Abstract
High-molecular weight phenol novolak resins (RN) and o-cresol novolak resins (oCR) were prepared in organic solvent. The molecular structure was determined by 1H and 13C NMR measurements. It was found that RN was a branched polymer and a microgel formation was observed, arising from intramolecular reaction (cyclization). The dilute solution properties of acetylated RN (Ac-RN) and acetylated oCR (Ac-oCR) were determined to elucidate the nature of highmolecular weight phenolic resins. The intrinsic viscosity [η] of Ac-RN and Ac-oCR was determined in good solvent and θ-solvent. The exponent values in MHS Eq. for Ac-RN were 0.24 in good solvent and 0.23 in θ-solvent, respectivity. AcRN behaved as a branched polymer. On the other hand, the exponent values in MHS Eq. for Ac-oCR were 0.43 in good solvent and 0.28 in θ-solvent, respectively. Each value was much smaller than that for polystyrene, which is a typical linear polymer. However, the values of expansion factor η3= [η]/[η]θ for Ac-oCR in THF were equal to those for polystyrene in toluene, indicating that Ac-oCR showed the excluded volume effect and behaved like a linear polymer in good solvent. We concluded that Ac-oCR with higher molecular weight showed linear polymeric properties such as polystyrene in solution. The properties of high-molecular weight phenolic resins will depend on the main chain structure composed from phenolic ring and methylene linkages.
