Path to achieving molecular dispersion in a dense reactive mixture

Abstract

A uniform dispersion of reactants is necessary to achieve a complete reaction involving multicomponents. In this study, we have examined the role of plasticizer in the reaction of two seemingly unlikely reactants: a highly crystalline hexamethylenetetramine (HMTA) and a strongly hydrogen bonded phenol formaldehyde resin. By combining information from NMR, infrared spectroscopy and differential scanning calorimetry, we were able to determine the role of specific intermolecular interactions necessary for the plasticizer to dissolve the highly crystalline HMTA and to plasticize the phenol formaldehyde resin in this crosslinking reaction. The presence of the plasticizer increased the segmental mobility, disrupted the hydrogen bonded matrix, and freed the hydroxyl units, which further increased the solubility of the HMTA. Both the endothermic and exothermic transitions are accounted for in the calorimetric data obtained. For the first time, it is possible to obtain the effective molar ratio of each component needed to complete the crosslinking reaction efficiently.

An analysis of the role of nonreactive plasticizers in the crosslinking reactions of a rigid resin

“…It also has kinked phenyl rings, preventing access to some of the reactive sites (unreacted ortho/para) especially when hydrogen bonds are present . HMTA is highly crystalline (>99% crystallinity) and has a high melting temperature of nearly 280 °C . In order to induce crosslinks between such dissimilar components, plasticizers are usually used to disrupt the hydrogen bonds providing mobility to the resin in order to dissolve and disperse HMTA .…”

“…HMTA is highly crystalline (>99% crystallinity) and has a high melting temperature of nearly 280 °C . In order to induce crosslinks between such dissimilar components, plasticizers are usually used to disrupt the hydrogen bonds providing mobility to the resin in order to dissolve and disperse HMTA . Due to the rigidity of the phenyl ring, the glass transition temperature can rise quickly during the crosslinking reaction creating a vitrified structure rapidly .…”

“…Its delocalized cyclic structure interacts favorably with the negatively delocalized phenyl ring of phenol in phenol formaldehyde prepolymer. It also has the polar group of aldehyde to disrupt various intermolecular interactions including hydrogen bonding in the phenolic resin . Although the freed hydroxyl groups of the phenolic resin do not participate directly in the crosslinking reaction, they interact through hydrogen bonding to dissociate HMTA in order to facilitate the crosslinking reaction .…”

“…It also has the polar group of aldehyde to disrupt various intermolecular interactions including hydrogen bonding in the phenolic resin . Although the freed hydroxyl groups of the phenolic resin do not participate directly in the crosslinking reaction, they interact through hydrogen bonding to dissociate HMTA in order to facilitate the crosslinking reaction . A plasticizer such as furfural should not dissolve the HMTA directly, allowing Nitrogen atoms to be accessible for reaction.…”

“…A plasticizer such as furfural should not dissolve the HMTA directly, allowing Nitrogen atoms to be accessible for reaction. In fact, the solubility of HMTA in furfural is extremely low at <2% by weight …”