Synthesis Of PA6-b-PDMS Block Copolymers And Their Applications In PA6/Silicone Rubber Blends

Blending is an effective method to improve properties of existing polymers. As a widely used kind of polyamides, polyamide6(PA6) shows high strength, excellent oil resistance and thermal stabilities. But PA6is highly notch-sensitive, and fails in a brittle manner under impact with high speed. A commonly employed practice in designing toughened PA6is blending with rubber. Meanwhile, considering the high water absorption of PA6, in this study PA6blending with highly hydrophobic Silicone rubber was investigated.The extreme incompatibility between PA6and Silicone rubber results in poor interfacial adhesion between the phases. This leads to an unstable morphology with inferior mechanical properties. So a class of polyamide-6-b-polydimethylsiloxane (PA6-b-PDMS) multi-block copolymers with different structures was synthesized and then used as the compatilizer in PA6/Silicone rubber blends. Finally, the relationship between the structure and properties was investigated.Firstly, a class of compatibilizer PA6-b-PDMS was prepared. A series of PA6-b-PDMS multi-block copolymers with different PDMS segments lengths and mass ratios was synthesized by the bulk polymerization of a binary carboxyl terminated PA6-2K, PDMS-NCO (PDMS modified by hexamethylene diisocyanate), and the coupling agent hexamethylene diisocyanate (HDI).Secondly, the mixing operation conditions were optimized, and the effects of the compatilizer, silica nanoparticles and2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) nitroxide were investigated. The results revealed that the PDMS segments lengths and mass ratios both influenced the morphological properties, and the multi-block copolymer Co-2-30with longer PDMS segments length and largest content of PDMS presents the best improvement. Meanwhile, silica nanoparticles also resulted in the refinement of the morphology. Because silica nanoparticles mainly went at PA/Silicone rubber interface, and prevented the coalescence of rubber droplets. The effect of TEMPO nitroxide was to control the crosslinking of Silicone rubber and assured sufficient dispersing time. The concentrations of TEMPO and crosslinking agents dicumyl peroxide (DCP) added in the mixtures were optimized (r=[TEMPO]/[DCP]=2.0).Finally, a series of PA6/Silicone rubber blends was prepared and the relationship between the structure and the properties was researched. The scanning electron microscope (SEM) analysis results showed that the number average radius of silicone rubber droplets were below1.5μm, and volume average radius were about2.0μm. After analysis of the degree of crystallinity, it was revealed that increasing the content of silicone rubber resulted in the decreasing ofχc, although PA6matrix still had good crystallinity. The notched impact strength showed a relationship with the distance of rubber particles τ. When τ<0.8μm, as the decreasing of τ, the σimp of the mixtures increased. And when τ was about0.5τm, the σimp of the mixtures was largest. But if τ continued to decreased, the σimp of the mixtures would decrease. The tensile strength and modulus of the mixtures decreased with the increasing of the content of silicone rubber, and when the content of the rubber was larger than20wt%, the elongations significantly decreased. On the other hand, the addition of silicone rubber resulted in the decreasing of χc, which was unfavorable for the reduction of water absorption. But the mixtures still showed significant decrease in water absorption comparing with pure PA6, so it’s still meaningful to reduce the water absorption by introduction of Silicone rubber.