Syntheses of allyl phenyl acrylates and their evaluation as reactive diluents in UV-curable coating compositions

Pro~ss

in 0rganic Coatiws, 21 (1993) 339-352

339

Syntheses of ally1 phenyl acrylates and their evaluation as reactive diluents in UV-curable coating compositions J. N. Rupa Vani, V. Viaya Lakshmi, B. S. Sitaramam and N. Krishnamurti* Indian Institute of Chemical

Technology,

Hgderabad

500007

(India)

(Received April 15, 1992; accepted July 30, 1992)

Abstract para-Substituted 2-ally1 phenyl acrylates, and diallyl, dipropenyl and dipropyl bisphenolA cliacrylates have been synthesised in high yield and purity and characterised by spectroscopic methods. UV-curable coating compositions have been formulated using these monomers as reactive dihrents. Their film propertieswere studied.

Introduction

A number of review articles [l-7] are available on the chemistry and technology of radiation-curable coatings. Much of the information regarding the formulations of W-curable coatings remains proprietary and is shielded by patents. Generally, they are known to consist of reactive polymerisable oligomers, reactive d&rents, photoinitiators, pigments and additives. Reactive polymerisable diluents are used to reduce the viscosity of the compositions to a workable consistency and also participate in the f?lm formation by copolymerising with the oligomers, when suitably initiated. Both mono- and multi-functional acrylates are used most commonly as reactive diluents. Typical multi-functional acrylates such as pentaerythritol triacrylate, hexanediol diacrylate, ethylene glycol diacrylate, etc. have been used as reactive dihrents. However, the mono- and di-acrylates based on 2-ally1 phenols and diallyl bisphenols which comprise aromatic structures have so far not been utilised as reactive diluents in UV-curable coating compositions. These monomers are expected to perform better (low odour, less toxic) than conventional diluents and give superior him properties and drying characteristics due to the presence of the phenyl moiety and allylic unsaturation. Hence in this communication we report the synthesis of acryiic esters of ally1 phenols and diallyl bisphenol-A and their evaluation as reactive diluents. Experimental

ally1 phen& ethers 2 (Scheme 1) These were synthesised by modification of a procedure described by Vogel [8] as shown in Scheme 1. The p-substituted phenol 1 (0.45 mol),

Syntheses of p-substituted

*To whom ah correspondence should be addressed.

0033-0655/93/$6.00

0 1993 - Elsevier Sequoia. All rights reserved

R z H -

(a)

CH3 (b)

= C(CH3)3 (cl = @

R

(d) 4

i) cH2=~~-c~2-~~,~2~0~,~e2co,10h ii) iii)

-

A.2OO'C , 3h 50%

Methanolic

KOH

Scheme 1.

TABLE 1 Physical properties of ally1 phenyl ethers Allylkliallyl ethers

Compound No. (Scheme 1)

Yield (961

Boiling point (“C/mmHg)

Refractive index, nP

phenyl 4-methyl phenyl 4-t-butyl phenyl 4-phqyl phenyl

2a

89 91 85 86

85/20 86/4.0 9614.0 71”

1.6200 1.5140 1.6125

2b

2c 2d

*Melting point.

anhydrous K&O3 (0.5 mol) and dry acetone (300 ml) were placed in a 500 ml two-necked round-bottom flask, equipped with a magnetic stirrer and a spiral reflex condenser. Ally1 bromide (0.54 mol) was added dropwise to ‘thisover a period of 1 h. The reaction mixture was stirred at reflex temperature for 10 h. After completion of the reaction, as observed by TLC methods, the contents were poured into distilled water and the organic layer separated. The aqueous layer was extracted with ether (4 X 30 ml portions). The ether extracts were combined and washed with 5% sodium hydroxide solution to free them from unreacted starting material. The organic layer was then washed with water and brine. The solvent was removed to obtain the crude ally1 ether which was purified in good yield by distillation under vacuum. The yields and physical properties are listed in Table 1. The compounds were characterised by IR, ‘H NMR and mass spectroscopic methods and the corresponding data are presented in Table 2.

341 TABLE Spectral

2 data of 2-ally1 pheuyl ethers

2-Ally1 ethers

phenyl

‘HNME6

Compound No. (Scheme 1)

IR (cm-‘)

2a

3080-2860; 1600; 1500; 1290; 740

1640; 1450;

4.5 (2, m); 5.0-5.5 (2, m); 5.5-6.5 (1, m); 6.7-7.4 (5, m)

@pm>”

4-methyl

phenyl

2b

3020-2860; 1600; 1490; 1290

1640; 1450;

2.31 (3, s); 4.50 (2, d); 5.12-5.5 (2, m); 6.0 (I, m); 6.93 (4, dd)

148 (M+); 131; 94; 55 (100%); 39; 29

4-t-butyl

phenyl

2c

3040-2860; 1510; 1210; 1020

1640; 1170;

1.31 4.43 5.43 6.00 7.02

190 @If); 175 (100%); 135

4-phenyl

phenyl

2d

3060-2840; 1600-l 500; 1290; 1130; 1010-970

1640; 1380;

4.62 (2, d); 5.31-5.50

(9, (2, (2, (1, (4,

s); d); m); m); dd)

(2, m>; 6.0 (1, m); 6.93-7.62

210 (M+); 169 (100%); 141; 41

(9, m) *For ‘H NMR data, figures in parentheses

are the number of protons

and the type of signal.

Thermal rearrangement of the ethers prepared as above was performed in a sealed tube in order to reduce the length of the reaction and the formation of polymers at high temperature. The compound was placed in a Pyrex glass tube and sealed; this was then immersed in a silicone oil bath preheated to 190 “C and maintained at this temperature for 3 h to effect the rearrangement. The reaction was monitored by the visual changes in eolour and increase in viscosity. Subsequently, the tube was opened and the contents dissolved in 10% sodium hydroxide to eliminate unwanted byproducts. After aci~~~a~on, the material was extracted with petroleum ether and worked-up by washing and evaporation. The phenolic compounds thus obtained were purified by crystallisation in the case of R= C,H, and by vacuum distillation for the remaining cases. The yields and physical properties are listed in Table 3. These compounds were then characterised by IR, ‘II NMR and mass spectroscopic methods. The spectral data are presented in Table 4. 2-Ally1 phenol 3a (25 g, 10.19 mol) was placed in a 500 ml single necked rood-bottom flask and 50% meth~olic KOH (75.0 ml) was added.

342 TABLE

3

Physical properties

of 2-shyI phenols and 2,2’-diahyl

bisphenol-A compounds

2-AIIyl phenoIs/diaIIyl bisphenol-A compounds (Schemes 1 and 2)

Compound No.

Yield

BoiIing point $C/mmHg)

Refractive index, ni”

viscosity

(%)

2aIIyl phenol 2-aIIyl-4-methyl phenol 2-aIIyl-4-t-butyl phenol 2-aI.Iyl-4-phenyl phenol 2,2’-diaIIy1 biiphenol-A 2,2’-dipropenyl bisphenol-A 2,2’-dipropyl biiphenol-A

3a

76 78 82 86 96 92 94

112115 7010.2 102/0.8 78= -

1.5455 1.5368 1.5218

-

1.5548

17.6 10.Sb 148.0

3b 3c 3d 7 8 9

1.5545

(P)

eMelting point. bin 60% ethanol solution.

TABLE

4

SpectraI data of 2-aIIy1 phenols Ally1 phenols

Compound (Scheme 1)

IR (cm-‘)

‘H NMR S

MS

(ppm)

(mlz)

2-ally1 phenol

3a

3400 (OH); 3080-2840; 1640; 1590; 1490; 1450; 760

3.43 5.00 5.25 6.00 7.00

2-aIIyl-4-methyl phenyl

3b

3460 (OH); 3040-2840; 1640; 1610; 1510; 760

2.37 (3, s); 3.43 (2, d); 5.18 (2, m); 6.06 (1, m); 6.68-7.06

2-AIIyl-4tbutyl

3c

3450 (OH); 3080-2880; 1640; 1610; 1500; 910; 810

(2, (1, (1, (1, (5,

d); m); m); m); m)

134 (M+); 83 (100%); 91; 77

148 @I+, 100%); 133 (M-15); 105; 91; 77

(3, m) phenyl

1.25 (9, s); 3.31 (2, d); 6.00 (1, m); 5.18 (1, m); 5.93 (1, m); 6.68-7.06

190 (M+); 175 (M-15, 147; 133; 107; 105

100%);

(3, m) 2-a&d-4-phenyl

phenol

3d

3500 (OH); 3020-2860; 1640; 1610; 1600-1500; 1020-760

3.50 (2, d); 5.12-5.31

210 @I+, 100%); 167; 165

(2, m); 6.0 (1, m); 6.81-7.31 (8, m)

‘For Signal.

‘H NMR data, the figures in parentheses

are the number of protons and the type of

343

After shaking the contents of the flask for 2-3 min, excess methanol was removed on a rotavapor at low pressure. The contents were heated to 120 “C on an oil bath for 4 h using an air condenser. The product thus obtained was neutrahsed carefully by adding cont. HCl dropwise at 5 “C. The neutrahsed product, on extraction with ether followed by washing with distihed water, brine and subsequent removitl of the solvent, yielded the crude compound which on distillation at low pressure gave a colourless low-melting solid. The compound was characterised spectroscopically when the following data was obtained. Boiling point: ‘H NMR 6 (ppm): IR (cm-‘): MS (m/z):

230 “C/760 mmHg; ds = 1.5795 1.5-2.0 (3H, dd); 5.5 (lH, br, s); 5.6-6.5 (2H, m); 6.5-7.3 (4H, m) 3360 (OH); 3040-2760; 1660; 1620; 1590; 1490; 1460; 1350; 1290; 980; 760 105; 91 134 @I+, 100%); 133; 119 (M-15);

Synthesis of diallgl ether of bisphmtol-A 6 (Scheme 2) 4,4’-Isopropylidene diphenol (bisphenol-A) (6) (114 g, 0.5 mol), anhydrous potassium carbonate (14.0 g, 1.0 mol) and 500 mi dry acetone were placed in a 2 1 three-necked flask equipped with a reflux condenser, a pressure equahsing dropping funnel and a sealed stirrer unit. Ally1 bromide (120 g, 1.O mol) was added dropwise into the flask while its contents were vigorously stirred. Subsequently the reaction mixture was refluxed with stirring for ca. 16 h. It was then poured into 1 1 water. The organic layer was separated and the aqueous layer extracted with ether (6 X 40 ml portions). The combined ethereal extracts were washed free of unreacted starting material and alIy1 bromide with 5% sodium hydroxide solution. The organic layer was washed with distilled water until neutral and then dried over anhydrous sodium sulphate. Removal of the solvent followed by column chromatography (silica gel 50 g) using petroleum ether (40-60 “C) as eluent, afforded 137 g of a pure colourless oily compound (yield, 81%; viscosity, 0.5 P; ng”= 1.5623). The following spectrai data was obtained: IR (cm-‘): ‘H NMR 6 (ppm): MS (m/z):

3040-2860; 1650; 1610; 1580; 1510; 1290; 1240; 1100; 780 1.63 (6H, s); 4.43 (4H, d); 5.12-5.37 (4H, m); 5.93 (2H, m); 6.93 (8H, dd) 308 (M+); 293 (M+ -15); 252; 211; 41 (100%)

Sgr&.&.s of 2,2’-diallyl bi.sphenoGA 7 (Scheme 2) Approximately 25-30 g of dialIy1 ether 6 was placed in a Pyrex gIass tube (75% of its volume), which was then sealed and kept immersed in a silicone oil bath, preheated to 200 “C and maintained at 2 10 “C. Rearrangement was complete in 50-60 min, with no side-product formation. The product had a high viscosity and was used as such without further purification. GC

0

OH

-df---

HO

;

0

Q-

OH

4

J iv

i) CH~:CH-CH~-&,

K2C03.Me2C0, 16h

ti) A .ZOo'C,lh iii)

50%

iv) H2 Scheme

Mcthanolrc KOH

, Pd I C , EtOH . 40 psig

2.

analysis of its dimethyl ether (b-p., 194-196 ‘C/1-2 mmHg) showed a purity greater than 99%; relevant spectroscopic data are listed in Table 5.

The transfer of the ally& double bond into a vinylic double bond was achieved using 50% methanolic KOH. The hydroxy compound (20.0 g, 0.06 mol) was placed in a 600 ml round-bottom flask and 50% methanolic KOH (120.0 ml) was added to it with thorough stirring. Excess methanol was removed under vacuum until the temperature reached 120 “CLTbe flask was then fitted with an air condenser and placed in a silicone oil bath at a temperature of 180-200 “C. The contents were refluxed for 3 h and then neutralised carefully in an ice bath with dropwise ad~tion of cont. HCl. Extraction with ether followed by concentration yielded the crude compound in the form of a semi-solid. This was passed through a small column of silica gel (SO-120 mesh, 20 g) using a 20% ethyl acetate/hexane mixture as eluent to obtain the eolourless compound. ha viscosity and refractive index are reported in Table 3.

345 TABLE 5 Spectral data of 2,2’-diallyl, 2,2’-dipropenyl Spectra

and 2,2’-dipropyl

bisphenold

compounds

Substituted bisphenol-A compounds (Scheme 2) 2,2’-Diallyl (7)

2,2’-Dipropenyl

IR (cm-‘)

3400 (OH); 3060-2400; 1630; 1600; 1450

3350 (OH); 3000-2840; 1640; 1600-1500

3360 (OH); 3000-2840; 1600-1500; 1445

‘H NMR 6 @pm)

1.62 (6, 3.32 (4, 4.93-5.19 6.01 (2, 6.65 (2, 7.03 (4,

1.68 (6, s); 1.87 (6, d); 5.93-6.3 (4, m); 6.8-7.0 (6, m)

0.93 (6, 1.62 (6, 2.54 (4, 3.64 (4, 6.62-6.93

13C NMR 6 @pm)

30.95; 35.17; 41.53; 115.27; 116.26; 124.61; 126.3; 128.87; 136.82; 143.56; 151.96

MS (m/z)

308 (M+); 293 (M- 15,100%); 159

308 @I+); 293 (M- 15,100%); 175; 159

312 @I+); 297 (100%); 161; 107; 91

s); d); (4, m); m); d); m);

(8)

2,2’-Dipropyl

(9)

t); s); t); m); (6, m)

For ‘H NMR data, the figures in parentheses are the number of protons and the type of signal.

Synthesis of 2,2’-dipropyl bisphenol-A 9 (Scheme 2) The Claisen product 7 was hydrogenated in dry ethanol in a Parr mediumpressure hydrogenator at 30 “C and 40 psig pressure, using 1% w/w of 10% palladium on charcoal as a catalyst. Hydrogenation was complete in ca. 4 h. Filtration of the compound through a Whatman filter paper (No. 41), followed by passage through a column of silica gel (60-120 mesh, 15 g) using 5% ethyl acetate/hexane as eluent and subsequent removal of solvent yielded a highly viscous compound of a sticky nature in high yield (> 90%). The physical properties of these compounds 7, 8 and 9 are listed in Table 3. All these compounds were characterised by IR, ‘H NMR, 13C NMR and mass spectral methods and their spectral data are presented in Table 5. Syntheses of acrylic esters of 2-ally1 phenols @%enw 3) These acrylic esters were prepared by reacting the a.llyl phenols with acryloyl chloride in the presence of a base as shown in Scheme 3. Into a 250 ml, two-necked flask equipped with a calcium chloride guard tube, magnetic stirring bead and a dropping funnel was placed the substituted phenol (0.5 mol) dissolved in an excess of 5% aqueous sodium hydroxide (0.5 mol). The mixture was stirred continuously at O-5 “C for 10 min. At

346

OH

P 0

i /ii

I

R

i) it)

CH2=CH-0X3.

SO%Aq

NoOH.

Tolwene

.

0-25-C

R z CdHg , 50% Aq NoOti . Toluene , retiux R’

:

CH2-CH = ctl2 CH =CH-CH3 CH2 -CH2

- CH3

Scheme 3.

this stage freshly prepared acryloyl chloride (0.55 mol) was added dropwise to the reaction mixture over a period of 15 min. After stirring for 20 min, the temperature was raised to 25 “C and kept at this value for 1.5-2.0 h. The reaction process was followed by TLC observations. On completion of esterification, the contents were diluted with water and the organic layer separated. The aqueous layer was then extracted with ether (3 x60 ml portions). All the extracts were combined and washed free of alkali and dried over anhydrous sodium sulphate. The solvent was removed using a rotavapor and the crude ester was purified by column chromatography using 5-10% ethyl acetatefhexane as eluent in order to eliminate the unreacted startSng compound and other coloured impurities. The compounds were further purihed by low-pressure distillation. The yields of the esters along with their physical properties are given in Table 6. Their spectral data are listed in Table 7.

Syntheses of diamylic

esters of substituted

bisphen.oGA conapounds

Diacrylates of substituted bisphenol-A compounds were synthesised by a much simpler method (Scheme 3) than the conventional Najxylene process [9 J. Typically, 7, 8 or 9 (0.1 mol) in 250 ml dry toluene was placed in a 1 1 three-necked flask equipped with an efficient stirrer, a dropping funnel

347 TABLE 6 Physical properties of acrylic esters of ally1 phenols and substituted bisphenol-A compounds Acrylic esters of

Compound No.

Yield @)

Boiling point (“C/mmHg)

Refractive index, ng*

2-allyi phenol (3a) 2-propenyl phenol (4) 2-ally&4-methyl phenol (3b) 2-allyi-4-t-butyl phenol (3~) 2-allyI-phenyl phenol (3d) 2,2’-diallyl b&phenol-A (7) 2,2’-dipropenyl bisphenol-A (8) 2,2’-dipropyl bisphenol-A (9)

10 11 12 13 14 15 16 17

75 74 73 71 73 72 71 69

10010.6 8210.5 1001B.8 168/l .o 140/O-7 -

1.5310 1.5459 1.5200 1.5155 1.5850 B = P

“Refractive index could not be determined since compound was coloured and viscous.

and a Dean and Stark trap. A con~en~ted aqueous solution of sodium hydroxide (8.8 g in 10 ml HaO) was added slowly to it, while the solution was vigorously stirred and heated to reflux. Refluxing was continued until azeotropic removal of water was complete. The contents of the flask were cooled to 40 “C and hydroquinone (1% relative to weight of bisphenol-A) added. Subsequently, 0.22 mol of freshly distilled acryloyl chloride was added dropwise into the stirred solution with the exclusion of moisture. Stirring was continued until TLC analysis indicated the attainment of maximum conversion. The contents of the flask were filtered through a small column of commercial silica gel (SO-120 mesh) to remove the sodium chloride formed and other coloured apples. F’inaJly,the compo~d was purified on a column of silica gel (finer than 200 mesh, 30 g), using 8% ethyl acetate/ hexane as eluent to eliminate the starting compound. The acrylates were used as such in UV-curable coatings and their spectral data are listed in Table 8. Evaluation of ally1 phenyl acrylates in W-curable coating compositiuns A set of W-curable coating compositions were prepared, keeping the reactive oligome=, i.e. 2,2’-diallyl b~phenol-A epoxy diacrylates, constant and varying the reactive diluents, e.g. 2-ally1 phenyl acrylate, 2-propenyl phenyl acrylate, 2-allyl-4-methyl phenyl acrylate, 2-allyl-4-t-butyl phenyl aerylate, 2-allyld-phenyl phenyl acrylate, 2,2’-dially1 bisphenol-A diacrylate, 2,2’-dipropenyl bisphenol-A diacrylate and 2,2’-dipropyl bisphenol-A diacrylate. The general recipe is presented in Table 9. The film properties of the coatings were evaluated and compared and the data are listed in Table 9. Other conventionally available reactive dihrents, which comprise aliphatic skeleton such as butyl aerylate, glycidyl acrylate, neopenQ1 glycol diacrylate and 1,4-butylene diaerylates were also used in the UV-curable coating cornpositions and their 6lm properties dete~ned (Table 10). The pe~o~~~e

348 ‘I’ARLE 7 Spectroscopic Acryhc of

esters

data of acrylic

esters of 2-aUy1 phenols

Compound gble

IR

‘H NMR

13C NMR

MS

(cm--‘)

6 @pm)”

6 Cppm)

(mk)

6)

2-ally1 phenol

10

3050-289~ 1750; 1640; 1410; 1160; 980

3.40 5.21 6.42 6.61 7.30

(2, (2, (2, (2, (4,

d); m); m); m); m)

2-propenyl phenol

11

3020-2900; 1740; 1620; 1400; 1240; 1150

1.80 5.80 6.10 6.42 7.21

(3, (2, (1, (2, (4,

d); m); m); m); m)

31.24; 34.31; 116.07; 124.45; 127.41; 131.10; 136.21; 149.12;

31.56; 34.80; 121.67; 127.23; 128.10; 132.29; 146.67; 164.71

188 @I+); 134 (M-55); 55 (100%)

2-allyl-4-methyl phenol

12

3100-2900; 1740; 1640; 1480; 1400; 1150; 980; 900; 790

2.39 3.26 5.10 6.01 6.56 7.12

(3, s); (2, d); (1,m); (2, m); (2, m); (3, m)

20.60; 116.27; 128.02; 131.67; 135.92; 146.79;

34.51; 122.13; 128.13; 132.5; 136.1; 164.76

202 @I+); 147; 55 (100%)

2-aIIyl-4-t-butyl phenol

13

3080-2840; 1740; 1640; 1460; 1430; 1400; 1240; 1150; 980; 910

1.29 (9, 3.32 (2, 4.94-5.08 (2, m); 5.96 (1, 6.48 (2, 6.73-7.26

31.06; 34.66; 121.49; 127.30; 132.28; 130.89; 164.60

34.13; 115.94; 124.31; 127.85; 136.01; 148.93;

244 (MC); 229 (M- 15); 137; 55 (100%); 41

s) d);

m); m};

188 (M’); 133; 55 (100%)

(3, m) 2-ahyl-4-phenyl phenol

‘For

14

‘H NMR data, the figures

3060-2900; 1740; 1640; 1480; 1390; 1150

in parentheses

3.33 5.13 6.01 6.87 7.51

(2, d); (2, m); (2,m); (2, m); (8, m)

34.6; 122.6; 127.2; 128.8; 132.3; 135.7; 140.6; 164.6

are the number

116.5; 126.2; 127.8; 129.2; 132.7; 139.4; 148.3;

of protons

264 (M+); 223 (M-41); 209 (M-55); 71; 55 (100%); 41

and the type of

SigSld.

of these reactive diluents vti-ci-uti ally1phenyl acrylates in UV-curable coating compositions on the Gh-nproperties of the latter was compared. The UV-curable coating compositions were formulated to a workable consistency (viscosity, 50-85 cP) by the addition of reactive diluents. Films of the clear laquers were cast on to mild steel panels (15.0~ 100X0.9 mm)

349 TABLE 8 Spectroscopic data of diacrylic esters of substituted bisphenol-A compounds Substituted bisphenol-A compounds (Scheme 3)

spectra

2,2’-Diallyl (16)

2,2’-Dipropenyl

IR (cm-‘)

2960-2900; 1740; 1640; 1400; 1150; 900; 790

3000-2850; 1740; 1640; 1400; 1150; 860; 760

3010-2800; 1730; 1630; 1500; 1290; 840; 760

‘H NMR 6 (ppm)

1.55 (6, s); 3.21 (4, d); 4.84-5.0 (4, m); 5.9 (2, m); 6.42 (4, m) 6.50 (2, m) 7.12 (6, m)

0.95 1.60 2.53 3.02 6.01 6.87 7.00

1.70 (6, 1.88 (6, 5.72 (4, 6.00-6.30 6.87 (2, 7.00 (7,

MS (m/z)

416 401 347; 138; 105;

416 (M+); 401 (M- 15); 375 (M-41); 361 (M-55); 91 (100%); 55; 41

(M+); (M - 15); 293; 123; 55 (100%)

(6, (6, (4, (4, (4, (2, (6,

t); s); t); m); m); m); m)

(16)

2,2’-Dipropyl

420 405 379 365 91; 41

(17)

s); d); m); (4, m); m); m)

(M+) (M - 15); (M-41); (M - 55); 55 (100%);

Bathefigures in parentheses are the number of protons and the type of signal.

and onto tin-coated mild steel panels (150X 50X 0.315 mm). In each case, the panels were abraded with emery paper and swabbed with xylene before application. Fihns were cured using a ‘Lab-Cure’ unit (Wallace Knight Ltd., UK) fitted with an air-cooled, 9 in. medium-pressure mercury vapour lamp rated at 200 W per linear in. (80 W per linear cm). The panels were exposed to the lamp by means of variable speed conveyor belt attached to the unit, which was operated at a speed of 0.5 m s-l; the films were evaluated 48 h after cure time. The coated panels were then subjected to (i) a conical mandrel bend test using l/16 in. mandrel, (ii) a mild impact resistance test (1 kg, 24 in. fall) and (iii) a cross-cut adhesion test using adhesive tape to pull the film off from the squares. The scratch hardness was evaluated using a standard Erichsen model 601 test unit. Impact tests were conducted as per DEF Standard 1053 (17a) (UK). The films were also tested for their resistance for 72 h to water, 5% sulphuric acid (w/w), 5% sodium hydroxide solution and solvents such as White Spirit, xylene and n-butanol as per Bureau of Indian Standards specZcation 101. Results

and discussion

Diallyl bisphenol-A diacrylates (16, 16, 18) gave superior overall film properties when compared with ally1 phenyl and p-alkyl-substituted ally1

350

TADbE 9 Film properties of UV-curable compositions based on various reactive diluents General rec@e: 2,2’-diallyl bisphenol-A epoxy acrylate Trimethylol propane triacrylate Reactive diluents (10-17) Darocur 116 Film properties”

Scratch hardness (g) IS. 101 (1961) Flexibility (mandrel bend) Adhesion (rating) Impact strength (DEF 1053 (17a))

30 parts 30 parts 37 parts 3parts

Reactive dlluents (Table 6) 10

11

12

13

14

16

16

17

750

800

1200

1050

1300

1700

1100

1400

l/16

l/16

l/16

l/16

l/l6

l/32

l/32

l/32

4

5

5

5

7

8

9

8

P

P

P

P

P

P

P

P

‘Notes: 1 Viscosity of compositions was maintained at 50 cP. 2 Film thickness of coatings was in the range 2530 km. 3 Adhesion Scotch Tape test: grade: 0 = poor; 10 = excellent. 4 No. of passes required to cure was 4-5. 5 All the coatings were resistant for 72 h to water, 5% I12S04,5% Na&O,, White Spirit, xylene and n-butanol. 6 P-passes. 7 Storage stability was found to be co. 4-6 months. 8 I.S. = Indian Standard specification. 9 Structure of acrylm ester diluents: 10: 2-a&1 phenol 11:2-propenyl phenol 12: 2-allyl-4-methyl phenol 13: 2-allyl-4-t-butylphenol 14: 2-allyl-4-phenyl phenol 16: 2,2’-diallyl bisphenol-A 16: 2,2’-dipropenyl bisphenol-A 17: 2,2’-dipropyl bisphenol-A

phenyl monoac~lates (N-14). Thiswas due to the occurrence of better crosslink between the more unsaturated moities present in the former (Table 9). Similar behaviour was observed between conventional monoacrylates (a, b) and diacrylates (c, d) used in the present study (Table 10). When ally1 groups were rearranged to propenyl groups, as in the case of 2-propenyl phenyl acrylate (11)and 2,2’-dipropenyl bisphenol-A diacrylate (16), the UV-cured 6lms obtained from coating compositions containing these two reactive diluents exhibited inferior properties overall (Table 9) since they are incapable of cure by UV radiation. This observation supports the fact that acrylic monomers containing ally1 groups function as better reactive d&rents than those containing propenyl groups.

351 TABLE 10 Film properties of W-curable coating compositions based on conventional reactive diluents General recipe: 2,2’-Diallyl bisphenol-A epoxy acrylate Trimethylol propane triacrylate Conventional reactive diluents Darocur 116 Film properties

Scratch hardness (g) I.S. 101 (1961) Flexibility (mandrel bend) Adhesion (rating) Impact strength (DEF 1053 (17a))

30 parts 30 parts 37 parts 3Parts

Conventional reactive diluents’ a

b

C

d

700

800

1000

1100

l/8

If8

l/16

l/16

4 F

4 F

5 P

5 P

“a = Butyl acrylate; b = glycidyl acrylate; c = neopentyl glycol diacrylate; d = 1,4-butylene diacrylate. F = failed; P = passed.

The best overall film properties were obtained when 2,2’-diallyl bisphenolA diacrylate (16) was used as the reactive diluent, since the ally1 groups assist in curing with acrylics when exposed to UV radiation. However, when the ally1 groups were hydrogenated to propyl groups, as in compound 16, the scratch hardness was reduced due to insufhcient crosslinking. Of the various reactive diluents, 2-ally1 phenyl acrylate (10) showed promising results in uniform wetting and fast curing relative to the alkylsubstituted ally1 phenyl acrylates 12 and 13 due to the steric effect of the alkyl group. In the case of the phenyl-substituted ally1 phenyl acrylate 14, the steric factor was compensated by the mesomeric effect of the phenyl ring. As a result, the overall properties of this compound were better than those of the other ally1 phenyl monoacrylates. Conventional monoacrylic ester reactive diluents (a, b) gave inferior scratch hardness and flexibility. They also gave brittle films and thus failed in the impact strength test. However, the conventional diacrylate reactive diluents gave better overall properties than the monoacrylates (Table 10). In conclusion, it is felt that the presence of an aromatic ring in the reactive diluents helps in the generation of tough films exhibiting better adhesion and flexibility. References 1 S. Saraiya and K. Hashimoto, Mod. Paint. Coat., 70 (1980) 37. 2 E. Levine, Mod. Paint. Coat., 73 (1983) 26. 3 R. Dowbenko, C. Friedlander, G. Gruber, P. Prucnal and M. Wismer, II (1983) 71.

Prog.

Org.

Coat.,

352 4 5 6 7 8

E. G. Slur, Am. Paint J., 57 (1972) 26, 58, 62, 64. J. R. Younger, 3. OzX Coknw Chem, Assoc., 59 (1976) 197. C. B. Rybny and J. A. Vend, J. Oat Cdow C&m. Assoc., 61 (1978) 179. P. C. Chattesjee and R. Ramaswamy,Br. Ink Maker, 17 (1975) 76. A. I. Vogel, Text Book of Practical Organic Chemistry, Longmans Green, London, 1978, p. 764. 9 B. S. Sitaramarnand P. C. Chatterjee, J. Appl. Polyp. SC&, 37 (1989) 33.