Molecular weight distributions in novolac type phenol-formaldehyde polymerizations

Abstract

In the acid-catalysed condensation polymerization of phenol and formaldehyde, the ortho and para positions of the phenol ring are known to exhibit different reactivities. Along with this on polymer molecules, the internal sites have lower reactivity due to molecular shielding. To model the novolac formation, five reactive sites have been proposed and their reactivities are assumed to be completely determined by the site involved. To find the molecular weight distribution (MWD) of the polymer from this information, a given polymer chain has been assumed to consist of these sites in the same relative ratio as in the reaction mass. A mass balance, on polymer molecules of given size, has been made and solved numerically as a function of time. The sensitivity analysis has been carried out to show that the MWD is little affected by the variation of reactivities of the internal sites. The reactivity of para external positions and the ratio of phenol and formaldehyde, however, play a major role in determining the MWD.