ABSTRACT In this work we demonstrate that aqueous hydrogen peroxide is an effective reagent for c... more ABSTRACT In this work we demonstrate that aqueous hydrogen peroxide is an effective reagent for chain scissioning or vis-breaking of polypropylene during melt-processing to produce controlled rheology product. The novel process involves the direct injection of aqueous hydrogen peroxide into the polypropylene melt under pressure. The polypropylene produced has reduced molar mass, narrowed molar mass distribution), and is indistinguishable in terms of melt flow rate, molar mass distribution, crystallinity and melt rheology from conventionally vis-broken polypropylene produced using an organic peroxide (2,5-dimethyl-2,5-di-tert-butylperoxyhexane (DHBP)). However, the polypropylene produced in the current process is notably free of the organic volatiles formed as by-products in the case of organic peroxides such as DHBP.
Phthalimidomethyl trithiocarbonates are used as reversible addition fragmentation chain transfer ... more Phthalimidomethyl trithiocarbonates are used as reversible addition fragmentation chain transfer (RAFT) agents to provide low polydispersity α-(phthalimidomethyl)polystyrene with number-average molecular weight in the range 1000−100000 g mol-1. The activity of the phthalimidomethyl trithiocarbonates in RAFT polymerization of styrene, which appears to be similar to that of analogous benzyl trithiocarbonates, is attributed to the electrophilic character of the phthalimidomethyl group. The trithiocarbonate functionality in the products was quantitatively transformed to inert chain ends either by radical-induced reduction with tributylstannane or by thermal elimination, allowing the phthalimido end groups to be cleanly converted to primary amine end groups by hydrazinolysis. Thermolysis experiments, in which the polymers are cleaved at the trithiocarbonate linkage, also provide information on the mechanism of RAFT polymerization. In the case of the symmetrical bis(phthalimidomethyl) trithiocarbonate the two chains grow stepwise indicating that this RAFT agent has a higher transfer constant than the phthalimidomethyl polystyrene trithiocarbonate and that polystyrene propagating radical is a better homolytic leaving group than the phthalimidomethyl radical.
ABSTRACT In this work we demonstrate that aqueous hydrogen peroxide is an effective reagent for c... more ABSTRACT In this work we demonstrate that aqueous hydrogen peroxide is an effective reagent for chain scissioning or vis-breaking of polypropylene during melt-processing to produce controlled rheology product. The novel process involves the direct injection of aqueous hydrogen peroxide into the polypropylene melt under pressure. The polypropylene produced has reduced molar mass, narrowed molar mass distribution), and is indistinguishable in terms of melt flow rate, molar mass distribution, crystallinity and melt rheology from conventionally vis-broken polypropylene produced using an organic peroxide (2,5-dimethyl-2,5-di-tert-butylperoxyhexane (DHBP)). However, the polypropylene produced in the current process is notably free of the organic volatiles formed as by-products in the case of organic peroxides such as DHBP.
Phthalimidomethyl trithiocarbonates are used as reversible addition fragmentation chain transfer ... more Phthalimidomethyl trithiocarbonates are used as reversible addition fragmentation chain transfer (RAFT) agents to provide low polydispersity α-(phthalimidomethyl)polystyrene with number-average molecular weight in the range 1000−100000 g mol-1. The activity of the phthalimidomethyl trithiocarbonates in RAFT polymerization of styrene, which appears to be similar to that of analogous benzyl trithiocarbonates, is attributed to the electrophilic character of the phthalimidomethyl group. The trithiocarbonate functionality in the products was quantitatively transformed to inert chain ends either by radical-induced reduction with tributylstannane or by thermal elimination, allowing the phthalimido end groups to be cleanly converted to primary amine end groups by hydrazinolysis. Thermolysis experiments, in which the polymers are cleaved at the trithiocarbonate linkage, also provide information on the mechanism of RAFT polymerization. In the case of the symmetrical bis(phthalimidomethyl) trithiocarbonate the two chains grow stepwise indicating that this RAFT agent has a higher transfer constant than the phthalimidomethyl polystyrene trithiocarbonate and that polystyrene propagating radical is a better homolytic leaving group than the phthalimidomethyl radical.
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