Modifications of alkyd resin

Despite the wide range of properties of unmodified alkyd resins mentioned above, alkyds suffer from some inherent limitations. In general, coatings based on alkyd resins have poor water, alkali and chemical resistance, yellowing tendency and poor exterior durability and gloss retention properties. In order to partly overcome 

Rosin modified Faster surface drying, adhesion, wetting, gloss 

Phenoiic modified Adhesion, resistance to water and corrosion 

Vinyiated Surface drying, water and chemical resistance, 

Acryiated Surface drying, weather resistance, hardness 

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These products are useful for modification of alkyd resins (qv), preparation of paint vehicles, and copolymeri2ation with other monomers. Substitution on the amino group occurs readily, giving bases stronger than the parent amines. 

Modification of Alkyd Resins by Blending with Other Polymers... 

Modification of alkyd resins with high proportions of silicones considerably reduces rates of attack, but the most spectacular extension of life is shown by fluorinated polymers such as polyvinylidene fluoride where erosion rates can be reduced to 0 -1 /tm/year. If this level of durability can be achieved an initial coating, if firmly adherent and free from any breaks, may often be expected to maintain protection over a metal substrate for the likely life of the structure. The considerably increased first cost, as compared with more conventional coatings, has to be balanced against the probable saving in maintenance costs or consequences of failure. 

MODIFICATION OF ALKYD RESINS BY BLENDING WITH OTHER POLYMERS 343... 

The main volume of d. goes into the manufacture of - polyamides. Modification of - alkyd resins is another application. 

Figure A. Effect of fatty acid modification on alkyd resin properties.

There are two main methods for preparation of alkyd resins. In the first one, called the fatty acid process, a free fatty acid is coesterified directly with the dibasic acid and the polyol at 200-240 °C. The reaction may be carried out without a solvent by first heating in an inert atmosphere. At the end, an inert gas may be blown into the resin from the bottom of the reaction kettle to remove water and unreacted materials. As a modification of this, a small quantity of a solvent may be used to remove water of esterification continuously by azeotropic distillation with the aid of moisture traps. 

The main use for phenolic resins is in oleoresinous varnishes. Apart from the chemical-resistant finishes produced with epoxy resins (Chapter 14), other outlets include modification of alkyds to improve resistance to water and alkali, combination with U/F resins (Chapter 13) to provide metal coatings and combination with polyvinyl formal or butyral resins to produce wire enamels. 

Silicone modification of alkyds, epoxies, acrylics and other coating resins are well-known for imparting improved gloss retention and weather resistance [1]. Copolymers of structure (Siloxane) = SiOCH2-(Resin) are prepared in organic solvents with relatively large proportions of silicone, since performance is approximately proportional to the silicone content. 

Significant improvements have been observed in the properties of alkyd resin after modification (grafting) with acrylates. The incorporation of MMA into alkyd at a level of 30-40% yields a binder suitable for formulation of high performance exterior paints [80]. 

A potential problem for direct application of vernonia oil in alkyd formulations is an anticipated reaction between its epoxy groups and the terminal carboxyl groups of the alkyd resins. Our results show that vernonia oil does not change the can stability of the formulations. Obviously, the epoxy groups of vernonia oil have low reactivity and do not react with the free carboxyl groups of the alkyd resins under test conditions for can stability. The low reactivity of the epoxy groups of vernonia oil has been confirmed by additional experiments (see Section 4. Modification of Epoxy Resins). 

Alkyd resins first found commercial application over 50 years ago, but, even with the wide array of other polymers that have appeared in more recent years, they still rank as the most important coating resin. The fundamental building blocks of alkyds are oils or fatty acids, dibasic acids and polyhydric alcohols. Although they are few in number, the permutation and combination possibilities of only these three basic components are enormous and there is no resin-forming reaction which lends itself to greater useful variation and modification than the formation of alkyd resins. 

In coatings and adhesives, isocyanates may be used as reactive species at room temperature, or by modification, at high temperatures. Most urethane varnishes, however, are probably solutions of alkyd resins modified by reaction of free hydroxyl groups with diisocyanates. 

Although blending with other coating resins provides a variety of ways to improve the performance of alkyds, or of the other resins, chemically combining the desired modifier into the alkyd stmcture eliminates compatibiUty problems and gives a more uniform product. Several such chemical modifications of the alkyd resins have gained commercial importance. 

Stripping of top coats soaked by rain or sea-water has occurred with alkyd-resin-based paint systems, mainly on ships. The risk of such intercoat failure is reduced if the time interval between application of coats is reduced, but is best controlled by modification of the alkyd resin with a proportion of a different material. 

Several applications of hyperbranched polymers as precursors for synthesis of crosslinked materials have been reported [91-97] but systematic studies of crosslinking kinetics, gelation, network formation and network properties are still missing. These studies include application of hyperbranched aliphatic polyesters as hydroxy group containing precursors in alkyd resins by which the hardness of alkyd films was improved [94], Several studies involved the modification of hyperbranched polyesters to introduce polymerizable unsaturated C=C double bonds (maleate or acrylic groups). A crosslinked network was formed by free-radical homopolymerization or copolymerization. 

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