Unsaturated polyesters with additives

TriaUyl cyanurate is used as a comonomer in small amounts with methacrylate esters and unsaturated polyesters. The addition of 5% or more of TAC to MMA in castings improves heat and solvent resistance as weU as thermooxidative stabUity (99). For optical appUcations, up to 20% TAC has been suggested. Reactivity ratios for TAC and methacrylate esters have been reported (100). 

Navale, P.B., Athar, J., Diwakar, R.P., Sadakale, V.G., and Agrawal, J.P. (1999) Unsaturated polyester with melamine based additives for inhibition of DB rocket propellants. Proc. Polymer 99 (Polymers Beyond AD 2000), IIT Delhi, Jan. 12-15,1999, pp. 778-781. 

In addition, Eq. (5.1) should not be applied in systems that exhibit different initial reactivities of functional groups, such as in the copolymerization of double bonds of a particular unsaturated polyester with styrene or in the formation of a polyurethane starting from 2,4-toluene diisocyanate. 

Unsaturated polyesters with terminal hydroxyl or carboxyl groups can also react at the same time with isocyanate groups and a vinyl monomer, such as styrene, to produce hybrid polymers. Two kinds of reactions, the NCO-OH addition reaction and radical polymerization by the vinyl groups, can occur. In parallel to the two reactions, interference between the two reactions also can occur. Detailed studies on the interference reactions were studied by Hsu et al. (190). 

One of the most important types of addition polymerization is free radical polymerization. This process is initiated by the action of free radicals (electrically neutral species with an unshared electron). Free radicals for the initiation of addition polymerization are usually generated by the thermal decomposition of organic peroxides or azo compounds. The polymerization of unsaturated polyesters with a peroxide catalyst is an example of a free radical polymerization process. 

The concept of treating addition polymers or copolymers with pendent or terminal hydroxyl residues with MA has been extensively explored and disclosed in the patent literature. Using this technique, it is possible to prepare a special type unsaturated polyester with potential applications in films, sheets, and moldings. 

The polycondensation of acid anhydrides (i.e., maleic and phthalic anhydrides) with diols (i.e., ethylene glycol) under microwave irradiation was also applied for the synthesis of unsaturated polyesters.In addition to the previous protocol, the reaction temperature was increased to 200 °C, and a Dean-Stark trap was applied to remove water from the reaction mixture. It was found that the reaction times for... 

The concept of unsaturated polyesters (international abbreviation UP) which can be cured and hardened by heating with sources of radicals was developed by C. Ellis in the 1930s [1-3], and the first patent application was submitted in 1936 Ellis also discovered that dilution of the unsaturated polyesters with vinyl monomers, such as styrene (most widely used) or vinyl acetate is favorable for most applications. The dilution reduces the viscosity. Eases the dissolution of additives and catalysts and lowers the costs. The most frequently used catalysts for the curing process are peroxides. The variation of their structure allows for optimization of the cure. The most important application of UPs are ... 

An alternative route to cross-linking is to start with a linear polymer and then cross-link the molecules by tying the molecule through some reactive group. For example, it is possible to cross-link unsaturated polyesters by an addition polymerisation across the double bond as shown schematically in Figure 2.12. 

Over the years many blends of polyurethanes with other polymers have been prepared. One recent example is the blending of polyurethane intermediates with methyl methacrylate monomer and some unsaturated polyester resin. With a suitable balance of catalysts and initiators, addition and rearrangement reactions occur simultaneously but independently to give interpenetrating polymer networks. The use of the acrylic monomer lowers cost and viscosity whilst blends with 20% (MMA + polyester) have a superior impact strength. 

The largest single use of maleic anhydride is in the preparation of unsaturated polyester resins. It is first esterihed with a polyalcohol (two or more hydroxyls) and then the double bond is copolymerized (crosslinked) with a vinyl monomer such as styrene to form a rigid structure. Such resins are usually reinforced with hberglass (FRP). Maleic anhydride is also used to make oil additives and agricultural chemicals. 

High-temperature cement formulations are basically polymer concrete. Mainly unsaturated polyesters or vinyl ester resins with allylphthalate as vinyl monomer are in use [927]. Cming is achieved with peroxides, which decompose sufficiently fast at temperamres between 120° and 200° C. Polymer concrete requires additional materials, which compensate shrinkage. 

Development of the third class, i.e. unsaturated polyester resins, remained rather slow until the late 1930s, but after commercial production of maleic anhydride by catalytic oxidation of benzene began in 1933, maleic anhydride and fumaric acid rapidly became the most important sources of unsaturated groups in polyesters. The mechanism of drying of these resins on their own and with the addition of drying oils (i.e. unsaturated compounds such as linseed oil) was... 

Glycolysis is also conducted to create polyols for unsaturated polyester usage. The PET can be dissolved in DEG to create polyols with ether linkages [30], The reaction can be carried out with propylene glycol [31] or by reacting with an unsaturated dibasic acid [32] and needed additives and catalysts [33],... 

Low-profile additives, which control shrinkage, have emerged as a distinct science and class of additive. Unsaturated polyester resins, as do all thermosetting polymers, shrink when cured. Low-profile additives are a major class of additives used to control shrinkage, which vastly improves surface quality. This science is credited with the opening of automotive markets where surface quality is of prime importance. In exterior automotive body panels, Class A surfaces are required for market acceptance. 

Sheet molding compounds (SMCs) and bulk molding compounds (BMCs) are the dominant materials used in automotive applications. These composites of unsaturated polyester resin, fillers and fiberglass have advantages of high stiffness, heat resistance and low coefficient of expansion. Coupled with low creep resistance, which is a distinct advantage over thermoplastic competition, and low-profile additives, which can yield Class A surfaces, these materials are well suited for applications from exterior body panels to under the hood components. 

Uses. About 60% of the MA produced is used to make unsaturated polyester and aikyd resins, which are formed by reaction of MA with glycols. Polyester resins are used in the fabrication of glass fiber reinforced parts. Applications include boat hulls, automobile body parts, patio furniture, shower stalls, and pipe. Aikyd resins are mostly used in coatings (paint, varnish, lacquers, and enamels). MA also is widely used as a chemical intermediate in the manufacture of plasticizers and dibasic acids (fumaric, maleic, and succinic). About 15% of MA production goes into the manufacture of viscosity index improvers and dispersants used as additives in lube oils. Several agricultural chemicals are based on maleic anhydride, the best known being Malathion. 

Addition poly(imide) oligomers are used as matrix resins for high performance composites based on glass-, carbon- and aramide fibers. The world wide market for advanced composites and adhesives was about 70 million in 1990. This amounted to approximately 30-40 million in resin sales. Currently, epoxy resins constitute over 90% of the matrix resin materials in advanced composites. The remaining 10% are unsaturated polyester and vinylester for the low temperature applications and cyanate esters and addition poly(imides) for high temperatures. More recently thermoplastics have become important and materials such as polyimides and poly(arylene ether) are becoming more competitive with addition polyimides. 

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