Reactive acrylic Diluent

Figure 1. EB conversion with reactive acrylate diluents...

Materials. The photopolymerizable resin was made of 3 main compounds (i) a photoinitiator that generates free radicals upon exposure to UV radiation (ii) a prepolymer end-cap with acrylate groups (iii) a reactive acrylic diluent to lower the viscosity of the resin. For most experiments, the selected photoinitiator was a,a dimethoxyphenylacetqihenone, DMPA (Irgacure 651 from Qba-Geigy), because of its high initiation efficiency. 

The hardness of coatings based on bisphenol-A-epichlorhydrin containing reactive acrylate diluents such as ) -carbonyl ethylacrylate or isobornylacrylate initially increases with time on exposure to UV radiation and then decreases [675]. 

Uses Reactive epoxy diluent for exposed aggregates, potting, flooring, casting, tooling, laminates, solv.-free coating systems, fiber-reinforced composites stabilizer for chlorinated hydrocarbons adhesion promoter for PVC, acrylic resins, PU Manuf./Distrib. Aldrich Raschig... 

Methoxy tripropylene glycol acrylate diluent, reactive fiber-reinforced composites Glycidyl ether 100 diluent, reactive floor adhesives N-Vinyl-2-caprolactam diluent, reactive flooring Butyl glycidyl ether... 

In tuning the properties the reactive diluent plays an important role as well. For instance, when the side chain of the acrylate diluent is changed from linear aliphatic to cycloaliphatic, the hardness of the network will increase without affecting the flexibility of the network. The hardness increases as well when the overall functionality of the diluents is increased so going from a monofunctional to a difunctional diluent results in a large increase in hardness. However, in this case the network becomes harder and more brittle. 

The disadvantages of epoxies include their two-component (or heat-cure) form, reduced performance on oily snrfaces, their inherent lack of toughness, and limited performance on thermoplastics reactive acrylics, cyanoacrylates and polyurethanes are usually superior in such departments. Also, the base resins are relatively high-molecular-weight species, so it is not possible to formulate very-low-viscosity adhesives unless reactive diluents are added, with a corresponding drop in performance. 

Pure UV-reactive organic diluents or mixtures from such origin are used in preparing photoreactive, solvent-free A-PSAs. The selection of suitable solvents is limited due to the following requirements. The photoreactive diluent has to exhibit Good solubility and compatibility with acrylic polymers, prepolymers and oligomers p- Excellent UV reactivity... 

A typical formulation of a photocurable composite resin contains four basic components a radical-type photo initiator, an acrylate functionalized oligomer, a reactive diluent and the clay mineral filler. The photoinitiator is usually an aromatic ketone which cleaves into two radical fragments upon UV exposure. The telechelic oligomer consists of a short polymer chain (polyurethane, polyether, polyester) end-capped by the very reactive acrylate double bond. An acrylate monomer is generally used as reactive diluent to reduce the resin viscosity. Figure 7.2 shows some typical compounds used in UV-curable acrylic resins. Different types of phyllosilicates were selected as mineral filler an organophilic clay (Nanomer I-30E from Nanocor), native hydrophilic clays (montmorillonite KIO and bentonite) and a synthetic clay (beidellite). 

A great variety of resia formulations is possible because other thermosets, such as epoxies or acrylates, and reactive diluents, such as o-diaUyl phthalate [131-17-9] triaUyl cyanurate [101-37-17, or triaUyl isocyanurate [1023-13-6J, can be used to further modify the BT resias. The concept is very flexible because bismaleimide and biscyanate can be blended and copolymerized ia almost every ratio. If bismaleimide is used as a major constituent, then homopolymerization of the excess bismaleimide takes place ia addition to the copolymerization. Catalysts such as ziac octoate or tertiary amines are recommended for cure. BT resias are mainly used ia ptinted circuit and multilayer boards (58). 

Since the commercially available epoxy acrylate is extremely viscous, it is necessary to thin the formulation with a reactive diluent. A mixture with satisfactory viscosity for brush-on application contains about 45% diluent. Of the diluents tested, TMPTA (trimethylolpropane triacrylate) proved most successful. 

The formulation which performed best contained 1% BAPO/HMPP photoinitiator, 50% acrylate ester of bisphenol A epoxy (Ebecryl 3700), 45% reactive diluent, 5% pigment, and a few drops of the fluorocarbon surfactant FC-171. 

It was found, when an attempt was made to conduct ship trials that the paint applier would be required to wear long sleeves, gloves, safety glasses, and a protective face shield. It is also a requirement that an eyewash fountain be nearby. These requirements were imposed because acrylates are skin, eye and respiratory tract irritants, but the problem lies mostly with the acrylated reactive diluent rather than with the acrylated resin (2,3). To avoid these problems, tests have been performed with use of trimethylolpropane trimethacrylate (TMPTMA) as a replacement for TMPTA. TMPTMA has been shown to be much less of an irritant than TMPTA, and is used in dental restorations. 

Two of the main considerations in the development of totally reactive liquid photopolymer systems are the resin(s) and the reactive diluents (monomers). The resins play a major role in determining the end properties and therefore the applications of the cured polymer. The reactive diluents are used to provide a fully reactive system with the appropriate reactivity, viscosity, coatability before cure and the desired crosslink density, chemical resistance and dielectric character once it is cured. The pho-toreactive monomers most commonly used are acrylate based derivatives because of the properties they impart, and their high reactivity and wide solubility range. 

A typical UV-cured coating has three or sometimes four main ingredients (1) a multifunctional acrylate monomer, (2) a reactive oligomer, (3) possibly a monoacrylate as reactive diluent, and (4) a photoinitiator (Table 2.20). 

The acrylate or methacrylate functional PIBs have also been used in UV-curable solventless coatings formulation in the presence of reactive diluents (multifunctional acrylate or methacrylate esters) and a UV-sensitizer [104]. The products were transparent, flexible films, with very little extractables, in which hard polyacrylate or polymethacrylate domains were dispersed in the soft PIB matrix. Tensile strength and ultimate elongation have also been obtained. 

A typical EB curable formulation will generally consist of a relatively high molecular weight solid or semi-solid difunctional acrylic resin reduced to application viscosity with combinations of liquid mono- and multifunctional acrylic monomers. These acrylic monomers, along with a few other selected polymerizable monomers, serve as reactive diluents and allow formulation of solvent-free compositions. Usually, small amounts of additives are also used in order to provide special properties, such as slip. 

Measurement of conversions of various formulations at various EB doses can be used to rank the reactivity of the formulation. A particularly useful procedure has been to prepare a standard mixture of an acrylate resin with various reactive diluent monomers in order to compare the volatility and reactivity of new monomers. For these studies, a mixture of 40 weight % of a Bis-phenol A epoxy dlacrylate resin with 60% of the test liquid monomer has proved convenient. A viscosity measurement of the mixture also provides information on the relative viscosity reducing ability of the test monomer. Illustrative examples of these measurements are shown in Table I and Figure 1. Mote from these examples that a monofunctional monomer, Monomer B, can be used to provide the low volatility and high reactivity typical of the multifunctional monomers, while also serving to reduce the crosslinking. Many other available monofunctional monomers are found to be either more volatile or less reactive than Monomer B. 

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