Polymer Journal, Vol.33, No. 10, pp 754—764 (2001)

Preparation of Polyoxetane Resins Anchoring Pendant Oligo(oxyethylene) Chains and Uses as Polymer Solvents for Ions

∗ Akihiko UEYAMA, Michiko MIZUNO, Hiroshi OGAWA, Shigeyoshi KANOH, and Masatoshi MOTOI

Department of Chemistry and Chemical Engineering, Faculty of Engineering, Kanazawa University, 2–40–20 Kodatsuno, Kanazawa 920–8667, Japan ∗New Materials Development Department, Industrial Technology Center of Fukui Prefecture, 61 Kawaiwashizuka, Fukui 910–0102, Japan

(Received May 10, 2001; Accepted July 22, 2001)

ABSTRACT: In the presence of the polyoxetane resin, R-1b, containing tri(oxyethylene) segments in the pendant chains, 1-bromooctane was converted to 1-iodooctane in 88% yield using solid NaI in hexane at 60◦C, but 1-iodooctane was formed in a very low yield with solid KI in place of solid NaI, suggesting that the pendant tri(oxyethylene) segments of polyoxetane matrices caught cations of NaI, but not potassium cations of KI, in the manner of cooperative coordination under anhydrous conditions. Although the corresponding di(oxyethylene) analogs hardly had such catalytic effect under the same conditions, when a polyoxetane resin anchored the pendant quaternary ammonium salts besides the pendant di(oxyethylene)s the yield of 1-iodooctane was remarkably improved. Under aqueous conditions using 60 wt% aqueous KOH and hexane, a polyoxetane resin anchoring both the pendant tri(oxyethylene) and primary ◦ moieties in an 1:1 mole ratio for OCH2CH2 and OH groups gave styrene quantitatively at 70 C from 2-iodoethylbenzene and in 92% yield from 2-bromoethylbenzene (12a) by adding NaI. Under the same conditions using NaI as additive, a polyoxetane resin having only the same hydroxy groups in the pendant chains also gave styrene in 51% yield from 12a, while R-1b, used in the above-mentioned halogen-exchange reaction, only gave a 9% yield of styrene. Thus, when used together with the pendant hydroxy groups, pendant tri(oxyethylene) segments act even under aqueous conditions as effective cosolvent species to carry NaI and KOH molecules into an organic layer. KEY WORDS Cationic Ring-Opening Polymerization / Polyoxetanes / Polymer Reaction / Oligo(oxyethylene)s / Polymer Solvent /

The synthesis and uses of functional polymers based various functional groups anchored through the spacer on polyoxetane backbones have attracted our atten- of polyoxetane backbones can be readily formed by tion, since we consider the polyoxetane backbones have a cationic ring-opening polymerization procedure and several properties required for supporting matrices of further chemically modified by polymer reaction. functional polymers, e.g., flexibility, thermal stabil- Poly(oxyethylene)s are regarded as polymeric media, ity (up to about 300◦C), -resistance, and moder- since moieties of poly(oxyethylene)s can catch ate polarity. Therefore, to find a way of using poly- alkali metal cations in a manner of cooperative coor- oxetane as supporting matrices, we prepared polyoxe- dination like that of crown .6, 7 The counteran- tanes having various functional groups in the pendants ion of such a cation acts as a or base, as and examined their functioning ability, for instance, reported for several reaction types.6, 8–10 In these reac- phase-transfer with pendant quaternary am- tions, polymer-supported poly(oxyethylene)s were use- monium salts,1 metal-adsorption with pendant chelat- ful as a phase-transfer catalyst (PTC) which was eas- ing ,2 and liquid-crystal formation with pendant ily recovered from the reaction mixture. As these sup- mesogens.3, 4 The cationic ring-opening polymerization porting matrices, divinylbenzene (DVB)-crosslinked of oxetane monomers is quite unsusceptible to polar polystyrenes so far have been often used, although functional groups involved in the pendants, such as crosslinked polyoxetanes have not been examined yet carboxylic- and sulfonic-, imido, azo, nitro, cyano, as matrices supporting poly(oxyethylene)s.11–15 Re- and halo groups. Additionally, it is a merit that a trou- cently, poly(oxyethylene)s prepared in the form of blesome procedure for drying oxetane monomers com- crosslinking and branching have attracted considerable pletely is not necessarily required for obtaining polyox- interest as promising materials for solid polymer elec- etane backbones by cationic polymerization, since the trolytes, since unmodified polyoxyethylene chains tend monomers are allowed to polymerize with trifluorobo- to crystallize in the presence of alkali metal ions at a rane in the presence of a trace amount of water,5 Thus, high concentration, reducing a metal-conductive effi-

754 Polyoxetane resins with pendant oligo(oxyethylene)s

Scheme 1. Oxetane monomers used. ciency in the polyoxyethylene media. For other polymeric media, we are interested in ob- taining polyoxetane-anchored alcohol moieties which organize mediating domains capable of solvating alkali metal ions, since alcoholic moieties are also used as media solvating alkali metal ions, e.g., alcoholic potash is used in an of alkyl halides to olefins and in a saponification reaction of , in which dissolves organic substrates and inor- ganic bases. Although poly(vinyl alcohol) (PVA) is re- garded as important materials of fiber-production, this polyol is scarcely used in chemical modification to ob- tain functional polymers. Thus, in this study, we prepared crosslinked poly- oxetane resins, which anchored the oligo(oxyethylene) and/or primary alcohol moieties through pendant spac- ers, by cationic ring-opening copolymerization of one or two of oxetane monomers, 1a–c, 2, and 4, with a crosslinking agent, 3, and by polymer reactions of the resulting pendant bromide or acetate (Schemes 1 and 2). Scheme 2. Polyoxetane resins used. Also see Table I for struc- The pendant oxyethylene and primary alcohol moi- tures. eties of the resins so obtained were examined as me- dia capable of solvating alkali metal cations by co- operative coordination or -bonding to gener- RESULTS AND DISCUSSION ate counteranions as or bases for halogen- exchange reactions of octyl bromide (11a) with sodium Preparation and Characterization of Polyoxetane iodide (NaI) or elimination reactions of 2-bromoethyl- Resins (12a) and 2-iodoethylbenzenes (12b) to styrene (13)in The terminal bromine atom of oxetane 2 was con- the presence of potassium (KOH). verted to the corresponding ether by phase-transfer catalytic reaction with di- and triethylene glycol monomethyl ethers to give 1a and 1b, respectively, and the corresponding butyl ether, 1c, was obtained in the same way. Cationic ring-opening polymerizations of

Polym. J., Vol.33, No. 10, 2001 755 A. UEYAMA et al.

Table I. Polyoxetane resins used Polymeric Monomers In structure Yieldc Modified FGe/mmol g−1 products in feeda R n X(1− k − x)/k/xb % resinsd OEU QA or OH f R-1a 1a/3 CH3 2 – 88/ 0/12 89 – 5.28 – f R-1b 1b/3 CH3 3 – 87/ 0/13 83 – 8.00 – f R-1c 1c/3 n-C4H9 3 – 87/ 0/13 99 – 7.20 – g R-5a 1a/2/3 CH3 2 Br 37/50/13 93 R-8a 2.45 0.51(QA) g R-5b 1b/2/3 CH3 3 Br 37/50/13 92 R-8b 2.67 0.96(QA)

R-6b-1 1b/4/3 CH3 3 OAc 50/38/12 91 R-9b-1 5.65 1.35(OH)

R-6b-2 1b/4/3 CH3 3 OAc 21/64/15 90 R-9b-2 2.85 2.90(OH)

R-7 4/3 CH3 3 OAc 0/70/30 95 R-10 – 3.51(OH) R-14 14/DVB – – – 83/17 83 –f 9.77 aMonomers charged as feed. bRatios of monomeric units for resins were regarded as feed ratios of monomers. cBased on the total weight of charged monomers. dObtained by polymer reaction of the pendant bromide or acetate. eAmounts of pendant functional groups (FG): OEU, QA, and OH refer to the oxyethylene, quaternary ammonium, and primary alcoholic moieties in the pendant, respectively. fResins not modified. gAmounts calculated from the elemental analysis data for N.

1 Figure 1. H NMR spectrum of 1a in CDCl3 at rt based on a TMS standard. oxetanes 1a–c with 0.12–0.13 equiv. of crosslinking agent, 3, were carried out in dichloromethane (DCM) at Figure 2. IR spectra of (A) 1a, (B) R-1a, and (C) R-6b-1. 0◦C using 0.03 equiv. of a trifluoroborane–ether (1:1) . − complex (BF3OEt2) to the total amount of the oxetane each other, although the bands at 985 and 840 cm 1 dis- ring. The crude products were collected by filtration appear in the IR spectrum of R-1a. R-8a and R-8b hav- of the reaction mixture and impurities were removed ing the pendant quaternary ammonium bromide besides by extraction from the crude products with acetone by the pendant oligo(oxyethylene)s were obtained by quat- Soxhlet’s apparatus, giving elastic gel products, insol- ernization of the terminal bromide in the pendants of uble in ordinary solvents. These polymerization results resins, R-5a and R-5b, prepared using 1a or 1b, 2, and are summarized in Table I. The 1H NMR spectrum of 3, with tributylamine. The contents of the pendant qua- 1a is exemplified in Figure 1 and the IR spectra of 1a ternary ammonium (QA) in these resins were estimated and R-1a in Figure 2. from elemental-analysis data for nitrogen atom. The Signals a–h are assigned readily to the corresponding acetate residues bound to resins R-6b-1, R-6b-2, and protons Ha–Hh in 1a. The IR spectrum shows absorp- R-7 were confirmed from absorption bands at 1745 and − tion bands at 985 and 840 cm 1 for the cyclic ether of 1245 cm−1, as shown in Figure 2C. These ester residues − oxetane ring and at 1115 cm 1 for the acyclic ether. IR were completely hydrolyzed to give the correspond- spectral patterns of 1a and its polymer, R-1a, resemble ing polyols, which showed broad absorption bands at

756 Polym. J., Vol.33, No. 10, 2001 Polyoxetane resins with pendant oligo(oxyethylene)s

Figure 3. Influence of resins on the halogen-exchange reaction between 11a and NaI in the presence of each (•) R-1a,() R-1b, () R-1c, and (×) R-14: 11a, 1.2 mmol; NaI, 3.6 mmol; OEU, 1.8 3 ◦ mmol; hexane, 5 cm ; temp, 60 C. (£) with KI in place of NaI in the presence of R-1b.

3600–3200 cm−1 due to hydroxy residues, but no ab- sorption bands at 1745 and 1245 cm−1 due to the es- ter. A distinct band appeared at 1115 cm−1 for the ether linkages of oligo(oxyethylene) pendants and a polyox- etane network. Thus, the desired polyoxetane resins anchoring oligo(oxyethylene) segments in the pendant side-chains were obtained by an easy synthetic proce- dure.

Phase-Transfer Catalysis Using Oligo(oxyethylene)- Anchoring Polyoxetane Resins in a Halogen-Exchange Reaction The oligo(oxyethylene)-anchoring resins, R-1a–c,so obtained, were used as a solid-liquid PTC in a halogen- exchange reaction giving octyl iodide (11b) from the corresponding bromide, 11a, using 2 equiv. of NaI par an oxyethylene unit (OEU) in hexane at 60◦C. These time–yield curves are shown in Figure 3. Scheme 3. A phase-transfer catalytic reaction mechanism for After 10 h-reaction, resin R-1b gave 11b in 88% the halogen-exchange through oxyethylene media in polyoxe- tane resins: (a) halogen-exchange between 11a and Nal, (b) yield, while R-1a and R-1c in very low yields of 26 counteranion-exchange around a sodium cation coordinated by and 7%, respectively. The oxyethylene segments neigh- oxyethylene media, and (c) taking in a sodium cation together with boring on bulky segments, such as the alkyl spacer of the iodide counteranion from the Nal solid phase. –CH2O(CH2)4– and the butoxy terminal, are thus re- strained from coordinating to a sodium cation coopera- shown in Figure 3. Therefore, NaI molecules were co- tively. Although polyoxetane supports contained ether ordinated by oligo(oxyethylene) segments of R-1a–c, linkages abundantly, these atoms could not cat- as illustrated in the phase-transfer catalysis with crown- alyze the halogen-exchange reaction between 11a and ethers and poly(oxyethylene)s, and the resultant iodide NaI, as shown by the fact that a resin which was pre- counteranion was accompanied into an organic phase to pared from 3-butoxymethyl-3-methyloxetane and 3 in nucleophilically attack the α-carbon of bromide, 11a, feed at a 7:3 molar ratio to obtain a model substance as shown in Scheme 3a. for the polymeric supports of R-1a–c had no catalyz- After the halogen-exchange on the α-carbon in an ing ability under the same reaction conditions as those organic phase, in some way the formed bromide

Polym. J., Vol.33, No. 10, 2001 757 A. UEYAMA et al.

Figure 4. Influence of OEU amount on halogen-exchange re-

actions between 11a and NaI in the presence of R-1b:() 1.8, (•) £ 1.4, () 0.9, (Æ ) 0.5, and ( ) 0.2 mmol of OEU. See conditions given in Figure 3 for others. Scheme 4. Preparation of DVB-crosslinked polystyrene, R-14, anchoring the pendant tri(oxyethylene) segments. A time–11b yield curve with R-14 is shown in Fig- ure 3 under the same conditions as for phase-transfer counteranion interchanges with an iodide anion lo- catalysis with R-1b. R-1b and R-14 gave 11b in 85 and cated in the solid phase (Scheme 3b) and/or in other 68% yields after 10 h-reaction, respectively, indicating way the oligo(oxyethylene) segments release the re- that the catalytic activity of R-1b was some what higher sultant NaBr to take in a NaI molecule located in than that of R-14. These polyoxetane resins, elastic the solid phase (Scheme 3c). These processes regen- but somewhat gummy and became more softened dur- erate the oligo(oxyethylene) segments containing NaI ing stirring in hot hexane, were not ground into pieces molecules. Potassium iodide (KI) did not produce the and could be used repeatedly in phase-transfer cataly- iodide counteranion effective for halogen-exchange re- sis, as shown in Figure 10 (see later). The polystyrene action with the oligo(oxyethylene) segments. When resin was ground into pieces during stirring with phase- the potassium cation larger than the sodium cation transfer catalysis. However, it is unable yet to tell forms a cooperative with pen- which resin is useful as a supporting matrix. Since dant oligo(oxyethylene) segments, the complex with polyoxetane and polystyrene resins have properties and KI is more sterically crowded than the analog with microstructures different from each other, these resins NaI, since more oligo(oxyethylene) arms are required must be used in situations suitable for their properties. to form the complex with KI than with NaI and such Figure 4 shows time–11b yield curves with R-1b a crowded complex is restrained from forming in poly- varying the amount of OEU from 0.2 to 1.8 mmol per mer matrices (see later). DVB-crosslinked polystyrenes 3.6 mmol of NaI. are widely used as supporting matrices in functional Although the amount of OEU charged was increased polymers synthesis. These matrices are hard (or rigid), from 1.4 to 1.8 mmol, the reaction rate was hardly brittle, and low degree of swelling with usual sol- improved, i.e., both reactions gave 11b in 82–88% vents, especially , while polyoxetane matri- yield after 10 h, possibly since the formation of NaI- ces are soft (or flexible), elastic, and swelled even containing oligo(oxyethylene) complexes is restricted with and ethanol, although to a small ex- in an appropriate concentration even in the presence of tent. Polyoxetane matrices containing ether linkages an increased amount of OEU so as to restrain steric re- are considered more polar than polystyrene matrices pulsion among the complexes formed in a high concen- composed of hydrocarbons only. To examine the in- tration. The oxyethylene segments located at inner sites fluence of these matrices on phase-transfer catalysis, of resins, softened and stretched in hot hexane, partic- a DVB-crosslinked polystyrene resin, R-14, was pre- ipate in forming the complex, resulting in a high con- pared by 2, 2-Azobis(isobutyronitrile) (AIBN)-initi- centration of OEU in the reaction system when using ated suspension polymerization of a styrene derivative, an increased amount of OEU. 14, with 0.17 equiv. of DVB (Scheme 4). Phase-transfer catalytic activity of R-1b was exam-

758 Polym. J., Vol.33, No. 10, 2001 Polyoxetane resins with pendant oligo(oxyethylene)s

Figure 5. Influence of solvents on halogen-exchange reactions between 11a and NaI with R-1b:() hexane, (•) cyclohexane,  3 (Æ ) , and ( ) dioxane (each 5 cm ). See conditions given in Figure 3 for others.

Scheme 5. Schematic diagram for interpreting the behavior of quaternary ammonium moieties in phase-transfer catalysis: (a) TBAB in benzene, (b) TBAB in oxyethylene media of resin, and (c) the pendant QA in hexane.

2.284 for hexane, cyclohexane, 1,4-dioxane, and ben- zene, respectively. The results may be interpreted as Figure 6. Influence of solvents on halogen-exchange reactions follows: since 1,4-dioxane and benzene involve nega-  • between 11a and NaI with TBAB (0.1 mmol): ( ) hexane, ( )cy- tively charged parts due to n-orπ-electrons in the ether  3 clohexane, (Æ ) benzene, and ( ) dioxane (each 5 cm ). See condi- oxygen or the aromatic ring, these parts tend to assem- tions given in Figure 3 for others. ble on the side of the sodium cation in the NaI solid ined in solvents, such as hexane, cyclohexane, 1,4- state, more or less reducing cohesion between ionic dioxane, and benzene (Figure 5), and compared with species of NaI. In such a situation, the iodide anion is the phase-transfer catalytic activity of tetrabutylammo- caught as the counteranion of TBAB, as illustrated in nium bromide (TBAB) used in these solvents (Fig- Scheme 5a. ure 6). However, when R-1b is used in 1,4-dioxane With R-1b, 11b was formed at the highest rate in and benzene, these solvents prevent the pendant hexane and at moderate rate in cyclohexane, but at oligo(oxyethylene) segments from coordinating a very lowered rates in 1,4-dioxane and benzene. TBAB sodium cation, since these solvents solvate the showed very high catalytic activity in 1,4-dioxane and oligo(oxyethylene) segments so as to inhibit coordina- benzene, but was inactive in hexane and cyclohexane. tion to a sodium cation. However, in hexane and cyclo- Thus, the catalytic activities of R-1b and TBAB were hexane the oligo(oxyethylene) segments are stabilized remarkably influenced by character of solvents used, al- by coordination to a sodium cation rather than by solva- though specific inductive capacitie (ε)at20◦C seemed tion with hexane and cyclohexane, which have no effect close to each other: ε = 1.890, 2.023, 2.209, and to dissociate a NaI molecule. It was confirmed in our

Polym. J., Vol.33, No. 10, 2001 759 A. UEYAMA et al.

Figure 7. Influence of water on halogen-exchange reactions Figure 8. Influence of pendant QA on halogen-exchange re-  between 11a and NaI with R-1b:()0,(Æ ) 0.05, and ( ) 0.1 actions between 11a and NaI with resins: (•) R-1a (OEU, 0.3 cm3 of water added and (•) a saturated aqueous NaI solution. See mmol), () R-8a (OEU, 0.3 mmol; QA, 0.1 mmol), and () a mix- conditions given in Figure 3 for others. ture of R-1a (OEU, 0.3 mmol) and TBAB (0.1 mmol) in hexane

and (Æ ) R-8a (OEU, 0.3 mmol; QA, 0.1 mmol) in benzene. See previous report that hexane was a good organic solvent conditions given in Figure 3 for others. in etherification of alcohols with alkyl bromides using TBAB and 50 wt% aqueous NaOH.16 In this case, the hydroxy O–H bond of the alcohol is polarized enough to generate the counteranion, an alkoxide anion, of a tetrabutylammonium cation in an aqueous phase (or phase-interface between aqueous and organic phases) by abstracting the hydroxy proton with a strong base, NaOH. The alkoxide anion so generated is accompa- nied with the tetrabutylammonium cation into a low- polar hexane solvent, in which the naked alkoxy anion reacts smoothly with an alkyl bromide, due to lowered desolvation energy of reaction species in the activation state of a SN2-type reaction. Thus, the pre-polarization of NaI to an adequate de- gree with a polar additive is required for a sodium cation to smoothly form a complex by cooperative co- ordination with oxyethylene segments. From this con- Figure 9. Influence of pendant QA on halogen-exchange re- sideration, a small portion of water was added to the actions between 11a and NaI with resins: (•) R-1b (OEU, 0.3   reaction system of phase-transfer catalysis. However, mmol), ( ) R-8b (OEU, 0.3 mmol; QA, 0.1 mmol), and ( )a as shown by time–11b yield curves in Figure 7, the mixture of R-1b (OEU, 0.3 mmol) and TBAB (0.1 mmol) in hex-

ane and (Æ ) R-8b (OEU, 0.3 mmol; QA, 0.1 mmol) in benzene. presence of water does not favor this halogen-exchange See conditions given in Figure 3 for others. reaction, although very small amounts of water are per- mitted to be present. Of course, when a saturated aque- oligo(oxyethylene) and QA moieties in the pendant ous solution of NaI was used in place of solid NaI, chains were used, as shown by time–11b yield curves no halogen-exchange reaction was observed. Water in Figures 8 and 9. molecules added solvate not only ionic species but also In Figure 8, R-8a having the di(oxyethylene) and oxyethylene segments, lowering the nucleophilicity of QA moieties in the pendant chains gave 11b in hex- iodide ions as well as the coordination ability of the ane at much a higher reaction rate than R-1a having oxyethylene segments to a sodium cation. only di(oxyethylene) pendants. However, when a mix- To further investigate the behavior of quaternary am- ture of TBAB and R-1a was used in hexane, 11b was monium salts in the present phase-transfer catalysis, hardly formed after 10 h-reaction. This may be inter- polyoxetane resins, R-8a and R-8b, anchoring both preted from the observations that TBAB was an inac-

760 Polym. J., Vol.33, No. 10, 2001 Polyoxetane resins with pendant oligo(oxyethylene)s tive catalyst in hexane (see Figure 6) and that R-1a also showed a lowered reaction rate even in the pres- ence of 1.8 mmol of OEU (see Figure 3); R-8a used in Figure 8 contained only 0.3 mmol of OEU. Addition- ally, R-8a which contained 0.1 mmol of QA unit gave 11b at a somewhat higher rate in benzene than in hex- ane, although this rate observed in benzene was con- siderably low relative to that observed with 0.1 mmol of TBAB in benzene (see Figure 6), suggesting that the QA moieties of R-8a behaved in a manner differ- ent from that of quaternary ammonium cations not im- mobilized to polymer matrices. Similarly, as shown in Figure 9, the QA units of R-8b used in hexane had ef- fect for enhancing the phase-transfer catalytic activity, while a mixture of R-1b and TBAB reduced the forma-

tion rate of 11b in hexane, as compared with that with Figure 10. Results for repeated use of resins: (••) 1st and

 Æ  only R-1b, obviously indicating that TBAB free from ( ) 5th stages for R-1b (OEU, 1.8 mmol) and ( ) 1st and ( ) 5th polymer matrices reduced the catalytic activity (or co- stages for R-8a (OEU, 0.3 mmol; QA, 0.1 mmol). See conditions given in Figure 3 for others. ordination capacity) of oxyethylene segments used in hexane. These results are interpreted from the consid- These resins were recovered by filtration from the re- eration that the oxyethylene segments capture the qua- action mixture and reused as a PTC at the next stage. ternary ammonium cation of TBAB, mixed with R-1a Thus, the resins were used repeatedly in the halogen- or R-1b, rather than the sodium cation, probably due exchange reaction between 11a and NaI, as exemplified to an affinity between a quaternary ammonium and an in Figure 10. ether oxygen, both of which are lipophilic species, and due to easy dissolution of a lipophilic salt, TBAB, even Phase-Transfer Catalysis Using Polyoxetane-Based in a low-polar hexane solvent (Scheme 5b). Here, it Polyols in a Hydrogen Halide-Elimination Reaction is noticeable that R-8a had a higher effect on enhanc- A polystyrene gel having hydroxy groups at the ing the reaction rate than R-8b, although the phase- ω-positions of poly(oxyethylene) pendants was used transfer catalytic activity of R-1a was considerably in- as a polymeric PTC in an elimination reaction of 2- ferior to that of R-1b (see Figure 3); yields of 11b af- bromooctane with aqueous KOH giving 1- and 2- ter 10 h were 7 and 68% for R-1a and R-8a, and 39 octenes, but not 2-octanol. In the elimination of hy- and 63% for R-1b and R-8b, respectively. As illus- drogen bromide from 2-bromooctane, the ω-hydroxy trated in Scheme 5c for the case of using R-8a, it may groups of the pendants played important roles in be considered that a NaI molecule is captured by coop- generating a strong base. An alkoxide anion may erative coordination with the oxyethylene and QA seg- thus be located at the ω-position of the pendant ments. In this structure, the resultant NaI-containing poly(oxyethylene), which coordinates the resultant complex is less sterically crowded, compared with that potassium cation as an 18-crown-6-like complex, or a of a complex formed with the di(oxyethylene) chains hydroxide anion hydrogen-bonded by the ω-hydroxy only, since the number of pendant di(oxyethylene) arms group of the 18-crown-6-like complex.6, 15 is reduced in the former complex. However, steric In this report, crosslinked polyoxetanes, R-9b-1 and crowding in the complex with R-1b is not appreciably R-9b-2, anchoring both oligo(oxyethylene) and ω- released by the aid of coordination with the pendant hydroxy groups in the pendant side chains were pre- QA moiety, since the tri(oxyethylene) arm keeps the pared to confirm the formation of strongly basic do- larger number of oxyethylene parts, which are efficient mains, in which 13 was produced by elimination reac- for forming a cooperative coordination complex, than tion of 12a and 12b in the presence of an aqueous KOH the di(oxyethylene) arm, i.e., the less sterically crowded or NaOH layer. To our knowledge, phase-transfer cat- complex with R-1b can be formed with a smaller num- alytic elimination reaction using polyols based on poly- ber of arms than the complex with R-1a. But the lat- oxetane matrixes is first reported in this paper. Table II ter complex is hardly formed due to a highly crowded shows the results of the elimination reaction. structure. Thus, since the complex with R R-8a is R-1b anchoring no ω-hydroxy groups converted 12b looser than that with R-8b, the nucleophilicity of the to 13 in 23% yield after 5 h-reaction (run no 2), iodide counteranion is enhanced in the former complex. while no 13 was detected in the reaction mixtures

Polym. J., Vol.33, No. 10, 2001 761 A. UEYAMA et al.

Table II. Elimination reaction of 2-haloethylbenzenes, 12a and 12b, by phase-transfer catalysisa Run Amount/mmol 13 yield Resins no OEU OH Nal % For 2-Iodoethylbenzene (12b): 1 None 0 0 0 0 2 R-1b 0.54 0 0 23 3 R-1c 0.54 0 0 0 4 R-9b-1 0.54 0.14 0 100b 5 TBAB 0.03e 00 3

For 2-Bromoethylbenzene (12a): 6 R-1b 0.54 0 0 0 7 R-1b 0.54 0 0.6 9 8 R-1b 0.54 0 0.6 0c 9 R-1b 0.54 0 0.6 0d 10 R-9b-1 0.54 0.14 0 20 11 R-9b-1 0.54 0.14 0 9d 12 R-9b-1 0.54 0.14 0.6 51 13 R-9b-2 0.54 0.55 0.6 92 14 R-9b-2 0.54 0.55 0.6 63d 15 R-10 0 0.56 0.6 51 16 PVA 0 0.55 0.6 0 17 TBAB 0.03e 0 0.6 6 a12b used in Run no 1–5, and 12a in Run no 6–17. 10a or 10b (0.6 mmol) was allowed to react in 60 wt% KOH (1.5 cm3), hexane (4.5 cm3), and decane (0.2 mmol, as an internal standard by glpc) at 70◦C for 5 h in the presence or absence of NaI as an additive. For OEU and OH, see footnote e in Table I. bReaction time, 4 h. cIn the absence of an alkaline solution. d50% NaOH (1.5 cm3) was used in place of 60% KOH. eAmount of TBAB. in the absence of R-1b (run no 1) and in the pres- of 12a has an electron-attracting (-I) effect, although it ence of R-1c containing the pendant butyl-terminated is weak. When the content of the pendant ω-hydroxy tri(oxyethylene) chains (run no 3). Therefore, the group in the resin was increased, as shown by compar- pendant methyl-terminated tri(oxyethylene) chains can ing between R-9b-2 and R-9b-1, the 13 yield reached transfer KOH molecules from the aqueous layer to 92% (run no 13). R-10 containing no tri(oxyethylene) the organic layer in polymer matrices containing 12b, segments gave 13 in 51% yield, which was compara- the β-proton of which is abstracted with the KOH ble to that observed by using R-9b-1 (run no 15 and molecules. The pendant ω-hydroxy groups of R-9b- 12). These results indicate that the pendant ω-hydroxy 1 had remarkable effect on the elimination reaction of groups act as media capable of transferring not only 12b (run no 4). However, when the corresponding bro- KOH but also NaI from the aqueous layer to the organic mide, 12a, was used as a substrate under the same con- one and that such transferring capacity of the pendant ditions as with R-1b and R-9b-1, 13 was formed only ω-hydroxy groups was also enhanced in the presence in 0 and 20% yields (run no 6 and 10), respectively, of the pendant tri(oxyethylene) segments. indicating that the bromine atom was a As shown by comparing the 13 yields between run inferior to the iodine atom. However, by adding NaI no 7 and 9; 10 and 11; and 13 and 14, respectively, to these reaction systems using 12a as a substrate, the the present elimination reaction proceeded smoothly 13 yield increased from 0% to 9% when using R-1b with a potassium cation rather than with a sodium (run no 6 and 7) and from 20% to 51% when using R- cation, although the potassium cation of KI was not 9b-1 (run no 10 and 12). These results indicate that effective in the halogen-exchange reaction under an- NaI is transferred into the organic layer by the pen- hydrous conditions (see Figure 3). This is ascribed dant tri(oxyethylene) segments to convert 12a to its io- to the facts that a sodium cation has an ion radius of dide and that this transferring ability is enhanced in 0.095 nm smaller than that of 0.133 nm for a potas- the presence of ω-hydroxy pendants (also see later). sium cation and that, when these cations are hydrated, Such halogen-exchange between 12a and NaI under the sodium cation has an ion radius of 0.217 nm larger the aqueous conditions is ascribed to the higher reac- than that of 0.175 nm for the potassium cation.17 There- tivity of 12a than that of 11a, since the phenyl group fore, since a sodium cation is hydrated by more wa-

762 Polym. J., Vol.33, No. 10, 2001 Polyoxetane resins with pendant oligo(oxyethylene)s

In conclusion, the pendant tri(oxyethylene) segments of polyoxetane matrices caught a sodium cation rather than a potassium cation in the manner of cooperative coordination under anhydrous conditions. Even un- der aqueous conditions, the pendant tri(oxyethylene) segments appear to act as solvent species to transfer NaI into hydrophobic polymer matrices. Pendant ω- hydroxy groups also acted as a cosolvent species taking in not only NaI but also KOH, rather than NaOH. Thus, the elastic, moderately hydrophobic polyether network of crosslinked polyoxetane is of much interest as one of materials supporting pendant media for ionic species.

EXPERIMENTAL

Materials Oxetane monomers, 1a–c and 2–4, were obtained according to the method of literatures.16, 18 These monomers were copolymerized in DCM at 0◦C for Scheme 6. Schematic diagram for interpreting KOH captured 24 h with 0.03 equiv. of BF3OEt2 to the total amount with the pendant hydroxy and oxyethylene groups of polyoxetane of the oxetane ring to produce 3-crosslinked resins, resin. R-1a–c, R-5a, R-5b, R-6b-1, R-6b-2, and R-7. R- 5a and R-5b with the pendant bromide were heated ter molecules than a potassium cation, the sodium with three-fold molar excess of tributylamine in N, N- cation must get more desolvation energy to be dis- dimethylformamide at 100◦C for 10 h1 and the resultant solved (or taken in) in the domains of the polar ω- resins were subjected to elemental analysis to estimate hydroxy and/or tri(oxyethylene) pendants by exclud- the content of the pendant quaternary ammonium bro- ing some hydrating water molecules from the sodium mide. cation, resulting in a lowered rate when using NaOH Anal. Found for R-5a: N, 0.72%; Br, 10.82%. Found as a base. However, it is difficult for the pendant for R-5b: N, 1.35%; Br, 8.88%. tri(oxyethylene) segments to coordinate potassium and The pendant acetate residues of R-6b-1, R-6b-2, sodium cations cooperatively in the aqueous layer, and R-7 were hydrolyzed with 15% aqueous NaOH in since much desolvation energy is required to exclude methanol under reflux to give polyols, R-9b-1, R-6b-2, the water molecules hydrating the cations and the and R-10. tri(oxyethylene) segments. Hydrated cations may pos- 11a, 11b, and 12a were purified by distillation of sibly be dissolved (or taken in) in domains of the polar commercial reagents, and 12b was obtained by reaction ω-hydroxy and/or tri(oxyethylene) pendants by replac- of 12a with NaI in acetone. ing the cation-hydrating water molecules partly with 13 was obtained by the following procedure. In a these polar pendants, accompanying the hydroxide and 500 cm3 three-neck flask, an m- and p-isomeric mix- iodide counteranions into the organic domain in the ture of chloromethylstyrene (10.0 g, 65.5 mmol), tri- resin, as illustrated in Scheme 6. ethylene glycol monomethyl ether (10.8 g, 65.5 mmol), In the other case, pendant ω-hydroxy groups may TBAB (1.06 g, 3.28 mmol), hexane (70 cm3), and 50 be converted to alkoxide anions, which act as strong wt% NaOH were placed and vigorously stirred at 25◦C bases in the organic phase, with concentrated aqueous for 4 h. The reaction mixture was poured into water KOH (or NaOH). However, the alkoxide anions did (100 cm3) and extracted with ether. The crude prod- not act as a nucleophile attacking 12a and 12b, since uct, obtained by removing the solvents, was distilled the ω-hydroxy-anchoring resins are used repeatedly in in the presence of hydroquinone to give 7.8 g of 14 phase-transfer catalysis. Under the same conditions, boiling at 135–136◦C (9.3 Pa). After being washed poly(vinyl alcohol) (PVA) had no phase-transfer cat- with 15% NaOH and saturated NaCl solutions succes- alyzing ability (run no 16), since very hydrophilic PVA sively and then dried in a vaccum, this fraction was used is so solvated with water molecules that the PVA can- as monomer for suspension polymerization: IR (neat) not shift into the hydrophobic organic phase, even if the 1635, 995, and 905 (vinyl), and 1110 cm−1 (aliphatic 1 PVA dissolve KOH and NaI. ether); H NMR (CDCl3) δ = 3.37 (s, 3, OCH3),

Polym. J., Vol.33, No. 10, 2001 763 A. UEYAMA et al.

3.67 (s-like, 12, OCH2CH2), 4.57 (s, 2, benzylic CH2), Bull. Chem. Sci. Jpn., 66, 1778 (1993). 5.19–5.30, 5.65–5.84, and 6.58–5.86 (dd, each 1, vinyl 4. H. Ogawa, T. Hosomi, T. Kosaka, S. Kanoh, A. Ueyama, and protons), and 7.2–7.4 (m, 4, aromatic protons). M. Motoi, Bull. Chem. Sci. Jpn., 70, 175 (1997). Suspension polymerization of 14 (1.94 g, 7.05 mmol) 5. J. B. Rose, J. Chem. Soc., 546 (1956). J. Org. Chem. 48 with an AIBN initiator (0.43 mmol) was carried out at 6. Y. Kimura and S. L. Regen, , , 195 (1983). ◦ 3 7. U. Heimann and F. V¨ogtle, Angew. Chem. Int. Ed., 17, 197 80 C for 3 h using a benzene layer (3.5 cm ) contain- (1978). 3 ing DVB (0.98 mmol) and an aqueous layer (50 cm ) 8. W. M. MacKenzie and D. C. Sherrington, Polymer, 21, 791 containing 0.5 wt% PVA (molecular weight 500). By (1980). washing with hot water and methanol successively and 9. a) A. Hirao, S. Nakahama, M. Takahashi, and N. Yamazaki, drying in a vacuum, 1.73 g 14 were obtained. Makromol. Chem., 179, 915 (1978). b) A. Hirao, S. Nakahama, M. Takahashi, and N. Yamazaki, Phase-Transfer Catalyses Using Resins Makromol. Chem., 179, 1735 (1978). A typical procedure is as follows: in a 50 cm3 10. E. Santaniello, A. Manzocchi, and P. Sozzani, Tetrahedron Lett., 47, 4581 (1979). round-bottomed flask equipped with a reflux condenser 11. S. L. Regen and L. Dilak, J. Am. Chem. Soc., 99, 623 (1977). and a stirring bar, R-1b (0.22 g, containing 1.8 mmol 12. W. M. MacKenzie and D. C. Sherrington, J. Chem. Soc. OEU), 11a (0.22 g, 1.2 mmol), tetradecane (0.16 g, Chem. Commun., 541 (1978). 3 0.2 mmol), NaI (0.54 g, 3.6 mmol), and hexane (5 cm ) 13. S. Yanagida, K. Takahashi, and M. Okahara, J. Org. Chem., ◦ were placed. The contents were stirred at 60 C, and 44, 1099 (1979). aliquots were drawn with a syringe after appropriate re- 14. J. G. Haffernan, W. M. MacKenzie, and D. C. Sherrington, J. action times to determine 11b yield by gas chromatog- Chem. Soc., Perkin Trans. 2, 514 (1981). raphy using tetradecane as an internal standard. 15. Y. Kimura, P. Kirszensztejn, and S. L. Regen, J. Org. Chem., 48, 385 (1983). 16. M. Motoi, H. Suda, K. Shimamura, S. Nagahara, M. Takei, REFERENCES and S. Kanoh, Bull. Chem. Sci. Jpn., 61, 1653 (1988). 17. R. Matsuura in “Gendai Mukikagaku Koza,” Gihodo Co. Ltd., 1. M. Motoi, K. Shimamura, C. Shimamura, S. Muramoto, S. Tokyo, 1971, vol. 7, p 126. Kanoh, and H. Suda, Bull. Chem. Sci. Jpn., 62, 2553 (1989). 18. M. Motoi, H. Suda, S. Nagahara, M. Yokoyama, E. Saito, O. 2. H.-Y. Xu, H. Ogawa, S. Kanoh, and M. Motoi, Polym. J., 31, Nishimura, S. Kanoh, and H. Suda, Bull. Chem. Sci. Jpn., 62, 143 (1999). 1572 (1989). 3. M. Motoi, K. Noguchi, A. Arano, S. Kanoh, and A. Ueyama,

764 Polym. J., Vol.33, No. 10, 2001