Unsaturated monomers

These compounds are usually added to negative-working photoresists, and provide sites of unsaturation, which take part in photopolymerization, in cases where the polymer itself does not contain pendant unsaturation [2]. The number of reactive double bonds per unit, the functionality, has a definite effect on cure speed. However, increasing amounts of monomer usually result in an increase in tack of the final coating. Therefore a balance must be achieved between minimizing tack and decreasing photospeed. The choice of monomer also affects the 

A few examples of the more common unsaturated monomers utilized are shown in Fig. 2.11. Many other suitable compounds are given in the Rohm and Haas patent [2] these compounds usually have carbon-carbon double bonds in conjugation with the carbonyl group of an ester or amide. 

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Tetrahydrofurfuryl acrylate and methacrylate reactive unsaturated monomers, are readily polymerized and easily cross-linked by exposure to heat, peroxide catalysts, or uv radiation. 

Table 2. Unsaturated Monomers Obtained From Steam Cracking ...

Glycol Dibasic acid or anhydride Unsaturated acid or anhydride Unsaturated monomer... 

The radicals then initiate chain growth by adding an unsaturated monomer molecule, M, to form growing chain... 

Vinyhdene chloride polymeri2es by both ionic and free-radical reactions. Processes based on the latter are far more common (23). Vinyhdene chloride is of average reactivity when compared with other unsaturated monomers. The chlorine substituents stabih2e radicals in the intermediate state of an addition reaction. Because they are also strongly electron-withdrawing, they polari2e the double bond, making it susceptible to anionic attack. For the same reason, a carbonium ion intermediate is not favored. 

Miscellaneous Reactions. Epoxy compounds yield chlorosubstituted carbonates (45). The reaction of chloroformates with hydrogen peroxide or metal peroxides results in the formation of peroxydicarbonates that are used as free-radical initiators of polymerization of vinyl chloride, ethylene, and other unsaturated monomers (46,47). 

Chloroformates are versatile, synthetic intermediates, based on the affinity of the chlorine atoms for active hydrogen atoms. Chloroformates should be considered as intermediates for syntheses of pesticides, perfumes, dmgs, polymers, dyes, and other chemicals. Some of these products, eg, carbonates, are used as solvents, plastici2ers, or as intermediates for further synthesis. A significant use of chloroformates is for conversion to peroxydicarbonates, which serve as free-radical initiators for the polymeri2ation of vinyl chloride, ethylene, and other unsaturated monomers. The most widely used percarbonate initiators are diisopropyl peroxydicarbonate (IPP), di-2-ethyIhexylperoxydicarbonate (2-EHP), and di-j -butylperoxydicarbonate (SBP). The following Hst includes most of the commercially used percarbonates. 

Polymerization Initiator. Some unsaturated monomers can be polymerized through the aid of free radicals generated, as transient intermediates, in the course of a redox reaction. The electron-transfer step during the redox process causes the scission of an intermediate to produce an active free radical. The ceric ion, Ce" ", is a strong one-electron oxidizing agent that can readily initiate the redox polymerization of, for example, vinyl monomers in aqueous media at near ambient temperatures (40). The reaction scheme is... 

Unsaturated polyester resin powders can provide a colored and finished exterior molded surface or a finish ready for painting. Normally, a primer/sealer must be appHed to molded articles prior to painting. In addition to the unsaturated polyester resin, multifimctional unsaturated monomers such as triaHyl cyanurate (TAC) [101-37-1] or diaHyl phthalate (DAP) [131-17-9] suitable peroxide initiators (qv) or mixtures thereof, and mold release agents (qv) are used to formulate the coating powder (46). 

A waterborne system for container coatings was developed based on a graft copolymerization of an advanced epoxy resin and an acryHc (52). The acryhc-vinyl monomers are grafted onto preformed epoxy resins in the presence of a free-radical initiator grafting occurs mainly at the methylene group of the aHphatic backbone on the epoxy resin. The polymeric product is a mixture of methacrylic acid—styrene copolymer, soHd epoxy resin, and graft copolymer of the unsaturated monomers onto the epoxy resin backbone. It is dispersible in water upon neutralization with an amine before cure with an amino—formaldehyde resin. 

Other natural product-based resins also became widely used, such as the light colored Lewis acid oligomerized products of terpenes such as a-pinene, p-pinene, and limonene. These natural product resins are relatively expensive, however, and formulators now often use the newer, less expensive synthetic resins in present day natural rubber PSAs. These are termed the aliphatic or C-5 resins and are Lewis acid oligomerized streams of predominately C-5 unsaturated monomers like cis- and /rawi-piperylene and 2-methyl-2-butenc [37]. These resins are generally low color products with compatibility and softening points similar to the natural product resins. Representative products in the marketplace would be Escorez 1304 and Wingtack 95. In most natural rubber PSA formulations, rubber constitutes about 100 parts and the tackifier about 75-150 parts. 

Resins from pure monomers. Some colourless resins can be produced from pure unsaturated monomers, such as styrene, oi-methylstyrene and vinyl-toluenes (Fig. 19). These monomers are used individually or as blends with terpenes or unsaturated aliphatics. 

Vinyl monomers with electron-withdrawing substituents (EWG) can be polymerized by basic (anionic) catalysts. The chain-carrying step is conjugate nucleophilic addition of an anion to the unsaturated monomer (Section 19.13). 

For almost all applications unsaturated polyesters are dissolved in an unsaturated monomer capable of free-radical polymerization with the unsaturations in polyester chains. This polymerizable comonomer is generally styrene, but other compounds, such as methyl methacrylate, vinyl toluene, a-methylstyrene, and diallylphthalate, are also used in some applications. Upon heating and in... 

Using magnesium ether carboxylates as emulsifier a porous polyvinylchloride can be made [218] and a propoxylated ether carboxylate is described as emulsifier to make an ethyl acrylate-styrene copolymer [219]. A crosslinked latex with a three-dimensional network is achieved by polymerizing an ethylenically unsaturated monomer with a reactive saturated monomer using ether carboxylate as emulsifier [220]. 

An example of an emulsifier for the polymerization of ethylenically unsaturated monomers is a 22 88 mixture of disodium a-sulfolaurate and sodium methyl a-sulfolaurate. The emulsion is stable for much longer than an emulsion with n-dodecylbenzenesulfonate as the emulsifier [92]. Ester sulfonates are also used as emulsifiers in the continuous manufacture of vinyl chloride polymers [93]. 

By contrast, addition polymers are those formed by the addition reaction of an unsaturated monomer, such as takes place in the polymerisation of vinyl chloride (Reaction 1.2). 

PTEE is a linear polymer of the addition type, formed by polymerisation of the unsaturated monomer tetrafluoroethylene, CF2=Cp2. Despite the fact... 

The polymerisation reactions that occur by the chain mechanism are typically those involving unsaturated monomers. The characteristic reaction begins with the chemical generation of reactive centres on selected monomer... 

The molecular formula of the condensation polymer is not an integral multiple of the formula of the monomer molecule owing to the elimination of a by-product, which in this case is water. The most important class of addition polymers consists of those derived from unsaturated monomers, such as the vinyl compounds... 

Addition polymerizations of unsaturated monomers leading to the formation of products of high molecular weight invariable proceed by chain reaction mechanisms. Primary activation of a monomer M (or a pair of monomers) is followed by the addition of other monomers in rapid succession... 

Table II.—Representative Addition Polymers Formed from Unsaturated Monomers... 

Polymerization of Unsaturated Monomers by Free Radical Mechanisms... 

The processes by which unsaturated monomers are converted to polymers of high molecular weight exhibit the characteristics of typical chain reactions. They are readily susceptible to catalysis, photoactivation, and inhibition. The quantum yield in a photoactivated polymerization in the liquid phase may be of the order of 10 or more, expressed as the number of monomer molecules polymerized per quantum absorbed. The efficiency of certain inhibitors is of a similar magnitude, thousands of monomer molecules being prevented from polymerizing by a single molecule of the inhibitor. ... 

Although all sources of reactive free radicals which have been tried initiate the polymerization of unsaturated monomers, the converse of this statement, namely, that all initiators are free-radical-producing substances, is not true. Thus, strong acids (in the Lewis sense) such as AICI3, BF3, and SnCL, which are characterized by a strong affinity for a pair of electrons, bring about rapid polymerization of certain monomers. These polymerizations also proceed by chain mechanisms. The propagating center is, in this case, a positively... 

The monomer must also be considered a potential transfer agent. It may perform the function of the solvent in reaction (30), an atom being transferred from the monomer to saturate the radical. Possibly a proton may be transferred from the carbon atom of the radical chain to the unsaturated monomer as follows ... 

It has been shown by Barb and by Dainton and Ivin that a 1 1 complex formed from the unsaturated monomer (n-butene or styrene) and sulfur dioxide, and not the latter alone, figures as the comonomer reactant in vinyl monomer-sulfur dioxide polymerizations. Thus the copolymer composition may be interpreted by assuming that this complex copolymerizes with the olefin, or unsaturated monomer. The copolymerization of ethylene and carbon monoxide may similarly involve a 1 1 complex (Barb, 1953). 

The crosslinking of ethylene-propylene copolymer rubber (EPR) in the presence of organic peroxides has been investigated by Natta and/or his coworkers (1-3) and others (4,5). Co-agents such as sulfur (3,4) and unsaturated monomers (6), including maleic anhydride (MAH)(3,7) have been utilized in an effort to increase the crosslinking efficiency in the EPR-peroxide system. 

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