The structure and viscoelasticity of novolac resins

Abstract

In this work, we discuss the dynamic viscoelasticity of three novolac resins with different molar masses and methylene linkage patterns (para-para′, ortho-ortho′ and ortho-para′ methylene linkages) to clarify the relationship between the structure and viscoelastic properties of novolac resins. The linkage patterns of the novolacs were evaluated using 13C nuclear magnetic resonance spectroscopy. Gel permeation chromatography (GPC) measurements showed that the number density distribution was similar to that predicted for hyperbranched chains. The dependence of the intrinsic viscosity on the molar mass indicated that the three novolacs had a compact branched chain structure similar to that of hyperbranched chains. The glass transition temperatures determined by differential scanning calorimetry (DSC) depended on the molar mass and were less sensitive to the methylene linkage pattern. The viscoelastic spectra obtained by the time-temperature superposition principle for the three resins were similar to each other because the glassy relaxation properties were dominant. Weak polymeric modes originating from the chain connectivity were observed at low frequencies in the composite curve and were well described by the dynamic scaling theory for hyperbranched chains. A clear effect from the linkage patterns on the mechanical properties was not observed.