Peresters of the formula: ROOC--R.sub.1 --COOOR wherein R is an alkyl group; R.sub.1 is selected from the group including ketone (unsubstituted or substituted) groups, and R.sub.1 is any group absorbing radiation between 250 and 800 nm such that R.sub.1 produces an excited state of sufficient lifetime to cause the decomposition to free radicals of the appended perester or peroxidic function.

The present invention is concerned with new organic compounds which are 
particularly suitable as photoinitiators. The present invention is 
especially concerned with peresters. The peresters of the present 
invention are especially useful as photoinitiators for the polymerization 
of ethylenically unsaturated materials. 
2. Background Art 
Photoinitiators are free-radical sources which decompose photochemically 
and are employed especially as initiators in the polymerization of 
ethylenically unsaturated materials. In view of the efficient control 
photoinitiated polymerization offers, such has assumed great importance in 
recent years in the printing and electronics industries such as in 
printing inks, paints and photoresist coatings. 
Among typical commercial initiators are three general types: mixtures of 
aryl ketones, benzoin ethers, or substituted acetophenones. In past years, 
highly halogenated aryl hydrocarbons were also used for initiators, but 
their use is now precluded because they are so highly toxic. 
Among the more important commercially used photoinitiators for acrylate 
polymerization is the so-called "Hammond initiator", 
benzophenone-Michler's ketone. 
A major advantage of the Hammond initiator is the rate by which it 
initiates radical chain reactions; two important disadvantages are the 
rather large amount of initiator needed to make the rate of polymerization 
sufficiently rapid for printing applications and the potential toxicity of 
one of the initiator partners--Michler's 
ketone(4,4'-bis(N,N-dimethylamino)benzophenone). 
To be of real practical significance as a photoinitiator, a compound must 
be relatively thermally stable but must also be labile when irradiated 
with wavelengths of UV or visible light. Accordingly, providing new 
compounds which possess this combination of properties is quite difficult. 
For instance, various benzophenone derivatives of benzoyl peroxide have 
been studied. For example, see Leffler et al; Journal American Chemical 
Society; 1971, 93, 7005 et seq. However, such derivatives are not 
especially stable thermally. It has also been noted that the photochemical 
efficiency of triplet benzophenone sensitized decompositions of peroxides 
in solution is low (e.g. see Walling et al., Journal American Chemical 
Society, 1965, 87, 3413 et seq.). 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide new compounds which have 
the requisite combination of relative thermal stability and efficient 
photodecomposability to be effective and practical photoinitiators. 
The compounds of the present invention are peresters which contain a light 
absorbing chromophoric moiety. The compounds of the present invention 
exhibit thermal stability characteristics. However, the compounds of the 
present invention, unlike prior known peresters, are readily 
photodecomposable and effective photoinitiators for the polymerization of 
ethylenically unsaturated compounds. The present invention also makes it 
possible to control or tune the photodecomposition of the compounds by the 
absorption characteristics of the light-absorbing chromophore portion of 
the compound. 
The compounds of the present invention are represented by the general 
formula: 
EQU Chromophore--COOOR 
EQU or 
EQU Chromophore--(CH.sub.2).sub.n --COOOR 
where chromophore is selected from the group including aryl groups, 
arylalkyl groups, or heteroaryl groups, absorbing radiation between 
250-800 nm, and R is an alkyl group or arylalkyl group. 
The compounds of the present invention are represented by the formula: 
EQU R.sub.1 Y--Ar COOOR 
where Ar is selected from the group including phenyl (unsubstituted or 
substituted) groups; naphthyl groups; anthryl groups, pyryl groups, 
phenanthryl groups, heteroaromatic groups, and heterocyclic groups, 
including furan, thiophene, benzothiophene, benzothiazole, etc; Y is 
selected from the groups including CH.sub.2, C.dbd.O, C.dbd.N; R is an 
alkyl group, and R.sub.1 is any group absorbing radiation between 250 and 
800 nm and R is an organic group such that the group R.sub.1 produces an 
excited state of sufficient lifetime to cause the decomposition to free 
radicals of the appended perester or peroxidic function. 
The present invention is concerned with the photoinitiated polymerization 
of vinylmonomers by benzophenone t-butyl peresters. 
The present invention is also concerned with photopolymerizable 
compositions comprising at least one photopolymerizable ethylenically 
unsaturated material and at least one of the above-discussed peresters. 
Moreover, the present invention is concerned with polymerizing the 
above-defined photopolymerizable compositions by subjecting such to light, 
and polymer obtained thereby.

DESCRIPTION OF BEST AND VARIOUS MODES 
The compounds of the present invention are represented by the formula: 
EQU R.sub.1 Y--Ar COOOR 
where Ar is selected from the group including phenyl (unsubstituted or 
substituted) groups; naphthyl groups; anthryl groups, pyryl groups, 
phenanthryl groups, heteroaromatic groups or heterocyclic groups, 
including furan, thiophene, benzothiophene, benzothiazole, etc; Y is 
selected from the group including CH.sub.2, C.dbd.O, C.dbd.N etc., R is an 
alkyl group, and R.sub.1 is any group absorbing radiation between 250 and 
800 nm and R.sub.1 is an organic group such that the group R.sub.1 
produces an excited state of sufficient lifetime to cause the 
decomposition to free radicals of the appended perester or peroxidic 
function. 
Examples of some suitable R.sub.1 groups are aryl groups, heteroaryl 
groups, polycyclic aryl groups, aralkyl groups, and substituted examples 
of all of these. Examples also include those containing heteroatoms such 
as oxygen, sulfur, nitrogen, phosphorus, etc. 
Examples of other suitable R.sub.1 groups are alkyl groups, cycloalkyl 
groups, and groups containing heteroatoms, such as oxygen, sulpher, 
nitrogen, etc. Generally the R.sub.1 groups contain from 1 to 22 carbon 
atoms, preferably 1-12 carbon atoms; and in conjunction with Y--Ar, they 
must absorb radiation between 250-800 nm. range. 
Examples of some alkyl groups are methyl, ethyl, t-butyl, t-amyl, hexyl, 
2-ethylhexyl, nonyl and octodecyl. 
Examples of some suitable aryl groups include phenyl, phenanthryl, and 
anthracyl. 
Examples of some cycloalkyl radicals include cyclopropyl, cyclopentyl, 
cyclobutyl, cyclohexyl, cycloheptyl, cyclooctyl, and cyclododecyl. 
Examples of some aralkyl groups are phenylmethyl and naphthylethyl. 
Examples of some alkaryl groups include tolyl, xylyl and cumyl. 
Examples of substituted aryl groups in addition to alkaryl include 
alkoxy-substituted aryl groups, such as methoxyphenol. The substituted 
aryl groups usually contain 1, 2 or 3 substitutions which are usually 
ortho and/or para with respect to the carbonyl group to which the 
substituted aryl group is connected. 
The heterocyclic groups generally contain 5-6 members in the range and 
contain S, O and/or N in the ring and include morpholinyl, piperidyl, 
thiophenyl, and furanyl. 
The preferred R.sub.1 groups are aryl and substituted aryl groups and the 
most preferred R.sub.1 groups are phenyl and alkyl and/or 
alkoxy-substituted phenyl wherein the alkyl and/or alkoxy groups contain 1 
to 2 carbon atoms and preferably 1-12 carbon atoms. 
The two carbonyl groups located on the benzene rings can be ortho, meta, 
or, preferably, para to each other. 
The synthesis was based on a general perester of the formula: 
##STR1## 
The initiators of interest are, with the exception of Formula II, 
non-conjugated peresters based on pyrene, anthracene, and fluorenone as 
indicated below. 
##STR2## 
The compounds of the present invention can be readily obtained from the 
corresponding carboxylic acids. In particular, the corresponding 
carboxylic acid can be reacted at elevated temperature (e.g. up to about 
60.degree. C.), preferably at reflux, with, for example, thionyl chloride 
to form the corrresponding acid chloride. Next, the acid chloride can be 
reacted with a hydroperoxide, such as tert-butyl hydroperoxide in the case 
of R being t-butyl, usually in the presence of a tertiary amine, 
preferably triethylamine. In addition, it is preferred that this stage of 
the preparation be carried out in the presence of a diluent, such as 
ether, benzene, or dichloromethane. 
The compounds of the present invention are especially useful as 
photoinitiators in the polymerization of photopolymerizable ethylenically 
unsaturated materials. The photopolymerizable materials can be monomeric 
or prepolymers containing one or more ethylenically unsaturated groups. 
Examples of some suitable photopolymerizable materials include esters of 
unsaturated monocarboxylic acids or dicarboxylic acids, e.g. esters of 
acrylic acid, methacrylic acid, .alpha.-cyanacrylic acid, sorbic acid, 
fumaric acid or itaconic acid with aliphatic, cycloaliphatic or aromatic, 
aliphatic monohydric to tetrahydric alcohols of 3 to 20 carbon atoms, e.g. 
methyl acrylate and methacrylate; n-, i- and t-butyl acrylate and 
methacrylate; 2-ethylhexyl acrylate; lauryl acrylate; 
dihydrodicyclopentadienyl acrylate and methacrylate; methylglycol 
acrylate; hydroxyethyl acrylate and methacrylate; hydroxypropyl acrylate 
and methacrylate; ethylene glycol diacrylate; diethylene glycol 
diacrylate; triethylene glycol diacrylate; neopentylglycol diacrylate and 
dimethacrylate; 1,4-dimethylolcyclohexane diacrylate; 
pentaerythritol-triacrylate,-tetraacrylate,-trimethacrylate and 
-tetramethacrylate; ethyl .alpha.-cyanoacrylate; ethyl crotonate, ethyl 
sorbate; diethyl fumarate; and the diacrylate and dimethacrylate or 
oxyalkylated bisphenol A; amides of acrylic acid or methacrylic acid which 
may or may not be substituted at the nitrogen by alkyl, alkoxyalkyl or 
hydroxyalkyl, e.g., N.sub.1 N'-di-methylacrylamide, N-isobutylacrylamide, 
diacetoneacrylamide; N-methylolacrylamide, N-methoxymethylacrylamide, 
N-butoxymethylolarylamide, N-butoxymethylmethacrylamide and ethylene 
glycol bis(N-methylolacrylamide)ether; vinyl esters of monocarboxylic 
acids or dicarboxylic acids of 2 to 20 carbon atoms; e.g., vinyl acetate; 
vinyl propionate, vinyl 2-ethylhexanoate, vinyl versatate and divinyl 
adipate; vinyl ethers of monohydric or dihydric alcohols of 3 to 20 carbon 
atoms, e.g., isobutyl vinyl ether, hexyl vinyl ether, octadecyl vinyl 
ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, 
butanediol divinyl ether and hexanediol divinyl ether; mono-N-vinyl 
compounds, e.g., N-vinyl-pyrrolidone, N-vinylpiperidone, 
N-vinylcaprolactam, N-vinylmorpholine, N-vinyloxazolidone, 
N-vinylsuccinimide, N-methyl-N-vinylformamide and N-vinylcarbazole; allyl 
ethers and allyl esters, e.g., trimethylolopropane diallyl ether, 
trimethylolpropane triallyl ether, pentaerythritol triallyl ether, diallyl 
maleate, diallyl fumarate or diallyl phthalate; vinyl and vinylidine 
halides, e.g., vinyl chloride and vinylidene chloride; and vinyl 
aromatics, e.g., styrene, alkyl styrenes, halostyrenes and 
divinylbenzenes. 
Examples of some polymeric photopolymerizable materials include unsaturated 
polyester obtained, for instance, from .alpha.,.beta.-unsaturated 
dicarboxylic acids, e.g., maleic acid, fumaric acid or itaconic acid, and 
aliphatic, cycloaliphatic or non-phenolic aromatic diols, e.g., ethylene 
glycol, diethylene glycol, triethylene glycol, propane-1,2-diol, 
propane-1,3-diol, butane-1,2-diol, butane-1,3-diol, butane-1,4-diol, 
but-2-ene, 1,4-diol, neopentylglycol, hexane-1,6-diol or oxyalkylated 
bisphenol A; unsaturated epoxide-acrylates obtained, for instance, from 
monofunctional epoxides and acrylic acid or methacrylic acid, by the 
method of U.S. Pat. No. 2,484,487, bifunctional epoxides and unsaturated 
fatty acids, by the method of U.S. Pat. No. 2,456,408 polyfunctional 
aromatic epoxides and crotonic acid, by the method of U.S. Pat. No. 
2,575,440 or polyfunctional aromatic or aliphatic fatty glycidyl ethers 
and acrylic acid or methacrylic acid, by the method of U.S. Pat. No. 
2,842,851; unsaturated polyurethanes (urethaneacrylates) prepared from 
hydroxyalkyl acrylates and diisocyanates, with or without polyols or 
polyamines; unsaturated copolymers, prepared, for example, by reacting 
copolymers, containing maleic anhydride groups, with unsaturated alcohols; 
or acrylic ester copolymers containing carboxylic acid groups or 
polyesters containing carboxylic acid groups with unsaturated epoxides, 
e.g., glycidyl acrylates; butadiene polymers in which the double bonds are 
predominantly present as vinyl side chains; diallyl phthalate prepolymers; 
and poly-N-vinylurethanes, e.g. prepared, for instance, by reacting vinyl 
isocyanate with saturated or unsaturated polyesterpolyols, 
polyether-polyols or polyfunctional alcohols. 
The peresters when employed as photoinitiators are usually present in 
amounts of about 1 to about 10%, and more usually about 1 to about 3% by 
weight based upon the weight of the photopolymerizable material present. 
The polymerization of such compositions can be carried out by subjecting 
or exposing the compositions on light (e.g., UV or visible) of appropriate 
wavelength absorbable by the chromophore moiety of the perester employed. 
The compounds of the present invention can be tailored by the particular 
chromophore group present to provide light absorption properties for a 
given wavelength selected from a broad spectrum of wavelengths, preferably 
in the visible and UV ranges. It is preferred that the chromophore group 
be selected so that it absorbs light in the range of about 250-800 nm. The 
particular wavelength to employ is determinable by those skilled in the 
art without undue experimentation once they are aware of the present 
invention and the particular chromophore group present. 
Polymers obtained from polymerization in the presence of the peresters of 
the present invention have been found to contain as end group the 
chromophore group from the perester employed; and, therefore, can 
subsequently be subjected to irradiation to achieve some crosslinking. 
Polymerization of the composition usually requires exposure to the light 
for about 30 seconds to about 10 minutes depending upon the amount of 
initiator present. The time and amount are inversely related. The 
crosslinking reaction is usually about 10.sup.2 to 10.sup.3 times slower 
than the polymerization and usually requires about 1 to about 20 hours 
depending upon the amount of initiator employed. 
The following non-limiting examples are presented to further illustrate the 
present invention: 
EXAMPLE 1 
Preparation of Peresters 
Starting materials and other reagents were obtained from Aldrich Chemical 
Company and purified, where necessary, by standard procedures. The 
monomers, MMA and styrene, were freed of inhibitor by washing with a 5% 
NaOH solution followed by repeated washing with distilled water. The 
monomers were then dried and distilled under reduced pressure just prior 
to use. All melting points are uncorrected. Ultraviolet spectra were 
obtained on a Varian Model 219 spectrometer. The intensity of the 
radiation was monitored constantly by benzophenone/benzhydrol actinometry 
at 30.degree. and observed to be 9.15.times.10.sup.17 quanta/minute, as 
described by L. Thijs, S. N. Gupta and D. C. Neckers, J. Org. Chem. 44, 
4123 (1979). 
4-Bromomethyl Benzoyl Chloride and -peroxybenzoic acid, tert-Butyl Ester 
(Crucial Perester Intermediate Formula I) 
4-Bromomethyl benzoic acid (18.53 g., 0.086 moles) which had been prepared 
by the Tuleen method, D. L. Tuleen and B. A. Hes, J. Chem Ed. 40, 476 
(1971), and finely powdered was refluxed for one hour with an excess of 
thionyl chloride and a few drops of pyridine. A rapid evolution of 
hydrogen chloride took place for a few minutes and then stopped. Excess 
thionyl chloride was distilled off under vacuum and the oily residue 
dissolved in hexane. Crystallization occurred soon in the refrigerator. 
Filtration gave 14.32 g (71% yield) of the acid chloride. 
Preparation of Formula I Perester 
To an ice-salt cooled solution of 13.22 g (56 mmols) of 4-bromoethyl 
benzoyl chloride in 125 ml of dry ether was added dropwise over 30 minutes 
under magnetic stirring a solution of 5.45 g (60 mmole) of tert-butyl 
hydroperoxide and 6.56 g (65 mmoles) of triethylamine in 50 ml of ether. 
After the addition of mixture was stirred for another hour. Filtration and 
evaporation left a solid. This was dissolved in dichloromethane and 
chromatographed over silica gel with dichloromethane as eluent. This gave 
16.46 g of a colorless perester (90% yield) which was further purified by 
vacuum sublimation. The pure sample melted at 93.degree.-4.degree.. 
IR(KBr) 1760 cm.sup.-1 (C.dbd.O perester). 
NMR (CDCL.sub.3) .delta.=1.44 s 9H CH.sub.3 ; 4.52, s 2H, CH.sub.2 ; 
7.44-8.00, 9H aromatics. 
Synthesis of 4-[(1-Pyrenyl)carbonyl]-Peroxybenzoic Acid, tert-Butyl Ester 
Formula II 
Pyrene, (6.75 g; 0.033 mol) was dissolved in 75 ml of dry benzene. 
4-Carbomethoxybenzoyl chloride (6.0 g; 0.030 mol) was added. To this 
solution 6.75 g (0.050 mol) of aluminum chloride was gradually added. A 
dark color developed. After the addition of AlCl.sub.3 the temperature 
increased slightly and then the temperature of the mixture was increased 
to 40.degree. with a water bath and gradually recooled to room 
temperature. The reaction mixture was then poured into an ice bath to 
which 5 ml of HCl has been added. The benzene was removed by steam 
distillation. The organic mixture was extracted with benzene and dried 
over magnesium sulfate. The solvent was evaporated and the residue 
chromatographed on silical gel with hexane. Elution with carbon 
tetrachloride gave pyrene, 3.2 g. Elution with carbon 
tetrachloride/chloroform (1:2) gave a yellow solid in two fractions (1.62 
g; 3.25 g). The former fraction contained some pyrene. The latter fraction 
was extracted with hot ethanol to give 2.55 g of a yellow solid (mp. 
141.degree.-144.degree.), identified as 4-[(1-pyrenyl)carbonyl]methyl 
ester. From the 1.62 g in fraction one of the eluted ketone, 1.01 g was 
obtained. 
4-[(1-Pyrenyl)carbonyl]benzoic acid, methyl ester (2.55 g; 7 mmol) was 
dissolved in 25 ml of benzene. A solution of 354 mg (6.4 mmol) of KOH in 5 
ml MeOH was added, and the mixture boiled. Precipitation of the potassium 
salt occurred. The mixture was extracted with water to give a yellow water 
layer which was acidified with dilute HCl to give a light yellow 
precipitate. Filtration gave 1.73 g (5 mmol) of the 
4-[(pyrenyl)carbonyl]benzoic acid. 
IR 3600-3350 cm.sup.-1 ; 1710 cm.sup.-1 ; 1665 cm.sup.-1. 
4-[(1-Pyrenyl)carbonyl]benzoic acid (1.73 g; 5 mmol) was refluxed with 10 
ml of SOCl.sub.2 and 3 drops of pyridine for 3 hours. A yellow/brown 
solution resulted. The excess thionyl chloride was evaporated and the 
residue triturated with ether/hexane and filtered to give the yellow acid 
chloride. 
IR: 1652 cm.sup.-1 ; 1770 cm.sup.-1. 
The acid chloride was dissolved in 60 ml of a benzene/chloroform mixture 
(50/10) and a mixture of tert-butyl hydroperoxide (5.2 mmol) and 
triethylamine (606 mg; 6 mmol) was added. After the addition the mixture 
was stirred for 2 hours at room temperature and then heated to 50.degree. 
for a few minutes. 
The solvent was evaporated and the residue dissolved in dichloromethane and 
chromatographed over silica gel. Elution with CH.sub.2 Cl.sub.2 gave a 
yellow band which oiled when the solvent contained no perester. Elution 
was continued in the dark to give 1.50 g of a dark yellow oil which, when 
heated with cyclohexane/benzene dissolved. After several days in the 
refrigerator light yellow crystals formed which analyzed as the Formula II 
perester. 
IR 1660 cm.sup.-1 (.nu.C.dbd.O ketone); 1770 cm.sup.-1 (.nu.C.dbd.O 
adjacent to perester). 
NMR (CDCl.sub.3) .delta.=1.43, s, 9H; CH.sub.3 ; .delta.=7.9-8.4 m, 13H; 
aromatic protons. 
Analysis: Calc. for C.sub.28 H.sub.22 O.sub.4 : C=79.55; H=5.25. Found: 
C=79.40; H=5.32. 
4-[(1-Pyrenyl)carbonyloxymethyl]Peroxybenzoic Acid, tert-Butyl Ester 
(Formula III) 
Pyrene-1-carboxylic acid (1 g, 4 mmoles) was converted into the dry 
potassium salt as previously described. A suspension of the potassium 
salt, 0.65 g of the bromomethyl Formula I perester (2 mmoles) and 60 mg of 
18 crown-6-(0.23 mmoles) was stirred for 60 hours in the dark. Evaporation 
and chromatography of the residue over silica gel with carbon 
tetrachloride/chloroform 1:1 as eluent gave 1.0 of yellow oil. 
Recrystallization from cyclohexane gave 0.82 g of crystals, 
m.p.=105.degree.-08.degree.. Another recrystallization raised the melting 
point 2.degree.. 
IR (KBr) 1750 cm.sup.-1 (.nu.C.dbd.O adjacent to perester), 1720 cm.sup.-1 
(.nu.C.dbd.O ester). 
NMR (CDCl.sub.3) .delta.=1.41, s, 9H, CH.sub.3 ; .delta.=5.56, s, 2H, 
CH.sub.2 ; .delta.=7.55-9.32, m, 13H aromatic protons with a doublet for 
one proton at .delta.=9.26, a doublet for another proton at .delta.=8.64 
and a doublet for 2 protons at .delta.=7.61 apparently as part of an AB 
system. 
Analysis: Calc; C=76.99; H=5.32. Found: C=76.81; H=5.39. 
Preparation of 4-[(9H-fluorenone-9-one-4-yl)carbonyloxymethyl]Peroxybenzoic 
Acid, tert-Butyl Ester (Formula IV) 
4-Carboxyfluorenone (896 mg, 4 mmoles) was treated was a suspension in 50 
ml of water with an equivalent amount of KOH solution (224 mg KOH; 
approximately 4 mmoles; pH of the solution close to 7.0). Filtration 
removed the small amount of undissolved solid and the obtained filtrate 
was evaporated to dryness. The so obtained potassium salt of the acid was 
thoroughly dried in an Abderhalen drying apparatus. A suspension was made 
of the potassium salt in 10 ml of dry acetonitrile and 0.65 of the 
4-bromomethyl Formula I perester (2 mmoles) and 60 mg of 18-crown-6(0.23 
mmoles) added. The mixture was stirred for 16 hr. in the dark while the 
progress of the reaction followed by TLC. Evaporation and chromatography, 
on silica gel with 1:1 carbon tetrachloride/chloroform as the eluting 
solvent gave 0.85 g of the perester as a yellow oil. Recrystallization 
from cyclohexane gave yellow crystals, mp. 102.degree.-104.degree.. 
IR (KBr): 1750 cm.sup.-1 (.nu.C.dbd.O adjacent to perester); 1725 cm.sup.-1 
(.nu.C.dbd.O ester); 1710 cm.sup.-1 (.nu.C.dbd.O ketone). 
Analysis: Calc; C=72.56, H=5.11. Found: C=72.65; H=5.15. 
NMR: (CDCl.sub.3) .delta.=1.4, s 9H, methyl; .delta.=5.4, s, 2H, methylene; 
.delta.=7.49-8.03, m, 11H aromatic protons, 
4-[(9-Anthryl)Carbonyloxymethyl]Peroxybenzoic Acid, tert-Butyl Ester 
(Formula V) 
Anthracene-9-carboxylic acid (888 mg., 4 mmol) was converted to the dry 
potassium salt by the same procedure as above. A suspension of the 
potassium salt in 10 ml of dry acetonitrile was stirred over the weekend 
with 0.65 g (2 mmol) of the bromomethyl Formula I perester, and 60 mg 
(10.23 mmol) of 18-crown-6. 
Evaporation and chromatography of the residue as before with carbon 
tetrachloride/chloroform (1:1) gave a yellow oil (0.82 g.). 
Recrystallization from cyclohexane gave 0.58 g of yellow crystals; m.p. 
118.degree.-119.degree.. 
IR (KBr) 1750 cm.sup.-1 (.nu.C.dbd.O adjacent to perester; 1720 cm.sup.-1 
(.nu.C.dbd.O ester). 
NMR: (d-benzene) .delta.=1.70, s, 9H, CH.sub.3 ; .delta.=5.28, s, 2H, 
CH.sub.2 ; .delta.=7.18-8.09, m, 13H, aromatic protons. 
EXAMPLE 2 
Decomposition of Peresters By Irradiation and Kinetics Thereof 
Photopolymerizations 
Photopolymerizations were carried out in sealed, degassed tubes (12 mm 
diameter) by irradiation at 366 nm with a high pressure mercury arc. After 
the irradiation period, the polymers obtained were precipitated in 
methanol and analyzed gravimetrically. 
Initiator concentrations for the bulk polymerizations were 
2.4.times.10.sup.-3 mol/l and in the case of solution polymerizations 
varied as specified in the particular experiment. 
Polymer molecular weights were determined in dichloromethane using a Waters 
Associate Model 440 GPC, and were calculated from elution volumes with 
reference to polystyrene standards. These standards were used for 
calibration at a solvent flow rate of 1.5 ml/min. and a polymer 
concentration of 1 mg/ml, by the method of U.S. Pat. No. 4,416,826. 
A series of peresters based on aromatic chromophores which absorb radiation 
at about 366 nm but which do not produce .eta.-.pi. * excited triplet 
states upon absorption are reported. Three of the peresters were 
synthesized from crucial intermediate bromomethyl Formula I perester by 
nucleophilic displacement of bromide ion. One of the Formula II peresters 
was synthesized directly from the appropriate carboxylic acid by a Friedel 
Crafts process. A series of routine nucleophilic displacement reactions is 
carried out on perester containing an appropriate leaving group without 
disturbing the --O--O-- bond of the perester unit. The physical and 
spectroscopic parameters of the peresters designed are reported in Table 
1. 
TABLE 1 
______________________________________ 
Characteristics of Formula II, III, 
IV and V Peresters 
Extinction 
Coefficient 
at 366 nm in 
CH.sub.2 Cl.sub.2 
Perester Structure 
1 mol.sup.-1 cm.sup.-1 
m.p..degree. C. 
Yield % 
______________________________________ 
Fluorenone perester 
2.73 .times. 10.sup.2 
102-104 79 
(Formula IV) 
Anthracene perester 
8.3 .times. 10.sup.3 
118-119 68 
(Formula V) 
Pyrene ketone perester 
1.0 .times. 10.sup.4 
122 65 
(Formula II) 
Pyrene ester perester 
1.82 .times. 10.sup.4 
107-109 80 
(Formula III) 
______________________________________ 
Uv spectra for the peresters synthesized are shown in FIG. 1. 
In every respect, the compounds reflect the photochemistry and the 
spectroscopy of the parent chromophore except that they are coupled to a 
tert-butyl perester functionality, either conjugated directly, or 
insulated by at least one methylene group included in the molecule. For 
these peresters to be useful photoinitiators they must absorb a light 
quantum and convert the derived energy to a bond homolysis reaction 
producing a tert-butoxy and an aryloxy free radical pair. G. Sosnovsky, 
Free Radical Reactions in Preparative Organic Chemistry, Mac Millan, New 
York, (1964); C. Ruchardt, Angew Chem. Intern. Edt. 9, 930 (1970). 
##STR3## 
The ability of the photoinitiators in Table 1 to produce free radicals 
which initiate vinyl polymerization was studied by measuring the rate of 
polymerization of methyl methacrylate and styrene under identical 
conditions of light intensity, initiator concentration, monomer 
concentration and temperature. The conversion versus time curves for the 
photopolymerization of methyl methacrylate using these initiators are 
given in FIG. 2. As is shown in FIG. 2, the rate of MMA 
photopolymerization decreases in the following seqeuence of perester 
structure: fluorenone&gt;pyrene ketoneZ&gt;pyrene ester&gt;anthracene. 
The photoinitiation of styrene initiated by each of these peresters was 
carried out similarly and is shown in FIG. 3. The rate of styrene 
photopolymerization decreased in the following order: pyrene ketone&gt;pyrene 
ester&gt;anthracene&gt;fluorenone. 
It is clear from FIG. 2 and FIG. 3 that the reactivity order of these 
aromatic peresters depends on the type of monomer being polymerized. Thus 
in the polymerization of MMA, the fluorenone perester, Formula IV, is the 
fastest, whereas in the polymerization styrene, it is the slowest. The 
rates of polymerization--at identical times for the two monomers, MMA and 
styrene, are compared in Table 2. 
TABLE 2 
______________________________________ 
Photo Polymerization (Bulk) of Vinyl 
Monomers Initiated by Various Peresters 
After 60 mins. 
After 3 hrs. 
MMA Rp Styrene Rp 
Initiator mol 1.sup.-1 sec.sup.-1 
mol 1.sup.-1 sec.sup.-1 
______________________________________ 
Pyrene ester perester 
1.1 .times. 10.sup.-4 
1.95 .times. 10.sup.-5 
(Formula III) 
Pyrene ketone perester 
1.54 .times. 10.sup.-4 
2.44 .times. 10.sup.-5 
(Formula II) 
Fluorenone perester 
1.92 .times. 10.sup.-4 
9.8 .times. 10.sup.-6 
(Formula IV) 
Anthracene perester 
5.63 .times. 10.sup.-5 
1.22 .times. 10.sup.-5 
(Formula V) 
______________________________________ 
Effects of Monomer and Perester Concentration on the Polymerization Rate 
The relationship between the rate of polymerization, Rp, and the 
concentration of the monomer is a function of both the structure of the 
initiator and the monomer being polymerized. Thus the Rp of MMA with 
fluorenone perester, Formula IV, as the initiator increases to a maximum 
as the monomer concentration is increased (to about 3.5M in benzene) and 
then levels off, as seen in FIG. 4. 
For styrene photopolymerization utilizing the same initiator, the 
concentration of styrene increases the rate of polymerization decreases, 
as seen in FIG. 5. 
In this instance either the excited state of the initiator is quenched by 
the monomer, or the monomer reacts with the initiator before bond 
homolysis occurs. 
Formula II and Formula III peresters present test cases by means of which 
the localization of energy in the excited state is assessed. The keto 
pyrene perester, Formula II, is quenced by styrene or at least the rate of 
polymerization decreases as the styrene concentration is increased, as 
seen in FIG. 6. 
The non-ketonic pyrene photoinitiator, Formula III, behaves more normally 
with the rate of styrene polymerization actually increases with 
concentration of monomer when it is used, as seen in FIG. 7. 
Styrene solutions of the non-ketonic pyrene initiator, Formula III, 
fluoresce while being irradiated in the monomer (styrene or MMA) for the 
purpose of studying them as photoinitiators, while the ketonic pyrene 
systems (Formula II) are non-emitting under identical conditions. 
FIG. 8 shows the rate of photopolymerization of styrene as a function of 
styrene concentration initiated by another .pi.-.pi. * photoinitiator, the 
anthracene derivatives, Formula V. As in the case of the pyrene perester, 
Formula III, the anthracene system is not quenched by styrene and the Rp 
increases with increasing styrene concentration. 
The effect of initiator concentration on the rate of polymerization is 
determined by the termination step of the radical chain as described by S. 
Gupta, I. Gupta and D. C. Neckers, J. Poly. Sci., Poly. Chem. Ed. 19, 103 
(1981), and is half order in initiator when termination is bimolecular in 
chain fragments. The rate, as a function of initiator concentration, also 
is a function of self-quenching of initiator excited states. Thus, the way 
the rate of polymerization of MMA could decrease as a function of pyrene 
perester concentration, as seen in FIG. 9, is if the excited state of the 
perester were quenched either by another perester ground state, or by a 
perester residue present in a polymer chain. Increasing the initiator 
fragments in the system increases the possibility of chromophore 
self-quenching and decreases the rate of initiation at higher 
concentrations of photoinitiator. 
Effect of Monomer and Perester Concentration on the Molecular Weight of the 
Polymer 
Table 3 and Table 4 show the effect of polymerization time and the 
structure of the aromatic perester photoinitiator on the molecular weight 
of the derived polymer, both in the case of methyl methacrylate and 
styrene. 
TABLE 3 
______________________________________ 
Photopolymerization of MMA (Bulk) Initiated by 
Various Peresters Molecular Weight Dependence on 
Initiator Structure and Polymerization Time 
Polymerization 
Mn 
Initiator Time (Mins.) 
(average) 
______________________________________ 
Pyrene ketone perester 
40 1.7 .times. 10.sup.4 
(Formula II) 70 2.23 .times. 10.sup.4 
Fluorenone perester 
10 3.15 .times. 10.sup.4 
(Formula IV) 25 3.87 .times. 10.sup.4 
40 4.15 .times. 10.sup.4 
70 5.0 .times. 10.sup.4 
Anthracene perester 
20 1.0 .times. 10.sup.5 
(Formula V) 35 1.3 .times. 10.sup.5 
70 7.9 .times. 10.sup.5 
Pyrene ester perester 
35 5.86 .times. 10.sup.4 
(Formula III) 45 7.0 .times. 10.sup.4 
60 7.9 .times. 10.sup.4 
100 1.58 .times. 10.sup.5 
______________________________________ 
TABLE 4 
______________________________________ 
Photopolymerization of Styrene (Bulk) 
Initiated by Various Peresters 
Photopolymerization 
Initiator Time (Hours) 
Mn 
______________________________________ 
Pyrene Ester Perester 
1 2.5 .times. 10.sup.4 
(Formula III) 3.15 5.6 .times. 10.sup.4 
5 6.3 .times. 10.sup.4 
Fluorenone Perester 
3 1.17 .times. 10.sup.5 
(Formula IV) 6 1.12 .times. 10.sup.5 
10.15 1.05 .times. 10.sup.5 
Pyrene Ketone Perester 
4.20 2.5 .times. 10.sup.4 
(Formula II) 6.15 3.1 .times. 10.sup.4 
10.30 1.4 .times. 10.sup.5 
Anthracene Perester 
1.30 1.78 .times. 10.sup.5 
(Formula V) 3 2.3 .times. 10.sup.5 
4.50 2.8 .times. 10.sup.5 
______________________________________ 
FIG. 10 shows that the molecular weight of the MMA formed from one of the 
aromatic photoinitiators is inversely proportional to the square root of 
the initiator concentration. 
FIG. 11 shows that the molecular weight of polystyrene formed from the 
anthracene perester photoinitiation increases as the monomer concentration 
increases. 
FIG. 12 shows the same relationship between styrene concentration and its 
polymer molecular weight where the initiator is the pyrene Formula III 
ester system. 
It is an anomoly that though the rate of polymerization of styrene with the 
Formula V initiator is 1 to 2 orders of magnitude larger than for the 
Formula III initiator, the Mn of polymers deriving from the Formula V 
initiator are higher than with the Formula III. The polycyclic aromatic 
hydrocarbons also serve as radical quenchers. Thus, these peresters also 
participate in non-initiating reactions with growing radical chains. This 
is demonstrated by polymerization on the appropriate monomer thermally 
with AIBN in the presence of the Formula II, III, IV and V initiators. All 
monomers except Formula IV terminate radical chains sufficiently to 
decrease the rate of polymerization by as much as 10% when present in 
concentrations equivalent to those of the AIBN initiator at 70.degree. C. 
To test the thermal stability of the perester, attempts are made to measure 
decomposition rates at 80.degree. C. in benzene. While Bz.sub.2 O.sub.2 
shows a decomposition rate comparable to the literature value, the 
peresters do not decompose at all at 80.degree. C. The thermal rates of 
decomposition in the dark are measured at 110.degree. C. in chlorobenzene 
and are comparable in value to the rates of decomposition of substituted 
tert-butyl perbenzoates. 
The peresters all provide efficient photochemical sources of free radicals. 
Important from a practical view is that their photodecomposition is 
controllable (effectively it can be tuned) by the absorption 
characteristics of the absorbing chromophore. 
EXAMPLE 3 
Synthesis of a photoinitiator, of a bisperester utilizing the same design, 
p'-tert-butylperoxycarbonyl-p-benzoyl-tert-butyl perbenzoate Formula VI: 
##STR4## 
The triplet energy of the benzophenone triplet state is approximately 
twice that of the bond dissociation energy of the O--O bond of the 
perester. Light absorption by the carbonyl group leads to dissociation of 
both peresters and a photoinitiator which is substantially more efficient 
than p-benzoyl-tert-butyl perbenzoate. When Formula VI is used as a 
photoinitiator for methyl methacrylate, it is more efficient than the 
monoperester benzophenone tert-butyl perbenzoate and, as measured by the 
rate of monomer polymerization, it also decomposes with a higher quantum 
yield. 
Synthesis of 4-Benzoyl(4'-tert-Butylperoxycarboxyl) tert-Butyl Perbenzoate 
(Formula VI) 
p, p'-Dimethylbenzophenone (7.0 g, 0.033 mol), sodium dichromate (27.0 g, 
0.10 mol), and 120 mL of water were placed in a 500-mL round-bottomed 
flask equipped with an unsealed mechanical stirrer. Concentrated sulfuric 
acid (75 mL, 1.4 mol) was added by means of a dripping funnel over a 
period of 30 min. After the addition of the acid was complete a reflux 
condenser was attached and the mixture heated to gentle boiling for 4 h. 
After cooling, the reaction mixture was added to 500 mL of ice water, 
filtered, and washed with copious amounts of cold water. The resulting 
crude acid was then transferred to a 1-L beaker, 200 mL of water 
containing 10 mL of sulfuric acid added, and the mixture digested on water 
bath for a short period of time to remove the excess chromium salts. After 
a subsequent filtration, the crude acid was purified by the addition of 
dilute NaOH, filtered to remove undissolved solids, acidified, and 
filtered. For structure confirmation, the purified acid, which has a 
melting point of which agreed with that reported in Koelsch, et al., J. 
Am. Chem. Soc., 67, 2041 (1945). 
The compound (Formula VII), benzophenone p, p'-dicarboxylicacid, 
##STR5## 
was converted to the diacid chloride (Formula VIII) by refluxing overnight 
with an excess of thionyl chloride. After removal of the excess thionyl 
chloride in vacuo and recrystallization of the product from 
hexane/dichloromethane, 85% of the dichloride (mp 133.degree. C.; lit. 
132-133) was obtained. 
##STR6## 
The bisperester (Formula VI) was obtained as follows: Formula VIII (0.74 g, 
0.0024 mol) was dissolved in 40 mL of dry ether and 20 mL of 
dichloromethane. The reaction mixture was stirred mechanically at room 
temperature for 15 min and cooled with an ice/salt bath. Tert-butyl 
hydroperoxide (0.5 mL, 0.005 mol) in 2 mL benzene and triethylamine (07 
mL, 0.005 mol) in 10 mL of ether were added slowly in the dark. The 
reaction mixture was held at ice temperatures for two hours, then allowed 
to warm to room temperature, and the solvent removed at room temperature 
in vacuo. The product was purified by column chromatography in the dark on 
silica gel. The crude bisperester was dissolved in dichloromethane and 
then eluted with dichloromethane (recovered yield 45%). The purified 
compound (mp 114.degree. C.) gave one spot on TLC (dichloromethane), 
.epsilon.366 nm=170 l/mol; IR: 1680, 1770 cm.sup.-1 ; NMR: 1.05 s (t-but), 
aromatic A.sub.2 B.sub.2. 
The rate of decomposition of the bisperester was studied by irradiation in 
benzene as per the techniques we have reported previously; .epsilon.366 
nm=1.74.times.10.sup.4 L/ms). 
The physical and spectral parameters of import for each of the studied 
peresters are outlined in Table 5 below. 
TABLE 5 
__________________________________________________________________________ 
Spectral Properties of Specific Peresters 
E.sub.t 
.epsilon. 366 nm 
Compound .phi. 
(kcal/mol) 
(CH.sub.2 Cl.sub.2) 
__________________________________________________________________________ 
##STR7## 0.94 67.7 121.5 
##STR8## 1.2 170 
##STR9## 127.6 
##STR10## 0.75 216.4 
##STR11## 0.80 67.4 108.1 
##STR12## 10.7 
__________________________________________________________________________ 
The polymerization of methyl methacrylate was carried out with the 
initiators in Table I under identical conditions of concentration, light 
intensity, monomer concentration, and temperature. All irradiations were 
carried out with a mercury arc source equipped with filters to isolate the 
366-nm line to prevent direct polymerization of the monomer even though, 
in at least the case of one of the peresters, this might not necessarily 
be the most ideal wavelength at which it should be irradiated. The 
conversion/time curves for photopolymerization of MMA with the various 
peresters are compared in FIG. 13. The bisperester (Formula VI) is a 
better initiator than the corresponding monoperester even though the 
spectral characteristics of the initiator chromophores are quite the same. 
Some differences appear in the monoperesters as a function of the 
substituent. The rates of polymerization with the substituted initiators 
decreased, as shown in FIG. 13. 
The photopolymerization of styrene, initiated by each of the peresters 
derived from benzophenone, was carried out similarly. FIGS. 13 and 14 
compare benzophenone-type peresters as photoinitiators for the monomers 
MMA and styrene. As observed from the MMA data, even very different 
monoperesters give a similar rate of polymerization. The diperester, on 
the other hand, gives the highest rate, while the p-bromomethyl perester 
is much the slowest. 
The polymerization of styrene initiated by each of the benzophenone 
derivatives is much slower than is the polymerization of MMA under the 
same conditions. This is due in part to the fact that the triplet energy 
of styrene is about 62 Kcal/mol and therefore lies much below the E.sub.t 
of the benzophenone chromophore. Since energy transfer is generally 
diffusion controlled, in bulk styrene monomer a high percentage of the 
excited states formed by light absorption into the benzophenone 
chromophore are quenched before the energy gets to the perester bond and 
dissociation can take place. MMA is also more reactive than styrene. For 
example, the chain transfer constant with carbon tetrachloride for styrene 
is 9.2.times.10.sup.-3 l/mol s for styrene, but 0.5.times.10.sup.-3 l/mol 
s for MMA at 60.degree. C. While k.sub.p for MMA=315 l/mol s, the k.sub.p 
of styrene is 74.+-.5 l/mol s at 25.degree. C. 
Irradiation of the p-benzoyl-tert-butyl perbenzoate produces three 
different radicals: the benzoyloxy radical, the aryl radical, and the 
tert-butoxy radical. Continued irradiation of the formed polymer increases 
molecular weight by dimerization reations deriving from the reactions of 
the benzophenone carbonyl function with the polymer. There is also some 
effect of initiator structure on the molecular weight of the polymer 
formed and the polymerization rate under identical conditions. This is 
shown by the data in Table 6. 
TABLE 6 
__________________________________________________________________________ 
Rate of Photopolymerization Rp of MMA (Bulk) 
Initiated by Various Benzophenone Peresters; 
Time 30 min, Peresters Concentration 
2.4 .times. 10.sup.-3 mol/1 
Initiator Rp (1 mol.sup.-1 S.sup.-1) 
M.sub.n 
__________________________________________________________________________ 
##STR13## 1.14 .times. 10.sup.-3 
2.5 .times. 10.sup.4 
##STR14## 7.9 .times. 10.sup.-4 
3.15 .times. 10.sup.4 
##STR15## 6.3 .times. 10.sup.-4 
4.67 .times. 10.sup.4 
##STR16## 7.0 .times. 10.sup.-4 
1.61 .times. 10.sup.4 
##STR17## 6.0 .times. 10.sup.-4 
2.33 .times. 10.sup.4 
##STR18## 9 .times. 10.sup.-5 
1.9 .times. 10.sup.5 
__________________________________________________________________________ 
Effect of the Monomer and the Polymer Concentration on the Rate of 
Polymerization 
The relationship between the rate of polymerization Rp and the 
concentration of MMA in benzene is shown in FIG. 15 for the disperester. A 
linear plot was obtained for Rp vs. [M] with a slope of 0.43 with a range 
of monomer concentrations from 1-6 mol. The behavior of the diperester and 
p-benzoyl-tert-butyl perbenzoate were similar. FIG. 16 traces the effect 
of monomer concentration of Rp for styrene. Unlike the polymerization of 
MMA, whose rate increases with monomer concentration, the rate of styrene 
polymerization decreases with increasing concentration of the monomer. 
Just as with the monoperester, the triplet state of the diperester is also 
quenched by the aromatic monomer, styrene. This is explained by the 
following mechanism: 
##STR19## 
The lower rate of polymerization for reactions initiated by the 
bromomethyl perester (Formula IX) 
##STR20## 
derives from the formation of radicals of different reactivity from that 
perester. Rather than dissociation of the perester O--O bond to form the 
incipient benozoyloxy radical and tert-butoxy radical, in the case of the 
p-bromomethyl perester, dissociation to the benzyl radical and bromine 
atom is preferred. These are both less reactive and rates of initiation 
therefore retarded. This observation is confirmed by product studies in 
this system, which indicate that the major products are bibenzyls with the 
perester function remaining intact. Photofragmentations of 
p-halobenzophenones have been the subject of numerous studies. 
p-Chloromethylbenzophenone, for instance, cleaves at the benzylic 
carbon-chlorine bond. See H. G. Heine, H. J. Rosenkranz and H. Rudolph, 
Angew. Chem. Int. Ed. English 11, 974 (1972). The products from this 
system is identical to those we are suggesting formed with the bromomethyl 
perester, e.g., (See Table 7 below). 
TABLE 7 
______________________________________ 
Thermal Polymerization of MMA 
Bulk at 70.degree. C. (in the Dark) 
Initiator Rp (1 mol.sup.-1 8.sup.-1) 
______________________________________ 
##STR21## 3.5 .times. 10.sup.-5 
##STR22## 2.0 .times. 10.sup.-5 
AIBN 3.9 .times. 10.sup.-4 
##STR23## 
______________________________________ 
The rate of polymerization is related to the initiator concentration by a 
square-root dependence. This is shown in FIG. 17 for the monoperester and 
in FIG. 18 for the bisperester. In both cases the monomer was MMA and the 
solvent was benzene. 
The data in FIGS. 15-18 show that the polymerization rate is half order in 
photoinitiator and first order in monomer. At high monomer concentration, 
the rate of polymerization increases because all of the radicals formed 
from the initiator are used to initiate polymerization. At lower monomer 
concentration, radicals are wasted in recombination in the solvent cage or 
by termination of fragments outside the cage before they can initiate 
polymer formation. 
The data for the monoperesters and the diperesters are shown in FIG. 19 
with styrene as the monomer. The rates of polymerization are given by the 
data in Tables 7 and 8. In the thermal reaction, the molecular weight of 
the polymer is unaffected by reaction time and it decreass gradually as 
the concentration of the perester used for initiation is increased. This 
indicates that, in the thermal reaction, the perester acts normally and as 
a chain transfer reagent for the growing polymer chain, whereas in the 
photochemical reaction the initiator fragment can react as a crosslinking 
entity as long as the light remains on. 
TABLE 8 
__________________________________________________________________________ 
Effect of Perester Structure on Rate of Polymerization 
of Styrene (Bulk) and the Molecular Weight of 
Polymer Obtained; [I] = 2.4 .times. 10.sup.-3 mol/1 
Polymerization 
Rp 
Initiator time (h) 
(1 mol.sup.-1 S.sup.-1) .times. 10.sup.-5 
Mn .times. 10.sup.5 
__________________________________________________________________________ 
##STR24## 3.15 4.45 6.45 1.30 3.00 5.00 
2.25 2.6 2.56 1.65 1.65 1.97 
2.95 2.95 2.95 2.95 2.8 3.0 
__________________________________________________________________________ 
FIG. 20 compares the thermal polymerization of MMA initiated by AIBN and 
both the monoperester and diperester. As anticipated from the known 
activation energies for thermolysis of tert-butyl perbenzoate and AIBN, 
the perbenzoates are much less effective initiators at 70.degree. C. 
FIG. 21 shows that the molecular weight of the polymer produced is 
inversely proportional to the square root of the initiator concentration 
for the photoinitiated polymerization of both MMA and styrene. This is 
explained by chain transfer of the growing polymer chain on the O--O bond 
of the perester. This situation is more severe for the disperester than 
for the monoperester, as shown in FIG. 21. 
FIG. 22 shows the relationship between the molecular weight of polystyrene 
produced and the concentration of the monomer. The molecular weight 
increases as the concentration of the monomer increases in the 
photochemically initiated reaction and this corresponds with the decreased 
rate of polymerization reported previously. 
Table 9 shows that the molecular weight of polystyrene formed from the 
photoinitiated reaction increases with conversion. This derives from 
photochemical crosslinking of the formed polymer by processes which 
involve the benzophenone triplet state of the carbonyl-capped polymer 
chain. The molecular weight of the polystyrene produced from the 
diperester is lower than that produced from the monoperester, due to chain 
transfer on the remaining perester functionality. 
##STR25## 
The above detailed description of the present invention is given for 
explanatory purposes. It will be apparent to those skilled in the art that 
numerous changes and modifications can be made in the preferred 
embodiments of the invention described above without departing from the 
scope of the invention. Accordingly, the whole of the foregoing 
description is to be construed in an illustrative and not in a limitative 
sense, the scope of the invention being defined solely by the appended 
claims.