C is very reactive, difficult to control and stabilize

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1 ynhesis of Polymers Prof. Paula ammond Lecure 25: Living aionic Polymerizaions, Examles of aionic Polymerizaion, Isobuyl ubber ynhesis, Polyvinyl Ehers aionic Polymerizaion ome differences beween caionic and anionic olymerizaion aes are faser for caionic (1 or more orders of magniude faser han anionic or free radical) is very reacive, difficul o conrol and sabilize more ransfer occurs more side reacions more difficul o form living sysems hard o mae olymers wih low PDI or bloc coolymers Living caionic only ossible for a secific subse of monomers Mos indusrial caionic rocesses are no living - recen develomens are imroving his comes off Kineic es for aionic Polymerizaion Iniiaion: Use cids Proonic cids (Bronsed): srong, bu wihou nucleohilic counerion lo 4, F 3 O 3, 2 O 4, FOO - lo wan o avoid recombinaion hrough counerion Lewis cids Ofen as iniiaor/coordinaion comlexes hels sabilize counerions and reven recombinaion BF 3 2 O [ BF - 3 O] ll 3 l [ ll - 4 ] bf 5 F [ bf - 6 ] Equilibrium beween anion-caion air iaion: Professor Paula ammond, ynhesis of Polymers Fall 2006 maerials, MIT OenourseWare (h://ocw.mi.edu/index.hml), Massachuses Insiue of Technology, Dae.

2 arbenium sals wih aromaic sabilizaion l bl 5 bl 6 Proagaion 2 iniiaion secies 2 2 vinyl monomer 2 oe: rearrangemens can occur, esecially if a more sable carbocaion can be formed (e.g. eriary carbocaion) (mos common for 1-alenes, α olefins) e.g. 2 mehyl buene secondary carbocaion eriary carbocaion This occurs via inramolecular hydride ( - ) shifs Usually slow: If rearrangemen rae, will ge rearranged roduc If > rearrangemen rae, will ge random coolymer s T, m (less rearrangemen) ae of rearrangemen does no increase as fas as rae of roagaion. 3 ydride shif OT common for conjugaed monomers lie: syrene, vinyl ehers and isobuylene and oher eriary carbocaions , ynhesis of Polymers, Fall 2006 Lecure 25 Prof. Paula ammond Page 2 of 7 iaion: Professor Paula ammond, ynhesis of Polymers Fall 2006 maerials, MIT OenourseWare (h://ocw.mi.edu/index.hml), Massachuses Insiue of Technology, Dae. 2 3 m

3 Terminaion and Transfer (everal Possibiliies) ) Terminaion wih counerion: ills roagaing caion, ineic chain ( ) i) ombinaion O,comb 2 F 3 OO 2 O F 3 ii) nion liing 2 BF 3 O,s 2 O BF 3 B) Transfer or erminaion o imuriy or solven O To 2 O, O, 3, O, ec. Iniiaor e.g. M M(IZ) X 2 Imuriy or olven r,s M M X(IZ) O 2 O more sable han no as reacive, acs as reardan - will no roagae furher or 2 -O 2 O wea acid will no iniiae ll hese rocesses ill chain lengh , ynhesis of Polymers, Fall 2006 Lecure 25 Prof. Paula ammond Page 3 of 7 iaion: Professor Paula ammond, ynhesis of Polymers Fall 2006 maerials, MIT OenourseWare (h://ocw.mi.edu/index.hml), Massachuses Insiue of Technology, Dae.

4 Transfer (Kineic hain Mainained) ) Proon ransfer o monomer 2 3 roagaes B) ydride ion ransfer from monomer roagaes In general, chain ransfer o monomer is favorable so M r, M can be sizeable. ) Proon ransfer o counerion ( sonaneous erminaion ) r,ci roagaing coninues Usually roagaes (does OT ill chain) usually goes on o iniiae again roic acid iniiaors are ossible Lewis acids are less liely , ynhesis of Polymers, Fall 2006 Lecure 25 Prof. Paula ammond Page 4 of 7 iaion: Professor Paula ammond, ynhesis of Polymers Fall 2006 maerials, MIT OenourseWare (h://ocw.mi.edu/index.hml), Massachuses Insiue of Technology, Dae.

5 Kineic Exressions Iniiaion: ssume Lewis cid Pair I 1. ZY Y(IZ) K i ( IZ) Y I ZY 2. Y(IZ) M YM(IZ) ofen rae limiing If se 2 is rae deermining, hen i i Y ( IZ) M K i I ZY M * i could be deermined based on se 1. Then he exressions would be differen. Proagaion YM j (IZ) M YM j1 (IZ) some number of monomer YMj ( IZ) M M M ssumion: chain lengh has lile effec on reaciviy Le [M ] oal concenraion of all-size roagaing carbocaions (ion airs free ions) Terminaion Mus deermine rimary means of erminaion (solven, imuriies, counerion combinaions, or all?) Examle case: erminaion by counerion combinaion YM(IZ),comb YMIZ, YM IZ, ( ) comb comb If we assume seady sae [M ] K M I ZY eady sae assumion is ha i i i K i i M I ZY M i Going bac o wih 2 i M Ki I ZY M second order in [M] Firs order in i , ynhesis of Polymers, Fall 2006 Lecure 25 Prof. Paula ammond Page 5 of 7 iaion: Professor Paula ammond, ynhesis of Polymers Fall 2006 maerials, MIT OenourseWare (h://ocw.mi.edu/index.hml), Massachuses Insiue of Technology, Dae.

6 (unlie free radical) P : o ransfer (o monomer, solven, counerion) M P P : If ransfer occurs r,m : o monomer creae new roagaing chain r, : o solven creae new caionic secies r,i : o counerion recreae iniiaion P, r, i r, M r wih r, i r, i r, M r, M M r, r, M P M r, i r, M M r, 1 r, i M P M M M r, M r, uose ransfer o solven or imuriy does no resul in furher roagaion. e.g. 3 (IZ) M M(IZ) 3 M M This mus be included in seady sae [M ] exression 2 Ki [][ I ZY ][ M ] erm from ransfer lie r, [ ] *does no effec Is sable o furher roagaion P exression (do no include in P calc) *oe: all of he above assumes he 2 nd iniiaion se is rae deermining. Validiy of eady ae ssumion o really valid - rxn raes very raid (seconds minues) - ofen i > , ynhesis of Polymers, Fall 2006 Lecure 25 Prof. Paula ammond Page 6 of 7 iaion: Professor Paula ammond, ynhesis of Polymers Fall 2006 maerials, MIT OenourseWare (h://ocw.mi.edu/index.hml), Massachuses Insiue of Technology, Dae.

7 - [M ] slowly increases wih ime - [M ] reaches maximum lae in olymerizaion hen decreases wih furher conversion licaion of equaions is merely an aroximaion of wha really haens , ynhesis of Polymers, Fall 2006 Lecure 25 Prof. Paula ammond Page 7 of 7 iaion: Professor Paula ammond, ynhesis of Polymers Fall 2006 maerials, MIT OenourseWare (h://ocw.mi.edu/index.hml), Massachuses Insiue of Technology, Dae.