151 Pyromellitic dianhydride

Pyromellitic dianhydiide (PMDA) is generally used in PET at concentrations ranging from 0.05 to 2%. Reactive extrasion of PET with PMDA has been reported by Incarnato et al. [9]. These authors used PMDA to increase the molecular weight of PET industrial scraps sourced from a PET processing plant. Tliey found that concentrations of PMDA between 0.50 and 0.75% promote chain extension reactions that lead to an increase of MW, a broadening of die MWD and branching phenomena which modify die PET scrap in such a way that makes 

A dramatic improvement in tire performance of PMDA in chain extension of PET is possible if the PMDA is added to tire extruder in a concentrate using a polycarbonate (PC) caiiier [10]. The reason being tliat if PMDA is compounded in a PET earner resin tlien a premature reaction results leading to ultra-high MW PET and gel problems. Alternatively, if PMDA is compounded in a polyolefin earner then degradation of tire polyolefin occurs whereas, when PMDA is compounded in a polycarbonate caiiier tliere is no premature reaction because PC contains no acid end groups (ratlier, -OH end groups instead). Furthermore, PC is quite miscible witli PET. 

Melt strength enhancement of PET and PBT for the prodnction of blown polyester foams 

As a melt viscosity and melt-strength-enhancing additive for modifying PET for film blowing and extmsion blow moulding apphcations Tensile strength enhancement of PET and PBT for strapping applications without the need for solid-state polycondensation 

Upgrading of recycled PET flake to resin suitable for bottling applications ( 0.80 dL/g) 

One of the main commercial uses of PMDA is to improve the melt strength of PET to allow it to be foamed. Unmodified PET cannot be foamed properly because its inherently low melt strength causes the cells to collapse and coalesce. 

Pyromellitic dianhydride (PMDA) is a solid having a melting point of 286°C. It contains two anhydride groups symmetrically attached to a benzene ring. Because of the compactness of the molecule, PMDA achieves very high crosslink densities and, therefore, high heat and chemical resistance. PMDA cured epoxy adhesives have a heat distortion temperature on the order of 280 to 290°C. 

The final two techniques described above are generally used in the preparation of PMDA cured adhesives. 

PMDA can be reacted with glycols to produce an adduct having the general structure shown in Fig. 5.8. These adduct resins form in the presence of solvent, under dry nitrogen. The reaction is continued until a clear solution is obtained. Such PMDA adducts are used in the formulation of high-temperature adhesive films. 

A PMDA dispersion is prepared by mixing finely powdered PMDA into liquid epoxy resins at room or slightly elevated temperature by stirring. No noticeable settling will occur in resins having an initial viscosity greater than 5000 cP. 

Because of its high functionality, PMDA can also be used in monoepoxy resins. These systems produce heat distortion temperatures on the order of 150°C. Cure times are relatively long, but may be accelerated by the addition of glycols or acidic accelerators. 

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Aromatic polyimides are the first example we shall consider of polymers with a rather high degree of backbone ring character. This polymer is exemplified by the condensation product of pyromellitic dianhydride [Vll] and p-amino-aniline [Vlll] ... 

Pis commonly have been synthesized from reactions of pyromellitic dianhydride [26265-89-4] (PMD A) or 3,3H,4 -benzophenone tetracarboxyUc dianhydride [2421-28-5] (B IDA) with a number of diamines like 2,2-bis(4-aminophenyl)propane, 2,2-bis(4-amino-3-methylphenyl)propane, I,I-bis(4-aminophenyl)-I-phenylethane, and 1,1-his(4-amino-3-methy1pheny1)-1-phenylethane (5). The PMDA-based Pis were thermally more stable than the corresponding Pis obtained from BTDA. 

Table 36. Physical Contants of Pyromellitic Acid and Pyromellitic Dianhydride...

Uses. Pyromellitic dianhydride imparts heat stabUity in applications where it is used. Its relatively high price limits its use to these applications. The principal commercial use is as a raw material for polyimide resins (see POLYIMIDES). These polypyromellitimides are condensation polymers of the dianhydride and aromatic diamines such as 4, -oxydianifine ... 

Because the heat distortion temperature of cured epoxy resins (qv) increases with the functionality of the curing agents, pyromellitic dianhydride is used to cross-link epoxy resins for elevated temperature service. The dianhydride may be added as a dispersion of micropulverized powder in liquid epoxy resin or as a glycol adduct (158). Such epoxies may be used as an insulating layer in printed circuit boards to improve heat resistance (159). Other uses include inhibition of corrosion (160,161), hot melt traffic paints (162), azo pigments (163), adhesives (164), and photoresist compounds (165). 

The pyromellitic dianhydride is itself obtained by vapour phase oxidation of durene (1,2,4,5-tetramethylbenzene), using a supported vanadium oxide catalyst. A number of amines have been investigated and it has been found that certain aromatic amines give polymers with a high degree of oxidative and thermal stability. Such amines include m-phenylenediamine, benzidine and di-(4-amino-phenyl) ether, the last of these being employed in the manufacture of Kapton (Du Pont). The structure of this material is shown in Figure 18.36. 

If trimellitic anhydride is used instead of pyromellitic dianhydride in the reaction illustrated in Figure 18.35 then a polyamide-imide is formed (Figure 18.37). The Torlon materials produced by Amoco Chemicals are of this type. 

Polyamide-imides may also be produced by reacting a diacid chloride with an excess of diamine to produce a low molecular mass polyamide with amine end groups. This may then be chain extended by reaction with pyromellitic dianhydride to produce imide linkages. Alternatively the dianhydride, diamine and diacid chloride may be reacted all together. 

In order to obtain cured products with higher heat distortion temperatures from bis-phenol epoxy resins, hardeners with higher functionality have been used, thus giving a higher degree of cross-linking. These include pyromellitic dianhydride IV, and trimellitic anhydride V. 

Heat distortion temperatures of resins cured with pyromellitic dianhydride are often quoted at above 200°C. The high heat distortion is no doubt also associated with the rigid linkages formed between epoxy molecules because of the nature of the anhydride. The use of these two anhydrides has, however, been restricted because of difficulties in incorporating them into the resin. 

The thermal properties of the resin are dependent on the degree of cross-linking, the flexibility of the resin molecule and the flexibility of the hardener molecule. Consequently the rigid structures obtained by using cycloaliphatic resins or hardeners such as pyromellitic dianhydride will raise the heat distortion temperatures. 

A considerable number of non-cross-linked aromatic and heterocyclic polymers has been produced. These include polyaromatic ketones, aromatic and heterocyclic polyanhydrides, polythiazoles, polypyrazoles, polytriazoles, poly-quinoxalines, polyketoquinolines, polybenzimidazoles, polyhydantoins, and polyimides. Of these the last two have achieved some technical significance, and have already been considered in Chapters 21 and 18 respectively. The most important polyimides are obtained by reacting pyromellitic dianhydride with an aromatic diamine to give a product of general structure (Figure 29.17). 

Epichlorohydrin with bisphenol A. The curing agents may pose significant health hazards, e.g. amines (triethylamine, p-phenylenediamine, diethylenetriamine) or acid anhydrides (pyromellitic dianhydride)... 

Potyimides obtained by reacting pyromellitic dianhydride with aromatic amines can have ladder-like structures, and commercial materials are available which may be used to temperatures in excess of 300°C. They are, however, somewhat difficult to process and modified polymers such as the polyamide-imides are slightly more processable, but with some loss of heat resistance. One disadvantage of polyimides is their limited resistance to hydrolysis, and they may crack in aqueous environments above 100°C. 

Various well established procedures are described in the literature273,274,296. The procedure generally used for polyesters is the phthalylation or acetylation of OH groups with phthalic or acetic anhydrides followed by back titration of excess carboxy groups. Moisture does not interfere but the addity of the sample must be taken into account. The use of pyromellitic dianhydride is also reported320. ... 

There are only two inexpensive dianhydrides 3,3,4,4,-benzophcnonctctracarbox-ylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA). Some other commercially available dianhydrides were used, like 3,3, 4,4 -biphenyltetracarboxylic dianhydride (BPDA), 2,2,-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), oxydiphthalic anhydride (ODPA), and 3,3/,4,4/-diphenylsulfonetetracarboxylic dianhydride (DSDA) (Fig. 5.29). Many other dianhydrides are reported in the literature (Fig. 5.30) ... 

Hedrick et al. reported imide aryl ether ketone segmented block copolymers.228 The block copolymers were prepared via a two-step process. Both a bisphenol-A-based amorphous block and a semicrystalline block were prepared from a soluble and amorphous ketimine precursor. The blocks of poly(arylene ether ether ketone) oligomers with Mn range of 6000-12,000 g/mol were coreacted with 4,4,-oxydianiline (ODA) and pyromellitic dianhydride (PMDA) diethyl ester diacyl chloride in NMP in the presence of A - me thy 1 morphi 1 i nc. Clear films with high moduli by solution casting and followed by curing were obtained. Multiphase morphologies were observed in both cases. 

PLA degradation, 43 Planar polymer, synthesis of, 505 PLLA. See Poly(L-lactic acid) (PLLA) PMDA. See Pyromellitic dianhydride (PMDA)... 

Recently siloxane-imide copolymers have received specific attention due to various unique properties displayed by these materials which include fracture toughness, enhanced adhesion, improved dielectric properties, increased solubility, and excellent atomic oxygen resistance 1S3). The first report on the synthesis of poly(siloxane-imides) appeared in 1966, where PMDA (pyromellitic dianhydride) was reacted with an amine-terminated siloxane dimer and subsequently imidized 166>. Two years later, Greber 167) reported the synthesis of a series of poly(siloxane-imide) and poly(siloxane-ester-imide) copolymers using different siloxane backbones. However no physical characterization data were reported. 

Polyimide-clay nanocomposites constitute another example of the synthesis of nanocomposite from polymer solution [70-76]. Polyimide-clay nanocomposite films were produced via polymerization of 4,4 -diaminodiphenyl ether and pyromellitic dianhydride in dimethylacetamide (DMAC) solvent, followed by mixing of the poly(amic acid) solution with organoclay dispersed in DMAC. Synthetic mica and MMT produced primarily exfoliated nanocomposites, while saponite and hectorite led to only monolayer intercalation in the clay galleries [71]. Dramatic improvements in barrier properties, thermal stability, and modulus were observed for these nanocomposites. Polyimide-clay nanocomposites containing only a small fraction of clay exhibited a several-fold reduction in the... 

Pyrocatechol, d428 Pyrogallol, t317 Pyromellitic acid, b27 Pyromellitic dianhydride, b28 Pyromucic aldehyde, f44 Pyrrolidinedithiocarbamate, p282... 

As a final example the spectra of molecular charge-transfer complexes are considered next. Electron acceptors such as pyromellitic dianhydride, chloranil and tetracyanobenzene... 

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