The Mechanism of Phenolic Resin Vulcanization of Unsaturated Elastomers

Abstract

It is well known that during the sulfur curing of unsaturated rubbers, two competing reactions occur: (a) crosslinking or vulcanization, and (b) reversion or devulcanization. In the case of butyl rubber, these two competing reactions have been summarized in earlier reports. Tire curing bag (bladder) compounds are usually made of butyl rubber (IIR), a copolymer of isobutene and isoprene, with typically 1–5% of the diene monomer. Curing bags were originally manufactured using sulfur cures. The high temperatures (140–180°C) employed in tire curing caused reversion, however, and these bladders had very short service lives. The deterioration of the IIR bladders was evidenced by a gradual softening of the surface. A major technical advancement for increasing the service life of curing bladders was the development of phenol/formaldehyde (resole) resins for vulcanizing IIR. These resins can give IIR cures with very thermally stable crosslinks. The vulcanizates are essentially immune to reversion, even at the high use temperatures of tire curing operations. The basic curing resins used are generally 2,6-dihydroxymethyl-4-alkylphenols 1 or their condensation polymers 2 (Scheme 1). These materials are produced via the base-catalyzed reaction of the p-substituted phenol with formaldehyde. R is typically methyl, t-butyl, or t-octyl in commercial resins. The use of a blocking substituent in the para position maximizes the formation of o-hydroxymethyl groups. R′ is either methylene (—CH2—) or dibenzylether (—CH2—O—CH2—), depending on the conditions of the resin synthesis or the cure.

Effect of dynamic cross-linking on melt rheological properties of polypropylene/ethylene-propylene-diene rubber blends

“…The rubber also acts as a plasticater for the rigid matrix of polypropylene. The torque maxima of rubber loading and the loading/fusion of PP show a decrease with rubber loading and is in accordance to expectation based 14 Schwarz 15 Fitch 16 Lattimer et al 11 Benzyl Cation Giller 20-22…”

“…Lattimer et al 11 gives a good survey of results of studies for the resole curing of rubber. They conclude that (i) the cross-links obtained by resole curing consist of bisphenol moieties and (ii) only chroman structures, whereas methylene crosslinks are not demonstrated.…”

RETRACTED ARTICLE: Investigation on the improvement of physico-mechnical, viscoelastic and morphological properties of isotactic polypropylene (iPP)/ethylene-propylene diene rubber (EPDM)/ nitrile rubber (NBR) elastomeric blends

“…Lattimer et al [16] gives a good survey of results of studies for the resole curing of elastomer. The product structures of resole cured elastomers as suggested by Cunneen et al [17], Hultzsch [18,19], Schwarz and Kamenskii [20] are therefore confirmed.…”

“…This behavior can be analyzed as a combined effect of both components of the blend. The cross-linked blends showed higher flexural strength and flexural modulus than the Lattimer et al [16] Cunneen [17] Sahwarz [20] Hultzsch [18,19] (Figs. 7 and 8).…”

Delaminations in Resin-EPDM Monomer Bondlines as a Result of Solvent Exposure and Adhesive-Induced Phenolic Resin Disproportionation Reactions

“…The (proprietary) EPDM formulation uses a brominated phenolic resin as its curative. Dibenzyl ethers of brominated phenolic resin can be used to increase the crosslink density under normal cure conditions for (KFEPDM) [1][2][3]. However, there is a side reaction (disproportionation) of the phenolic resin that can reduce the crosslink density of the cured polymer and lower its mechanical strength.…”