synthesis and characterization of photocrosslinkable functional polymer having pendant chalcone...

Reactive & Functional Polymers 49 (2001) 77–86www.elsevier.com/ locate / react

Synthesis and characterization of photocrosslinkable functionalpolymer having pendant chalcone moiety

*R. Balaji, S. NanjundanDepartment of Chemistry, Anna University, Chennai 600 025, India

Received 22 February 2001; received in revised form 9 April 2001; accepted 19 April 2001

Abstract

New methacrylate monomer, 4-methacryloyloxyphenyl-39-methylstyryl ketone (MPMSK) containing pendant chalconemoiety was synthesized by reacting 4-hydroxyphenyl-39-methylstyryl ketone (HPMSK) with methacryloyl chloride in thepresence of triethyl amine. The monomer, MPMSK was polymerized in ethyl methyl ketone solution at 70618C at nitrogen

1atmosphere using benzoyl peroxide as a free radical initiator. The polymer was characterized by UV, FT-IR, H-NMR and] ]13C-NMR spectra. The molecular weights (M and M ) of the polymer were determined by gel permeation chromatography.w n

The thermal stability of the polymer was measured by thermogravimetric analysis in air. The glass transition temperature ofthe polymer was determined by differential scanning calorimetry. The photosensitivity of the polymer was investigated invarious solvents in the presence and absence of various triplet sensitizers. The effect of solvent on the rate ofphotocrosslinking of the polymer was also studied. 2001 Elsevier Science B.V. All rights reserved.

Keywords: Poly(4-methacryloyloxyphenyl-39-methylstyryl ketone); Photocrosslinking; Chalcone moiety; Photoresist

1. Introduction energy exchange materials [11], liquid crys-talline display [12–14], etc.

Synthesis of polymers carrying reactive func- Photosensitive polymers with a combinationtional groups have been an active field of of properties such as high photosensitivity, goodresearch in polymer science in recent years solubility, the ability to form films, good ther-[1–3]. Polymer containing pendant a,b-unsatu- mal stability, resistance towards solvents afterrated carbonyl groups (also named chalcone crosslinking are very important for practical usegroups) undergo crosslinking upon irradiation as commercial negative photoresist materials.with UV light and are regarded as negative-type The synthesis and photocrosslinking propertiesphotoresists. The technological applications of of polymers such as cinnamoylated poly-the photosensitive polymers are applied in the vinylamine and polyvinylalcohol [15,16], polyfields of microlithography [4–6], photoconduc- (2-vinyloxy carbonyl chalcones) [17], poly (cin-tors [7], nonlinear optical materials [8–10], namoyloxy ethyl methacrylate) [18] and other

systems have been reported [19–21].The aim of the present work involves the*Corresponding author. Fax: 191-44-235-2870.

E-mail address: [email protected] (S. Nanjundan). synthesis, characterization and photocrosslink-

1381-5148/01/$ – see front matter 2001 Elsevier Science B.V. All rights reserved.PI I : S1381-5148( 01 )00062-1

78 R. Balaji, S. Nanjundan / Reactive & Functional Polymers 49 (2001) 77 –86

ing property of new methacrylate polymer con- 5.55 (Found), 5.54taining chalcone as pendant group. The effect of (calcd);

21different solvents on the rate of photocrosslink- IR (KBr, cm ): y 53183 (–OH), 1644ing for using the polymer as negative resist (.C5O) and 1603material were also assessed. (–CH5CH–), 1565

and 1460 (Ar, C5Cstretching) and 835and 780 (C–H out of2. Experimentalplane bending).

1H-NMR (CDCl , ppm): d 510.25 (1H,O–H),2.1. Materials 3

8.01–7.35 (8H, aro-4-Hydroxyacetophenone and 3-methylbenzal- matic), 6.85 (2H,

dehyde from Fluka were used as received. –CH5CH–) and 2.05Benzoyl peroxide (BPO) (Aldrich) was re- (3H, CH ).3

crystallized from methanol–chloroform (1:1)mixture. Methacryloyl chloride was prepared 2.2.2. Synthesis of 4-methacryloyloxyphenyl-according to the method of Stempel et al. [22]. 39-methylstyryl ketone (MPMSK)(2)All other chemicals were of analytical grade and The chalcone HPMSK (13 g, 0.054 mol) andused without further purification. All the sol- triethylamine (7.6 g) were dissolved in 100 mlvents were distilled before use. of ethyl methyl ketone (EMK) in a 250 ml three

necked flask and cooled between 25 and 08C.Methacryloyl chloride (5.3 g, 0.054 mol) in 302.2. Preparationsml of EMK was then added dropwise with

2.2.1. Synthesis of 4-hydroxylphenyl-39- constant stirring and cooling at 25 to 08C.methylstryl ketone (HPMSK)(1) After stirring the reaction mixture at room

4-Hydroxyacetophenone (13.6 g, 0.1 mol) in temperature for 2 h, the precipitated quaternary60 ml of ethanol and a solution of sodium ammonium salt was filtered off. The organichydroxide (8 g) in distilled water (40 ml) were layer was evaporated with a rotatory vacuumplaced in a three-necked flask equipped with evaporator to get the crude monomer. It wasmechanical stirrer, thermometer and droping dissolved in ether and was washed successivelyfunnel and were cooled in an ice bath. 3- with 5% aqueous sodium hydroxide solutionMethylbenzaldehyde (13.6 g, 0.1 mol) dissolved and distilled water. The ether layer was driedin 50 ml of ethanol was added dropwise with over anhydrous sodium sulphate. Then etherconstant stirring such that the temperature was was evaporated to get crude solid methacrylatenot exceeded 208C. After stirring the reaction monomer, MPMSK. It was recrystallized frommixture at room temperature for 12 h, it was methanol to get shining yellow crystals. Yieldneutralized with dilute HCl to isolate the prod- 14.6 g (80%); m.p. 95–968C.uct. The precipitated solid product was filtered, The structure of the monomer, MPMSK was

1washed with ice cold water, dried and recrystal- identified by elemental analysis, IR and H-lized from ethanol to get pale yellow crystals. NMR spectra and found to be consistent withYield 17.7 g (70%); m.p. 138–1398C. the assigned structure.

The formation of the HPMSK was confirmed1 Elemental analysis (%): C578.34 (found),by elemental analysis and IR and H-NMR

78.41 (calcd) H55.85spectroscopy.(found), 5.92 (calcd)

21Elemental analysis (%): C580.52 (Found), IR (KBr, cm ): y 51736 (ester .C5

80.65 (calcd); H5 O), 1658 and 1640

R. Balaji, S. Nanjundan / Reactive & Functional Polymers 49 (2001) 77 –86 79

(ketone .C5O), to tetramethylsilane as internal standard in] ]

CDCl . The number (M ) and weight (M )1604 (olefinic .C5 3 n w

average molecular weights and polydispersityC,), 1500 and 1410index values of the polymer were determined(aromatic C5Cwith a Waters 501 gel permeation chromato-stretching) and 770graph equipped with three ultrastyragel columnsand 732 (out of planeand a differential refractive index (RI-401)bending of5C–H).

1 detector. The molecular weights of the polymerH-NMR (CDCl , ppm): d 58.35–7.25 (8H,3were calibrated against polystyrene standardsAr–H), 6.33 and 5.93using tetrahydrofuran as mobile phase. Thermo-(4H; –CH5CH– andgravimetric analysis were performed with aCH 5), 2.36 (3H,2Mettler TA 3000 thermal analyser in an airCH ) and 2.03 (3H,3 21atmosphere at a heating rate of 158C min . Thea–CH ).3glass transition temperature (T ) of the polymerg

was determined with a Perkin–Elmer DSC d72.3. Polymerizationdifferential scanning calorimeter at a tempera-

21ture raise of 108C min in nitrogen atmos-Homopolymerization of the methacrylatephere.monomer, MPMSK was carried out as a 2 M

solution in ethyl methyl ketone using benzoyl2.5. Photoreactivity measurementsperoxide (0.5 wt% with respect to the monomer)

as a free radical initiator at 70618C. RequiredThe photoreactivity of the polymer was

amounts of MPMSK, BPO and EMK werestudied by dissolving the sample in chloroform

mixed in a polymerization tube, flushed withsolution (0.005%) and irradiated with high

oxygen free nitrogen for 30 min and kept in apressure mercury lamp (Toshiba SHL -100 UV,

thermostat at 70618C. After 10 h, the reaction 218 W, 254 nm ) at a distance of 10 cm from themixture was poured into excess methanol to

light source for different intervals of time. Theisolate the polymer. The crude polymer, poly-

path length of the quartz cell used for polymer(MPMSK) (3) was purified by reprecipitation of

solution irradiation was 1 cm. After each ir-the polymer by methanol from chloroform

radiation, the UV spectra were recorded on UV–solution and finally dried under vacuum at 408C.

Visible spectrophotometer. The rate of disap-Yield 45–50%.

pearance of the double bond in the reactivechalcone groups was followed by using the

2.4. Measurements expression:

A –AElemental analysis were performed with a 0 T]]]Extent of Conversion (%) 5 3 100Perkin–Elmer C–H analyser. UV spectra were A –A0 `

recorded on a Shimadzu UV-1601, UV–Visiblewhere A , A and A are absorption intensities0 T `spectrophotometer. Infrared spectra were ob-due to C5C after irradiation times t 5 0, t 5 Ttained as a potassium bromide pellet with aand t 5 ` respectively.Nicolet Avatar 360 FT-IR spectrophotometer.

1H-NMR spectra were obtained with a JEOL400 MHz spectrometer at room temperature 3. Results and discussionusing 10 wt% solutions with tetramethylsilane

13as an internal reference in CDCl solution. C- 3.1. Synthesis3

NMR spectrum was run on the same instrumentoperating at 125.77 MHz at room temperature The photoreactive monomer, 4-and chemical shifts were recorded with respect methacryloyloxyphenyl-39-methylstyryl ketone


(MPMSK) having a free radical polymerizable such as dimethyl formamide, dimethyl sulph-methacryloyl group and a photosensitive cin- oxide, dioxane and tetrahydrofuran. It wasnamoyl phenyl group (chalcone unit) was syn- insoluble in hydroxy-group-containing solventsthesized according to Scheme 1. The structures such as methanol, ethanol, 2-propanol and waterof HPMSK and MPMSK were identified by and in hydrocarbons like benzene, toluene and

1elemental analysis and IR and H-NMR spec- xylenes. The polymer was insoluble when thetroscopy and the results were in good agreement conversion was above 60%. This might havewith the structure of the compounds. The poly- been due to the crosslinking of the olefinicmer, poly(MPMSK) was synthesized by solu- group present in the pendant chalcone moiety oftion free-radical polymerization of MPMSK in the polymer.ethyl methyl ketone using benzoyl peroxide(Scheme 1) at 70618C. The polymerization 3.2.2. UV Spectraconversion has been restricted to 45–50% in The poly(MPMSK) exhibits a UV absorptionorder to avoid any possibility of crosslinking at band at 316 nm due to the p–p* transitions ofhigher conversions. .C5C, of the pendant chalcone moiety

which is flanked by a keto and a phenyl group.3.2. Polymer characterization

3.2.3. Infrared spectra3.2.1. SolubilityThe FT-IR spectrum of poly(MPMSK) (Fig.The solubility of the photosensitive polymer

211) shows an absorption band at 3050 cm dueis one of the important requirements for practi-to the aromatic C–H stretching vibrations. Thecal use of this polymer. The poly(MPMSK) was

21strong absorptions at 1750 cm is characteris-a white solid, easily soluble in chlorinatedtic of esteric carbonyl group stretchings. Thesolvents such as chloroform, dichloromethane,ketonic carbonyl group absorption is observedchlorobenzene and in polar aprotic solvents

21with a strong peak at 1662 cm . A strong band21at 1606 cm may be attributed to the olefinic

double bond in conjugation with keto andphenyl groups. The aromatic .C5C, stretch-

21ing vibrations are observed at 1503 cm . Thearomatic C–H out of plane bending vibrations

21are observed at 781 and 735 cm .

13.2.4. H-NMR spectra1The H-NMR spectrum of poly(MPMSK) is

presented in Fig. 2. The multiplet resonancesignals at 8.09–7.19 ppm are due to the aro-matic protons as well as olefinic protons. Thepeak at 7.25 is due to the residual protons in thesolvent CDCl . The signal at 2.28 ppm corre-3

sponds to the methyl (CH ) group at the meta3

position of the chalcone unit. The backbonemethylene protons signals appear at 1.60 ppm.The resonance signal centered at 1.46 and 1.23ppm are due to the a–CH protons, thus3

Scheme 1. indicating the presence of tacticity.


Fig. 1. FT-IR Spectrum of Poly(MPMSK).

1Fig. 2. H-NMR Spectrum of Poly(MPMSK).

133.2.5. C-NMR spectra 121.46 ppm. The signals at 54.50 and 46.4913The proton decoupled C-NMR spectrum of ppm are due to the backbone methylene and

poly(MPMSK) is presented in Fig. 3. The tertiary carbons, respectively. The signal atchemical shift assignments were made from the 22.06 ppm corresponds to the a-methyl carbonoff-resonance decoupled spectra of the polymer. of the polymer. The methyl carbon at the metaThe resonance signals at 189.11 and 175.29 position of the chalcone unit appears at 20.17ppm are assigned to ketone and ester carbons, ppm.respectively. The aromatic carbon attached tothe ester oxygen atom is observed at 154.19. 3.2.6. Molecular weights

]The resonances of other aromatic and ethylenic The number average (M ) and weight averagen]group carbons are observed between 145.98– (M ) molecular weights of poly(MPMSK) de-w


13Fig. 3. Proton decoupled C-NMR Spectrum of Poly(MPMSK).

termined by gel permeation chromatography4 4 21(GPC) were 2.69310 and 5.04310 g mol ,

] ]respectively. The polydispersity index (M /M )w n] ]value is 1.87. The theoretical values of M /Mw n

for polymers produced via radical recombina-tion and disproportionation are 1.5 and 2.0,respectively [23]. In the free radical homo-polymerization of methacrylate monomers, thepolymeric radicals undergo termination mainlyby disproportionation [24]. Hence, the polydis-persity index value of poly(MPMSK) suggests agreater tendency for chain termination by dis-proportionation than radical recombination,which is the case with many methacrylates.

3.2.7. Thermal propertiesThe thermal stability of the polymer was

studied by thermogravimetric analysis in airatmosphere. The TGA and DTG traces ofpoly(MPMSK) is shown in Fig. 4. Table 1 givesthe differential thermogravimetric analysis dataof the polymer. The polymer undergoes threestage decomposition and the initial decomposi-tion temperature (IDT) is around 2648C. Thefirst stage decomposition temperature of thepolymer ranges between 264 and 3588C and thesecond and third stages occur between 362 and Fig. 4. TGA and DTG traces of poly(MPMSK) in air.


Table 1Thermogravimetric analysis data of poly(MPMSK) in air

Decomposition Temperature (8C) at differenttemperature range (8C) weight loss (%)

Stage 1 Stage 2 Stage 3 10% 25% 50% 75% 90%

264–358 362–490 506–650 300 348 400 542 601

4908C and 506–6508C, respectively. These dataindicate that the poly (MPMSK) possesses avery good thermal stability required for a nega-tive type photoresist.

The glass transition temperature (T 8C) of theg

poly (MPMSK) determined by differential scan-ning calorimetry is 1138C. This high T value ofg

the polymer may be due to the presence of rigidand bulky pendant chalcone units and also dueto the presence of short chain attached to theback bone which facilitate chain entanglement.

3.2.8. Photocrosslinking propertiesThe photocrosslinking property of the poly- Fig. 5. Changes in the UV Spectral pattern of poly(MPMSK) in

CHCl solution upon irradiation. Top to bottom, after irradiation(MPMSK) was studied in chloroform solution 321 time t50,5,10,20,45,75,135,225 and 615 s.with concentration of 44 mg l (path length 1

cm) in the presence and absence of photo-pendant chalcone unit as shown in Scheme 2.sensitizers. Samples were irradiated with a highThe UV absorption intensity decreases withpressure mercury lamp in the presence of air.irradiation time because of the formation ofInitially the poly(MPMSK) shows a UV absorp-cyclobutane ring by the 2p12p cycloadditiontion band at 316 nm due to the p–p* transitionswhich destroys conjugation in the entire p-of .C5C, of the pendant chalcone moiety.

The effect of UV irradiation on the poly- electron system. Thus, poly(MPMSK) reacts(MPMSK) was monitored by measuring the photochemically according to the mechanismchanges in the UV absorption intensity at 316 similar to that found for cinnamic acid and itsnm at the various irradiation time interval. Fig. derivatives in which cyclobutane structure were5 shows the UV spectra of poly(MPMSK) formed [25–27].before and after irradiation at different intervals When a slightly higher concentration (500

21of time, in which the maximum absorption of mg l ) of the polymer in CDCl was irradiated3

the C5C bond (316 nm) decreases drastically for 2 h and the solvent was evaporated, theupon irradiation. An isobestic point is observed residue obtained was found to be insoluble in allat 263 nm due to the cis–trans isomerization of organic solvents. This suggests that the decreasethe double bond in chalcone moiety. The UV in UV absorption is not due to the cleavage ofabsorption at 316 nm is almost completely pendant groups but due to the cyclisation lead-disappeared within 10 min of irradiation. This ing to the cyclobutane ring. The IR spectra ofbehaviour clearly indicates that the crosslinking the irradiated polymer does not show the ab-of the polymer chains occur through 2p12p sorption due to the olefinic bond in the chalconecycloaddition of the .C5C, group of the moiety and also the carbonyl peak is shifted to


Scheme 2.

21higher wave length (1715 cm ) due to the loss 25%, 50% and 75% were reached after 5,20 andof conjugation in the crosslinking reaction. 50 s of irradiation. About 95% of conversion

The rate of disappearance of .C5C, group occurs within 4 min of irradiation. The rate ofof the polymer in chloroform solution is shown photocrosslinking of the poly(MPMSK) appearsin Fig. 6. The photoconversion values of about to be very fast in solution because the free

volume for phenyl rotation is available in dilutesolution [28].

The effect of solvents on the rates of cross-linking were studied on the poly(MPMSK) invarious solvents and the results (Table 2) indi-cate that there is not much difference in the rateof photocrosslinking (Fig. 6) in aprotic solventssuch as dioxane, dimethyl formamide (DMF)and tetrahydro furan (THF) and chlorinatedsolvents such as chloroform (CHCl ) and di-3

chloromethane (CH Cl ).2 2

The photocrosslinking reactions of the poly-(MPMSK) was studied in the presence ofvarious triplet sensitizers like Michler’s ketoneand benzoin but there was no sensitizing effecton the rate of disappearance of .C5C, of thechalcone moiety of the polymer which is similar

Fig. 6. Rate of disappearance of photoactive .C5C, of poly- to that reported for some other photoresists(MPMSK) with irradiation time in different solvents; (d) in

[21,26,29]. This strongly suggests that theCHCl ; (m) in CH Cl ; (j) in dioxane; (.) in THF and (3) in3 2 2

DMF. photocrosslinking of the poly(MPMSK) may


Table 2UV data for poly(MPMSK) at various solvents

Solvent Concentration Maximum wavelength %21(mg l ) Conversion

l Initial Isobestic [(Time) (s)]C5C

absorbance point (l)

CHCl 44.0 316 2.0245 263 94.043

(225)CH Cl 44.4 317 1.9712 263 93.012 2

(225)Dioxane 44.4 313 1.8521 263 91.12

(256)THF 43.6 314 1.9982 263 88.02

(225)DMF 46.0 318 2.0024 263 87.14

(225)

take place not through the triplet state (T) chloroform solution with high pressure mercuryelectrons but through excited singlet state elec- lamp and the changes in the UV spectral patterntrons leading to a one-step concerted 2p12p of poly(MPMSK) for different time intervals ofcycloaddition [30]. Thus the poly(MPMSK) irradiation at room temperature in the presencewith a pendant chalcone moiety has a higher and absence of photosensitizer has been re-rate of photocrosslinking even in the absence of corded. The rate of photocrosslinking of thephotosensitizer. poly(MPMSK) in chloroform solution was very

fast due to free movement of pendant phenylunit. The photocrosslinking reaction of thepoly(MPMSK) performed in the presence of4. Conclusionsphotosensitizers has no accelerating effect on

The methacrylate monomer (MPMSK) hav- the rate of disappearance of .C5C, of theing a pendant chalcone moiety was synthesized pendant chalcone unit. As poly(MPMSK) withand polymerized to obtain poly(MPMSK) by a pendant chalcone moiety has a high rate offree radical solution polymerization. The forma- photocrosslinking even in the absence of sensit-tion of the poly(MPMSK) was confirmed by izer, it might be expected that the poly-

1 13UV, FT-IR, H-NMR and C-NMR spectral (MPMSK) can be used for negative photoresisttechniques. The polymer was soluble in chlori- applications.nated solvents and polar aprotic solvents. It isinsoluble in non-polar solvents, alcohols and Acknowledgementswater. GPC data of poly(MPMSK) clearlyindicates that a strong tendency for chain termi- One of the authors (R.B) acknowledge thenation by disproportionation. TGA results clear- CSIR, Government of India, for offering SRFly indicate that the poly(MPMSK) has very for this research work.good thermal stability as required for negativephotoresists. The high T value of the polymerg Referencesmay be due to the presence of bulky and rigidpendant chalcone units and the short side chains

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synthesis and characterization of photocrosslinkable functional polymer having pendant chalcone...

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