Influence of structure on the coating properties and viscoelasticities of the oil-soluble phenol resin films

Abstract

As unsubstituted phenol (C₆H₅OH)-formaldehyde resin has a strong polarity, it is insoluble in drying oil.
On the contrary as para alkyl and aryl substituted phenols are two functional and cannot form crosslinked_or three-dimentional structure and the substituent group has the oil-soluble property, the substituted_phenol formaldehyde resins are oil soluble.
The 100 % phenol resin varnishes are used widely as the insulation varnishes and alkali resistance coating because of the excelent drying property, hardness, humidity resistance and chemical resistance.
The reactivity of phenol with formaldehyde and the physical and chemical properties of the oleoresinous, varnishes depend greatly upon the size, the sort, and the property of the substituent group and the phenol-formaldehyde mol ratio.
Five kinds of the para alkyl and aryl substituted phenol-formaldehyde resins and four kinds of the octyl phenol formaldehyde resins varied in formaldehyde/phenol mol ratio (both series are novolac type resins). were synthesized and the oil solubility, the oil reactivity and the coating properties of oleoresinous, varnishes were studied. The dynamic elasticity (E') and tan δ of oxidative-polymerized films were measured by Vibron Type II from room temperature to 200°C, and the relation of the chemical structure and viscoelasticity was studied.
The results are as follows.
(1) The order of reactivity of substituted phenol with formaldehyde is as follows. ρ-cresol>ρ-tert butyl phenol>ρ-phenyl phenol>ρ-octyl phenol>ρ-nonyl phenol.
This order depends on the inductive effect of substituents.
(2) The longer the chain length of substituents of 100% phenol resin is, the better is the oil solubility.
(3) The higher the phenyl nucleus concentration of phenol resin and the more formaldehyde/phenol mol ratio are, the weaker is the reactivity between phenol resin and oil (gel time).
(4) The relation on the oleoresinous varnishes is as follows. The higher the phenyl nucleus concentration and formaldehyde/phenol mol ratio are, the better are the drying property and the hardness, and. the smaller are the solubility and the degree of swelling mineral spirits and aceton on its cured films, and the higher are the glass transition temperature (Tg) and the elasticity at high temperature (En'). When kinds of oil and oil length are the same, the degree of crosslinking should be chemically same. Whereas on the results of experiment Tg and En' varied because of the physical crosslinking. When the resin is rigid and the intermolecular cohesive force is stronger, the apparent degree of crosslinking becomes higher.