Hydroxy functionalized acrylic

Kinetic Model. All of the coatings used in this study are hydroxy functional acrylic copolymers crosslinked with melamine formaldehyde crosslinkers. The chemistry of crosslinking with melamine formaldehyde crosslinkers has been discussed in detail elsewhere (5.11). The type and rate of the reactions depend primarily on... 

Polyurethane-acrylic coatings with interpenetrating polymer networks (IPNs) were synthesized from a two-component polyurethane (PU) and an unsaturated urethane-modified acrylic copolymer. The two-component PU was prepared from hydroxyethylacrylate-butylmethacrylate copolymer with or without reacting with c-caprolactonc and cured with an aliphatic polyisocyanate. The unsaturated acrylic copolymer was made from the same hydroxy-functional acrylic copolymer modified with isocyanatoethyl methacrylate. IPNs were prepared simultaneously from the two-polymer systems at various ratios. The IPNs were characterized by their mechanical properties and glass transition temperatures. 

A second route (route B in Fig. 1) relies on an initiation process with an (meth)acryl hydroxyl compound and is adopted from the chemical ROP of lactones. The controlled character of these polymerizations ensures a virtually quantitative initiation and thus incorporation of hydroxy-functional initiator (e.g., acrylate) into the polymer chain. However, this is not automatically the case for lipase-catalyzed ROP due to the different mechanism. The latter follows an activated monomer mechanism in which the lipase activates any carbonyl group of a carboxylic acid derivative present in the system. It has recently been shown that acrylation using hydroxy-functional acrylate initiators like hydroxy ethyl(meth)acrylate (HEMA or... 

Urethane acrylates Urethane acrylates are formed by the reaction of isocyanates with hydroxy-functional acrylate monomers. After UV cure, they produce tough, flexible materials, which exhibit a good abrasion resistance. 

It is common in acrylic structural adhesives to use oligomers that have a desirable backbone and are terminated with free-radical-polymerizable bonds. A variety of isocyanate-terminated polyurethanes can be adapted to use in acrylic structural adhesives by reacting the terminal isocyanates with a hydroxy functional acrylic monomer such as 2-hydroxyethyl methacrylate.76,92 93... 

The clear-coat is referred to as a two-component (2K) clear-coat when isocyanate is used as the cross-linker. The isocyanate must be added to the hydroxy functional acrylic just prior to spray application to prevent premature cross-linking (or gelation). For this reason, the two-part mixing is referred to as 2K. Cure conditions for isocyanate-cured clear-coat range from room temperature (car refinish) to 250°F for 30 min. 

Some commonly used graft monomers are acrylates, such as methacrylic acid (to enhance adhesion), acrylic esters and hydroxy functional acrylates (that can couple with polar materials, as wood). Maleic anhydride and n-vinyl pyrrolidone are also used, but with care taken to avoid potential volatilization during processing. The former is used as an adhesion promoter, the latter to enhance bio-compatibility. Specific properties depend both on the backbone or base material that is being grafted and on the graft monomer (Fig. 1). 

Figure 3. Elementary crosslinking and hydrolytic degradation reactions Involved In melamine formaldehyde ONCHjOCH.) crosslinking reactions with hydroxy functionalized acrylic copolymers (ROH).

An infrared analysis method was developed for determining the hydroxyl number in samples of polyesters formed by the copolymerisation of a hydroxy-functional acrylic oligomer with adipic acid and 1, 6-hexanediol. The method was shown to be sufficiently accurate, to be faster than chemical analysis and to reduce exposure to irritating, toxic and corrosive chemicals. 9 refs. 

An analogous approach involves particles of dimeric TDI, which have been surface deactivated by an amine or water, and then dispersed in a polyol.The polyols used in the examples given were derived from hydroxy-functionalized acrylate resins. The two-phase mixtures are said to be stable for at least three months, and can be readily cured at 70-180°C. Presumably the particles melt and the two phases mix on heating, which causes the system to react. 

Diethyl malonate blocked diisocyanates cross-fink polyols at 120°C for 30 min. The reaction with alcohols does not srield urethanes, rather transesterification occurs (134), and reaction with amines srields amides, not ureas. Storage-stable coatings can be formulated by using monofimctional alcohol in the solvent (135). Clear coats for automobiles that have both excellent environmental etch and abrasion resistance have been formulated with a combination of a hydroxy-functional acrylic resin, malonic ester blocked HDI and IPDI trimers, and an ME resin (136). 

Tris(alkoxycarbonylamino)triazine (TACT), a mixed methyl and butyl carbamate derivative of melamine, acts as an alcohol blocked isocyanate (21). TACT is much more reactive than conventional alcohol blocked isocyanates, since it is activated by the triazine ring. It cross-links hydroxy-functional acrylics at 125°C in 30 min, comparable to (or lower than) oxime blocked isocyanates. The reaction is not catalyzed by tin compounds it is catalyzed to a small extent by dodecylbenzene sulfonic acid. 

In special cases only one method is available, namely in those cases in which the higher selectivity of the Outside-in method is required. For instance, in the case of a triol the Inside-out method will result in a gel, whereas such a three-functional urethane acrylate can be made by the Outside-in method. An extreme example is that the Outside-in technology makes it possible to use hydroxy-functional acrylics (polymers with at least ten OH groups per chain) as the polymers in the preparation of urethane acrylates. 

The solvent-borne clearcoat is spray-applied over the basecoat at a dry film thickness of 1.8 to 2.0 mils. The clearcoat, responsible for UV protection, chemical resistance, chip resistance, and so on, is most often composed of a hydroxy functional acrylic binder together with a melamine or an isocyanate cross-linker. Ultraviolet light absorbers and hindered amine light stabilizers also are added to achieve better free-radical oxidative degrada-... 

Another route to the production of hydroxy functional acrylic is via a carboxy functional acrylic, which is subsequently post reacted with the glycidyl ether of Versatic acid (Cardura ElO, Shell chemicals), see Figure 4-3. 

Hydroxy functional acrylics are normally cured with amino resins or amino/epoxy resin combinations at temperatures ranging from 120°C to 150°C. Typical crosslinking reactions are shown in Figure 4-4. 

Hydroxy functional acrylics will cure with all types of amino resins, including urea formaldehyde, melamine formaldehyde (MF) and benzoguanamine formaldehyde types. Urea formaldehyde resins are faster curing and cheaper than the other two main types, but they are rarely used with acrylics due to inferior film performance (e.g. resistance properties and exterior durability). 

Alkyds can be used in combination with either acrylamide or hydroxy functional acrylics. Very often this results in an improvement in application solids. However, the alkyd must be carefully chosen, firstly in terms of compatibility with acrylics, and secondly from the point of view of what it will contribute to (or detract from) film performance. Clearly, the colour retentive alkyds are most likely to be selected so that the excellent colour and colour retention of the acrylic is not compromised. 

Cardura ElO based alkyds have been found to have excellent compatibility with both acrylamide functional and hydroxy functional acrylics . In general, a maximum level of 30% alkyd on solid binder is recommended, which can, depending upon the choice of alkyd, result in an increase in solids content and an improvement in exterior durability. 

Hydroxy Functional Acrylics for General Industrial Stoving Finishes by N Tuck PhD BSc... 

Hydroxy functional acrylics are used in general industrial (GI) stoving rinishes in two distinct capacities. They are used to impart highly durable finishes for exterior components such as tractor sheet metal and cabs, fenders for earth moving equipment, or as one coat finishes in more wide ranging metal finishing such as office furniture, irons, microwave ovens, toasters, food mixers and blenders. 

The second attribute is the formulatory flexibility of the hydroxy functional acrylic. A myriad of acrylics can be formulated by careful consideration of the following parameters ... 

The second component in the two pack is a polymeric multi functional isocyanate. The isocyanate group is extremely hydrogen acquisitive and will therefore abstract hydrogen from the hydroxy functional acrylic resin, forming a urethane link in the process. The multi functionality of the isocyanate ensures the formation of a network structure. Reactions take place at ambient temperatures or can be forced along at slightly above ambient temperatures, e.g. 60°C for 20 minutes as a typical cure cycle. 

V MAJOR EUROPEAN SUPPLIERS OF HYDROXY FUNCTIONAL ACRYLICS... 

Listed below are the major European resins manufacturers who offer hydroxy functional acrylics for cross linking with isocyanate adducts. 

---