Reactive Diluent Monomers

As pointed out in the introduction, unsaturated polyester resins are commonly combined with reactive diluent monomers (Table 12.3). Styrene is most frequently used for this purpose.However, monomers such as methyl methacrylate, diallyl phthalate, triallyl cyanurate, vinyl toluene,a -methylstyrene, p-t rt-butylstyrene, and chlorostyrene have also been studied (Table 12.3), showing varying degrees of utility. 

Monomer Boiling point (°C) Volume shrinkage (%) Characteristics 

Styrene 145 15 Low cost, high reactivity, fairly good heat distortion temperature, high flex strength 

Vinyl toluene 171 12.5 Reduced volatility and shrinkage, high reactivity, more flexibility 

Chlorostyrene 187 12 Reduced volatility, low shrinkage and fast coreaction 

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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. 

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. 

Reactive Diluents Monomers and Their Performance Properties... 

Monomers. In radiation-curable systems, the solvent is replaced by reactive diluents (monomers) which are incorporated in the network during cross-linking. These monomers have two important functions they reduce the viscosity of the mixture and they strongly influence the physical and chemical properties of the final coating. Monomers can be divided into three groups ... 

Uses Curing agent reactive diluent monomer (UV EB resin) and modifier for radiation-cured coatings, inks, electronics applies., paints, textile finishes, adhesives, industrial and textile coatings Features Resists UV degradation... 

Unsaturated polyesters are based on macromolecules with a polyester backbone in which an unsaturated acid or combination of a saturated with an unsaturated acid are condensed with a glycol. A three-dimensional structure is produced when the macromolecule is crosslinked through the unsaturation. Commercial unsaturated polyester resin formulations, neglecting consideration of additives, initiators, extenders, and fibrous reinforcing materials, consist essentially of a linear resin, a crosslinking (reactive diluent) monomer (ca. 18-40 wt. %), and inhibitors to retard crosslinking until the resin is used by the fabricator. The simplest member of the polyester series, ethylene maleate (or ethylene fumarate), is prepared as follows ... 

Unsaturated polyester-acrylic acid mixtures have been polymerized in situ on polyester fibers to provide graft polymer sizes that are easily removed by neutralization with a base. This type of combination has also been claimed for producing photopolymerized printing plates.These two patents give examples of how unsaturated polyesters may be mixed and polymerized with unconventional reactive diluent monomers to meet new special needs. 

The major use of vinylpyrrohdinone is as a monomer in manufacture of poly(vinylpyrrohdinone) (PVP) homopolymer and in various copolymers, where it frequendy imparts hydrophilic properties. When PVP was first produced, its principal use was as a blood plasma substitute and extender, a use no longer sanctioned. These polymers are used in pharmaceutical and cosmetic appHcations, soft contact lenses, and viscosity index improvers. The monomer serves as a component in radiation-cured polymer compositions, serving as a reactive diluent that reduces viscosity and increases cross-linking rates (see... 

Glycidyl and Vinyl Esters. Glycidyl neodecanoate [26761-45-5] sold commercially as GLYDEXXN-10 (Exxon) or as CarduraElO (Shell), is prepared by the reaction of neodecanoic acid and epichl orohydrin under alkaline conditions, followed by purification. Physical properties of the commercially available material are given in Table 3. The material is a mobile Hquid monomer with a mild odor and is used primarily in coatings. Eor example, it is used as an intermediate for the production of a range of alkyd resins (qv) and acryHcs, and as a reactive diluent for epoxy resins (qv). 

Because of its low price, compatibility, low viscosity and ease of use styrene is the preferred reactive diluent in general purpose resins. Methyl methacrylate is sometimes used, but as it does not copolymerise alone with most unsaturated polyesters, usually in conjunction with styrene in resins for translucent sheeting. Vinyl toluene and diallyl phthalate are also occasionally employed. The use of many other monomers is described in the literature. 

This monomer has been used as the basis of a laminating resin and as a reactive diluent in polyester laminating resins, but at the present time its principal value is in moulding compositions. It is possible to heat the monomer under carefully controlled conditions to give a soluble and stable partial polymer in the form of a white powder. The powder may then be blended with fillers, peroxide catalysts and other ingredients in the same manner as the polyester alkyds to form a moulding powder. Similar materials may be obtained from diallyl isophthalate. 

At the downstream of the extrusion process a suitable reaction catalyst, reactive diluent, e.g., crosslinking monomer, is fed into the molten polymer mix. 

The photoinitiator selected for this study was 1-benzoyl cyclohexanol (Irgacure 184 from Ciba Geigy), a compound known for its high initiation efficiency and the weak coloration of its photoproducts. The multifunctional monomer was an epoxy-diacrylate derivative of bis-phenol A (Ebecryl 605 from UCB). A reactive diluent, tripropyleneglycol diacrylate, had to be introduced in equal amounts, in order to lower the viscosity of the formulation to about 0.3 Pa.s. 

Generally, a non-reactive diluent is added to a monomer to decrease the glass transitions of a growing polymer during polymerization, thus helping driving the polymerization to completion at a lower temperature. 

Bisphthalonitrile monomers were cured neat, with nucleophilic and redox co-reactants, or in combination with a reactive diluent. Dynamic mechanical measurements on the resulting polymers from -150 to +300°C turn up several differences attributable to differences in network structure. Rheovibron results were supplemented with solvent extraction, differential scanning calorimetry (DSC), vapor pressure osmometry, and infrared spectroscopy to characterize the state of cure. 

Table I). A fourth monomer (structure IV in Table I) was designed with a single reactive phthalonitrile nucleus to serve as a "reactive diluent" in these network-forming systems. 

Multifunctional monomer(s) creating cross-links between segments of the oligomer and also acting as reactive diluent(s). ... 

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). 

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. 

The yields of radiation-induced polymerizations can be very high. No additives are required, which makes it possible to synthesize very pure polymers. The initiation step is temperature independent giving rise to an easily controlled process at any desired temperature. These features account for the commercial interest in radiation polymerization. The very high speeds attainable within the layers of monomers subjected to powerful electron beams explain the wide use of this technique in radiation curing of adhesives, inks and coatings. The corresponding formulations are "solvent-free" and involve pre-polymers and monomers as reactive diluents. 

Selected reactive diluents are employed to reduce the viscosity of Uvimer M formulations and to Impart a greater flexibility to the cured product. The choice of a monomer or reactive diluent for a Uvimer ig based on a number of factors, including compatibility with the base resin, odor, volatility, toxicity, and its effect on specific properties such as adhesion. Changing the diluent monomer does not drastically alter the basic properties of the resin so that it is possible to supply a given UvimerTM with a choice of diluents in order to comply with particular user requirements. 

Example (1) Unsaturated monoalcohol (acryloesterol) and styrene monomer are reacted with a polyisocyanate in the presence of a urethane catalyst and a radical polymerization catalyst to form hybrid resins (52). Styrene monomer acts as a crosslinker and at the same time, acts also as a reactive diluent. The trade name of a commercial product of such systems is Arimax (Ashland Chemical) (107). 

Small molecule epoxides, and some epoxy oligomers also are used as reactive diluents, mixing them with other polymers for crosslinking purposes. An example of epoxide used as curing additive is poly(limonene dioxide) or poly[1-methyl-4-(2-methyloxiranyl)-7-oxabicyclo[4.1.0]heptane], CAS 29616-43-1. This compound can form ether bonds upon heating or by photoinduction in the presence of aryl substituted sulfonium salts. Poly(dicyclopentadiene dioxide), CAS 29987-76-6, has similar properties. The idealized structure of the two monomers with the intact epoxy groups are shown below ... 

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