give a dimeric 1‐alkoxy‐3‐acetoxytetrabutyldistannoxane distributed along the polymer chains. The exact role of this tin compound in the ester–alkoxysilane reaction was elucidated through reactions of the tetraalkoxysilane with parent tin compounds: tributylethoxytin, dimeric diacyloxydistannoxane and finally a dimeric 1‐alkoxy‐3‐acyloxydistannoxane, obtained by reaction of the dibutyltin oxide with a model ester instead of the EVA‐ester pendant group. Ligand exchanges on tin atoms characterized by multinuclear NMR spectroscopy (1H, 13C and 119Sn) showed that substitutions were selective and concern only the exo‐cyclic tin ligand (OR or OCOR′) without alteration of the dimeric distannoxane structure. Furthermore, these ligand exchanges occurred at room temperature. This approach with model compounds gave evidence that the crosslinking occurred via an alkoxy‐Sn/alkoxy‐Si exchange on the exo‐cyclic sites of the distannoxane structure formed in situ. This distannoxane was shown to be an efficient catalyst of this transesterification. The temperature of formation of this catalytic species governed the temperature of the beginning of the crosslinking reaction. Copyright © 2004 Society of Chemical Industry

Dioxomolybdenum(VI) and dioxotungsten(VI) complexes: efficient catalytic activity for crosslinking reaction in ethylene‐vinyl acetate copolymer/alkoxysilane composites

“…[8][9][10] Common ways of EVA crosslinking involve (i) macroradical formation via thermal decomposition of organic peroxides, [11] (ii) high-energy irradiation (γ-ray or electron beam), [12] and (iii) compounding with alkoxysilane coupling agents that form organic/inorganic network-structures via transesterifications of vinyl acetate moieties in EVA. [13,14] Each method has its own distinct advantages depending on the applications and environments. The last crosslinking technology has been developed by Bounor-Legaré et al [14] and has recently been attracting much attention because the organic/inorganic hybrid materials offer the opportunity to combine the desirable properties of organic polymers (toughness and elasticity) with those of inorganic moieties (hardness, heat, and chemical resistance).…”

Ester interchange reactions catalyzed by tin compounds in reactive processing: NMR contribution via reactions with model compounds

“…Recently, Bounor-Legare et al [18] extended this type of catalysis to ester/alkoxysilane exchange reactions between polymer-ester pendant groups and a tetraalkoxysilane giving access to hybrid crosslinked materials easily obtained during processing. In this case, the reactions with model compounds have shown that the catalytic efficiency was due to very efficient exchanges between alkoxy groups of catalytic exo tin sites and the alkoxy silane crosslinking agent.…”

In situ ester–amide exchange reaction between polyamide 6 and ethylene‐vinyl acetate rubber during melt blending

“…In the presence of ester and amide groups, DBTO reacts with ester and amide groups through insertion of [SnO] link at elevated temperatures as shown in Scheme , generating the distannoxane intermediate species, 1‐alcoxy‐3‐acyloxytetrabutyldisannoxane (A, B), which acts as the catalytic species for the exchange reaction between free ester or amide groups and distannoxane, and finally leads to the exchange reaction of ester and amide groups. The reaction mechanism for the ester–amide exchange reaction between PA6 and EVM is proposed in Scheme .…”