TRANSITION METAL CATALYZED LIVING RADICAL POLYMERIZATION

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Features of the atom transfer radical polymerization process

For the accurate control and the effective use of the ATRP method in polymer synthetic strategies, the reactivity relationships between the different components of the ATRP reactions need careful evaluation. The synergistic effect between the initiator, monomer, metal catalyst, ligand, solvent and reaction temperature is essential for good control of the polymerization process. The choice of monomer and initiator and the resultant stability of the halide end group display a pronounced solvent dependence. In general, to choose a good initiator, the structure of the alkyl group of the alkyl halide initiator should be similar to the dormant polymer species, that is, 1-phenylethyl halide derivatives which resemble dormant polystyrene chain ends and α-halopropionates which approximate dormant acrylate end groups.

The use of functionalized initiators for the ATRP of vinyl monomers: The

simplest way to obtain chain end functionalized polymers by ATRP methods is to use functionalized initiators that contain the desired functional group for the polymerization of styrenic and (meth)acrylate monomers. The most widely used functionalized initiators to prepare functionalized polymers are activated alkyl or acyl halides and sulfonyl halide compounds. A wide variety of functionalized initiators have been employed in ATRP reactions to produce chain end functionalized polymers with functional groups such as the hydroxyl, cyano and amine groups regiospecifically introduced at the α-terminus of the polymer chain. Matyjaszewski and coworkers191 demonstrated that chain end functionalized polymers with thiol,130 phthalic,192 cyano, allyl, 1,3-bis{1-methyl-1-[2,2,2-trichloroethoxy)carbonylamino]ethyl}benzene ester,193 cholesteryl,128 amine and carboxyl functional groups can be prepared via ATRP methods using functionalized initiators.

HYDROXYL CHAIN END FUNCTIONALIZED POLYMERS BY ATOM

TRANSFER RADICAL POLYMERIZATION: USE OF FUNCTIONALIZED INITIATORS. In ATRP reactions, the initiator structure determines the nature of the polymer chain ends in the process of preparation of well defined polymers. By using functionalized initiators in ATRP reactions, hetero-telechelic polymers are formed directly, without the need for post-polymerization modification reactions. When functionalized organohalides are used as initiators in ATRP reactions, the functional group is introduced at the α-terminus of the polymer chain. Many hydroxyl functionalized organohalides or organosulfonyl compounds were 43 employed as initiators in styrene and methyl methacrylate polymerization to form hydroxyl functionalized polymers.

Purification of Reagents

4-Hydroxybenzophenone: (Sigma – Aldrich Chemical Company, 98%) was recrystallized from a mixture of ethanol and water (80/20), mp = 133-136 oC.210 Tetrahydrofuran: Tetrahydrofuran (THF, Saarchem, Pty Ltd) was freshly distilled from Na/benzophenone after stirring at room temperature for 24 hours. Distillation was conducted when the solution had a purple-blue color which is an indication of the dryness of the solvent and absence of reactive impurities. Sodium metal was added in excess to ensure the complete conversion of benzophenone to the benzophenone radical anion since traces of unreacted benzophenone would sublime upon distillation of THF.18,210 Styrene: Styrene (Sigma – Aldrich Chemical Company, bp = 145-146 oC) was stirred over freshly ground calcium hydride for 12 hours, followed by vacuum distillation into a flask containing molecular sieves and purged with argon before use.210 Methyl methacrylate: Methyl methacrylate (Sigma – Aldrich Chemical Company, bp = 100 oC) was stirred over freshly ground calcium hydride for 12 hours and then vacuum distilled into a flask containing molecular sieves and purged with argon before use.

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Size Exclusion Chromatography (SEC)

Size exclusion chromatography (SEC) was used for the determination of the number average molecular weights and molecular weight distributions of polymers. SEC analyses were conducted using a Waters Alliance SEC autosampler equipped with a Phenogel guard column and a Phenogel column (5 µ, 500 A pore size, 1K-150 K MW range, 300 x 7.8 mm) in series with Refractive Index and Dual Angle Laser Light Scattering Detectors. Polystyrene (Aldrich Chemical Company) and poly(methyl methacrylate) standards (Sigma – Aldrich Chemical Company) were used for the calibration of the dual angle lazer light scattering detector of the SEC instrument, where applicable.

TABLE OF CONTENTS :

DECLARATION
ABSTRACT
ACKNOWLEDGEMENTS
LIST OF ABBREVIATIONS
CHAPTER 1 INTRODUCTION
CHAPTER 2 HISTORICAL REVIEW
- 2.1 CONTROLLED FREE RADICAL POLYMERIZATION
- 2.2 NITROXIDE MEDIATED FREE RADICAL POLYMERIZATION (NMP)
- 2.3 REVERSIBLE ADDITION FRAGMENTATION CHAIN TRANSFER POLYMERIZATION (RAFT)
- 2.4 TRANSITION METAL CATALYZED LIVING RADICAL POLYMERIZATION
- 2.5 ATOM TRANSFER RADICAL POLYMERIZATION (ATRP)
  - 2.5.1 Features of the atom transfer radical polymerization process
- 2.6 FUNCTIONALIZED POLYMERS BY ATOM TRANSFER RADICAL POLYMERIZATION
- 2.7 HYDROXYL CHAIN END FUNCTIONALIZED POLYMERS
- BY ATOM TRANSFER RADICAL POLYMERIZATION: USE OF FUNCTIONALIZED INITIATORS
- 2.8 THE PREPARATION OF CHAIN END FUNCTIONALIZED POLYMERS USING FUNCTIONALIZED 1,1-DIPHENYLETHYLENE DERIVATIVES
CHAPTER 3 EXPERIMENTAL
- 3.1 MATERIALS AND GLASSWARE
  - 3.1.1 Chemicals and solvents
  - 3.1.2 Purification of Reagents
  - 3.1.3 Glassware
- 3.2 CHARACTERIZATION
  - 3.2.1 Gas Chromatography (GC)
  - 3.2.2 Size Exclusion Chromatography (SEC)
  - 3.2.3 Thin Layer Chromatography (TLC)
  - 3.2.4 Nuclear Magnetic Resonance Spectrometry (NMR)
  - 3.2.5 Fourier Transform Infrared Spectroscopy (FTIR)
  - 3.2.6 Non – Aqueous Titrations

CHAPTER 4 RESULTS AND DISCUSSION
- 4.1 ATOM TRANSFER RADICAL POLYMERIZATION: SYNTHESIS OF SILOXYL CHAIN END FUNCTIONALIZED POLYMERS
  - 4.1.1 Siloxyl Functionalized Initiator Precursor: Synthesis of 1-(4-tbutyldimethylsiloxyphenyl)-1-phenylethylene, (1)
  - 4.1.2 Synthesis of α-Siloxyl Functionalized Polystyrene, (3)
  - 4.1.3 Synthesis of α-Siloxyl Functionalized Poly(methyl methacrylate), (4)
  - 4.1.4 Synthesis of α-Hydroxyl Functionalized Polystyrene, (5)
  - 4.2.1 Disiloxyl Functionalized Initiator Precursor: Synthesis of 1,1-bis(4-tbutyldimethylsiloxyphenyl)ethylene, (6)
  - 4.2.2 Synthesis of α-Bis(siloxyl) Functionalized Polystyrene, (8)
  - 4.2.3 Synthesis of α-Bis(siloxyl) Functionalized Poly(methyl methacrylate), (9)
  - 4.2.4 Synthesis of α-Bis(hydroxyl) Functionalized Polystyrene, (10)
- 4.3 ATOM TRANSFER RADICAL POLYMERIZATION: POLYMERIZATION KINETIC STUDIES
  - 4.3.1 Synthesis of α-Siloxyl Functionalized Polystyrene, (3)
  - 4.3.2 Synthesis of α-Bis(siloxyl) Functionalized Polystyrene, (8)
  - 4.3.3 Synthesis of α-Siloxyl Functionalized Poly(methyl methacrylate), (4)
  - 4.3.4 Synthesis of α-Bis(siloxyl) Functionalized Poly(methyl methacrylate), (9)
CHAPTER 5 SUMMARY
- REFERENCES
- APPENDIX