J.-U. Sommer, K. Saalwächter.
Segmental Order Parameters and Swelling
in Polymer Networks.
Macromol. Symp. 291-292, 251-257 (2010).
We study segmental order parameters in polymer networks in good solvent. In
particular we consider the tensor order parameter which characterizes the degree
of orientational order of segments and which is directly related to the residual
coupling constant obtained in NMR-experiments. Using a simple relation between
the order parameter and the force acting on the chain end at a given extension
we derive an universal relation for the order parameter for concentrations above
the overlap threshold. Considering polymer gels at the equilibrium state of
swelling we predict a unique relation between the tensor order parameter and the
correlation length (blob size) of the gel. Experiments applying multi-quantum
NMR-methods to both end-linked and randomly cross-linked polymer networks are in
excellent agreement with this prediction. We critically discuss the widely used
Flory-Rehner model of network swelling and show that initial decay of the tensor
order parameter as observed in experiments at low degrees of swelling can be
explained as a solvent effect without making additional assumptions about
constraint release processes during swelling.