The Polym er iza tion of M ethyl M ethacryla te w ith a New Nd (O i-pr) 3 A I(i-Bu) 3 Ca ta lyst System 3

Transcription

1 Chem ical R esearch in Ch inese U n iversities V o l. 13 N o. 4 (1997) The Polym er iza tion of M ethyl M ethacryla te w ith a New Nd (O i-pr) 3 A I(i-Bu) 3 Ca ta lyst System 3 SU N J un2quan (D ep ṫ of P olym. S ci. and E ng ineering, Z hej iang U n iversity, H ang z hou, ) (T he labora tory of R a re2e a rth Chem istry and P hy sics Chang chun Institu te of (A pp lied Chem istry, A cad em ia S in icia, Chang chun, ) (R eceived A ugust 29, 1996) M ethyl m ethacrylate (MM A ) w as po lym erized w ith the rare earth coo rdination catalyst system of N d (O i2p r) 3 in to luene. T he influences of variou s ligands in neodym ium comp lexes, mo lar ratio of A lgn d, catalyst concen tration, catalyst ag2 ing tim e, so lven ts, the th ird componen t CC l4, temperatu re and tim e on the po ly2 m erization of MM A w ere studied. T he resu lts show ed that the po lym erization con2 version reached mo re than 80% at a catalyst concen tration of mo lgl. T he app rop riate mo lar ratio of CC l4gn d w as 4. H ydrocarbon w as p referred fo r the po lym erzation to ob tain a h igh conversion and a h igh M W of PMM A. T he 1 H NM R spectra of PMM A indicated that the low er the temperatu re, the h igher the syndio2 tactic con ten t of PMM A w as ob tained. Ke yw o rds R are earth catalyst, N eodym ium catalyst, N eodym ium triisop ropox2 ide, Coo rdination catalyst, Po lym erization, M ethyl m ethacrylate In troduction Since 1991, rare earth coo rdination catalysts have been successfu lly devel2 oped fo r the po lym erization of acrylate [1 ], bu t up to now on ly a few repo rts have described the po lym erization of acrylate by these catalysts such as N d (P204 ) g A l (i2bu) 3, N d ( P 204 ) 3gA l ( i2bu ) 3gCC l4, N d (oct ) 3gA l ( i2bu ) 3, Y ( acac ) 3g A l (i2bu) 3gBuL i and N d (naph) 3gBuL i [2 5 ]. A ll the rare earth com pounds m en2 tioned above are stab le in atm o sphere. R ecen tly w e have syn thesized neodym ium triisop ropox ide N d (O i2p r) 3 w h ich is very sen sitive to m o istu re. Com pared w ith the rare earth com pounds m en tioned above, at room tem peratu re N d (O i2 P r) 3 coo rdinates w ith alkyl alum in ium m o re vigo rou sly to p roduce active species. In the p resence of N d (O i2p r) 3 A l ( i2bu) 3, the po lym erization of MM A in to luene gives PMM A, w h ich po ssesses a h igh syndio tactic con ten ṫ T he stere2 o specificity of the po lym erization depends on the po lym erization tem peratu re. 3 Suppo rted by the N ational N atural Science Foundation of Ch ina.

2 T he effects of A lgn d m o lar ratio, po lym erization tem peratu re, catalyst concen2 tration and o ther condition s on the po lym erization are studied in the p resen t pa2 per. T he excess A l (i2bu) 3 m ay act as the tran sfer agen t in the p resen t po lym er2 ization. Exper im en tal 1 M a te ria ls MM A w as w ashed w ith dilu ted N ao H un til it becam e co lo rless, fo llow ed by being dried over anhydrou s M gso 4, then it w as distilled over calcium hydride under a reduced p ressu re. N dl 3 (L = naph, P 204, acac, i2o ct) w as p repared and pu rified acco rding to ref. [ 6 ], w here naph = naph thenate, P 204 = (RO ) 2P (O ) O, R = CH 3 (CH 2) 3CH (C 2H 5) CH 2, acac= acetyl acetonate, i2o ct= ethylhex2 anoate, nam ely iso2octano ic acid. N d (O i2p r) 3w as syn thesized from anhydrou s N dc l3 w ith sch lenk techno logy under pu rified n itrogen atm o sphere [7 ]. A l (i2bu) 3 w as ob tained from Ro th Com pany. A ll the so lven ts fo r the po lym erization w ere refluxed over N a and distilled befo re being u sed. 2 C a ta lys t P re pa ra tion a nd P o lym e riza tion T he catalyst w as p repared by adding sto ich iom etric am oun ts of A l (i2bu) 3 to N d (O i2p r) 3 to luene so lu tion, and then aged fo r som e tim e at the con stan t tem 2 peratu re. T he po lym erization w as carried ou t in am pou les w h ich w ere baked, vacuat2 ed and filled w ith pu re n itrogen fo r several cycles. T he so lven t, MM A and the catalyst so lu tion w ere in jected by hypoderm ic syringe sequen tially in to the am 2 pou le at the po lym erization tem peratu re. T he po lym erization w as term inated by adding ethano l con tain ing 5% hydroch lo ric acid, and the po lym er p recip itated w as w ashed w ith ethano l, dried at 50 under vacuum. 3 M e a surem e nt T he in trin sic visco sity of PMM A in CHC l3 w as determ ined at 30 w ith an U bbelohde2type viscom eter. T he visco sity2average m o lecu lar w eigh t w as calcu2 lated w ith the fo llow ing equation: [ Γ]= M 0. Γ 8 (ml g) [8 ], MW D values w ere m easu red on the GPC ch rom atogram s w ith W aters A ssociates2m 730 at 30 u sing TH F as eluen ṫ T he GPC ch rom atogram w as calib rated again st stan2 dard po lystyrene sam p les at 30. T he 1 H NM R spectrum of PMM A fo rm ed w as reco rded at 60 on JEOL FX290 u sing CDC l3 as the so lven ṫ Results and D iscuss ion In Ziegler2N atta catalytic po lym erization, the changes in the ligands of tran2 sition m etal com p lexes can greatly affect the behavio r of the catalysṫ V ariou s ligands w ith differen t steric sizes and electron negativities lead to the variation of the stereo specificity and coo rdinating ab ility of catalyst. 345

3 A s show n in T ab le 1, the ligands of neodym ium com p lexes no t on ly have a great influence upon the po lym erization conversion bu t also dram atically affect the m o lecu lar w eigh t (M w ) of PMM A. M ak ing a com parison betw een N d (O i2 P r) 3 and o ther neodym ium com p lexes, one can see that bo th the conversion and M w of PMM A by N d (O i2p r) 3 catalyst are obviou sly h igher than tho se of PM 2 M A by o therṡ It m ay be related to the structu res of neodym ium com p lexes. Be2 cau se the oxygen atom s w h ich coo rdinate w ith neodym ium in N d (O i2p r) 3 are less than tho se in all the o ther rare earth com p lexes, w h ich leads to the increase of the coo rdination ab ility of N d (O i2p r) 3 w ith alkyl alum in ium and m onom er to p roduce m o re active species fo r the po lym erization. T ab le 1 T he effect of variou s ligands in neodym ium comp lexes on po lym erization 3 Comp lex N d (O i2p r) 3 N d (P 204) 3 N d (naph) 3 N d (i2o ct) 3 N d (acac) 3 Conv. (% ) M Γ A lgn d= 10; [N d ]= mo lgl ; [MM A ]= mo lgl ; To luene; 333 K; 7 h. A s w e know, alkyl alum in ium can no t on ly reduce tran sition m etal atom s in the po lym erization bu t also elim inate im pu rities, such as m o istu re, oxygen and o thers w h ich h inder the po lym erization. F ig. 1 show s the resu lts analogou s to literatu re [ 1 ]. T he conversion increases as the m o lar ratio of A lgn d increaseṡ Bu t the conversion decreases gradually w hen the m o lar ratio of A lgn d is larger than 30. It m ay be attribu ted to the disp ropo rtion reaction betw een the active species and excess alkyl alum in ium. O n the o ther hand, the M w of PMM A drop s as the m o lar ratio of A lgn d increases. It m ay be cau sed by the chain tran sfer ac2 tion of uncoo rdinated excess alkyl alum in ium. GPC p lo t (F ig. 2) suggests that no m atter w hether MM A w as po lym erized at - 30 o r 60, the PMM A p ro2 duced w as a m ix tu re com po sed of tw o parts w ith a h igher M w and a low er M w, w h ich indicates that there m ay be tw o active species in the po lym erization p ro2 F ig. 1 T he effect of mo lar ratio of A lgn d on the po lym erization fo r 8 h. O ther conditions are the sam e as tho se in T able F ig. 2 GPC spectra of PMM A p repared. W ith the mo lar ratio of A lgn d = 10 at 333 K (a) and 243 K (b).

4 cess, nam ely the coo rdinated com p lex and alkyl alum in ium respectively. T he PMM A w ith the low er M w m igh t be ascribed to additional uncoo rdinated alkyl alum in ium, w h ich m igh t be the species w h ich are ab le to p roduce low er M w po ly2 m ers [1 ]. M o reover, alkyl alum in ium can induce chain tran sfeṙ F ig. 3 dem on strates that the increase in catalyst concen tration cau ses the re2 m arkab le increase of conversion, w h ile the M w of PMM A has a m ax im um value at a catalyst concen tration of m o lgl. W hen the catalyst concen tration is over m o lgl, the M w of PMM A drop s con siderab ly. Bu t w hen the catalyst concen tration is low er than m o lgl, a part of the catalyst m igh t be con sum ed in the elim ination of im pu rities to decrease the chain tran sfer reaction, cau sing the M w of PMM A to increase w ith the increase in catalyst con2 cen tration. F ig. 3 T he effect of catalyst concen tration on the po lym erization fo r 8 h. O ther conditions are the sam e as tho se in T able 1. F ig. 4 T he effect of aging tim e of cata2 lyst on the po lym erization. T he conditions are the sam e as tho se in T able 1. T he influence of catalyst aging tim e on the po lym erization is indicated in F ig. 4. T he conversion and the M w of PMM A reach their m ax im a respectively as aging tim e is 45 m in. W hen aging tim e is m o re o r less than 45 m in, the conver2 sion and the M w of PMM A drop slow ly, w h ich m ay indicate that the in teraction of catalyst com ponen ts is no t com p lete befo re 45 m in and after 45 m in som e ac2 tive species are u sed up in the side reaction, such as disp ropo rtion o r the reaction w ith im pu ritieṡ T he fu rther study dem on strates that hydrocarbon s are good so lven ts fo r the po lym erization of MM A (T ab le 2). Am ong them, hep tane and petro leum ether p recip ita te the po lym er p roduced, thu s y ield ing a h igher conversion and the h igher M w of PMM A. Po lar so l so lven ts such as tetrahydrofu ran (TH F) and ethyl acetate are poo r so lven ts, w h ich m ay be due to the fact that their coo rdination w ith active species h inders the coo rdination of MM A. 347

5 T ab le 2 T he effect of so lven ts on po lym erization 3 So lvent n2h ep tane Petro leum ether To luene T etrahydrofuran E thyl acetate Conv. % M Γ h, o ther conditions are the sam e as in T able 1. F ig. 5 T he effect of temperatu re (A ) and tim e (B ) on the po lym erization. T he conditions are the sam e as tho se in T able 1. T he tem peratu re dependence of the po lym erization w as exam ined in detail ( F ig. 5 (A ) ). F rom 40 to 70, the h igher the tem peratu re, the low er the M w of PMM A and the larger the conversion of MM A. T h is m ay be due to the reason that the rate of chain p ropagation becom es faster as the ratio of active m onom er m o lecu les rises at h igher tem peratu res, w h ile the life tim e of catalyst active species decreases, hence the M w of PMM A drop s gradually. F ig. 5 (B ) illu strates the effect of tim e on the po lym erization of MM A. T he conversion and the M w of PMM A increase gradually w ith in 10 h and then reach a p lateau. T he M w of PMM A does no t decrease w ith the p ro longation of po lym er2 ization tim e, suggesting that no degradation ex ists du ring po lym erization. F ig. 5 (B ) also show s that the M w of PMM A increases linearly w ith in 10 h w ith the increase in conversion, it indicates that catalyst active species have a longer lifetim e, w h ich m ay be due to the living po lym erization. T he effect of CC l4 as a th ird com ponen t on the po lym erization of MM A has been investigated in detail (F ig. 6). T he op tim um m o lar ratio CC l4gn d is fou r, as show n in F ig. 6. T he ratio s above and below the op tim um m o lar ratio of CC l4g N d m ake the po lym erization conversion decrease obviou sly, indicating that ex2 cess CC l4 has a dam aging effect on the catalyst. Bu t the M w of PMM A does no t drop w ith in the m o lar ratio of CC l4gn d studied. T h is resu lt indicates that excess CC l4 does no t affect chain p ropagation [9 ]. T he fu rther study on the 1 H NM R spectra of PMM A (F ig. 7) show s that the low er the po lym erization tem peratu re, the h igher the syndio tactic con ten t of PMM A ob tained. T he po lym erization m igh t p roceed in coo rdinated an ion ic m echan ism, in w h ich the stereo selection is chain end2con tro l m echan ism, the ac2 348

6 F ig. 6 T he effect of CC l4 on the po lym erization. A lgn d = 10, [N d ] = mo lgl, F ig. 7 1 H NM R spectra of PMM A ob tained at 333 K (a ), 278 [MM A ]= 6. 0 mo lgl, To luene, 333 K, 6 h. K (b) and 243 K (c). tive grow th cen ter operating in syndio tactic m ode m u st invert ch irality regu larly du ring each addition of m onom er. T he larger coo rdination num ber of N d atom is advan tageou s to the syndio tactic p ropagation occu ring alternately at the tw o lig2 and po sition ṡ T he driving fo rce fo r syndio tactic p lacem en t w ith N d (O i2p r) 3 A l (i2bu) 3 catalyst system in the po lym erization of MM A is also the repu lsion be2 tw een side group R on the incom ing m onom er and side group R on the active ter2 m inal m onom er un it of the p ropagating chain [10 ]. O n the o ther hand, the above resu lt is in acco rdance w ith the difference betw een the activation free energies fo r syndio tactic and iso tactic p lacem en ts, w h ich is favou rab le fo r an increasing tendency tow ard syndio tacticity w ith decreasing po lym erization tem peratu re [11 ]. A cco rding to the m echan ism m en tioned above, w e can p redict that the h igher syndio tactic con ten t m ay be ob tained by fu rther decreasing po lym erization tem 2 peratu re. Re fe re nce s [ 1 ] Zheng, W., W en, W., L ongp ing, L. and Zh iquan, S., J. Zhejiang U niv. (N atural sci. ), 25, 114 (1991) [ 2 ] W en, W., Zheng, W., Zh iquan, S., Po lym er m aterials Sci. and Eng., 4, 11 (1991) [ 3 ] Junquan, S., Guangm ing, W., Zh iquan, S., Y ingyong H uaxue, 10 (4), 1, (1993) [ 4 ] J ianfei, L., Junquan, S., Zh iquan, S., Chem ical R esearch in Ch inese U niv., 9 (2), 148, (1993) [ 5 ] J ianfei, L., Zh iquan, S., Junquan, S., Eur. Po lym. J., 12 (17), 883 (1996) [ 6 ] Yangjun, E., Zh iquan S., Co llection of Synthetic R ubber Catalyzed by R are2eearth Catalysts, Bei2 jing, Sci. P ress, 1980, p 113 [ 7 ] M isera, S. N., M isra, T. N., M eh ro tra, R. C., A usṫ J. Chem., 21, 797 (1968) [ 8 ] Changren, Z., MW and DMW of Po lym er, Beijing, Chem. Ind. P ress, 1980, p 402 [ 9 ] John Boo r, J., Ziegler2N atta Catal. and Po lym n., N ew yo rk, A cadem ic p ress Inc., 1979, p 213 [10 ] O dian, G., P rincip les of Po lym n., 2nd ed., N ew Yo rk, John W iley Sons, Inc., 1981, p 606 [11 ] T alam ini, G. and V ido tto, G., M ak romo l. Chem., 100, 48 (1967) 349