Insight Into Supramolecular Interactions of Etherified Alkyl Phenolic Resoles

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Abstract
Alkylated phenolic resole resins are of special interest in the adhesive industry due to their attractive features such as tackiness, compatibility with a variety of substrates, and low cost. 4‐ tert ‐Butylphenol –formaldehyde resole (PTBF) and its etherified derivatives using isopropyl alcohol (PTBF‐IPA), n ‐Propanol (PTBF‐NPA), n ‐Butanol (PTBF‐NBA) and tert ‐Butanol (PTBF‐TBA) were synthesized and characterized. Glass transition temperature and adhesive property (lap shear strength) retention were found to be superior by 43% and 75%, respectively, for PTBF‐NBA‐based contact adhesive upon repeated testing. This inspired us to investigate the observation through molecular simulations and experimental measurements. This paper unveils an unexplored potential of these resins viz., self‐assembly in solid state, which is an intriguing phenomenon in molecular dynamics since the mechanism cannot be explained by a single category of molecular interaction. The mechanisms and impact of this self‐assembling phenomenon on practical application in an adhesive system have been thoroughly examined and correlated. The studies revealed that the chain motif (chain length and branching) influenced the type and extent of supramolecular interactions including hydrogen bonding and hydrophobic interactions, leading to self‐assembly and consequent physical, thermo‐physical, mechanical, and interface properties. Among the different alkyl homologues used for end‐capping, n‐ Butyl modified 4 ‐tert ‐Butylphenolic resin (PTBF‐NBA) exhibited the strongest hydrogen bonding, mediated through crystallization and van der Waals interactions, which resulted in widely differing physical and mechanical properties. It is unequivocally proven that the adhesive processed using PTBF‐NBA bears commendable capability. Also, it is evident that as branching of the end‐capped alkyl chain increased, the effect of hydrogen bonding with phenolic hydroxyl groups became less prominent. Thus, this work opens up new avenues for supramolecular interaction‐facilitated applications in interfacial chemistry.

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