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Polyurethane networks with controlled architecture of dangling chains
Author(s) -
Dušek Karel,
DuškováSmrčková Miroslava,
Fedderly Jeffry J.,
Lee Gilbert F.,
Lee John D.,
Hartmann Bruce
Publication year - 2002
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/1521-3935(200209)203:13<1936::aid-macp1936>3.0.co;2-c
Subject(s) - branching (polymer chemistry) , polymer chemistry , chain (unit) , intermolecular force , materials science , gel point , glass transition , side chain , chemistry , polymer science , composite material , molecule , polymer , physics , organic chemistry , astronomy
Network formation from A x + B y precursors (A + B → A − B) with functionality and molecular weight distributions is described by the statistical theory of branching processes. Network formation is described in terms of sol and gel fractions, dangling chains, elastically active network chains (EANC), elastically active crosslinks, free chain ends and branch points partitioned between sol and gel. Various definitions of an EANC are considered. The general relations are applied to a special case of A1 + A2 + A3/B2 system. It is shown how the size and weight fractions of dangling chains can be varied independently by varying the functionality or molecular weight distributions. This is demonstrated experimentally analyzing corresponding polyetherurethane networks prepared from mixtures of polyoxypropylene polyols. The width of the main transition region correlates with the fraction of material in dangling chains. The dependence of the equilibrium shear modulus on the concentration of EANC's indicates much weaker intermolecular interactions for networks with many short dangling chains compared with systems having few longer dangling chains.Schematic representation of a part of the incompletely reacted gelling system A1 + A2 + A3/B2: DC – dangling chain, EANC – elastically active network chain, EAC – elastically active crosslink.