Polystyrene-Supported Onium Salts as Phase-Transfer Catalysts

Chapter 19

Polystyrene-Supported Onium Salts as Phase-Transfer Catalysts Their State and Reactivity in Phase-Transfer Reaction Conditions

Downloaded by MONASH UNIV on August 28, 2013 | http://pubs.acs.org Publication Date: February 1, 1997 | doi: 10.1021/bk-1997-0659.ch019

Noritaka Ohtani, Yukihiko Inoue, Jun Mukudai, and Tsuyoshi Yamashita Department of Materials Engineering and Applied Chemistry, Mining College, Akita University, Akita 010, Japan Intraresin microstructure is decisive for the interpretation of the kinetics and mechanism of triphase catalysis. The linear polystyrenes containing onium salts have been used to evaluate the intraresin microstructure under liquid-solid-solid triphase conditions or liquid-solid-liquid triphase conditions. Their solution viscosity behavior under one-fluid systems and their phase separation behavior under two-fluid systems have strongly suggested that intraresin microstructure of a microporous polymer catalyst varies with the reaction conditions and governs transport phenomena of reagent ions and organic substrates. The microstructure also determines the.microenvironment where polymer-bound onium salts collide to react with organic substrates. The role of ionic aggregation under liquid-solid-solid triphasé conditions and the interfacial reaction mechanism under liquid-solid-liquid triphasé conditions will be discussed.

A substantial effort in our laboratory has been directed toward polymer-supported reactions. The most significant examples are triphasé catalysis of nucleophilic reactions (1,2), base-catalyzed reactions using a fluoride form of ammonio-attaching polystyrenes (5), hydrolysis and ester exchange of water-insoluble amino acid esters using carboxylate or ethylene diamine-attaching polystyrenes with metal ions (4), and similar reactions catalyzed by chymotrypsin that is supported on the above polymers (5). This paper deals with the recent development of the first subject promoted by our work. Polymer-supported phase-transfer catalytic systems generally consist of three phases; a bulk organic solution phase, a bulk aqueous solution or solid reagent phase, and an insoluble ρ oly mer cataly st ρ hase. Undoubtedly, chemical react ion takes ρ lace in the resinous phase. Besides the tremendous reports on synthetic aspects of triphasé catalysis, there have been many kinetic studies on the triphasé catalysis (6~ 12). However, most of the kinetic studies have interpreted the over-all rates without considering what is a main ionic species diffusing through the resin interior, what is a real reacting ionic species, and in what kind of microenvironment the species collide to react with the organic substrate. It is important to clarify the microstructure of the resin interior that is formed when the resin is placed under a given reaction condition, because the microstructure should be responsible not only for the mass-transport of the substrate and ionic species but also for the real reactant ionic species. Most © 1997 American Chemical Society In Phase-Transfer Catalysis; Halpern, M.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.

19.

OHTANI ET AL.

Polystyrene-Supported Onium Salts

249

Τ

gh0^CH N -R X r

^CH

2

PxBuX

+

AxRX -ÇH^CH -CH^ 2

CH -rjlH3 X" 3

CH LAxRX 3

HCI^-CH>F dissociated ions. Figure 2 shows the effect of solvent on the viscosity behavior of LAlOMeCl. Nitromethane and methanol showed typical polyelectrolyte effects. In contrast, in a solvent with low 1 dielectric constant, such as chloroform or THF, we could not observe the polyelectrolyte effect. Figure 2. Viscosity behavior of LAlOMeCl The reduced viscosity rather in several solvents at 25 °C. decreased with decreasing ionomer concentration. The ionomer behaves like non-ionic polymers. In toluene or THF, the reduced viscosity of an ionomer with chloride counterions was always decreased with an increasing ion content. A typical example is shown in Figure 3 and Figure 4a. This decrease in the reduced viscosity shows that an ionomer domain contracts with ion content, which indicates the formation of intrachain aggregates in such a low AN solvent. The solvation to 1 chloride ions is very weak in such a solvent. Thus, the intrachain aggregation takes place. In Figure 3. Viscosity behavior of LPxBuCl in chloroform, on the other hand, THF at 25 °C. LA*OcCl and LPxBuCl gave a similar value of reduced viscosity irrespective of their ion content; the value was close to that of each parent chloromethylated polystyrene (Figure 4a), indicating few aggregation between ionic groups due to a strong solvation to the counter ions.

0.8 £ 0.6 0.4 0.2


i

0 0.1 0.2 0.3 0.40.5 0.6 Ionomer Concentration/ g dL

0 0.2 0.4 0.6 Ionomer Concentration /gdL'

Conformations of an Ionomer Chain in Solutions. If an ionomer is dissolved in a solvent, interchain aggregation no longer plays an important role. Therefore, solvations to the ionic groups are important also for the dissolution of an ionomer. When an ionomer is solubilized in a solvent, the ionomer may be extended with the dissociation of the ionic groups. This extended conformation may be taken in methanol or acetonitrile that has a high dielectric constant. Alternatively, the ionomer may be contracted by the intrachain aggregation of ionic groups. Toluene

In Phase-Transfer Catalysis; Halpern, M.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.

19. OHTANI ET AL.

0.5 J Ό

*b>0.4


toluene chloroform methanol

= 1

f 0.3 .t


251

Ι

5 10 15 prs (χ) in LPxBuCI (a) Reduced Viscosity of LPxBuCI (DP = 350)

0.5

toluene chloroform acetonitrile methanol

10 20 30 40 prs (x) in PxBuCI (b) Swelling of PxBuCI

Figure 4. Solution viscosity and swelling of linear and crosslinked ionomers in several solvents at 25 °C. and THF give LAJCRCI or LPxBuCI this contracted conformation that resembles a reversed micelle. The volume of the ionomer domain may be very close to that of the parent polymer if a nonpolar solvent has a great affinity to solvate either small quaternary cations or small counter anions of the ionomer (75). Interestingly, by adding low-molecular-weight onium salts, ionomers with high ionic loading are solubilized in such a nonpolar solvent as toluene or THF. With an increasing concentration of trioctylmethylammonium chloride (TOM AC), the reduced viscosity of LA7.50cCl in THF increased and approached the value of its parent chloromethylated LA7.50cCl Og/dl polystyrene (16). This shows an 2.5 LA7.50cCl 0.1g/dl expansion of the ionomer chain and LA7.50cCl 0.25g/dl suggests a decrease in the intrachain aggregation among the ionomer ionic groups. Linear ionomers are soluble to •• even in water provided the ionic < loading is not extremely low. They show poly electrolyte behavior in water (16). The addition of an 0.5 electrolyte to the aqueous solution diminishes the polyelectrolyte effect. oHI- -3 As shown in Figure 5, the aqueous io Ι Ο Ι Ο 10° 10 LA7.50cCl solution solubilizes a [CTAC] / mmolL" water-insoluble neutral dye, sudan III. The amount of the solubilization Figure 5. Sudan III solubilization by increased with the ionomer aqueous LA7.50cCl at 25 °C. -2

-1

1

1



252

PHASE-TRANSFER CATALYSIS

concentration. When we add cetyltrimethylammonium chloride (CTAC) into the aqueous solution, the solubilization of sudan III increases sharply beyond the critical micelle concentration of CTAC (ca. 0.9 mmol/L). These results suggest that the ionomer takes a polysoap-like conformation in water. Swelling of crosslinked ionomers corresponds well to their solution viscosity behavior (Figure 4b). In nonpolar solvents with low AN values such as toluene and THF, the swelling of an ionomer was relatively small. The swellability decreases with the ion loading This is the reflection that the interchain aggregation takes place. In contrast, in a polar solvent like acetonitrile or methanol, the swelling rather increases with an increasing ion content. The appearance of dissociated ions within the resin explains this result. In a nonpolar solvent, the swelling of a crosslinked ionomer (A12BuCl) also increases with an addition of soluble quaternary salts such as tributylhexadecylphosphonium chloride (76). The swelling in methanol presented a contrast to the behavior in toluene. The addition of a quaternary salt sharply decreased the swelling in methanol. Therefore, the ionomer swelling becomes higher in toluene rather than in methanol in the presence of the quaternary salts (76). In chloroform, however, we could not observe these salt effects for swelling behavior. The effect of low-molecular-weight onium salts may be explained as shown in Figure 6. The ionomers with high ionic content are insoluble in nonpolar solvents due to an extensive interchain aggregation. They are only able to swell. The swelling of crosslinked ionomers is also reduced by the interchain aggregation. With an addition of a soluble onium salt,Q2X, the interchain aggregates may be replaced by the aggregates between ionomer-bound ionic groups and the added onium salt. The elimination of the inter-ionomer aggregation would induce the salting-in effect. Moreover, the decrease in the intrachain aggregation would increase the reduced viscosity. On the other hand, the behavior in polar solvents may be explained in the same way as the accepted theory about the aqueous polyelectrolyte solution (77) as well as the theory on ion-exchange resins (18).

crosslinked ionomer (Aggregation with Added Salt)

Figure 6. Expansion of ionomer chain with soluble quaternary salts.


19.

OHTANI ET AL.


253

100 CO

CO

ε

ε

ο

Ô

ε

ε


0.01 Particle Diameter / mm (a) Particle Size Effect (A170cCl)

10 20 30 40 prs(x) in AxRCI (b) Ion Content Effect (at 90 °C)

Figure 7. Noncatalytic reactions of AJCOCCI with decyl methanesulfonate in toluene. 4.0 mL of toluene, 0.05 mmol of quaternary salts, and 0.82 mmol of DcOMes.

Noncatalytic Reactions of Ionomers. In nonpolar solvents such as toluene or THF, the intraresin microstructure of crosslinked ionomers may be homogeneous with the ionic aggregates scattered all within the resin interior. The noncatalytic reaction between decyl methanesulfonate and A170cCl in toluene gave a clean second-order kinetics. The rate constant was barely dependent on the particle size, indicating that the intraresin diffusion of the organic substrate was very fast compared to the rate of the chemical reaction (Figure 7a). Similar results have been obtained unless the ionomer has an extremely high ion content or a high covalent crosslinking density (2). In toluene, however, reactivity depended on the ion content of ionomers (Figure 7b). The apparent nucleophilicity decreased with an increasing ionic loading of AxRCI. This indicates that the enhancement of the aggregation decreases the average reactivity of the chloride counter anions and that the life of an aggregate is much shorter than the time-scale of the reaction. This also suggests that monomeric ion pairs are more reactive than the ionic aggregates such as triplet ions, dimers of ion pairs, and higher multiple ions. If chloroform or acetonitrile was used as a solvent, the reactivity did not depend on the ion content irrespective of the catalyst particle size (2). A high solvation to the small ionic groups or dissociation of the ionic groups is responsible for the disappearance of ionic aggregates. Rates of Liquid-Solid-Solid Triphasé Catalysis. The rates of liquid-solid-solid triphasé catalysis where reagent inorganic salt was in large excess over decyl methanesulfonate have been examined in detail (2). Solvent efficiency for this triphasé catalytic reaction was similar to that of non-catalytic reactions. Most of the reactions did not follow pseudo-first-order kinetics; a large reaction rate observed at the initial stage, a slowdown after that, and a subsequent gradual autoacceleration.


254



100

0

5 Tim10 e / h15

20

Figure 8. Liquid-solid-solid triphasé catalytic reactions of decyl methanesulfonate with solid potassium acetate or sodium chloride catalyzed by A17DoCl at 60 °C (acetonitrile and chloroform) or at 110 °C (toluene). 4.0 mL of solvent, 0.05 mmol of A17DoCl, 10 mmol of KOAc or NaCl, 0.07 mL of DcOMes. The phenomenon was significant when toluene was used as a solvent and when the reaction temperature was high (Figure 8). The formation of a by-product, 1chlorodecane, was observed when the resin with chloride counter anions was used as a catalyst. The by-product, which was caused by the residual chloride ions remaining in the catalyst resin, was formed only at the initial stage of the reaction course. Most of the reaction rates in toluene were dependent on the particle size of ionomer catalyst. All these features clearly indicate the presence of a strong mass-transport limitation of nucleophiles under the liquid-solid-solid conditions using toluene as a solvent. This may be due to either low solubility of inorganic salts into the solvent, scarce contact between the ionomer particle surface and the solid reagent surface, or slow intraresin ion-transport. However, it still remains unsolved how fast anion exchange between polymer-bound quaternary salts occurs through the transient aggregation among the ionic groups that makes the intraresin ion-transport possible. When acetonitrile was used as an organic solvent, on the other hand, a relatively clean pseudo-first-order kinetics was observed. A relatively high solubility of inorganic salts in the solvent may diminish the ion-transport limitation in the triphasé catalysis, although noncatalytic reactions proceeds simultaneously at considerable rates in the solvent (2). Liquid-Solid -Liquid Triphasé Catalysis. In this triphasé system, crosslinked ionomers imbibe water or aqueous solution in addition to organic solvent (7, 19). In toluene, as shown already, the ionic groups tend to aggregate, forming a reverse micelle-like structure. In water, the polymer backbone shrinks, forming a poly soap-like or normal micelle-like structure. These



19.

OHTANI ET AL.


255

Figure 9. Ionomer solubility in toluene/water system. conformations remind us of the property of surfactants. When two immiscible solvents are both present, however, linear ionomers are scarcely soluble in either of the two phases. The pictures in Figure 9 show the change in appearance when we add water to a 25 mmol/L solution of LA5.0OcCl in toluene at 60°C, where w represents molar ratio of water to onium groups. A minimal amount of water was enough to precipitate the ionomer. The system became turbid. Interestingly, the precipitated ionomer was then solubilized to afford an apparent homogeneous solution. With further addition of water, the ionomer gave an opaque gel. The gel further absorbed water and toluene and bulk water phase did not appear until the whole system became a gel. The phase-separation behavior depends on the salt concentration as well as the kind of salt and ionomer's ion content (Ohtani, N. unpublished data). The results clearly show that the hydration to the ionomer ionic groups never eliminates their ionic aggregates that is formed in nonpolar solvents. The action is rather opposite. The hydration strengthens the interaction between ionic groups. The behavior strongly suggests that the interior of crosslinked ionomers is 'not' homogeneous under liquid-solid-liquid triphasé conditions. The water imbibed into the crosslinked ionomer does not simply solvate the ionic groups. The water makes a certain structure with the organic solvent that was absorbed simultaneously. The presence of covalent crosslinkages should modify the structure because of the limited swellability. Interfacial Reaction Mechanism for Triphasé Catalysis. We proposed fifteen years ago a reversed micelle model for triphasé catalysis (13) as is illustrated in Figure 10. The interior of the resin consists of two phases: one is an organic phase that contains the hydrophobic polymer backbone solvated by the organic solvent and the other is an aqueous phase that contains water and dissociated anions. Quaternary cations are present on the interface of the phases. Substrate and ionic nucleophile diffuse through the continuous organic and aqueous phases, respectively. Chemical reaction takes place at the interface: the organic substrate collides with the nucleophile that is present on the interface in the form of ion pairs. Therefore, the most important feature of this model is the continuities of organic (or oil) and aqueous (or



256


water) phase (1). The continuities may be primarily determined by the volume ratio of oil to water absorbed by the crosslinked ionomer. When an ionomer imbibes more oil than water under a given reaction condition, the microstructure of the ionomer tends to be a water-in-oil type: oil phase is continuous and water phase is discontinuous. The quaternary salts that are situated on isolated water droplets are able to react only once but the catalytic action does not continue because the quaternary salts are not recovered to their original form due to the absence of nucleophile supply from bulk aqueous phase. On the other hand, the quaternary salts that are _ .... situated on the water channel, ^ * which is continuous to bulk solid-liquid triphasé catalysis, aqueous phase, are able to react with substrate repeatedly since the counter anions may be recovered readily. Since it is known that reverse micelles exchange each other their contents after their collisions (20), it should be considered that the microstructure of crosslinked ionomer is not necessarily fixed and that the dispersed droplets are more or less mobile to contact each other, though the movement is extremely restricted. Such droplets behave as if they were completely isolated during the catalytic reactions. If an ionomer imbibes more water than oil, the microstructure would be reversed. In this case, organic substrate may not reach isolated oil droplets buried in deep resin interior, while nucleophile anions reach every site of the resin interior. The importance of resin microstructure under liquid-solid-liquid triphasé catalysis is summarized in Figure 11. With an increasing content of organic solvent and/or with a decreasing water content, the resin interior becomes a w/o microstructure. In a reverse case, the resin tends to consist of a o/w microstructure that may be exemplified by lightly crosslinked ion-exchange resin. The kind of reagent salt and its concentration in bulk aqueous solution as well as the organic solvent affinity on polymer backbone directly influences the microstructure. The structural factors of catalyst ionomers influence the microstructure in consequence of the amounts of imbibed oil and water. The extents of attainable regions of substrate and nucleophile in resin interior will be varied according to the oil and water composition. The ratio of ion pair on the interface over total nucleophiles in the resin may be also varied according to the volume and anion concentration of the resinous water phase. Consequently, the over-all catalytic activity of an ionomer may follow the curve that has a maximum as shown in Figure 11(b). ¥ i

r Q

10

R e v e r s e

m i c e l l e

% Λ 1 m o d e l f o r

h


m d

19. OHTANI ET AL.


257

Oil Content Water Content Microstructure


w/o

Bicontinuos

QX Loading

large

QSize XSize

large

Spacer Chain Salt Concentration

large

O/W

long

large

Solvent Affinity to Chain

(a) Factors Determining Microstructure Y" Attainable Region >

jJX Attainable \ Region

_< «ο υ

\

Ion Pair Formation

(b) Microstructure and Triphasé Activity Figure 11. Catalyst microstructure and triphasé catalysis. Our early study suggested the restriction of intraresin ion-transport (27). There have been recently reported some experimental evidence to support that simple nucleophilic substitutions do occur also in microemulsion systems via interfacial mechanism (22, 23). When water-uptake is small compared to oil-uptake, the microstructure is assumed to be a w/o or bicontinuous structure. The nucleophile transport may be restricted in this case. In order to examine the influence of aqueous phase continuity in ionomer particles, the constituents in bulk aqueous phase was varied and the effect on the apparent catalyst activity was studied in this articleContinuities of Resinous Aqueous Phase and Catalytic Activity. The rate of triphasé catalysis depends on the salt concentration of the bulk aqueous phase. We pointed out first the phenomena (79, 27). A maximum rate was usually observed at a certain concentration in each catalytic reaction. The concentration dependence differed according to the kind of reagent salt and leaving group of the substrate. The rate changes were relatively sharp when cyanide or acetate was a nucleophile, as shown in Figure 12. At the saturated concentration of inorganic salts in the bulk aqueous solution, the formation of the by-product derivedfromthe residual counter ions of the used catalysts was often observed even after prolonged preconditioning of the catalysts, indicating the presence of the intraresin region to which reagent nucleophiles could not get.


258


An addition of sodium hydroxide to bulk aqueous solution also affects the rate of triphasé catalysis. The effect was significant when iodide ions were present in the reaction system. The rate of the reaction of 1-iododecane with sodium chloride was significantly decreased by the presence of sodium hydroxide, although the initial rate 100


i

io

Ô

ε

es

.*

1

CO

Ο

- O - A17DoCl, NaCN, 90 °C -«K- A17DoCl, NaCN, 110 °C - O - A30OcCl, NaOAc, 110°C TOMAC, NaOAc, 110 °C

0.1 0.1 1 10 100 Molar Ratio of Water to Sodium Salt in Bulk Aqueous Solution

Figure 12. Effect of salt concentration on triphasé catalysis of 1bromodecane with aqueous salt. 4 mL of toluene, 0.36 mmol of DcBr, 10 mmol of reagent salt, and 0.05 mmol of catalyst. was quite enlarged by the presence of sodium hydroxide as shown in Figure 13. As shown in Table I, the presence of sodium hydroxide always enhanced the reactions catalyzed by TOMAC. However, ionomer-catalyzed reactions were not always accelerated. The reaction with sodium cyanide was slightly decelerated. The reaction with sodium iodide was significantly decelerated. These effects, that is, salt concentration and sodium hydroxide addition, are explained by the change in the amount of water within the ionomer catalyst and the continuity of the resinous aqueous phase. A decrease in water content in an ionomer particle would decrease the aqueous continuity and increase the region to which reagent ions are not attainable. Our model easily explains both pseudo-first-order kinetics and catalyst particlesize effect that are usually observed for triphasé catalysis. All other models proposed for the triphasé catalysis did not take into account the possible change in the resin microstructure that was induced due to the external factors of the reaction conditions. Reaction-intraparticle diffusion model adopted by reaction chemical engineers (77, 72) necessiates both continuous water-filled pores and continuous oilfilled pores in catalyst particles. It is well-known that the more active triphasé catalyst has a morphological structure of gel-type resin that becomes porous only when swollen by solvent(s). Such gel-type of resin does not have large surface area that are quantitatively measured by BET method. The aqueous phase or water-filled pores are formed only because the ionomer contains hydrophilic ionic groups: unfunctionalized polystyrene hardly absorbs water, much less aqueous solution even if it has permanent micropores. Oscillation model, which assumes that polymerbound quaternary groups go into and come backfromresinous aqueous phase on the



19.

OHTANI ET AL.


0

0.5

1

1.5 2 2.5 Time / h

3

259

3.5

Figure 13. Effect of NaOH addition to aqueous sodium chloride on triphasé catalytic reaction of 1 -iododecane catalyzed by A17BuCl at 90 °C. 1.0 mL of toluene, 2 mL of aqueous phase (10 mmol of NaCl), 0.4 mmol of Del, and 0.025 mmol of catalyst. analogy of the Stark's model of phase-transfer catalysis, rules out the participation of the oscillation rates that should limit the over-all rate of the triphasé reaction: the liquids imbibed by the resin should be stagnant even if the whole reaction system is vigorously stirred. It is known that the stirring speed is one of the crucial factors for unbound phase-transfer catalysts to function well. This model is also obliged to presume the presence of permanent pores that are fulfilled with the bulk aqueous solution. The model that the resin interior is composed of a homogeneous microstructure without any aggregation of ionic groups seems very doubtful since the amount of water imbibed by the catalyst ionomer is much larger under the triphasé conditions than the estimated hydration numbers of the corresponding low-molecularwei^it quaternary salts. This model also involves the problem as to ion transport in the catalyst particles, while there is a similar problem to be solved for liquid-solidsolid triphasé catalysis. Experimental Materials. Linear and crosslinked ionomers were prepared and characterized by the method reported previously (2, 14). The degree of polymerization of linear ionomers is 200 unless otherwise stated. The crosslinking density of AxRX and PxBuX was adjusted to 1% with divinylbenzene and particle size was -200+325 mesh unless otherwise stated. General Procedures. Viscosity and swelling measurements were done in the same way as described previously (14). The solubilization of sudan III was analyzed spectrophotometrically. The absorbance at 490 nm of the filtrate was measured after an ionomer aqueous solution and an excess amount of solid sudan III were equilibrated at 25 °C in a test tube with a Teflon-lined screw cap. All the kinetic runs were carried out using a 40 mL culture tube equipped with a Teflon-lined screw cap and a Teflon-coated stirring bar and the reaction mixtures were analyzed by GLC in a usual way (2). The reaction conditions are given in each figure or table.


260


Table I Influence of Addition of Sodium Hydroxide on the Reactions of Decyl Methanesulfonate with Aqueous Sodium Salts under Phase-Transfer Conditions at 90 *C 5

Catalyst

Salt

A17BuCl

NaCl NaCN Nal

TOMAC

NaCl Nal

10kobsd /s" H20 3.6 16 13 92 200

1

50wt%NaOH 7.7 14 1.6 130

260

Reaction conditions: catalyst, 57 umol; DcOMes, 0.28 mmol; reagent salt, 10mmol; toluene, 2 mL; aqueous phase, 2 mL of water or 50 wt% NaOH solution.


Literature Cited 1. Ohtani, N. J. Synthetic Org. Chem. Jpn. 1985, 43, 313. 2. Ohtani, N.;Nakaya, M.; Shirahata, K.; Yamashita, T.J. Polym. Sci., Part A 1994, 32, 2667. 3. Ohtani, N.; Inoue, Y.; Nomoto, Α.; Ohta, S. Reactive Polymers 1994, 24, 73. 4. Ohtani, N.; Inoue, Y.; Inagaki, Y.; Fukuda, K.; Nishiyama, T. Bull. Chem. Soc. Jpn. 1995, 68, 1669. 5. Ohtani, N.; Inoue, Y.; Kobayashi, Α.; Sugawara, T. Biotechnol. Bioeng. 1995, 48, 42. 6. Regen, S. L. Angew. Chem. Int. Ed. Engl. 1979, 18, 421. 7. Montanari, F.; Landini, D.; Rolla, F. Top. Curr. Chem. 1982, 101, 147. 8. Ford, W. T.; Tomoi, M. Adv. Polym. Sci. 1984, 55, 49. 9. Telford, S.; Schlunt, P.; Chau P. C. Macromolecules 1986, 19, 2435. 10. Svec, F. Pure Appl. Chem. 1988, 60, 377. 11. Wang, M. L.; Yang, H. M. Ind. Eng. Chem. Res. 1991, 30, 2384. 12. Desikan, S.; Doraiswamy, L. K. Ind. Eng. Chem. Res. 1995, 34, 3524. 13. Ohtani N.; Wilkie, C. Α.; Nigam, Α.; Regen, S. L. Macromolecules 1981, 14, 516. 14. Ohtani, N.; Inoue, Y.; Mizuoka, H,; Itoh, K. J. Polym. Sci., Part A 1994, 32, 2589. 15. Ohtani, N.; Inoue, Y.; Kaneko, Y.; Okumura, S.J.Polym. Sci., Part A 1995, 33, 2449. 16. Ohtani, N.; Inoue, Y.; Kaneko, Y.; Sakakida, Α.; Takeishi,I.;Furutani, H. Polymer J. 1996, 28, 11. 17. Rice, S. Α.; Nagasawa, M. Polyelectrolyte Solutions, Academic Press, New York, 1961. 18. Katchalsky, Α.; Lifson, S.; Eisenberg, H. J. Polym. Sci. 1951, 7, 571. 19. Ohtani, N.; Regen, S. L. Macromolecules 1981, 14, 1594. 20. Lang, J.; Mascolo, G.; Zana, R.; Luisi, P. L. J. Phys. Chem. 1990, 94, 3069. 21. Serita, H.; Ohtani, N.; Matsunaga, T.; Kimura, C. Kobunshi-Ronbunshu 1979, 36, 527. 22. Shomäcker, R. J. Chem. Res. 1991, 92. 23. Ohtani, N.; Inoue, Y.; Shinoki, N.; Nakayama, K. Bull. Chem. Soc. Jpn. 1995, 68, 2417.


Polystyrene-Supported Onium Salts as Phase-Transfer Catalysts

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