Synthesis and characterization of novel photoactive nanocrystalline catalysts

Synthesis and Characterization of Novel Photopolymerizable Multifunctional 2-Propenyl Ether Analogues

JAMES V. CRlVELLO* and DONG-HACK SUH

Department of Chemistry, Rensselaer Polytechnic Institute, Troy, New York 121 80

SYNOPSIS

Monomers bearing two, three, four, and six cationically polymerizable aryl 2-propenyl groups were synthesized and characterized. These compounds can be readily prepared by the catalytic isomerization of the corresponding ally1 compounds. Strong bases and tris (triphenylphosphine) ruthenium( 11) dichloride were used as the catalysts for these isomerizations. A study of the cationic photopolymerizations of these novel monomers was carried out using a diaryliodonium salt photoinitiator. The polymerization involves a step- wise condensation of the monomers followed by an intramolecular ring closure to form polyindanes. The resulting photopolymerized polymers underwent thermal oxidative de- composition at temperatures over 430°C. 0 1993 John Wiley & Sons, Inc. Keywords: multifunctional aryl 2-propenes 2-propenyl ether analogues allyl-2-propenyl isomerizations cationic photopolymerization

I NTRO DUCT10 N

Recent work in this laboratory has focused on the synthesis of novel monomers that polymerize by a cationic mechanism. Both alkyl and aryl vinyl ethers are known to be highly reactive towards cationic polymerization. The high reactivity of these mono- mers is of considerable interest for many applica- tions such as coatings and adhesives in which the monomers are very rapidly polymerized using cat- ionic photoinitiators. However, polymer films pre- pared by the cationic polymerization of simple alkyl vinyl ethers show poor oxidative and thermal sta- bility.' Substitution of the alkyl groups in vinyl ethers with aryl groups leads to aromatic vinyl ethers which are more oxidatively stable. Unfortunately, they are also more prone to hydrolysis and in ad- dition, instead of normal vinyl polymerization, they undergo a rearrangement as shown in eq. ( 1 ) to give low molecular weight poly ( hydroxystyrenes ) with pendant hydroxyl groups in the ortho and para po- sitions:

* To whom all correspondence should be addressed. Journal of Polymer Science: PartA Polymer Chemistry, Vol. 31,1&47-1857 (1993) 0 1993 John Wiley & Sons, Inc. CCC OSS7-624X/93/071S47-11

bn

Studies of the cationic polymerization of aromatic propenyl ethers have shown that similar rearrange- ments occur, and that these compounds are even more hydrolytically sensitive than aryl vinyl ether^.^

It is well known that compared to styrene, 4- methoxystyrene (I) , and other alkoxy substituted styrenes undergo anomalously high rates of cationic polymeri~ation.4-~ This can be readily understood if one views the structure of I as a phenylogous vinyl ether. Similarly, we have recently reported that re- lated compounds such as 4-methoxy-a-methylsty- rene (11)" and alkyl ethers of isoeugenol (111)" which are respectively, isopropenyl and 2-propenyl ether analogues, also readily polymerize under cat- ionic polymerization conditions. In addition to the high reactivity expected of vinyl and 2-propenyl ethers, these three monomers have the advantage over the latter compounds that they are very hy- drolytically stable.

1847

1848 CRIVELLO AND SUH

I I1 III

With these preliminary data in hand, an inves- tigation was undertaken to determine whether these concepts could be extended to the preparation of additional types of di- and multifunctional vinyl and 2-propenyl ether analogues. The present article pre- sents the results of these preparative studies as well as a brief investigation of their cationic polymeriza- tion.

EXPERIMENTAL

Materials

2-Allylphenol, alkyl iodides, N,N-dimethylaniline and various a,o-dibromoalkanes were used as pur- chased from the Aldrich Chemical Co. [(C6- H5)3P]3R~C12 was obtained from the Alfa Products Division of Morton Thiokol, Inc. The preparation of the photoinitiator, 4-octyloxyphenyl ) phenyl- iodonium hexafluoroantimonate, has been described previously.12

The course of the isomerization reactions was followed using thin layer chromatography employing silica coated TLC plates and a 1 : 1 volume mixture of dichloromethane and petroleum ether as the eluent. Kinetic runs were carried out small clean vials sealed with rubber septa and immersed in a constant temperature bath. Samples were with- drawn periodically and submitted for 'H-NMR analysis. 'H-NMR spectra were obtained using a Varian XL-200-MHz Spectrometer a t room tem- perature in CDC13. All chemical shifts were mea- sured using tetramethylsilane (TMS ) as an internal standard. Elemental analyses were performed by Quantitative Technologies, Inc.

Synthesis of 2,6-Diallylphenol l 3

Into a round bottom flask were combined 0.2 mol of 2-allylphenol, 0.23 mol of potassium carbonate, 0.3 mol of allyl bromide, and 100 mL of acetone. The mixture was refluxed for 48 h under nitrogen. Ally1 2-allylphenyl ether (bp 75-76"C, 0.5 mm) l4 was ob-

tained after fractional distillation and was rear- ranged by heating at 200-210°C with 0.2 mol of N, N-diethylaniline for 24 h. The reaction mixture was cooled to room temperature and then taken up in 200 mL petroleum ether and the solution was exhaustively extracted with 2N H2S04 remove the N,N-dimethylaniline, washed with 10% aq. NaHC03 and then dried over MgS04. After removing the sol- vent on a rotary evaporator, the product, 2,6-dial- lylphenol, (bp 84-86"C/0.5 mm, 85% yield) was purified by vacuum distillation.

Synthesis of 2,4,6-Triallylphenol l 3

To a solution of 0.1 mol of sodium metal in 100 mL of absolute ethanol at 90°C in an oil bath there was added 0.1 mol of 2,6-diallylphenol. Next, 0.15 mol of allyl bromide was added and the solution held at room temperature for 16 h. The reaction mixture was extracted with light petroleum ether and the resulting solution filtered through A1203. The sol- vent was removed on a rotary evaporator and the crude product fractionally distilled to give pure allyl 2,6-diallylphenyl ether, (bp 82-86OC/O.3 mm). This material was heated with N,N'-diethylaniline for 24 h at 200-210°C. After workup as described above and vacuum distillation, 2,4,6-triallylphenol (bp 97- 101"C/0.2 mm) was obtained in 81% yield.

General Procedures for the Synthesis of Alkyl 2,6-Diallylphenyl Ethers, Bis [ 2,6-diallylphenoxy] Alkanes, Alkyl 2,4,6-Triallylphenyl Ethers, and Bis [ 2,4,6-triallylphenoxy] Alkanes

In a round bottom flask, 0.2 mol of 2,4,6-triallyl- phenol, 0.23 mole of potassium carbonate, 0.3 mol of the alkyl iodide or 0.1 mol of the a,w-dibromoal- kane, and 100 mL of acetone were combined. The mixture was refluxed for 48 h under nitrogen. The solution was filtered, dried with MgSO, and the sol- vent removed on a rotary evaporator. The oily prod- ucts were purified either by fractional distillation under reduced pressure or by column chromatog- raphy on silica gel using a 1 : 1 mixture of petroleum ether and dichloromethane as the eluent.

General lsomerization Procedures for the Synthesis of Alkyl 2,6-Di (2-propenyl ) phenyl Ethers, Bis [ 2,6-di ( 2-propenyl)phenoxy] Alkanes, Alkyl 2,4,6-Tri (2-propenyl ) phenyl Ethers, and Bis[ 2,4,6-tri (2-propeny1)phenoxyl Alkanes

The following are examples of the procedures em- ployed for the synthesis of the aryl propenyl mono- mers shown in Table I.

PHOTOPOLYMERIZABLE PROPENYL ETHER ANALOGUES 1849

Table I. Structure of Multifunctional Propenyl Ether Analogues

Structure Rorn Notation MW

G”” CH,

CH, CH,

n = 6 n = 8

VII VIII

CH3 M CHzCH3 X

n = 6 n = 8

XI MI

188 202

430 458

228 242

5 10 538

Method 1: Ruthenium-Catalyzed lsomerization

Preparation of Ethyl 2,6-Di(2-propenyl)phenyl Ether (VI) . To 0.01 mol (2.02 g) of the ethyl 2,6-diallyl- phenyl ether, there were added 1 X lop5 mol(O.0096 g) of [ (CGH5)SPISRuClZ as catalyst. The reaction mixture was heated in an oil bath at 140°C and pe- riodically monitored by ’H-NMR. After 4 h, the spectrum showed the absence of bands due to the ally1 methylene group at 6 3.4 ppm. The crude liquid monomer was purified by column chromatography

using chloroform as the eluent. The yield was quan- titative.

ANAL. Calcd for CI4Hl80: C, 82.94%; H, 8.57%. Found C, 82.03%; H, 8.50%.

Preparation of 1,8-Bis [ 2,6-di(Z-propenyl)phen- oxy ] octane (VIII). Combined together were 0.01 mol(4.58 g) 1,8-bis ( 2,6-diallylphenoxy) octane and 1 X mol (0.0096 g) of [ ( CsH5)3P]3RuC12 as catalyst. The reaction mixture was heated together

1850 CRIVELLO AND SUH

in an oil bath at 140°C for 8 h. The crude product was purified by column chromatography on silica gel using a 1 : 1 mixture of petroleum ether and dichloromethane as the eluent. The colorless oily monomer was obtained in quantitative yield.

ANAL. Calcd for C32H4202: C, 83.83%; H, 8.89%. Found C, 83.10%; H, 8.41%.

Synthesis of 1,8-Bis [ 2,4,6-tri(2-propenyl)phen- oxy ] octane (XII). The subject compound was pre- pared and purified as described above by heating 0.01 mol (5.38 g) of 1,8-bis (2,4,6-triallylphen- oxy)octane and 1 X mol (0.0096 g) of [ ( C6H5)3P]3RuClP together in an oil bath at 140°C for 8 h. The desired 1,8-bis [ 2,4,6-tri (2-pro- penyl) phencrxy ] octane was obtained in quantitative yield and purified by column chromatography.

ANAL. Calcd for C38H5202: C, 85.40%; H, 8.89%. Found: C, 85.30%; H, 8.91%.

Method 2: General Procedure

The previously mentioned ally1 precursors were iso- merized to the corresponding 2-propenyl compounds by heating them at 130°C with an equimolar amount of KOH in DMSO for 5 h. The reaction mixtures were worked up by diluting with water and extract- ing with ether. The organic layer was washed several times with water and then dried over MgSO,. The monomers were then purified as described before by column chromatography.

Photopolymerizations

Photopolymerizations were carried out by irradiat- ing 1-2 mg thin (ca. 1 mil) film samples of the liquid monomer containing 0.5-3 mol % of the photoini- tiator, ( 4-octyloxyphenyl ) phenyliodonium hexa- fluoroantimonate, on NaCl plates with a General Electric Co. 200 W medium-pressure Hg arc lamp. The progress of the photopolymerizations was fol- lowed by periodically recording infrared scans on a Perkin-Elmer Model 1800 Fourier Transform In- frared Spectrometer. Photopolymerizations were also monitored using a Perkin-Elmer DSC-7 Dif- ferential Scanning Calorimeter equipped with a photocalorimeter accessory fitted with a Hanovia 100 W mercury-xenon lamp as the UV-light source. The polymerizations were carried out isothermally at 50°C on 2-3 mg samples of the monomer con- taining 0.5 mol % of the photoinitiator.

Thermogravimetric Analyses

Thermogravimetric analysis data were obtained us- ing a Perkin-Elmer TGA-7 Thermogravimetric An- alyzer. The analyses were carried out on 4-6 mg samples of the photopolymerized polymer film which contained 0.5 mol % of (4-octyloxyphenyl) - phenyliodonium hexafluoroantimonate photoini- tiator. Samples were heated to 800°C in a nitrogen atmosphere at a heating rate of 40"C/min.

RESULTS AND DISCUSSION

The Design of Novel Cationically Polymerizable Monomers

The observation that compounds 1-111 may be re- garded as vinyl and 2-propenyl ether analogues and undergo facile cationic polymerization suggested that perhaps, other related compounds may behave similarly. For example, the series of compounds; 2- propenyl anisole (IV ), 2,6-di (2-propenyl) phenyl methyl ether (V), and 2,4,6-tri (2-propenyl) phenyl methyl ether, as well as other alkyl ether derivatives may also be regarded respectively, as mono-, di-, and trifunctional 2-propenyl ether analogues.

IV V CH3

I X

Preliminary investigations showed that, indeed, IV as well as other alkyl ether derivatives of this com- pound could be polymerized using various cationic initiators." Details of this work are described in a separate arti~1e.I~ The work described herein focuses first on general synthetic approaches for the prep- aration of a series of multifunctional compounds exemplified by V and IX. Subsequently, the pho- toinitiated cationic polymerization of the monomers synthesized is described.

The Synthesis of Multifunctional 2-Propenyl Ether Analogues

Two general synthetic pathways which can be ap- plied to the preparation of V and related compounds are shown in Scheme 1. A similar series of reactions may be used for the synthesis of trifunctional 2-

PHOTOPOLYMERIZABLE PROPENYL ETHER ANALOGUES 186 1

again repeated to give the 2,4,6-triallylphenol. Next, as depicted in eq. (4), the 2,6-diallylphenol was iso- merized to the corresponding 2,6-di ( 2-propenyl ) - phenol. Alternatively, a better route consists of first alkylating the phenol [ eq. (5) ] and then carrying out the isomerization of the alkyl ether to the corresponding di ( 2-propenyl ) phenyl alkyl ether

on ~

K 2 c q . -

cq. 2

[eq. (6) l .

aiahytniline

on

propenyl derivatives, such as IX. The synthesis be- gins with the 0-allylation of the commercially avail- able 2-allylphenol as shown in eq. ( 2 ). Claisen rear- rangement [ eq. ( 3 ) ] of the allyloxy-2-allylbenzene to 2,6-diallylphenol can be readily achieved in good yields by simply heating at 200-210°C for 24 h in the presence of diethylaniline as a catalyst and sol- vent.13 In the case of IX these first two steps were

The key steps in Scheme 1 are the isomerization of the inactive, readily available allyl compounds to their cationically polymerizable 2-propenyl coun- terparts. In the course of this work, several methods of isomerization of terminal to internal olefins were investigated. Among these methods, potassium-t- butoxide or KOH in dimethylsulfoxide has been re- ported to be an especially effective as a catalyst in the isomerization reaction from allyl ethers to pro- penyl ethers.l6vl7 Although we have found that the base-catalyzed rearrangement of, e.g., V proceeds under mild conditions, it suffers from two major dis- advantages; first, rather large amounts (equimolar ) of potassium-t-butoxide with respect to the allyl groups are required and second, poor yields of the desired 2-propenyl isomeric products are obtained due to the difficulties encountered in the workup of the reaction mixtures. For these reasons, we decided to explore alternate catalytic methods. An especially active rearrangement catalyst for the olefinic double bonds in general and for allyl ethers to propenyl ethers in particular, is tris (triphenylphosphine ) - ruthenium( I1 ) di~hlor ide .~~ '~* '~

1

li 3 f

TMS

c 4 i n ' ' I " "Q I n l " I " ' ) 8 I "J ' ' I n ' i ! ' , ' I I ' 1 I I I I I ' ' 4 I I l '" 'J '""" ' / " " " " ' , j ' ' " " ' PRI I_

Figure 1. 'H-NMR spectrum of 2,6-diallylphenyl ethyl ether in CDC13.

1852 CRIVELLO AND SUH

I P I I 1 , 1 t I I I I I 8 , ~ m r l r ~ ~ r ! I ri I p I I ' 1 I I I 1 1 I I 11 r r r r T v ~ r i T T ~ T S m 0 9 A 7 6 5 4 3 v r - 7

Figure 2. 'H-NMR spectrum of 2,6-di( 2-propeny1)phenyl ethyl ether (VI) in CDCl3.

We have undertaken a detailed study of the rear- rangement of allyl-substituted aromatic compounds to their propenyl isomers with this catalyst using model compounds. Figures 1 and 2 respectively, give the 'H-NMR spectra of 2,6-&allylphenyl ethyl ether and its isomerization product, 2,6-di ( 2-propenyl) - phenyl ethyl ether. Two important conclusions can be drawn from these spectra. First, the isomerization proceeds cleanly to yield only the desired 2-propenyl derivatives with essentially no major byproducts. Second, the 2-propenyl compounds which are formed consist of both E and 2 isomers. This may be clearly seen in the spectra by the doubling of most of the peaks indicating the presence of both configurations about the double bonds. Hence, monomer VI is a mixture of E , E ; E ,Z ; and Z ,Z isomers.

Figures 3 and 4 show the rate of consumption of starting material versus time plots at different molar ratios respectively, of 2,6-diallyl- or 2,4,6-triallyl- phenyl ethyl ether to ruthenium catalyst. Reactions were carried out in neat starting materials at 120°C. Analysis of the product by 'H-NMR showed quan- titative loss of the peaks due to the protons on the allyl group and replacement by those assigned to the 2-propenyl groups. The course of the reaction was determined by the integration ratio of the allyl methylene group (at 6 3.45 ppm) to methylene (at 6 3.85 ppm) adjacent to oxygen as an internal stan- dard. Previous work on the rearrangement of allyl ethers to 2-propenyl ethers using the ruthenium

catalyst showed that the isomerization went to completion in 1-2 h.7 In contrast, rearrangements of the allyl group to the 2-propenyl group in our systems required a longer reaction times. It also may be seen in these two figures, that contrary to expec- tation, higher levels of the catalyst actually result in longer reaction times. These results suggest that there is an optimum level of catalyst and that higher

0 1 2 3 4 5 6

Time (hr)

Figure 3. Study of the effect of variation in the con- centration of [ ( CsHS)3P]3R~ClZ on the isomerization of 2,6-diallylphenyl ethyl ether to 2,6-di (2-propeny1)phenyl ethyl ether (VI) a t 120OC: (0) 1 mol %, (*) 0.5 mol %.

PHOTOPOLYMERIZABLE PROPENYL ETHER ANALOGUES 1853

l i m e (hr)

Figure 4. Effect of the concentration of [(c,- H,)3P I3RuCl2 on the isomerization of 2,4,6-triallylphenyl ethyl ether to 2,4,6-tri( 2-propeny1)phenyl ethyl ether (X ) a t 120°C: (0 ) 1 mol %, ( 4 ) 0.5 mol %, ( m ) 0.1 mol %.

catalyst concentrations may have an inhibiting ef- fect on the isomerization. Figure 5 depicts the effect of temperature on the isomerization of 2,6-diallyl- phenyl ethyl ether. The reaction was most rapid at the higher temperatures although considerable darkening of the reaction mixture was evident. Con- sequently, isomerizations were generally carried out at 120-140°C using 0.1 rnol % [ ( CsH5)3P]3R~C12.

The structures of the multifunctional propenyl ether analogues prepared during the course of this work are given in Table I. Besides simple di- and trifunctional compounds, tetra- and hexafunctional monomers were prepared by coupling of the corre-

iE E 0

8 > c 0 0

- 2

l i m e (hr)

Figure 5. Effect of temperature on the isomerization of 2,6-diallylphenyl ethyl ether: (0) 100°C, ( 4 ) 12OoC, (m) 140°C.

sponding di- and triallyl phenols with dibromoalkanes followed by isomerization with [ ( C & , ) ~ P ] & U C ~ ~ . Typically, the yields are very high and, in many cases, they are quantitative. These eight monomers were liquid mixtures of isomers with both E and Z configurations about the 2-propenyl double bonds. The monomers were purified prior to their use in cationic photopolymerization by column chroma- tography. The ruthenium catalyst and other color- producing impurities are strongly absorbed on the column and are removed during purification.

Figure 6 shows a comparison of the isomerization rates of various multifunctional monomers at 12OoC using 0.1 mol 5% [ ( CsH5)3P]3R~C12. The highest rate of isomerization was obtained for the trifunctional monomer, X, while the slowest rate was observed for the hexafunctional monomer, XII. The 'H-NMR spectra of tetrafunctional ( VII ) and hexafunctional (XII) monomers are respectively, shown in Figures 7 and 8. Comparison of these spectra with the model compounds given in Figures 1 and 2 shows the ab- sence of allyl groups and presence of the 2-propenyl double bonds.

Cationic Photopolyrnerization of Multifunctional 2-Propenyl Ether Analogues

The photoinitiated cationic polymerizations of the monomers given in Table I were briefly studied using ( 4-octyloxyphenyl ) phenyliodonium hexafluoroan- timonate as the photoinitiator.

A

8 Y - m 8 I

L

c)

m C

m - c. L

ti ; E 0 0

0 2 4 6 8 1 0 1 2

Time (hr)

i

Figure 6. Comparison of the rates of isomerization for various allyl substituted precursors to give monomers: (0) VI, (4 ) VIII, (m) x , (0) XII.

1854 CRIVELLO AND SUH

i , , , , , " " r , , , , , , , , , , , , I I , , , , , , , , ' " ' I 1 1 I ~ I I I 1 1 1 1 1 1 , , , , ~ , 1 , 1 ~ 1 , , , , , , , , , , , , , , , , , , , , , , , , , ,,,, I 4 pR( 0

Figure 7. 'H-NMR spectrum of 1,6-bis [ 2,6-di (2-propenyl) phenoxyl hexane (VII) in CDC13.

This photoinitiator was selected because of its good solubility in all eight monomers to give homogeneous solutions which can be readily photopolymerized by

irradiation using an unflitered 200 W medium-pres- sure mercury arc lamp. All of the monomers undergo photopolymerization under these conditions to give

r n

1 1 1 ( 1 1 1 1 1 1 1 1 I I I I I I I 1 1 I I 1 ~ ' ' ' I " ' ' I I I I I I I I I I I , , , , 1 1 1 1 ~ , 1 1 1 ( 1 , 1 1 ~ 1 1 1 1 I , , , ~ , , , , , , , , ~ , , , , , , , , I , , , , , 9 E 7 6 4 I - 0

Figure 8. in CDC13.

'H-NMR spectrum of 1,8-bis [ 2,4,6-tri( 2-propeny1)phenoxyll octane (XII)

PHOTOPOLYMERIZABLE PROPENYL ETHER ANALOGUES 1855

solid, crosslinked films after 1-5 min. Studies of the reactivities of the monomers were conducted using differential scanning photocalorimetry in which the exothermic heat of the polymerization was moni- tored as a function of irradiation time. For example, the differential scanning photocalorimetry curve for monomer VI is shown in Figure 9. After the shutter is opened at 0.5 min, polymerization takes place rapidly and is completed over the course of 1.5-2.0 min UV irradiation.

In a previous article from this laboratory," we offered evidence that the UV irradiation of 4-me- thoxy-a-methylstyrene in the presence of cationic photoinitiators leads chiefly to the formation of an indane compound [path ( a ) ] rather than polymer- ization [ path ( b ) ] as shown in eq. ( 7) :

( 7 )

Further, difunctional monomers containing isopro- penyl groups were shown to undergo primarily linear

polymerization to form poly ( indanes ) . Similarly, the treatment of aryl-2-propenes bearing electron donating groups with acids has been shown by Al- Farfan) et al. to produce indanes." An example of this reaction is shown in eq. (8) :

0 Q L O

Several stereoisomeric indanes were isolated by these workers from the acid-catalyzed cyclization of isosaffrole. The products may be rationalized by noting that dimerization and the subsequent Frie- del-Crafts cyclization reaction to form the indane are facilitated by the presence of the electron-do- nating methylenedioxy substituent on the aromatic ring.

In Figure 10 is shown the infrared spectrum of the photopolymerization 2,6-di ( 2-propenyl ) phenyl ethyl ether (VI) containing 0.5 mol % of the above photoinitiator before and after 1, 2, and 3 min ir- radiation. The double bond absorption at 980 cm-' was monitored. As the spectra show, as the photo- polymerization proceeds, a decrease in the intensity

1.00

0 50

0 00

-0 50

-1 00 ''3

0 50 1 50 2 50 3 50 4 . 5 0

Time (min.)

Figure 9. Photo-DSC curve for the exothermic cationic photopolymerization of monomer VI in the presence of 0.5 mol % (4-octyloxyphenyl) phenyliodonium hexafluoroantimonate (irradiation source; Hanovia 100 W mercury-xenon lamp).

1856 CRIVELLO AND SUH

100.0 -.

90.0 -

80.0 - 70.0 -

h

# 6 0 . 0 -

c) 50.0- v

5 .% 40.0 -

30.0-

20.0 - 10.0 - 0.0 -+

1w IU I4a 12sl I I m M-I i

Figure 10. Infrared spectra of 2,6-di (2-pro- peny1)phenoxy ethyl ether (VI) in the presence of 0.5 mol % (4-octyloxyphenyl)phenyliodonium hexafluo- roantimonate after 0, 1, 2, and 3 min UV irradiation.

I 1 I

of the 980 cm-' band takes place. Other changes in the double bond and aromatic absorption bands at 1580-1620 cm-' are also visible and there is a general broadening of all of the absorption bands as the po- lymerization proceeds. During photopolymerization, it was noted, that despite the high functionality of the monomers, the polymers remained soluble and only underwent crosslinking upon prolonged irra- diation.

Based on these observations and results, it is pro- posed that the structure of the polymers generated by the photopolymerization of the monomers shown in Table I also contain indane moieties as part of their backbones. Thus, for example, the polymer- ization of difunctional monomer VI would yield a polymer with a partial backbone structure as shown in eq. (9) :

L A"

Since network formation is noted during the latter stages of the photopolymerization, crosslinks can also be generated by normal, vinyl type polymeriza- tion and perhaps, also by intermolecular Friedel- Crafts alkylation processes between the polymer chains. With the objective of attempting to gather some information concerning the structure of the polymers we have examined the 'H-NMR of the sol- uble oligomers formed by the photopolymerization

Figure 1 1. VI, VII, IX, and XI in nitrogen at 40"C/min.

Thermogravimetric analysis curves for photopolymerized films of monomers

PHOTOPOLYMERIZABLE PROPENYL ETHER ANALOGUES 1857

of ethyl-2,6-dipropenylphenyl ether, however, the results are difficult to interpret since the spectra are very broad. Presumably, this is due to the very com- plex structure of the polymer backbone which is a result of the presence of many different structural units arising from different modes of indane ring closure as well as the presence of many chiral cen- ters.

Figure 11 shows the thermogravimetric analysis (TGA) curves for four photopolymers carried out under nitrogen at 40°C/min. All the polymers ex- hibit good thermal stability with thermal decom- position starting at approximately 430°C. The poly- mer resulting from the photopolymerization of the tetrafunctional monomer, VIII, is slightly more stable than the others. The good thermal stability exhibited by these photopolymers can be attributed, in part, to the polyindane structure of their back- bone~.".'~

Work is currently in progress to optimize the photopolymerization conditions and to further de- termine the mechanical characteristics of the poly- mers which are produced.

CONCLUSIONS

A series of reactive, multifunctional monomers that can be readily photopolymerized in the presence of diaryliodonium salt cationic photoinitiators have been prepared. A simple, direct synthetic method has been developed which involves the base or ru- thenium catalyzed rearrangement of ally1 benzene derivatives to the corresponding 2-propenyl isomers. The high sensitivity of these aromatic analogues of 2-propenyl ethers toward photoinduced cationic po- lymerization has been demonstrated. The best evi- dence indicates that these monomers undergo in- ternal cyclization as part of the chain extension process to yield polymers containing indane groups.

The authors would like to thank the IBM Corporation for their financial support of this work and the Perkin-Elmer

Corporation for their assistance in the acquisition of the TGA-7 Thermogravimetric Analyzer.

REFERENCES AND NOTES

1. C. E. Schildknecht, Vinyl and Related Polymers, Wiley, New York, 1952, p. 620.

2. J. B. Niederl and E. A. Storch, J. Am. Chem. SOC., 5 5 , 2 8 4 (1933); J. Am. Chem. SOC., 60,1905 (1938).

3. K. Yamamoto and T. Higashimura, J. Polym. Sci. Polym. Chem. Ed., 1 2 , 613 (1974).

4. N. Kanoh, A. Gotoh, T. Higashimura, and S. Oka- mura, Makromol. Chem., 6 3 , 1 0 6 , 1 1 5 (1963).

5. R. Cotrel, G. Sauvet, J. P. Vairon, and P. Sigwalt, Macromolecules, 9 , 931 ( 1976).

6. A. M. Goka and D. C. Sherrington, Polymer, 1 6 , 8 1 9 (1975) .

7. J. V. Crivello and D. A. Conlon, J. Polym. Sci. Polym. Chem. Ed., 2 2 , 2105 (1984).

8. J. Ericcson and A. Hult, Polym. Bull., 18,295 ( 1987). 9. J. Woods, U.S. Pat. 4,543,397 (1985) to Locktite Corp.

10. J. V. Crivello and A. Ramdas, J. Macromol. Sci. Pure Appl. Chem., A 2 9 ( 9 ) , 753 (1992); Polym. Prepr., 3 2 ( 2 ) , 175 (1991).

11. J. V. Crivello and A. M. Carter, Polym. Prepr., 32 ( 2 ) , 177 (1991) .

12. J. V. Crivello and J. L. Lee, J. Polym. Sci. Polym. Chem. Ed., 2 7 , 3951 (1989) .

13. K. Schmid, W. Haegele, and H. Schmid, Helu. Chim. Acta., 37, 1080 (1954).

14. T. Dittmer, F. Gruber, and 0. Nuyken, Makromol. Chem., 1 9 0 , 1771 (1989).

15. J. V. Crivello and A. M. Carter, manuscript in prep- aration.

16. C. Price and W. Snyder, J. Am. Chem. SOC., 83,1772 (1961) .

17. G. Kesslin and C. Orlando, J. Org. Chem., 31, 2682 ( 1966).

18. T. Prosser, J. Am. Chem. SOC., 8 3 , 1701 (1901). 19. A. Hubert, A. Georis, R. Warin, and P. Teyssie, J.

20. E. Al-Farfan, P. Keehn, and R. Stevenson, J. Chem. Chem. SOC. Perkin Trans. 2, 366 ( 1972).

Research ( S ) , 36 (1992).

Received September 25, 1992 Accepted December 7, 1992