Small-Angle Neutron Scattering Study on Defect-Controlled Polymer Networks

Abstract

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 “<i>p</i>-tuned” Tetra-PEG gels by tuning the reaction probability, <i>p</i>, 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 <i>p</i>. 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