Anionic polymerization of acrylates and methacrylates

Details Anionic polymerization of acrylates and methacrylates Anionic polymerization of acrylates and methacrylates

1999-06-08

2001-07-17

Pezzuto, Helen L. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S089000, C526S090000, C526S123100, C526S170000, C526S319000, C526S326000, C526S328500, C526S329700

Reexamination Certificate

active

06262213

ABSTRACT:

The present invention relates to a process for preparing homopolymers, copolymers-or block copolymers which comprise acrylates or methacrylates, by anionic polymerization, and to the use of the resultant reaction mixtures for free-radical polymerization.
Processes for preparing polymers from acrylates and methacrylates by anionic polymerization have been known for a long time. A review is given, for example, in J.M.S.-Rev. Macromol. Chem. Phys., 1994, C34, pp. 243-324.
Examples of proven effective initiators for anionic polymerization are systems based on organolithium compounds, alkoxyalkoxides and lanthanoid metallocene compounds. EP-A 0 524 054 describes the polymerization of, for example, 2-ethylhexyl acrylate in the presence of diphenylmethyllithium as initiator and CH
3
(OCH
2
CH
2
)
2
OLi as additive. JP-A 2258808, JP-A 6306112 and JP-A 6093049 describe the polymerization of acrylates and methacrylates using lanthanoid metallocenes, such as (C
5
Me
5
)
2
Sm(THF)
2
.
All known anionic polymerization processes are dependent on the use of an inert solvent, inter alia to prevent premature chain termination. Tetrahydrofuran (THF), toluene, ethylbenzene or any desired mixture of these components very frequently form a suitable reaction medium for anionic polymerization. A disadvantage in the use of the latter solvents, in particular in samarocene-initiated anionic polymerization, is the pronounced gel formation which occurs primarily at the end of the polymerization and which hinders straightforward work-up and therefore also scaling up an industrial process. In addition, this phenomenon frequently leads to broad molecular weight distributions and incomplete monomer conversion.
It is an object of the present invention to develop a reaction medium for anionic polymerization, which medium does not have the disadvantages mentioned and furthermore gives reproducibly good polymerization results independently of the initiator system and the size of the batch which are used.
We have found that this object is achieved by means of a process for preparing reaction mixtures comprising homopolymers, copolymers or block copolymers, and of homopolymers, copolymers and block copolymers, which comprise acrylates or methacrylates or acrylates and methacrylates, by anionic polymerization, in which olefinically unsaturated compounds which are not acrylate derivatives or methacrylate derivatives are employed as solvent or as solvent components. In a preferred embodiment, vinyl-aromatic compounds are employed as solvent or solvent component.
In principle, suitable unsaturated olefinic compounds are those which are described by the formula (I):
(R
a
)(R
b
)C═C′(R
c
)(R
d
)  (I),
where:
R
a
, R
b
, independently of one another, are hydrogen, unsubstituted or substituted, straight-chain or branched, C
1
-C
14
-alkyl such as methyl, ethyl, isopropyl, n-propyl, isobutyl, n-butyl, tert-butyl, unsubstituted or singly- or multiply substituted C
6
-C
14
-aryl, such as phenyl or tolyl, unsubstituted or substituted C
3
-C
7
-cycloalkyl, such as cyclopropyl, cyclopentyl or cyclohexyl, C
2
-C
10
-alkenyl, such as vinyl, allyl, butenyl or butadienyl, and
R
c
, R
d
, independently of one another, are hydrogen, unsubstituted or substituted, straight-chain or branched, C
1
-C
14
-alkyl such as methyl, ethyl, isopropyl, n-propyl, isobutyl, n-butyl, tert-butyl, unsubstituted or singly- or multiply substituted C
6
-C
14
-aryl, such as phenyl or tolyl, unsubstituted or substituted C
3
-C
7
-cycloalkyl, such as cyclopropyl, cyclopentyl or cyclohexyl, C
2
-C
10
-alkenyl, such as vinyl, allyl, butenyl or butadienyl, or, together with C′, are unsubstituted or singly- or multiply-substituted cyclopropyl, cyclopentyl or cyclohexyl.
Examples of suitable olefinically unsaturated compounds are ethylene, propylene, 1-butene, 2-butene, butadiene, 1,4-hexadien, 1,5-hexadiene and 1-octene. The radicals R
a
, R
b
and/or R
c
, R
d
and the radicals R
a
, R
c
and/or R
b
, R
d
can respectively form an unsaturated carbocycle or heterocycle, such as cyclopentene, cyclohexene, cyclopropylidene, cyclopentylidene or fulvene.
Examples of vinylaromatic compounds particularly suitable as solvents or solvent components for the novel process are styrene, &agr;-methylstyrene, o-, m- and p-methylstyrene and any desired mixtures of the abovementioned vinylaromatic compounds. Styrene, and also butadiene and ethene, are preferably used as solvent or as solvent component, styrene being particularly preferred. If vinylaromatic compounds and/or the unsaturated compounds as claimed in claim
1
form a component of a solvent system, then the proportion of this component, based on the total amount of solvent, is preferably in the range from 5 to 99% by volume.
In addition, tetrahydrofuran, diethyl ether, dimethoxyethane, toluene, ethylbenzene, cyclohexane or any desired mixture of the abovementioned solvents may be employed, for example, as further solvent constituents. Suitable solvent systems are, for example, styrene/tetrahydrofuran, styrene/toluene and styrene/tetrahydrofuran/ethylbenzene.
In principle, however, any inert, aprotic, polar or non-polar solvent is suitable as further solvent component.
Using the novel process, it is possible to obtain either homopolymers or copolymers or block copolymers from vinyl monomers having polar groups. Homopolymers, copolymers and block copolymers containing acrylates or methacrylates are preferably prepared. It is possible, for example, to prepare copolymers consisting of acrylates or methacrylates or of a mixture of acrylates and methacrylates. Furthermore, both two-block and multiblock copolymers consisting of acrylates and/or methacrylates are obtainable, for example n-butyl acrylate-2-ethylhexyl acrylate or methyl methacrylate-2-ethylhexyl acrylate block copolymers. For the purposes of the invention, homopolymers, copolymers and block go copolymers are not only the isolated polymers, but also the reaction mixtures obtained using anionic polymerization and comprising homopolymers, copolymers or block copolymers.
Examples of suitable acrylate monomer building blocks are C
l
-C
20
-alkyl acrylates, C
1
-C
10
-alkyl acrylates being preferred and C
1
-C
8
-alkyl acrylates being particularly preferred. The alkyl radicals may be either linear or branched or form a ring or contain ether groups or amino groups and be partially or completely substituted with halogen. Examples of compounds which may be employed are 2-ethylhexyl acrylate, 2-ethylpentyl acrylate, 2-ethylbutyl acrylate, 2-methylhexyl acrylate, 2-methylpentyl acrylate, 2-methylbutyl acrylate, 2-methylpropyl acrylate, 3-ethylhexyl acrylate, 3-ethylpentyl acrylate, 3-methylhexyl acrylate, 3-methylpentyl acrylate, 3-methylbutyl acrylate, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, isopentyl acrylate, n-hexyl acrylate, n-decyl acrylate, 4-tert-butylcyclohexyl acrylate, stearyl acrylate, lauryl acrylate, ethyl diglycol acrylate, 2-ethoxyethyl acrylate, 2-methoxyethyl acrylate and dimethylaminoethyl acrylate. Other suitable acrylates are those having an olefinically unsaturated ester moiety, such as dihydrodicyclopentadienyl acrylate, allyl acrylate, 3- or 4-vinylbenzyl acrylate and 2-allyloxyethyl acrylate, and those with aromatic groups,-such as phenyl acrylate and 2-phenoxyethyl acrylate, or vinylaromatic groups. Preference is given to methyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, dihydrodicyclopentadienyl acrylate and allyl acrylate, in particular 2-ethylhexyl acrylate.
Examples of suitable methacrylate monomer building blocks are alkyl methacrylates having from 1 to 20 carbon atoms, preferably from 1 to 10 and in particular from 1 to 8 carbon atoms, in the ester group. The alkyl radials may be either linear or branched or form a ring, and may be partially or completely substituted with halogen, or may contain ether or amino groups. Examples of groups which may be used are 2-ethylhexyl methacrylate, 2-ethylpent

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