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Block Copolymers

المؤلف:  A. Ravve

المصدر:  Principles of Polymer Chemistry

الجزء والصفحة:  631

2026-02-25

451

Block Copolymers

These polymers consist of two or more strands of different polymers attached to each other. There does not appear to be any general stipulation to the minimum size of each block. There does appear to be, however, a general agreement that each sequence should be larger than just a few units. In describing a block copolymer, it is helpful if the following structural parameters are available to characterize the material:

 1. Copolymer sequence distribution as well as the length and the number of blocks.

 2. The chemical nature of the blocks.

3. The average molecular weight and the molecular weight distribution of the blocks and of the copolymer. Block copolymers, particularly of the A—B—A type, can exhibit properties that are quite different from those of random copolymers and even from mixtures of homopolymers. The physical behavior of block copolymers is related to their solid-state morphology. Phase separation occurs often in such copolymers. This can result in dispersed phases consisting of one block dispersed in a continuous matrix from a second block. Such dispersed phases can be hard domains, either crystalline or glassy, while the matrices are soft and rubber-like. An interesting example of block copolymers is work by de Ruijter et al. [348], who prepared a series of block copolymers that contain rigid liquid crystal forming blocks of poly(p-phenylene terephthalamide) and flexible blocks of hexamethylene adipamide. The polymers have been prepared in a one-pot procedure by a low-temperature polycondensation reaction in N-methyl-2-pyrrolidone.