Phthalic acid polyester monomer

In this review of the history of polyarylates, only those products of an aromatic dicarlDoxylic acid (or derivative) and a diphenol (or derivative) will be considered. Structurally similar aromatic polyesters based on p-hydroxybenzoic acid have received considerable interest due to the resultant liquid crystalline behavior of these materials. They, however, will not be covered in this paper. The primary polyarylate discussed herein is leased on Bisphenol A (2,2-bis(4-hydroxyphenyl)propane) and tere/iso-phthalic acids. These monomers are large volume commercial products and are utilized in the primary commercial polyarylates available today. 

There are numerous possible monomers that can be used in the backbone of the polyester prepolymer. However, typical monomers are 1,2-propanediol, as just mentioned, with maleic acid (usually added as the anhydride) to provide the sites of unsaturation, and phthalic acid (again usually added as the anhydride) to act as the second of the two diacid species. The structures of these latter two substances are shown in Figure 4.1. 

Mixed xylenes are used as an octane improver in gasoline and for commercial solvents, particularly in industrial cleaning operations. By far, most of the commercial activity is with the individual isomers. Para-xylene, the most important, is principally used in the manufacture of terephthalic acid and dimethyl terephthalate en route to polyester plastics and fibers (Dacron, films such as Mylar, and fabricated products such as PET plastic bottles). Ortho-xylene is used to make phthalic anhydride, which in turn is used to make polyester, alkyd resins, and PVC plasticizers. Meta-xylene is used to a limited extent to make isophthahc acid, a monomer used in making thermally stable polyimide, polyester, and alkyd resins. 

These polyesters are primarily copolyesters of propylene glycol with maleic and phthalic acids, dissolved in styrene monomer, and cured by peroxides activators (1, 4, 5). In a typical general-purpose polyester, a 103 excess of propylene glycol is cooked with an equimolar mixture of maleic and phthalic anhydrides for eight or more hours at 150-200°C to produce a viscous liquid polyester of 1000-5000 molecular weight. This is then partially cooled, diluted about 60/40 with styrene monomer, cooled to room temperature, and stored. It is later mixed... 

The oxidation of cyclohexanone by nitric acid leads to the generation of nitrogen dioxide, nitric oxide, and nitrous oxide. The first two gases can be recycled for the synthesis of nitric acid. Nitrous oxide, however, is an ozone depleter and cannot be recycled. Indiscriminate nitrous oxide emission from this process is therefore the cause of considerable concern. As shown by 8.9, part of the cyclohexanone can also be converted to the corresponding oxime and then to caprolactam—the monomer for nylon 6. Phthalic acids are one of the monomers for the manufacture of polyesters. As shown by Eq. 8.10, it is made by the oxidation of p-xylene. A general description of polyamides (nylons) and polyesters are given in Section 8.4. 

All cross-linked polymers tend to be difficult to disrupt, and they can be regarded as one giant molecule. This makes them of use when durability is needed. Many of the polymers mentioned above can be modified so as to form extensive cross-linking by increasing the number of reactive groups on the monomers. For example, the polyester formed by phthalic acid and glycerol (Scheme 6.5) can cross-link to form a polymer that is used in bake-on car paints. 

By incorporating unsaturated dicarboxylic acids (e.g. maleic acid), besides phthalic acid, into the polycondensation reaction, unsaturated polyesters are formed. These are then cross-linked with a low-molecular unsaturated monomer, usually styrene, in the presence of a peroxide catalyst and a cobalt compound as accelerator. Unsaturated polyesters are applied as cast resins or glass fibre-reinforced composites. The latter product was the first large-scale plastic material in the self-extinguishing category for the building industry... 

Unsaturated low molecular weight (M between 1000 and 10000), often branched, used as macromonomers for synthesis of thermosets (polyester resins), or thermosetting materials by themselves (alkyd resins). They are prepared from several monomers, namely phthalic and maleic anhydrides, adipic acid, iso-phthalic acid, natural fatty acids or triglycerides, and a great variety of multifunctional alcohols. In a few special cases, they may be saturated and/or linear for use as macromonomers in the production of polyurethanes or other polymers. 

The relatively low contribution of adverse reactions compared to the main one led to regular structure of final polyester. The totally aromatic polyesters of following chemical constitution were studied in [132] polymer OTT-40 consisting of three monomers (terephthaloyl-bis( -oxybenzoic) acid, tere-phthalic acid, phenylhydroquinone and resorcinol) entering to the polymeric... 

Small die castings are conveniently bonded with polymethylmethacrylate dissolved in its monomer together with a peroxide initiator. Metal naphthenates are to be avoided as accelerators and hence the so-called second generation or toughened acrylics are not recommended for use with zinc. Other acrylics may be used but are slow curing after evaporation of solvent. Polyester adhesives cured with styrene monomer frequently contain some free phthalic acid as an impurity and this militates against their use. Polyurethane adhesives cured with isocyanate should behave quite satisfactorily. 

Poly(ethylene terephthalate) is a linear polyester obtained from the reaction of difunctional monomers. Branched or network polyesters are obtained if at least one of the reagents is tri- or multifunctional. This can be achieved either by the use of polyols such as glycerol in the case of saturated polyesters (glyptal) or by the use of unsaturated dicarboxyhc acids such as maleic anhydride in the ease of unsaturated polyester. In the preparation of glyptal, glycerol and phthalic anhydride reaet to form a viseous liquid initially, which on further reaction hardens as a result of network formation (Equation 2.31). 

Network polyester resins may be categorized into saturated and unsaturated polyesters. Unlike linear saturated polyesters such as PET, which are made from difunctional monomers, saturated polyesters (glyptal) are formed by the reaction of polyols such as glycerol with dibasic acids such as phthalic anhydride. 

Polyester resins are condensation products of di- or polyfunctional monomers containing hydroxyl groups and carboxyl groups. The development of saturated polyesters began in 1901 with Glyptal resins , formed from glycerol and phthalic anhydride (Smith, United States). Soluble resins obtained with fatty acids were first employed in 1925. Alkyd resins formed from unsaturated fatty acids can be cured by atmospheric oxidation (see Section 2,6). Other unsaturated polyester resins are discussed in Section 2.8. 

Unsaturated polyester resins are mainly made by condensing a dibasic acid (1,2-propanediol) with an anhydride (maleic or phthalic anhydrides), by forming ester linkages between the dibasic acid (or their anhydrides) and glycols. Then a reactive monomer (mostly styrene or vinyl toluene, MMA or diallyl phthalate) is used to crosslink the system when needed. Unsaturated denotes the uncompleted chemical activity (double bond) in the original structure, which are used for crosslinking afterwards. In this context, an excess of styrene as the crosslinker (10 to 50 %) is usually added to have it ready in the system, as well as to reduce the viscosity. There are also certain accelerators used (such as, cobalt naphthenate or tertiary amines like dimethyl aniline) to facilitate the cure at ambient temperatures. In addition, there may be pigments, fillers, various inhibitors, accelerators, stabilisers and flame retardants, added to the system. Polymerisation is activated whenever a catalyst (i.e., benzoyl or methyl-ethyl-ketone peroxide) is added. 

General purpose polyesters are based on phthalic anhydride as the saturated monomer and are the lowest-cost class of resin. These general purpose resins are not normally recommended for use in corrosive service. They are adequate for use with nonoxidizing mineral acids and corrodents that are relatively mild. Tests have indicated that general purpose resins will provide satisfactory service with the following materials up to 125°F (52°C) ... 

These polyester resins use isophthalic acid in place of phthalic anhydride as the saturated monomer. This increases the cost to produce, but it improves physical properties and corrosion resistance. 

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