Unsaturated polyester-styrene mixture

Photocuring of commercial unsaturated polyester-styrene mixture was effectively done in the presence of the VOL2CI photoinitiator complex. The chlorine atom produced by the scission of V—Cl bond in the VOL2CI complex is proven to be the initiating species for the photocuring process 168]. 

Crosslinking polyurethanes in the presence of unsaturated polyester-styrene mixtures produce unique topologically interpenetrating networks. The cured mixtures exhibited one glass transition tem-... 

The solution of the precursors of the thermosetting polymer (mixture of monomers or oligomers with or without initiators, catalysts and different additives) is usually a liquid at room temperature e.g., unsaturated polyester styrene, some epoxy anhydride and epoxy amine formulations, cya-nate esters, one-stage phenolics, etc. Cooling any of these solutions below room temperature leads to a glass. The temperature at which the glass-liquid transition of the initial formulation takes place is denoted as Tg0. Some other particular formulations, such as two-stage phenolics (novo-lac-hexa mixtures), some epoxy-amine systems, etc., exhibit a Tg0 above room temperature. 

The initiator was weighed into a test tube (radius = 10 mm.), 20 grams of fresh (stored at 0°C.) unsaturated polyester/styrene solution (Vestopal A) were added, the mixture was stirred well with a glass rod,... 

A special form of the SMC is used for bandages. A mixture of unsaturated polyesters, styrene, and benzoin derivatives is applied to nylon netting. The mixture cures under ultraviolet light. An advantage of these bandages over plaster of Paris is the lower weight, the water resistance, and the transparency to X-rays. 

As discussed in earlier sections, UPE resins are a mixture of an unsaturated polyester, styrene and an inhibitor. When the resin is mixed with a peroxide initiator and activator (cobalt octoate/napthenate), free radicals are formed. At the initial stage, all or most of the free radicals generated are consumed by the inhibitor. The driving force for the preferable reaction of free radicals with the inhibitor is the higher stability of inhibitor radicals. Once the inhibitor molecules are depleted, free radicals, produced from the initiator, initiate polymerisation of the polyesters. Styrene serves as an agent to link the adjacent polyester molecules. The curing of UPE resin (polyester + styrene) involves different types of reactions ... 

Ketone Peroxides. These materials are mixtures of compounds with hydroperoxy groups and are composed primarily of the two stmctures shown in Table 2. Ketone peroxides are marketed as solutions in inert solvents such as dimethyl phthalate. They are primarily employed in room-temperature-initiated curing of unsaturated polyester resin compositions (usually containing styrene monomer) using transition-metal promoters such as cobalt naphthenate. Ketone peroxides contain the hydroperoxy (—OOH) group and thus are susceptible to the same ha2ards as hydroperoxides. 

Forty grams of unsaturated polyester (see above, Section 2.4.2.1), 26.7 g of styrene, and 10 mg of hydroquinone are weighed into a plastic beaker. The mixture is stirred and slightly warmed, if necessary, until complete dissolution. Then, at room temperature, 0.25 mL Co(II) 2-ethylhexanoate (note a below) and 1.0 mL of 2-butanone peroxide (MEKP, note b below) are added to the stirred mixture. The mixture gels after a 10-20-min period (stir during this period) and solidifies after ca. 1 h (Scheme 2.55)424. 

The crosslinking of unsaturated polyesters (Sec. 2-12a) is carried out by copolymerization [Selley, 1988]. Low-molecular-weight unsaturated polyester (prepolymer) and radical initiator are dissolved in a monomer, the mixture poured, sprayed, or otherwise shaped into the form of the desired final product, and then transformed into a thermoset by heating. Styrene is the most commonly used monomer. Vinyltoluene, methyl methacrylate, diallyl phthalate, a-methylstyrene, and triallyl cyanurate are also used, often together with styrene. 

Maleic anhydride [R1 equals -CH=CH- in Eq. (2.7) cis isomer] is reacted with aliphatic diols to form low molar mass unsaturated polyesters, UP. For molar masses higher than 1000 g/mol, products are diluted with a liquid vinyl monomer, most often styrene. This reactive mixture, generally called unsaturated polyester, UP resin, can be transformed into crosslinked polymers through a free-radical chain polymerization (see Sec. 2.3). 

This approach can be illustrated by unsaturated polyesters based on an almost equimolar combination of maleate and phthalate of propylene glycol, crosslinked by styrene (45 wt%) (Mortaigne el al., 1992). Six samples differing by the prepolymer molar mass were analyzed. The chain-ends concentration, b, was determined by volumetric analysis of alcohols and acids in the initial reactive mixture. Then, the system was cured, elastic measurements were made in the rubbery state at Tg + 30° C, and the shear modulus G was plotted against chain-ends concentration (Fig. 14.7). The following relationship was obtained ... 

Fig. 12-. Schematic representation of the produclion of an unsaturated polyester resin and subsequent cross-linking by polymerizing the styrene in a mixture of this monomer with the polyester.

H5V and 2H5P have also been used as monomers for incorporation into polymerizing mixtures of unsaturated polyesters and styrene. Experiments were carried out with oligomeric polyesters made from maleic anhydride, phthalic anhydride, 1,3-dihydroxypropane (TO wt. ) and styrene (30 wt. ) ( 5.). Under the normal reaction conditions (benzoyl peroxide as the initiator), the two polymerizable benzotri-azole derivatives were essentially quantitatively incorporated when the feed ratio was between 0.5 and 5 mol. ... 

Unsaturated resins are usually mixtures of vinyl monomers and prepolymers, such as unsaturated polyesters, polyurethane acrylates, and ac-rylated epoxides of the bisphenol A type. Polymerization of styrene-based resins involves the formation of a three-dimensional network via the cross-linking of prepolymer chains by styrene radicals. These standard thermoset resins are therefore characterized by great hardness (Shore D over 80, DIN 53505, arbitrary scale 0-100 based on the penetration of a needle point in the tested material), do not melt, and are not soluble in organic solvents. 

The plastic binder is added as a solution in acetone. Most of the solvent evaporates during mixing and granulation. This is not a standardized formula but similar "castable mixtures have been reported by others. Unsaturated polyester with added styrene has also been tried for this purpose. 

Finally, the unsaturated polyester is free-radically cross-linked by copolymerization with, for example, styrene or methyl methacrylate. Mixtures of the actual unsaturated polyester with these monomers are commercially known as unsaturated polyester resins. The properties of the thermosets can be matched to the application by variations in the acids, glycols, or vinyl monomers. Copolymerization with electronegative comonomers such as styrene or vinyl acetate leads, for example, to alternating copolymers, that is, to short cross-link bridges and therefore, to more rigid thermosets. Alternatively, electropositive comonomers such as methyl methacrylate form long methyl methacrylate bridges between the polyester chains and so produce more flexible polymerizates. 

Chemically, these are acrylic esters and not vinyl esters. Like the unsaturated polyester resins, vinyl esters are offered for sale as mixtures with styrene consequently they are often classified as unsaturated polyesters. A few other compounds, for example,... 

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