The Role of Self-Dilution in Step-Growth Polymerizations

✍ Scribed by Hans R. Kricheldorf

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 248 KB
• Volume: 29
• Category: Article
• ISSN: 1022-1336
• DOI: 10.1002/marc.200800366

✦ Synopsis

Abstract

In step‐growth polymerizations, the molar concentration of reactive linear species (oligomers and polymers) decreases with higher conversions and finally reaches zero at 100% conversion. This self‐dilution favors cyclization at the expense of chain‐growth. Cyclization reduces the average lengths of the linear species, and thus, induces a kind of “self‐acceleration”. Both effects together overcompensate the decreasing cyclization tendency resulting from increasing chain lengths. This influence of the self‐dilution is also operating in the case of “ab~n~” monomers, so that at 100% conversion (defined for the “a” functional groups) all hyperbranched polymers will have a cyclic core. With modifications, the “law of self‐dilution” also applies to “a~2~ + b~3~” or “a~2~ + b~4~” polycondensations. Furthermore, the “law of self‐dilution” is valid for both kinetically‐ and thermodynamically‐controlled polycondensations.

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