CA1041692A - Process for preparing an elastomeric copolymer block - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Fully esterified carboxylic acids, such as the lower alkanol derivatives of benzoic and pivalic acid, are used as linking agents in a polar solvent medium to link together polymer blocks in forming an elastomeric copolymer block A-B-A, such as styrene-1,3-butadiene-styrene. The ester linking agent is very effective even in polar solvent media such as are used to form the A and/or B polymer blocks.

Description

; 1~9~9~ 2505 This invention relates to a process for preparlng an elastomeric block copolymer of the ~eneral formula A-B-A, where A is a non-elastomeric polymer block derived from an alkenyl-aromatic compound with an average molecular weight of between 200 and 100,000 and B is an ela tomeric polymer block with an average molecular weight of between 20,000 and 500,000 of the type comprising by polymerizing one or more monomers into a -~
i ~ .
`~ non~èlastomeric polymer block by means of a monofunctional -anionic inltiator, then polymerizing one or more monomers into 110 an ela~tomeric polymer block joined to the said non-elastomeric ~¦~polymer block, and linklng the resulting block copolymer to `;~
form the A-B-A bloak copolymer in a polar medium by the addltion of a linking agent. The invention also relate~ to artefacts `~
;~~ consisting wholly or partly of such elastomeric block copolymers.
~ Such block copolymers have elastomexlc properties in the un~ulcanized state, unli~e many other synthetic elasto-mers, which can only be used as elastomers after a vulcanization treatment. Another advantage o~ such block copoLymers is that they can be processed by methods that are commonly~used for ther~oplastic materlals, such as, for example, extru~io~ and i`njectlon moulding.
The usual block copolymers of this type are made up ~ ~.
of an alkenyl-aromatic compound e.g. styrene or a-methyl styrene :-~
~and a conjugated diene e.g. l~oprene or butadiene-1,3, ` ;~
~ Block copolymers of this type can be prepared by polymerizing one or more monomers lnto a non-elastomeric polymer block by means of a monofunctional anionic initiator, 3 then polymerlzing a monomer or monomers lnto an elastomeric `~
'~ polymer block joined to the non-ela~tomeric polymer block, and J30 finally linking the resulting block copolymers to form the B-A block copolymer by the addition of a linktng agent.
.~' i - 2 - ;

` Such a method of preparation is commonly carried out :~
in a non-polar solvent. In special instances however, it may be useful, or necessary to carry out the block copolymeri~ation : -completely or partly in a polar medium. Thus in the preparation ~ ~-5 of A-B-A b10ck copolymers whose non-elastomeric polymer blocks .~-~
`~ ~ A are made of ~-methyl styrene, it i9 necessary to carry out . .
:~ . the polymerization of the a-methyl styrene ih the presence of .. ~.
.,~ . . . .. .
j . a polar solvent to achieve a sufficiently rapid polymerization ;~ of this monomer~
. 10 Simllarly the preparation of A-B-A ~l~ck copolymers . .`
who~e elastomeric polymer block B is made of a styrene/butadiene ~. :
: copolymer ox of.polybutadiene, in w~ich the incorporation of the~butadiene in the polymer chain is pr~dominantly 1,2- and rans-1,4, requires the presence o a polar solvent, at least ~ ~ ; 15 in the pol~merization step to form the elastomeric polymer block.
... Y :. The presenae of a polar solvent at~any stage.in the ~:
.~ pre~aration of such block copolymer~ generally implies that the :
~ lin~ing. rea~tion wlll also have ~o be carried out in a polar -~
:~ med~u~. Hence, thexe is a need of link~ng agents that wlll .
':`J` ~ ~ ~ 20 pro~uae proper ilnkage in such a medium.
Many compounds have. previously been.propo ed as ~ : llnhlng agents~ for the l1nking reaction in a process for ~ . . preparing elastomeric block copolymers of the type A-B-A. Good .
,',!~ ' ' results aan be obtained in a non-polar medium if t~e linking ~ 2$. agent used is an ester of an alcohol and a carboxylic acid, `~
!1 e,g.l, an es~er of a monoba~ic carboxylic acid and a monohydric ;~
l. . alcohol,.Sùch esters are cheap and ln ample ~upply.
.~ It has appeared, hGwever, that, if the linking i , reaatlon wlth the3e compounds is carried out in a polar medium, ~ 30 the mechanical properties o the block cop~lymers ~hus obtained :
..are as a rule c~nsiderably inferi~r to those ~btain~d by . . - 3 -.

2, linklng with these compounds in a non-polar medium.
~' The invention enables linking in a polar medium to be effected to yield block copolymers having good mechanical properties by the use of a particular class of esters as linking agents.
-. ~
The invention provides a process for preparing an elastomeric block ` copolymer of the general formula A-B-A, where A is a non-elastomeric polymer block derived from styrene and/or ~-methylstyrene with an average molecular `~ ~
weight between 200 and 100,000 and B is an elastomeric polymer block with an ~ -average molecular weight between 20,000 and 500,000 comprising polymerizing styrene and/or ~-methylstyrene into a non-elastomeric polymer block by means .. ~ . . .
of a monofunctional anionic initiator, then polymerizing isoprene and/or 1,3-butadiene into an elastomeric polymer block joined to the said non-elastomeric polymer block, and linking the resulting block copolymers in a polar medium to form the A-B-A block copolymer by the addition of a linking agent which is a fully esterified carboxylic acid in which no hydrogen atom is attached to the a-carbon atom and which is used in a proportion between 0,2 and 1 mole per mole of the anionic initiator used in the polymerization.
Esters used as linking agents according to the invention may be ~
derived from polycarboxylic acids and preferably from monocarboxylic acids ~`
particularly Cl-C12 and more particularly Cl-C8 acids containing no hydrogen atom attached directly to the ~-carbon atom. Particularly useful esters are :
those derived from an aliphatic or aromatic carboxylic acid, preferably, i containing from S to 20, particularly from 5 to 12, carbon atoms per molecule.
Particular examples of esters suitable for use according to the i~ invention are those derived from aromatic acids, e.g. benzoic acid, substit-i uted derivatives thereof, for example o-, m-, or p-methyl benzoic acid, ,~
~ ethyl benzoic acid, propyl benzoic ~ `-.. :j :' . :.
'':~ '` ~, :-: _ 4 _ 1`~ 2 acid, dimethyl benzoic acid, me-thyl-ethyl benzoic acid, pivalic ~'~
acid, phthallc acid, isophthalic acid, terephthalic acid, ,~,~,a~-tetramethyl adipic acid, a,a,a~ ,a'-tetraethyl adipic -' ' acld, a,a,a',a'-glutaric acid, a,a,al,a'-succinic acld, `t :
~ 5 ~,a-malonic acid, a,a,a',~'-pimelic acid, preferably benzoic '~
;~i acid or pivalic acid. ;~
Examples of alcohols from which esters su1table for ~;
}! uselaccording to the invention may be derived are methanol, ; ethanol, propanol-l, propanol-2, butanol, isobutyl alcohol, -ter~iary-butyl alcohol, amyl alcohol, glycol, glycerol an~
~ 'benlyl alcohol. ~ ~' '~ The esters used in linking reaction according ' ' to the invention are generally in a proportion between 0.2 and mole per mole of initlator u~ed for the polymerization, 15 although larger amounts may possibly be used. I use is ~ade `~ ~
~ of $n ester'from a mono-carboxylic acid and mono hydroxy alco- ~ ' '~ ' hol/ the amount used is preferably about 0.5 mole per mole of `~
lni~i~ator used.
he~process according to the invention can be carried out with any monofunctlonal anion1c inLtiator, preferably initiators which contain lithiun.Partidularly preferred initia~
tors are organolithium compounds containing from 2 to 12 carbon atoms per molecule and particularly those in which the lit~ium ; '~
atom i9 attaohed to a secondary carbon atom, as such inltiators ';~ ;' '~ 25 have a ~hort induction period. ' '~
.. -. . . .
''~ Particular examples of anionic initiators suitable for ~ use in the process of the invention are methyl lithium, ethyl -`

''':; lithium, butyl llthium, propyl lithlum, pentyl lithium, hexyl ' '' lithium~ cyclopentyl lithium, cyclohexyl lithlum and diphenyl-hexyl lithium. PartiaularIy good results are obtained with ~ n-butyl and secondary butyl lithiumO ' "' :.~ , ' ' ' ' ., ~

. . . .

~4~ 9Z
In the formation of the non-elastomeric polymer ~' blocks A, an alkenyl-aromatic compound, e.g., styrene9 nucleo-substituted derlvatives, and especially a-methyl styrene may be used as starting material. It is al~o possible to use ' 5 monomers that upon polymerization yield a copolymer or a block ', copolymer consisting of two or more segments.
~i The elastomeric polymer block B may be formed from ,, . ~. .
~ any monomer or monomer mixture that will yield an elastomeric ~`' ,., ,! . polymer b}ock upon polymerization. Excellent results are ob- ' ' : i . :. .
"~ 10 tained by the u~e of a'conjugated diene containing 4 to 12, ~1 preferably 4~to 8, carbon atoms per molecule. Examples of such ~' '''i dienes are isoprene, butadiene'-1,3, and pentadiene-1,30 Mixtures ~ ' . :~ . . i. .~
~, - 'of conjugated dienes or mixtures of conjugated dienes with a ;~ mlnor proportion of monovinyl aromatLc hydrocar~ons can be ' used i~ desired ~ The 11nking reactlon in the process according to the '~ ' lnv~ti~n 1s~car~ied out in a polar medium. In most instances -~ the polar ~edium ls already present at a stage preceding the '-' ;
linklng reaction. Thuc ih the prepàratlon of a block copolymer 0 ~contalning ~-methy1 sty~rene, the polymerization is'carried out ' '~
~"~,' $n a ~olar ~edium. Another possib111ty is to change from a non~
~ polar to a polar medium du~ing ~he block copolymerlzatlon, e.g. `;
'~ - by addlng a polar solvent to a non-polar solvent, The reaction - '~
~1 ~ medium in whlch the llnklng reaction 1~ effected preferably '~' 25 co~tains a hetero compound, i.e. a compound containing, besides carbon:and hydrogen, one or more other elements, preferably, ~ oxygen, nltrogen,~phosphor, and/or ~ulphur Examples of such '~ aompounds, which are usually polar, are tetrahydrofuran, ' methyl tetrahydrofuran, triethyl amine, hexamethyl phoephor triamine and'dim~thyl'sulphoxide. '' -, 5 "'-i ' . . - . ~.~. , ' ~34~92 ; ~. i The block copolymers obtained by the process according . to the invention may be used for many purposes, e.g. in the manufacture of fibres, foot-wear, underlays for floor covering, .~? adhesives, and coatings. It is also possible to incorporate the 5 block copolymers in other polymers or polymer compounds to ---,.,''D i~prove their properties, or they may be present during the polymerization o~ monomers into polymers eOg. polystyrene.
he ~ollowing Examples of the invention are provided, ~.
together with Comparative Experiments. In the Examples and . 10 Experiments the tensile strength, modulus at 300 % elongation, and elongation at rupture were measured according to NEN 5602, ::
the permanent elongation accordlng tot NEN 5606, and the meIt .. index according to ASTM-D 1238.

5~ e~æ~ v~ ~D~
.. ~i 400 ml of dried cyclohexane and 16.4 grams of styrene . dlstilled over calcium hydride were successively introduced ^~ : . int;o a dried, l-lltre rea~tor.provided with a stirrer, cooler ~ : and~thermometer. Thls mixture:was then heated to 55 C with .. ``~ .::20 stlrring, 1.1 mmoles of secondary butyl lithium added to ~:
.. i initiate~polymer1zation. The polymerization was continued for ~ 60 minutes,~while maintaining the temperature at 55 C. ~he. temperature was then lowered to 30 C and 40 grams.of purified .`~ .. butadiene-1,3 were introduced into the reaction mixture over ;~ 25 a period of 30 minutes. The polymarization was then continued ~-~or.a further 60 minutes, and ~inally 0.55 mmole of amyl acetate ~ -was added with intense stirring. The block copolymer thus ? obtained was recovered from the solution by adding methanol and ~-pouring into acetone. After drying, 56.5 grams of a block copo-1 30 lymer of the type polystyrene-polybuta~en~polystyrene were .~ obtained havlng the following properties upon measurement~
.? ~`
`1 : 7 ;:
~, .
.

~,~4~92 ~:
, , Tensile strength 309 kg/cm2 Mo~ul~ at 300 % elongation 31 kg/cm2 Elongatlon at rupture 680 % - ~
Permanent elongation 8 % '~ , , 5 Melt index (190 C, 1~ kg) 0.8 g/10 min. - ;
,~ The above experiment was repeated except that 10 ml ;: i; ~. .. .
,,' of tetrahydrofuran distilled over sodium were added prior to --', the addition of butadiene-1,3. After linking, which was conse- ' ;, quently effected in a polar medium, a block copolymer was ob- ' !~ 10 tained ha~ing the following properties: -'Tensile strength 111 kg/cm2 I,j Modulus at 300 % elongation 32 kg/cm2 ;' Elongation at rupture 650 ~ ' , Permanen~ elongation 7 ,~, 15 Melt index ~190 C, 10 kg) 6.4 g/10 min.
These,experiments show that block copo,lymers with a '~
high tensile strength cannot b~ obtained by linking a polar ' medium with amyl acetatç, such as may be obtained in a non-~
... ,:j . : ' ' ~
polar medlum.
, 20 ~ ' ~ Even if the tetrahydrofuran was added after the poly~
'1 ~ ' - merization of the butadiene and subsequently was linked wi~
"'"~"'1 "~amyl~acetate~ a ~lock copolymer with a relatively low tensile ~ `
;.. . . . .. ..
~ rength was obtained. , ~ ', ;, . . . ;:..: ..~, ~ . , .
~ Co~earative E~eeriment 2 ~ ~ ' `,1 : : . ~ , Comparatlve Experiment 1 was repeated, except that ''`' ' the linking agent used was ethyl propionate. A block copolymer , ~ with the following propertie, was obtained.
,.'1, ' ~', . .
.

,'~,, ;, .. ,..... , ... , , .. . ".. , , :
.. , ~ .. .... .. .

with without .. tetrahydroruran .
,~ Tensile strength 123 kg/cm2 295 kg/cm2 - ' Modulus at 300 ~ elongation 33 kg/cm 31 kg/cm2 ,~! . 5 Elongation at rupture 650 % 660 %
;.1 Permanent elongation 6 % 9 ~ '':;'i . ~....... . .
':;'., . Melt index (190 C, 10 kg) 5.7 g~10 min 0.8 g/10 min .~:
hese runs demonstrate that block copolymers with :j~; ' a high tensile qtrength can be obtained by linking with ethyl ., ., . . ,-, :
' 10 prop-ionate. in a non-polar medium, but not in a polar medium. ,- ~

.. ',.~ .: ~ , Comparatlve Experiment 1 was repeated, except that :: :
;,j ,, the~linking agent used was ethyl benzoate. The linking with . e~hyl-benzoate.was effected both in a non-polar medlum~ (not according to the invention) and in a'polar medium, A block :copolymer,was o~tained,.having the followinq properties~
, ' with . without ~ tetrahydrofuran ;~ ~ Tensile strength 300 kg/cm2 215 kg/cm2 , '~ :
~ 20 Modulus at 300 % elongation 45 kg/cm2 ~ 46 kg/cm2 ::
.. `.~ ~ Elongatlon at rupture ~ ~ 570 % 550 %
:.,.`.~ . '. :Permanent,elongation ~7 % 4 %
'~ Melt index ~:190 C,-lO'kg) 0.7 g/10 mLn 0.8 g/10 min ~;
~ These.runsjindicate that block copolymers wlth a good .,,~ 25 tensile.strength are obtained by the use accordlng to the lnvention of ethyl bensoate, a compound with no hydrogen atom ~`
on the a-carbon atom, in a polar medium. .:
,.,.~ . ~ ~.

~, ' ' . ' :~

~, _ g _ ,gz ~:
~-~ Comparative Ex~eriment 3 50 ml of ~-methyl styrene distilled over calcium hydride, 150 ml of dried cyclohexane, and 10 ml of tetrahydro-9 furan distilled over sodium wire were successively introduced `; 5 into a dried reactor provided with a stirrer, cooler, and thermometer. The mixture was cooled to -20 C with stirring, - after which 3.3 mmoles of secondary butyl lithium were added, ; to lnitiate the polymerization. The polymerization was cont1nued ~ . . .
~;for 60 minutes, the temperature being maintained at -20 C. Sub- `~
. ,j :
-10 sequently 3 ml of styrene distilled over calcium hydride, were ~1added, after which the reaction mixture was maintained~at 20 C for 15 mlnutes. After addition of 600 ml of cyclohexane, `
1 120 grams of purified butadiene-1,3 were added over a period ;~
of time of 90 minutes, the temperature being maintained at 30 C ;~
The polymerlzation was then continued at 30 C for another 60 minutes. Fihàlly 1.65 mmoles of amyl acetate were added with i ~
intense stirrlng.`
The block copolymer thus obtained was recovered from the solution by adding methanoL and pouring into acetone. After dryingi 167 grams of a block copolymer of the type poly(a-methyl ~` styrene~-polystyrene-polybutadiene-polystyrene-polyta-methyl styrene~ were obtained which had the following properties~
Tensile strength 165 kg~cm2 ~ Modulus at 300 % elongation 43 kg/cm `'',~2~ 25 ~longation at rupture 650 % `~
1 ~ Permanent elongation ~0 ~ Melt 1ndex (190 C, 10 kg) 1.0 g/10 minO

',',. ` ~ :~
. .
: :.
~ . . !
-- 1 0 -- '~.
," 1 ' ' '~' ." .
'''i ' .
~ ."' ' .' . ' '.` ' . . ' ' . ' ` ' . ' ' ' ' ,, ' ' " ` ' ' ' ' , ' ' " ' ' . ' ' ' ' ' ' '; ~ ' , ' ' ' ' .' ' Example 2 Comparative Experiment 3 was repeated, except that , the linking agent used was ethyl benzoate. A block copolymer - -with the following properties was dbtained.
. ,~ , .
, i! 5 Tensile strength 224 kg/cm j Modulus at 300 % elongation 40 kg/cm2 ^, Elongation at rupture 580 %
Permanent elongation 14 Melt index ~190 C, 10 kg) 1.0 g/10 min.
.
. . :;,~ ~ , .
~ 10 Example 3 ,.. ,,.~ . - .:
~, Example 1 was repeated, except that the linking` ~ ~
: ~
agent used was methyl pivalate. A block copolymer with the ~j~ - following properties was obtained.
~I wlth without ~;
,I ~ 15 tetrahydrofuran -i`?i Tensile strength 205 kg/cm2 2aO kg/cm ^f ~ Modulus at 300 ~ elongation 33 kg/cm 31 kg/cm2 Elongation at rupture 630 % 650 ` Permanent elongation ` 6 ~ 9 %
Z0 Melt index ~190 ~, 10 kg~ 0,8 g/10 min 0.8 g/10 min.
`'if ' ' ,' ' .. ,~ . , . . .: .
i','~ : .::

;:: ~ i . , . :,:

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:`, :
::
.. ~, ; i .

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for preparing an elastomeric block copolymer of the general formula A-B-A, where A is a non-elastomeric polymer block derived from styrene and/or .alpha.-methylstyrene with an average molecular weight between 200 and 100,000 and B is an elastomeric polymer block with an average molecular weight between 20,000 and 500,000 comprising polymerizing styrene and/or .alpha.-methylstyrene into a non-elastomeric polymer block by means of a monofunctional anionic initiator, then polymerizing isoprene and/or 1,3-butadiene into an elastomeric polymer block joined to the said non-elastomeric polymer block, and linking the resulting block copolymers in a polar medium to form the A-B-A block copolymer by the addition of a linking agent which is a fully esterified carboxylic acid in which no hydrogen atom is attached to the .alpha.-carbon atom and which is used in a proportion between 0.2 and 1 mole per mole of the anionic initiator used in the polymerization.

2. A process according to claim 1, wherein the ester is an ester derived from a C5-C20 carboxylic acid with 5 to 20 carbon atoms per molecule.

3, A process according to claim 1, wherein the said ester is derived from a C5-C8 carboxylic acid.

4. A process according to any of claims 1 to 3, wherein the ester is an ester derived from an aliphatic or aromatic carboxylic acid.

5. A process according to claim 1, wherein the ester is an ester derived from a monobasic carboxylic acid.

6. A process according to claim 5, wherein the ester is an ester derived from benzoic acid or pivalic acid.

7. A process according to claims 1 to 3, wherein the ester is an ester derived from C2-C8 alcohol.

8. A process according to claim 1, wherein the ester is an ester derived from a monohydric alcohol.

9. A process according to claim 8, wherein the ester is an ester derived from methanol or ethanol.

10. Elastomeric block polymers whenever obtained by a process accord-ing to any of claims 1 to 3.