Polyesters Unsaturated

An unsaturated polyester resin consists of a linear polyester whose chain contains double bonds and an unsaturated monomer such as styrene that copolymerizes with the polyester to provide a cross-linked product. The most common unsaturated polyester is made by step growth polymerization of propylene glycol with phthalic and maleic anhydrides. Subsequent treatment with styrene and a peroxide catalyst leads to a solid, infusible thermoset. 

Unsaturated polyesters are relatively brittle and about 70% are used with fillers, of which glass fiber is easily the most popular. Glass fiber-reinforced polyester for small boat hulls consumes one quarter of unsaturated polyesters. Automobiles, furniture, and construction also make use of this thermoset resin. 

Unsaturated polyesters are a group of polymers and resins used in coatings or for castings with styrene. These polymers normally have maleic anhydride moiety or an unsaturated fatty acid to impart the required unsaturation. A typical example is the reaction between maleic anhydride and ethylene glycol  

Phthalic anhydride, a polyol, and an unsaturated fatty acid are usually copolymerized to unsaturated polyesters for coating purposes. Many other combinations in variable ratios are possible for preparing these resins. The 1998 U.S. production of polyesters was approximately 1.7 billion pounds. 

Unsaturated polyesters with molecular weights of several thousand are made commercially by condensing maleic anhydride or phthalic anhydride with ethylene glycol or propylene glycol. The subsequent free radical copolymerization with 30-35% by wt styrene leads to a cross-linked product which possesses exceptionally good mechanical properties, particularly when reinforced with glass fiber. The thermosetting properties 

The crosshnking of unsaturated polyesters (Sec. 2-12a) is carried out by copolymerization [SeUey, 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. St5uene is the most commonly used monomer. Vinyltoluene, methyl methacrylate, diaUyl phthalate, a-methylstyrene, and triallyl cyanurate are also used, often together with styrene. 

The crosslinking process involves copolymerization of the added monomer with the double bonds of the unsaturated polyester 

The photo-oxidation of aliphatic unsaturated polyesters such as poly(l,2-maleate) (4.46) [2188] and poly(propylene-l,2-maleate) (4.47) [1099, 1357, 1474, 1475, 1814] is accompanied by extensive chain scission, crosslinking and yellowing. 

Coatings based on mixed unsaturated aromatic polyesters which have benzene nuclei, such as poly(l,2-maleate-propylene-o-phthalate) (4.48), are also susceptible to photo-oxidative degradation [1375, 1814]. On exposure to sunlight, gradual changes take place in their chemical and physical properties, starting at the surface to produce microcracks and chalking. 

The photolysis of unsaturated polyesters shows the disappearance of double bonds and partial decomposition of ester carbonyl groups to carbon monoxide and carbon dioxide molecules. This type of polyester contains a distinct conjugated system of double bonds and carbonyl groups (4.49), which absorbs UV radiation and exists in the triplet state (Tj) as a resonance form (4.50)  

The resonance form allows the existence of several different intermediate reactive biradicals  

The spin components of the two excited electrons are neither paired nor unpaired they are independent and delocalized. The observed rapid crosslinking is interpreted as being due to reactions of the intermediate radicals with a segment of the same or neighbouring macromolecules  

The second synthetic thermoset resin discovered in early 1940 (after phenolic resin) was unsaturated polyester (UPE) resin. UPE consists of an unsaturated polyester, a monomer, and an inhibitor. UPE gained wide industrial applications due to their low viscosity, which offers easy processability, low cost and rapid cure schedules. 

Krigbaum [12] has reported on the use of glass fiber-reinforced composites based on Cyglas 685 unsaturated polyester BMC and Cyglas 695 vinyl ester resin BMC (Cytec Industries) in automotive valve covers and other engine cover applications. He reviews development programs that led to the successful introduction of these components. The recyclability of thermoset composite valve covers is also discussed. 

Various polyamides, particularly polyamide 6,6 and polyamide 11, have been used in the manufacture of radiator tanks [13-15], rocker covers [16-22], Audi pedal boxes [23], connecting rods, fan blades, and other components [24], Glass fiber reinforcement is used in these applications [17-24], 

The requirements for radiator tanks are good heat stability, vibration resistance, and resistance to coolant additives [18], 

Audi and others [20-22] use 25% glass fiber and 15% mineral reinforced nylon 

6 for the fabrication of rocker covers for the Audi A4 and VW Passat engines. These covers have good dimensional stability even at elevated temperatnres, which 

The materials in this group are linear copolyesters. One of the dicarboxylic acids is an aliphatic unsaturated diacid. The unsaturation is introduced into the polymer backbone for the purpose of subsequent crosslinking. Unsaturated polyester technology was developed for use in glass fiber laminates, thermosetting molding compositions, casting resins, and solventless lacquers. 

Propylene glycol is often used as the diol. To a lesser extent, other glycols, like diethylene glycol, are also used for greater flexibility, or neopentyl glycol for a somewhat better thermal resistance. Bisphenol A (2,2 bis(4-hydroxyphenyl) propane) is used when better chemical resistance is needed. Use of mixed diols is conunon. Many unsafturated dicarboxylic acids can be used, but maleic (as an anhydride) or fumaric acids are the most common. Chloromaleic or chlorofumaric acids are also employed. 

The saturated dicarboxylic acids act as modifiers. While aliphatic dicarboxylic acids can be used, the most common one is orthophthalic acid (added to the reaction mixture as an anhydride). The acid improves compatibility with styrene that is polymerized in the presence of the polyester to form hard, rigid, crosslinked materials. Other modifiers are used to obtain special properties. When a flexible product is needed, adipic or sebacic acids may be used instead. For better heat resistance endomethylene tetrahydrophthalic anhydride (nadic anhydride) may be utilized. Hame retardancy is achieved by using chlorinated dicarboxylic acids, like tetrachlorophthalic. 

Styrene is the most common monomer used in crosslinking unsaturated polyesters. When special properties are required, other monomers like methyl methacrylate may be employed. Sometimes this is done in combination with styrene. Diallyl phthalate and triallyl cyanurate form better heat-resistant products. 

An example of a typical batch preparation of a polyester is one where 1.2 moles of propylene glycol, 0.67 mole of maleic anhydride, and 0.33 mole of phthalic anhydride are combined. Propylene glycol is used in excess to compensate for loss during the reaction. The condensation at 150-200 °C lasts for 6-16 hours, with constant removal of water, the byproduct. An aromatic solvent, like toluene or xylene, is often added to the reaction mixtures to facilitate water removal by azeotropic distillation. Esterification catalysts, like toluene sulfonic acid, reduce the reaction time. In addition. 

When considering the use of MA in condensation polymers, it is automatic to think of unsaturated polyesters. In fact, the demand for MA is keyed primarily to the growth of these resins. In 1980, about 172 MM lb of MA were used to produce polyester resins in the United States.This represented approximately 52% of the 330 MM lb of MA demand in the United States in 1980 (see Sec. 1.4.1). MA is also very useful in other condensation polymers, including about 6 MM lb in alkyd resins. The value of using MA to prepare, crosslink, and/or modify condensation and addition polymers is discussed in this chapter. In recent times, the synthesis of maleinated vinyl esters and maleimide resins have had significant study. Because of this interest, we also give some attention to the use of MA in vinyl ester and maleimide technology. 

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  

Saturated dibasic acids are commonly employed with the unsaturated acid to modify the degree of unsaturation and thereby the reactivity of the resulting polyester. Muskat showed that the inclusion of phthalic anhydride into the polyester formulation reduced the tendency of the resin to crystallize and improved the compatibility of the resin with styrene. 

In addition to MA, phthalic anhydride, and ethylene glycol, other common intermediates used for the production of unsaturated polyesters are fumaric acid, isophthalic acid, adipic acid, propylene glycol, diethylene glycol, and dipropylene glycol. Table 12.1 provides a summary of both common and specialty building blocks used in polyesters and contributions made by these intermediates to the properties of the products. Recycled polyethylene terephthalate beverage bottles may one day become an important raw material for unsaturated polyester resin production, providing an alternative for a substantial part of the petroleum-based intermediates. 

Unsaturated polyesters prepared from the intermediates in Table 12.1, formulated with various vinyl-type unsaturated monomers such as styrene, have been widely studied, patented, and discussed in the literature.Bjork-sten s book gives a good presentation of the early studies on the chemistry, production, and applications of unsaturated polyesters. 

Nonwoven hemp mats and imsaturated polyester resin have been used for the fabrication of biocomposites (58). The amoimt of hemp fiber added has been optimized by mechanical measurements. 

The effect of four surface treatments of industrial hemp fibers on mechanical and thermal properties of biocomposites was studied. The treatments done were Alkali treatment, silane treatment, an UP matrix treatment, and a treatment with acrylonitrile of the hemp materials has been studied. 

Both mechanical and thermal properties of the biocomposites were foxmd to be improved due to the surface treatments. In order to get a reasonable balance in the properties, a hybrid composite of industrial hemp and glass fibers was tested (58). 

Major polymer applications composites, corrosion protection, surfboards, cultured stones, composites, bathroom sinks and vanity tops, countertops 

Important processing methods injection molding, compression molding, resin transfer molding, pultrusion, casting, encapsulation 

Typical fillers calcium carbonate, aluminum hydroxide, glass fiber, crashed marble, glass fiber, antimony trioxide, carbon black, quartz, saw dust 

Typical concentration range aluminum hydroxide - 30-80 wt%, quartz - up to 90 wt%, saw dust -20-50 wt%, calcium carbonate - 50-74 wt% glass fibers - 20 wt% 

Auxiliary agents silane maleic anliydride treatment of saw dust  

The conversion at the onset of auto-acceleration (the heat flow minimum) is close to 60%. Beeause it occurs at a much more advanced conversion than gelation, the term gel effect for indicating the auto-acceleration is somewhat 

The different conversion-dependence of rj is related to the molecular weight evolution and network development. For addition step-growth polymerisation systems, the molecular weight of the polymer chains gradually increases, while for (linear) free radical chain-growth polymerisations the 

It also should be pointed out that the auto-acceleration at high conversion closely before the onset of vitrification is not observed for step-growth polymerisation thermosetting systems [42,68,80,83-85]. 

---

Used as fibres, particularly in textiles and film. Many other polyester polymers are of importance, e.g. unsaturated polyester resins from phthalic anhydride, propylene glycol and maleic anhydride used with reinforcement in boats, cars, etc. (alkyd resins). U.S. production 1983 1-7 megatonnes. 

Organic peroxides are used extensively for the curing of unsaturated polyester resins and the polymerization of monomers having vinyl unsaturation. The —O—O— bond is split into free radicals which can initiate polymerization or cross-linking of various monomers or polymers. 

Alkyds are formulated from polyester resins, cross-linking monomers, and fillers of mineral or glass. The unsaturated polyester resins used for thermosetting alkyds are the reaction products of polyfunctional organic alcohols (glycols) and dibasic organic acids. 

Unsaturated Polyesters. Unsaturated polyesters are produced by reaction between two types of dibasic acids, one of which is unsaturated, and an alcohol to produce an ester. Double bonds in the body of the unsaturated dibasic acid are obtained by using maleic anhydride or fumaric acid. 

Aromatic polyester Unsaturated polyester Alkyd molding compounds ... 

Polyester-silicone Polyesters, thermoplastic Polyesters, unsaturated Polyester urethanes Polyester-wool blends Polyether antibiotics Polyether carboi lates Polyether elastomers... 

ALCOHOLS,HIGHERALIPHATIC - SURVEY AND NATURALALCOHOLSMANUFACTURE] (Voll) Unsaturated polyester resins... 

Uses. The a2obisnitriles have been used for bulk, solution, emulsion, and suspension polymeri2ation of all of the common vinyl monomers, including ethylene, styrene vinyl chloride, vinyl acetate, acrylonitrile, and methyl methacrylate. The polymeri2ations of unsaturated polyesters and copolymeri2ations of vinyl compounds also have been initiated by these compounds. 

A new class of materials called smart tagged composites has been developed for stmctural health monitoring appHcations. These composites consist of PZT-5A particles embedded into the matrix resin (unsaturated polyester) of the composite (16). 

Molybdenum Oxides. Molybdenum was one of the first elements used to retard the flames of ceUulosics (2). Mote recently it has been used to impart flame resistance and smoke suppression to plastics (26). Molybdic oxide, ammonium octamolybdate, and zinc molybdate ate the most widely used molybdenum flame retardants. Properties ate given in Table 5. These materials ate recommended almost exclusively for poly(vinyl chloride), its alloys, and unsaturated polyesters (qv). 

Unsaturated Polyesters. There are two approaches used to provide flame retardancy to unsaturated polyesters. These materials can be made flame resistant by incorporating halogen when made, or by adding some organic halogen compound when cured. In either case a synergist is needed. The second approach involves the addition of a hydrated filler. At least an equal amount of filler is used. 

Synergists. The effect of antimony oxide on the flammabiUty of unsaturated polyesters that contain chlorine is shown in Table 11. A similar effect on the flammabiUty of unsaturated polyester containing 2inc stannates and bromine instead of chlorine is given in Table 12. 

Table 11. Effect of Chlorine and Antimony Oxide on the Oxygen Index of Unsaturated Polyesters...

Table 12. Oxygen Index of Unsaturated Polyesters Containing Bromine ...

Antimony oxide and 2inc borate are also used as synergists for unsaturated polyesters. Their combined effect on the flame spread index (25) is ... 

Table 14. Oxygen Index and Smoke Reduction of Unsaturated Polyester Containing Molybdenum Oxide and Antimony Oxide...

TetrabromophthalicAnhydride. Tetrabromophthalic anhydride [632-79-1] (TBPA) is widely used as a reactive flame retardant in unsaturated polyesters as weU as the precursor to a number of other fine retardants. Polyesters prepared from this compound have relatively poor photochemical stabiUty and tend to discolor upon exposure to light. This tendency to discolor can be reduced, but not eliminated, by the use of uv stabilizers. 

Bromine as a Reactive Flame Retardant. Bromine and chlorine are the starting materials for all of the commercial compounds described. Bromine is also used in a somewhat different way to impart flame retardancy. That is, it is used to brominate the resin in interest directly. This is practiced commercially in the case of unsaturated polyesters (59). 

Tetrachlorphthalic Anhydride and Tetrachlorphthalic Acid. Tetrachlorphthalic anhydride [117-08-8] (TCPA) is manufactured by the ferric chloride catalyzed chlorination of phthalic anhydride. The relatively low chlorine content and the lower flame retardant efficiency of the aromatic chlorides limit use to unsaturated polyester resin formulations that do not requite a high degree of flame retardancy. 

Chlorendic Acid. Chlorendic acid [115-28-6] and its anhydride [115-27-5] are widely used flame retardants. Chlorendic acid is synthesized by a Diels-Alder reaction of maleic anhydride and hexachlorocyclopentadiene (see CyclopentadlENE and dicyclopentadiente) in toluene followed by hydrolysis of the anhydride using aqueous base (60). The anhydride can be isolated directly from the reaction mixture or can be prepared in a very pure form by dehydration of the acid. The principal use of chlorendic anhydride and chlorendic acid has been in the manufacture of unsaturated polyester resins. Because the esterification rate of chlorendic anhydride is similar to that of phthalic anhydride, it can be used in place of phthalic anhydride in commercial polyester... 

Polyols. Several important polyhydric alcohols or polyols are made from formaldehyde. The principal ones include pentaerythritol, made from acetaldehyde and formaldehyde trimethylolpropane, made from -butyraldehyde and formaldehyde and neopentyl glycol, made from isobutyraldehyde and formaldehyde. These polyols find use in the alkyd resin (qv) and synthetic lubricants markets. Pentaerythritol [115-77-5] is also used to produce rosin/tall oil esters and explosives (pentaerythritol tetranitrate). Trimethylolpropane [77-99-6] is also used in urethane coatings, polyurethane foams, and multiftmctional monomers. Neopentyl glycol [126-30-7] finds use in plastics produced from unsaturated polyester resins and in coatings based on saturated polyesters. 

The weatherabihty and hydrolytic stabiUty of unsaturated polyesters based on neopentyl glycol have made it a popular intermediate for use in formulations exposed to severe conditions, eg, in gel coats for cultured marble and marine appHcations (see Coatings, marine) (13). 

Esters. Neopentyl glycol diesters are usually Hquids or low melting soflds. Polyesters of neopentyl glycol, and in particular unsaturated polyesters, are prepared by reaction with polybasic acids at atmospheric pressure. High molecular weight linear polyesters (qv) are prepared by the reaction of neopentyl glycol and the ester (usually the methyl ester) of a dibasic acid through transesterification (37—38). The reaction is usually performed at elevated temperatures, in vacuo, in the presence of a metallic catalyst. 

Trimethyl-l,3-pentanediol (7) is a white, crystalline soHd. It is used in surface coating and unsaturated polyester resins. It also appears promising as an intermediate for synthetic lubricants and polyurethane elastomers and foams. 

Cydohexanedimethanol, 1,4- dim ethyl o1 cycl oh exa n e, or 1,4-bis (hydroxymethyl) cyclohexane (8), is a white, waxy soHd. The commercial product consists of a mixture of cis and trans isomers (6). This diol is used in the manufacture of polyester fibers (qv) (64), high performance coatings, and unsaturated polyester molding and laminating resins (5). 

Other common radical-initiated polymer processes include curing of resins, eg, unsaturated polyester—styrene blends curing of mbber grafting of vinyl monomers onto polymer backbones and telomerizations. 

Diacyl peroxides are used in a broad spectmm of apphcations, including curing of unsaturated polyester resin compositions, cross-linking of elastomers, production of poly(vinyl chloride), polystyrene, and polyacrjlates, and in many nonpolymeric addition reactions. 

Aromatic diacyl peroxides such as dibenzoyl peroxide (BPO) [94-36-0] may be used with promoters to lower the usehil decomposition temperatures of the peroxides, although usually with some sacrifice to radical generation efficiency. The most widely used promoter is dimethylaniline (DMA). The BPO—DMA combination is used for hardening (curing) of unsaturated polyester resin compositions, eg, body putty in auto repair kits. Here, the aromatic amine promoter attacks the BPO to initially form W-benzoyloxydimethylanilinium benzoate (ion pair) which subsequentiy decomposes at room temperature to form a benzoate ion, a dimethylaniline radical cation, and a benzoyloxy radical that, in turn, initiates the curing reaction (33) ... 

Wheieas the BPO—DMA ledox system works well for curing of unsaturated polyester blends, it is not a very effective system for initiating vinyl monomer polymerizations, and therefore it generally is not used in such appHcations (34). However, combinations of amines (eg, DMA) and acyl sulfonyl peroxides (eg, ACSP) are very effective initiator systems at 0°C for high conversion suspension polymerizations of vinyl chloride (35). BPO has also been used in combination with ferrous ammonium sulfate to initiate emulsion polymerizations of vinyl monomers via a redox reaction (36). 

---