Process for the anionic polymerization of acrylic monomers and optionally of vinyl comonomers

A process for the polymerization of acrylic monomers and optionally of vinyl comonomers using (i) an initiator of formula (I): EQU R--M (I) in which M denotes a metal selected from the group consisting of alkali metals and alkaline earth metals and R denotes a straight-chain or branched alkyl radical containing 2 to 6 carbon atoms or an aryl radical, and (ii) at least one non-nitrogenous macrocyclic complexing agent. The polymerization process is used to make products of acrylic polymers having a narrow distribution of molecular masses.

BACKGROUND OF THE INVENTION 
The present invention relates to a process for the polymerization of 
acrylic monomers and optionally of vinyl comonomers using an initiator of 
formula (I): 
EQU R--M (I) 
in which M denotes a metal chosen from the group selected from alkali 
metals and alkaline earth metals and R denotes a straight-chain or 
branched alkyl radical containing 2 to 6 carbon atoms or an aryl radical. 
Processes for the polymerization of acrylic or methacrylic monomers, such 
as alkyl acrylates and methacrylates, as well as processes for the 
copolymerization of acrylic or methacrylic monomers with vinyl comonomers, 
in the presence of various initiators, especially those of formula (I) 
given above are known. Examples of such initiators are sec-buthyllithium, 
napthalenesodium, 1,4-disodio-1,1,4,4-tetraphenylbutane, 
diphenylmethylpotassium, diphenylmethylsodium, 1'-methylstyryllithium, 
1,1-diphenyl-3-methylpentyllithium and others, such as tertiary 
alcoholates of lithium and compounds containing trimethylsilyl groups. 
In polymerizing acrylic monomers and optionally non-acrylic comonomers, it 
is known to use additives or various catalysts, especially cocatalysts or 
additives containing, for example, sources of fluoride, cyanide or acid 
ions or consisting of a Lewis acid. Finally, the use of an alkali metal or 
alkaline earth metal salt of an inorganic acid is known from European 
Patent Application No. 0,185,641. 
On the other hand, French Pat. No. 2,201,304 describes the polymerization 
of vinyl monomers, especially of alkyl or cycloalkyl acrylates and 
methacrylates, with anionic initiators in an organic solvent medium and in 
the presence of a nitrogenous macroheterocyclic complexing agent in a 
quantity that is at least equimolar relative to the anionic initiator. 
This patent further describes the polymerization of methyl methacrylate at 
-78.degree. C. and +25.degree. C. in benzene or tetrahydrofuran. The 
French certificate of addition No. 2,398,079, attached to this patent, 
describes a variation in which the polymerization occurs in the absence of 
a solvent. In the case of methyl methacrylate, the polymerization is 
carried out at -40.degree. C. and -80.degree. C. respectively and leads to 
polymers having number average molecular masses of 150,000 and 400,000, 
respectively. 
SUMMARY OF THE INVENTION 
It has now been discovered that it is advantageous to carry out the 
polymerization of acrylic or methacrylic monomers, where appropriate with 
vinyl comonomers, by polymerizing the acrylic or methacrylic monomers in 
the presence of (i) initiator of formula (I) R--M and (ii) a 
non-nitrogenous macrocyclic complexing agent. In formula (I), M denotes a 
metal selected from the group consisting of alkali metals and alkaline 
earth metals and R denotes a straight chain or branched alkyl radical 
containing 2 to 6 carbon atoms or an aryl radical. 
The present inventors have observed that the use of a non-nitrogenous 
macrocyclic complexing agent in addition to the initiator of formula (I) 
R--M offers remarkable advantages. This complexing agent enables a 
narrower distribution of masses of the resulting polymers and copolymers 
and polymers having predetermined structures and masses to be prepared. 
Without being bound by theory, it is believed that the use of a 
non-nitrogenous macrocyclic complexing agent in the process according to 
the invention enables the reactivity of the initiator to be controlled. It 
is believed that the complexing agent advantageously reduces the 
reactivity of this initiator and makes it selective towards the double 
bond of the acrylic or methacrylic monomer rather than towards the ester 
group of this monomer. 
The above and other features and advantages of the present invention will 
be made more apparent from the following description of the preferred 
embodiment. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Examples of the non-nitrogenous macrocyclic complexing agents that can be 
used as additives within the scope of the present invention include cyclic 
polyethers, which are also known as crown ethers, and cyclic 
polythioethers, such as macrocyclic polyethers. The macrocyclic ring of 
the polyether preferably contains at least 14 carbon and oxygen atoms. 
Each oxygen atom of the ring is preferably separated from the other oxygen 
atoms of the ring by two or three carbon atoms. Such macrocyclic 
polyethers have already been described in U.S. Pat. No. 3,687,978. 
More precise examples are in particular: 
1,4,7,10,13,16-hexaoxacyclooctadecane, 
2,3,11,12-dibenzo-1,4,7,10,13,16-hexaoxacyclooctadeca-1,11-diene, 
2,3,12,13-dibenzo-1,4,11,14-tetraoxacycloeicosa-2,12- diene, 
2,3,12,13,22,23-tribenzo-1,4,11,14,21,24-hexaoxacyclotriaconta-2-12-22-trie 
ne, 
2,2,7,7,12,12,17,17-octamethyl-21,22,23,24-tetraoxaquaterene, 
2,3-benzo-1,4,7,10,13-pentaoxacyclopentadeca-2-ene, 
2,3-(4'-t-butyl)-1,4,7,10,13,16-hexaoxacyclooctadeca-2-ene, 
2,3,9,10-dibenzo-1,4,8,11-tetraoxacyclotetradeca-2,9-diene, 
2,3,32,33-dibenzo-1,4,7,10,13,16,19,22,25,28,31,34,37, 
40,43,46,49,52,55,58-eicosaoxacyclohexaconta-2,32-diene, 
2,3,16,17-dibenzo-1,4,15,18-tetraoxacyclooctacosa-2,16-diene, 
2,6,13,17-tetraoxatricyclo[16.4.0.0.sup.7,12 ]docosane, 
2,5,8,15,18,21-hexaoxatricyclo[20.4.0.0.sup.9,14 ]hexacosane, 
2,5,12,15,18-pentaoxatricyclo[17.4.0.0.sup.6,11 ]tricosane, 
2,6,13,16,19-pentaoxatricyclo[18.4.0.0..sup.7,12 ]tetracosane, 
9,10-benzo-2,5,8,11,14,17-hexaoxabicyclo[16.4.0]-docosa-9-ene, 
2,3,9,10-dibenzo-1,4,8,11,14,16-hexaoxacyclooctadeca-2,9-diene, 
2,3,11,12-dibenzo-1,4,7,10,13,16,18-heptaoxacycloeicosa-2,11-diene, 
2,3,13,14-dibenzo-8-pentamethylene-1,4,7,9,12,15,18-heptaoxacycloeicosa-2,1 
3-diene, 
2,3,13,14-dibenzo-1,4,7,9,12,15,18,20-octaoxacyclodocosa-2,13-diene, 
2,4-(1',8'-naphthylene)-1,5,8,11,14-pentaoxacyclohexadeca-2-ene. 
Acrylic acid esters, methacrylic acid esters, dialkyl(meth)acrylamides, 
acrylonitrile, methacrylonitrile and their mixtures may advantageously be 
employed as acrylic monomers in the process according to the invention. 
The acrylic monomer is preferably an alkyl methacrylate having an alkyl 
radical containing 1 to 18 carbon atoms. The alkyl radical can be either 
substituted or unsubstituted. Examples of such alkyl methacrylates include 
methyl methacrylate, 2,2,2-trifluoroethyl methacrylate and butyl 
methacrylate. The alkyl methacrylate can also preferably be a secondary or 
tertiary alkyl acrylate having an alkyl group containing from 3 to 8 
carbon atoms. The alkyl group can be either substituted or unsubstituted. 
More particularly, such secondary or tertiary alkyl acrylates include 
isobutyl acrylate, tert-butyl acrylate and 2-ethylhexyl acrylate. 
A vinyl comonomer such as, for example, butadiene, isoprene, styrene, 
vinylnaphthalene, 2-vinylpyridine, 4-vinylpyridine, alpha-methyl-styrene 
and tert-butylstyrene can be advantageously employed as a non-acrylic 
comonomer in the process according to the invention. 
In the process according to the invention, the proportion of 
non-nitrogenous macrocyclic complexing agent relative to the initiator may 
vary widely. For example, this quantity of the complexing agent may be in 
a large excess relative to the molar quantity of the initiator. The 
quantity of the complexing agent may also be equal to or less than the 
molar quantity of the initiator. The complexing agent is preferably in a 
molar proportion relative to the initiator which is at least equal to 0.5 
and which may range up to approximately 5. 
According to one embodiment of the process according to the invention, the 
polymerization reaction may be carried out in the presence, in addition, 
of an alkali metal or alkaline earth metal salt. Preferably, a halide or a 
boride of such a metal such as, for example, sodium tetraphenylboron or 
lithium chloride is used. This salt may be employed in a molar proportion 
ranging up to approximately 2 relative to the initiator. 
The process according to the invention enables polymers and copolymers 
having ends of chains functionalized by at least one group, such as a 
carboxylic group (COOH), to be prepared and block copolymers to be formed. 
In the process according to the invention, the polymerization or the 
copolymerization is preferably carried out in the absence of moisture and 
oxygen, and in the presence of at least one solvent. The solvent is 
preferably chosen from aromatic solvents, such as benzene and toluene, 
tetrahydrofuran, diglyme, tetraglyme, orthoterphenyl, biphenyl, decalin or 
tetralin. 
As regards the polymerization of copolymerization temperature, it may vary 
between approximately -78.degree. C. and 0.degree. C. 
The process according to the invention enables the preparation of a whole 
range of homopolymers and block copolymers generally having a number 
average molecular mass of between approximatley 10,000 and 300,000 and a 
polydispersity index generally between approximately 1.1 and 4. The block 
copolymers include, as new polymers, particularly the following: polymers 
containing at least one poly(2,2,2-trifluoroethyl methacrylate) block and, 
where appropriate, a polymer block of a monomer other than 
2,2,2-trifluoroethylene methacrylate. These polymers are defined by a 
polydispersity of between approximately 1.1 and 4 and by a number average 
molecular weight of the poly(2,2,2-trifluoroethyl methacrylate) block 
preferably between approximately 10,000 and 300,000. 
Such polymers are well suited for use in the production of photoresists for 
printed circuits. For such use, a solution is prepared at a concentration 
between about 4% and 20% by weight of the polymer in an inert solvent such 
as ketone. This solution is then deposited onto a substrate, such as 
silicium, before the solvent is evaporated to allow the formation on the 
substrate of a polymer film having a thickness of, for example, in the 
range of about 0.2 to 2 microns. Other polymers formed by the process of 
the present invention include polymers containing at least one secondary 
alkyl acrylate polymer block, the alkyl group containing from 3 to 10 
carbon atoms, and, where appropriate, a polymer block of a monomer other 
than a secondary alkyl acrylate. These polymers are defined by a 
polydispersity of between approximately 1.1 and 4 and by a number average 
molecular weight of the poly(secondary alkyl acrylate) block preferably 
between approximately 10,000 and 100,000.

The process according to the invention is illustrated by the following 
non-limiting examples. 
EXAMPLE 1 
0.37 gram (0.75.times.10.sup.-3 mole) of 
2,3,11,12-dibenzo-1,4,7,10,13,16-hexaoxacyclooctadeca-1,11-diene marketed 
by JANSSEN CHIMICA under the name "dibenzo-18-crown-6" is introduced under 
a nitrogen atmosphere into a round-bottomed flask which has been dried 
beforehand. 
150 ml of previously dried tetrahydrofuran are added and a 0.2 molar 
solution of naphthalenesodium in tetrahydrofuran is added dropwise, with 
stirring, until a red color appears that persists. When this color is 
reached, 7.5 ml of the naphthalene-sodium (1.5.times.10.sup.-3 mole) are 
added. The mixture is cooled to a temperature of -78.degree. C. using a 
mixture of acetone and solid carbon dioxide and after 1/2 an hour, while 
still maintaining the temperature at -78.degree. C., 90 ml of a solution 
containing 0.057 mole of 2-ehtylhexyl acrylate in tetrahydrofuran, which 
has previously been dried using triethylaluminum (1 ml of a 1M solution in 
benzene) and distilled, are added. 
The reaction is stopped after 5 hours by adding 5 ml of methanol, after 
which the solvent is removed. Poly(2-ethylhexyl acrylate) is obtained with 
a yield of 76%. 
The analysis of the polymer by gel permeation chromatography gives the 
following values: 
M.sub.n (number average molecular mass): 10,800 
M.sub.w /M.sub.n (polydispersity index): 1.7 
In the present example as well as in the following examples, the 
tetrahydrofuran was dried beforehand over sodium/benzophenone. 
EXAMPLE 2 
0.252 gram (0.0007 mole) of "dibenzo-18-crown-6" and 29 mg of lithium 
chloride (0.0007 mole) are introduced under a nitrogen atmosphere into a 
round-bottomed flask which has previously been dried. 150 ml of previously 
dried tetrahydrofuran are added dropwise with stirring, and a 0.2 molar 
solution of naphthalenesodium in tetrahydrofuran is added, with stirring, 
until a red color appears that persists. When this color is reached, 3.75 
ml of the naphthalenesodium solution (0.00075 mole) are added. 
The mixture is cooled to a temperature of -78.degree. C. using a mixture of 
acetone and solid carbon dioxide and after 1/2 hour, a tetrahydrofuran 
solution containing 5 g of 2-ethylhexyl acrylate (0.028 mole), which has 
previously been dried using triethylaluminum and distilled, is added. 
After maintaining the temperature at -78.degree. C. for 3 hours, during 
which period the red color persists, the temperature is raised to 
-20.degree. C. and maintained at this level for 20 hours (a yellow color 
appears). The reaction is then stopped by adding 5 ml of methanol, after 
which the solvent is removed. 4.9 g of the polymer are obtained (yield: 
98%). 
The analysis of the polymer by gel permeation chromatography gives the 
following values: 
______________________________________ 
M.sub.n = 19,500 
M.sub.w /M.sub.n = 2.1 
______________________________________ 
EXAMPLE 3 
0.277 g (0.0008 mole) of "dibenzo-18-crown-6" is introduced, under a 
nitrogen atmosphere, into a round-bottomed flask which has previously been 
dried. 
150 ml of previously dried tetrahydrofuran are added thereto and a 0.2 
molar solution of naphthalenesodium in tetrahydrofuran is added dropwise, 
with stirring, until a red color appears that persists. When this color is 
reached, 4 ml of the naphthalenesodium solution (0.0008 mole) are added. 
The mixture is cooled to a temperature of -78.degree. C. in a mixture of 
acetone and solid carbon dioxide and after 1/2 an hour, while still 
maintaining the temperature at -78.degree. C., 90 ml of a solution 
containing 0.046 mole of 2,2,2-trifluoroethyl methacrylate in 
tetrahydrofuran, which has previously been dried using triethyl aluminum 
(1 ml of a 1M solution in benzene) and distilled, are added. 
The reaction is stopped after 4 hours by adding 5 ml of methanol, after 
which the solvent is removed. 7 g of the polymer are obtained to produce a 
yield of 100%. 
The analysis of the polymer by gel permeation chromatography gives the 
following values: 
______________________________________ 
M.sub.n = 26,000 
M.sub.w /M.sub.n = 1.23 
______________________________________ 
EXAMPLE 4 
The experiment in Example 3 is repeated with the following exception: 
before introducing the "dibenzo-18-crown-6", 29 mg of lithium chloride 
(0.0007 mole) are introduced into the round-bottomed flask. After 4 hours 
of reaction, 7 grams of poly(2,2,2-trifluroethyl methacrylate) are 
obtained to produce a yield of 100%. 
The analysis of the polymer by gel permeation chromatography gives the 
following values: 
______________________________________ 
M.sub.n = 96,000 
M.sub.w /M.sub.n = 1.22 
______________________________________ 
EXAMPLE 5 
10.sup.-3 mole of "dibenzo-18-crown-6" is introduced, under a nitrogen 
atmosphere, into a round-bottomed flask which has previously been dried. 
One liter of previously dried tetrahydrofuran and a living chain member of 
poly(methylmethacrylate) initiated by diphenylmethylsodium (the latter at 
a rate of 10.sup.-3 mole, as a molar solution in tetrahydrofuran) are 
added. The mixture is cooled to a temperature of -78.degree. C. using a 
mixture of acetone and solid carbon dioxide and a solution of 25 g of 
2,2,2-trifluoroethyl methacrylate in tetrahydrofuran, which has previously 
been dried and distilled, are then added. The reaction is stopped after 4 
hours by adding methanol, after which the solvent is removed. A copolymer 
containing methyl methacrylate/2,2,2-trifluoroethyl methacrylate blocks is 
obtained with a yield of 100%. The analysis of the copolymer by gel 
permeation chromatography gives the following values: 
______________________________________ 
M.sub.n (total) = 33,000 
M.sub.w /M.sub.n = 1.33 
M.sub.n (methyl methacrylate block) = 
4,500 
m.sub.n (2,2,2-trifluoroethyl methacrylate block) = 
28,500 
______________________________________ 
EXAMPLE 6 
5.times.10.sup.-3 mole of "dibenzo-18-crown-6" is introduced, under a 
nitrogen atmosphere, into a round-bottomed flask which has previously been 
dried. 1 liter of previously dried tetrahydrofuran and 1.2.times.10.sup.-3 
mole of diphenylmethylsodium as a molar solution in tetrahydrofuran are 
added. The mixture is cooled to a temperature of -78.degree. C. using a 
mixture of acetone and solid carbon dioxide and a solution of 150 g of 
2,2,2-trifluoroethyl methacrylate in tetrahydrofuran, which has previously 
been dried and distilled, is then added. The reaction is stopped after 3 
hours by adding methanol, after which the solvent is removed. The polymer 
is obtained with a yield of 90%. 
The analysis of the polymer by gel permeation chromatography gives the 
following values: 
______________________________________ 
M.sub.n = 185,000 
M.sub.w /M.sub.n = 1.33 
______________________________________ 
Such a polymer is well suited for the production of photoresists for 
printed circuits. 
EXAMPLE 7 
0.2.times.10.sup.-3 mole of "dibenzo-18-crown-6" is introduced, under a 
nitrogen atmosphere, into a round-bottomed flask which has previously been 
dried. 120 ml of previously dried tetrahydrofuran and 0.2.times.10.sup.-3 
mole of naphtahlenesodium as a molar solution in tetrahydrofuran are 
added. The mixture is cooled to a temperature of -78.degree. C. using a 
mixture of acetone and solid carbon dioxide and a solution of 5 g of 
isobutyl acrylate in tetrahydrofuran, which has previously been dried and 
distilled, is then added. The reaction is stopped after 4 hours by adding 
methanol, after which the solvent is removed. Poly(isobutyl acrylate) is 
obtained with a yield of 90%. 
The analysis of the polymer by gel permeation chromatography gives the 
following values: 
______________________________________ 
M.sub.n = 37,000 
M.sub.w /M.sub.n = 2.0 
______________________________________ 
EXAMPLE 8 
The experiment in Example 7 is repeated with the following exception: 
before introducing the "dibenzo-18-crown-6", 0.4.times.10.sup.-3 mole of 
sodium tetraphenylboron is introduced into the round-bottomed flask. After 
4 hours of reaction, the poly(isobutyl acrylate) is obtained with a yield 
of 100%. 
The analysis of the polymer by gel permeation chromatography gives the 
following values: 
______________________________________ 
M.sub.n = 36,000 
M.sub.w /M.sub.n = 3.6 
______________________________________ 
EXAMPLE 9 
10.sup.-3 mole of "dibenzo-18-crown-6" is introduced, under a nitrogen 
atmosphere, into a round-bottomed flask which has previously been dried. 
400 ml of previously dried tetrahydrofuran and 0.2.times.10.sup.-3 mole of 
naphthalenesodium as a molar solution in tetrahydrofuran are added. The 
mixture is cooled to a temperature of -78.degree. C. using a mixture of 
acetone and solid carbon dioxide and a solution of 5 g of isobutyl 
acrylate in tetrahydrofuran, which has previously been dried and 
distilled, is then added. The reaction is stopped by adding methanol, 
after which the solvent is removed. Poly(isobutyl acrylate) is obtained 
with a yield of 81%. 
The analysis of the polymer by gel permeation chromatography gives the 
following values: 
______________________________________ 
M.sub.n = 23,000 
M.sub.w /M.sub.n = 1.5 
______________________________________ 
EXAMPLE 10 
0.2.times.10.sup.-3 mole of lithium chloride and 0.4.times.10.sup.-3 mole 
of "dibenzo-18-crown-6" are introduced, under a nitrogen atmosphere, into 
a round-bottomed flask which has previously been dried. 100 ml of 
previously dried tetrahydrofuran and 0.2.times.10.sup.-3 mole of 
naphthalenesodium as a molar solution in tetrahydrofuran are added. The 
mixture is cooled to a temperature of -78.degree. C. using a mixture of 
acetone and solid carbon dioxide and a solution of 5 g of 
methacrylonitrile in tetrahydrofuran, which has previously been dried and 
distilled, is then added. The reaction is stopped after 1 hour by adding 
methanol, after which the solvent is removed. The polymer is obtained with 
a yield of 62%.