CA2219464A1 - Metalation and functionalization of polymers and copolymers - Google Patents

Abstract

There is provided a method of introducing functionality into a copolymer of an isoolefin and an alkylstyrene at the alkylbenzyl carbon atom comprising the steps of: forming a solution of said copolymer in a hydrocarbon solvent; adding to said polymer solution an alkali metal Cs, K, Na alkoxide and an alkyl lithium compound to form a superbase with the polymer solution; and adding an electrophile to said base polymer solution also provided are the metalated copolymers and the functionalized derivative therefrom.

Description

METAI~TION AND FUNCIIONALIZATION OF POLYMERS
AND COPOLYMERS

INVENTORS:Jean M. Fréchet, Shah Haque, Joachim Steinke, Hsien-Chang Wang This application is a Co~ on-in-Part of Title: "Metalation and Function~li7~fion of Polymers and Copolymers" Inventors: Jean M.J. Frechet, ShahHaque, Joachim Steinke, and Hsien Wang, USSN 08/447,131, filed May 22, 1995 which is a Continuation-in-Part of USSN 08/444,951, filed May 19, 1995.

Field of the Invention:
.

This invention relates to copolymers cont~ining alkyl styrene comonomers which are met~ ted using a superbase to provide a mP~t~ ted copolymer which may be functionatized by addition thereto of an electrophilic reagent.

Background of the Invention:

Helelofc"e, butyl rubbers, i.e., copolymers of isobutylene and small 20 amounts of isoprene as a comonc-m~r, and/or halobutyl rubbers, i.e., a halogPn~ted derivative of a butyl rubber, have been used as an Pl~etomPr for forming blend compositions with therrnoplastic co"~p~ullds and other elastomer compounds for use in tire production and the like. The butyl and/or halobutyl rubbers impart anumber of desirable physical p, ol)e, lies to such blends, such as low air 25 permeability, relatively low glass transition te~"pe~lu~e (Tg), broad da"lpillg peaks, environment~l aging ~e~ cP, etc. that are eignific~nt in the production of tires of superior pe,rc",lance plopellies. However, various difficulties are encountered with the use of the butyl and/or halobutyl rubbers for this purpose,chief among which is their high inco~ libility with most other polymers, inc~ ing 30 even unsaturated elastomeric compounds to which they have weak adhesion.
Hence, that aspect of a butyl rubber that provides properties which make it desirable as a component in blends for tire production, namely the fhP.mic~l "inertness" that results from the unrea~livelless of the hydrocarbon backbone of the butyl rubber polymer, also results in its low reactivity and incc....p~l;bility with most 35 other materials and this has limited its use in many areas.

W 096/36650 PCTrUS96/07278 -- 2 --Recently, in U.S. Patent No. 5,162,445 a unique copolymer of isobutylene has been disclosed together with a procedure for introducing non-backbone functionalities into this copolymer, which well suits it to use as a blend component having all the plopclLy advantages of a butyl and/or halobutyl rubber, but whichs o~clcun-es the incc,---palil,ility disadvantage of a butyl and/or halobutyl rubber. In its broadest description, the new copolymer is a direct reaction product of an isoolefin having from 4 to 7 carbon atoms with a para-alkylstyrene, isobutylene and para-methylstyrene being the p-crc--cd mc~nomers; wl-cuein the copolymer has a ~Ub~ y homogeneous compositional disL-ilJulioll. Derivatives of this IB-PAS
10 copolymer having function~lities that render it co...l.~l;hle and/or cross-linkable with other polymer materials, both thermoplastic and ~ tomP.ric polymers, are ~ produced through a halo~n~ted interme~ te that is produced by a free radical initi~ted halogenation ofthe IB-PAS copolymer.

In U.S. Patent 5,162,445 a p-crc -cd copolymer is that of isobutylene and para-methylstyrene and this copolymer is blc,...i.)~ecl to provide a copolymer having a portion of its para-methylstyrene content bro...i~ ed at the para-methyl group. The l~lo.. ~ed copolymer being ec~nti~lly a high molecular weight, narrow molecular weight distribution polymer of isobutylene-para-methylstyrene-para-bromo...~ll.ylstyrene. The benzylic bromine atoms are highly reactive undermild conditions in the presence of a nucleophilic reagent. It was found that a wide variety of functional groups could be introduced at the site of the blC,. . .;~ ed para-methyl carbon atoms of the pendant phenyl groups to tli~p~ e at least a portion of the bromine atoms without disruption of the backbone structure or altering the m--lec~ r weight and/or molecular weight distribution characteristics of the backbone of this copolymer.

Helcloru-c, styrenic polymers have reportedly been met~ ted with lithium by reaction with an alkyl lithium co...pùu-ld activated with N,N,N',N'-tcL~ncLLyl ethylene diamine (TMEDA), and the mP.t~l~ted de-ivaLivc then co-~vc-led by reaction with an clccl-ophilic reagent to a variety of functionalized derivatives.
Harris et al. U.S. Patent 4,145,490 and Macromolecules. 19, 2903-08 (1986) describes the met~l~tic~n of copolymers of isobulylene with styrene and/or a methylated styrene with lithium as a means of introducing fi-n-~.tion~lity into the copolymer to prepare it for polymeri7~tiQn with pivalol~ctone. The procedure described by Harris et al. ~p~enLly results in introducing fiunctionality into both W096/36650 ~CTrUS96107278 the p~ ly and tertiary benzylic carbon atoms of a methylated styrene comonomer unit, as well as the aromatic ring carbon atoms thereof. Huge excess of the reagent (alkyl-Li/TMEDA) is required, inco"~plete met~l~tion of p-methyl group of styrene ~ unit, and long reaction time are some of the disadvantages ~so~i~ted with the Harris et al. procedure. Hence, it appears that the possible advantage of following the Harris et al. procedure as a means for introducing functionality into the new IB-PAS copolymers disclosed by U.S. Patent No. 5,162,445 would be achieved at the significant disadvantage of disrupting the hydrocarbon nature of the backbone chain of this copolymer by also introducing lithium at the tertiary benzylic carbon atoms of the copolymer backbone.

~ Reports have also appealed concerning the co",l,in~lion of an alkyl lithium compound with an alkoxide of a heavier alkali metal to form a reagent, which hasbeen r~re..ed to as a "superbase," which is very reactive for pe,ru""i,-g met~l~tion 15 reactions in organic synthesis and polymer çhPmictry. The application of a su~ell,ase reagent formed from an alkyl lithium and a potassium ~lknxide to the met~l~tion of aromatic hydrocarbons like benzene, toluene, ethylben7PnP, and cllmPne to form a met~ ted species in which the counterion is the heavier alkalimetal rather than lithium have been described in articles like J. Ol~ano...el~llic Chemistry. 28, 153-158 (1971); J. Or~anometallic Chemistry. 326, 1-7 (1987);
Tetrahedron Letters~ 32 (I l),1483-86 (1991).

Even with respect to such simple aromatic molecules, a variety of inte,...~ e met~ ted products, as deduced from the product rçslllting from the 25 reaction of the met~ ted intermetli~te with methyl iodide, have been reported. In addition to the products whose structures were not dt;lt;-",ined, the other products of the alkyl Li/K alkoxide ~up~,l,ase met~l~tion reaction cc~ ise structures wherein both an alkyl side chain carbon atom and/or an aromatic ring carbon atomare mP.t~ ted Lo-hm~nn et al. in Polym. Mat. Sci. Eng.~ 69, 426-7 (1993) and Polymer Pleplinls~ 34(2!, 588-9 (1993) have desc,ibed the met~l~tion of homopoly~lylelleand a dendritic polyether with an alkyl Li/potassium tert-pPntoxide ~upe~base reagent as a means for introducing functionalities wher~y the functionalized 35 polymer materials may then be converted to graft copolymers or multi-functinn~li7ed dendrimers of significantly altered prope-lies. It is again reported CA 022l9464 l997-ll-l7 that main chain met~l~tiQn -- i.e., mP,t~l~tion of the tertiary benzylic carbon atom of the polymer backbone chain -- occurs to an even greater extent with an alkyl lithium/potassium tert-pentoxide superbase reagent than that which occurs with an alkyl lithium/TMEDA reagent like that used previously by Harris et al. The 5 mP~t~l~tion of such backbone carbon atoms would disrupt the hydrocarbon natureof the polymer backbone of the new copolymer materials described by U.S. Patent No. 5,162,445 with potential adverse effects upon its çhPmic~l inelll-ess. Further, a eignific~nt degree of met~l~tion at aromatic ring carbon atoms is also reported to occur with the alkyl lithium/pol~ss;ulll tert-pPntoxi-le superbase reagent.

It is desirable to devise a way by which to convert the new copolymer materials into fim~tiQn~li7pd derivatives without altering the inert hydrocarbonstructure of the backbone of the copolymer.

SUMMARY OF TElE INVENTION

This invention provides a method by which an isobutylene-para-alkylstyrene copolymer, as described in U.S. Patent No. 5,162,445, may be filncti~n~li7ed at the 20 benzylic carbon site of the para-alkyl group of the styrenic comonomer without ei~nifis~ntly altering the backbone micro-structure of the copolymer, molcc~ r weight or molcc~ r weight distribution or the nature of the aromatic ring carbons of the aromatic group pendant to that copolymer backbone. The method comprises Ll~:aLllg the isobutylene-para-alkylstyrene copolymer while in solution in 25 a hydrocarbon solvent to the action of a superbase. The superbase formed by the interaction of an alkyl lithium ccslllp~uild with a higher atomic weight alkali metal alkoxide to form a mPt~ ted species wherein the counterion is the higher atomic weight alkali metal (Na, K, Cs) which is localized to the para-alkyl carbon site of the styrenic comonomer. It has been found that the desired mpt~ ted polymer 30 species is formed very quickly, in a matter of ...;...~ee, making it possible to produce the desired met~ ted polymer species by a continuous flow reaction procedure. The met~ ted copolymer may be contacted with an electrophilic reagent to convert the mP.t~ ted copolymer into a derivative having the fim~.ti~n5~1 group carried by the electrophilic reagent covalently bonded to the benzylic carbon 35 atom of the para-alkyl group of the aromatic group pendant to the copolymer backbone.

CA 022l9464 l997-ll-l7 _ 5 _ The con~itiQn~ of the mP.t~l~tion reaction of the copolymer in terms of the mole ratio of the alkyl lithium compound to the mole content of the para-alkylstyrene units of the copolymer, the mole ratio of the heavier alkali metal 5 ~lkoxide to the alkyl lithium compound and the te"lpe,~ re of the met~l~tiQn reaction are all sPlPcted to ~ e the occurrence of met~l~fion reaction at aromatic ring carbon atom sites while Ill;1x;l~ mP.t~l~fion at the plilll~y benzylic carbon atom sites.

o It has been found that the tertiary benzylic carbon atom of the copolymer is not met~ ted (and thereafter functionalized) under the sPIected reaction conditions and therefore the initial microstructure of the copolymer backbone ispreserved intact in the functionalized derivatives thereof which result as a product of the practice of this method. Further, it has been found that by proper selection of the rolegoh~g conditions, coupled with the choice of the superbase (Na, K or Cs), that the met~l~tion of aromatic ring carbon sites can be reduced to an ~mol-nt which is in~ignific~nt and/or çssçnti~lly Pl;~ e~, thus red~1çins~ or P];.l,;~ g the introduction of functionalities at these sites in the final product. Still further, it has been found that, with rerelellce to the para-alkylstyrene content of the copolymer, the degree of met~l~tion and hence functionalization can be accompli~hPd to any extent desired, up to eSspnti~lly one hundred percent if desired. It has been found that the met~l~tiQn reaction can be carried to its opL;Illuln extent in terms ofcompleteness and specificity for reaction with the mPt~ ted benzylic site co",~ared to aromatic met~ ted sites in a relatively brief period, generally less than 10 ~I;"~le~, and without need for use of a subsl~lLial excess of the ~upe~base ,~p~"l~ In addition to p~""iLLi"g production of the met~ ted copolymer by a continuous flow reaction process, this also permits use of smaller qll~ntities of nucleophilic reagents for the Ll~ -l in situ of the mPt~ ted copolymer to convert it to a fiunctionalized copolymer product. Also, since the filnction~lity incorporated into the copolymer via the met~ ted copolymer is introduced through the use of electrophilic reagents, it is now possible to introduce certain types of functional groups into the isobutylene-para-alkylstyrene copolymer which are not possible of introduction through the blo,,li,l~lion-nucleophilic reagentprocedure as described in U.S. Patent No. 5,162,445.

CA 022l9464 l997-ll-l7 W O 96/366S0 PCTrUS96/07278 Accoldill~ly, there is provided a method of met~ ting a copolymer of an isoolefin and an alkylstyrene at the alkylben_yl carbon atom, the method colll~lising the steps of: forming a solution of said copolymer in a hydrocarbonsolvent; adding to said polymer solution an alkali metal ~lkoxi~e and an alkyl lithium compound to form a superbase with the polymer-solution; and recovering the m--,t~ ted copolymer. In accordance with this invention, there is also provided a method of introducing filnctinn~lity into a copolymer of an isoolefin and a para-alkylstyrene at the alkylbenzyl carbon atom, the process comprising the steps of:
forming a solution of said copolymer in a hydrocarbon solvent; adding to said o polymer solution an alkali metal ~lkcxide and an alkyl lithium compound to form a superbase with the polymer solution; adding an electrophile to said base polymersolution; and recovering the fim~tion~li7ed copolymer. There is also provided novel random copolymers r~l ~sellled by the emperical formula:

(CH2- C~CH2- C)~H2_ R2 "~ ~
R3- IC(3M(3 R3 - C -R4 4 (I) wherein "a" is in the range of 1 to 70,000, "b" is in the range of 1 to 7,000, and "c"
is in the range of O to 7,000, Rl and R2 are each independently Cl-Cs alkyl or hydrogen, provided that at least one of Rl and R2 is alkyl and Rl+R2 is C5 carbon atoms; R3 and R4 are each independently one of hydrogen, a Cl-C4 alkyl group, and M is an alkali metal other than lithium. E~ t;l~1y the alkali metal is one of so~lillm, pot~ m or cesium. Also pl~r~l~bly the alkylstyrene is para-alkylstryene. In another aspect of this invention, the met~ ted copolymer is conf~cted with an electrophile to provide an electrophiled alkylstryrene.

Also provided is the filn~.tion~li7pd derivative of I. These functionalized polymers comprise the product resulting from reaction of a copolymer of a monoisoolefin and an alkyl styrene with a superbase and an electrophilic reagent.
30 The copolymers are rep,esenled by the formula:

~1 H ~1 - (CH2 - C~cH2 - I )6~ H2 - lC~
R2 ~ ~

wht;leill "a" is in the range of 1 to 70,000, "b" in the range of 1 to 7,000, and "c" in the range of 0 to 7,000, Rl and R2 are each indep~ntl~ntly a Cl to Cs alkyl or hydrogen, provided that at least one of Rl and R2 is alkyl ~ and R1 + R2 ~ 5 carbon atoms; R3 - R4 are each independently one of hydrogen, a C1 to C4 alkyl group fragment and F is an electrophile.

The lllonoisoolefin-para-alkyl~lyl~;ne copolymers that are suitable for the met~l~tion-functionalization process of the method of this invention are those as described in U.S. Patent No. 5,162,445, the disclosure of which is hereby 15 incorporated by reference as if fully set forth and described herein. Those copolymers of particular interest and hence the plert:lled copolymers are those of isobutylene (I13) and para-alkylstyrene (PAS) and particularly those of isobutylene and para-m~Lllyl~Lyl~ile (PMS), which may he~t;~Lel be referred to as an IB-PMS
copolymer. Of these IB-PMS copolymers, the most p~er~ ;d are the IB-PMS
20 copolymers that exhibit elastomeric ploptlLies, these generally having a weight percent content of IB monomeric units of from about 99.5 to about 50 and a PMS
ollomt;lic content of from about 0.5 to about 50 weight percent. Generally, the elastomeric IB-PMS copolymers have a number average molec~lS r weight (Mn) of 500 or greater, preferably of 25,000 or greater, ranging up to about 2,000,000 and 25 their molecular weight disL,ibuLion is less than 6.0, preferably less than 4.0, and most plerel~ly less than 2.5.

The IB-PMS elastomeric copolymers, when functionalized in accorclance with this invention, are especially useful and desired as colllpou,lded rubber 30 compositions and as b'~~tling components for the formulation of blend WO 96/36650 PCI~/US96/07278 compositions with other thermoplastic and/or elasLo,..c,ic polymers used in the production of carcass, side wall, tread and other components of pn~l-m~tic tireshaving superior pc-ro~ ance properties.

The Superbase Met~l~tion Reagent That reagent used to treat the IB-PMS copolymer to form its met~ tecl counterpart is the product obtained by reaction of an alkyl lithium compound (AkLi) and a heavier alkali metal alkoxide (AkOM) while both are in a neutral, 0 non-polar solvent such as a hydrocarbon solvent.
The Alkyl Lithium Compound One criterion for the selection of the alkyl lithium compound used to form the superbase is to select one wherein the alkane analogue of the alkyl lithium compound would have a pK value that is greater than the pK value of the H-bond of a benzylic carbon atom.

The Alkali Metal ~llr~ x;~le Compound The heavier alkali metal ~lkQxil1e reagent may be prepared by reacting sodium (Na), potassium (K), rubidium (Rb) or cesium (Cs) metal with an alkanol in a nonpolar solvent. The alkoxy structure (AkO) of the alkali metal alkoxide reagent then co"esponds to the alkanol (AkOH) from which it was prepared.
Arnong the alkali metal alkoxide reagents that are suitable for practice of thisinvention are those resulting from the reaction of an alkali metal with isop,upanol~
sec-butanol, tert-butanol, 2-pentanol, 3-pentanol, tertpentenol, 3-methyl 3-p~nt~n~l, 2-hexanol, 3-h.oY~nol~ 2-methyl 2-hexanol, 2-heptanol, 3-heptanol, 4-l(-) menthol heptanol, 3-methyl 3-hexanol, 2-ethyl 2-hexanol, 3-ethyl 3-h~Y~nol, 2-propyl 2-p~nt~nr~l, 2-isop,o~yl 2-pçnt~nol, 3-propyl 3-pentanol, 3-isopropyl 3-p~nt~nc~l meth~nol, and the like. Generally, for purposes of convenience of w~"kup and recovery of the by-products of the function~li7~tion reaction, it is p~crcllcd to use an alkali metal alkoxide reagent the alkynol precursor of which has a boiling point of 200~C or less at 1 atmosphere. The alkali metal ~lkoxille reagents most p,crc"ed are the alkali metal reaction products of 2-ethyl 2-hexanol (~F.t~XOH)~ menthol (MenOH), tertiary pentanol (t-PeOH).

CA 022l9464 l997-ll-l7 _ g _ - S~ .l,as~ For ~ti~

~= Solvents which may be employed for the formation of the alkyl lithium, 5 alkali metal alkoxide, and/or the super base which results from the interaction Ll-er~elw~;:en are neutral non-polar liquids, such as, and p-~;;re-~bly, hydrocarbon solvents that have boiling points from about 0~C to about 200~C. When approp.iate, higher or lower te--lpel~L-Ires can be employed. The hydrocarbon solvent may be an aliphatic or cycloaliphatic hydrocarbon and pl~;re-~bly is a ~o hydrocarbon in which the IB-PMS copolymer is soluble to at least the extent of about 2 wt.%. Among the suitable solvents, p-~;;re--ed solvents include pentane, n-hexane, heptane, octane, decane, cyclohexane, methylcyclohexane, and the like.

The superbase reagent may be formed separate from the polymer solution 15 to which it is later added or it may be formed in situ in the polymer solution by adding the alkyl lithium and alkali metal alkoxide compounds to the polymer solntion When formed in sifu in the polymer solution it is p-c;~--~d to first add the alkali metal ~lknxitle and Lllele~ler to add the alkyl lithium compound. Themolar amount of the superbase will be equal to the molar amount of alkyl lithium20 employed in its p~p~lion.

Rr-rti_: Conditions for Met~l~tiQ

With respect to the extent that the alkyl benzylic carbon atom as conl~a ed 25 to the aromatic ring carbon atoms ofthe styrenic unit of the IB-PAS copolymer are met~ tetl, the following reaction pal ~llelel ~ have been observed to exert a ~eignific~nt inflnence on the course and nature of the reaction: (1) the mole ratio of the superbase compound to the styrenic co.--ollolller content of the copolymer; (2) the mole ratio of the alkyl lithium compound to the alkali metal alkoxide col..pou..d 30 used to prepare the superbase; (3) the nature of the alkali metal atom ~I) used for the superbase; (4) the temperature of the polymer solution during the met~l~tionreaction; (5) the nature of the alkyl moiety of the alkyl lithium collll~oulld selected for prep~lion of the superbase; and (6) the mixing conditions under which the met~l~tion reaction is carried out. With proper choice of con~lifione the met~l~tion 35 reaction may proceed to the extent of çeeenti~lly total met~l~tion of the styrenic content of the copolymer. Reaction of the tertiary benzylic carbon atom -- i.e., the CA 022l9464 l997-ll-l7 benzylic atom in the polymer backbone chain -- either does not occur or occurs to such a small extent as to not be detect~ble by standard NMR analysis methods.

The mole ratio of superbase to para-alkylstyrene copolymer can range from 5 about 1 to about 2, with 2.0 being pl~rell~d. Amounts of alkyl lithium in a mole ratio to the styrenic comonomer content of greater than 2.0 may be employed.
Generally, ~m( llnt~ of the superbase that exceed the 2:1 ratio may not be desirable since such a~-~O~ would increase the amount of nucleophilic reagent needed to treat the in situ met~ ted copolymer to convert it to a functinn~li7ed product.
lO The amount of alkali metal alkoxide used in plel)~i"g the superbase reagent may range as a mole ratio to the amount of alkyl lithium used from about 1 to about 5, p,c;rel~bly from about 1.1 to about 3.0, and more plerelably at or about 3Ø
Generally, it is pl c;rt;" ed to employ an excess of alkali metal alkoxide relative to the alkyl lithium, with a mole ratio of alkali metal ~lkoxi-le to alkyl lithium of about 3 :1 15 being prere"ed for the prep~d~ion of the superbase. Within these ranges the greater degree of met~l~tion with the greatest degree of specificity for met~ ting the benzylic carbon of the para-alkyl group of the styrenic comollo",er in cc""pa, ison to aromatic carbon sites occurs wherein the mole ratios of AkLi/AkOM/styrenic comollo",er content is on the order of 2/6/1.

Further, when the alkyl lithium and alkali metal alkoxide compounds are employed in the amoullLs as plt:relled the greatest degree of m~.t~l~tiQn of thebenzylic carbon site of the para-alkyl group of the styrenic comonomer with the g,eaLe~L degree of specificity colllpaled to aromatic carbon sites occurs when the 25 alkali metal of the alkali metal alkoxide reagent is cesium (Cs), next to which is potassium (K), and least p,~relled is sodium (Na). Further, within the context of the p,er~"ed Cs and K alkoxides, the ~l~ale~L degree of specific m~,t~l~tion of the benzylic carbon site of the para-alkyl group of the styrenic col,lollol,ler unit is realized when the alkyl lithium reagent is one wherein the Li atom is associated to a 30 secon-l~ry carbon atom of the alkyl moiety rather than a tertiary carbon atom.

~ lt;re,led superbase systems for met~l~tion of an isobutylene-para-alkylstyrene copolymer are those of s-butyl lithium and either t-PeOK or MenOCs.The most p,erelled is MenOCs.. Within this m~t~l~tion system the met~l~ti~n 35 reaction proceeds over a broad te",pe,aL-Ire range which extends from just above the freezing point of the solvent utilized to just below the boiling point of the -Wo 96/36650 PCT/US96/07278 solvent. The extent and specificity to which the mP~t~l~tion reaction proceeds does not appear to be dr~m~tic~lly affected by the temperature at which it is con~luctecl The met~l~ti-~n reaction is preferably con~ cte~l at a te""~e,~ re bcl~ccl- 15 and 85~C, desirably 20-70~, more preferably at about ambient te",pc~lure -- i.e., about 20-25~C.

The met~lqtiQn reaction proceeds relatively quickly, with times typically ranging on the order of ...;.~les, as like from about 2 to 30 min-lt~s, and p,ere,~ly about 15 minlltes, being the time within which the reaction proceeds to the lO optimum extent. Reaction times longer than 60 mimltes are not required and may in some in~t~nces degrade the quality of the reslllting product from the opLimu"~
that is otherwise achieved by a shorter reaction time.

Funct;o ~qli7q~icn of the l~'let-q~qte~ Product An electrophilic reagent, neat or in solution, may be added to the solution CU~ the met~ ted isob.itylene-para-allr~;lls.-y~,ene cûpoly",er to cor,vert it to a derivative product.

An electrophilic reagent with (FMo) is a molecule that COIll~illS an electron d~o.fic;~nt atom or group (F) which will react with the electron rich atom of nucleophile. The moiety of the electrophilic reagent may comprise any molecular arrangement (Mo) inclllrling any number of functional groups (F). The electron deficient atom of the electrophilic reagent reacts with the met~ te~l carbon atoms of the met~ ted copolymer, these being ess~nti~lly the met~ te(l benzylic carbonatom of the para-alkyl group of the styrenic co",ollo",er, which are cle~lloll rich and capable of ~on~tin~ a pair of electrons. The reaction, wherein P ,cl"esenls the polymer chain, may thus be represented as:

W O 96/36650 ~CTrUS96/07278 The electrophilic reagent adds to the benzylic carbon atoms of the para-alkyl group to itself form the fiml~tion~l group of the product composition -- as in the case of carbon dioxide to form a call,oxylic acid functional group or dimethylcarbonate to form a methyl carboxylate filnction~l group -- or carry a preexisting functional group into the product composition -- as in the case of 3-bromo-l-propene to form a 4-butylene pendant group.

The electrophilic reagents that are suitable include organic or inorganic compounds. Illustrative of the organic classes of Lewis acids that are suitable as o electrophilic reagents are compounds bearing a carboryl carbon atom such as aldehydes, ketones, esters; compound co..l~;.,;.,~ a halogen atom such as the organic halides, acyl chloride (acrylyl chloride, mPth~crylyl chloride), trialkylsilyl halides (bromides and chlorides), trimethylsilyl chloride, sulfonyl chloride, benzyl halides, aliphatic, or silylic halides; enones, fluoloa~ -lalic compounds substituted with electron withdrawing groups such as para-fluoro-nitrobenzyne and para-fluoro-bel~ophenone; compounds c~ epoxide functionality such as ethylene oxide; and C02.

The composition resulting from reaction of a mPt~ ted copolymer of a monoisoolefin and a para-alkylstyrene is in effect a new copolymer or terpolymer, depending upon the extent that the copolymer of monoisoolefin and para-alkyl~lyleile was met~ ted prior to its reaction with the electrophilic reagent.Wherein the copolymer was met~ ted to less than the full extent of its para-alkylstyrene comonomer content, then the product res ~lting from its reaction with an electrophilic reagent is a terpolymer of monoisoolefin-para-alkylstyrene-para-function~li7ed alkylstyrene, wherein the term "para-filnction~li7P,d alkyl styrene" is intPntled to mean the comonomer composition which results from the reaction of amet~ ted para-alkylstyrene comonomer with an electrophilic reagent. Although we have described the invention with regard to the alkyl~Lylelle being p-alkyl, the m-alkyl, the o-alkyl can also be employed.

These polymers are used in tires, production of polymer blend, in production of Pnginl~ring plastic blends, in the formation of air barriers and in the production of adhesive and sealant materials, CG~lI;..g~, and me-.h~ni~lly molded goods.

CA 022l9464 l997-ll-l7 EXAMPLES
-General Procedure A:
Met~ ion of Isobutylene-para-m~ll,ylslyr. e Copolymer Purified and dried isobutylene-para-methylstyrene copolymer is dissolved in a hydrocarbon solvent, pler~ably cyclohexane (c-hexane) or hexane (n-hexane), and the homogeneous solution is stirred. The concentration of polymer in this solution is 5% (w/v). Before addition of an alkali metal alkoxide (an app.~x;.. ,~lely 0 1 molar solution of alkali metal alkoxide in hexane or cyclohexane) the solution is cooled down or heated up to a temperature as indicated in Tables l and 2. After ~ddition of the alkali metal ~lkoxid~, the alkyl lithium co.-.ponenL, which unless otherwise intlic~ted is an app-c~x;..,~1ely 1.3 molar solution of s-BuLi in hexane, is added also. The color of the solution ~ Fçs almost ;,~ eously from 15 colorless to yellow, orange, red or deep dark red depending on the choice of alkoxide and the molar q~1~ntitiçs of reagents (alkali metal alkoxide and alkyl lithium) used. The formation of superbase (SB) is allowed to proceed for usually15 mim-tes Addition of an excess of a suitably chosen electrophile (neat or in solution), 1ike l.i~neLl~ylsilylchloride (TMSCI), leads to a clear and almost colorless 20 solution. Stirring continlles for at least an hour before work-up.

General Proced~.re B:
Work-up of Functio-~1i7e~ Isobutylene-para-mell.yl~ly.~ ~ Copolymer The organic phase, co.~ ;.. ;.-g the metal functionalized polymer is extracted with 10% aqueous HCI (twice), lN aqueous NaOH (twice), s~Lu-~Led aqueous sodium bicarbonate solution (twice), and finally with water. The organic layer is separated from the aqueous one. ~rec;l,;l;1l;Qn into acetone, isop.opanol or meth~nol (depending on the solubility characteristics of the functionalized polymer) 30 affords the desired polymer product. The organic liquid is dec~nted and the r~...,.;..;"~ polymer is washed several times using ~--~ ol Finally the polymer is , dried at room temperature or a somewhat elevated temperature (60~C) under vacuum.

WO 96/36650 ~CT/US96/07278 General Procedure C:

Tim~Dep~ nt Studies on the M~t~ tin~. of Isobutylene-para-m~ll,~

Purified and dried isobutylene-para-methylsytrene is dissolved, plc;reldbly in a hydrocarbon solvent such as hexane or cyclnhPY~ne. ArlditiQn of a metal 7~lkn~ide follows under contimled stirring. Anelw~-ls the solution is cooled down or w~ ed up as indicated in Tables 1 and 2. An alkyl lithium compound is added lO quickly, leading, almost i~ eously, to a dark red colored solution. At given time intervals aliquots of the m~-,t~l~ted polymer solution are drawn and added swiftly to a 4-8 fold excess of TMSCI, stirred at room temperature. After 1 hourthe reaction mixture is precipitated into 5 to 10 times its volume of acetone. The supe"~al~l liquid is dec~nted and the re~ i";"g polymer is washed several times using meth~nol, before it is dried at 60~C under vacuum for at least 24 hours.

METALATION EXAMPLES

The molar qll~ntitiP,s given for the isobutylene-para-methylstyrene copolymer refers to the number of p-methylstyrene units present in the polymer.
Reactions were carried out as described under General Procedure A. The time between addition of an alkyl lithium compound and TMSCI is 15 min-ltes if not stated otherwise. Work-up is described under General Procedure B, without extraction of the organic phase. The polymer products were dried at 60~C under vacuum for at least 24 hours. l~e~ctiQn~ carried out at times in~lic~ted as other than 15 ...;.."lee were carried out as described in General Procedure C.

Tables 1 and 2 below give a ~ull)~ y of the superbase reagents and 30 reaction conditions of met~l~tion as in-~ic~ted by the silylation derivative. In the Tables "Eq" = molar equivalents used with regard to the number of p-methylstyrene units present in the copolyrner isobutylene-para-methylstyrene;
"benzylic/ring" = degree of silylation at the benzylic and ring position within the p-methyl styrene unit of copolymer; "RT" = room te".pe,~lu.t:. The degree of 35 silylation at the benzylic/ring positions was dele"""led by ~-NMR and is the mole CA 022l9464 l997-ll-l7 pe,ct;lllage of silylation at these sites based upon the mole content of the p-methyl styrene comonomer of the copolymer.
Ta ~le 1 Alkyl T ithillm So1vent Silylation (%) ~Eq)* ,~lkoxicle (Eq)'' T(~C)/t(min) Benzylic/Ring s-BuLi (1) t-PeOK (1) c-hexane RT/15 44/9 s-BuLi (1) t-PeOK (3) c-hexane RT/15 59/5 s-BuLi (1) t-PeOK (10) c-hexane RT/15 75/20 s-BuLi (2) t-PeOK (6) n-hexane -78/120 70/22 s-BuLi (2) t-PeOK (6) n-hexane--48/15 76/10 s-BuLi (2) t-PeOK (6) n-hexane--48/263 77/12 s-BuLi(2) t-PeOK (6) c-hexane RT/15 84/7 s-BuLi(2) t-PeOK (6) c-hexane RT/1860 70/1 s-BuLi (2) t-PeOK (6) c-hexane 65/15 79/3 s-BuLi (2) t-PeOK (6) c-hexane 65/43 87/3 s-BuLi (2) t-PeOK (6) c-hexane 70/10 52/12 s-BuLi (1.1) I-MenONa c-hexane RT/15 5/0 (1.25) s-BuLi (1.1) I-MenOK (1.25) c-hexane RT/15 36/4 s-BuLi (1.1) I-MenOK (1.25) c-hexane 35/3 s-BuLi (1.1) I-MenOCs c-hexaneRT/15 71/1 (1.25) s-BuLi (1.1) I-MenOCs c-hexane RT/1534 50/3 (1.25) s-BuLi (2) I-MenOCs (2) c-hexane RT/15 94/5 s-BuLi (2) I-MenOCs (4) c-hexane RT/15 88/3 s-BuLi (2) I-MenOCs (6) c-hexane RT/15 99/2 * Eq means molar ~val~ t~ emplyed with regards to the total number of p-methyl styrene units in the co~l~ r solvti~mc WO 96/36650 PCT/US96tO7278 Runs reported in Table 2 were carried out in accoldallce with General Procedures A and B except, as inr1ic~te-1 in some runs the superbase was suppl~m~nted with TMEDA or a Proton Sponge additive 1,8-bis(dimethylamino)n~phth~lene (Proton-sponge) which, in the ql~ntiti~s indicated, 5 was added to the polymer solution at the time of alkali metal alkoxide addition.

Table 2 Alkyl T ithillm ~lkoxide (Eq) Additive(Eq) Solvent Silylation (%) (Eq) T(~C)/t(min) Benzylic Ring s-BuLi (2) t-PeOK (6) TMEDA (8) c-hexane 79/27 t-BuLi (2) t-PeOK (6) c-hexane 68/10 t-BuLi (2) t-PeOK (6) TMEDA(8) c-hexane 70/8 t-BuLi (2) t-PeOK (6) Proton c-hexane 64/9 Sponge RT/15 ~ n. le An isobutylene-para-methylstyrene (0.32 g; 0.139 mmol para-methylstyrene/gram polymer) is dissolved in cyclohexane (3.5 ml). 8.3 ml (0.833 mmol) of freshly prepared, cesium 1-(-) ~ h,~.;de or potassium 1-(-) m~nthoxide (0.10 molar solution in cyclohexane) is added followed by 0.214 ml (0.278 mmol) of s-BuLi (1.30 molar solution in hexane). The deep dark red solution is stirred for 15 mimltes at room temperature and then qll~nrh~cl with a 4-fold excess of TMSCl. The q~n~.he~l reaction mixture is stirred for 1 hour and then pl~ e into 10 times its volume of isoplopanol. The solvent is cleç~nte-l, the ~
polymer is washed several times with meth~nol and finally dried at 60~C under 20 vacuum for at least 24 hours. The degree of silylation as delellllllled by lH-NMR
is greater than 99% for the benzylic position and about 2% of silylation occurs on the aromatic ring of the p-methyl styrene group.

- =

FUNCTIONALIZATION EXAMPLES
-General Procedure D
,. .
Functionalization reactions using electrophiles other than TMSCl are carried out as described under General Procedure A, replacing TMSCl as in-lic~ted with a reactive electrophile. With regard to the number of p-methyl styrene units, 2 equivalents of a s-BuLi and 6 equivalents of t-PeOK are used as the mçt~ tin~
reagent. The mP.t~l~tion reaction is q~lPnched after lS ...;....les by using an excess 10 of the inrlic~ted electrophile. In the case of electrophiles prone to side reacti~n~
(such as cros~linking) inverse addition of the mçt~ tecl polymer solution into asolution of hydrocarbon and electrophile was plerelled. Work up is described under General Procedure B. Deviations from this genera1 procedure are stated individually in the prt;~ lion procedure it concerns.

Gase~ - For~l ~' yde Pyrolysis of dried para-formaldehyde was carried out at about 130~C in an inert atmosphere. The rçsulting gas was introduced to the solution of mçt~ ted polymer. Once the dark red color of the reaction mixture had faded to a yellow, 20 the reaction was worked up as described. Yield: 70%.

This reaction was also carried out at elevated telll~)el~ res (40-50~C).
l?edll-fion ofthe amount of SB used (s-BuLi (l.l Eq)/t-PeOK (l.5 Eq) is possiblewith little affect on the yield. Yield: 60%.

Parafo ~ de Para-formaldehyde was dried over P2Os under reduced ples:iule. It was added to the solution of mçt~ ted polymer at room tell,pe,~L~lre upon which the dark red solution slowly turned yellow. After 1 hour the reaction r,l,~Lu,e was 30 worked up. Yield:40%.

Metalfor~ de Dried metalformaldehyde was added to a solution of mçt~ ted polymer.
The dark red color turned to yellow within l0 mimltes and the reaction was 35 wc"l~dup after l hour. Yield: 57%.

Ethylene Oxide Ethylene oxide was introduced as a gas to the solution of m~t~ tecl polymer. The reaction took place i.. ~edi~ely, I~.h~n~ing the color of the dark red solution to yellow. Although an excess of ethylene oxide was used, chain 5 propagation was not observed. Yield: 50-70%.

With repl~c~m~nt of the potassium pPntoxide with cesium l-(l)-m~nthoxide, chain propagation was observed. The yield, however, was not improved.

1O Croto ~l~ehyde Freshly distilled crotonaldehyde was added dropwise to a solution of met~ ted polyrner. Af[er 1 hour the reaction mixture was worked up as described. Yield: 45%.

15 Citral Freshly distilled citral was added dropwise to a solution of met~ ted polymer. After 1 hour the reaction mixture was worked up as described. Yield:
40%.

20 2.2.2-Trimethyl Acetaldehyde Freshly di~tilled t-butyl aldehyde was added dropwise to a solution of met~ qted polymer. After 1 hour the reaction ~ u. ~ was worked up as described. Potassium pentoxide was replaced by cesium l-(-)-m~ntho,Yi-le in thisreaction to study the effect of a chiral alkoxide on the reaction ...e~l.~,-i~,., 25 Mea~u.c~---t;--L of the optical rotation of the product showed a small but ~ignific~nt positive value. The optical rotation of the alkoxide solution is negative howevt;l.
Hence chiral intlncti~n was observed. Yield: 70%

Terephth~ rboxyaldehyde A 12-fold excess of terephth~ icarboxy aldehyde was dissolved in a mixture of cycloh~Y~ne and THF (2:1 v/v). The met~l~ted polymer solution was added dropwise at room te ~-pe-~ re. The dark red color was c~-~n~h~d eously. At the end of the addition the solution had acquired a reddish color. THF was added to form a clear sol~ltion before the reaction mixture was 35 stirred overnight after adding aqueous HCI (10%). The rest of the work up is described in the General Procedure B. Yield: 15%. The 1,~ )l with acid lead CA 022l9464 l997-ll-l7 to the Pl;.";"i~l;on of water. Therefore the final product col.L~ined carboxyl snhstituted stilbene units.

Dimethylcarbonate 5To neat, dried and ~lictilled dimethyl carbonate was added dropwise and under vigorous stirring a solution of met~l~ted polymer. The dark red color was q~l~n~hed imme~i~tely, leading to a clear and yellow solution. After stirring continued at room te---pe-~lu~e overnight, the reaction mixture was worked up asdesc.ibed under General Procedure B. In this particular case extractions with base o were avoided. Yield: 23%

Carbon Dioxide A solution of met~l~tecl polymer was t-~ns~e--ed onto a large excess of solid carbon dioxide. The polymer solidified. Additional carbon dioxide was 15 layered on top of the polymer before an equal volume of THF was added. Upon warming the dark red color of the polymer disappeared at the same rate as the polymer went into solution. The q~len~ ed reaction l-~;xlure was left stirring at room te-lll)el~lu-e overnight after aqueous HCI (10%) was used to obtain the carboxylic groups in their plololl~led state. The product was pure enough so that 20 the functi~ n~li7ed polymer could be dried without prior p.e~ iLalion (yield =
74%). A met~l~tion was carried out with higher excess of superbase (PMS/s-BuLi/t-PeOK=1/4M.3). The met~l~tion was çc~nti~lly completed with 2 min-ltç~
The yield was high (94%) by reacting with carbon dioxide and no cletect~ble ringcarboxylation in the product.

Allyl Br~ i 'e Freshly tli~tilled allyl bromide was added dropwise to a solution of met~l~ted polymer. Upon addition the dark red colored solution turned to yellow.Stirring was continued for 1 hour. Work up inrl~-ded precipitation, washing and 30 drying (see General Procedure B). Yield: 40%

2-Chloroell.,~l Vinyl Ether Freshly distilled 2-chloroethyl vinyl ether was added dropwise to a solution of met~l~ted polyrner. Upon ~d-lition the dark red solution turned yellow. Stirring 35 was contin~led for 1 hour. Work up in-l~lded plec~ ;on, washing and drying (see General Procedure B. Yield: 50%

2,2,5,~Tetramethyl-1-(3-chloropropyl)-1-aza-2,5-disilacyclore~ e The silane protected amine was dictilled prior to use. It was disso1ved in cyr,1ohP,Y~ne (about 0.60 molar) and added at room temperature to a solution of S mPt~l~ted polymer. The dark red color of the polymer solution was q11ent~hf~d n.oously upon addition. After the ~d~litiQn the light yellow solution was stirred for 1 hour. One fifth of the solution volume was added as acetic acid (50%
V/V) and the reaction mixture was heated to reflux for 1 hour. The milky solution was cooled to room tt;~ ;la~-lre before it was extracted with isoplc.panoVaqueous 1O KOH (about lH; isoplopallol/H2O 1:10 v:v). It was extracted further 6 times with isoplopanol/H2O (1:1 v:v). The organic layer was concellLI~ed and finally the polymer solution was ple~i~iL~Led into 5 times its volume of isoplopanol. The polymer was washed with iSOpl opallol several times. The primary amine function~li7P,d polymer was dried under vacuum at 65~C for at least I day. Yleld:
70%

Ethylene Sulfide Freshly distilled ethylene sulfide was added dropwise to a solution of met~l~ted polymer. The reaction took place immedi~t~1y, in~ic~ted by a color 20 change from dark red to a clear solution with a yellow touch. The reaction was q~P~nrhed by using a 10-fold excess of methyl iodide after I hour. Stirring continues, first at room lelllp~ ule, then followed by heating the solution to reflux for 3 hours. The reaction mixture was worked up as described under General Procedure B, except during the drying step at room tel~pe,~L~le under 2s vacuum the polymer crosclinkecl N,N-D~ ylrOr ~ i'r (DMF) To a stirred ~m11lciQn of freshly distilled DMF in n-hexane at -78~C. a solution of met~1~ted polymer (-78~C) was added in a slow stream. The dark red 30 color, characteristic of the mPt~l~teci polymer, disappe~ed ;~.c~ eously uponaddition. Vigorous stirring continued for 30 min11tes before aqueous HCI (10%), about half the volume of the organic phase, was added. The stirred suspension was slowly warmed to room temperature. The aqueous phase was separated from the organic phase a~er 3 hours and a con~ç~ led solution of the polymer in n-hexane 35 was p,~ dled into ~cetone. The supelllal~lll Iiquid was dec~nted aLle, w~ds and the meth~nc-l was used to wash the ~ g polymer several times. The sample CA 022l9464 l997-ll-l7 was dried at room temperature under vacuum for at least 24 hours. The dried polymer could not be redissolved into hydrocarbon solvents or T~. Metalation of Isobutylene-para-methylstyrene differed in this procedure conlpaled to the one sm.. ~ ed under "General P.epa~Lion," in that only 1.25 Eq of s-BuLi and 1.50 5 Eq of t-PeOK were used.

l-Formyl Fi~
Reaction conditions and observations are id~ntir.~l to the ones described for when DME is used as electrophile.

A slight excess of D20 was added to the met~lztecl polymer solution (PMS/s-BuLi/t-PeOK=1/1.5/3). The color of the solution r.h~nged from dark red to colorless. The deuterated copolymers was recovered with 70% yield.

Claims (24)

CLAIMS:

1. A method of introducing functionality into a copolymer of an isoolefin and an alkylstyrene at the alkylbenzyl carbon atom comprising the steps of:
forming a solution of said copolymer in a hydrocarbon solvent; adding to said polymer solution an alkali metal Cs, K, Na alkoxide and an alkyl lithium compound to form a superbase with the polymer solution; and adding an electrophile to said base polymer solution.

2. The method of Claim 1, wherein the superbase is present in an amount relative to the alkylstyrene content of the copolymer to provide a mole ratio of from about 1:1 to about 2:1.

3. The method of Claim 1 wherein the alkali metal alkoxide and alkyl lithium are added sequentially.

4. The method of Claim 1 wherein the alkali metal alkoxide and alkyl lithium are first reacted to provide superbase and the superbase is added to the polymer solution.

5. The method of Claim 1, wherein the alkali metal alkoxide is an alkoxide of cesium or potassium.

6. The method of Claim 5, wherein the alkali metal alkoxide is an alkoxide of cesium.

7. The method of Claim 5, wherein the alkyl lithium compound is a secondary alkyl lithium compound.

8. The method of Claim 7, wherein the alkyl lithium compound is sec-butyl lithium.

9. The method of Claim 1 wherein the alkylstyrene is p-alkylstyrene.

10. The method of claim 1 wherein the p-alkylstyrene is p-methylstyrene.

11. The method of Claim 1, wherein the copolymer is an isobutylene-para-methylstyrene copolymer.

12. The method of Claim 1, wherein the electrophile is selected from the group consisting of acyl chlorides, CO2, CS2, aliphatic chlorides, benzylic chlorides, allylic chlorides, fluoroaromatics substituted with an electron withdrawing group, silylchloride, aldehydes, ketones, carbonates, esters and anhydrides.

13. A composition comprising:
the product resulting from reaction of a reaction product of a copolymer of a monoisoolefin and a alkylstyrene with a superbase and an electrophilic reagent.

14. The composition of claim 13 represented by the formula:

wherein "a" is in the range of 1 to 70,000, "b" in the range of 1 to 7,000, and "c" in the range of 0 to 7,000, R1 and R2 are each independently a C1 to C5 alkyl or hydrogen, provided that at least one of R1 and R2 is alkyl and R1 + R2 ~ 5 carbon atoms; R3 - R4 are each independently one of hydrogen, a C1 to C4 alkyl group fragment and E is an electrophile.

15. The composition of Claim 14 wherein the fragment is from one of aldehydes, ketones, esters, organic halides, acyl halides, trialkylsilyl halides, sulfonyl halides benzyl halides, aliplatic halides, silylic halides, enones, fluoroaroaramatyl, epoxides, episulfides CO2, and polymeric fragments containing electrophillic groups.

16. The composition of Claim 15 wherein the fragment is CO2, ethylene oxide or episulfides.

17. A random copolymer represented by the formula:

wherein "a" is in the range of 1 to 70,000, "b" in the range of 1 to 7,000 and "c" in the range of 0 to 7,000, R1 and R2 are each independently a C1-C5 alkyl or hydrogen, provided that at least one of R1 and R2 is alkyl and R1 + R2 ~ 5 carbon atoms; R3 and R4 are each independently one of hydrogen, a C1-C4 alkyl group, and M is an alkali metal other than lithium.

18. The copolymer of Claim 17 wherein M is Na, K, Cs.

19. The copolymer of Claim 18 wherein 10 to 100% of M has been replaced by an electrophile.

20. The copolymer of Claim 18 wherein the alkylstyrene and metallated alkylstyrene are p-alkyl and p-metallated alkylstyrene.

21. The copolymer of Claim 19, wherein the alkylstyrene and the functionalized alkylstyrene are p-alkyl and p-functionalized alkylstyrene.

22. A method of metallating a copolymer of an isoolefin and an alkylstyrene at the alkylbenzyl carbon atom, said process comprising the steps of: forming a solution of said copolymer in a hydrocarbon solvent; adding to said polymer solution, an alkali metal alkoxide and an alkyl lithium compound to form a superbase with the polymer solution; and recovering the metallated copolymer.

23. The method of Claim 22 wherein the alkali metal alkoxide and the alkyl lithium are added sequentially.

24. The method of Claim 22 wherein the alkali metal alkoxide and the alkyl lithium are first reacted to provide the superbase and the superbase is added to the polymer solution.

Functionalization of isoolefin-alklylstyrene copolymers via metalation with alkali metal Cs, K, Na alkoxide and alkyl lithium superbase formation is previously unknown. Metalation of other styrenic polymers with alkyl lithium activated with TMEDA in prior art, and with alkyl lithium/K alkoxide superbase, results in product wherein main chain and/or aromatic ring carbon atoms are metalated and functionalized, and/or incomplete metalation/functionalization of p-alkyl group of the styrene unit. In accordance with this invention, little or no main chain/aromatic ring metalation occurs and essentially complete metalation of the p-alkyl group of the styrene unit can be obtained.