Small-angle neutron scattering study on defect-controlled polymer networks

Tetra-PEG gels are classified to near-"ideal" networks with significantly low inhomogeneities, which were confirmed by small-angle neutron scattering (SANS). In this study, we systematically introduced two types of defects into Tetra-PEG gels and investigated effects of defects on structure. First, we prepared defect-rich networks by simply reducing prepolymer concentration, and observed the evolution of network structure by time-resolved SANS during gelation process. In this case, both the scattering intensity and the correlation length increased with reaction time in the φ < φ* region, while they scarcely changed in the φ > φ* region. Here, φ and φ* are the polymer volume fractions at observation and that at chain-overlap concentration, respectively. Second, we prepared "p-tuned" Tetra-PEG gels by tuning the reaction probability, p, and soaked them in water to expose the inhomogeneities. It was revealed that SANS profiles of as-prepared gels did not change noticeably, while those of swollen gels systematically changed with decreasing p. On the basis of these results, we discuss the relationship between the defects of polymer network and inhomogeneities by using simple schematic pictures of polymer network.