Engineering polymer blends based upon phenolic-modified polyolefins

Alkylphenol-formaldehyde resins or resoles are preferred crosslinking agents in commercial rubber/plastic blend or thermoplastic vulcanizates (TPVs), which are thermoplastic elastomers (TPEs) prepared by dynamic vulcanization. These substances have also been used in the chemical modification of polyolefins. This work explores mechanisms, which might lead to the chemical reaction pathways during mixing in molten state. We seek a basic understanding of the thermal reactions of the resoles in the presence and absence of polyolefins. Kinetics and mechanistic studies as well as measurement of mechanical and rheological properties of blends, with and without catalyst were considered.; It was found that modification of a crystalline polyolefin catalyzed by stannous (II) chloride dehydrate gave a remarkably fast reduction in the amount of o-methylene ether linkages or terminal hydroxyl groups of resoles. The modification of the polyolefin gave enhanced mechanical properties to the rubber/plastic blends after dynamic vulcanization. Moreover, the presence of catalyst reduces the rate of deactivation of resoles. The kinetic studies revealed that the rate and efficiency of modification (bound phenolic compound as a % of the polyolefin) depends on types of polyolefins, concentrations of resoles, catalyst and mixing time. Also, the presence of catalyst can increase the degree of modification more than two fold.; In mechanistic or model compound studies, it was found that the uncatalyzed reactions of a model resole and olefin gave the formation of simple chroman derivatives as major products, followed by methylene-bridge dimerization products and other products in minor amount; whereas, the catalyzed reaction gave mononuclear phenols, which have olefinic substituents at o-positions, followed by dimerization resole products and small amounts of dimeric chromans. Chromans are inert byproducts, whereas, the olefinic substituted phenols are models for modified polyolefins. From this evidence, the pathways for the catalyzed phenolic modification of the crystalline polyolefins, which have at least one double bond on the polymer chain, were postulated.; The mechanical and rheological properties of blends and TPVs prepared by catalyzed or uncatalyzed modification of polyolefin, followed by dynamic vulcanization, were investigated. It was found that catalyzed-modified polyolefin blends and TPVs exhibit enhanced mechanical properties more than do the uncatalyzed and simple ones. We also noted that dynamic vulcanization greatly improved the final properties of the compatibilized blends. The viscosity of blends and TPVs prepared by the catalyzed modification increased more than it did in the case of the uncatalyzed modification. Also, the chemical modification can give increased pseudoplastic behavior. Moreover, catalyzed-modified TPVs showed a decrease in power law exponent (n) while consistency indices (K) increase as more rubber is added to the blend, which is consistent with the general theory for the rheology of suspensions where resistance to flow of a composite increases exponentially with content of the dispersed phase.