Toughening of Polyamide-6 With Poly(styrene-alt-maleic anhydride)-Polystyrene-Block-Poly(n-butyl acrylate)-Block-Polystyrene Copolymer (SMA-SBAS) Synthesized Via RAFT Mini-Emulsion Polymerization

Poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymers is one of the main commercial thermoplastic elastomers (TPE) due to their excellent mechanical properties, and commonly used as impact modifier for polyamides with maleic anhydride grafting through reactive blending. The impact performances of polyamides can be greatly enhanced by filling with block copolymers.

On the other hand, controlled/living radical polymerizations (CLRP) have been investigated extensively over the last few years because these methods are compatible with almost all types of vinyl monomers and with emulsion polymerization processes where water is used as polymerization media.

Well-designed amphiphilic block copolymers, in analogy to water/oil emulsions, create novel nanostructured blends in a few minutes of mixing. Block copolymers, embedded into polyamide matrix, produce the cocontinuous nanostructure, and could have great toughening effects without altering significantly the elastic modulus.

Based on the method of reversible addition-fragmentation chain transfer radical polymerization (RAFT), the styrene/butyl acrylate block copolymer (SMA-SBAS) was successfully synthesized, mediated by maleic anhydride/styrene alternating copolymer (SMA) as the amphiphilic co-oligomer macroRAFT agent. After melt mixing, PA-6/SMA-SBAS blends achieve an ideal dispersion of the scale in the polyamide matrix and significantly improve the impact strength, with decreased water absorbency. The influence of the rubber content (butyl acrylate), block copolymer chain length is investigated. SEM results showed the major toughening mechanisms, TEM observations indicates that SMA-SBAS particles self-assembled the cocontinuous nanostructure in the polyamide matrix due to phase separation. This work demonstrated that the RAFT mini emulsion polymerization holds good promise for synthesis of unique structures of block copolymers, which makes affordable engineering polymer blends with extraordinary performance. Compared to current industrial process, SBS synthesis by anionic polymerization, compatilizer introduced by melt grafting, the TPE impact modifier synthesized by RAFT emulsion process would like to be energy-saving and environmentally friendly.

Graph 1: Synthesis of the macroRAFT agent

Graph 2: Synthesis of SMA-SBAS amphiphilic copolymer