Novel polyurethane coating technology through glycidyl carbamate chemistry

Abstract

Glycidyl carbamate chemistry combines the excellent properties of polyurethanes with the crosslinking chemistry of epoxy resins. Glycidyl carbamate functional oligomers were synthesized by the reaction of polyfunctional isocyanate oligomers and glycidol. The oligomers were formulated into coatings with several amine functional crosslinkers at varying stoichiometric ratios and cured at different temperatures. Properties such as solvent resistance, hardness, and impact resistance were dependent on the composition and cure conditions. Most coatings had an excellent combination of properties. Studies were carried out to determine the kinetics of the curing reaction of the glycidyl carbamate functional oligomers with multifunctional and model amines. Detailed kinetic analysis of the curing reactions was also undertaken. The results indicated that the glycidyl carbamate functional group is more reactive than a glycidyl ether group.T hermosetting epoxy and polyurethane polymer systems are widely used in many applications, including protective coatings, composite materials, and adhesives. These systems involve the reaction of functional polymers or oligomers with other materials containing mutually reactive groups. The composition of the reactants used determines the final properties of the thermoset coatings. Epoxy coatings generally exhibit good corrosion performance while polyurethane systems result in coatings having good toughness, abrasion resistance, and durability. Glycidyl carbamate chemistry has the potential of combining epoxy and polyurethane technology into a single system and has been shown to improve toughness in epoxy-amine systems. 1Reactions of amine with oxirane will occur at different rates depending on reactivity of the active amine hydrogen 2 and stoichiometric concentration of the amine relative to oxirane. 3,4 Amines used with epoxy resins are primary, secondary, or tertiary amines. Tertiary amines can, in turn, catalyze epoxide homopolymerization 5 (etherification). Amine structure also plays a factor in the overall reactivity of the primary and secondary amines. Reactivity is a function of steric factors 6,7 and amine basicity. 7-13 Amine reaction mechanisms using tetraglycidyl-4,4'-diaminodiphenylmethane (TGDDM) are also established in literature. 6,14-16 TGDDM reactions demonstrate that epoxide type also influences kinetics and deviates from diglycidyl ether bisphenol A (DGEBA) resins. 4,6 In this study, we will examine the crosslinking of trifunctional glycidyl carbamate resins with several amines.The glycidyl carbamate (GC) group is readily synthesized from the reaction of an isocyanate with glycidol 17 ( Figure 1). Two types of intermolecular reactions are possible with the glycidyl carbamate group. The first is the reaction of the oxirane with the amine and the second is the selfcrosslinking reaction. We have seen from earlier work that the self-crosslinking reaction in the absence of amine forms a thermoset coating with an excellent combination of properties. 18 In the presence of amine ...

The influence of structural modification and composition of glycidyl carbamate resins on their viscosity and coating performance

“…Figure 1 is a schematic representation of the reaction for the synthesis of GC resins. 8 The synthesis of GC resins can be highly exothermic and can become uncontrolled if appropriate heat transfer techniques are not implemented. Beside this, the amount of catalyst added and the temperature at which the catalyst is added can influence the exothermic nature.…”

“…8 However, BGC resin has a very high viscosity in the range of 3210000-3680000 mPa.s. The high viscosity of the resin is probably due to the large number of hydrogen bonding groups (-NH and -C=O) in the resin structure which could facilitate the formation of a dense network of inter chain hydrogen bonds.…”

“…An excellent combination of mechanical and chemical properties has been shown with GC coatings. 8 However, these GC resins have very high viscosity-in the range of millions of mPa.s-and a significant amount of organic solvent is required to achieve suitable application viscosity. Thus, it is of interest to determine if the resins can be modified to yield lower viscosity.…”

In Coatings, Adhesives, and Laminates

“…Oligomeric dimethylol propionic acid carbamate and citric acid carbamate formulated into clearcoats with melamine formaldehyde resin displayed higher solids, lower VOCs, comparable etch resistance, and better scratch and mar resistance than 2K polyurethane clearcoats [47] . Coatings with excellent performance characteristics have been reported by crosslinking oligomeric glycidyl carbamate with multifunctional amines [48] . Carbamates dispersed in amino resins are used in powder slurry compositions [49] .…”

Thermal and surface properties of hybrid materials obtained from epoxy-functional urethane and siloxane

“…Obtaining of a lower viscosity system by employing epoxy-functional urethane oligomer which at later stages is crosslinked by means of an amine at the presence of functionalized polysiloxane has a beneficial pro-environmental effect involving reduction of volatile organic compounds (VOC) in the final product. While synthesis of polyurethane thermosets from urethane derivatives containing epoxy groups has been reported [14,15], this approach so far has not been employed in obtaining of hybrid poly(urethane-siloxanes). Additionally, we employed a novel type of functionalized polysiloxane with a comb-like chain structure, which has rarely been used for polyurethane modification [16].…”