Application of lithium/halide exchange reactions to the synthesis of complex polymer architectures: Investigation of their self-assembling properties at the air/water interface.

摘要

An entire set of hydrocarbon-soluble polycarbanionic initiators and macroinitiators was synthesized by using a simple halogen-lithium exchange reaction (Gilman's reaction) carried out on multibromo molecule and macromolecule precursors. Using these multicarbanionic (macro)initiators an entire set of complex polymer architectures has been synthesized by anionic polymerization using a divergent method.; This strategy was first applied to the preparation of simple polymer architectures such as poly(styrene-b-butadiene-b -styrene) triblock copolymers with excellent mechanical properties, obtained using a new hydrocarbon soluble dicarbanionic organolithium initiator containing a side C15-alkyl chain.; The same exchange reaction has been successfully applied to generate tri- and tetracarbanionic species from tris- and tetrakis-bromoaryl compounds. The use of a sigma/mu ligand was instrumental in obtaining polycarbanionic initiators soluble in apolar medium, and the subsequent preparation of various well-defined three and four-armed polystyrene and polybutadiene stars synthesized by the "core-first" method. The efficiency of the latter was even exploited to synthesize poly(butadiene-b-ethylene oxide) (PB-b-PEO)n amphiphilic star block copolymers and poly(styrene-b-butadiene-b-methyl methacrylate) (P(S-b-B-b-M) n) star block terpolymers (n = 3 or 4).; The potential of PB-b-PEO star block copolymer to self-assemble at the air/water interface was exploited to synthesize a two-dimensional polymeric nanomaterial consisting of a continuously cross-linked polybutadiene two-dimensional network with poly(ethylene oxide) domains of controlled sizes trapped within the network. To reach that goal, novel (PB(Si(OEt)3)-b-PEO) 3 star block copolymers were designed by hydrosilylation of the pendant double bonds of (PB-b-PEO)3 star block copolymer precursors with triethoxysilane. Self-condensation of the triethoxysilane groups under acidic conditions led to a successful cross-linking of the polybutadiene blocks directly at the air/water interface without any additives or reagents.; Finally, the Gilman reaction was extended on o,o'-dibromo chain-end polymers after the introduction of a branching agent whose halogen atoms are carried by separate aryl rings to afford hydrocarbon-soluble polycarbanionic macroinitiators. This provided an efficient synthetic route to the asymmetric and "miktoarm" star (co)polymers based on the combination of different polymers such as polystyrene, polybutadiene, and polyisoprene. By the reiteration of this sequence of reactions (branching and halogen-lithium exchange reactions) starting from a tetrafunctional initiator, dendrimer-like PS and PB up to the seventh and third generations, respectively, could be successfully synthesized.