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Interaction of phenol-formaldehyde condensates with isoprene rubber

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Roca Perez, Rafael (1983) Interaction of phenol-formaldehyde condensates with isoprene rubber. Doctoral thesis, Polytechnic of North London.

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Abstract

The study is concerned with the interaction between p-tertiary butyl phenol-formaldehyde condensates and isoprene rubber under conditions resembling those used in industrial vulcanization processes, and involves investigations of reaction rates, mechanisms of reactions and structures produced. The work is an extension of an earlier study (A. Fitch, Thesis for Ph.D. (C.N.A.A.), 1978).

'Model' phenol-formaldehyde condensates (2-methylol 4- tert.butyl 6-methyl phenol and the ether derived from it by thermal condensation) are shown to interact with isoprene rubber (cis-l,4-polyisoprene) to form adducts containing chroman structures. The ether reacts somewhat more quickly and more efficiently than the methylol compound. 'Lewis acid' catalysts will greatly accelerate the reaction, but cause concurrent structural isomerization of the isoprene rubber, to an extent depending on the nature of the catalyst.

In separate experiments involving only rubber and catalyst, it is found that, of the three catalysts examined, tin(II) chloride dihydrate causes extensive isomerization, tin(II) chloride (anhydrous) causes little isomerization and zinc(II) chloride (anhydrous) causes negligible isomerization, under the appropriate reaction conditions. The structural changes are evaluated, and involve cis-trans interconversions double-bond shifts, cyclization and crosslinking.

Using zinc(II) chloride as catalyst, a study is made of the effectiveness of five different polyfunctional phenol- formaldehyde condensates as vulcanizing agents for isoprene rubber. The condensates consist of 2,6-dimethylol 4-tert. butyl phenol and four of its derivatives containing different molar proportions of methylol, dibenzyl ether and diaryl methane groups. One of the derivatives is a commercially-available vulcanizing agent. Measurements of rubber-combined phenolic material and of crosslink concentrations are made at different times of reaction, and results show that the condensates containing high proportions of dibenzyl ether links are the most efficient vulcanizing agents. Efficiency may be further improved by the addition of a formaldehyde donor to suppress side-reactions. The results indicate that, in all cases, combination with the rubber occurs through chroman linkages and the crosslinks contain at least two phenolic nuclei joined by dimethylene ether or methylene links.

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