Regensburg 2010 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 49: Elastomers and Gels
CPP 49.6: Talk
Friday, March 26, 2010, 11:30–11:45, H48
NMR observation of "quantized" defect structures in hydrogels — •Frank Lange1, Takamasa Sakai2, and Kay Saalwächter1 — 1Institut für Physik - NMR , Betty-Heimann-Str. 7, 06120 Halle, Germany — 2Department of Bioengineering, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
We present data on a new class of hydrogels, the so called Tetra-PEG. These biodegradable gels are made from four-arm macromers with well-defined molecular weight. End-linking of the precursor macromers in semi-dilute solution results in gels with a highly homogeneous microstructure and advanced mechanical properties, in contrast to conventional hydrogels, which are usually very heterogeneous. Investigations were performed at a low-field NMR spectrometer with a proton multiple-quantum pulse sequence.
Analysis of the data shows a step-like increase of the normalized double-quantum buildup curve, which is due to a well-defined microscopic defect structure of the hydrogels. Such unique structural details are here observed for the first time. The observation becomes possible because of the unique overall homogeneity of the samples. The residual dipolar coupling constant derived from the buildup curves is proportional to the inverse of the network chain molecular weight, and based on this we conclude that the defects are due to multi-linking between two macromers. The dependence of the amounts and types of defects on various parameters such as concentration or stoichiometry variations is investigated in detail.