A low temperature polycondensation for the preparation of highly fluorinated poly(arylene ether sulfone)s containing crosslinkable pentafluorostyrene moieties

The polycondensation of pentafluorophenyl sulfone (PPSO) with hexafluorobisphenol A (6F-BPA), or a model compound, 4-phenoxylphenol (POPOH), has been studied in order to find optimized reaction conditions for the preparation of fluorinated poly(arylene ether sulfone)s (FPAESs). It was found that PPSO had a very high reactivity in N,N-dimethylacetamide (DMAc), allowing the reaction to occur at temperatures as low as 22 degrees C, even in the absence of any catalyst. This reaction was promoted by the addition of a trace amount of potassium fluoride (KF). Increasing the amount of KF to 1.05 equiv enhanced the conversion and allowed the reaction to be completed in a short time. Under this reaction condition, KF acted as a catalyst to activate the phenol group and also acted as a base to absorb the HF, which was a by-product of the polycondensation, to produce high molecular weight polymer. The use of calcium hydride (CaH2) instead of KF as a base in this reaction produced a similar effect with a slightly lower reaction rate. Both base systems were also applicable to the reaction of pentafluorostyrene (FSt) with 6F-BPA. However, a much higher reaction temperature (125 degrees C) was required due to the low reactivity of FSt. Reacting FSt with an excess of 6F-BPA produced a mixture of mono- and di-substituted products of FSt with a controllable ratio, which could further react with PPSO to produce a polymer containing crosslinkable FSt moieties both as end-capping groups and inserting units. This structure allowed the molecular weight of the polymer and the content of FSt to be adjusted independently. Cross] inked films of this polymer demonstrated an excellent processability and performance in waveguide applications, having refractive indices of 1.5061 (TE) and 1.5038 (TM), and a straight waveguide loss of 0.7 dB center dot cm(-1).