Note: Descriptions are shown in the official language in which they were submitted.
64693-4239
~3~70~6
BLOCK POLYMERS OF METHACRYLATES
The present invention relates to block polymers
comprising methacrylic acid and derivatives of
methacrylic acid as well as a method for the preparation
of such block polymers. In the past, carboxylic acid
containing polymers have been typioally synthesized by
the direct ~ree radical polymerization of various
carboxylic acids, as well as ester, or anhydride
derivatives thereof with various vinyl comonomers. The
corresponding carboxylic salt derivatives or ionomers
are typically prepared by partial or complete
neutralization of carboxylic acid groups with various
basic compounds. Previously known synthetic routes have
resulted;in the random placement of such acid or ionic
groups along polymer backbones. It would be desirable
to provide similar polymeric structures having
controlled composition and architecture, predictable
molecular weights and narrow molecular weight
distributions.
It is pre~iously known to use anionio
polymerization techniques for the preparation of block
polymers having controlled morphology and composition as
C~36,843-F
": . . . .
` - 2 - ~3~7~4~
64693-4239
well as architecture and predictable molecular weights, as well
as narrow molecular weight distributions.
~ oreoverl it is previously known that tertiary butyl
methacrylate may be polym~rized by anionic techniques. All
methacrylate block copolymers of methyl methacrylate/ethyl
methacrylate, methyl methacrylate/n-butyl methacrylate and
methyl methacrylate/t-butyl methacrylate were disclosed in
Polymer Preprints 26(1) 1985, pg. 247-248.
According to one aspect of the present invention there
is provided a block copolymer comprising, in polymerized form,
one or more aryl or alkyl methacrylate esters having from 6 to 20
carbons in the ester group and one or more monomers selected from
the group consisting of methacrylate acid and salt of methacrylic
acid.
According to a further aspect of the present invention
there is provided a process for preparing a block copolymer
comprising, in polymerized form, one or more aryl or alkyl
methacrylate esters having from 6 to 20 carbons in the ester
group and methacrylic acid, the steps of the process comprising:
preparing a methacrylate ester block copolymer by polymerizing
under anionic polymerization conditions one or more aryl or alkyl
methacrylate esters, other than tertiary alkyl methacrylate
esters, having rom 6 to 20 carbons in the ester group, and one
or more tertiary alkyl esters of methacrylic acid having from
to 7 carbons in the ester group; terminating the anionic poly-
merization; and selectively hydrolyzing the tertiary alkyl
methacrylate ester functionality of the block copolymer to ~orm
methacrylic acid functionality.
2 -
iB
- 2a - ~ 3 ~ 1a~ $
64693-4239
In a preferred embodiment these block polymers
correspond to the formula AB~BA)n (I) or BA~AB)n (II~ wherein:
A is a homopolymer or copolymer comprising, in
polymerized form, one or more moieties selected from the group
consisting of hydrolyzable esters of methacrylic acid having
from 2 to 7 carbons in the ester group, methacrylic acid and
salts of methacrylic acid; a copolymer of more than one such
hydrolyzable ester of methacrylic acid, methacrylic acid or a
salt thereof; or a block or random copolymer of one or more
hydrolyzable esters of methacrylic acid, methacrylic acid or
salts thereof with one or more copolymerizable comonomers/
lB 2a -
- . . ~ . -
~ 3 ~
-3- 64693-4239
B is a homopolymer comprising, in polymerized
form, a non-hydrolyzable methacrylate ester moiety
having from 6 to 20 carbons in the ester group; a
copolymer comprising more than one such methacrylate
ester; or a block or random copolymer of one or more of
the foregoing non-hydrolyzable methacrylate esters with
one or more copolymerizable comonomers, and
n is a number from 0 to 6.
Anionic polymerization techniques are well
known and previously disclosed in the art. See, for
example, M. Morton, "Anionio Polymerization Principles
and Practice", Academic Press ~1983). Brie~ly, a living
anion is prepared by use of a reactive anionic
polymerization initiator. Suitable initiators include
the well known metals such as sodium and lithium as well
as the more preferred organo metal compounds
particularly lithium compounds. A particularly
20 preferred monofunotional anionic initiator is 1,1-
diphenyl-3-methylpentyl lithium. Preferred di~unctional
anionic initiators include those compositions disclosed
in U.S. Patents 4,172,190; 4,196,154; 4,172,100;
4,182,818; 4,196,153; 4,200,718; 4,205,Q16; 4,201,729;
25 and 3,663,634,
.Ç-36,843-F -3-
`~
.
_4_ 1 3 ~ 7 ~
The polymers of the present invention may be
prepared according to any suitable technique. Simple
repeating diblock and triblock copolymers may be
prepared by sequential addition of the respective
monomers. Suitably, a mono~unctional organometallic
anionic polymerization initiator may be contacted with
the monomer or monomers comprising block A of Formula I
tor block B o~ Formula II~ under anionic polymerization
condition~. The polymerization is continued and the
monomer or monomers comprising the remaining blocks are
polymerized. Symmetrical multiblock polymers may be
produced by contacting the living polymer anion with a
coupling agent of functionality n~1.
An alternative technique ~or preparing such
symmetrical multiblock polymer~ utilizes a
multifunctional organometallic anionic polymerization
initiator of functionality n+l. The monomer or~
monomers for block B (~or formula I polymer~) or for
block A (~or formula II p~lymers) are contacted with
the polymerization initiator under anionic
polymerization conditions, and after complete
polymerization, the remaining monomer~ are added to the
reactor and polymerized. I~ vinylaromatic or diene
monomers are employed in the invention, their
polymerization must precede the polymerization of any
e~ter~ of methacrylic acid.
By later applied conventional technique~, the
hydrol~zable e~ter functionality of the block polymer
may be altered to yield acid or neutral ~alt
derivative~ having an ordered placement o~ ~unctional
groups.
36~843-F -4-
~ '
,
~5~ 7~6
A central discovery according to the present
invention i the fact that certain methacrylate e~ters
form de irable block copolymerq which surpriqingly are
relatively stable under skandard acid catalyzed
hydrolysi~ reactions. The re~ulting polymers are also
pre~erably relatively rubbery thereby making the
products well adapted for use in elastomeric or
adhe~ive application Thus, one o~ the methacrylate
eqter msietie~ initially present in the polymers of the
preqent invention may be hydrolyzed to ~orm the
corre~ponding acid functionality and further treated to
~orm additional derivatives without at the same time
substantially a~ecting the non-hydrolyzable
1~ methacry1ate e~ter functionality. Becauqe the
methacrylio polymer blocks are highly qaturated, the
products o~ the invention in a preferred embodiment are
highly resiqtant to environmental degradation due to
ultraviolet light.
As used herein, the term "non-hydrolyzable"
re~er~ to the fact that one methacrylate ester
functio~ality of the polymer~ iq not substantially
hydrolyzed under conditionq leading to sub3tantial
hydrolysi~ of other methacrylate e3ter functionality in
the ~ame polymer. That is, greater than 50 mole % of
one methacrylate ester functionality should remain
under conditions wherein greater than 50 mole % of
another methacrylate ester functionality in the polymer
i9 hydrolyzed. Preferably, greater than 75% of one
methaorylate e~ter functionality is hydrolyzed. Most
preferablyt substantially all o~ one methacrylate ester
Yunotionality is unhydrolyzed while 3ubstantially all
o~ another methacrylate ester ~unctionality in the same
polymer i~ hydrolyzed.
36,843-F -5-
-6~ '7 ~ ~ ~
As the non-hydrolyzable methacrylate sster,
either aryl or alkyl esters of from 6 ~o 20 oarbons are
preferred, a most preferred non-hydrolyzed methacrylate
e~ter is 2-ethylhexylmethacrylate. The block polymers
o~ the invention may be in the form of diblock-,
triblock-, or star block polymers and may have
standard, random, or tapered geometry. Those block
polymer~ posqes~ing elastomeric properties preferably
have glass transition temperatures less than about 25C,
most preferably le s than about 0C.
The block polymers of the present invention may
be prepared utilizing conventional anionic
polymerization conditions and initiator~. Certain of
the monomers are preferably reacted at temperatures
Prom -100 to -10C. However, certain of the
hydrolyzable methacrylate e~ters, especially the t-
alkyl methacrylates, may be reacted at temperatures up
to about 35C or even higher. In the first step, a
living pQlymer anion is prepared by anionic
polymerization techniques and retained in solution for
u~e in the next ~tep. Suitably, t;his polymer i~
compriqed of either the non-hydrolyzable methacrylate
or the hydrolyzable methacrylate. The initial
polymerization i9 preferably conducted in a qolvant,
particularly an inert, aprotic, organic liquid such as
toluene, hexane ? tetrahydrofuran, etc. A pre~erred
~olvent is tetrahydrofuran.
Next, the living polymer anion is oontacted
with the remaining methacrylate e~ter monomer under
anionic polymerization condition~ so as to prepare a
second polymer block. The re3ulting block polymer must
comprise at lea3t one block of a non-hydrolyzable
36,843-F -6-
~'7~l~g
--7--
methacrylate ester and one block o~ a hydrolyzable
methacrylate e~ter.
Additional copolymerizable monomers may be
included in the polymerization process i~ desired in
order to modify the resulting block copolymer
propertie~. The copolymerizable monomers may be
incorporated as separate blocks or added concurrently
to the polymerization, resulting in the formation of
tapered block copolymers Suitable copolymerizable
monomers include monovinylidene aromatic monomers such
as styrene9 a-methyl~tyrene, t-butyl styrene, etc.;
acrylonitrile; N,N-dialkyl acrylamides; conjugated
dienes; reaotive coupling agent~ such as divinyl
benzene, ethylene glycol dimethacrylate; etcO Certain
of the ~oregoing monomers may be employed to modify
speci~ic polymer properties. For example, t-butyl
tyrene containing polymers posse~ls enhanced ~olubility
in aliphati¢ 301vents such a hexane. However, because
the basicity of the living anion is aP~ected by the
addition of methacrylate ~unctionality, the above
described additional copolymeriza~le monomer~ are
generally incorporated into the polymer prior to
polymerization o~ either the hydrolyzable methacrylate
or the non-hydrolyzable methacrylate. In addition, it
may be deqirable to employ a protectin~ ~roup such as
1,1-diphenylethylene in order to prevent reaction of
such ~unctionality with the carbonyl functionality of
later added methacrylate monomers. For the foregoing
reason , pre~erred polymers according to the invention
comprise only hydrolyzable methacrylate ester moieties
or derivati~es thereof and non-hydrolyzable
methacrylate ester moieties~
36, 843 F 7-
.
-8- 131~g
The addition of the methacrylate ester~ to the
living anion has been found to be bene~icially advanced
by the addikion to the reaction mixture of a polar,
dry, aprotic organic compound in a quantity sufficient
to modify the polymerization rate o~ the reaction.
Suitable polar, aprotic~ organic compounds are
exempli~ied by the cyclic ether~, particularly
tetrahydrofuran. Preferably, the polar, aprotic,
organic compound i3 employed in an amount from 0.5 to
go weight percent, most preferably from 25 to 75 weight
percent based on ~otal qolvent welght~
A~ter- complete polymerization o~ the various
monomers, the living polymer is terminated by any
~uitable technique. Recovery and work up are easily
performed utilizing previou~ly di~olosed techniqueQ
such a~ precipitation and devolatilization.
To praduce the highly desired methacrylic acid
containing block polymers of the invention, the
hydrolyzable methacrylate ester functionality of the
initially prepared block polymers is hydrolyzed. As an
aid in such hydroly~is, it i3 de~irable that the
hydrolyzable methacrylate e~ter be selected to provide
ea~e of operating condikions and good selectivity to
the methacrylic acid derivative upon hydrolyQi~. Thus,
pre~erred hydrolyzable methyl acrylate esters are those
capable of addition under anionic polymeri~ation
conditions to a living anion9 pre~erably at a
temperature from 0C to 35C, and capable of removal
under non-aqueous hydrolysi~ reaction conditions.
Preferred hydrolyzable methacrylate esterQ for use in
the present invention are the tertiary alkyl
methacrylate~ due to the previou~ly mentioned ability
to employ such monomers at polymerization temperatures
36,843-F -8-
,
, : ' '. .
'' :, ~ '
~ 7~l~6
on the order of 0C to about 35C. The u3e of such
elevated reaction temperatures i9 believed to be due to
the ~tability of the t-alkyl methacrylate enolate anion
at ~uch temperatures.
Suitably, the hydroly~i~ is conducted by
heating the resulting polymer containing hydrolyzable
methaorylate ester group~, optionally in the presence
o~ a catalytic amount of an acid. Such heating results
in alkyl-oxygen cleavage and the release of relatively
volatile aliphatic reaction products and the formation `
of the desired methacrylic acid functionalized block
polymer~. Suitable acid3 for the above hydrolyqis
include the aromatic sulfonic acidq, especially toluen0
sulfonio acid. It is underqtood that hydrolysiq of
only a portion of the eqter functionality may be
obtained according to the pre~ent method if deqired.
Preferre~ temperaturecl on the order of 50 to 150C are
employed. A cluitable ~olvent selected to maintàin
solubility of the polymer may be employed to lead to
higher degree3 of hydrol~sis. Examples of suitable
solvents for t`he hydrolyqis include toluene, xylene,
chlorobenzene, etc., ~or use particularly where the
amount of an incorporated hydrolyzable methacrylate
ester ~unctionality is less than about 10 percent by
weight. Block polymers containing additional amounts
o~ hydrolyzable methacrylate ester ~unctionalit~ are
preferably maintained in ~olution by the use of more
3 polar ~olvents such a~, for example, alcohols. In a
deqirable embodiment, the hydrolysis reaction i~
conducted quantitatively in order to be able to more
accurately control the ~inal acid or ion content of the
block polymer.
36,843-F -9-
~o ~3~ 7~
In addition to the catalytic acid hydrolysis,
the methacrylate ester Punctionality may also be
hydrolyzed by the use of an alkali metal superperoxide
quch a~ potassium ~uperperoxide in a suitable solvent
such as a mixture of dimethyl ~ulfoxide and
tetrahydrofuran. This technique has been taught ~or
example by R. D. Allen, et al., Coulombic Interactions
in Macromolecular Systems, A.C.S. Symposium Series,
#302, pg. 79-92 (1986). The resulting hydrolyzed
product may be acidified with small amounts o~ an acid
such as hydrogen chloride to improve ~olubility~ Due
to the difficulty in handling such reagents, the latter
method is not preferred for commercial use.
Because 4-7 carbon membered alkanes which are
the alkanes resulting from hydrolysi~ of tertiary
butyl-, or 2-methyl-2-butyl-, and other 4~7 carbon
tertiary alkyl methacrylate esters are easily
volatilized, theqe compounds are the preferred tertiary
alkyl methacrylate esters ~or use in the present
invention. A highly preferred hydrolyzable, tertiary
alkyl methacrylate is t-butyl methacrylate.
Where de~ired, the acid functionality o~ the
methacrylic acid containing block polymers may be
neutralized by contacting with a suitable basic
reagenk. Examples include ammonium and metal
hydroxide particularly the alkali metal hydroxides.
Particularly desirable metal salts of methacrylic acid
include ~odium, potassium, aluminum9 tin, zinc, or
nickel ~alts. By ~uch tec~nique~, ionomeric block
copolymers containing methacrylic acid salt moieties
are prepared.
36,843-F 10-
3~7~
Although any de~ired amount of neutralization
of the acid functionality may be employed, in a
pre~erred embodiment ~rom 1 to 75 percent by weight of
the functional moietie~ of the block polymer are the
neutral 9alt9 thereof. In other re pect~, the
neutralization process to produce ionomeric
functionality in the requlting block polymers i~ as
previously known in the art.
Having described the invention, the ~ollowing
example~ are provided as further illustrative and are
not to be construed a~ limiting.
Exam~le~ 1-6
Block copolymer~ (1A, a diblock utilizing 1,1-
diphenyl-3-methylhexyl lithium initiator and lB a
tribloek using 1,4-dilithio-1,1,4,4-tetraphenyl butane
initiator) ompri~ing ~-butyl methacrylate and 2-
ethylhexylmethacrylate in the amount~ indicated inTable I were prepared and characterized. A portion o~
each was then subjected to hydroly~is to yield the
corre~ponding block copolymers (2A, 2B) containing 2-
ethylhexylmethacrylate and methacrylic acid moietiesO
Potas3ium containing block ionomer~ (3A, 3B) were
~ub~equently prepared by neutralization of a portion of
the block copolymer~ (2A and 2B) with potassium
hydroxide.
3 U~ri~l~
t-Butyl methacrylate wa~ obtained ~rom Rohm-
Tech, and 2-ethylhexylmethacrylate was obtained from
Polyscience~ Inc. Both monomer~ were stirred over
~inely ground calcium h~dride ~or 2-3 days, followed by
di3tillation under reduced pres~ure. The monomers were
36,843-F 11
:
-12- 13~ 7~
then tran~Eerred to a clean, dry bottle via a double
ended needle and stored at -20C under a nitrogen
atmosphere. Immediately before use, the monomers were
di~tilled under reduced pre sure from a trialkyl
aluminum or dialkyl aluminum hydride complex. In some
cases, the final purification of the monomer was
accomplished by complexing the calcium hydride purified
monomer with the aluminum compound in one vessel, and
then passing this solution throu~h a column of
activated basic alumina (Fisher). The clear effluent
was then degassed under reduced pressure or under a
nitrogen purge. The trialkyl aluminums and dialkyl
aluminum hydrides were obtained from the Ethyl
Corporation aJ 25 weight percent solutions in hexane.
t-butyl lithium wa~ obtained from the Lithco Division
of FMC as a ~olution in cyclohexane (1.4M). The
polymerization solvent was tetrahydrofuran (THF)
(Fisher eertified grade) which was distilled under dry
nitrogen immediately before use from the purple
sodium/benzophenone ketyl.
Difugotional Initiator Formation
The difunctional initiator that was employed
was 1,4-dilithio-1,1,434-tetraphenylbutane which was
prepared in a 250-ml one-necked round-bottomed ~lask
equipped with a glass-encased magnetic stirring bar,
and a rubber septum wired on with copper wire for a
tight seal. The flask had been flamed with a nitrogen
purge and waY kept under an atmosphere of 6-8 psi dry
nitrogen. A four-fold molar excess o~ lithium wire
(alpha Inorganics, Ventron) waA placed quickly into the
flask and a new septum wired on. The reaction ~lask
wa3 again flamed under a dry nitrogen purge, and kept
under 6-8 psi nitrogen until cool. The solvent (THF)
36,843-F -12-
~ 3~ 7~
-13-
was then transferred to the flask via a double ended
needle. The solvent was then degassed with a nitrogen
purge and a calculated volume of 1,1~diphenyl ethylene
was syringed into the reaction vessel. The reaction
mixture was ~tirred under a 6-8 psi nitrogen atmosphere
at room temperature for about 5 hours. The bright red
initiator qolution was removed by syringe.
Pol~merization
The polymerization procedure ~or the
preparation o~ block polymer IA was by the sequential
a~dition technique utilizing the monofunctional
initiator~ diphenyl-3-methylpentyl lithium (DMPL),
prepared by reacting 1,2-diphenyl ethylene with t-butyl
lithium in hexane solvent. t-Butyl methacrylate waY
reacted first.
The procedure using the di~unctional initiator
was very similar. The solution o~ initiator was added
dropwise until the red color o~ the initiator was
~tabilized, indicating that final impurities in the
polymerization reactors were titrated, then the
calculated volume of initiator was charged. The
monomers were then added dropwi~e to the initiator
solution, with the center block being polymerized
fir~t.
All polymerizationQ were conducted in
tetrahydro~uran solvent at -78C. Polymerization o~
each block wa~ conducted for 20 minutes. The
polymerlzation~ were then terminated with degas~ed
methanol and the polymer~ precipitated in
methanol/water (80/20) and dried in vacuo overnight at
ca. 60C. Amounts of the variou~ monomers employed and
36,843-F 13
.
-14~
the re ulting polymer compo3itions are liqted in Table
Io
TA~LE I
Ex. Type E~MAl (g) TBMA2 (g~ Wt. ratio3 x(10 3)4
lA 14 .10 . 4S . 3/97 --
211~ 14 . 4 0 . 6 2/96/;~ 136
3 n 13.8 1.2 4/92~d. 149
4 n 13 . 2 1. 8 6/88~6 187
5 n 12 . 6 2 . 4 a/~l4/s 128
12 . 0 3 . 0 10~80~10 168
1 2-othylhexyl methac~ylate
2 t-butyl methacrylate
3 ~eight ratio TBMA/E~MA or TEIMA~E~MA/TBUA
4 number ave~ags molecular ~ight
ExamP.~
A triblock polymer wa9 made b~ sequential
polymcrization uqing DMPL initiator to polymerize 0.45g
tert-butylmethacrylate first then 14.10g 2-
ethylhexylmethacrylate. Instead of terminating the
diblock polymer, 0.45g more tert-butyImethacrylate was
added to make a 3/94~3 TBMA/EHMA/TMBA compo~ition. The
number average molecular weight a3 determined by GPC
using polystyrene calibration was~113,700.
Example~ 8~
The poly(t butyl methacrylate~ containing bloek
polymer~ of Example3 1-6 were hydroly2ed with acid
36~843-~ -14~
.
,
~3~7~ ~
-15-
catalysis at mild temperature~ (80C). Typically, 5-10
weight percent (based on t-butyl ester content) of p-
toluene qulfonic acid was used. The block polymers
were dis301ved in toluene (Fisher, certified grade~ at
ca. 5% solids with the acid and heated to 80 for 8
hourq. A ~low nitrogen purge through the headspace
helped facilitate the removal of the volatile
isobutylene product of the hydroly is. After
hydrolysiq, the polymers were precipitated in cold
methanol (-78C) and dried in vacuo overnight at 100C.
The re~ulting block copolymer~ were 2A, 2-
ethylhexylmethacrylate/methacrylic acid block
copolymer, Example 8, and 2B, methacrylic acld/2-
ethylhexylmethacrylate/methacrylic acid blockcopolymer, Examples 9-13.
Neutralization
Examples 14-1
The bloek-ionomer~ wera formed by
neutralization of the acid-containing polymers of
Examples 8-14 with methanolic potassium hydroxide (KOH~
Fi~her certi~ied, 0.1 N). The acid polymers were
dis~olved in THF at ca. 5~ solid~ and titrated at
ambient temperature and atmosphere to a phenolphthalein
endpoint. To avoid the possibility of indicator
oontamination in the polymers that were to be tested, a
known amount of the acid containing polymer was
titrated to a phenolphthalein endpoint, and the volume
of ba~e required to titrate a larger amount of the
polymer was ba~ed on that titration. The ionomers were
then precipitated ln methanol (-78C~, or film~ were
cast directly from the neutralization qolvent a~ter
filtration and dried in vacuo overnight at 100C. The
36,843 F -15-
-16-
resulting block copolymers were 3A, 2 ethylhexyl
methacrylate/~CH-C(CH3)(C00-K+)t-ionomer blook
copolymer9 Example 14, and 3B, tCH-C(CH3)~C00-K+)~/ 2-
ethylhexylmethacylate/tCH-C(CH3)(C00-K+)t ionomer block
copolymer, Examples 15-19.
Characterization
. .
Molecular weight and molecular weight
distributions of the precursors and acid-containing
polymers were determined by gel permeation
chromatography (GPC). A Water~ 590 GPC equipped with
columns o~ 500 Angstroms, 103 Angstroms, 104 Angstrom ,
105 Angstromq wa~ utilized. Both poly(methyl
methacrylate) and poly~tyrene standard~ (Polymer
Laboratories) were used in these characterizations.
Fourier transform infrared spectroscop~ (FTIR)
wa~ performed on a Nicole-t MX-1 ~pectrometer. Nuclear
magnetic resonance spectroscopy (NMR) wa~ per~ormed on
a Bruker ~P-270 high resolution spectrometer. The
result~ con~irmed the assigned identities o~ the
polymers.
36,843-F -16-
