Radical Polymerizations II Special Cases

Transcription

1 Radical Polymerizations II pecial Cases Devon A. hipp Department of Chemistry, & Center for Advanced Materials Processing Clarkson University Potsdam, NY Tel. (315) , Fax (315) Copyright 2016 Devon A. hipp 46

2 Living Polymerizations bjectives Continuous chain growth No termination Well-defined chains Chain structure Chain length Molecular weight distribution Block copolymer synthesis Requirements Initiation must be fast R i >> R p Termination must be eliminated r at least reduced to insignificance Problems with free radical polymerization Initiation is slow Radical-radical termination is fast 47

3 Reversible-Deactivation Radical Polymerizations (RDRP) ften called living radical polymerization Dormant polymer activation deactivation Active polymer radical + capping group Monomer (Propagation) Monomer repeat unit In Initiator (α) end Y Functional terminal (ω) end ("capping") group X n Y Molecular Weight DP = Δ[M] [In] 0 % Monomer Conversion Polydispersity <

4 Features of Living Polymerizations Linear increase in molecular weight Vs. monomer conversion Low polydispersity M w /M n < 1.5 (often ~ 1.1) Pre-defined molecular weight DP n = M n /FW M = Δ[M] / [Initiator] First-order monomer consumption ame as conventional radical polymerization 49

5 Terminology/Tests for Living Polymerization Controversy over terminology Controlled, living, pseudo-living, quasi-living, living/controlled, living/controlled, reversible-deactivation, IUPAC definition of living polymerization: Absence of irreversible transfer and termination Cannot be applied to any radical polymerization! ome tests for RDRP: Continued chain growth after addition monomer added Molecular weight increases linearly with conversion Active species (i.e. radicals) conc. remains constant Narrow molecular weight distributions (low M w /M n ) Block copolymers may be prepared (subset of first test) End groups are retained yields end-functionalized chains Moad and olomon The Chemistry of Radical Polymerization, 2 nd edition, 2006, page

6 Examples of RDRP Data Atom transfer radical polymerization (ATRP) tyrene. M n at 100% (theoretical) = 10,000 (DP = 100) T.E. Patten, J. Xia, T. Abernathy, K. Matyjaszewski, cience, 1996, 272, 866. K. Matyjaszewski, T.E. Patten, J. Xia, J. Am. Chem. oc., 1997, 119,

7 Calculated MWDs Moad and olomon The Chemistry of Radical Polymerization, 2 nd edition, 2006, page

8 Materials From RDRP D.A. hipp, Polym. Rev., 2011, 51,

9 RDRP: Types & Requirements Main types Nitroxide-Mediated Polymerization NMP Atom Transfer Radical Polymerization ATRP Reversible Addition- Fragmentation Chain Transfer Polymerization RAFT ther types Metal-mediated polymn Iniferter Group transfer polymn Requirements All chains begin at the same time Fast initiation Little or no termination Low radical concentration All chains grow at the same rate Fast exchange Iodo and methacrylate-based degenerate transfer 54

10 Nitroxide-Mediated Polymerization Nitroxides table free radicals P n -X Do not react with -centered radicals React fast with C-centered radicals k d ~ M -1 s -1 Do not initiate polymerization k a k d P n + X k p Monomer N Ph N TEMP 2,2,6,6 tetramethylpiperidim-noxyl nly good for styrene (co)polymers αh nitroxides tyrene, acrylates, acrylonitrile, 1,3- butadiene Rizzardo, olomon, et al. U Patent 4,581,429, Aust. J. Chem., 1990, 43, Chem. Aust., 1987, 54, 32. Ph n Ph Ph N k a k d Ph n Ph Ph Ph Propagation N TEMP 55

11 Georges/Xerox Approach to NMP BP n+1 Heat Ph Ph n Ph N TEMP Heat Ph n Ph N Ph n Ph N Propagation Molecular weight distributions of polystyrene produced by NMP using BP and TEMP. M n and M w /M n of samples I IV are as follows: (M n :M w /M n ) 1700:1.28, 3200:1.27, 6800:1.21, 7800:1.27. M.K. Georges et al., Macromolecules, 1993, 26,

12 Hawker Approach to NMP (Using TEMP) Alkoxyamine C.J. Hawker, J. Am. Chem. oc., 1994, 116,

13 Newer Nitroxides: α-hydrido-derivatives Wider range of monomers & functionalities Common nitroxides/ alkoxyamines cheme 3. Functional alkoxyamines P. Tordo, Y. Gnanau, et al., J. Am. Chem. oc., 2000, 122, C.J. Hawker, et al., J. Am. Chem. oc., 1999, 121, R.B. Grubbs, Polym. Rev., 2011, 51,

14 ffiffiffiffi The Persistent Radical Effect (PRE) Idea developed by H. Fischer, and furthered by T. Fukuda dr dt ¼ k di k c RY 2k t R 2 ; dy dt ¼ k di k c RY ¼ dr dt þ 2k tr 2 : Y ¼ð6k t K 2 eq I 2 0 Þ1=3 t 1=3 ; R ¼ K eqi 0 1=3t 1=3 6k t : 59 Chem. Rev. 2001, 101,

15 Consequences of the PRE Better control over polymer growth Faster deactivation Fewer radicals lower termination (R t ~ [R] 2 ) lower polymerization (R p ~ [R]) Better chain end functionalization dd polymerization kinetics Approx. t 1/3 dependence instead of t Can add some extra persistent radical (e.g. nitroxide) to improve PDI, slow rate, better end group control Chem. Rev. 2001, 101,

16 Atom Transfer Radical Polymerization Cu I Br + R R N N or N N N Metal catalyst (& ligand, L) Active propagating radical n Cu II Br 2 + ligand xidized metal catalyst P n -X + Mt q k a /L P n * + X-Mt q+1 /L k d P m * k p k t D + 2 X-Mt q+1 /L Monomer Dormant chain with halogen (X) n Br Dead chains H n n n m J.-. Wang, K. Matyjaszewski, J. Am. Chem. oc., 1995, 117, M. Kato, M. Kamigaito, M. awamoto, T. Higashimura, Macromolecules, 1995, 28, V. Percec, B. Barboiu, Macromolecules, 1995, 28,

17 Initiators for ATRP Best to copy end of growing polymer ATRP initiators ATRP polymers ther ATRP initiators used include: K. Matyjaszewski, J. Xia, Chem. Rev. 2001, 101,

18 Monomers for ATRP tyrenics Acrylates Methacrylates ther monomers, such nitriles, can be polymerized. Nucleophilic functionalities (e.g., amines, acids) can cause problems. K. Matyjaszewski, J. Xia, Chem. Rev. 2001, 101,

19 Catalysts for ATRP Ru, Ni, Fe & Cu Cu most used 64 K. Matyjaszewski, J. Xia, Chem. Rev. 2001, 101, Common ligands used with Cu ATRP catalysts based on other metals K. Matyjaszewski, N.V. Tsarevsky, Nat. Chem. 2009, 1,

20 Functional Polymers by ATRP End-group functionalization easy to perform with various alkyl halide reactions Click chemistries oup modifications Amine Epoxy Hydroxy Phosphines Macromers Vinyl K. Matyjaszewski, N.V. Tsarevsky, Nat. Chem. 2009, 1,

21 ome Mechanistic Details K Halogen exchange exch RBr + CuCl/L RCl + CBr/L Cl Br K. Matyjaszewski et al. Macromolecules 1998, 31,

22 How to Utilize Halogen Exchange Better control of homopolymerizations K. Matyjaszewski et al. Macromolecules 1998, 31,

23 Utilizing Halogen Exchange 2 Better block copolymers D.A. hipp, J.-L. Wang, K. Matyjaszewski Macromolecules 1998, 31,

24 Reverse ATRP Add regular initiator (e.g. AIBN), with oxidized metal (e.g. Cu II Br 2 ) & ligand Less trouble handling Cu II (c.f. Cu I ) Uses common initiator till provides good control, etc. Related to ICAR ATRP Initiators for continuous activator regeneration Allows for lower Cu concentrations J.-. Wang, K. Matyjaszewski Macromolecules, 1995, 28, K. Matyjaszewski et al. Proc. Natl. Acad. ci. U..A., 2006, 103,

25 Activator (Re)Generated by Electron Transfer (AGET & ARGET) ATRP Problem: use of Cu metal salts contaminates polymer Usually ends up being green Adds expense to polymerization vercome this by regenerating Cu(I) by using a reducing agent such as amines, glucose, ascorbic acid, etc., as well as Cu(0) wire Much lower [Cu] K. Matyjaszewski et al. Angew. Chem. Int. Ed. 2010, 49, Chem. Rev. 2007, 107,

26 ARA ATRP vs. ET LRP Controversy over ARGET-type approach ARA = supplemental regeneration of activators cheme 2 Key differences between the ARA ATRP mechanism and the ET-LRP mechanism. The ET-LRP mechanism assumes that Cu 0 is the major activator of alkyl halides (green dashed line) and that disproportionation (blue dashed line) is the dominant fate for Cu I complexes. ARA ATRP (red solid lines) assumes that Cu I is the major activator of alkyl halides and that Cu I species predominantly activate alkyl halides rather than disproportionate (reprinted with permission from ref. 72. Copyright 2014 the American Chemical ociety). 71 ARA-ATRP: Polym. Chem. 2014, 5, ET-LRP: Chem. Rev. 2009, 109,

27 eatrp Electrochemical ATRP Reduces Cu(II) A B B Fig. 4. (A) Conversion (solid circles) and applied potential (dashed line) with respect to time and (B) M n and M w /M n with respect to conversion. Toggling between active and dormant states is represented by changes of the E app values between 0.69V and 0.40 V versus Ag + /Ag, respectively. Reaction conditions are identical to those stated in Fig. 2. K. Matyjaszewski et al. cience 2011, 332,

28 ome Interesting Polymers from ATRP tars Macromolecules 2003, 36, Gradients & brushes MMA + HEMA-TM TM ATRP 1.ite Transformation to Macroinitiator Random Brush 2 Grafting From 1.ite Transformation to Macroinitiator 2 Grafting From Macromolecules 2002, 35, Continuous addition of HEMA-TM TM ATRP Gradient Brush 73

29 Degenerate Transfer Reversible chain transfer P m k tr P n + TG P n TG + P m k -tr k p monomer transfer group k p monomer Examples Iodine-mediated (TG = I atom) Methacrylic macromonomers Thiocarbonylthio (RAFT) polymerization 74

30 Iniferters 1 Initiator, transfer agent, terminator Disulfides High amounts of transfer Examples Diaryl disulfides Dithiuram disulfides (most successful) tsu et al. Makromol. Rapid Commun., 1983, 3, 127 & 133 X X Dithiocarbamyl end groups Thermally stable Photochemically labile N C C N 75

31 Iniferters 2 Initiation N C Δ or hν C N 2 N C Chain Transfer N C C N N C C N Termination / Reinitiation N C hν N C 76

32 RAFT Polymerization Reversible addition-fragmentation chain transfer Initiation / Chain Transfer I 2 Δ or hν P n monomer Z R CN C 2 CH 3 C N 2 CH 3 C 2 CH 3 Ph Ph dithioesters trithiocarbonates dithiocarbamates xanthates k add P n R P n R k β P n R k p Z k -add Z Z k p monomer monomer Chain equilibrium k add P n P m P n P m k β P n P m Z k -add Z Z k p k p monomer G. Moad, E. Rizzardo, et al., Macromolecules, 31, 5559 (1998) G. Moad, E. Rizzardo, et al., Patent W98/01478 (1998). Z. Zard et al. Patent W98/58974 (1998) monomer 77

33 Iodine & Methacrylic Macromonomers Iodine-mediated polymerizations Tatemoto (Eur. Patent A1, 1992) Matyjaszewski (Macromolecules, 1995, 28, pp and 8051) P m k tr P n + I P n I + P m k -tr k p monomer Polymerization of vinyl acetate Iovu & Matyjaszewski (Macromolecules, 2003, 35, 9346) k p monomer 78

34 Macromonomer Method Methacrylate-based macromonomers Moad et al. (Macromolecules, 1996, 29, 7717) k P Pm add n P n P m k β P n P m k p C 2 CH 3 k β C 2 CH 3 k add C 2 CH 3 k p monomer monomer 79

35 Macromonomer Mechanism Moad et al. Macromolecules, 1996, 29,

36 rganoheteroatom-mediated Polymerization rganotellurium A. Goto et al. JAC, 2003, 125, 8720 rganostibine. Yamago et al. JAC, 2004, 126, rganobismuthin. Yamago et al. Angew. Chem. Int. Ed., 2007, 46, 1304 Two concurrent mechanisms:. Yamago Chem. Rev., 2009, 109,

37 Cobalt-Mediated Polymerization rganometallic mediated polymerization (MRP) Various metals can be used (Ti, V, Fe, s, Mo, Cr) but most successful is Co Co-mediated polymerization mechanism depends on conditions Degenerate transfer (DT) if high radical conc. Reversible-deactivation (RD) if low radical conc. Largely works for vinyl acetate & acrylates Ti okay for MMA and derivative 82