Metal-Carbon a-Bonds in the Main Chain

About twenty years ago, synthetic polymers containing metal-carbon a-bonds in the main chain were reported. They include copper- and mercury-poly-yne polymers for which the structure (SO) was proposed. However, their insolubility prevented purification and characterization of the polymer. 

Organometallic Polymers with Metal-Carbon a-Bonds in the Main Chain 364... 

Polymers comprising metal-carbon a-bonds in the main chain... 

Another method is based on the metal-catalyzed polymerization from carbon—halogen bonds in the main-chain units, which was applied for the synthesis of C-3 and C-4.430 For C-3, the main chain polymers with controlled molecular weights were prepared via the copper-catalyzed radical polymerization of tri-methylsilyl-protected HEMA followed by the transformation of the silyloxyl group into 2-bromoisobu-tyrate. The pendant C—Br bonds were subsequently activated by the copper catalysts to polymerize styrene and nBA. A more direct way is employed for C-4 i.e., via conventional radical polymerization of 2-[(2-bromopropinonyl)oxy]ethyl acrylate followed by the copper-catalyzed graft polymerization of styrene and nBA from the C—Br substituent. 

The metal-catalyzed copolymerization from carbon-halogen bonds in the main chain can be employed widely for graft polymer synthesis. A combination of nitroxide-mediated and copper-catalyzed living radical polymerizations, for example, gives graft copolymers G-6, where the main chain is prepared by the former.432 The chlorobenzyl unit in the copolymer is not active during the polymerization but, upon copper catalysis, it can initiate living radical polymerizations of styrene and methacrylates. 

Acetylene and its derivatives can be polymerized by chain growth in the presence of suitable transition metal catalysts to give high molecular weight (MW) polymers (Equations (l)-(4)). The monomers include acetylene, mono- and disubstituted acetylenes, and a,tv-diynes. The polymers possess carbon-carbon alternating double bonds along the main chain and exhibit unique properties (e.g., metallic conductivity) that are not expected with vinyl polymers. 

Alkoxysilane termination forms new bonds between the silicon of the alkoxysilane and the carbon polymer atoms in the polymer end group. Wear resistance is improved by about 50% and tensile strength is increased by some 30%. Further developments aim to maximize the effect by reacting an organolithium compound with a polymer in the presence of an alkali metal alkoxide, producing a polymer in which the main chain has been metallated with a plurality of lithium atoms, and then attaching a plurality of alkoxysilane molecules to the chain. 

---