ISSN 0012�5008, Doklady Chemistry, 2010, Vol. 432, Part 1, pp. 144–147. © Pleiades Publishing, Ltd., 2010.Original Russian Text © A.Ya. Vainer, K.M. Dyumaev, S.A. Mareeva, M.G. Gorb, I.I. Desyatnik, A.I. Tarnopolskii, 2010, published in Doklady Akademii Nauk, 2010, Vol. 432,No. 3, pp. 343–346.

144

Aromatic polyethers (APs) with perfluorophe�nylene fragments in the backbone posses a set of valu�able properties such as high thermal and chemical sta�bility, good mechanical and insulating properties, andlow water absorption. Owing to these parameters,these polymers are promising for aerospace industryand microelectronics [1–3].

This prompts the idea of modifying the propertiesof APs in order to extend the scope of their applica�tions. A possible chemical transformation of APs isintroduction of trifluorovinyl groups into the sidechains of macromolecules. The high reactivity of thesegroups in radical cyclopolymerization [4–6] and thethermal stability of the polymers thus formed makethis modification quite reasonable for the develop�ment of a new generation of thermally stable negativephotoresists. However, APs with trifluorovinyl sidegroups have not been described in the literature so far.

Here, we propose a new strategy for the synthesis ofcarboxyl�containing AP derivatives with trifluorovinylside groups. We carried out simple and convenientsynthesis of such unsaturated polymers by exhaustiveesterification of APs with carboxyl side groups throughthe reaction with 4�(trifluorovinyloxy)benzyl alcohol.In addition, thermal and photochemical transforma�tions of the resulting prepolymers were studied and thelithographic parameters of the negative photoresistsbased on these polymers in the formation of topologi�cal structures were estimated.

The starting APs were prepared by condensation ofdecafluorobiphenyl with phenolphthalein accordingto the procedure we developed previously [7]. The tri�fluorovinyl fragments were introduced into the sidechains of the carboxyl�containing polymer by esterifi�cation of the synthesized prepolymer (ηred 0.92 dL/g,

0.5% solution in N�methylpyrrolidone (N�MP),30°C) with 4�(trifluorovinyloxy)benzyl alcohol,which was prepared by a reported procedure [8].3�Pyridinecarboxylic anhydride (PCA) was used asthe condensing agent. This was prepared by a reportedprocedure [9]. 4�Dimethylaminopyridine (DMAP)was added to the reaction mixture to accelerate theprocess.

Modification was carried out in acetonitrile solu�tion (under argon at room temperature) under micro�wave activation (a Biotage Initiator Sixty microwavereactor). The process duration was 20 min. The unsat�urated alcohol, PCA, and DMAP were added to thesolution of APs in equimolar amounts with respect tothe carboxyl groups. The final polymer was precipi�tated with isopropanol; the precipitated modified APwas filtered off, washed many times with ether, anddried in vacuum at 70°C.

The resulting unsaturated APs and the products oftheir subsequent thermal transformations were identi�fied using IR and 1H, 13C, and 19F NMR spectra.Analysis of the obtained data demonstrates that underthe esterification conditions chosen, the carboxylgroups have been consumed almost completely.Indeed, the IR spectrum of the target polymer nolonger contains the absorption band at 1675 cm–1 or3520–3200 cm–1 (C=O and OH stretching vibrationsof the carboxyl groups, respectively). Instead, thespectrum contains new absorption bands for trifluo�rovinyl groups at 1833 cm–1 (–O–CF=CF2) and at1319, 1275, 1217, 1178, and 1143 cm–1 (C–F). Inaddition, a new absorption band at 1736 cm–1 (C=Oof the ester side groups) can be noted.

The 1H NMR spectrum of the saturated targetpolymer does not exhibit a broad signal at 12.48 ppmfor the carboxyl protons, but contains new signalscaused by various protons of the 4�(trifluorovinyl�oxy)benzyl groups introduced in the AP side

CHEMISTRY

Derivatives of Carboxyl�Containing Aromatic Polyethers with Pendant Trifluorovinyl Groups: Synthesis

and Thermo� and Photochemical TransformationsA. Ya. Vainer, Corresponding Member of the RAS K. M. Dyumaev, S. A. Mareeva,

M. G. Gorb, I. I. Desyatnik, and A. I. Tarnopolskii

Received November 24, 2009

DOI: 10.1134/S0012500810050071

All�Russia Institute of Medicinal and Aromatic Plants, Russian Academy of Agricultural Sciences, ul. Grina 7, Moscow, 113628 Russia

DOKLADY CHEMISTRY Vol. 432 Part 1 2010

DERIVATIVES OF CARBOXYL�CONTAINING AROMATIC POLYETHERS 145

chains [8]. Of analytical value is the signal at δ 4.48ppm (methylene group protons of the side fragments).

In the 13C NMR spectrum of the modified poly�mer, the signal for the carboxyl carbon atoms(169.4 ppm) disappears from the region of carbonylatoms, while a new signal appears at 164.5 ppm due tothe ester carbon atoms of the benzoate groups.In addition, the spectrum exhibits new signals at

133.55 ppm (CF2=CF–) and 147.0 ppm (CF2=CF–).Finally, the 19F NMR spectrum of the target polymerexhibits new signals at –119.8, –126.7, and –134.9 ppmdue to the fluorine atoms of the trifluorovinyl sidegroups [5, 8, 10].

The foregoing allows one to represent the chemicalmodification of APs that we carried out as follows:

The thermal transformations of the synthesizedAPs with trifluorovinyl side groups were studied by dif�ferential scanning calorimetry (DSC). The DSC ther�mograms of the polymers measured in the 25–350°Ctemperature range show a broad exotherm starting at146°C and reaching a maximum at 244°C. The secondrecording of the thermograms for the same samples isaccompanied by a sharp decrease in the exotherm,which is now ~16% of the initial value. This exothermdisappears almost completely in the third recording ofthe thermograms. However, the thermograms alsoshow no endotherms that could be assigned to the glasstransition temperatures of the cross�linked polymericfilms.

The exothermal polymerization of the trifluorovi�nyl groups in the side fragments of the synthesized APsoccurs only partly under the chosen heat treatmentconditions, the degree of consumption of these unsat�urated groups being 83% if the conversion of thesegroups is estimated from the decrease in the intensityof the absorption band at 1833 cm–1 in the IR spectraof thermolyzed polymers.

As indicated by analysis of publications [4–6, 8,10,11], the thermal solid�phase polymerization of tri�fluorovinyl ethers follows a [2π+2π] cycloadditionmechanism to give hexafluoro�containing cyclobu�tane structures. The microstructure of the heat treatedtarget APs was identified by solid�state 19F NMR spec�troscopy. In the obtained spectra, the signals at –119.8, –126.7, and –134.9 ppm caused by the fluorineatoms in the trifluorovinyl side groups are smaller thanthese signals in the 19F NMR spectra of the initialpolymers.

In turn, the spectra of heat treated APs derivativesexhibit new signals at –126.4, –127.4, –127.9,⎯128.5, –129.2, –129.9, –130.4, –131.0, and⎯131.6 ppm, which are typical of fluorine atoms inhexafluorocyclobutane structures [4]. In addition, theIR spectra of these polymers show a new band at968 cm–1 associated with the above�noted 1,2�substi�tuted hexafluorocyclobutane rings [12]. Thus, ther�molysis of the target unsaturated polymers under thechosen conditions affords intermolecular cyclobutanestructures, the trifluorovinyl groups being coupledaccording to the head�to�head pattern.

According to thermogravimetric analysis (TGA),during thermolysis under argon, these unsaturatedAPs start to lose weight at 410°C, a 5% weight loss tak�ing place at 448°C. This high thermal stability is quiteadequate to the modern lithography.

In a study of the photochemical properties of thesynthesized unsaturated APs, the films of these poly�mers were irradiated under argon at room temperaturewith UV light at 365 nm. The intrinsic light sensitivityof the polymers is negligibly low under these exposureconditions. When developing negative photoresistsbased on APs with trifluorovinyl side groups, in thiswork, we made use of the fact that photoinitiated cat�ionic polymerization of vinyl ethers proceeds at a highrate in the presence of an acid photogenerating agentsuch as (5�propylsulfonyloxyimino�5H�thiophen�2�ylidene)�(2�methylphenyl)acetonitrile (PTMA) [13].

Commercial PTMA (Ciba Specialty Chemicals)was added to the polymer system in a 5 wt % amountwith respect to unsaturated APs. The acid

O C

H

O

F F

FF

FF

F FCOOH

n

OCFHOCH2 CF2+

APs, DSC

–H2O O C

H

O

F F

FF

FF

F FCOOH

n

COOR

146

DOKLADY CHEMISTRY Vol. 432 Part 1 2010

VAINER et al.

(C3H7SO3H) generated on photodecomposition ofthis compound in this matrix initiates the cationicpolymerization of the unsaturated groups, resulting instructurization of the exposed regions of the polymericfilm. Photoinitiated polymerization of trifluorovinylside groups takes place upon post�exposure heat treat�ment of the exposed layer at 90°C for 15 min.

The cationic polymerization in the matrix of thesynthesized unsaturated APs was monitored by solid�phase 19F NMR spectroscopy. The formation of three�dimensional network upon UV irradiation of the poly�mer film was accompanied by considerable decrease inthe signal intensity of fluorine atoms of the trifluorovi�nyl groups. New signals due to fluorine atoms of thesaturated fragments of the resulting network appearsimultaneously, in particular, broad multiplets in theranges of –111 to –117 ppm (CF2) and –134 to⎯139 ppm (CF). Under above�noted exposure condi�tions (exposure dose 200 mJ/cm2) and the post�expo�sure heat treatment, the conversion of the unsaturatedgroups determined from the decrease in the bandintensity at 1833 cm–1 in the IR spectrum of the cross�linked polymer reaches 65%.

In the development of negative photoresists, 1,1,1�tris(4�trifluorovinyloxyphenyl)�2,2,2�trifluoroethanewas added as a photostructuring agent [5] in a 25 wt %amount relative to the unsaturated polymer toenhance the system photosensitivity. The resultingnegative photoresists possess a light sensitivity of about80 mJ/cm2, which is 3.5–4 times as high as thisparameter for commercial photoresists based onmethacrylate derivatives of polyamino acids. The pho�toresists had a high resolution, which was about twiceas good as that of methacrylate resists: patterns with aminimal printing feature of 0.8 μm were formed in a1.0 μm�thick polymeric film based on APs with triflu�orovinyl side groups. A thermal stability adequate tothe modern lithography and high light sensitivity andresolution make the negative photoresists based on thesynthesized AP fairly promising for the manufacture ofsemiconductor devices.

The thermal properties of AP derivatives were stud�ied on Thermal Analysis Co instruments under argonat a heating rate of 5 K/min. DSC analysis was per�formed on a TA Instruments Q 2000 instrument. TGAwas measured on a TA Instruments TGA 2050 unit.

The spectral measurements were carried out forpolymer samples as 1–2 μm�thick films cast on quartzplates from solutions in N�MP. IR spectra were mea�sured on a Perkin�Elmer Spectrum 1000 FT IR spec�trophotometer in the frequency range of 400–4000 cm–1.

1H and 13C NMR spectra were recorded on aBruker Avance DSX750 spectrometer operating at750.22 and 188.65 MHz, respectively, in DMSO�d6

solutions (tetramethylsilane as the internal standard).The NMR signals were assigned using proton–protonand carbon–proton shift correlation spectroscopyprocedures (COSY, HMBC, and HSQC).

19F NMR spectra were recorded on a BrukerAvance 600 spectrometer operating at 564.5 MHz inDMSO�d6 solutions (trichlorofluoromethane as theexternal standard) as recommended in the literature[15]. The high�resolution solid�state 19F NMR spectrawere recorded on a Bruker DRX 600 spectrometerwith sample spinning at 10 kHz frequency. The work�ing frequency was 564.1 MHz.

The chemical shifts are presented in the δ scale(ppm).

Thus, the possibility of preparing derivatives of car�boxyl�containing AP with trifluorovinyl side groupswas demonstrated for the first time. We developed afacile and convenient method for the synthesis of theseunsaturated polymers by exhaustive esterification ofAPs containing carboxyl side groups through the reac�tion with 4�(trifluorovinyloxy)benzyl alcohol. Thethermal transformations of these polymers in the 25–350°C range were studied. It was found that thermoly�sis of the target polymers under chosen conditionsyields intermolecular 1,2�substituted hexafluorocy�clobutane structures, the trifluorovinyl groups beingcoupled according to the head�to�head pattern. It wasshown that the unsaturated AP can be used to developpromising negative photoresists with high lithographicparameters.

REFERENCES

1. Goodwin, A.A. and Mercer, F.W., J. Polym. Sci.: Polym.Phys. Ed., 1997, vol. 35, no. 12, pp. 1963–1971.

2. Lee, H.�J., Lee, E.�M., Lee, M.�H., et al., J. Polym.Sci.: Polym. Chem. Ed., 1998, vol. 36, no. 16, pp. 2881–2887.

3. Jeong, M.�H., Lee, K.�S., and Lee, J.�S., Macromole�cules, 2009, vol. 42, no. 5, pp. 1652–1658.

4. Ghim, J., Lee, D.�S., Shin, B.G., et al., Macromole�cules, 2004, vol. 37, no. 15, pp. 5724–5731.

5. Jin, J., Topping, C.M., Chen, S., et al., J. Polym. Sci.:Polym. Chem. Ed., 2004, vol. 42, no. 20, pp. 5292–5300.

6. Budy, S.M., Suresh, S., Spraul, B.K., and Smith, D.W.,J. Phys. Chem. C, 2008, vol. 112, no. 21, pp. 8099–8104.

7. Vainer, A.Ya., Dyumaev, K.M., Mareeva, S.A., andTokarskaya, S.V., Dokl. Phys. Chem., 2001, vol. 377,nos. 4–6, pp. 96–98 [Dokl. Akad. Nauk, 2001, vol. 377,no. 5, pp. 649–652].

8. Spraul, B.K., Suresh, S., Jin, J., and Smith, D.W.,J. Am. Chem. Soc., 2006, vol. 128, no. 21, pp. 7055–7064.

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DERIVATIVES OF CARBOXYL�CONTAINING AROMATIC POLYETHERS 147

9. Mukaiyama, T. and Funasaka, S., Chem. Lett., 2007,vol. 36, no. 2, pp. 326–327.

10. Jin, J., Smith, D.W., Topping, C.M., et al., Macromol�ecules, 2003, vol. 36, no. 24, pp. 9000–9004.

11. Mifsud, N., Mellon, V., Jin, J., et al., Polym. Int., 2007,vol. 56, no. 9, pp. 1142–1146.

12. Kennedy, A.P., Babb, D.A., Bremmer, J.N., and Pasz�tor, A.J., J. Polym. Sci.: Polym. Chem. Ed., 1995, vol. 33,no. 11, pp. 1859–1865.

13. Lousenberg, R.D. and Shoichet, M.S., J. Polym. Sci.:Polym. Chem. Ed., 1999, vol. 37, no. 16, pp. 3301–3308.

14. Asakura, T., Yamato, H., and Ohwa, M., J. Photopolym.Sci. Technol., 2000, vol. 13, no. 2, pp. 223–230.

15. Barchi, J.J., Karki, R.G., Nicklaus, M.C., et al., J.Am. Chem. Soc., 2008, vol. 130, no. 28, pp. 9048–9057.