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The Role of Self‐Dilution in Step‐Growth Polymerizations
Author(s) -
Kricheldorf Hans R.
Publication year - 2008
Publication title -
macromolecular rapid communications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.348
H-Index - 154
eISSN - 1521-3927
pISSN - 1022-1336
DOI - 10.1002/marc.200800366
Subject(s) - dilution , monomer , polymer , molar mass , molar ratio , polymer chemistry , polymerization , chemistry , chain (unit) , materials science , chemical engineering , thermodynamics , organic chemistry , catalysis , physics , astronomy , engineering
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.