Crosslinking alkyd resins

The synthesis of alkyd resins using vegetable oils proceeds in two stages. For example, pentaerythritol, the tetraol of choice and mainly responsible for the degree of branching of the alkyd [64], and a vegetable oil are reacted to form an ester by transesterification. Then, a slight excess of phthalic anhydride is added to obtain a crosslinked alkyd resin (Fig. 3.21) [65]. Both reactions are monitored by acidity and viscosity measurements [66]. 

Miniemulsion polymerization enables to incorporate water-insoluble materials such as resins, organic pigments, polymers, etc into the polymer matrix. The additive seed allows to control the particle number and particle size during the production process. Furthermore, miniemulsion polymerizations and copolymerizations carried out with acrylic and methacrylic monomers in the presence of unsaturated alkyd resins lead to the production of stable hybrid latex particles containing grafted and crosslinked alkyd resin/acrylic products as coating polymer [114]. In the reaction, the multifunctional resin acts as a hydrophobe as well as the costabilizer of the miniemulsion. 

Idealised crosslinking reaction of UF resin with alkyd resin... 

Polyester-based networks are typically prepared from polyester prepolymers bearing unsaturations which can be crosslinked. The crosslinking process is either an autoxidation in the presence of air oxygen (alkyd resins) or a copolymerization with unsaturated comonomers in the presence of radical initiators (unsaturated polyester resins). It should also be mentioned that hydroxy-terminated saturated polyesters are one of the basis prepolymers used in polyurethane network preparation (see Chapter 5). 

Urethane alkyds and urethane oils are oil and alkyd resin-modified polyurethanes dissolved in a volatile solvent. Upon application and solvent evaporation, the coating is crosslinked and cured via oxidation by atmospheric oxygen. 

Another commercially important crosslinking process that involves unsaturated polymer precursors is the so-called drying of alkyd resins in paints. This process is not drying at all, at least not in the sense of mere loss of solvent to leave behind a solid residue. Instead, the main process is the conversion of high relative molar mass molecules to a crosslinked structure via... 

There are over 400 different commercial alkyd resin formulations based on phthalic anhydride used in the coatings business. Alkyd resins for paints are made by reacting phthalic anhydride with a poly-alcohol (usually from naturally occurring sources rather than synthetic) that contains unreacted double bonds. The paint dries by the resin crosslinking through reaction of the double bonds under the influence of oxygen in the air. 

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. 

Today, glycerol has over 2000 different applications, in cosmetics, pharmaceutics, foods and drinks, tobacco, paper, inks and printing colors, the production of phthalic and maleic alkyd resins and crosslinked polyesters, and as a hydraulic agent. Polyglycerols have a wide range of applications as emulsifiers, and technical esters of glycerol with fatty acids are used as synthetic lubricants [4]. 

Of technical importance are radically crosslinking reactions on finished articles of polyolefins by means of electron beams in order to increase, for example, the thermostability. The technical importance of networks consisting of polydienes and other rubbers, polyurethanes, formaldehyde resins, alkyd resins, and silicones has already been explained in Sects. 1.3.3.3,4.1 and 4.2. 

Another way of producing highly crosslinked polyesters (see Exercise 64) is to use glycerol. Alkyd resins are a polymer of this type. The polymer forms very tough coatings when baked onto a surface and is used in paints for automobiles and large appliances. Draw the structure of the polymer formed from the condensation of... 

From the present study and the studies of other investigators (discussed earlier), it is clear that crosslinked networks in many epoxy resins and in some alkyd resins are heterogeneous in nature. 

Figure 17.9 Radical crosslinking of urethane alkyd resins...

Uses Ureth for high gloss coatings, floor sealers, wood coatings, concrete impregnation for interior use crosslinking agent with alkyd resins for two-component sterns... 

Features Used in polyester, acrylic, and alkyd resins which are crosslinked with melamine resins... 

Uses Alkyd resins paints dynamite ester gums perfumery lubricants softener bacteriostat penetrant emollient antifreeze prod, of antibiotics plasticizer for regenerated cellulose film, sodium silicate foundry resins solvent (printing inks) humectant (tobacco, starch adhesives, textile sizes) solvent, humectant, plasticizer, bodying agent for foods, food pkg., cosmetics plasticizer, solvent, solubilizer, preservative for pharmaceuticals PU crosslinker heat costabilizer (PVC) sweetener preservative plasticizer in food-contact coatings Use Level 0.2-65.7% (topicals), 1-50% (liq. orals), 50% (parenterals), 7-10% (dentifrices), 0.5-3.0% (ophthalmics)... 

Uses Conditioner alkyd resin comonomer mfg. of varnishes, synthetic drying oils, urethane foams and coatings, silicone lube oils, lactone plasticizers, textile finishes, surfactants, epoxidation products crosslinking agentfor PU reactive diluent for radiation-cured inks, lacquers heat costabilizer for PVC in food-pkg. adhesives in food-contact coatings... 

Both paints and adhesives are commonly formulated as polymer blends or grafts. In fact, some compositions resemble semi-IPN s or AB crosslinked copolymers (Section 8.7). For example, epoxy adhesive resins are often cured with polyamides (Bikerman, 1968). The product is tougher than materials cured with low-molecular-weight amines, possibly because of a separate amide phase in this AB crosslinked copolymer. A more complex molecular architecture is exhibited by the alkyd resins common in oil-based paints (Martens, 1968, Chapters 3 and 4). The major component is a polyester, which often forms a network structure on drying. The polyester component is reacted with various drying oils, such as linseed oil or tung oil (Martens, 1968, Chapters 3 and 4). These oils form an ester link to the polyester structures and also polymerize through their multiple double bonds. Latex paints always contain thickeners, such as cellulosics, poly(acrylic acid), casein. 

Uses Mfg. of nylon and polyurethane foams intermediate for paints prep, of esters for use as plasticizers and lubricants alkyd resin comonomer starch crosslinking agent buffer in cosmetics adhesives textile treatments wet str. paper resins synthetic flavoring agent, leavening agent, acidulant, buffer, neutralizer in foods baking powders buffer, neutralizer in pharmaceuticals... 

---