Poly Formal s

A/jAf-dimethylacetamide pMAc), DMSO, hexamethylphosphoric triamide (HMPA), and A-methyl-2-pyrrolidone (NMP) may be used as cosolvents. 

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 of Bisphenol 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 of Bisphenol AF, resulting in the formation of Bisphenol AF poly(formal) (7) with reduced viscosity of 4.62 dl/g in a 87% yield at 75°C.  

Copoly(formal)s (8) with high reduced viscosities are readily obtained in high yields irrespective of the feed ratio of Bisphenol AF (1) and Bisphenol A (4) (Table 9.6). 

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, 

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 

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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 9.6. Preparation of Fluorine-Containing Poly(Formal)s ...

Polyformals of bisphenols and dichloromethane were prepared by polyetherification in dimethylsulfoxide at 80 °C (22). The poly(formal)s of bisphenol-A, tetramethylbisphenol-A (TMBA), and their copolymers were generated by this method. High molecular weight polymers were obtained, except in the case of TMBA homopolymers where crystallization led to premature precipitation. Incorporation of 70% TMBA afforded an increase in Tg from 88 C to 113 C. The l,4-dihydroxy-2-cyclohexenols were prepared under phase-transfer conditions with dibromomethane (23). These polymers were evaluated as self-developable resists. 

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