Crosslink Reaction Mechanisms of Diene Rubber with Dicumyl Peroxide

RECYCLING BEHAVIOR OF THERMOREVERSIBLY DIELS–ALDER CROSSLINKED EPM

The recyclability of thermoreversibly Diels–Alder (DA) crosslinked EPM has been studied. The retro DA reaction dominates over the dehydration–aromatization process of the DA adduct. Moreover, a negative influence of air occurred as a result of a crosslinking in air flow. Nevertheless, rubber compounds prepared from EPM-g-furan and carbon black can be recycled several times without losing mechanical strength, a feature attributed to a strong antioxidant effect of the carbon black.

Influence of Modified Epoxy Resins on Peroxide Curing, Mechanical Properties and Adhesion of SBR, NBR and XNBR to Silver Wires. Part I: Application of Monoperoxy Derivative of Epoxy Resin (PO)

The research was aimed at checking the effect of monoperoxy derivative of epoxy resin (PO) on the possibility of rubber crosslinking and a subsequent adhesion of the modified rubber to silver wires. Three of the commonly industrially used rubbers were selected for the study: styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR) and carboxylated acrylonitrile-butadiene rubber (XNBR), together with the popular, commercially available Epidian 6 epoxy resin, subjected to the functionalization. An improvement in the adhesion of rubbers to silver wires was observed when using the modified resin. In some cases, an improvement in the mechanical properties of the rubber was observed, especially when the resin was used for crosslinking together with dicumyl peroxide (DCP). Crosslinking synergy between dicumyl peroxide and the modified resin could be observed especially in the case of PO applied for peroxide curing of SBR and NBR.

Influence of Modified Epoxy Resins on Peroxide Curing, Mechanical Properties and Adhesion of SBR, NBR and XNBR to Silver Wires-Part II: Application of Carboxy-Containing Peroxy Oligomer (CPO)

This research was aimed at verifying the effect of carboxy-containing peroxy oligomer (CPO) addition on the possibility of rubber crosslinking and a subsequent adhesion of the modified rubber to silver wires. Three commonly industrially used rubbers were selected for the study: styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR) and carboxylated acrylonitrile-butadiene rubber (XNBR), together with carboxy-containing peroxy oligomer (CPO). An improvement in the adhesion of rubbers to silver wires was observed when applying the oligomeric peroxide with functional groups, with no deterioration of mechanical properties of the vulcanizates. Crosslinking synergy between dicumyl peroxide (DCP) and the modifier could hardly be observed. Nevertheless, the studies demonstrated, that to a small extent, even the CPO itself can crosslink NBR and especially XNBR, resulting in a material of notable elasticity and adhesion to silver wires.

Recyclability of Photoinduced Cross-Linked EPM Rubber with Anthracene-Grafted Groups: Problems and Their Solutions

In this paper, we present the formation of reversible covalently cross-linked networks in ethylene propylene rubber with grafted anthracene groups (EPM-g-AN) based on the principles of photoinduced anthracene dimerization. First, an industrial-grade EPM rubber grafted with maleic anhydride functional groups (EPM-g-MA) was modified with 9-anthracenemethanol. By irradiating EPM-g-AN with UV light (365 nm), the anthracene moieties dimerize via [4 + 4]cycloaddition, forming a covalent network. The network cleavage proceeds at high temperatures (>170 °C), even if with considerable (chemical) degradation. Furthermore, one of the degradation routes has been identified by ¹H NMR to occur via the ester bond cleavage releasing 9-anthracenemethanol. Nevertheless, the reversibility of cross-linking has been achieved by performing the reverse reaction in decalin. The UV-vis spectroscopy clearly shows that the de-cross-linking process in these conditions is due to the anthracene dimer cleavage. Although the recovery in mechanical properties upon recycling is yet to be optimized, the disclosed results pave the way toward the use of anthracene chemistry in thermally reversible networks with possible industrial perspective applications.

Rheology of nitrile rubber with hybrid crosslinked network composed of covalent bonding and hydrogen bonding

A hybrid crosslinked network composed of covalent bonding and non-covalent bonding was constructed in nitrile rubber (NBR) by using a compound crosslinking agents dicumyl peroxide (DCP) and N,N-methylenebis acrylamide (MBA).

Cross-linking process of cis-polybutadiene rubber with peroxides studied by two-dimensional infrared correlation spectroscopy: a detailed tracking

Detailed mechanism of cis-BR cross-linking with peroxides was studied using PCMD2D and 2D correlation FTIR, and a 5-step process was determined.

STABILIZATION OF RAW DIENIC SYNTHETIC RUBBER POLYMERS

The mechanism of rubber polymer autoxidation is briefly reviewed with an emphasis and an appreciation for what these uninhibited free radical reactions can do to polymer properties and quality. Significant differences between hydrocarbon and rubber oxidation are discussed. Differences in polymer substructure are described which affect the mode of oxidation as well as the choice of stabilizer to protect these materials. An explanation of color formation and color prevention for 2,6-dialkyl-4-methylphenols is provided which also includes a discussion of how their oxidized transformation products interact with the rubber polymer. Additional factors that affect polymer quality include proxidative effects of the stabilizer, oxygen diffusion, and the formation of gel. Studies which varied the steric bulk of the alkyl groups in the 2,6 position were conducted to optimize the antioxidant activity of this system in its function in the hydrogen atom donor—hydrogen atom acceptor mechanism of stabilization. A description of the preparation and activity impact of the secondary antioxidant synergist Wingstay® SN-1 is included. Finally, the discovery of highly active 2,6-di(alkylthiomethyl) substituted phenols is described which led to the discovery of Wingstay® K and its contained synergist methylene-bis(dodecylsulfide). This material is a highly persistent auto synergistic stabilizer which is outstanding for the protection of emulsion-styrene butadiene rubber when used 50/50 with Wingstay® 29. When used by itself in polybutadiene rubber polymers, it is highly effective against the effects of oxidation and also for the prevention of gel formation and Mooney viscosity changes.

Responsive solids from cross-linked block copolymers

Novel responsive solids were prepared by randomly cross-linking the polyisoprene chains of a disordered polystyrene-polyisoprene block copolymer. Our experiments show that block copolymer chains, composed of hundreds of repeat units, can undergo reversible order-disorder transitions despite the quenched randomness that arises due to the attachment of one of the blocks to a cross-linked network. The structure, properties, and phase behavior of these materials are determined by a delicate interplay between the density of cross-links and the nature of the ordered state.