ISSN 0012�5008, Doklady Chemistry, 2011, Vol. 438, Part 1, pp. 140–143. © Pleiades Publishing, Ltd., 2011.Original Russian Text © A.Ya. Vainer, K.M. Dyumaev, S.A. Mareeva, V.D. Alekseev, M.B. Bruskina, A.A. Glagolev, 2011, published in Doklady Akademii Nauk, 2011, Vol. 438,No. 3, pp. 341–344.

140

Aromatic polyethers (APEs) with perfluorophe�

nylene fragments in the backbone have a number of

valuable properties such as high thermal and chemical

stabilities, good mechanical and insulating properties,

and low water absorption. Therefore, these polymers

are promising for aerospace industry and microelec�

tronics [1–3].

We suggested that APEs of this type containing

additionally 2,6�bis(4�azidotetrafluorobenzylide�

ne)cyclohexanone fragments and styryl groups in the

backbones of the macromolecules may present practi�

cal interest as binders of thermally stable negative pho�

toresists. Note that new styryl�containing bisphenols

that have been recently synthesized [4] are suitable as

building blocks in the design and synthesis of APE,

which are promising, in our opinion, for the produc�

tion of such photoresists. However, such APEs have

not yet been reported.

In this work, we propose for the first time a strategy

for the synthesis of azide�containing APEs with styryl

groups in the macromolecule backbones. We per�

formed a facile and convenient synthesis of such

unsaturated polymers by exhaustive esterification of

APEs containing carboxyl side groups by 2,6�bis(4�

azidotetrafluorobenzylidene)�4�(2�hydroxyethyl)cyc�

lohexanone (bisazide�OH). In addition, thermal

transformations of the synthesized polymers and their

photochemical curing induced by the products of

photolysis of azide�containing fragments were stud�

ied, and the systems were evaluated as negative photo�

resists.

The starting unsaturated APEs were prepared using

decafluorobiphenyl (Aldrich) and E,E�1,2,4,5�tet�

rafluoro�3,6�bis(3'�carboxy�4'�hydroxy�1'�styryl)ben�

zene (bisphenol I) and E,E�1,2,4,5�tetrafluoro�3,6�

bis(4'�hydroxy�1'�styryl)benzene (bisphenol II),

which we synthesized by reported procedures [4];

these monomers were introduced in the reaction mix�

ture in 12 : 1 : 11 molar ratio, respectively. The con�

densation of these compounds was performed as rec�

ommended in the literature [2, 5] in a dimethylacet�

amide (DMA)– benzene mixture (10 : 1 v/v) with

K2CO3 as the catalyst. The reaction was carried out at

130°C for 6 h under argon. The process was homoge�

neous. The final polymer was precipitated by a meth�

anol–water mixture (3 : 1 v/v). The precipitated

styryl�containing APE was filtered off, repeatedly

washed with methanol and ether, and dried in vacuum

at 70°C. The polymer was readily soluble in amide sol�

vents, acetonitrile, tetrahydrofuran, and diglyme at

room temperature. The polycondensation can be rep�

resented by Scheme 1 (only bisphenol I and the car�

boxyl�containing fragments of APEs are shown for the

sake of simplicity).

CHEMISTRY

Aromatic Polyethers with 2,6�Bis(4�azidotetrafluorobenzylidene)cyclohexanone Side

Fragments and Styryl Groups in the BackboneA. Ya. Vainer, Corresponding Member of the RAS K. M. Dyumaev, S. A. Mareeva,

V. D. Alekseev, M. B. Bruskina, and A. A. Glagolev

Received December 17, 2010

DOI: 10.1134/S0012500811050041

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

DOKLADY CHEMISTRY Vol. 438 Part 1 2011

AROMATIC POLYETHERS 141

Scheme 1.

In the IR spectrum of unsaturated APE (ηred

0.56 dL/g, a 0.5% solution in DMA, 25°C), the back�bone styryl groups account for the absorption band at960 cm–1 important for structural diagnostics andcaused by out�of�plane =CH bending vibrations intrans�disubstituted alkenes and for the band at859 cm–1 corresponding to the bending vibrations ofthe alkene�bonded aromatic rings. In addition, notethe bands at 1675 and 3520–3200 cm–1 (C=O and OHstretching vibrations of carboxyl groups, respectively).

The 1H NMR spectrum of styryl�containing APEexhibits signals at δ 6.99, 7.12, 7.17, and 7.34 ppm cor�responding to the trans�alkene protons and a signal atδ 11.44 ppm corresponding to carboxyl protons. In the13C NMR spectrum of this polymer, the most infor�mative region for unsaturated groups contains signalsat 123.2 and 128.5 ppm due to the trans�alkene carbonatoms.

The selection of bisazide�OH as the modifyingagent for imparting inherent light sensitivity to thesynthesized APE on exposure of the polymer film tolight at 365 nm was based on the following reasons.Aromatic bisazides are widely used as light�sensitivecomponents of negative photoresists. As regards themanufacture of topological structures with optimallight sensitivity and resolution, it is important toincrease the yields of insertion reactions of the singletnitrenes formed upon azide photolysis. In severalstudies [6–8], it was shown that introduction of fluo�rine into the aromatic ring increases substantially theyield of insertion products in the target (in this case,the polymer matrix) upon photolysis. In particular, itwas found that perfluorinated aromatic bisazides aresuitable for producing negative photoresists with highlight sensitivity and resolution [8].

The bisazide fragments were introduced into theside chains of carboxyl�containing polymers via ester�ification of the synthesized prepolymer by bisazide�OH, which we prepared by the reaction of 4�azidotet�rafluorobenzaldehyde [8] with 4�(2�hydroxy�

ethyl)cyclohexanone [9] in alkaline medium as rec�ommended in the literature [9, 10]. The bisazideobtained in this way was purified by preparative high�performance liquid chromatography (HPLC). Itsstructure was determined by MALDI TOF mass spec�trometry [11], 1H and 13C NMR spectroscopy, and IRspectroscopy and confirmed by analytical HPLC andelemental analysis data.

MALDI TOF MS: for C22H12F8N6O2 [M]+, calcd.544.3671, found 544.3656.

3�Pyridinecarboxylic anhydride (PCA) was used asthe condensing agent in the esterification of the car�boxyl�containing APE. This agent was synthesized bya reported procedure [12]. For accelerating the pro�cess, 4�dimethylaminopyridine (DMAP) was addedto the reaction mixture. Modification was carried outby a previously reported procedure [13] in acetonitrilesolution (argon, room temperature) with microwaveactivation (Biotage Initiator Sixty microwave reactor),the process time was 20 min. Bisazide�OH, PCA, andDMAP were added to a solution of APE in equimolaramounts in relation to the number of carboxyl groups.The final polymer was precipitated by isopropanol,and the precipitated modified APE was filtered off,repeatedly washed with ether, and dried in a vacuumat 70°C.

The azide�containing unsaturated APE we pre�pared and the products of their subsequent thermaland photochemical transformations were identified bythe data from IR and 1H and 13C NMR spectra. Anal�ysis of this information shows that under the esterifica�tion conditions chosen, the carboxy groups have beenconsumed almost completely. The IR spectrum of thetarget polymer no longer contains the absorptionbands at 1675 or 3520–3200 cm–1 but contains newabsorption bands due to the azide side fragments:2161, 2123 cm–1 (azide groups), 1665 cm–1 (cyclohex�anone C=O), and 1581 cm–1 (exocyclic –C=C–groups). In addition, a new absorption band is presentat 1736 cm–1 (C=O of the ester side groups).

F F

F F

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CH CH

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FF

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142

DOKLADY CHEMISTRY Vol. 438 Part 1 2011

VAINER et al.

The 1H NMR spectrum of the target polymer doesnot exhibit a broad signal at 11.44 ppm for the carboxylprotons, but contains new signals caused by variousprotons of the bisazide side fragments. The signals at δ2.52 ppm (methylene protons of the cyclohexanonering) and 6.72 ppm (protons at exocyclic doublebonds) are analytically significant.

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 carbonyl

carbons. Instead, new signals appear at 164.5 ppm(ester carbonyl carbon atoms in the benzoate groups)and 190.2 ppm (cyclohexanone C=O). In addition,the spectrum exhibits a new signal at 136.8 ppmcaused by carbon atoms in the exocyclic alkenegroups.

Thus, the structure of the obtained light�sensitivepolymer can be depicted as follows (only azide�con�taining fragments are shown for simplicity):

The molar fraction of the monomer units based onbisphenol I in the APE we synthesized was 4.2 mol %(13C NMR data). One can calculate that on completeconversion of the carboxy groups, the content of thebisazide side groups in the final polymer would be14.3% relative to the modified APE weight.

The thermal transformations of the starting styryl�containing APE were studied by differential scanningcalorimetry (DSC). The DSC thermograms of thepolymers measured in the 25–300°C temperaturerange show a broad exotherm starting at 235°C andreaching a maximum at 305°C. Analysis of the IRspectra of heat�treated styryl�containing APE samplesshows a considerable decrease in the intensity ofthe band at 960 cm–1, indicating partial consumptionof the trans�vinyl bonds during the thermal cross�linking.

The DSC thermograms of azide APE derivativesexhibit a broad exotherm with the onset of curing at174°C and a maximum at 282°C. This shift in the cur�ing temperature range for polymers with bisazide sidegroups toward lower values as compared with the start�ing APEs is caused by additional cross�linking of thesepolymers by the products of thermolysis of the azidegroups. The possible endotherm that would corre�spond to their decomposition is covered in these ther�mograms by the large thermal curing exotherm. Anal�ysis of the IR spectra of the heat�treated samples of

these APE derivatives reveals a sharp decrease in theintensity of the azide band at 2123 cm–1, which startsat about 170°C. In addition, the IR spectra of the heat�treated azide�containing APE samples measured afterDSC thermogram recording show markedly reducedintensity of the absorption bands at 960 cm–1 (trans�alkene groups) and 1581 cm–1 (exocyclic –C=C–groups); the degree of decrease in the number of dou�ble bonds after thermolysis of the final APE derivativesmarkedly exceeds the loss of these bonds upon a simi�lar heat treatment of the starting polymers.

In a study of the photochemical properties of thesynthesized APEs, the films of these polymers wereirradiated under argon at room temperature with UVlight at 365 nm. The proper light sensitivity of thestyryl�containing polymers is negligibly low underthese exposure conditions. The UV/Vis spectra of theexposed APE films are characterized by invariableintensity of the absorption of the trans�stilbene groupsin the range of 300–360 nm with respect to that in thespectrum of non�irradiated polymers. Thus, trans–cisisomerization of stilbenes known from the literature[14] does not take place under the chosen exposureconditions.

Conversely, the obtained APEs with bisazide sidefragments have a photochemical activity needed forthe use in negative photoresists. The exposure dose ofthe corresponding protective layers is 125 mJ/cm2,

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DOKLADY CHEMISTRY Vol. 438 Part 1 2011

AROMATIC POLYETHERS 143

which lies in the range of values typical of commercialphotoresists based on unsaturated polyimide deriva�tives [5].

The UV/Vis spectra of the exposed azide�contain�ing APE films show a bathochromic shift of theabsorption maximum from 332 nm in the initial filmto 385 nm and decrease in the absorption intensity.These changes of the UV/Vis spectra are probablyrelated to cross�linking of macromolecules. The cross�links are N�aryl� and N�alkyltetrafluoroaniline deriv�atives connected to the polymer chains. These anilineproducts are the adducts formed upon insertion of thephotogenerated singlet perfluorophenylnitrenes intoaromatic and alkene fragments, respectively [6].

The resists are distinguished by high resolution:topological structures with a minimum element size of0.75 μm are formed in a 1.0 μm�thick polymer layers.Furthermore, the synthesized APEs with bisazide sidefragments are highly thermally stable. According tothe thermogravimetric analysis data, the weight loss ofthe exposed and post�exposure heat�treated (170°C,5 min) film based on the final polymer starts at 415°C.

Thus, the synthesis of APEs with bisazide side frag�ments and styryl groups in the backbone was accom�plished for the first time. We developed a facile andconvenient method for the synthesis of these polymersby exhaustive esterification of the carboxyl side groupsof the starting unsaturated APE via the reaction withbisazide�OH. The thermal and photochemical trans�formations of these polymers were studied. Theseazide�containing systems were shown to be promisingas negative photoresists with high lithographic param�eters.

The analytical procedures were reported previously[13].

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