Poly-formal

Hay et al.w,n have prepared high-molecular-weight a Bisphenol-A-derived poly(formal) (6) using a phase-transfer catalyst in DCM. A Bisphenol-AF-derived poly(formal) (7) is also synthesized by solution polycondensation of Bisphenol AF (1) with DCM in highly polar cosolvents in the presence of potassium hydroyxide (Scheme 3).12 Aprotic polar solvents such as A/W-dimethylformamide... 

A large excess of DCM to Bisphenol AF (1) is required for production of high-molecular-weight Bisphenol A poly(formal) (7) because DCM acts as the reactant as well as the cosolvent. The most suitable molar amount of DCM is about 12 times that ofBisphenol AF (1). 

The effects of cosolvents on the reduced viscosity and yield are summarized in Table 9.5. DMAc and NMP lead to the formation of high-molecular-weight Bisphenol AF poly(formal) (7) in a high yield. The optimum reaction conditions are 48 mmol of DCM, 14 mmol of potassium hydroxide, and 5 ml of NMP for 5 mmol ofBisphenol AF, resulting in the formation ofBisphenol AF poly(formal) (7) with reduced viscosity of 4.62 dl/g in a 87% yield at 75°C.12... 

Bisphenol-A-derived poly(formal) (6) shows poor solubility and is only soluble in dichloromethane, chloroform, THF, HMPA, and NMP. However, poly(formal)s containing the Bisphenol AF moiety are easily soluble in a wide variety of organic solvents, such as acetone, ethyl acetate, benzene, toluene,... 

Table 9.5. Effect of Cosolvent on the Yield and Reduced Viscosity of Bisphenol-AF-Derived Poly(Formal)12... 

Resistance to acids is improved by the introduction of fluorine atoms. Bisphenol A poly(formal) (6) decomposes rapidly with significant coloration in strong acids, whereas Bisphenol AF poly(formal) (7) is stable in concentrated sulfuric acid.12... 

A contact angle by water is 86° for Bisphenol A poly(formal) (6), is increased to 93° by the introduction of 28 mol% of hexafluoroisopropylidene unit, and then becomes almost constant irrespective of fluorine content.12 As... 

Table 9.6. Preparation of Fluorine-Containing Poly(Formal)s12...

Figure 9.1. TG-DTA curves for Bisphenol A-derived poly(formal) (A) and Bisphenol AF-derived poly(formal) (AF).

The FTIR spectra of the gas mixture evolved in thermal decomposition of Bisphenol AF poly(formal) (7) at various temperatures suggest the existence of benzene rings, C—O—C bonds, and C=C bonds. In a pyrogram of pyrolysis gas chromatography (Py-GC) of Bisphenol A (3), a-methylstyrene, phenol, p-cresol, 4-hydroxy-amethylstyrene, and isopropyl phenol are observed as major peak products. The cleavage reactions shown in Scheme (5) is suggested for the formation of phenol and 4-hydroxy-a-methylstyrene from Bisphenol A (3). 

In a pyrogram of Bisphenol A poly(formal) (6), the peak products are identified as a-methylstyrene, phenol, 4-hydroxy-a-methylstyrene, and isopropyl phenol by Py-GC/MS. These products are identical with the degradation products from Bisphenol A. In addition to the decomposition products of Bisphenol A, 4-isopropenyl anisole is also identified as a product. The pyrograms of Bisphenol AF poly(formal) (7) contain only two major species, pentafluoroisopropenyl benzene (product T) and pentafluoroisopropenyl anisole (product 2 ). They correspond to a-methylstyrene, 4-hydroxy-amethylstyrene from Bisphenol A poly(formal) (6) and are produced by the cleavage of phenylene-oxy bonds and oxy-methylene bonds according to (Scheme 6). 

The bond dissociation energy of phenylene-oxy bonds is not very different from that of oxy-methylenebonds. Accordingly, the two-step decrease in weight of hexafluoroisopropylidene-unit-containing poly(formal)s, especially Bisphenol AF poly(formal) (7), is not brought about by a different reaction mechanism from... 

Table 9.7. Thermal Properties of Fluorine-Containing Poly(Formal)s ...

The solid-phase method of building up polyformals is applicable only to high-melting polymers. The required melting point is not known, but the poly-formal of trarw-l,4-cyclohexanediol melted at 206°—10° C. and that of the cis-/ trans- mixture of 2,2,4,4-tetramethyl-l,3-cyclobutanediol melted appreciably higher. The solution method did not appear to be applicable to building up the polyformals of these two diols, since inherent viscosities below 0.4 were obtained. The solution method may be most applicable to primary diols, such as cyclohexanedimethanol and decanediol, which gave polyformals with inherent viscosities of 0.9. 

In these experiments with tetramethylcyclobutanediol, it was found that methanedisulfonic acid gave higher polyformals than the other catalysts. Inherent viscosities up to 1.7 were obtained, whereas values of only 0.8 to 0.9 resulted with camphorsulfonic acid or p-toluenesulfonic acid and 0.7 when perchloric acid was used. It was necessary to use 0.002 to 0.005 equivalent of camphorsulfonic acid or toluenesulfonic acid per mole of diol in order to obtain the poly formal, but 0.001 equivalent of perchloric acid or 0.001 to 0.002 equivalent (0.0005 to 0.001 mole) of methanedisulfonic acid was sufficient to catalyze the polymerization in the various solvents. When appreciably less catalyst was used, the polymers did not build up, and when appreciably more was used, brown polymers were obtained. 

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