To elucidate chemistry taking place during thermal degradation of polyamide 66 in the presence of phosphorus flame retardants and understand how commonly used phosphorus flame retardants achieve their flame retardancy, PA66 and a series of model compounds which include N,N'-dibutylhexanediamide, 1-butylazepane-2,7-dione and 1,8-diazacyclotetradecane-2,7‑dione have been subjected to thermal treatments together with melamine polyphosphate, aluminum diethylphosphinate or their combination respectively. Analyses of degradation products indicate that aluminum diethylphosphinate accelerates a cyclization reaction but does not change degradation mechanisms of polyamide 66 and its model compounds while melamine polyphosphate significantly shifts their degradation pathways to dehydration via a modified Hofmann elimination reaction which produces adiponitrile and water. Adiponitrile intumesces strongly when heated with polyphosphoric acid. Water hydrolyzes amides to amines, accompanied by the formation of amino-6-oxohexanoic acid which cyclizes to cyclopentanone. Water and amines together convert aluminum diethylphosphinate to diethylphosphinic acid. On the basis of the identification and transformation of reactive species, modes of flame retardant action of the combination of aluminum diethylphosphinate and melamine polyphosphate for PA66 have been proposed.
Recyclable polyvinylidene fluoride/silicone rubber (PVDF/SR) thermoplastic vulcanizates (TPVs) containing a high mass ratio of SR (50%) with excellent mechanical performances and shape memory behavior were fabricated. The inert PVDF was first dehydrofluorinated via β-H elimination reaction to introduce reactive double bonds. Then, the functional groups were initiated by dicumyl peroxide (DCP) during dynamic vulcanization to realize interfacial grafting (SR-g-PVDF) simultaneously. In situ grafted PVDF chains tightly bridge the immiscible phases, leading to the excellent interfacial adhesion. Consequently, the tensile strength, elongation at break, and tensile toughness were significantly increased to 14.5 MPa, 174.6%, and 12.3 kJ/m3, respectively, which were almost 2.0, 13.6, and 10.3 times than that without interfacial grafting reaction (7.2 MPa, 12.8%, and 1.2 kJ/m3). Also, their excellent mechanical properties were almost perfectly maintained after multiple repetitive processing. Furthermore, the chemical anchoring structure of SR-g-PVDF across the interface could effectively and quickly transfer the force, contributing to the shape memory performances. The obtained TPVs (m60 and m80) showed an impressive shape recovery ratio (>80%) even after two fixing-recovery cycles.
危险品化学品经营许可证（带存储）