Copolymers, graft anionic polymerization methods

Several graft copolymers were prepared based on the anionic polymerization method to overcome some of the major problems encountered in radical-initiated grafting. This method is used to prepare a living synthetic polymer with mono- or dicarbanions to react with modified cellulosic substrates under homogeneous conditions. For example, polyacrylonitrile carbanion was prepared to react with cellulose acetate to generate a cellulose acetate-polyacrylonitrile graft polymer [142]. 

During the last 5 years, there have been several reports of multiblock copolymer brushes by the grafting-from method. The most common substrates are gold and silicon oxide layers but there have been reports of diblock brush formation on clay surfaces [37] and silicon-hydride surfaces [38]. Most of the newer reports have utilized ATRP [34,38-43] but there have been a couple of reports that utilized anionic polymerization [44, 45]. Zhao and co-workers [21,22] have used a combination of ATRP and nitroxide-mediated polymerization to prepare mixed poly(methyl methacrylate) (PMMA)Zpolystyrene (PS) brushes from a difunctional initiator. These Y-shaped brushes could be considered block copolymers that are surface immobilized at the block junction. 

Anionic polymerization of functionalized cyclotrisiloxanes is a good method for the synthesis of well-defined functionalized polysiloxane with control of molecular mass, polydispersion, and density and arrangement of functional groups. These polymers may serve as reactive blocks for the building of macromolecular architectures, such as all-siloxane and organic-siloxane block and graft copolymers, star-, comb- and dendritic-branched copolymers and various polysiloxane-inorganic solid hybrids. 

Another example of ionic graft copolymerization is a reaction carried out on pendant olefinic groups using Ziegler-Natta catalysts in a coordinated anionic-type polymerization. The procedure consists of two steps. In the first, diethylaluminum hydride is added across the double bonds. In the second the product is treated with a transition metal halide. This yields an active catalyst for polymerizations of a-olefms. By this method polyethylene and polypropylene can be grafted to butadiene styrene copolymers. Propylene monomer polymerization results in formations of isotactic polymeric branches ... 

The major forte of anionic polymerization has been the ability to prepare polydlene and polystyrene polymers and copolymers with control over the major variables affecting polymer properties. Researchers continue to exploit this method for the preparation of model block copolymers, graft copolymers, and branched copolymers, and homopolymers with controlled, well-defined structures. The ability to prepare well-defined polymers and copolymers with functionalized end groups, especially ionic or ionizable groups, is also generating considerable current interest. Methods are also being explored to anionically pol)rmerize and copolymerized a variety of polar monomers with controlled structures. The current interest in blends and... 

Grafting onto reactions. This method of anionic polymerization has contributed to the development of tailor made synthetic molecules. It is used to synthesize amphiphilic graft copolymers in which hydrophilic grafts are linked to a hydrophobic backbone. Well defined comb-like homopolymers were made by the same technique.In spite of its tremendous potential, the "grafting onto" anionic polymerization process has yet to be applied to the synthesis of cellulosic graft copol3nners. 

Block and graft copolymers are made by special methods. If we first initiate polymerization of monomer A, then add some B, then add A again, and so on, we can obtain a block polymer with alternating segments of blocks of A units, then B units, and so on. This is particularly easy with anionic polymerizations, where there are no significant termination steps. 

Novel polyimide-g-nylon 6 and nylon 6- polyiniide-] nylon 6 copolymers were synthesized by polycondensation and subsequent anionic, ring-opening polymerization methods. The graft and triblock copolymer structures were characterized with FTIR, GPC, selective extractions, DSC,TGA, tensile test and DMA. The effective reinforcement of nylon 6 with the incorporation of only a few wt% polyimide was demonstrated by the sigmOcant improvements in the copolymers thermal and mechanical properties, and chemical resistance. 

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