Hydroquinone polyester monomer

Tecquinol . [Eastman] Hydroquinone antioxidant for latexes, fats, oils, monomers, polyester resins. 

The reactive monomer responsible for the cross-linking reaction is normally styrene, vinyl toluene, methyl methacrylate, or diallyl phthalate. The unsaturated polyester prepolymers are, by themselves, relatively stable at ambient temperatures. When they are added to the cross-linking monomers, however, the blend is extremely unstable. To prevent premature gelation and to control the cross-linking process, inhibitors like hydroquinone are added to the blend. The cross-linking process is usually initiated by an organic peroxide added by the end user. The peroxide may be activated by heat. For room-temperature cure, accelerators and activators such as cobalt salts are also added. The cross-linking reaction can be represented as follows (Equation 5.2) ... 

Polyesters prepared by the polycondensation of monomers based on terephthalic acid (TA) and hydroquinone (HQ) or p-hy-droxybenzoic acid (HBA) are insoluble and exhibit very high melting temperatures, which are in the decomposition range (Fig. 3) [4]. Melting temperatures of 600 °C... 

Even higher glass transition temperatures are achievable if4,4 -functionalized 1,1 -binaphthyl monomers are used [28 b, 30]. For example, the homopolyester derived from 4,4 -dihydrox-1,1 -binaphthyl (BDP) and phenylterephthalic acid with an inherent viscosity of 1.90 dl/g has a Tg of 183 °C. The polyester is nematic up to its decomposition temperature and forms a nematic glass below Tg. In a similar homopolyester based on 4,4 -dicarboxy-1,1 -binaphthyl and t-butyl-hydroquinone the Tg was found to be 189 °C. In both cases, good solubility in common chlorinated solvents is maintained. This type of monomers was, for example, also used to modify wholly aromatic copolyesters based on 6-hydroxy-2-naphthoic acid (HNA) and 2,6-naphthalene dicarbox-ylic acid (NDA) [25 a]. 

Chemistry. They are made by reaction of methaciylic acid with epoxy resins (Fig. 3.16). The reaction is catalyzed by benzyl trunethyl ammonium chloride, or oxo-nium or phosphonium salts (Table 3.25). Like polyesters, they are dissolved in liquid styrene monomer and stabilized by hydroquinone. And, like polyesters, they are cured by organic peroxides activators, at room temperature to 150°C. 

Hydroquinone -kwi- non [ISV] (ca. 1872) (p-dihydroxybenzene, hydroquinol, p-hydroxyphenol, qui-nol) n. C6H4(OH)2. A white crystalline material derived from aniline, used, as are many of its derivatives, as an inhibitor of free-radical polymerization in unsaturated polyester resins and in monomers such as vinyl acetate. 

Most of the monomers that are added are somewhat unstable at room temperature. Consequently, to control shelf Ufe and viscosity, inhibitors are incorporated into the polyester system. The most widely used inhibitors are hydroquinone and p-tert-butylcatechol. 

Figure 3 summarizes the molecular architecture used to promote polyester melt anisotropy at reasonable temperatures. The Celanese, DuPont and Eastman laboratories have outlined most of the key approaches to lower polymer melting point via crystalline order disruption. This is accomplished while maintaining sufficient molecular symmetry to preserve the melt anisotropy inherent in linear aromatic polyesters, that is, polyesters derived typically from symmetric monomers as p-hydroxybenzoic acid, terephthalic acid, hydroquinone, 4,4 -biphenol and the like. 

DuPont workers have described (7) a wide variety of tractabilizing molecules and the thermotropic polyesters derived therefrom. Their research has focused for the most part on ring substituted monomers such as chloro, methyl or phenyl substituted hydroquinone and swivel" or linked ring molecules, examples of which are 3,4 or 4,4 functionally (hydroxy or carboxy) disubstituted diphenyl ether, sulfide or ketone monomers. Use of the parallel offset or crankshaft" geometry provided by 2,6 functionally disubstituted naphthalene monomers has been the major thrust of the Celanese Corporation development of easily processed, high performance wholly aromatic thermotropic polyesters. 

Polyesters dissolved in monomers must be protected against premature polymerisation. For this purpose inhibitors, such as hydroquinones or benzoquinones, are contained in the resins. 

Another method of introducing flexibility in the polyesters is to use 4-carboxybenzenepropionic acid as a monomer with the substituted hydroquinones ... 

Once unsaturated polyesters are synthesized, they are diluted in reactive diluents that are capable of polymerizing thermally. Therefore, care needs to be taken at this stage to keep the temperature as low as possible. As an additional precaution during thinning, as well as to have better stability on storage, a polymerization inhibitor such as p-tert-butylcatechol or hydroquinone are necessarily added to the monomers in the thinning tank before resin dissolution. 

---