Selective radical mediated graft modification of polyolefins

The thermolysis of bicumene at temperatures ranging from 220°C to 310°C is used to initiate the radical-mediated graft addition of vinyltriethoxysilane (VTEOS) to polyethylene. In addition to providing remarkable kinetic chain lengths, high-temperature bicumene-based processes can induce fragmentation such that the effects of radical combination on melt viscosity are counteracted. As a result, alkoxysilane-modified polymers that moisture-cure efficiently can be produced without incurring the undesirable increases in molecular weight that accompany conventional grafting processes.; The radical-mediated addition of alkyl thiols to the terminal unsaturation of polypropylene (PP) and polyethylene (PE) is used to prepare functional polyolefin derivatives without altering the molecular weight of the parent material. The sulfide product of thiol-ene addition, as well as the internal olefin resulting from a remarkable thiyl radical-mediated olefin migration, are characterized using a model hydrocarbon, 2,4-dimethylhept-1-ene. The yield of 3-mercaptopropyltrimethoxysilane (MPTMS) addition to atactic-PP is examined in detail, and the functionalization of high molecular weight isotactic-PP is used to produce moisture-curing resins that bind to siliceous fillers. Moisture curable sulfide derivatives of PE are synthesized using the same approach. The robustness of the mechanism is demonstrated by its tolerance towards antioxidants.; A range of modification strategies is presented, each exploiting triallyl trimellitate or its derivatives to counteract the effects of macroradical fragmentation on molecular weight.; Model compound studies, as well as examinations of atactic-PP reaction products, show that allylic ester activation occurs predominately by a radical addition-hydrogen transfer sequence. Cografting of TATM and maleic anhydride (MAn) leads to maleated PP of high melt viscosity, while the apparent incompatibility of TATM with vinyltrimethoxysilane (VTMS) requires the use of TATM-assisted thiol-ene addition and/or diallyl silane grafting to produce moisture-curable PP derivatives. Extensive addition of PP to triallyl trimesate (TAM) is shown to establish a hyper-branched chain population at the expense of modified chains in the dominant, lightly-branched fraction of the material. The mechanisms through which unimodal composition and molecular weight distributions evolve toward a bimodal condition are discussed.