Polysulfone chloromethylation

Chloromethylation was also carried out to modify the polysulfone for preparing membrane materials.171... 

Techniques for chloromethylating polyarylether sulfones, polyphenylene oxide, phenolic resins, and model compounds were described recently [191]. When the subsequent products are cmiverted to quaternary amines, there is a decrease in the quatemization rate with increase in degree of substitutimi. This may be due to steric effects imposed by restricted rotation of the polymeric chains [191]. This phenomenon was not observed in quatemization of poly(chloromethyl styrene). The chloromethylation reaction of a polysulfone with chloromethyl ether, catalyzed by stannic chloride, can be illustrated as follows ... 

CLh Chloromethylated polysulfone 6.0 DOPO (pendant) Enhanced (nitrogen) No 22... 

Polysulfonates with reactive pendent chloromethyl groups (63) can be synthesized by solution polymerization of bisepoxides (64) with disulfonyl chlorides (65) (207). 

If the anion exchange membrane is prepared from a monomer (approach a ), polysulfone, polyethylene, or styrene and divinylbenzene are most commonly used for traditional hydrocarbon type membranes, from which the membrane is usually prepared by chloromethylation followed by quaternary amination. Numerous references exist in the alkaline membrane fuel cell literature for homogeneous anion exchange membrane preparation using this method (see, for instance, [4, 5]). 

Quaternary ammonium ion exchange resins were produced initially by chloromethylating crosslinked polystyrene beads with chloromethyl methyl ether, followed by quaternization with tertiary amines. We have circumvented exposure to the highly carcinogenic bis(chloromethyl) ether, a common contaminant of commercial chloromethyl methyl ether, by employing l,4-bis(chloromethoxy)butane or 1-chloromethoxy-4-chlorobutane and have produced chloromethylated poly(oxy-2,6-dimethyl-1,4-phenylene) and polysulfone. Alternatively, chloromethyl methyl ether can be generated from acetyl chloride and methylal, and the reaction mixture utilized directly in chloromethylation of activated aromatic repeat units. 

Chloromethylatlon of Polysulfone A solution of chloromethyl methyl ether (6 mmole/ml) in methyl acetate was prepared by adding acetyl chloride (141.2 g, 1.96 mol) to a mixture of dimethoxymethane (180 ml, 2.02 mol) and anhydrous methanol (5.0 ml,0.12 mol). The solution was diluted with 300 ml of 1,1,2,2,-tetrachloroethane and SnCl (1.05 ml, 0.009 mol) was added. After the mixture was brought to reflux, a solution of polysulfone (40 g, 0.09 eq) in 500 ml tetrachloroethane was added slowly. Refluxing was maintained for 3 hours before the catalyst was deactivated by injecting 5 ml of water into the reaction mixture. The reaction volume was reduced to 400 ml before precipitating the chloromethylated polysulfone, in methanol. After reprecipitating from chloroform in methanol,... 

The second order nature of quaternization reactions in our system was confirmed by rate studies on model compounds. Although benzyl chloride is usually selected as the model for chloro-methylated polymers , we chose to synthesize a difunctional model that would be sensitive to neighboring group effects. Condensation of 4-chlorophenyl phenyl sulfone with the disodlum salt of bis-phenol-A yielded an excellent model for the polysulfone segment, Quantitative chloromethylation of with a chloromethyl methyl ether/ methyl acetate mixture in the presence of stannic chloride afforded the corresponding bischloromethyl adduct,... 

The equivalent reactivity of the two chloromethyl groups on 2 is contrary to the observations of Chow and Fuoss, who reported that the quaternization of the second nitrogen in the bis-pyridyl-alkanes was much slower. This negative deviation was attributed to the extramolecular electrostatic field effect produced by the positive charge on the first nitrogen. It is obvious that the electrostatic effect did not appear in the polysulfone model system. 

A survey of the reaction conditions required to quaternize chloromethylated condensation polymers in a homogeneous media revealed that mixed solvent systems would be required to handle poly(oxy-2,6-dimethyl-3-chloromethyl-1,4-phenylene), The reaction of triethylamine with chloromethylated polysulfone proceeded cleanly in pure DMSO, and a model compound was easy to synthesize. Therefore, we focused our initial attention on polysulfone derivatives. 

Chloromethylated polysulfone containing an average of 1.9 chloromethyl groups per repeating unit, 3, was treated with triethylamine in DMSO. We expected the isolation of active sites demonstrated with the model 2 would prevail in the polysulfone system. This was not the case, as is evident in Figure 3. The kinetic plots are concaved downward because the quaternlzation of the polysulfone proceeds less and less rapidly as the degree of conversion increases.The quaternlzation of with TEA can be modeled by two reaction rate constants, kg and Normally, three... 

Most observations of rate retardation in polymer modifications have been attributed to steric hindrance. In order to estimate the steric influence of the relatively bulky triethyIbenzylammonium substituent on unreacted site during quaternization, quinuclidine was chosen as nucleophile. It is well known that nucleophilicity of quinuclidine in displacement reactions is greater than that of triethylamine, since bicyclic amines are less sterically hindered. Preliminary experiments on the quaternization of chloromethylated polysulfone with quinuclidine in DMSO showed that the reaction velocity was too rapid to investigate using our experimental techniques, i.e., 85% conversion was obtained with three minutes. Therefore, we were forced to add a less polar solvent to DMSO in order to reduce the reaction rate. It was found that a 50 50 (v/v) mixture of dioxane and DMSO dissolved both chloromethylated and quaternized polysulfone so the rate could be measured in a homogeneous system. The introduction of a nonpolar solvent reduced the initial rate of triethylamine substitution fourfold (Table III, run 17). 

Chloromethylated polysulfone indeed exhibits different kinetic behavior in the quaternization with TEA than its corresponding model compound. From experimental results, it is clear that the rate retardation is not due to steric hindrance, the degree of chloro-methylation on the polymer chain, or a salt effect. Stereoisomeric effects are not a potential factor, since chloromethylated polysulfone consists of only one detectable isomer. In spite of these results, we knew that the polymer backbone must play an important role in this reaction. Under the same experimental conditions used to quaternize chloromethylated polysulfone, poly(vinylbenzyl chloride) exhibited normal second-order kinetics with an Ea of 10.4 kcal/mole, as shown in Figure 6. Noda and Kagawa also observed the same phenomenon in the quaternization of chloromethylated polystyrene with TEA in DMF (Ea = 10.5 kcal/mole)The major difference between these two systems is the polymer backbone polysulfone... 

Yang JS, Li QF, Cleemann LN et al (2013) Cross-linked hexafluoropropylidene polybenzimidazole membranes with chloromethyl polysulfone for fuel cell applications. Adv Energy Mater 3 622-630... 

Among the available commercial polysulfones, UDEL has been largely reported in the literature. The advantage of this polymer is its better solubility in organic solvents compared to other polysulfone (i.e. RADEL) which enables to use different reactions for the chemical modification i.e. (i) electrophilic substitution which lead to chloromethylation, halogenation, and sulfonation, (ii) nucleophilic substitution by use of lithiation chemistry. 

One of main routes to achieve new characteristics of polysulfones is polymer modification. There are two ways to functionalize PSFs. The first way is post-polymerization modification, in which the polymer is functionalized after polymerization. PSF can be chemically modified by both electrophilic and nucleophilic reactions to yield new polymers with specific properties. Electrophilic reactions (for example sulfonation, chloromethylation followed by aminolysis) take place in the electron-rich bisphenol A part of PSFs [4-9], whereas nucleophilic reactions (in example lithiation with Li-organic compounds followed by reaction with aldehydes, ketones or carboxylic acid esters) can be performed in the electron-deficient diarylsulfone [10-17]. 

Schema 6.3 Reaction between chloromethylated polysulfone and different phosphorus compounds.

Polysulfone (from di(4-hydroxyphenyl) sulfone and bisphenol A), chloromethylated... 

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