Poly electron-withdrawing groups

The nucleophilic aromatic substitution reaction for the synthesis of poly(arylene ether ketone)s is similar to that of polysulfone, involving aromatic dihalides and aromatic diphenolates. Since carbonyl is a weaker electron-withdrawing group titan sulfonyl, in most cases, difluorides need to be used to afford high-molecular-weight polymers. Typically potassium carbonate is used as a base to avoid the... 

The polyetherification route to polyethersulfones can be adapted to the synthesis of polyethers containing strongly electron-withdrawing groups other than sulfone groups. Poly(l,4-oxyphenylenecarbonyl-l,4-phenylene) [27380-27 4] (6) is produced by condensation of 4,4 -dihydroxybenzophenone or by the self-condensation of 4-chloro-4 -hydroxybenzophenone. It has a melting point of 367°C and a glass-transition temperature of 154°C (83). 

The chain-growth condensation polymerization leading to aromatic polyether can be applied to the synthesis of a well-defined poly(ether sul-fone) by the condensation polymerization of 25, which is different from other monomers for chain-growth condensation polymerization in that the nucleophilic site and electrophilic site are on each benzene ring connected with an electron-withdrawing group, a sulfonyl group (Scheme 94). In the polymerization of 25 in the presence of an initiator and 18-crown-6 in sulfolane at... 

Both simple and fused poly substituted pyran-2-ones can be obtained from the reaction between substituted allenyl esters and ketones activated by an electron-withdrawing group. A base-catalysed nucleophilic conjugate addition affords a homoallylic ester and lactonisation completes the one-pot sequence (Scheme 19) <06S2731>. 

The second general method into the thiochrom-4-one ring involves the interaction of a thiophenol with compounds possessing a carbon atom bonded by at least two electron withdrawing groups, usually in the presence of a dehydrating agent (phosphorus pentoxide or poly-phosphoric acid). The first application of this was by Simonis and Elias and is illustrated in Eq. (19). The most successful active methylene substrates have been /3-ketoesters, i )3-cyanoketones, ... 

As indicated above, the introduction of electron-withdrawing groups is one of the strategies for improving the sensitivity of PMMA-type resists. This is best exemplified by fluorination in the ester moiety of PMMA, which has produced many useful electron-beam resists, such as poly(perfluorobutyl methacrylate) (XXII),... 

The analysis of NMR spectra of aliphatic and aromatic poly anhydrides has been reported by Ron et al. (1991), and McCann et al. (1999) and Shen et al. (2002), and C NMR has been reported by Heatley et al. (1998). In NMR, the aliphatic protons have chemical shifts between 1 and 2 ppm, unless they are adjacent to electron withdrawing groups. Aliphatic protons appear at about 2.45 ppm when a to an anhydride bond and can be shifted even further when adjacent to ether oxygens. Aromatic protons typically appear with chemical shifts between 6.5 and 8.5 ppm and are also shifted up by association with anhydride bonds. The sequence distribution of copolymers can be assessed, for example in P(CPH-SA), by discerning the difference between protons adjacent to CPH-CPH bonds, CPH-SA bonds, and SA SA bonds (Shen et al., 2002). FTIR and NMR spectra for many of the polymers mentioned in Section II can be found in their respective references. 

Various synthetic approaches have been demonstrated for the synthesis of PAEs since early days [35 0], PAEs were synthesized by Ullmann condensation between bisphenols and aryl fcis-halide monomers using Cu(I) salt/pyridine as catalyst [36], General Electric developed the first commercially successful PAE poly(2,6-dimethyl phenylene oxide) (PPO) [38], It was prepared by oxidative coupling of 2,6-dimethyI phenol. However, this process has its own restrictions, because it does not allow much structural variation or inclusion of any electron-withdrawing group into the polymer main chain. First attempts to synthesize polysulfones (PSF) were successfully done by Friedel-Crafts sulfonylation reaction of arylenedisulfonyl chlorides, for example, diphenyl ether-4,4 -disulfonyl chloride with diaryl ethers, for example, diphenyl ether, or by self-condensation of 4-phenoxy benzene sulfonyl chloride in the presence of FeCls [41], Whereas the former reaction involves side reactions (sulfonylation not only in the para- but also in the ort/io-position), the latter produces only the desired linear all-para products. 

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