Polymer Journal, Vol. 27, No. 10, pp 1068-1070 (1995)

SHORT COMMUNICATIONS Synthesis of Poly(cyclic orthoester)s by the One-Pot Reaction of Potassium Perfluoroalkylcarboxylates with Epibromohydrin Using Two-Step Catalysis of Quaternary Onium Salts

Atsushi KAMEYAMA, Hiroyuki HASHIKAWA, Nobuyuki KIJIMA, and Tadatomi NISHIKUBO*

Department of Applied Chemistry, Kanagawa University, Rokkakubashi, Kanagawa-ku, Yokohama 221, Japan

(Received June 12, 1995)

KEY WORDS Perfluoroalkylcarboxylates / Epibromohydrin / Poly(cyclic orthoester)s / Phase Transfer Catalysts / Quaternary Onium Salts / Crown Ethers / Two-Step Catalysis /

Quaternary onium salts and crown ethers are perfluoroalkylcarboxylates using the catalysts, exteremely useful as phase transfer catalysts which provide five-membered cyclic orthoes­ (PTC) in synthetic organic chemistry and ters. It was also found that although the reac­ polymer synthesis. Our research group has tion of oxiranes with alkyl carboxylates such studied in detail chemical modifications 1 of as ethyl acetate or ethyl benzoate did not pro­ polymers such as poly(chloromethylstyrene) ceed at all, the reaction with alkyl perfluoroalk­ using PTC. Moreover, photosensitive poly­ ylcarboxylates proceeded very smoothly in the mers2 and photoresponsive polymers3 for solar presence of the catalysts. This means that energy storage were successfully synthesized by perfluoroalkyl groups activate the adjacent the chemical modifications using PTC. carbonyl group to react the oxiranes. Further­ Meanwhile, the authors reported new more, the cycloaddition reaction was success­ catalytic activity of quaternary onium salts or fully applied for the synthesis of poly(cyclic crown ether complexes on the addition re­ orthoester)s9 by the cycloaddition polymeriza­ actions of cyclic ethers or sulfides with car­ tion of bis( oxirane )s with bifunctional trifluor­ boxylic acid derivatives.4 For example, the ocarboxylates. It was also suggested that those addition reaction of oxiranes5 or thiiranes6 cycloadditon reactions using conventional with S-phenyl carboxylates using the afore­ Lewis acids such as BF 3 • OEt2 did not proceed mentioned catalysts proceeded smoothly and because of the acid-induced ring-opening regioselectively to give the corresponding prod­ polymerization of the used oxiranes, even ucts. As an application, new acyl group trans­ though synthesis of orthoesters by the acid­ fer polymerization 7 of thiiranes was suc­ catalyzed reaction of oxiranes with certain car­ cessfully achieved using carboxylic acid de­ bonyl compounds has been known. Thus, it rivatives as initiatores and quaternary onium should be emphasized that an advantage of salts or crown ether complexes as catalysts. the reactions using quaternary onium salts or More recently, we reported a unique crown ether complexes is the selective transfor­ cycloaddition reaction8 of oxiranes with alkyl mation of cyclic ethers under neutral condi-

* To whom all correspondence should be addressed.

1068 Synthesis of Poly(cyclic orthoester)s

Table I. Synthesis of P-1 by one-pot reaction [F(CF2)lov] of KTFA with EBH using TBAB n: 1 (KTFA) in various solvents" 2 (KPFA) Intermediate

Solventb a+x· as polymn. cat. Yield/¾c

Anisole 0 n: 1 (P-1) Chloro benzene 0 2 (P-2) THF 77 11600 1.44 Scheme 1. NMP 73 8600 1.27 DMAc 64 11000 1.31 tions. DMSO 40 I 1000 1.58 From this background, we designed a "The reaction was carried out with KTFA (3 mmol) and one-pot synthesis ofpoly(cyclic orthoester)s by EBH (3 mmol) using TBAB in solvent (I ml) at 90°C for the reaction of perfluoroalkylcarboxylate der­ 24 h. bTHF, tetrahydrofuran; NMP, N-methyl-2-pyrroli­ ivatives with a oxirane based on a two-step done, DMAc, N,N-dimethylacetamide; DMSO, dimethyl sulfoxide. 'Insoluble parts in n-hexane. d Estimated by catalysis of quaternary onium salts or crown GPC based on polystyrene standards. ether complexes. In the reaction, glycidyl ester derivatives as intermediates were initially pro­ Table II. Effect of catalysts on the reaction duced by phase transfer catalysis of those ca­ of KTFA with EBH using TBAB" talysts. Then, the cycloaddition polymeriza­ tion of the formed glycidyl ester derivatives Catalystb Yield/%' M/ MwfM. proceeds to give the corresponding poly(cyclic None 56 6700 1.37 orthoester)s. TBAC 60 11900 1.32 In this paper, we wish to report new synthesis TBAB 73 8600 1.27 of poly(cyclic orthoester)s by one-pot reaction 15-C-5 54 10400 1.29 18-C-6 59 10100 1.32 of potassium perfluoroalkylcarboxylates with epibromohydrin using quaternary onium salts • The reaction was carried out with KTFA (3 mmol) and as phase transfer catalysts and polymerization EBH (3 mmol) using catalyst in NMP (I ml) at 90°C for catalysts. 24 h. b TBAC, tetrabutylammonium chloride; TBAB, tetra­ butylammonium bromide; 15-C-5, 15-crown-5; 18-C-6, The reaction of potassium trifluoroacetate 18-crown-6. 'Insoluble parts in n-hexane. d Estimated by (KTFA) with EBH was conducted using GPC based on polystyrene standards. 8 mol % of tetrabutylammonium bromide (TBAB) as a catalyst in various solvents at to give the polymer with Mn of 11000 in 90°C for 24 h. The results are summarized in moderate yields. Therefore, it was suggested Table I. When the reaction was carried out in that the phase transfer catalysis of the sub­ low polar solvents such as anisole or stitution reaction of KTFA with EBH is the chlorobenzene, the corresponding polymer was important process on the one-pot reaction. not obtained. This means that the first The effect of the catalysts on the reaction of nucleophilic substitution reaction of KTF A KTFA with EBH was examined in NMP at with EBH catalyzed by TBAB as PTC scarcely 90°C for 24 h (Table II). When the reaction proceeded in the low polar solvents. On the was carried out without catalysts, the polymer other hand, the reaction proceeded smoothly with Mn of 6700 was obtained in 56% yield. in N-methyl-2-pyrrolidone (NMP) to afford the It seems that the substitution reaction ofKTFA targeted polymer with number-average mo­ with EBH proceeds gradually in the high-polar lecular weight (Mn) ofabout 9000 in 73% yield. solvent to form the corresponding interme­ The reaction was efficiently enhanced in diate, glycidyl trifluoroacetate, eliminating KBr N,N-dimethylacetamide or tetrahydrofuran in the first step, and then the produced KBr

Polym. J., Vol. 27, No. 10, 1995 1069 A. KAMEY AMA et al.

catalyzed 10 the following cycloaddition poly­ reaction of KTFA with EBH. merization of the intermediate. The one-pot reactions of other potassium The reaction was enhanced by the addition perfluoroalkylcarboxylates with EBH using of quaternary onium salts or crown ethers TBAB were also carried out in NMP under the under the same conditions. When the reaction similar conditions, The reaction of EBH with was carried out using 18-crown-6 ( 18-C-6), the potassium pentafluoropropionate (KPF A) corresponding polymer with Mn of 10000 was proceeded to give the corresponding polymer obtained. The increase of the molecular weight (P-2) with M. of 8000, might be ascribed to the incorporation of the In summary, it was demonstrated that the produced KBr by 18-C-6 to form the cor­ one-pot reaction of potassium perfluoroalk­ responding crown ether complex. Tetrabutyl­ ylcarboxylates with epibromohydrin proceeded ammonium chloride (TBAC) and TBAB also successfully using quaternary onium salts to enhanced the reaction, in particular, the reac­ give new polymers with five-membered cyclic tion using TBAC gave the polymer with the orthoester structures in the backbones. The highest Mn of 12000. This means that qua­ quaternary onium salts act as phase transfer ternary onium salts efficiently catalyze the sub­ catalysts in the first step and polymerization stitution reaction in the first step as PTC catalysts during the one-pot reaction. followed by polymerization in the second step during the reaction of KTFA with EBH. REFERENCES The structure of the resulting polymer (P-1) was ascertained by IR and 1 H NMR 1. a) T. Nishikubo, T. Iizawa, K. Kobayashi, and M. spectroscopies. The IR spectrum showed peaks Okawara, Makromol. Chem. Rapid Commun., 1, 765 (1980); b) T. Nishikubo and T. Jizawa, J. Syn. Org. at 2962 cm - 1 due to C-H stretching, at Chem. Jpn., 51, 157 (1993). 1 1280 cm - due to C-F stretching, and at 1184 2. a) T. Nishikubo, T. Iizawa, and M. Hasegawa, J. and 1116 cm - 1 due to the C-O-C stretching. Polym. Sci., Polym. Let/. Ed., 19, 113 (1981); b) T. Furthermore, no peaks due to carbonyl group Iizawa, T. Nishikubo, E. Takahashi, and M. and oxirane ring were observed in the Hasegawa, Makromol. Chem., 184, 2297 (1983). 3. a) T. Nishikubo, T. Shimokawa, and A. Sahara, corresponding regions. As shown in Scheme 2., Macromolecules, 22, 8 (1989); b) K. Kishi, H. Ban-no, 1H NMR spectral data was identified with A. Kameyama, and T. Nishikubo, Kobunshi Ronbun­ reference to the spectral data of a poly(cyclic shu, 51, 295 (1994); c) T. Nishikubo, A. Kameyama, K. Kishi, and C. Hijikata, Reactive Polymers, 24, 65 orthoester) previously reported by Hall. 11 (1994). Thus, it was proved that the targeted polymer 4. T. Nishikubo and A. Kameyama, Prog. Polym. Sci., with five-membered cyclic orthoester in the 18, 969 (1993). mam chain was obtained by the one-pot 5. a) T. Nishikubo, T. Iizawa, M. Shimojo, and M. Shi-ina, J. Org. Chem., 55, 2536 (1990). b) T. Nishikubo, T. Kato, Y. Sugimoto, M. Tomoi, and

Ha Ha Hb S. Ishigaki, Macromolecules, 23, 3406 (1990). OXCF3i 6. A. Kameyama, M. Kiyota, and T. Nishikubo, 0 (')i)f\ Tetrahedron Lett., 35, 4571 (1994). 7. A. Kameyama, K. Shimotsuma, and T. Nishikubo, He~ n Macromol. Rapid Commun., 15, 335 (1994). 8. A. Kameyama, Y. Hatakeyama, and T. Nishikubo, 1H-NMR data Tetrahedron Lett., 36, 2781 (I 995). (ppm, CDC13, TMS) 9. A. Kameyama, K. Machida, and T. Nishikubo, 3.62-3.94 (m, 2H, Ha) Macromolecules, 28, 3490 (1995). 3.94-4.09 (m, IH, Hb) 10. T. Nishikubo, Y. Sugimoto, and K. Sato, Nippon 4.09-4.30 (m, IH, He) Kagaku Kaishi, 1506 (1991). 4.30-4.81 (m, IH, Hd) 11. Y. Yokoyama, A. Buy le Padias, Fr. De Blau we, and Scheme 2. H. K. Hall Jr., Macromolecules, 13, 252 (1980).

1070 Polym. J., Vol. 27, No. 10, 1995