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Controlled “living” radical polymerization
Controlled radical polymerization (CRP) is a polymerization process occurred via radical reaction, therefore it can be applied in many types of vinyl monomers. The mechanism of the controlled /living processes depend on reversible reaction of initiating components; nitroxide as known in NitroxideMediated Controlled/ Living Radical Polymerization (NMP) [31, 32], thioester as known in Reversible Addition-Fragment Chain-Transfer (RAFT) [33, 34] and catalyst as known in Atom Transfer Radical Polymerization (ATRP) [35-42]. The feature of the initiator unit in their system, types of monomer, advantages and disadvantages of each technique are present in the Table 3.3.
The CRP is composed of four criteria which are different from conventional radical polymerization. These are: 1) Liner kinetic plots in semilogarithmic coordinates Ln[M]0/[M] versus time (Figure 3.10) demonstrating constant amount of active radical in the system, 2) Linear evolution of molecular weights or degree of polymerization (DPn ) with conversion (Figure 3.11), 3) Polydispersity (PDI) decreases with conversion and 4) End functionalities are not affected by slow initiation and exchange but are reduced when chain breaking reactions become important. By this technique, production of various compositions and molecular structures of target polymer can be achieved. Among various methods of CRP, ATRP is our particular interest for preparation of graft copolymer based on natural rubber.
Atom Transfer Radical Polymerization (ATRP)
Atom transfer radical polymerization (ATRP) is one of the controlled/living radical polymerizations. It is based on the catalyzed, reversible cleavage of covalent bond in the dormant species via a redox process. The key step in controlling the polymerization is atom (group) transfer between growing chain and a catalyst. The basic step of ATRP is derived from a key ideal of Kharasch addition (Figure 3.12), a technique used for increasing number carbon atom in organic compound. In this reaction, it was composed of alkyl halide (RX, 1), vinyl group (C=C-Y, 3), transition metal and amine ligand. It was found that amount of vinyl group is the most important factor to control a number of carbon atom of product.
LIST OF FIGURES
LIST OF ABBREVIATIONS
CHAPTER I INTRODUCTION
CHAPTER II OBJECTIVE
CHAPTER III LITERATURE REVIEWS
3.1 Graft Copolymers
3.1.1 Grafting “onto” technique [13]
3.1.2 Grafting “from” technique
3.1.2.1 Ionic polymerization
3.1.2.2 Radical polymerization
3.1.2.3 Controlled “living” radical polymerization
3.2 Atom Transfer Radical Polymerization (ATRP)
3.2.1 Various types of ATRP
3.2.2 ATRP technique for graft copolymerization
3.3 Natural Rubber (NR)
3.3.1 Chemical modification of NR
3.3.1.1 Bromination reaction
3.3.1.2 Epoxidation reaction
3.3.1.3 Epoxide ring opening reaction of ENR
3.3.1.4 Graft copolymerization of vinyl monomer from NR
CHAPTER IV METERIALS AND METHODS
4.1 Materials and Instruments
4.2 Study on Model of Natural Rubber
4.2.1 Synthesis of 4-methyloct-4-ene (a model of natural rubber)
4.2.2 Synthesis of 4,5-epoxy-4-methyloctane, 1 (a model of epoxidized natural rubber)
4.2.3 Synthesis of bromoalkyl-functionalized natural rubber models
4.2.4 Preparation of amine ligand
4.3.3 Synthesis of PI-g-PMMA by ATRP in toluene solution.
4.3.4 Acidolysis of PI-g-PMMA using trifluoroacetic acid
4.4 Study on Natural Rubber
4.4.1 Synthesis of epoxidized natural rubber (ENR).
4.4.2 Synthesis of bromoalkyl-functionalized natural rubber (NRBr).
4.4.3 Synthesis of NR-g-PMMA by ATRP in toluene solution.
4.4.4 Synthesis of NR-g-PMMA by Normal ATRP in dispersed medium
4.4.5 Synthesis of NR-g-PMMA by AGET ATRP in dispersed medium.
4.4.6 Acidolysis of NR-g-PMMA using trifluoroacetic acid
4.5 Characterization
4.5.1 Chemical structure
4.5.1.1 By infrared spectroscopy
4.5.1.2 By 1H and 13C NMR spectroscopy
4.5.2 Determination of epoxidation level
4.5.3 Determination of bromoalkyl-functionalized unit in modified rubber using 1H NMR
4.5.3.1 Reaction of epoxidized rubber with 2- bromopropionic acid (A1)
4.2.4.1 N-(n-octyl)-2-pyridylmethanimine (NOPMI)
4.2.4.2 N-(n-octadecyl)-2-pyridylmethanimine (NODPMI)
4.2.5 The procedure for the ATRP of MMA in toluene solution
4.2.5.1 General procedure of polymerization by ATRP technique in toluene solution
4.2.5.2 The procedure for the ATRP of MMA
4.2.5.3 General procedure of homopolymerization of PMMA by ATRP technique in dispersed medium.
4.3 Study on Synthetic Cis-1,4-polyisoprene
4.3.1 Synthesis of epoxidized polyisoprene (EPI)
4.3.2 Synthesis of bromoalkyl-functionalized polyisoprene (PIBr).
4.5.3.2 Reaction of epoxidized rubber with 2- bromo-2-methylpropionic acid (A2)
4.5.4 Determination of monomer conversion by 1H NMR
4.5.5 Determination of amount of PMMA in graft copolymer by 1H NMR
4.5.6 Molecular weight determination by Size Exclusion Chromatography (SEC)
4.5.7 Separation technique by Analytical HPLC 71
4.5.8 Thermal analysis by Differential Scanning Calorimeter (DSC)
CHAPTER V RESULTS AND DISCUSSION
5.1 Study on 4-Methyloct-4-ene, a Model of cis-1,4Polyisoprene and Natural Rubber
5.1.1 Preparation of 4-methyloct-4-ene
5.1.2 Preparation of 4,5-epoxy-4-methyloctane
5.1.3 Addition of bromoalkyl carboxylic acid on 4,5- epoxy 4-methyloctane
5.1.3.1 Addition of 2-bromopropionic acid onto 4,5-epoxy-4-methyloctane
5.1.3.2 Addition of 2-bromo-2-methylpropionic acid onto 4,5-epoxy-4-methyloctane
5.1.4 ATRP of MMA using bromoalkyl-functionalized NR models as an initiators
5.1.4.1 Influence of initiator structure
5.1.4.2 Influence of reaction temperature
5.1.4.3 Influence of ligand structure
5.1.4.4 Influence of side products
5.1.4.5 Influence of water
5.2 Study on Synthetic Cis-1,4-polyisoprene (PI)
5.2.1 Synthesis and characterization of bromoalkyl-functionalized polyisoprene (PIBr)
5.2.2 ATRP of MMA using bromoalkyl-functionalized polyisoprene as initiators
5.2.2.1 Influence of ligand structure
5.2.2.2 Influence of the amount of bromoalkylfunctionalized polyisoprene units in PIBr
5.3 Study on Natural Rubber
5.3.1 Synthesis and characterization of bromoalkyl- functionalized NR
5.3.1.1 Preparation of epoxidized NR
5.3.1.2 Addition of bromoalkyl carboxylic acid on ENR
5.3.1.3 Parameters affecting on the addition of acid onto epoxidized natural rubber (ENR)
5.3.1.3.1 Influence of reaction time
5.3.1.3.2 Influence of reaction temperature
5.3.1.3.3 Effect of amount of acid
5.3.1.3.4 Effect of reaction concentration
5.3.1.3.5 Effect of type of acid
5.3.2 ATRP of MMA using bromoalkyl-functionalized NR as initiators
5.3.2.1 Normal ATRP process
5.3.2.1.1 Normal ATRP in solution
5.3.2.1.2 Normal ATRP in dispersed medium
5.3.2.2 AGET-ATRP in dispersed medium
5.4 Thermal properties
5.4.1 Thermal property of epoxidized NR (ENR)
5.4.2 Thermal properties of bromoalkyl-functionalized NR
5.4.3 Thermal properties of NR-g-PMMA
CHAPTER VI CONCLUSIONS
REFERENCES
APPENDIX
BIOGRAPHY
