The Role of Self‐Dilution in Step‐Growth Polymerizations

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 “abn” 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 “a2 + b3” or “a2 + b4” polycondensations. Furthermore, the “law of self‐dilution” is valid for both kinetically‐ and thermodynamically‐controlled polycondensations.magnified image

Simultaneous Chain‐Growth and Step‐Growth Polymerization—A New Route to Cyclic Polymers

“…If the conversion of functional groups proceeds according to Equation (2), the concentration of bifunctional chains decreases to a level of 10 À22 mol Á L À1 that is discussed in more detail in a recent feature paper. [2] At 100% conversion of the functional groups all reaction products are necessarily cycles. In contrast, the conversion of monomers according to Equation (1) has no direct influence on the endgroups of the reaction products but on their average molecular weight.…”

“…[2] At 100% conversion all linear species have vanished and the reaction mixture exclusively consists of cycles.…”

“…Therefore, scenario II may be studied and discussed under two complementary aspects. First, monomers and reaction conditions originally designed for a normal SGP are varied in such a way that the polymerization process follows the pattern of CGP as described above by points [1][2][3][4][5][6] N-alkylaminobenzoates will result in a mixture of cyclic and linear polyamides having a broad MWD in a normal SPG. However, addition of an electrophilic initiator (here phenyl 4-nitrobenzoate) and anionic activation of the monomers at low temperatures results in a polymerization process showing the typical features of a CGP.…”

Cyclic polymers: Synthetic strategies and physical properties

“…This relationship can be explained on the basis of eq 4, the so-called law of self-dilution, which is a direct consequence of eq 1. 50 Only linear species possess reactive endgroups, and thus, molar concentration decreases with higher conversions until all functional endgroups and all linear species have vanished at 100% conversion. This self-dilution is characteristic for step-growth polymerization and does not exist for the reactive chains in chain-growth polymerizations.…”

Biodegradable Polymers Composed of Naturally Occurring α‐Amino Acids

“…According to the polycondensation theory of Kricheldorf [54,55] , a substantial portion of macromolecules obtained via AP have no terminal functional groups, since they form macrocycles.…”