Sequence-controlled polymers chain-growth polymerization

Sequence-controlled Polymers Prepared by Chain-growth Polymerization... 

Asides from chain-growth, step-growth, and multi-step growth strategies, sequence-defined polymers may also be prepared using polymerization concepts inspired by biological polymerizations such as replication, transcription, and translation. For instance, sequence-defined templates can be used for monomer sequence regulation in non-natural polymerizations. Alternatively, catalytic molecular machines inspired by biocatalysts such as enzymes and ribozymes have been tested for the synthesis of sequence-controlled polymers. These developments are summarized in this last section of the chapter. 

Biomacromolecules such as proteins derive their function from their three-dimensional shape and the precise functional group placement on the surface and interior of the structure. Also known as the tertiary structure, this shape is a result of a perfectly controlled monomer sequence, or primary structure. Synthetic polymers containing a perfect monomer sequence are inaccessible using contemporary techniques. However, recent advances in polymerization techniques allow for the fabrication of multi-block polymers with narrow molecular weight distributions " and materials with relatively controlled monomer sequences by step-growth and chain-growth... 

As with all living polymerizations, the formation of bloek eopolymers is possible if the active chain end of one polymer block can initiate the polymerization of a second monomer. This may mean that when block copolymers are prepared, the sequence of monomer addition may be critical. In this respect, the CRP techniques are no different from the other ionic reactions, but they do have one specific advantage. Because many of the CRP processes do not reach 100% conversion, it is best to separate and purify the polymer adduct formed in the first step, which can then be stored and used as a macroirfitiator for the growth of the second block, with no loss of activity. The use of such a macroinitiator helps to control the subsequent reaction more effectively and produces products with very low polydispersities, because for the macroinitiator, diffusion and reactivity are decreased, thereby mininuzing radical-radical coupling. 

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