Chapter 10. Step-Reaction and Ring-Opening Polymerization

Transcription

1 Chater 0. Ste-Reactin and Ring-ening Plymerizatin 0.. Ste-Reactin Plymerizatin - Kinetics Ste-Reactin Plymerizatin. Difunctinal mnmers Linear lymers B tye, and BB. Plyfunctinal mnmers Functinality > etwrk lymers 3. Plymers retain their functinality as end grus at the cmletin f lymerizatin 4. Single reactin (cf. initiatin, ragatin,and terminatin in chain-reactin lymerizatin)

2 5. M.W. increases slwly Carthers equatin DP extent f reactin 6. High-yield reactins and an exact stichimetric balance are necessary t btain high-m-w linear lymer 7. Frmatin f cyclic byrduct HCH CH H H + - H CH CH,4-dixane lyether majr H CH CH CH CH - H H HCH CH CH C lactam yln 4 majr

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5 Kinetics f Ste-Grwth Plymerizatin Flry s assumtin The reactivity f a functinal gru is indeendent f the length f the chain t which it is attached. Examle: dibasic acid + glycl lyester ssumtin. The reactivity f a functinal gru is unaffected by reactins f ther functinal grus in the mlecule

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7 The rbability f chemical reactin with the increase f the MW: The rate f mlecular diffusin decreases, i.e., larger time intervals between encunters (fewer encunters f functinal grus er unit time) Greater duratin f each encunter (a larger number f cllisins f functinal grus er encunter)

8 Kinetics. Catalyzed [cat]k k [cat] is unchanged If lymerizatin reactin is first rder w.r.t. each functinal gru ( & B) Plymerizatin rate d[ ] k[ ][ B] [ ] ( ) [ ] dt kt If [] [B] [ ] DP d k[ ] [ ] [ ] dt r By integratin DP [ ] kt + kt [ ] [ ] DP t [ ] [ ] k DP [ ] If k is knwn, time can be calculated. kt

9 . Uncatalyzed (self-catalyzed) HC - CH + H H lymer Carbxylic acid: rle f catalyst [ ] d dt k [ ] [ B] ssume [] [B] [ ] d dt Integratin k[ ] 3 [ ] [ ] kt [] [] ( - ) [ ] ( ) [ ] ( ) DP [ ] kt + kt [ ] + kt M.W. increases mre gradually than when acid catalyst is added.

10 Catayzed [ ] kt DP + DP Uncatayzed DP kt [ ] + t

11 0.3 Stichimetric Imbalance Three ways t limit M.W. in ste lymerizatin. T quench the lymerizatin reactin by raid cling when the desired M.W. is attained.. T use an excess f ne mnmer. 3. T use small amunts f mnfunctinal reactant

12 Stichimetric imbalance factr B r where initial # f functinal grus B initial # f B functinal grus By cnventin r reactin extent f ( - ) ( ) ( ) r r r B B # f mlecular chains at ( ) ( ) ( ) r r r B B B B B r cf.

13 # mnmers ( ) B + Since B r + + r r r verage degree f lymerizatin r r r r r r DP If r If DP r r DP +

14 If mnfunctinal reagent is added Imbalance factr r' B B' where B # f mnfunctinal B grus Factr : each B mlecule is equally as effective as ne excess BB mnmer in limiting the M.W.

15 0.4 M.W. Distributin # f ttal mlecules at # f x-mers x M - (M) x- -M - where extent f reactin rbability f reactin n x x x rbability f finding an unreacted gru x x ( ) initial # f mnmers x ( ) n x mle fractin f x-mers x ( )

16 0.99 Mnmer: the mst abundant secies Wt fractin f x-mers x M x w x M x x cf. x x ( ) where M mass f reeating unit Wt fractin distributin w x x ( ) x The mst abundant secies dw dx x x ( ) + ( ) x ( ) ( + xln) 0 x x ln x ln

17 ( ) ( ) ( ) M M x M xm n M n M x x x x n ( ) x x x cf. ( ) 3 x x x + ( ) ( ) ( ) ( ) M M x M xm w M w M 3 x x x x w + + Plydisersity index cf. M M n w + M M n w s,

18 Fig 0. Mle fractin distributin in linear ste-reactin lymerizatin n x

19 Fig 0. Weight fractin distributin in linear ste-reactin lymerizatin w x

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21 0.5 etwrk Ste Plymerizatin Equimlar mixture HC CH CH HCH CH H H HCH CHCH H Functinality verage functinality f av. 5 4 initial # f mnmers # f mlecules at # f functinal grus reacted ( ) Initial # f functinal grus f av

22 ( ) f av f av f av f av DPf av cf. DP t gel int av DP c Critical extent f reactin f If f av.5, c 80% (cf: difunctinal mnmers : DP 5) If mixture 3 ml f, ml f 4 ( 3 ) + ( 3) f av 5.4 c.4 83%

23 f - B - B # f mlecules B C f f B f C f > Functinality Imbalance factr B C C B B C C f f f f r + + C C C C C C C C f f f f f + + ρ extent f reactin fr B extent f reactin fr B rp

24 f- [B B ] i B B f- ( B ( - ρ) ) i B ρ (r ( - ρ) ) i rρ Branching rbability rbability that a functinal gru n a branch unit leads t anther branch unit α i 0 [ ( ) ] i r ρ rρ r rρ ( ρ)

25 3 Trifunctinally branched netwrk lymer i th envele Y i branch ints n the i th envele # f branch ints n (i + ) th envele Y i + Y i α Criterin fr gelatin Y i + > Y i Y i α > Y i α c generally that is α c α > f

26 α c critical branching rbability f f r rρ c ( ρ) c r ( - ρ) c (f - ) r ρ c (r r ρ + f r ρ r ρ) c c [ r + ( f ) rρ] If r If ρ If r ρ c [ + ( f ) ρ] - ll f c [( f ) r] c ( f )

27 HC CH CH H + CH H gelatin t c CH H α c c 0.58 Theretcal (statistical) α ( 3 ) c f c c Carthers equatin (nnstatistical) ( 3 ) + ( 3) f av 5 av.4 c c 83% f.4 Exerimental values f c fall between the values calculated by statistical and nnstatistical methds. Deviatin frm statistical methd () Intramlecular branching reactins leading t wasted ls () Differing reactivities f the functinal grus Reactivity f secndary alchl < Reactivity f rimary alchl In glycerl

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29 0.6 Ste-Reactin Clymerizatin HC CH HC CH HCH CH H BB CC : BB : CC : : Randm clymer + CC CC - - CC BB - (CC - CC BB) - lternating clymer

30 Ste lymers : true telechelic lymers H lyether H + C lyurethane C Cl lyether C lyurethane C H H (B) multiblck clymer C lyester C Cl + H lyamide H C lyester C H lyamide H H lyether H + C lyurethane C H lyether C H lyurethane H C B triblck clymer lyether H

31 0.7 Ste Plymerizatin Techniques ) Bulk lymerizatin Free f cntaminants Disadvantage: high viscsity; elevated tem fr effective stirring and remval f byrducts High vacuum t remve byrducts ) Slvent lymerizatin Lw viscsity Remval f byrduct by azetric distillatin Remval f water in situ by use f effective dehydrating agent ecessity f remving slvent

32 3) Interfacial lymerizatin Slutins f tw mnmers in searate, immiscible slvents (ne usually water) Plymer is frmed at the interface e.g., Schtten Baumann synthesis nyln re trick Raid stirring t maximize the interfacial area increases the yield f lymer Characteristics f interfacial lymerizatin () Reactin ges raidly at lw tem. () Reactin is s raid, diffusin f mnmer t the interface is rate determining (3) Mnmer reacts with the grwing chains at the interface mre raidly than it diffuses thrugh the lymer film t initiate new chains; hence M.W.s tend t be significantly higher. (4) n exact stichimetric balance is nt necessary.

33 Interfacial lymerizatin: the nyln re trick

34 4) Phase-transfer catalysis (PTC) queus hase and rganic hase Catalyst: quarternary ammnium salt Functin by transrting a nuclehilic mnmer frm the aqueus hase t rganic hase, where its nuclehilicity is greatly enhanced because f reduced slvatin effects rganic hase aqueus hase rganic hase ClH C CH Cl + C CH CC(CH 3 ) 3 PhCH + (C H 5 ) 3 Cl - ah, H / benzene CH CH C C CC(CH 3 ) 3 rganic hase

35 queus hase Q + X - + M + Y - Q + Y - + M + X - Interface rganic hase [Q +, X - ] + R-Y [Q +, Y - ] + R-X Q + PhCH + (C H 5 ) 3 X - Cl - - M + a + Y - CCHCC(CH 3 ) 3 R-X ClH C CH Cl Q + R 4 +, R 4 P + Quarternary nium salt selected due t its high slubility in the rganic hase Q + transfers anin Y - int the rganic hase as [Q +, Y - ], which then react with an alkyl halide RX t give the substitutin rduct R-Y The rduced Q + X - is raidly recnverted int Q + Y - by anin exchange with nuclehile M + Y - frm the aqueus hase.

36 0.8 Dendritic Plymers Ptential alicatins: drug delivery systems, cntrlled release f agricultural chemicals, mlecular sensrs, rhelgy mdifiers Characteristic features f dendrimers. Three cmnent arts: a central cre, an interir dendritic structure, and an exterir surface. Macrmlecular dimensins are easily cntrlled by a reetitive sequence f synthetic stes. 3. Mre sluble than linear lymers High surface functinality 4. Lack f chain entanglement Lw viscsity 5. Suramlecular assemblies by incrrating guest mlecules amng the interir branches f the dendrimer.

37 Tw araches t cnstruct dendrimers. Divergent synthesis Branch ints are cnstructed in a stewise fashin frm a central cre.. Cnvergent synthesis Branch segments are cnstructed searately and then jined t a multifunctinal cre.

38 Divergent synthesis Plyamidamine (PMM) dendrimers H CH CH CCH 3 (CH CH CCH 3 ) 3 H CH CH H (CH CH CHCH CH H ) 3 H H H H H H H H H H H H H H H H H H H 0th generatin H H # f surface functinal grus 3 x Surface area: 00 times

39 Cnvergent synthesis Br + H H H base H. CBr 4, PPh 3. H H base H H

40 Scheme 0.3 Cnvergent synthesis f a dendrimer frm dendritic segments.

41 Hyerbranched lymers Mre randm architectures and d nt emanate frm a central cre. Synthesized frm B x functinal mnmers Plymerizatin ccurs via dendritic branching with n ssibility f crsslinking

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43 Ring-ening Plymerizatin Mechanisms. Mnmer is attacked by inic r crdinatin secies (X*) Ring ening ex X* G G G X G* X G G*... R - CH CH CH CH RCH CH - RCH CH CH CH - CH CH. Mnmer is attacked by X* Crdinatin secies Secnd mnmer Ring ening... G X* G G G* X G* G X G* G ex CH CH H H CH CH CH CH HCH CH CH CH CH CH...

44 Reactivity frm ring strain 3 > 4 > 8 > 7 > 5 > 6 6-membered cyclic esters (lactnes) lyesters 6-membered cyclic amides (lactams) X lyamides 5-membered cyclic esters (lactnes) X lyesters 5-membered cyclic amides (lactams) lyamides Cyclic ethers Reactivity 3 > 4 > 8 > 7 > 5 > 6 X lyether

45 Plyesters Plyamides Ring-ening Plymerizatin f -Carbxy nhydrides The rduct lymer is a ly(amin acid) r lyetide r synthetic rtein. This articular reactin is ntewrthy because it is a chain reactin that ccurs with exulsin f a small mlecule (C ). Such reactins are very rare.

46 Silicnes Plyhshazenes n examle f an lymer with an inrganic backbne that can als be made by ste lymerizatin. n examle f a cmletely inrganic lymer that can be functinalized with rganic grus after lymerizatin.

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