photo cross-linking of some unsaturated poly ether urethane

ELSEVIER Materials Chetnistl~ and Physics 55 ( 1998) 122-130

Photo cross-linking of some unsaturated polyether urethane

S.H. El-Hamouly a,*, A.Z. El-Fayoumy a, E.H. El-Shamy ‘, N.A. Abd-El-Malak b

Received 15 July 1997; received in revised form 3 January 1998; accepted 7 January 1998

Abstract

Different unsarurared polyether urethanes have been prepared either by the reaction of methacrylic epoxide copolymers having different methacrylate moiety, with phenylisocyanate or by the reaction of bisphenol (A) of epichlorohydren (Araladite) with methacrylic acid followed by the addition of toluene diisocyanate. The composition of such unsaturated polyether urethane were determined quantitatively by ‘H-NMR spectroscopy. The ultrasonic pulse echo technique was used in the range of frequencies between 2 and 8 MHz and temperatures between 240 and 360 K to detect the secondary relaxation both in the presence of a photoinitiator before and after cross-linking by using ultraviolet irradiation. The apparent activation energies for such relaxation were calculated and interpreted according to the flexibility ofthese polymers. Differential thermal analysis (DTA) and (TG) thermograms as well as IR spectroscopy were also measured and confirmed the formation of cross-linked polyether urethane. 0 1998 Elsevier Science S.A. All rights reserved.

Kq>vords: Photo cross-linking; Unsaturated polyethcr urethane

1. Introduction

Oxirane groups in the side chains of copolymers provide active sites for chemical modification of these copolymers and find several applications, such as coatings and biomaterial [ 1 ] and as a basis for the production of photo cross-linkable polymers [ 2,3] usedin relief printing plates and printing inks. Polyurethanes have been from a class of industrially useful materials because of their excellent properties [4], and the end products of polyurethanes have a widely diverse char- acter, such as fibers, film forming, thermoplastics, thermo- setting or elastomeric materials.

Many attempts have been made to systematize the approach to the naming of the many observed secondary relaxation processes that occur below the glass transition temperature in polymeric materials [ 5 ] . These processes are designated by letters of the Greek alphabet. cy representing the highest temperature transition. with ,& y, 6, etc., representing other dispersion regions in decreasing order of temperature. Such processes can be studied over a wide frequency range by dynamic mechnical techniques. dielectric methods, nuclear magnetic resonance [ 61 and recently by an ultrasonic technique [ 7,8].

The aim of this work is to use the ultrasonic technique to investigate the secondary relaxations of prepared polyether urethanes having different unsaturated moiety, and to study

* Corresponding author.

the effect of UV irradiation on the secondary relaxation in the presence of a photoinitiator.

2. Experimental

2.1. Materials

Most reagents were purchased from Aldrich, except methyl methacrylate, 2,2’ azobisisobutyronitrile (AIBN) which were obtained from Merck Darmstadt, bisphenol (A) of epichlorohydren from Ciba-Giegy under the name of araladite (G-Y 250). Methyl methacrylate (MMA) was first washed with 10% aqueous sodium hydroxide to remove the inhibitor, then with distilled water to neutral PH, after drying over anhydrous sodium sulphate, the monomer was distilled twice under nitrogen. Glycidyl methacrylate (GMA) and methacrylic acid (MA) were distilled under reduced pres- sure. AIBN was purified by recrystallization from absolute ethanol m.p ( 105°C). Triethylamine (catalyst), hydroquinone (inhibitor), benzoin methylether (photoinitiator), phenylisocyanate, toluone diisocyanate and araladite were used without further purification.

2.2. Methods

2.2.1. Copo~ynzerization Copolymerization of MMA-GMA were prepared by a

published procedure [ 9, lo]. Ampoules of Pyrex glass weTe charged with the monomer mixtures, solvent and initiator.

0254-0584/98/$ - see front matter 0 1998 Eisevier Science S.A. All rights reserved. PZISO254-0584(98)00051-O

S.H. El-Hamouly er nl. /Materials Chrrnisq md Physics 55 (1998) 122-130 123

Copolymerizations were carried out in a thermostat at 65°C for conversions below 10%. The contents of the ampoules were then poured into a large excess of cold methanol. The copolymers obtained were purified by reprecipitation from chloroform by petroleum ether (60-80°C). The copolymers were finally dried to constant weight in a vacuum oven at 40°C.

quinone for 1 h using vigrous stirring. The contents were then poured into a large excess of distilled water as the precipitat- ing agent at room temperature, it should be pointed out that the terminated isocyanate could only react with water under a specific reaction condition (up to 80°C) [ 111. The precip- itated was washed with methyl alcohol then dried in a vacuum oven at room temperature.

2.2.2. Reaction with mtthacqlic acid 2.2.4. DryJilms

Copolymers of MMA-GMA having the molar ratios (70:30,85: 15) were reacted in benzene solution with a three- fold excess of MA, an equivlent amount of triethylamine as catalyst and 1.5% of hydroquinone as the polymerization inhibitor. The mixtures were refluxed for 24 h at 8O”C, then cooled to 0°C and decanted. The viscous precipitate was dissolved in chloroform reprecipitated in n-hexane at room temperature and finally dried in a vacuum oven at room temperature. Similarly, epichlorohydren of bisphenol A was treated with a three-fold excess of MA in toluene solution for 6 h at 80°C. The viscous product was then purified as men- tioned above.

Dry films of mono- and diunsaturated polyether urethane were obtained by casting chloroform and acetone solution containing 3% of benzoin methyl ether (photoinitiator) on a mercury surface in the dark.

2.3. Spectral measurements

IR spectra were measured for KBr discs using a Perkin- Elmer 598 (4000-200 cm-‘) spectrophotometer ‘H-NMR (CDCL, and DMSOd6 and D20) varian Gemini 2000- 200 MHz spectrophotometer.

2.4. Thermal analysis

2.2.3. Preparation qf mono- and diunsaturatedpolyether urethane

Unsaturated polymcthacrylic copolymers having 30% and 15% methacrylate moiety in the side chain were refluxed in dioxane at 65°C with a three-fold excess of phenylisocyanate and 1.5% hydroquinone for 3 h using vigrous stirring. After distillation of excess dioxane, the filtrate was then solidified with diethylether, then dried in a vacuum oven at room temperature. Similarly, diunsaturated polymethacrylate of bisphenol A was refluxed in dimethyl formamide at 80°C with three-fold excess of toluene diisocyanate and 1.5% hydro-

Differential thermal analysis (DTA) was performed at a heat rate of 15°C mir- ’ using a shimadzu XD-30 thermal analysis. TG thermograms were obtained at a heating rate of 10°C min- ’ using a shimadzu DT-30B. Thermal analysis (Shimadzu, Kyoto, Japan).

2.5. Ultraviolet irradiation

Irradiation was carried out using a UV lamp with filter model vL. 3OLc (1 X 15 w 365 nm tube, 1350 p,w cm-‘, long wavelength) from M. viber lourmat (Marine La vallee,

CH I 3 y3 r FH3 -I I-

H2C=k

LO

+ HZC=$ --t

c=o

H2C-f ,CH2-,:H+ +H2C - ?+-+2-fH~

AIBN c=o ;=o y

FH3

:, b 65 ‘c :, b CH2=C - COOS

cc0 x ;=(J y

c d b I I (C2H5 )3 N I

CH3 CH2 CH3 C”2 CH3 AH,

CH\ I

MMA I 0 CH\ CR-OH

CH( 1 Y-0

CH2 CH2-O- :-C’CH2

GMA Co -&MMA- G MA&Po!ymer 0 CH3 Co -+M MA-G MA +- ester

--I- H2C - CH2 -

tH3

CH3 .C

Q-‘i _ C6H5NC0 1

I 65 ‘c 7H2 0 H

i/ I CH-O-C-N - C6H5

CH2-O- ;--F = CH2

b CH3

Polyurethane Copolymer Scheme 1.

124 S.H. El-Hamonly et al. /hMerials Chemisrry and Physics 55 (1998) 122-130

CH?

Eisphenol A of epichorohydrin

NC0 .

NC0

CH3 C”3

PoLyethcr urethane

Scheme 2.

France). The irradiation assembly included lamps, collecting lens and shutter. The sample was set at distance of 20 cm. A dry film of 4 mm thickness was used. The temperature of irradiation was 30°C and the time of irradiation was 30 min.

2.6. Ultrasonic measurements

The pulse echo technique [6] was used in this measure- ment. Only one transducer was applied as a transmitter and receiver at the same time, In our measurements an ultrasonic flow detector (USM3) produced by Krautkramer (Ger- many) was used, which operates in a range extending from room temperature to 40°C. Since the temperature range

Also, epichlorohydren of bisphenol A was treated with methacrylic acid in the presence of triethylamine as acatalyst. The obtained diunsaturated polymethacrylate ester was treated with toluene diisocyanate in dimethyl formamide at 65°C (specimen E). The two syntheses are represented by the reaction shown in Schemes 1 and 2. The composition of

Table 1 Chemical shifts of MMA-GMA copolymers, unsaturated polymethacrylic ester and unsaturated polyether urethane

required for the present investigation is wider than this range, the probe was replaced by ceramic crystals with fundamental frequencies of 2,4, 6 and 8 MHz. The transducer was con- nected to the specimen in the sample holder which was then inserted in an electric furnace or dewar containing liquid air. When coupling the transducer to the solid sample [ 121, the bond must be very thin to eliminate the phase shifts within it. The measurements were conducted in the temperature range extending from 240 to 360 K. When the ultrasonic pulses are applied to the specimen under investigation, a train of echoes result on the face of the cathode ray oscilloscope (CRO). The attenuation coefficient (~2) must be measured as the logarithm of the ratio of the amplitude of two successive echoes (L,, &)

CY= 20 log L,ILz dB cm-l

2d

where d is the thickness of the sample.

3. Results and discussion

Copolymers of MMA-GMA with 15% and 30% oxirane ring in the side chain were prepared in a benzene solution at 65°C in the presence of AIRN as a free radical initiator. Unsaturated polymethacrylate esters were prepared by reaction of the oxirane ring with methacrylic acid in the presence of triethylamine as a catalyst. Unsaturated polyether urethanes were obtained by the reaction of unsaturated polymethacrylate copolymers with phenylisocyanate in dioxane solution at 65°C (specimens A and C) .

MMAGMA copolymers

Resonance Proton signal

(wm)

Assignment

Unsaturated polymethacrylic ester Unsaturated polyether urethane

Resonance Proton Assignment Resonance Proton Assignment signal signal

(wm) iwm)

3.6-3.9 3H

2.4-3.6 3H

0-CH3 (MMA)

C<z~WGW

0

3.5-3.8 3H 0-CH3 3.4-3.8 3H O-C%

5.5-6.4 2H C=CH? 7.2-7.6 5H -Ph

Peak area integration Molar composition (mol%)



3H 3H 3H 2H 3H 5H 36 16 69.25:30.75 69 20 69.7:30.3 60 45 69:3 1 30 5.5 84.50:15.49 34 4 85:15 30 9 85:15

S.H. El-Hamouly et al. / Marerials Chemisiv and PhjXCs ST (1998) 122-130 125

Table 2 Chemical shifts of epichlorohydren, diunsaturated polymethacrylate and diunsaturated polyether urethane of epichlorohydren

Bisphenol A Diunsaturated polymethacrylic ester Polyether urethane

Resonance Proton Assignment Resonance Proton Assignment Resonance Proton Assignment signai signal signal

(wm) (mm) IwIn)

2.6-3.5 6H

6.7-7.4 8H

2c\H273H(Gm) 5.4-6.3 4H 2C=CH, 5.5-6.2 4H 2C=CHZ

0 Ph-Ph 6.7-7.4 8H Ph-Ph 7.8-8.2 6H 2Ph-NH-CH,-NC0 P-disubstituted P-disubstituted

4.6-5.1 2H 2NH a

*The NH band was confirmed by shaking with a few drops of deuterium oxide ( DZO). The active hydrogen of the NH group is exchanged with deuterium and consequently the resonance of the NH signal disappeared completely from the spectrum (Figs. 1 and 2).

these copolymers, unsaturated polymethacrylate esters and unsaturated polyether urethanes, diunsaturated polymethacrylate ester and diunsaturated polyether urethane were determined quantitatively by ‘H-NMR spectroscopy on the basis of the characteristic bands represented in Tables 1 and 2. Figs. 1 and 2 show the ‘H-NMR spectra of the copolymers (70:30), unsaturated polymethacrylate ester, polyether urethane and bisphenol A of epichlorohydrin, unsaturated polymethacrylate ester and diunsaturated polyether urethane respectively.

The photoinitiated polymerization was studied in a solid state matrix in the presence of benzoin methyl ether (3 wt.%) as a photo labile initiator.

C,H,-C-CH-C,H, hv 340 nm ) W-F-‘+ C6Hq-C’y-OCH3

+ + chain propagation and

cross-linking

The kinetics of polymerization was followed by an ultrasonic technique. The measurements were carried out on a film of 4 mm thickness at frequencies of 2,4, 6 and 8 MHz, and at temperatures between 240 and 360 K. The changes in attenuation of ultrasonic waves with temperature was studied for the unsaturated polyether urethane both in the absence (specimens A, C and E) and in the presence of 3 wt.% benzoin

Table 3 The maximumabsolute temperature r,,, at which the peaks occur in relation to the operating frequencies for matrices before and after UV irradiation

Lx (K) Before irradiation After irradiation

f A C E B D F (MHz) 70:30 85:15

2 250 268 253 268 283 258 4 271 293 278 288 303 288 6 302 313 298 313 318 308 8 318 323 318 323 328 323

CHz -Cl

0-CH3 \f-

CH2 -C

12)

CH2-Ct

CH3-0 f

(1)

10 a Fig. 1, ‘H-NMR spectra of ( 1) mated poly methacrylic ester; D,O.

6 4 L v

copolymer (MMA-GMA) 70:30; (2) unsat- (3) unsaturated polyether urethane (4) with

126 S.H. El-Hmmrl~ ei al. /Materials Chemist??: and Physics 55 (1998) 122-130

I ph-C-ph

I

C”2

CH.

I

(I b 4 2

wm

Fig. 2. ‘H-NMR spectra of ( 1) bisphenol A of epichlorohydrin; (2) unsaturated poly methacrylic ester; (3) diunsaturated polyether urethane; (4) with DZO.

methyl ether as the photoinitiator (specimens B, D and F) in solid state matrix, where E and F are specimens of diunsa- tutrated polyether urethane of araladite before and after cross- linking respectively. From Figs. 3-5, it is clear that the absorption of the ultrasonic waves increases with increasing temperature to reach a maxmium value and then decreases giving rise to a series of peaks which indicates some sort of relaxational processes. These peaks have been attributed to loss mechanism of the standard linear solid type, with low dispersion and Arrhenius-type relaxation times. Formally the loss has been ascribed to the presence of particles or groups of particles moving in double well potentials [ 131. This pre- sented a central force model of the magnitude of the two-well barrier heights and deformation potential occuring in the phenomenological theory. Also, these peaks are shifted to higher temperature with increasing frequency. This phenom- enon is essential in the interpretation of activation energy

xfore cross - linking ‘0

I

(B) .

after cross - linking

220

I I , ec 260 300 340

Temperature ( ‘K 1

ad0

Fig. 3. Ultrasonic attenuation coefficient dB cm- ’ vs. T,,, (k) at various frequencies for the unsaturated polyether urethane (70:30), benzoin methylether 3 wt.% (A) Before UV irradiation. (B) After UV irradiation.

which rule out in the transitional motion of atoms or groups of atoms arising from rupture of atomic bonds. This trend is similar to that found previously in the case of nylon 6, nylon 66 [ 141 and acrylate copolymers [ 71.

By exposing the B, D and F matrices to the UV irradiation, the peaks are found to shift to a higher temperature and also became higher. The maximum absolute temperature (T,,,) at which these peaks are observed in the temperature regions are given in Table 3.

The apparent activiation energies (w) of the relaxational processes of the unsaturated polyether urethane were calculated using the Arrhenius Eq. (8).

S.H. EL-Hamody et al. / Mnrcrials Chemistry and Physics 55 (1998) 122-130 I27

(0 -..o 2 MHz -K- 4 MHz - 6 MHz -+- 8 MHz

*o.. “0. * ‘.

CI *O...

2 .- before cross - linking .u z 0. I I I

after cross - linking

I I ,

1 260 300 340 :

Temperoture Ci< I

Fig. 4. Ultrasonic attenuation coefficient dB cm- ’ vs. r,,, (k) at various frequencies for the unsaturated polyether urethane (85:15), benzoin methyl ether 3 wt.%. (C) Before UV irradiation. (D) After UV irradiation.

wherefis the operating frequency,f, is the natural frequency of the sample, r,,, is the maximum absolute temperature at which the relaxational processes occur and k is Boltzmann constant. The relation between lnfand 1 /T,,, is represented by a straight line in the form

The slopes of these lines gives the values of w/k from which the apparent activation energies of the relaxational processes of unsaturated polyether urethane are calculated. Plots are shown in Fig. 6. The correlation factors of these plots are found to be better than 0.99. The apparent activation

0

6-

.-o-- 7 MHz

Before cross -1inkinq

11 After :,ss- Linyng ,

220 260 300 340 380

Temperature (‘K )

Fig. 5. Ultrasonic attenuation coefficient dB cm- ’ vs. r,,,,, (k) at various frequencies for diunsaturated polyether urethane benzoin methyl ether 3 wt.%. (E) Before W irradiation. (F) After W irradiation,

energies are represented in Table 4; these values are expected to be for P-relaxation, and are comparable with those found in the literature [ S-17].

Table 4 The apparent activation energy W in Kcal/mole for matrices A, C, E before UV irradiation and matrices B, D, F after UV irradiation

Before irradiation After irradiation

A C E B D F

w 3.09 4.28 3.31 4.18 5.66 3.52

S.H. El-Hnnmul~ et al. /Materials Chemists and Physics 5.5 (1998) 122-130

--o-- before XL

(D) \

2.8 3.3 3.8 2.8 3.3 3.8

l/Tm x lG3

2.8 3.3 3.8

Fig. 6. Relationship between logyand lOOO/(T,, (k)) for (A), (C) and (E), before UV irradiation and (B), (D) and (F) after UV irradiation in presence of 3 wt.% benzoin methylether in a solid state matrix.

4000 2000 1500 1000 MO

Wavenumber (cm’ )

Fig. 7. JR spectra of unsaturated polyetber urethane (70:30) before and after UV irradiation.

For the ,f3 relaxation processes whether in crystalline or amorphous polymer ( l-1 0 kcal) it can be concluded that the relaxation of the different unsaturated poiyether urethane where the activation energy in the given range of temperature is of secondary or P-type which could be attributed to side chain rotation. It is also clear that w increases after exposure to UV irradiation. The increase can be attributed to the increase in the rate of photo cross-linking which results in an increase in the rigidity of the matrix. The increase in w was found to be 45%,43% and 37%.

10( 100 200 300 400

Temperature (‘cl Fig. 8. (1) TG thermograms for unsaturated polyether urethane (70:30), (A) Before UV irradiation; (B) after UV irradiation. (2) Unsaturated polyether urethane (85:15). (C) Before UV irradiation: (D) after UV irradiation. (3) Diunsaturated polyether urethane of bisphenol A. (E) Before W irradiation: (F) after UV irradiation.

The relaxation process can be ascribed to molecules moving in a double well potential corresponding to a two equilibrium configuration arising out from a defect structure in the chain network. The ultrasonic waves disturb the equilbrium of this molecule and produce a relative energy shift between

S.H. El-Hnmortly et al. / Materials Chrmistq and Physics 55 (1998) 122-130 129

(A)

(E) --k

(F)

100 200 300 100

Temperature ( ‘c)

bb0 300

Fig. 9. Glass transition temperatures of (A) unsaturated polyether urethane (70:30) before UV irradiation; (B) unsaturated polyether urethane (70:30) after UV irradiation; (C) unsaturated polyether urethane (85:15) before UV irradiation; (D) unsaturated polyether urethane (85:15) after UV irradiation; (E) diunsaturated polyether urethane of bisphenol A before UV irradiation: (F) diunsaturated polyether urethane of bisphenol A after UV irradiation.

the minima of the two wells by an amount (AE) . Thus the ultrasonic waves are thermal in equilibrium and the relaxation process sets up to restore the equilibrium again [ 181. This explains the increase in the activation energy of the relaxation process in the cross-linked sample.

The structure of the unsaturated polyether urethane before and after the formation of cross-linking was investigated by IR spectroscopy. As an example, the IR spectra of 70:30 unsaturated polyether urethane both before and after the formation of cross-linking are shown in Fig. 7. It shows bands at 3250, 3200, 3050, 2950, 1735, 1680, 1600, 1580, 1550, 1440, 750 and 690 cm-’ which correspond to YNH, zCH aromatic, wCH vinyl, YCH aliphatic, zC=O ester carbonyl, vC=O of the vNH-CO, 6NH bending vibration, LC=C vinyl and aromatic, and out of plane bending vibration of aromatic monosubstituted. In B the bands at 1600 cm-‘, which correspond to the C = C of vinyl, disappear completely after UV irradiation.

Finally, the TG thermograms (Fig. 8) for unsaturated polyether urethane both before and after cross-linking were measured under nitrogen. It has been found that the weight remaining was increased after UV irradiation, confirmed by the formation of cross-linking. On the contrary, it should be noted that the T,,, of polyether urethane after UV irradiation was found to be higher than that before irradiation, which was also confirmed by the formation of cross-linking. Fig. 9 shows the variation in T,,,,, before and after UV irradiation.

Acknowledgements

The authors acknowledge Professor Dr K.N. Abd El-Nour, Head of Microwave Physics Department, National Research Center, for his valuable discussion.

130 S.H. El-Hamouly et al. /Materials Chemists and Physics 55 (1998) 122-130

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photo cross-linking of some unsaturated poly ether urethane

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