Acrylate oligomers

The free radicals then initiate curing by attacking residual double bonds in acrylic oligomers and monomers, or in styrene and unsaturated polyester resins. Since most pigments absorb u.v. radiation and can prevent it reaching sufficient photoinitiator molecules, this technique is best suited to transparent coatings or thin pigmented layers (e.g. inks). 

Coating materials may be based on short or medium-oil alkyds (e.g. primers for door and window frames) nitrocellulose or thermoplastic acrylics (e.g. lacquers for paper or furniture finishes) amino resin-alkyd coatings, with or without nitrocellulose inclusions, but with a strong acid catalyst to promote low temperature cure (furniture finishes) two-pack polyurethanes (furniture, flat boards) unsaturated polyester resins in styrene with free-radical cure initiated by peroxides (furniture) or unsaturated acrylic oligomers and monomers cured by u.v. radiation or electron beams (coatings for record sleeves paperback covers, knock-down furniture or flush interior doors). 

Unsaturated acrylic oligomers are made from unsaturated acrylic monomers. For example, an epoxy acrylate may be made by reaction of acrylic acid with epoxy resin. 

Figure 12 shows the HPGPC DRI traces of four high solids acrylic oligomers. The results of paint performance evaluation... 

As a design to develop a polyvinyl-type poly(sodium carboxylate), acrylate copolymers containing hydroxyl or carbonyl groups which are susceptible to the enzymatic reaction, were prepared. It is presumed that the copolymer is first cleaved at a hydroxyl or carbonyl group as in the case of PVA, then the resultant acrylate oligomer is further assimilated by the microbes. The biodegradation of oligomeric acrylic acid (11), in fact, occurs as shown in Table I. 

The curing reaction of acrylates is typical of vinyl monomers. Therefore, the degree of double-bond conversion is the measure of the degree of cure. The best results are obtained when using oligomers as binders and monomers as reactive thinners. Examples of difunctional and polyfunctional acrylates are in Table 4.4. A partial list of the most common acrylate oligomers is below. - ... 

Improved heat-resistant UV compositions for optical fiber applications These compositions are nonurethane UV cure compositions that have neither carbamate moieties nor long-chain poly(alkylene oxide) soft segments and exhibit inherently better thermal stability measured by thermogravimetric analysis (TGA) than typical coatings for optical fibers based on urethane acrylate oligomers. 

A partial list of most common acrylate oligomers follows.14 39 40... 

Similarly to UP resins, VE resins consist of an unsaturated oligomer dissolved in styrene. The unsaturated oligomer is based on the epoxy chemistry (Sec. 2.2.4). When one mole of a DGEBA monomer is reacted with 2 moles of (meth)acrylic acid, an a, oo-di(meth)acrylate oligomer is obtained ... 

The technical success of the UV-drying inks may be attributed to the introduction of a number of types of acrylated oligomer and photo-initiator. The broad categories of acrylated oligomers include polyesters, epoxies, urethanes, ethers, and polyacrylates. Photo-initiators generally are derived from compounds that on exposure to UV light cleave into free radicals or abstract hydrogen to form free-radical species. 

Figure 103 shows the sequence of curing a letterpress ink, with benzilketal (an initiator often used) and epoxydiacrylate as acrylate oligomer. Free-radical polymerization of an acrylate oligomer can be initiated by both the methyl and benzoyl radical it has been found that the latter makes the greater contribution, as shown in Figure 104. 

Epoxy acrylate oligomers that are used in uv/EB curing are very low-viscosity systems with high vapor pressures. Within this group of oligomers, there are several major subclassifications aromatic difunctional epoxy acrylates, acrylated oil epoxy acrylate, novolac epoxy acrylate, aliphatic epoxy acrylate, and miscellaneous epoxy acrylates. Characteristics of these various classes are summarized in Table 4.8. 

In general, the acrylates classified as "oligomers" are too high in viscosity for extensive use in the very low viscosity formulations required by UV curable inkjet inks. However, acrylate oligomers do possess several properties that can be very beneficial, even when used at additive levels. 

An acrylic oligomer is a higher molecular weight functional acry-lated molecule which may be, for example, polyesters of acrylic acid and methacrylic acid. Other examples of acrylic oligomers are the classes of urethane acrylates and urethane methacrylates. Urethane acrylates are manufactured from aliphatic or aromatic or cycloaliphatic diisocyanates or polyisocyanates and hydroxyl-containing acrylic acid esters. 

In an earlier investigation by Yang [1] triblock urethane acrylate oligomers terminated with acrylic acid were prepared and used in curable pressure sensitive adhesive compositions. 

Moisture curable n-butyl acrylate oligomers materials containing a dimethox-ymethyl hydrosUane termini were prepared by Ohshiro [2] and the author [3] that had good heat resistance, weatherability, oil resistance, and low staining properties. 

Berlin AA, Korolev GV, Kefeli TYa, Sivergin YuM (1983) Akrilovye oligomery i materialy na ih osnove (Acrylic oligomers and materials on thdr base) Nauka, Moscow, p232... 

Figure 3.84. Voxel obtained by irradiation of a mixed urethane acrylate oligomer and a urethane acrylate monomer in the presence of a mixture of benzoyl cyclohexanol and morpholino phenyl amino ketones at 780 nm using a 150-fs pulsed Ti sapphire mode-locked laser operating at 76 MHz, where light was focused by a 1.4 numerical aperture objective lens (a) scanning electronic microscopic images of the voxel and (b) longitudinal and lateral voxel size as function of the exposure time. (From Ref. [580] with permission of the American Institute of Physics.)...

The uncured conformal coatings are clear, transparent liquids with viscosities of 700 to 1400 cp at 25°C. A typical composition which has a viscosity of 820 cp at 25°C consists of 43 wt % of a high viscosity urethane acrylate oligomer, 49 wt % of a low viscosity monoacrylate diluent, 5 wt % of a polyfunctional thiol, 2 wt % of benzopinacol and 1 wt % of alpha, alpha-dimethoxy-alpha-phenylacetophenone. A trace amount of a fluorescent dye may be added, if desired, to facilitate inspection of the finished coating. 

The most common acrylic polymer is polymethyl methacrylate, which is obtained by polymerization of methyl methacrylate (MMA). The material consists of a highway-grade aggregate and a matrix produced by cross-linking MMA with trimethylol propane trimethacrylate or other polyfunctional acrylic oligomers. 

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