Amine resins, hydrophobic-hydrophilic

Note that the highest IDT was obtained with the cyclopenta-methylenehydantoin resin derived from cyclohexanone. It is tempting to speculate that this inflexible alkylene moiety was ineffective in shielding the hydantoin ring, but subsequent comparison of the hydrophobic-hydrophilic balance of amine-cured resins appeared to rule out this explanation probably the stiff spiro structure contributed to the high Tg, just as it contributed to the high melting point of the resin itself (lie). 

Since the hydrophobic-hydrophilic balance of amine-cured resins was so sensitive to alkyl substituents on the hydantoin ring, it is not surprising that it was also sensitive to the hydrocarbon moieties of the amine curatives. The range of behavior depended on the resin substituents. For example, the already hydrophobic ethyl amyl substituted Resin Ilk showed moderate but significant increases in hydrophobicity when cured with cycloaliphatic, highly branched aliphatic, or formulated aromatic amines. See Table V. 

Silane coupling agents may contribute hydrophilic properties to the interface, especially when amino functional silanes, such as epoxies and urethane silanes, are used as primers for reactive polymers. The primer may supply much more amine functionality than can possibly react with the resin at the interphase. Those amines that could not react are hydrophilic and, therefore, responsible for the poor water resistance of bonds. An effective way to use hydrophilic silanes is to blend them with hydrophobic silanes such as phenyltrimethoxysilane. Mixed siloxane primers also have an improved thermal stability, which is typical for aromatic silicones [42]. 

A somewhat different aspect of the hydrophobic shielding effect of alkyl substituents was reflected in the relative hydrophilicity of aliphatic amine-cured resins. A standard room temperature-curing polyamine, triethylenetetramine (TETA), was used to cure a series of resins at room temperature. The... 

Steric factors - branching at or close to the hydantoin ring - raised the glass transition temperature while maintaining the shielding effect. Amines of different structures were used as room temperature curatives with a few representative resins, to observe the effect on hydrophilic-hydrophobic balance. Solvent effects were examined on aromatic amine-cured resins the most hydrophilic cured system proved to have the broadest range of lyophobicity. 

Polyacrylates as binders consist of copolymers of acrylate and methacrylate esters. Other unsaturated monomers (e.g., styrene and vinyltoluene) may also be incorporated, but usually to a lesser extent. Copolymers formed exclusively from acrylates and/or methacrylates are termed straight acrylics. The comonomers differ as regards the alcohol residues of the ester group, which also allow incorporation of additional functional groups. Choice of suitable monomers allows wide variation of the physical and chemical properties of the resulting polymer. Hydrophilicity, hydrophobic-ity, acid base properties as well as can be adjusted resins containing hydroxyl, amine, epoxy, or isocyanate groups can also be produced. 

Additional improvements on the degree of conversion of the adhesive systems were observed with new and less hydrophobic initiators of polymerization. Camphorquinone and aromatic amines are the most commonly used photoinitiator systems for light-activated dental resins, but they can be excessively hydrophobic making it difficult to activate the more hydrophilic monomers at the adhesive systems. The addition of alternative initiators such as 1-phenyl-1,2-propanedione (PPD), 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (Lucerin-TPO) and bisacylphosphine oxide (BAPO) improve resin polymerization within hydrophilic domains and reduce susceptibility to inactivation by... 

Not every molecule of epoxy present during the polymerisation is modified by reaction with the acrylic, as shown in Figure 2-22. Some epoxy is left unmodified and some acid functional acrylic resin is formed, which is not grafted onto an epoxy backbone. The molecules of epoxy which are grafted with acrylic perform an important function as they contain both hydrophobic and hydrophilic parts on them, which when neutralised with amine, give them the classical features of an emulsion stabiliser. They can be drawn with the ionised carboxylic acid groups on pendant side chains attached to the main epoxy backbone as shown in Figure 2-23. 

A wide variety of other specialty monomers are also used to provide specialized performance properties for coating applications. For example, amine functional monomers can be used to improve adhesion to aged alkyd substrates. Specialized monomers can also be used to improve exterior durability, for example VEOVA (vinyl ester of vesatic acid) monomers can improve the hydrolysis resistance of vinyl acetate polymers, and n-butyl methacrylate can be used to enhance the durabiHty of BA-MMA acrylics. Polymer hydrophobicity can be fine tuned by varying the levels of hydrophobic and hydrophilic monomers in the composition and styrene or ethyl hexyl acrylate are used to increase film hydrophobicity and reduce water permeability in BA-MMA systems. Specialty monomers are also used to provide specific chemical functionality to polymer compositions. For example, hydroxyethyl methacrylate can be used to provide hydroxyl functionality to acrylic resins, allowing these polymers to be used in cross-linkable thermoset coatings which cure via melamine chemistry. While specialty monomers are used at relatively low levels in polymer compositions, they frequently provide the performance features needed for the successful application of emulsion polymers in many coating areas. 

---