PYRIDINE AND AMINE FUNCTIONALIZED POLYMERS BY ANIONIC AND CONTROLLED FREE RADICAL POLYMERIZATION METHODS MZIKAYISE PATRICK NDAWUNI

Transcription

1 PYRIDINE AND AMINE FUNCTINALIZED PLYMERS BY ANINIC AND CNTRLLED FREE RADICAL PLYMERIZATIN METDS by MZIKAYISE PATRICK NDAWUNI Submitted i fulfillmet of the requiremets for the DCTR F PILSPY i the subject CEMISTRY at the UNIVERSITY F SUT AFRICA SUPERVISR: PRFESSR G J SUMMERS JULY 2009

2 Studet umber: I declare that PYRIDINE AND AMINE FUNCTINALIZED PLYMERS BY ANINIC AND CNTRLLED FREE RADICAL PLYMERIZATIN METDS is my work ad that all the sources that I have used or quoted have bee idicated ad ackowledged by meas of complete refereces. SIGNATURE (MR M.P. NDAWUNI) DATE The exact wordig of the title as it appears o the copies of your dissertatio, submitted for examiatio purposes, should be idicated i the ope space ii

3 ACKNWLEDGEMENTS I wish to exted my sicere thaks ad appreciatio to: My supervisor, Professor GJ Summers, for broadeig my uderstadig of aioic ad free radical polymerizatio ad for his costat guidace, friedship ad motivatio durig this project. Natioal Research Foudatio (South Africa) ad Water Research Commissio (South Africa) for fiacial assistace. My family for their cotiuous support, uderstadig, love ad ecouragemet throughout my studies. Above all God Almighty! iii

4 ABSTRACT The sythesis of dipyridyl fuctioalized polysulfoes with improved hydrophilicity, ehaced membrae morphology ad excellet ATRP polymeric ligad properties was coducted by the followig method: (a) the formatio of lithiated polysulfoe from umodified polysulfoe ad the subsequet reactio with 2,2'-viylideedipyridie i tetrahydrofura at -78 o C uder argo atmosphere to afford the correspodig dipyridyl fuctioalized polysulfoe. The stoichiometry of the reactio affects the degree of fuctioalizatio of the product. Whe equimolar amouts of 2,2'- viylideedipyridie are added to the lithiated polysulfoe, the degree of fuctioalizatio obtaied was 45%. owever, the additio of 10% ad 20% molar excess of 2,2'-viylideedipyridie to the correspodig lithiated polysulfoe produced dipyridyl fuctioalized polysulfoes with degrees of fuctioalizatio of 80% ad 95%, respectively; ad (b) the membraes obtaied from umodified polysulfoe as well as dipyridyl fuctioalized polysulfoes were characterized by atomic force microscopy, scaig electro microscopy, pure water permeatio measuremets ad cotact agle measuremets. Amie chai ed fuctioalized polystyree ad poly(methyl methacrylate) were prepared by Atom Trasfer Radical Polymerizatio (ATRP) methods as follows: (a) -Amiopheyl fuctioalized polystyree was prepared i quatitative yields by ATRP methods usig a ew primary amie fuctioalized iitiator adduct, formed i situ by the reactio of 1-(4-amiopheyl)-1-pheylethylee ad (1- bromoethyl)bezee i the presece of copper (I) bromide/2,2'-bipyridyl as catalyst i diethyl ether at 110 o C, for the polymerizatio of styree. iv

5 (b) New -bis(amiopheyl) ad,ω -tetrakis(amiopheyl) fuctioalized polymers were prepared i quatitative yields by the ATRP method usig the followig sythetic strategy: (i) the iitiatio of styree polymerizatio with a ew primary diamie fuctioalized iitiator adduct, geerated i situ by the reactio of stoichiometric amouts of 1,1-bis(4-amiopheyl)ethylee with (1-bromoethyl)bezee i the presece of copper (I) bromide/2,2'-bipyridyl as catalyst, afforded - bis(amiopheyl) fuctioalized polystyree; ad (ii) -bis(amiopheyl) fuctioalized poly(methyl methacrylate) was prepared by the ATRP method usig the primary diamie fuctioalized iitiator adduct as iitiator for methyl methacrylate polymerizatio; ad (iii) well defied,ω -tetrakis(amiopheyl) fuctioalized polystyree was prepared by the post ATRP chai ed modificatio reactio of - bis(amiopheyl) fuctioalized polystyree with 1,1-bis(4-amiopheyl)- ethylee at the completio of the polymerizatio reactio. (c) Similarly, -bis(4-dimethylamiopheyl) fuctioalized polystyree was prepared by usig a ew tertiary diamie fuctioalized iitiator adduct, formed i situ by treatmet of equimolar amouts of 1,1-bis[(4-dimethylamio)pheyl]- ethylee with (1-bromoethyl)bezee i the presece of copper (I) bromide/2,2'- bipyridyl as the catalyst i dipheyl ether at 110 o C for the iitiatio of styree polymerizatio by the ATRP method. Furthermore, the ATRP of methyl methacrylate, iitiated by the ew tertiary diamie fuctioalized iitiator adduct, produced -bis(4-dimethylamiopheyl) fuctioalized poly(methyl methacrylate). I additio,,ω -tetrakis(4-dimethylamiopheyl) fuctioalized polystyree was sythesized via a post ATRP chai ed modificatio reactio of -bis(4- dimethylamiopheyl) fuctioalized polystyree with equimolar amouts of 1,1- bis[(4-dimethylamio)pheyl]ethylee at the completio of the polymerizatio process. v

6 Quatitative yields of the differet amie fuctioalized polymers with predictable umber average molecular weights (M = 1.3 x x10 3 g/mol), arrow molecular weight distributios (M w /M = ) ad cotrolled chai ed fuctioality were obtaied. Polymerizatio kietics data was employed to determie the cotrolled/livig character of each ATRP reactio leadig to the formatio of the differet amie chai ed fuctioalized polymers. The polymerizatio processes were moitored by gas chromatographic aalyses. Polymerizatio kietics measuremets for all reactios show that the polymerizatios follow first order rate kietics with respect to moomer cosumptio. The umber average molecular weight of the amie fuctioalized polymers icreases liearly with percetage moomer coversio ad polymers with arrow molecular weight distributio were obtaied. The ATRP of styree, catalyzed by a ovel dipyridyl fuctioalized polysulfoe/cubr supported catalyst system, afforded well defied polystyree with predictable umber average molecular weight ad arrow molecular weight distributio i a cotrolled/livig free radical polymerizatio process. The substituted 1,1-dipheylethylee iitiator precursor derivatives ad the fuctioalized polymers were characterized by uclear magetic resoace spectrometry, fourier trasform ifrared spectroscopy, thi layer chromatography, colum chromatography, size exclusio chromatography, o-aqueous titratios, differetial scaig calorimetry ad thermogravimetrical aalysis. Keywords: Aioic polymerizatio, polysulfoe, polymer membraes, cotrolled/livig polymerizatio, atom trasfer radical polymerizatio, amie fuctioalized polymers, telechelic polymers, amie substituted 1,1-dipheylethylee derivatives, supported catalyst. vi

7 TABLE F CNTENTS TITLE PAGE. i DECLARATIN... ii ACKNWLEDGEMENTS.. iii ABSTRACT.. iv TABLE F CNTENTS. vii LIST F FIGURES. xi LIST F ABBREVIATINS... xv CAPTER 1 INTRDUCTIN.. 1 CAPTER 2 LITERATURE REVIEW Chemical Modificatio of Polysulfoe by Aioic Methods Fuctioalizatio of Polymers with 1,1-Diarylethylee Derivatives Free Radical Polymerizatio Nitroxide Mediated Free Radical Polymerizatio Reversible Additio-Fragmetatio Chai Trasfer Free Radical Polymerizatio Atom Trasfer Radical Polymerizatio Mechaism of Atom Trasfer Radical Polymerizatio Characteristics of the ATRP reactio Fuctioalized Polymers by ATRP Amie Fuctioalized Iitiators for ATRP Primary Amie Fuctioalized Iitiators for ATRP Tertiary Amie Fuctioalized Iitiators for ATRP Supported Catalyst Systems for ATRP CAPTER 3 EXPERIMENTAL Materials ad Glassware Characterizatio. 52 vii

8 3.3 Aioic Sythesis of Fuctioalized Polysulfoe Purificatio of Polysulfoe, (1) Sythesis of 2,2'-viylideedipyridie, (2) Sythesis of Dipyridyl Fuctioalized Polysulfoe, (3) Membrae Preparatio Atom Trasfer Radical Polymerizatio: Sythesis of Amie Chai Ed Fuctioalized Polymers Primary Amie Fuctioalized Iitiator Precursor: Sythesis of 1-(4-Amiopheyl)-1-pheylethylee, (4) Sythesis of -Amiopheyl Fuctioalized Polystyree, (6) Primary Diamie Fuctioalized Iitiator Precursor: Sythesis of 1,1-Bis(4-amiopheyl)ethylee, (7) Sythesis of -Bis(amiopheyl) Fuctioalized Polystyree, (9) Sythesis of -Bis(amiopheyl) Fuctioalized Poly(methyl methacrylate),(10) Sythesis of,ω -Tetrakis(amiopheyl) Fuctioalized Polystyree, (11) Tertiary Diamie Fuctioalized Iitiator Precursor: Sythesis of 1,1-Bis[(4-dimethylamio)pheyl]ethylee, (12) Sythesis of -Bis(4-dimethylamiopheyl) Fuctioalized Polystyree, (14) Sythesis of -Bis(4-dimethylamiopheyl) Fuctioalized Poly(methyl methacrylate), (15) Sythesis of,ω -Tetrakis(4-dimethylamiopheyl) Fuctioalized Polystyree, (16) A New Supported Catalyst System for the Atom Trasfer Radical Polymerizatio of Styree Amie Fuctioalized Polymers by Atom Trasfer Radical viii

9 Polymerizatio: Polymerizatio Kietics Studies Sythesis of Polystyree, (17) usig Dipyridyl Fuctioalized Polysulfoe, (3) as Ligad: Polymerizatio Kietics Studies 72 CAPTER 4 RESULTS AND DISCUSSIN Chemical Modificatio of Polysulfoe by Aioic Methods Sythesis of 2,2'-viylideedipyridie, (2) Sythesis of Dipyridyl Fuctioalized Polysulfoe, (3) Atom Trasfer Radical Polymerizatio: Sythesis of Chai Ed Fuctioalized Polymers Sythesis of Primary Amie Fuctioalized Polymers by Atom Trasfer Radical Polymerizatio Primary Amie Fuctioalized Iitiator Precursor: Sythesis of 1-(4-Amiopheyl)-1-pheylethylee, (4) Sythesis of -Amiopheyl Fuctioalized Polystyree, (6) Primary Diamie Fuctioalized Iitiator Precursor: Sythesis of 1,1-Bis(4-amiopheyl)ethylee, (7) Sythesis of -Bis(amiopheyl) Fuctioalized Polystyree, (9) Sythesis of -Bis(amiopheyl) Fuctioalized Poly(methyl methacrylate), (10) Sythesis of,ω -Tetrakis(amiopheyl) Fuctioalized Polystyree, (11) Sythesis of Tertiary Amie Fuctioalized Polymers by Atom Trasfer Radical Polymerizatio Tertiary Diamie Fuctioalized Iitiator Precursor: Sythesis of 1,1-Bis[(4-dimethylamio)pheyl]ethylee, (12) Sythesis of -Bis(4-dimethylamiopheyl) Fuctioalized Polystyree, (14) 101 ix

10 4.4.3 Sythesis of -Bis(4-dimethylamiopheyl) Fuctioalized Poly(methyl methacrylate), (15) Sythesis of,ω -Tetrakis(4-dimethylamiopheyl) Fuctioalized Polystyree, (16) Sythesis of Amie Chai Ed Fuctioalized Polymers by Atom Trasfer Radical Polymerizatio: Polymerizatio Kietics Studies Sytheses of -Amiopheyl Fuctioalized Polystyrees, (6) Sytheses of -Bis(amiopheyl) Fuctioalized Polystyrees, (9) Sytheses of -Bis(4-dimethylamiopheyl) Fuctioalized Polystyrees, (14) A New Supported Catalyst System for the Atom Trasfer Radical Polymerizatio of Styree Sythesis of Polystyree, (17) usig Dipyridyl Fuctioalized Polysulfoe, (3) as Ligad Sythesis of Polystyree, (17) usig Dipyridyl Fuctioalized Polysulfoe, (3) as Ligad: Polymerizatio Kietics Studies 119 CAPTER 5 CNCLUSIN Chemical Modificatio of Polysulfoe by Aioic Methods Atom Trasfer Radical Polymerizatio: Sythesis of Amie Chai Ed Fuctioalized Polymers A New Supported Catalyst System for the Atom Trasfer Radical Polymerizatio of Styree 126 REFERENCES APPENDIX x

11 LIST F FIGURES Figure 1. 1 NMR spectrum of 2,2'-viylideedipyridie, (2) Figure 2. FTIR spectrum of 2,2'-viylideedipyridie, (2) Figure 3. 1 NMR spectrum of dipyridyl fuctioalized polysulfoe, (3), PFPS Figure 4. FTIR spectrum of dipyridyl fuctioalized polysulfoe, (3), PFPS Figure 5. TGA thermograms of the differet polysulfoe samples, PS, PFPS-45, PFPS Figure 6. AFM micrographs of the differet polysulfoe membraes, PS, PFPS-45, PFPS Figure.7 SEM micrographs of the cross-sectio of the differet polysulfoe membraes, PS, PFPS-45, PFPS Figure 8. SEM micrographs of the top view of the differet polysulfoe membraes, PS, PFPS-45, PFPS Figure 9. SEM micrographs of the bottom view of the differet polysulfoe membraes, PS, PFPS-45, PFPS Figure 10. Plot of pure water flux versus pressure for the differet polysulfoe membraes, PS, PFPS-45, PFPS Figure NMR spectrum of 1-(4-amiopheyl)-1-pheylethylee, (4) Figure 12. FTIR spectrum of 1-(4-amiopheyl)-1-pheylethylee, (4) Figure 13. SEC chromatogram of -amiopheyl fuctioalized polystyree, (6) Figure NMR spectrum of -amiopheyl fuctioalized polystyree, (6) Figure 15. FTIR spectrum of -amiopheyl fuctioalized polystyree, (6) Figure NMR spectrum of 1,1-bis(4-amiopheyl)- ethylee, (7) Figure 17. FTIR spectrum of 1,1-bis(4-amiopheyl)ethylee, (7). 155 xi

12 Figure 18. Figure 19. Figure 20 Figure 21. Figure 22. Figure 23. Figure 24. Figure 25. Figure 26. Figure 27. Figure 28. Figure 29. Figure 30. Figure 31. Figure 32. Figure 33. Figure 34. SEC chromatogram of -bis(amiopheyl) fuctioalized polystyree, (9) NMR spectrum of -bis(amiopheyl) fuctioalized polystyree, (9) FTIR spectrum of -bis(amiopheyl) fuctioalized polystyree, (9) SEC chromatogram of -bis(amiopheyl) fuctioalized poly(methyl methacrylate), (10) NMR spectrum of -bis(amiopheyl) fuctioalized poly(methyl methacrylate), (10) SEC chromatogram of,ω -tetrakis(amiopheyl) fuctioalized polystyree, (11) NMR spectrum of,ω -tetrakis(amiopheyl) fuctioalized polystyree, (11) NMR spectrum of 1,1-bis[(4-dimethylamio)- pheyl]ethylee, (12) FTIR spectrum of 1,1-bis[(4-dimethylamio)pheyl]- ethylee, (12) SEC chromatogram of -bis(4-dimethylamiopheyl) fuctioalized polystyree, (14) NMR spectrum of -bis(4-dimethylamiopheyl) fuctioalized polystyree, (14) FTIR spectrum of -bis(4-dimethylamiopheyl) fuctioalized polystyree, (14) SEC chromatogram of -bis(4-dimethylamiopheyl) fuctioalized poly(methyl methacrylate), (15) NMR spectrum of -bis(4-dimethylamiopheyl) fuctioalized poly(methyl methacrylate), (15) SEC chromatogram of,ω -tetrakis(4-dimethylamiopheyl) fuctioalized polystyree, (16) NMR spectrum of,ω -tetrakis(4-dimethylamiopheyl) fuctioalized polystyree, (16) Plots of percetage moomer coversio versus time for the ATRP of styree iitiated by the adduct xii

13 Figure 35. Figure 36. Figure 37. Figure 38. Figure 39. Figure 40. of 1-(4-amiopheyl)-1-pheylethylee, (4) ad (1-bromoethyl)bezee i the presece of CuBr/bpy catalyst i dipheyl ether at 110 o C First order kietics plots for the ATRP of styree iitiated by the adduct of 1-(4-amiopheyl)-1- pheylethylee, (4) ad (1-bromoethyl)bezee i the presece of CuBr/bpy catalyst i dipheyl ether at 110 o C Plots of M ad molecular weight distributio versus percetage moomer coversio for the ATRP of styree iitiated by the adduct of 1-(4-amiopheyl)- 1-pheylethylee, (4) ad (1-bromoethyl)bezee i the presece of CuBr/bpy catalyst i dipheyl ether at 110 o C Plots of percetage moomer coversio versus time for the ATRP of styree iitiated by the adduct of 1,1-bis(4-amiopheyl)ethylee, (7) ad (1-bromoethyl)- bezee i the presece of CuBr/bpy catalyst i dipheyl ether at 110 o C First order kietics plots for the ATRP of styree iitiated by the adduct of 1,1-bis(4-amiopheyl)- ethylee, (7) ad (1-bromoethyl)bezee i the presece of CuBr/bpy catalyst i dipheyl ether at 110 o C Plots of M ad molecular weight distributio versus percetage moomer coversio for the ATRP of styree iitiated by the adduct of 1,1-bis(4-amiopheyl)ethylee, (7) ad (1-bromoethyl)bezee i the presece of CuBr/bpy catalyst i dipheyl ether at 110 o C Plots of percetage moomer coversio versus time for the ATRP of styree iitiated by the adduct of 1,1-bis[(4-dimethylamio)pheyl]ethylee, (12) ad (1-bromoethyl)bezee i the presece of CuBr/bpy catalyst i dipheyl ether at 110 o C xiii

14 Figure 41. Figure 42. Figure 43. Figure 44. Figure 45. Figure 46. Figure 47. Figure 48. First order kietics plots for the ATRP of styree iitiated by the adduct of 1,1-bis[(4-dimethylamio)pheyl]- ethylee, (12) ad (1-bromoethyl)bezee i the presece of CuBr/bpy catalyst i dipheyl ether at 110 o C Plots of M ad molecular weight distributio versus percetage moomer coversio for the ATRP of styree iitiated by the adduct of 1,1-bis- [(4-dimethylamio)pheyl]ethylee, (12) ad (1-bromoethyl)bezee i the presece of CuBr/bpy catalyst i dipheyl ether at 110 o C NMR spectrum of dipyridyl fuctioalized polysulfoe, (3), PFPS SEC chromatogram of polystyree, (17) prepared by the ATRP of styree i the presece of the dipyridyl fuctioalized polysulfoe/cubr supported catalyst system i dipheyl ether at 110 o C NMR spectrum of polystyree, (17) prepared by the ATRP of styree i the presece of the dipyridyl fuctioalized polysulfoe/cubr supported catalyst system i dipheyl ether at 110 o C Plot of percetage moomer coversio versus time for the ATRP of styree i the presece of CuBr/PFPS-95 supported catalyst complex i dipheyl ether at 110 o C, [M] 0 /[I] 0 = First order kietics plot for the ATRP of styree i the presece of CuBr/PFPS-95 supported catalyst complex i dipheyl ether at 110 o C, [M] 0 /[I] 0 = Plots of M ad molecular weight distributio versus percetage moomer coversio for the ATRP of styree i the presece of CuBr/PFPS-95 supported catalyst complex i dipheyl ether at 110 o C, [M] 0 /[I] 0 = 200. = Theoretical M values; = Experimetal M values xiv

15 LIST F ABBREVIATINS ATRP aq Boc BP Bu Bpy CuBr CRP DBU DMA DMF dnbpy DPA DP DPE E + Et Fmoc FTIR Cl MTETA hrs I KF L Me 6 TREN M MBP Me MMA MPC NMP Atom Trasfer Radical Polymerizatio Aqueous Butoxycarboyl Bezoyl peroxide Butyl 2,2'-Bipyridyl Copper bromide Cotrolled Radical Polymerizatio 1,8-diazabicyclo(5.4.0)udece-7-ee 2-(dimethylamio)ethyl methacrylate N,N-dimethylformamide 4,4'-Di(-oyl)-2,2'-bipyridie 2-(diisopropylamio)ethyl methacrylate Degree of polymerizatio Dipheyl ether Electrophile Ethyl 9-fluoreylmethoxycarboyl group Fourier Trasform Ifrared Spectrometry ydrochloric acid 1,1,4,7,10,10-hexamethyltriethyleetetramie ours Iitiator Potassium fluoride Ligad Tris[2-(dimethylamio)ethyl]amie Moomer Methyl 2-bromopropioate Methyl Methyl methacrylate 2-(methacryloyloxy)ethyl phosphorylcholie Nitroxide Mediated Free Radical Polymerizatio xv

16 NMR Nuclear Magetic Resoace Spectrometry PDI Polydispersity idex PMMA Poly(methyl methacrylate) PMDETA N,N,N',N'',N''-petamethyldiethyleetriamie Ph Pheyl PS Polysulfoe RAFT Reversible Additio-Fragmetatio Chai Trasfer Polymerizatio RT Room temperature R Alkyl SEC Size Exclusio Chromatography TF Tetrahydrofura TLC Thi Layer Chromatography TEMP 2,2,6,6-tetramethylpiperidiy-1-oxy TMS Tetramethylsilae wt Weight xvi

17 CAPTER 1 INTRDUCTIN Polysulfoe ad its derivatives are the most importat egieerig thermoplastic materials used as precursors to fabricate membraes for may idustrial applicatios such as fuel cell techology 1-13 ad liquid ad gas separatio processes 14-34, electrodialysis ad polymer electrolyte membrae electrolysis The chemical ad physical characteristics of polysulfoe, such as good thermal ad chemical stability, mechaical stregth ad excellet oxidative resistace, make polysulfoe the material of choice for use as membrae substrates owever, due to its hydrophobic ature, polysulfoe membraes are susceptible to foulig 40 by various mechaisms that reduce the applicatio of polysulfoe membraes i the treatmet of food streams ad biological separatios. Thus, the sythesis of ew fuctioalized polysulfoe polymers ad its subsequet use as membrae matrix polymers has bee the focus of idustrial ad academic research i order to meet the icreased idustrial eed for polysulfoe membraes with icreased hydrophilicity, high flux ad low foulig I particular, the regiospecific chemical icorporatio of bulky amie groups pedat to the polysulfoe chai has bee a challege due to deleterious side reactios associated with amiatio reactios with polysulfoe derivatives The preset research focuses o the sythesis of dipyridyl fuctioalized polysulfoes with improved hydrophilicity, ehaced membrae morphological characteristics ad excellet ATRP polymeric ligad properties. The polymer fuctioalizatio process ivolves the formatio of lithiated polysulfoe from umodified polysulfoe ad the subsequet reactio with 2,2'- viylideedipyridie i tetrahydrofura at -78 o C uder argo atmosphere to afford the correspodig dipyridyl fuctioalized polysulfoe. Atom trasfer radical polymerizatio 45 (ATRP) is oe of the most versatile ad powerful sythetic techiques i polymer sciece. ATRP allows the sythesis of polymers with well defied umber average molecular weight, arrow molecular weight distributio, good cotrol of chai ed fuctioality, 1

18 compositio ad molecular architecture. The most commo ATRP reactio ivolves the reversible homolytic cleavage of a carbo haloge bod of a alkyl halide iitiator derivative by a redox reactio with a trasitio metal/ligad complex, followed by moomer additio to form well defied polymers. A essetial feature of the ATRP process is the equilibrium betwee a low cocetratio of active propagatig species ad a large umber of dormat chais via a electro trasfer process promoted by a trasitio metal/ligad complex. I the classical ATRP process, the topology of the polymer chais is such that the ω -termial group is a haloge atom with the iitiator fragmet at the -termius of the polymer chai. Thus, with the selectio of a appropriate fuctioalized iitiator molecule or fuctioalized iitiator system, a wide variety of chai ed fuctioalized polymers ca be prepared via the ATRP techique 45. The use of fuctioalized 1,1-dipheylethylee derivatives i polymer sythesis provides oe of the best polymer sythesis methods to produce well defied polymers The sythesis of chai ed fuctioalized polymers utilizes the additio reactios of active polymer chai eds with fuctioalized 1,1-dipheylethylee derivatives for the followig reasos: (a) the additio is simple ad quatitative; (b) due to steric factors, oly mooadditio occurs, i.e., o oligomerizatio of the 1,1-dipheylethylee uit is observed; ad (c) a variety of substituted 1,1-dipheylethylee derivatives ca easily be prepared by stadard orgaic reactios. By ATRP methods, well defied amie fuctioalized polymers ca be prepared usig a geeral, quatitative, oe pot, fuctioalizatio method, which employs appropriate amie fuctioalized 1,1-dipheylethylee derivatives as amie fuctioalized iitiator precursors for the polymerizatio of styree ad methyl methacrylate 53. The curret study outlies the preparatio of ew amie chai ed fuctioalized polystyree ad poly(methyl methacrylate) by Atom Trasfer Radical Polymerizatio (ATRP) methods by the followig sythetic pathways: (a) The use of a ew primary amie fuctioalized iitiator adduct, formed i situ by the reactio of 1-(4-amiopheyl)-1-pheylethylee ad (1-bromo- 2

19 ethyl)bezee i the presece of copper (I) bromide/2,2'-bipyridyl as catalyst i diethyl ether at 110 o C, for the polymerizatio of styree to provide a ew method for the sythesis of -amiopheyl fuctioalized polystyree 54. (b) The sythesis of ew -bis(amiopheyl) ad,ω -tetrakis(amiopheyl) fuctioalized polymers by ATRP methods usig the followig sythetic strategy: (i) the iitiatio of styree polymerizatio with a ew primary diamie fuctioalized iitiator adduct, geerated i situ by the reactio of stoichiometric amouts of 1,1-bis(4-amiopheyl)ethylee with (1-bromoethyl)bezee i the presece of copper (I) bromide/2,2'-bipyridyl as catalyst, to afford a uique sythetic route for the preparatio of -bis(amiopheyl) fuctioalized polystyree; (ii) the sythesis of -bis(amiopheyl) fuctioalized poly(methyl methacrylate) by ATRP methods usig the primary diamie fuctioalized iitiator adduct as iitiator for methyl methacrylate polymerizatio; ad (iii) the preparatio of well defied,ω -tetrakis(amiopheyl) fuctioalized polystyree by a post ATRP chai ed modificatio reactio of - bis(amiopheyl) fuctioalized polystyree with 1,1-bis(4-amiopheyl)- ethylee at the completio of the polymerizatio reactio. (c) A ew tertiary diamie fuctioalized iitiator adduct, formed i situ by treatmet of equimolar amouts of 1,1-bis[(4-dimethylamio)pheyl]ethylee with (1-bromoethyl)bezee i the presece of copper (I) bromide/2,2'- bipyridyl as the catalyst i dipheyl ether at 110 o C, ca be employed as iitiator for styree polymerizatio by ATRP methods to provide a ew method for the sythesis of -bis(4-dimethylamiopheyl) fuctioalized polystyree. Furthermore, the ATRP of methyl methacrylate, iitiated by the ew tertiary diamie fuctioalized iitiator adduct, provides a ew method for the preparatio of -bis(4-dimethylamiopheyl) fuctioalized poly(methyl methacrylate). I additio,,ω -tetrakis(4-dimethylamiopheyl) fuctioalized polystyree ca be prepared via a post ATRP chai ed modificatio reactio of -bis(4-dimethylamiopheyl) fuctioalized polystyree with equimolar 3

20 amouts of 1,1-bis[(4-dimethylamio)pheyl]ethylee at the completio of the polymerizatio process. The curret research ivestigates the polymerizatio kietics data of each ATRP reactio to determie the cotrolled/livig character of each ATRP reactio leadig to the formatio of the differet amie chai ed fuctioalized polymers. Furthermore, oe of the limitatios of the ATRP process for idustrial developmet is the presece of residual metal catalyst i the fial polymer product, which is detrimetal to the quality of the polymer product as well as the eviromet. A potetial way to overcome the drawback of cotamiatio, cost ad recovery of the catalyst is to immobilize the metal catalyst oto a solid carrier, which could be readily removed from the fial product ad reused for further ATRP reactios 55. The preset study describes the preparatio of a ovel dipyridyl fuctioalized polysulfoe/cubr supported catalyst system ad the determiatio of its efficiecy for the ATRP of styree. 4

21 CAPTER 2 LITERATURE REVIEW 2.1 Chemical Modificatio of Polysulfoe by Aioic Methods Polysulfoe ad its derivatives are widely used as egieerig thermoplastic materials to fabricate membraes for applicatios i fuel cell techology 1-13, ultrafiltratio, reverse osmosis ad liquid ad gas separatio processes such as carbo dioxide strippig from atural gas streams ad productio of high purity itroge from air. I particular, polysulfoes are used as io exchage membraes i electro-membrae processes such as electrodialysis ad polymer electrolyte membrae electrolysis The chemical ad physical characteristics of polysulfoe, such as good thermal ad chemical stability, mechaical stregth ad excellet oxidative resistace, make polysulfoe the material of choice for use as membrae substrates owever, due to its hydrophobic ature, polysulfoe membraes are susceptible to foulig 40 by various mechaisms that reduce the applicatio of the polysulfoe membrae i the treatmet of food streams ad biological separatios. Furthermore, it is well kow that the icorporatio of bulky pedat groups oto the polymer backboe effects sigificat chages to the gas permeability, permselectivity, mechaical ad surface properties of polysulfoe membraes. Thus, the sythesis of ew fuctioalized polysulfoe polymers ad their subsequet use as membrae matrix polymers have bee the focus of idustrial ad academic research i order to meet the icreased idustrial eed for polysulfoe membraes with icreased hydrophilicity, high flux ad low foulig I particular, the regiospecific itroductio of amie groups pedat to the polysulfoe chai has bee a challege sice the rigorous reactio coditios lead to ucotrolled, multiple sites of amiatio as well as chai scissio ad cross-likig without ay cotrol of the degree of fuctioalizatio. 5

22 Several reviews o the chemical modificatio of polysulfoe by differet chemical mechaisms to effect the facile itroductio of the fuctioal groups oto the polysulfoe backboe have bee reported For example, Daly ad coworkers 41 reported the amiatio of polysulfoe by the direct itratio of polysulfoe with a ammoium itrate/trifluoroacetic acid mixture. The itermediate itro derivative was coverted to the amie by reductio with sodium borohydride. owever, some degree of polymer degradatio was observed without ay cotrol of the positio ad degree of fuctioalizatio: C 3 C 3 S (i) N 4 N 3 / CF 3 C (ii) NaB 4 2 N C 3 C 3 S N 2 Naik 42 ad Coigham 43 reported a more efficiet amie fuctioalizatio process which ivolves the itratio-reductio reactios of poly(ether ether sulfoes) ad poly(ether sulfoes), respectively. Each process shows that the polysulfoe is itrated exclusively o the hydroquioe uit. The reductio of the itro group affords the correspodig amie fuctioalized polysulfoe derivative: S 1. N 3 / 2 S 4 / 0 o C 2. Pd/C; Et 3 N, C 2 S N 2 6

23 Kahaa ad coworkers 44 reported the itroductio of the amie fuctioality o the polysulfoe backboe usig the phthalimido methylatio route with N- chloromethyl phthalimide as reaget: C 3 C C 3 S i) N C 2 Cl ii) N 2 N 2 / RT / CCl 3 C 3 C C 3 C 2 N 2 S To meet the demad for a regiospecific, well cotrolled polymer modificatio reactio, a more attractive, site specific ad efficiet approach i the chemical modificatio of polysulfoe is required. Guiver ad coworkers 14-17,35-37 developed a ovel route, which was later exploited by Jaasch ad coworkers 1-7 for the regiospecific itroductio of fuctioal groups o the polysulfoe backboe. The process ivolves the chemical modificatio of commercially available polysulfoe usig carbaio chemistry to itroduce fuctioal groups oto the polymer backboe. By the treatmet of umodified polysulfoe with a orgaolithium compoud ad the subsequet reactio of the lithiated polysulfoe derivative with the appropriate electrophiles afforded a wide variety of fuctioalized polysulfoe derivatives i quatitative yields. The lithiatio process is well cotrolled ad takes place regiospecifically at the ortho positio relative to the 7

24 sulfoe groups of the polymer backboe. The subsequet additio of differet electrophilic systems (E + ) leads to the itroductio of differet fuctioal groups such as the carboxyl, haloge, alkyl, aldehyde, sulfoate, primary amie ad silyl groups pedat to the polymer backboe 14-17,35-37, as outlied as follows: C 3 C 3 S (i) RLi / TF / -78 o C (ii) E C 3 C 3 E S E I particular, for the preparatio of amie fuctioalized polysulfoe, umodified polysulfoe was reacted directly with -butyllithium at low temperature. The lithiated polysulfoe was the coverted quatitatively to the azide polysulfoe derivative by treatmet with tosyl azide. Subsequet reductio of the azide groups to the primary amie groups by the additio of sodium borohydride gave the amie fuctioalized polysulfoe i quatitative yields. The polymeric amie precursors are used extesively i cross-likig or chai extesio reactios to achieve reduced brittleess i thermosettig resis: 8

25 C 3 C 3 S (i) 2.1 eq. -butyllithium (ii) tosyl azide C 3 C 3 N 3 S N 3 NaB 4 C 3 N 2 C 3 S N 2 Recetly, Jaasch ad coworkers 5-7 prepared mechaically strog ad flexible polysulfoe membrae substrates by graftig poly(viylphosphoic acid) side chais oto polysulfoe. Lithiatio of umodified polysulfoe by butyllithium produced lithiated polysulfoe which acted as iitiator for the aioic polymerizatio of diethylviylphosphate from the polysulfoe backboe. The direct polymerizatio from the lithiated sites o polysulfoe gave very low yields of the desiged product eve after log reactio times. Thus, to overcome the iefficiet ucleophilic power ad the iitiatig capacity of the lithiated polysulfoe, 1,1-dipheylethylee was added to the reactio mixture to form the dipheylalkyllithium aio prior to the additio of the diethylviylphosphate moomer. Polymerizatio proceeded via a well cotrolled reactio ad, after the quatitative cleavage of the ester fuctio, polysulfoe-g-poly(viylphosphoic acid) copolymers were produced: 9

26 C 3 C 3 S lithiatio butyllithium C 2 activatio C 3 C 3 Ph S Li Ph graftig Et P Et C 3 C 3 Ph Ph S Et Li m P Et hydrolysis Cl (aq), reflux C 3 C 3 Ph Ph S P m 10

27 The results idicate that the crossover reactio of lithiated polysulfoe with the bulky 1,1-dipheylethylee electrophile proceeded quatitatively with the itroductio of oly oe 1,1-dipheylethylee uit pedat to the polymer chai. I the curret study, the preparatio of dipyridyl fuctioalized polysulfoe is described 39. The method ivolves the quatitative lithiatio of polysulfoe ad subsequet additio of 2,2'-viylideedipyridie to produce the correspodig dipyridyl fuctioalized polysulfoes with degrees of fuctioalizatio ragig betwee 45% - 95% as determied by proto uclear magetic resoace spectrometry. The fuctioalized polymers were characterized by size exclusio chromatography, 1 NMR, FTIR, differetial scaig calorimetry ad thermogravimetric aalysis. Membraes obtaied from umodified polysulfoe as well as dipyridyl fuctioalized polysulfoes were characterized by atomic force microscopy, scaig electro microscopy, pure water permeatio measuremets ad cotact agle measuremets. 2.2 Fuctioalizatio of Polymers with 1,1-Diarylethylee Derivatives The reactio of polymeric carbaioic ceters with fuctioalized 1,1-dipheylethylee derivatives is oe of the most versatile methods for the itroductio of fuctioal groups at the polymeric chai ed. Quirk ad coworkers developed a geeral, quatitative, livig, aioic fuctioalizatio method, idepedet of the specific fuctioal group, based o the additio reactio of simple ad polymeric orgaolithium compouds to 1,1-dipheylethylee derivatives. A feature of such reactios is that, due to steric effects, the 1,1-dipheylethylee uit does ot homopolymerize ad udergo oly quatitative mooadditio reactios with the aioic species. Thus, the fuctioalized 1,1-dipheylethylee uit readily reacts with orgaolithium compouds to quatitatively produce 1:1 adducts. For example, dimethylamio fuctioalized polystyree was prepared by the reactio of polystyryllithium (PSLi) with 1-[4'-(N,N-dimethylamiopheyl)]- 1-pheylethylee 46 as outlied below: 11

28 PSLi + C 2 Bezee PS C C Li RT N(C 3 ) 2 N(C 3 ) 2 Me PS C C PS = Polystyryl N(C 3 ) 2 Similarly, ω -amiopolystyree 51 was prepared i quatitative yields by reactig polystyryllithium with 1-[4'-{N,N-bis(trimethylsilyl)amio}pheyl]-1-pheylethylee i bezee at room temperature, followed by the removal of the silyl protectig group by hydrolysis with 1% cocetrated Cl ad eutralizatio with 20 wt% Me 4 N + - i methaol: PSLi + C 2 N(SiMe 3 ) 2 Bezee RT PS C C Li N(SiMe 3 ) 2 Me PS C C 1. 1% Cl, TF 2. Me 4 N PS C C PS = Polystyryl N 2 N(SiMe 3 ) 2 12

29 Recetly, Kim ad coworkers 52 outlied a aioic chai ed fuctioalizatio reactio whereby tertiary amie groups are itroduced at oe ed or at both eds of the polymer chai usig 1,1-bis[(4-dimethylamio)pheyl]ethylee as fuctioalizig aget. Fuctioalized polymers with aromatic tertiary amie groups at both the - ad ω - termii of the polymer chai were prepared by the crossover reactios of -butyllithium with the dipheylethylee aalogue to form a iitiator itermediate for styree polymerizatio, followed by the chai ed fuctioalizatio reactio by the additio of 1,1-bis[(4-dimethylamio)pheyl]- ethylee at the ed of the polymerizatio process: N(C 3 ) 2 N(C 3 ) 2 R C 2 CLi R C 2 C C 2 C C 2-1 CLi N(C 3 ) 2 N(C 3 ) 2 (i) C 2 ( 3 C) 2 N N(C 3 ) 2 (ii) C 3 N(C 3 ) 2 N(C 3 ) 2 R C 2 C C 2 C C 2 C N(C 3 ) 2 N(C 3 ) 2 13

30 The curret research work describes the sythesis of fuctioalized polymers via cotrolled free radical polymerizatio usig fuctioalized 1,1-dipheylethylee compouds as amie iitiator precursors. The method ivolves the preparatio of well defied primary ad tertiary amie fuctioalized polymers by a geeral, quatitative, oe pot ATRP fuctioalizatio process, usig appropriate fuctioalized iitiator systems derived from primary ad tertiary amie substituted 1,1-dipheylethylees as well as post ATRP chai ed fuctioalizatio reactios. 2.3 Free Radical Polymerizatio Free radical polymerizatio is the most widely used idustrial method for the preparatio of polymers. The advatages of covetioal free radical polymerizatio are its low reactat purity reactios ad that a wide variety of moomers ca udergo polymerizatio ad copolymerizatio uder simple experimetal coditios. owever, polymers with o cotrol of the umber average molecular weights ad molecular weight distributios are obtaied. The high cocetratio of reactive free radicals cause side reactios, such as termiatio ad chai trasfer reactios, to take place to a great extet. ece, more cotrolled polymerizatio techiques are eeded for the preparatio of polymers with well-defied structures. Several ew cotrolled/livig free radical polymerizatio methods (CRP), which allow the preparatio of well defied polymers by free radical mechaisms, were developed over the past decade. The most widely used CRP methods for the sythesis of well defied polymeric materials are itroxide mediated free radical polymerizatio (NMP) 56, reversible additio-fragmetatio chai trasfer polymerizatio (RAFT) 57 ad atom trasfer radical polymerizatio (ATRP)

31 2.3.1 Nitroxide Mediated Free Radical Polymerizatio To overcome the deficiecies of ucotrolled polymer growth experieced i the traditioal free radical process, the itroxide mediated free radical polymerizatio (NMP) method, havig characteristics of a livig polymerizatio process, has bee developed 58. The NMP method is the simplest of the various techiques curretly used for CRP. 59 The techique is based o the reversible dissociatio of a (macro)alkoxyamie 60 species, which decreases the irreversible termiatio reactios. As a result, a majority of dormat livig chais ca grow util the moomer is cosumed, producig a polymer with equal chai legth ad with a reactive chai ed: self termiatio products k t M N k d1 k c1 N + M M M +1 N livig chais k p + M M +2 N k d k c M +1 + N k t dead chais Although the NMP method may ot strictly obey the defiitio of a livig polymerizatio, it does satisfy may of the requiremets, hece the use of the terms livig or pseudolivig. The stimulus for the curret iterest i the NMP process is the report of Georges 61, where it is show that polystyree with arrow molecular weight distributio ca be prepared usig a mixture of bezoyl 15

32 peroxide (BP) ad 2,2,6,6-tetramethylpiperidiy-1-oxy (TEMP) as a iitiatig system. The success of the NMP method ca be related to the ability of stable itroxide free radicals, such as TEMP, to react at ear diffusio cotrolled rates with the carbo cetered free radical of the growig polymer chai ed i a thermally reversible process. The process dramatically lowers the cocetratio of free radicals i the polymerizatio system ad, coupled with the iability of the itroxide free radicals to iitiate ew chai growth, leads to cotrolled polymerizatio. The features of the NMP process have bee exploited i the preparatio of star ad graft polymers 62-65, hyperbrached systems 66 ad radom ad block polymers with arrow molecular weight distributios 63-,66. The NMP method has bee applied to the polymerizatio of styree ad its derivatives as well as the copolymerizatio of styreics with other moomers such as acrylates, methacrylates ad acryloitriles 67. owever, poor cotrol i the polymerizatios of moomers other tha styreics 68 have bee obtaied by the NMP method. The NMP method has bee exploited for the preparatio of chai ed fuctioalized polymers usig fuctioalized uimolecular iitiators. For example, awker 69 ad Braslau 70 prepared amie chai ed fuctioalized polymers by usig amie fuctioalized alkoxyamie iitiators for styree polymerizatio. Icorporatio of the amie chai ed fuctioality of greater tha 97% ito polymers was achieved ad polymers with umber average molecular weights up to g/mol were obtaied: 16

33 N N N S o C, 6 hrs N S 2 NMe 2 NMe Reversible Additio-Fragmetatio Chai Trasfer Free Radical Polymerizatio Reversible additio-fragmetatio chai trasfer free radical polymerizatio (RAFT) is a versatile ad robust cotrolled free radical polymerizatio process based o the use of a covetioal radical polymerizatio iitiator i the presece of (thiocarboyl)sulfayl compouds of geeral structure S=C(Z)-SR (i) 71. S R S Z (i) ii) Z = Ph, R = C(C 3 ) 2 Ph iii) Z = Ph, R = C(C 3 )Ph iv) Z = Ph, R = C 2 Ph v) Z = Ph, R = C(C 3 )(CN)C 2 C 2 Na vi) Z = Ph, R = C(C 3 )(CN)(C 2 ) 2 C 2 vii) Z = Ph, R = C(C 3 ) 2 CN viii) Z = C 3, R = C 2 Ph ix) Z = Ph, R= C(C 3 )(CN)C 2 C 2 17

34 The (thiocarboyl)sulfayl compoud (i) acts as a efficiet reversible additio fragmetatio chai trasfer aget ad cofers livig characteristics to the polymerizatio. RAFT ca be distiguished from other cotrolled/ livig free radical polymerizatio methods by its use i the polymerizatio of a wide rage of moomers with varyig reactio coditios. I each case, RAFT provides polymers with cotrolled umber average molecular weights ad arrow molecular weight distributios (usually <1.2). The RAFT process ivolves free radical polymerizatio i the presece of reaget (i) as show below: P + S C Z S R P S C Z S R (i) A P S C Z S + R R + Moomer P m P m Moomer + S C S P Z (i) P m S C Z B S P P m S C S + P Z Moomer Additio of a propagatig radical (P ) to a (thiocarboyl)sulfayl compoud (i) gives a adduct radical A which ca fragmet to form a polymeric (thiocarboyl)sulfayl compoud P -SC(Z)=S ad a ew radical R. The reactio of R with a moomer M forms a ew propagatig radical P m. A dyamic 18

35 equilibrium is subsequetly established betwee the active propagatig radical (P ad P m) ad dormat polymeric (thiocarboyl)sulfayl compouds (P -S- C(Z)=S) such that there is a equal probability of growth for all chais, resultig i polymers with arrow molecular weight distributios 72. The effectiveess of reagets (i - ix) i providig livig character to the RAFT process is attributed to their very high trasfer costats which esure a rapid rate of exchage betwee dormat ad livig chais. The choice of Z ad R i reaget (i) is crucial to the success of the RAFT process. To esure a high trasfer costat, Z should activate (or at least ot deactivate) the C=S double bod toward radical additio. Suitable Z groups are aryl ad alkyl groups. The R group should be a good free radical leavig group (e.g. cumyl, cyaoisopropyl) ad the expelled radical should be effective i reiitiatig free radical polymerizatio. RAFT ca be carried out i bulk, solutio, emulsio or suspesio polymerizatio processes. The advatage of the RAFT process is its compatibility with a very wide rage of moomers icludig fuctioal moomers cotaiig acid (e.g. acrylic acid), acid salt (e.g. styree-sulfoic acid sodium salt), hydroxyl (e.g. hydroxyl ethyl methacrylate) or tertiary amie (e.g. dimethylamioethyl methacrylate) groups. The RAFT process ca also be used for the preparatio of block copolymers with arrow molecular weight distributios 73. The RAFT polymerizatio method ca be adapted for the sythesis of ed fuctioalized polymers by the careful choice of the RAFT aget 57. If the R- groups of the RAFT aget cotai a fuctioal group, -fuctioalized polymers are obtaied. For example, Moad ad coworkers 74 prepared amie fuctioalized polymers by itroducig the amie fuctioality via a phthalimido methyl RAFT precursor. The sythesis of -phthalimidomethylpolystyree ivolved the use of a phthalimido RAFT aget for the iitiatio of styree polymerizatio at 110 o C. ydraziolysis of the phthalimido ed group afforded a polymer with the desired 19

36 -amio fuctioality. The RAFT aget fuctioality was removed prior to deprotectio of the amie group by reactio with tri--butylstaae as outlied below: N S S S C C N Ph S S C4 9 S tri--butylstaae Bu 3 S Ph 2 N -1 Ph N 2 N 2, DMF 80 C, 12 h N Ph -1 Ph 2.4 Atom Trasfer Radical Polymerizatio Trasitio metal catalyzed free radical polymerizatio was developed idepedetly by Matyjaszewski ad Wag 75,76 ad Sawamoto ad coworkers 77 i I particular, the copper mediated method, called atom trasfer radical polymerizatio (ATRP) has prove to be more successful for the cotrolled/ livig (co)polymerizatio of a wide rage of moomers icludig styrees, acrylates ad methacrylates. I the classical ATRP method, developed from redox catalyzed telomerizatio reactios 78 as well as atom trasfer radical additio reactios (ATRA) 79, a trasitio metal/ligad complex catalyst acts as a carrier of the haloge atom i a reversible redox process 80,81 durig the ATRP method. The ATRP techique is a powerful tool for the sythesis of polymers with cotrolled umber average molecular weights, arrow molecular weight distributios, cotrolled chai fuctioality, compositio ad morphology 76,82,83. 20

37 The classical ATRP method ecompasses the reversible homolytic cleavage of a carbo-haloge bod of a alkyl halide iitiator molecule i the presece of trasitio metal salt complexed with a suitable bi- or tridetate ligad as catalyst, followed by the additio of the moomer to form a polymer. Cotrolled radical polymerizatio is based o the maiteace of a low, statioary cocetratio of the active free radical species ad the establishmet of a fast, dyamic equilibrium betwee the active ad dormat species 84, Mechaism of Atom Trasfer Radical Polymerizatio I the ATRP method, the active species is formed whe the haloge i the alkyl halide is abstracted by the metal complex, M t, to form the oxidized species, XM +1 t ad the carbo cetered radical, R. I the subsequet step the radical R reacts with a alkee C 2 =CY to form a trasiet radical R-C 2 CY species. The reactio betwee XM +1 t ad R-C 2 CY results i the target product R-C 2 CY-X ad regeerates the reduced trasitio metal species M t which agai reacts with R-X to promote a ew redox cycle 76 as illustrated i the followig reactio scheme: R-X + M t k'act k'deact R + XMt +1 R + Y k add XM t +1 R Y XM t +1 k p Y R XM t +1 Y Y XM t +1 k deact k act k deact k act M t M t M t M t R Y X R Y Y X 21

38 I the ATRP process, the deactivatio rate must be higher tha the activatio rate i order to create a low cocetratio of propagatig radicals. Thus, the equilibrium betwee the dormat ad the active species must be greatly shifted towards the dormat species. If deactivatio is very slow or o-existet, the polymerizatio reactio becomes ucotrolled 86. The overall rate of the reactio is highly depedet o the redox potetial of the metal complexes: Br N N Cu N N + R-Br N N Cu N N + R The ATRP process i the presece of copper as catalyst takes place i two major kietic steps: iitiatio ad propagatio. Termiatio reactios also occur, but o more tha a few percetages of the growig chais udergo termiatio i ATRP reactios 76. Iitiatio R-X + Cu(I)X/ligad R + X-Cu(II)X/ligad (X=Cl, Br) k p R + moomer P 1 Propagatio P -X + Cu(i)X/ligad P + moomer K eq P + X-Cu(II)X/ligad k p P +1 Termiatio P + P m k t P +m The followig rate laws are derived from the iitiatio ad propagatio steps: 87 22

39 Cu( II) X ( ) [ ] k P act K eq = = kdeact Cu I PX ( ) ( ) Cu I X R p =kp[ P][ M ] =kpkeq [ I] M 0 Cu II X [ ] R p is based o the assumptio that the termiatio step ca be eglected ad that a fast pre-equilibrium is established. The propagatig rate (R p ) of the polymerizatio process is first order with respect to moomer cocetratio [M], iitiator cocetratio [I] ad activator cocetratio [Cu(I)X]. owever, i the begiig, the reactio is egative with respect to deactivator cocetratio [Cu(II)X]. This is due to the persistet radical effect ad the irreversible formatio of Cu(II)X i the iitial stages of the polymerizatio 88. There are three primary experimetal features which determie a cotrolled/ livig free radical polymerizatio 89 process, amely: (i) the first order rate plot of l[m] 0 /[M] versus time should be liear. This is a idicatio that the cocetratio of active radical species is costat throughout the reactio. The plot should have a gradiet equal to the pseudo first order rate coefficiet, K app, which gives a idicatio of the rate of reactio. K app is defied by: [ M] [ M] l 0 =K * app p Pol =K t where [M] is the moomer cocetratio, [M] 0 is the iitial moomer cocetratio, K p is the propagatio rate coefficiet, [Pol*] is the cocetratio of active propagatig species ad t is time. t (ii) the molecular weight distributios of the polymers should be below

40 (iii) a observed icrease i the umber average molecular weight of the polymer as moomer coversio proceeds should be liear, idicatig that all the chais are growig at the same rate, described by the equatio below: [ M] [ ] theory %coversio M = 0 MW m+mw 100 I i 0 where [M] 0 ad [I] 0 are the iitial cocetratios of moomer ad iitiator respectively, ad MW M ad MW i are the molecular weights of moomer ad iitiator, respectively Characteristics of the ATRP reactio Moomers A variety of viyl moomers such as styrees 76,88-92, acrylates 76,77,93-97 ad methacrylates 92,96, udergo polymerizatio by ATRP methods. ther moomers such as acryloitrile 105,106 ad (meth)acrylamide , which cotais substituets that ca stabilize a propagatig radical, also udergo facile ATRP reactios. Some examples of moomers that udergo polymerizatio by ATRP methods are show below: 24

41 N R R =, Me, t-bu, Br F, CF 3, Ac N N Iitiators I ATRP reactios, the iitiator geerates the growig chais. Thus, the iitiator cocetratio determies the molecular weight of the resultig polymer. The theoretical degree of polymerizatio (DP) ca be calculated accordig to the followig equatio 110 : DP = [ M] [] I o o x coversio I ATRP reactios, the iitiator is typically a alkyl halide (RX). For the formatio of polymers with arrow molecular weight distributios, it is importat that the iitiatio rate is higher tha the propagatig rate, i order to get all the chais growig at the same time. Icomplete iitiatio leads to polymers with higher umber average molecular weights tha the targeted values ad with broader molecular weight distributios 86. Aother importat factor is that the iitiator must show little or o tedecy to udergo side reactios. It has bee show that 25

42 tertiary alkyl halides are better iitiators tha the secodary ad primary alkyl halides, respectively. ther variables that are importat to take ito accout whe choosig iitiators are steric effects, polar properties ad redox potetials 111. e easy rule to follow is that the R-group i the alkyl halide should be similar i structure to that of the moomer. For example, (1-bromoethyl)bezee is usually used for the polymerizatio of styree 76. Compouds such as ethyl-2-bromoisobutyrate ad ethyl-2-bromopropioate are used for the polymerizatio of (meth)acrylates 92 ad 2-bromopropioitrile ca be used for acryloitrile polymerizatio 105,106. owever, other iitiators work well for differet moomers. The haloge atom i ATRP iitiators is usually a bromie or chlorie atom. The ATRP of acrylates 112 ad styree 90,91 with iodie-based iitiators has bee reported. rgaofluorie compouds do ot work i ATRP due to the strog C-F bod, which caot udergo homolytic cleavage. Some examples of ATRP iitiators are show below: Br N Br Br Br Cl S Cl Cl Cl Cl Cl Trasitio metals Several trasitio metal catalysts have bee used i trasitio metal catalyzed free radical polymerizatio reactios. Catalyst based o copper is by far the most widely used metal catalyst due to its relatively low cost ad versatility i ATRP 26