CA1317046C - Block polymers of methacrylates - Google Patents

Abstract

ABSTRACT

Novel methacrylate ester block polymers comprising both a hydrolyzable and a non-hydrolyzable ester functionality are capable of being partially hydrolyzed and neutralized to yield the corresponding methacrylic acid and methacrylic acid salt (ionomer) derivative. The compositions are usefully employed in the preparation of thermoplastic elastomers, adhesives and laminating film 36,843-F

Description

~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~

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.

iB

- 2a - ~ 3 ~ 1a~ $

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 ~

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 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~

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~ ~

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-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-

Claims (6)

1. 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 methacrylic acid and salts of methacrylic acid.

2. A block copolymer according to claim 1 comprising 2-ethylhexyl methacrylate.

3. 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 from 6 to 20 carbons in the ester group, and one or more tertiary alkyl esters in methacrylic acid having from 4 to 7 carbons in the ester group;
terminating the anionic polymerization and selectively hydrolyzing the tertiary alkyl methacrylate ester functionality of the block copolymer to form methacrylic acid functionality.

4. A process according to claim 3 wherein the tertiary alkyl methacrylate ester functionality is selectively hydrolyzed by contacting the block copolymer with an acid at a temperature from 50 to 150°C.

5. A process according to claim 3 wherein the tertiary alkyl ester of methacrylic acid is polymerized at a temperature from 0 to 35°C.

6. A process according to claim 3 wherein the aryl or alkyl methacrylate ester is 2-ethylhexyl methacrylate and the tertiary alkyl ester is tertiary butyl methacrylate.