Structure and physical properties of dried Tetra-PEG gel

We investigated crystal structure, and thermal, swelling, and deformation behaviors of dried tetrafunctional (polyethylene glycol) gel, Tetra-PEG gel, with narrow molecular distribution. Tetra-PEG gel consists of two kinds of symmetrical tetrahedron-like PEG macromonomers with a fixed molecular weight. In spite of network structure with rather small molecular weight between cross-links (Mc) (≈5000), the dried Tetra-PEG gels were found to be capable of crystallization. The crystalline melting temperature (Tm) and the degree of crystallinity (Xc) of dried Tetra-PEG gels obtained by differential scanning calorimetry (DSC) were substantially constant against the polymer volume fraction at preparation (ϕ0). Furthermore, the corrected elastic modulus (G) of dried Tetra-PEG gels did not depend on ϕ0. These experimental results indicate that the there exist negligible entanglements in the dried Tetra-PEG network irrespective of ϕ0. In other words, Tetra-PEG gels do not have significant topological inhomogeneities.