Block sequences radical polymerization, synthesis

Liquid crystalline amphiphilic diblock copolymers poly(ethylene oxide)-h/oc -ll-[4-(4-butylphenyl-azo)phenoxy]-undecyl methacrylate, PEOn,-h-PMA(Az) , as shown in Fig. 16, prepared by atom transfer radical polymerization [61], were composed of hydrophilic PEOn, sequences and hydrophobic PMA(Az) , with azobenzene moieties such as mesogen connected by a flexible spacer. The synthesis of such amphiphilic liquid crystal block copolymers has been recently reported [62]. In diblock copolymers PEO ,-h-PMA(Az)n, m and n indicate the degree of polymerization of PEO and PMA(Az) components, respectively. Differential scanning calorimetry (DSC) of PEO ,-f>-PMA(Az)n gives a clear picture of the thermal properties of these liquid crystaUine polymers, as shown in Fig. 17, for PEOn4-h-PMA(Az)2o [58, 61]. 

This chapter is concerned primarily with the simultaneous polymerization of two monomers to produce statistical and alternating copolymers. The different monomers compete with each other to add to propagating centers, which can be radical or ionic. Graft and block copolymers are not synthesized by the simultaneous and competititive polymerization of two monomers. Each monomer undergoes polymerization alone. A sequence of separate, noncompetitive polymerizations is used to incorporate the different monomers into one polymer chain. The synthesis of block and graft copolymers and variations thereof (e.g., star, comb) are described in Secs. 3-15b-4, 3-15b-5, 5-4, and 9-9. 

Major commercial synthetic specialty polymers are made by chain-growth polymerization of functionalized vinyl monomers, carbonyl monomers, or strained ring compounds. Depending on monomer structure, the polymerization may be initiated free radically, anionically, or cationically. Copolymers or terpolymers with random, alternating, block, or graft sequences can be prepared under appropriate reaction conditions. There are numerous mediods used to prepare specialty polymers in the research laboratory. However, only a few are of commercial interest. Of particular commercial interest is synthesis of specialty polymers in solutions, dispersions, suspensions, or emulsions. 

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