PolymerizationPolymerization ““LivingLiving””/Controlled/Controlled PolymerizationPolymerization PolymerizationPolymerization forfor NanotechnologyNanotechnology 중합반응에중합반응에 관한 관한 소개 소개 (나노기술과(나노기술과 관련 관련 있는 있는 중합 중합 방법) 방법) 1/32 PolymersPolymers withwith ControlledControlled ArchitecturesArchitectures Many Natural Polymeric Materials Å Perfect Monodisperse Macromolecules Successive condensation of monomers with polymer end-groups activated by enzymes “Living”/Controlled Polymerization Radical, Cationic, Anionic, ROMP, Coordination Synthetic Polymeric Materials (via Chain-Growth Polycondensation) with Controlled Architecture Dendritic Macromolecules & Linear Oligomers (Stepwise synthesis via Step-Growth Condensation) 2/32 1 Dendrimers Commercially Available Dendrimers 3/32 Synthesis of Dendrimers DSM’s Poly(propylene imine) Dendrimer (Fifth Generation – 64 primary amine Group) 4/32 2 Well-Defined Dendrimers Frechet J. M. J. et al. Chem. Rev. 2001, 101, 3855. Well-Defined (Monodisperse & Controlled) Branched vs. Linear & Folded 5/32 “Living”/Controlled“Living”/Controlled PolymerizationPolymerization vs.vs.Step-GrowthStep-Growth PolymerizationPolymerization “Living”/Controlled Polymerization DP = [M]0/[I]0 PDI ≅ 1 Step-Growth Polymerization DP = 1/(1-p) Molecular Weight (DP) Control of Molecular Weight chain DPn = (1+r)/(1-r), if p = 1 r = [A]/[B], p = conversion Mn living Mw/Mn = 1+p If p = 1, PDI = 2 Conversion step 0100%conversion 6/32 3 Types of Chain Polymerizations of Various Unsaturated Monomers Types of Initiation Monomers Radical Cationic Anionic Ethylene + - + 1-Alkyl olefins (α-olefins)--- 1,1-Dialkyl olefins - + - 1,3-Dienes + + + Styrene, α-methyl styrene + + + Halogenated olefins + - - Vinyl esters (CH2=CHOCOR) + - - Acrylates, methacrylates + - + Acrylonitrile, methacrylonitrile + - + Acrylamide, methacrylamide + - + Vinyl ethers - + - N-Vinyl carbazole + + - N-Vinyl pyrrolidone + + - Aldehydes, ketones - + + Exceptions: Z-N OR (CH2)nH α-olefins 1,1-dialkyl olefins vinyl ethers O O CH2 C OCH2CH2 Ring Opening: n O 7/32 Living Polymerization (LP) vs. Controlled Polymerization (CP) Living Polymerization and Polydispersity Æ Weak Correlation a. Chain-breaking reactions: increase of DPw/DPn with increasing DPn and conversion b. Slow initiation and slow exchange: decrease DPw/DPn and DPn with increasing conversion c. Polydispersity alone is a poor criterion for judging the living character of a polymerization 1. Living polymerizations can have DPw/DPn > 2 (slow exchange) 2. Polymers with DPw/DPn < 1.1 can have 50% terminated chain ends LP LP & CP CP Living Polymerization: Controlled Polymerization: Chain growth Chain or Step growth No chain breaking (no transfer/termination) Limited chain breaking possible - slow initiation possible - fast initiation - slow exchange possible - fast exchange - uncontrolled molecular weights possible - controlled molecular weights - high polydispersities possible - low polydispersities 8/32 4 Experimental Evaluation of “Living”/Controlled System Necessarily, Rtr = Rt = 0 (a truly living system) Ideally, Ri ≥ Rp, Rexch ≥ Rp, propagation is irreversible When these conditions hold, the following can be used to experimentally evaluate the livingness of a polymerization: DPw/DPn ~ 1 + 1/DPn DP [M]0 w ln Mn [M] DPn time conversion (%) conversion (DPn) Real Systems Overall Effecta Kinetic characteristic on Rp on Mn/Mn, th on DPw slow initiation (rel. to propagation) slow exchange (rel. to propagation) transfer ( to anything other than polymer) termination a = increase; = decrease; = unaffected 9/32 Conventional vs. Controlled (Radical Polymerization) ¾ Conventional Radical Polymerization kd I 2 R TT ~ ~ 8080 ±± 2020ooCC ki R + M P1 -5-5 -1-1 M /M > 1.5 kkdd~~ 1010 ss n w n M kp kk ~~ 101033 ±±11 MM-1-1ss-1-1 P1 + M Pn+1 pp kk ~~ 101077±±11 MM-1-1ss-1-1 kt H = tt Pn + Pm Pn + Pm 0 0.2 0.4 0.6 0.8 1 Conversion ¾ “Living”/Controlled Radical Polymerization ka R X R + X kd oo M /M < 1.5 TT ~ ~ 120120 ±± 2020 CC w n k 00 ±±22 -1-1 R M i P kk ~~ 1010 ss + 1 aa n k 88 ±±11 -1-1 M = [M] /[I] p kkd ~~ 1010 ss o o P1 + M Pn+1 d 44 ±±11 -1-1 -1-1 kt H = kkpp~~ 1010 MM ss Pn + Pm P + P n m 77±±11 -1-1 -1-1 kktt~~ 1010 MM ss ka 0 0.2 0.4 0.6 0.8 1 Pn X Pn + X Conversion kd 10/32 5 Controlling Radical Polymerizations a. The problem with conventional radical polymerizations: 7 -1 -1 1. diffusion-controlled termination (kt = 10 M s ) 2 termination is bimolecular: Rt = kt [M •] b. The solution: keep [M •] low through slow initiation: 2. slow initiation -5 -1 -1 -2 Ri = 2 f kd [I] (kd = 10 M s ; [I]0 = 10 M) Therefore, high polymer is still possible in spite of the high termination rate constant because of slow initiation and termination rate (WARNING! rate ≠ rate constant!). c. Designing a Controlled Radical Polymerization - HOW? 1. By definition, Ri ≥ Rp and [I]0 = concentration of propagating chains. 2. Additionally, for any controlled polymerization: Δ [M] [M]0 DPn ==(at full conversion) [I]0 [I]0 -2 consider full conversion for DPn = 1000; [M]0 = 10 M; [I]0 = 10 M. 3. However, from the definition of DPn : R p kp [M] [M ] kp [M] DP = = n R 2 = t kt [M ] kt [M ] and: kp [M] [M ] = kt DPn (instantaneous concentration of radicals) 2 -1 -1 7 -1 -1 -7 for DPn = 1000; [M]0 = 10 M; kp = 10 M s ; kt = 10 M s ; [M •] = 10 M 11/32 Control of Radical Polymerization • Extending life of propagating chains (from <1s to >1 h) (similar rates?) • Enabling quantitative initiation (From Ri << Rp to Ri >> Rp) • Controlling DPn (D[M]/[I]o), MWD, Functionality, Composition, Topology • BY EQUILIBRIA BETWEEN RADICALS AND DORMANT SPECIES kact ¾ Reversible deactivation by coupling Pn-T Pn* + T* kdeact – Nitroxide-mediated polymerization kp Monomer ¾ Reversible deactivation by atom transfer kact n n+1 Pn-X + Mt /L Pn* + X-Mt /L – ATRP kdeact kp ¾ Degenerative transfer Monomer – Alkyl iodides ktr Pn* + Pm-X Pn-X + Pm* – Unsaturated polymethacrylates (CCT) k-tr k – Dithioesters (RAFT) p kp Monomer Monomer 12/32 6 RAFT: Reversible Addition Fragmentation Chain Transfer CH3 CH3 S R CH3 CH3 S k R CH2 C CH2 C* SC a CH2 C CH2 C S C* CO CH CO CH Z 2 3 2 3 k-a Z CO2CH3 CO2CH3 kp M kβ Monomers: Styrenes, (Meth)acrylates, Acrylic acid, Vinyl Benzoate, DMAEMA, etc CH3 CH3 S *R Transfer Agents: Dithioesters CH2 C CH2 C SC kp Z Initiators: AIBN, BPO CO2CH3 CO2CH3 M [M]: bulk, solution Mn Mw/Mn -1 -2 [TA] : 10 to 10 M expt Limit < 1.1 o Mn [In] /[TA] : 0.1 to 0.6 -2 o o kp/kex < 10 Temp: 60-150 oC M theo Time: 2-20 hours n Blocks: possible but limits Conversion Conversion Moad, G.; Rizzardo, E. et. al. Macromolecules 1998, 31, 5559; 1999, 33, 2071 Le, T.P.; Moad, G.; Rizzardo, E.; Thang, S.H. PCT Int. Appl. WO 9801478 A1 980115. 13/32 Nitroxide/TEMPO Polymerization NO* O P EtO OEt H H kact H *O N CH2 C CH2 C O N CH2 C CH2 CH* Tordo, P.; Gnanou,Y. kdeact ACS Symp. Ser. 1998 685, 225. C6H5 C6H5 C6H5 C6H5 kp R M Monomers: Styrenes & comonomers N O* Initiators: Alkoxyamines or -> Acrylates & Lower Temp Ph BPO/Nitroxides Additives & New Nitroxides Hawker, C. et al [M]: bulk (Acids, Dicumyl peroxides) JACS 1999, 121, 3904. -1 -2 [In]o: 10 to 10 M M /M o ln(Mo/M) Mn w n Temp: 120-140 C Limit ~ 1.1 M expt Time: >10 hours n • Self initiation dominates R theo p Mn -11 • kact/kdeact ~ 10 M • Side reactions Time Conversion Conversion (H-abstraction by TEMPO) Solomon,D.H.,. et al. U.S. Patent, 1986 4,581,429. Georges, M.K., et al. Macromolecules 1993 26, 2987. 14/32 7 ATRP: Atom Transfer Radical Polymerization H H kact H n n+1 CH2 C CH2 C X + Mt Y/L CH2 C CH2 CH* + X-Mt Y/L kdeact R R R R kp Monomers: Styrenes , (Meth)acrylates, AN, ... M Initiators: Alkyl halides or AIBN/XMtn+1/L • Rate =f(K, [RX], [Mtn], [XMtn+1]) Mt: Cu, Fe, Ru, Ni, Pd, Rh,… -9 -6 • kact/kdeact = 10 to 10 M L: Bpy, amines, phosphines,… • Side reactions X: Cl, Br, I, SCN,… – potential redox of radicals [M]: bulk, solution, emulsion, suspension, – C-Mt bonding disp. M /M -2 ln(Mo/M) Mn w n [In]o: 1 to 10 M expt Limit ~ 1.1 Temp: 20-140 oC Mn Time: 1 to 10 hours theo Mn Time Conversion Conversion Sawamoto, M.,. et al. Macromolecules 1995 28, 1721. Matyjaszewski, K., et al. JACS 1995 117, 5614. 15/32 Component for ATRP -1 -1 ka ~ 1 M s X n n+1 + Mt /Ligand + X Mt /Ligand 7 -1 -1 Y kda ~ 10 M s Y M kp Y should stabilize radical by resonance/inductive effects. – Can be: -Phenyl, Carbonyl, Ester, Cyano, Multiple halogens. X must rapidly exchange between Mtn/L & chain end – Generally a halogen (Cl, Br, I), can be pseudo-halogen (-SCN, -N3) n Mt /Ligand should allow selective & fast exchange. n –Mt : Cu, Ru, Ni, Fe, Pd, etc.; preferred 1 el. redox – Ligand: adjusts equilibrium, solubilizes metal, assures selectivity. • Bipyridines, functionalized pyridines, linear & branched amines, cyclic amines, phosphines, phosphites, carboxylates, phenoxides, etc. Temp., Solvent & Counterion: affect equilibrium, rates & selectivity. Æ Structure-Reactivity Correlation for: R(Y), X, M, Mt, L, S, T, etc. Æ Precise structure of catalysts, active and dormant species 16/32 8 How ATRP Works: Styrene, CuBr/dNbpy, 110 oC R' R-R 8 -1 -1 + R' + kt< 10 M s R' R' R X N -1 -1 N N ka =0.45 M s N Cu H3C Br + R + X Cu N N k =1.1 107 M-1s-1 N d M R' N R' 3 -1 -1 R' kp=1.6 10 M s R' Frequency of molecular events at chain end; τ =1/(k [C]) Concentrations: [M] =5 M – activation: τ = 22 s [R-Br] = 10-1 M – propagation: τ = 0.12 ms [CuIBr/2dNbpy] = 10-1 M [CuIIBr /2dNbpy] = 5X10-3 M – deactivation: τ = 0.018 ms (6 times faster than propagation !!!) 2 [P*] » 1X10-7 M – termination: τ = 0.1 s ( i.e.