Differential scanning calorimetry (DSC) and pulsed field
gradient
spin echo nuclear magnetic resonance (PFGSE NMR) were used to characterize
water in hydrogels of ethoxylated trimethylolpropane tri-3-mercaptopropionate
(ETTMP) and poly(ethylene glycol) diacrylate (PEGDA). Freezable and
nonfreezable water were quantified using DSC; water diffusion coefficients
were measured using PFGSE NMR. No freezable water (free or intermediate)
was detected from DSC for hydrogels of 0.68 and greater polymer mass
fractions. Water diffusion coefficients, from NMR, decreased with
increasing polymer content and were assumed to be weighted averages
of free and bound water contributions. Both techniques showed decreasing
ratios of bound or nonfreezable water mass per polymer mass with increasing
polymer content. Swelling studies were used to quantify the equilibrium
water content (EWC) to determine which compositions would swell or
deswell when placed in the body. At 30 and 37 °C, fully cured,
non-degraded ETTMP/PEGDA hydrogels at polymer mass fractions of 0.25
and 0.375, respectively, were shown to be at EWC.