Controlled molecular weight cresol-formaldehyde oligomers

Controlled molecular weight, linear, ortho- and para-cresol novolac oligomers have been synthesized by using calculated amounts of a monofunctional 2,6-dimethylphenol endcapping reagent. It was found that an excess of formaldehyde was needed to achieve the targeted molecular weights, thus suggesting that a dynamic equilibrium exists in these reactions whereby formaldehyde adds and eliminates from the cresol rings. Reaction progression was monitored by both 13C NMR and GPC. Number average molecular weights of these oligomers were confirmed using 13C NMR spectra and were found to be comparable to the targeted molecular weights.The glass transitions and viscosities of both the ortho- and para-cresol novolacs were compared at equivalent number average molecular weights. The Tgs increased as the molecular weights increased, but there were no observable differences between the Tgs of ortho- and para-cresol novolacs with similar molecular weights. The melt viscosities of ortho- and para-cresol novolcas with similar molecular weights were almost identical.