Sulfonium polymers

Purification of precursor sulfonium polymer 10 is achieved by dialysis to remove small oligomeric material (typically < 5000 g/mol depending on dialysis... 

Development of xanthate and dithiocarhamate derivatives overcomes several drawbacks of the sulfonium monomer (Scheme 7.2b and c). Xanthates and dithiocarbamates are easily prepared by the reaction of bis(halomethyl)benzene with alkylxanthate and dialkyldithiocarbamate salts respectively. Both precursors are stable at room temperature and soluble in organic solvents. This means the polymerization of these monomers can be performed in organic solvents e.g. THE) with the addition of alkoxide base e.g. potassium tert-butoxide). For the dithiocarhamate precursor, lithium bis(trimethylsilyl)amide can be used as the base and the polymerization proceeds at 35 The elimination temperature of these precursor polymers is typically lower than that of the sulfonium polymers with xanthate elimination at 160-250 °C and dithio-carbamate at 180 °C. It has been found that elimination of dithiocarbamate gave materials with reduced structural defects. Both xanthate and dithiocarbamate routes avoid the corrosive acid byproducts (HCl) present in the sulfonium elimination. This is particularly advantageous in device fabrication as adds have a negative impact on indium tin oxide electrodes and interfaces. ... 

Sulfonium Polymers. Polysulfonium salts have been extensively studied because of the versatile possibilities of their application. They can be used as ion-exchange resins, polymer supports in peptide synthesis, polymeric reagents, and... 

Other methods that have been used for the conversion of sulfonium polymers to PPV include the use of strong acids [101] and microwave heating [102]. It is also possible to grow films of PPV from the sulfonium precursor polymer electrochemically. The formation of PPV is thought to arise from a local increase in the pH around the electrode due to hydrolysis reactions, leading to elimination of the precursor polymer [461. 

Linear and aromatic conjugated polymers have gained great interest in last decade for several reasons. The problem of inprocessibility was circumvented either by the use of substituted monomers [e.g. poly(alkylthiophene) (i), poly(al-kylphenylene) (2), etc.] or by preparation via precursor polymers as shown for polyacetylene (3), poly-p-phenylene (4) and poly(arylene vinylene) (5). The latter ones are mainly prepared via sulfonium polymers in a condensation reaction. This gives bad control of the average molar mass and of the molar mass distribution. 

Poly(arylene vinylenes). The use of the soluble precursor route has been successful in the case of poly(arylene vinylenes), both those containing ben2enoid and heteroaromatic species as the aryl groups. The simplest member of this family is poly(p-phenylene vinylene) [26009-24-5] (PPV). High molecular weight PPV is prepared via a soluble precursor route (99—105). The method involves the synthesis of the bis-sulfonium salt from /)-dichloromethylbenzene, followed by a sodium hydroxide elimination polymerization reaction at 0°C to produce an aqueous solution of a polyelectrolyte precursor polymer (11). This polyelectrolyte is then processed into films, foams, and fibers, and converted to PPV thermally (eq. 8). 

In an attempt to prepare sulfonium-ylide polymer, Tani-moto and coworkers [57,58] carried out the reaction of a sulfonium salt polymer with benzaldehyde in the presence of a base and obtained styrene oxide. The reaction was considered to process via a ylide polymer formation (Scheme 24), which may be unstable and has not been isolated. 

The structures of these ylide polymers were determined and confirmed by IR and NMR spectra. These were the first stable sulfonium ylide polymers reported in the literature. They are very important for such industrial uses as ion-exchange resins, polymer supports, peptide synthesis, polymeric reagent, and polyelectrolytes. Also in 1977, Hass and Moreau [60] found that when poly(4-vinylpyridine) was quaternized with bromomalonamide, two polymeric quaternary salts resulted. These polyelectrolyte products were subjected to thermal decyana-tion at 7200°C to give isocyanic acid or its isomer, cyanic acid. The addition of base to the solution of polyelectro-lyte in water gave a yellow polymeric ylide. 

In a pioneering article, Farrall et al. [61] reported the preparation of fuUy regenerable sulfonium salts anchored to an insoluble polymer and their use in the preparation of epoxides by reaction of their ylides with carbonyl compounds. Their results clearly indicate that... 

Kondo maintained his interest in this area, and with his collaborators [62] he recently made detailed investigations on the polymerization and preparation of methyl-4-vinylphenyl-sulfonium bis-(methoxycarbonyl) meth-ylide (Scheme 27) as a new kind of stable vinyl monomer containing the sulfonium ylide structure. It was prepared by heating a solution of 4-methylthiostyrene, dimethyl-diazomalonate, and /-butyl catechol in chlorobenzene at 90°C for 10 h in the presence of anhydride cupric sulfate, and Scheme 27 was polymerized by using a, a -azobisi-sobutyronitrile (AIBN) as the initiator and dimethylsulf-oxide as the solvent at 60°C. The structure of the polymer was confirmed by IR and NMR spectra and elemental analysis. In addition, this monomeric ylide was copolymerized with vinyl monomers such as methyl methacrylate (MMA) and styrene. 

The sulfonium precursor route may also be applied to alkoxy-substituted PPVs, but a dehydrohalogenation-condensation polymerization route, pioneered by Gilch, is favored 37]. The polymerization again proceeds via a quinomethide intermediate, but die syndicsis of the conjugated polymer requires only two steps and proceeds often in improved yields. The synthesis of the much-studied poly 2-methoxy-5-(2-ethylhexyloxy)-l,4-phenylene vinylene], MEH-PPV 15 is outlined in Scheme 1-5 33, 35]. The solubility of MEH-PPV is believed to be enhanced by the branched nature of its side-chain. 

The final elimination step in which the conjugated PPV derivative (63) is generated from the sulfonium polyelectrolyte precursor polymer (62) was reported by Wessling and Zimmerman to be heating in vacuo to 200 - 300°C. The target PPV derivative is formed with elimination of dialkyl sulfide and hydrogen halide the process can be easily monitored by UV/Vis spectroscopy. PPVs... 

RW Lenz, C-CHan, J Stenger-Smith, and FE Karasz, Preparationofpoly(phenylene vinylene) from cycloalkylene sulfonium salt monomers and polymers, J. Polym. Sci., Part A, 26 3241-3249, 1988. 

Polyether 618 The sulfonium polyelectrolyte 617 was dissolved in a minimal amount of methanol. The solution was stirred for 1 week under argon, during which pendant polyether 618 precipitated from the solution. The tacky yellow material was completely soluble in CHC13 and THF. Polymer 618 can be dissolved in THF and passed through a 0.2-mm filter for GPC or for use in film casting and device fabrication. Cast films can be completely redissolved into CHC13 or THF. GPC in THF (polystryrene standards) gave A/w = 91,500 and Mn = 33,800. 

Analyses were performed on each of the resist components to determine the source of the background acid. Background acid was present in all three resist components — polymer, sulfonium salt, and casting solvent. However the sulfonium salt contained the highest concentration of acid by two orders of magnitude. Residual acid in sulfonium salt may be due to the method of preparation which involves an aqueous metathesis step to exchange the hexafluoroantimonate ion for bisulfate. This procedure is likely to produce hydrogen fluoride due to hydrolysis of hexafluoroantimonate salt (14). 

Table 1. Acid Production and Quantum Yields from Irradiation at 254 nm of Polymer 3 Films Containing 1% Sulfonium Salt 4...

Thus the quantum yield for acid production from triphenylsulfonium salts is 0.8 in solution and about 0.3 in the polymer 2 matrix. The difference between acid generating efficiencies in solution and film may be due in part to the large component of resin absorption. Resin excited state energy may not be efficiently transferred to the sulfonium salt. Furthermore a reduction in quantum yield is generally expected for a radical process carried out in a polymer matrix due to cage effects which prevent the escape of initially formed radicals and result in recombination (IS). However there are cases where little or no difference in quantum efficiency is noted for radical reactions in various media. Photodissociation of diacylperoxides is nearly as efficient in polystyrene below the glass transition point as in fluid solution (12). This case is similar to that of the present study since the dissociation involves a small molecule dispersed in a glassy polymer. 

Use of a Difunctional Crosslinker. An alternate approach to chemically amplified imaging through electrophilic aromatic substitution is shown in Figure 6 below. In this approach a polyfunctional low molecular weight latent electrophile is used in a three component system also including a photoactive triaryl sulfonium salt and a phenolic polymer. In this case again crosslinking of the polymer is observed upon... 

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