Exchange of chain-end functionalized polyolefins on the clay surface

This chapter discusses a unique chain-end functionalized polyolefin structure that contains a reactive terminal group for forming a strong interaction with clay surfaces, resulting in exfoliated polyolefin/clay nanocomposites. Two commercially important polymers, including isotactic polypropylene (PP) and poly(vinylidene fluoride) (PVDF), have been studied to illustrate the research idea and experimental results. The chemistry to prepare chain-end functionalized PP containing a terminal OH or NH₃⁺Cl⁻ group involves metallocene-mediated propylene polymerization using rac-Me₂Si[2-Me-4- Ph(Ind)]₂ZrCl₂/MAO complex in the presence of styrene derivatives (St-f) and hydrogen, which serve as the chain transfer agents. On the other hand, the chain end functionalized fluoropolymer is prepared by a specific borane control radical initiator that bears a reactive Si(OR)₃ group that is directly transferred to the beginning of the polymer chain. Despite the extremely low concentration of the chain-end group in PP and PVDF polymers, the terminal OH, NH₃⁺Cl⁻, and Si(OR)₃ groups show good accessibility and reactivity toward the clay surfaces and form hydrogen bond, ion-exchange the cations (Li⁺, Na⁺, etc.), and chemical bonding, respectively. Such strong interactions anchor the PP or PVDF chain to the clay surfaces. On the other hand, the remaining unperturbed end-tethered high molecular weight PP or PVDF tail exfoliates the clay layers. This exfoliated structure is maintained even after further mixing with pure neat PP or PVDF polymers.