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Stimuli-responsive amphiphilic polymers: controlled polymerizations of tertiary amine methacrylates via ATRP
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Type
Thesis
Author
Mao, Bao Wei
Supervisor
Gan, Leong Huat
Abstract
This thesis describes the synthesis and characterization of new tertiary amine methacrylate-based stimuli-responsive amphiphilic polymers. The thesis consists of six chapters. An introduction of atom transfer radical polymerization (ATRP) and the aims of studies are presented in Chapter One. The literature review is presented in Chapter Two.
Polymerization of 2-(diethylamino)ethyl methacrylate (DEAEMA) via homogeneous ATRP and its block copolymers with tertiary butyl methacrylate (tBMA) are described in Chapter Three. For both monomers polymerization under various reaction conditions, the effects of the initiators and solvents were examined. With 1,1,4,7,10,10-hexamethyl triethylenetetramine/copper(I) chloride/p-toluenesulfonyl chloride as the ligand/catalyst/initiator system in methanol, the polymers with a polydispersity index as low as 1.07 were synthesized. Kinetic studies demonstrated the polymerization was very well controlled and exhibited the living characteristic of the process. Well-defined block copolymers of DEAEMA and tBMA were successfully synthesized. The copolymers could be synthesized with equally good results by starting with either poly(DEAEMA) or poly(tBMA) as the macroinitiators. However, only the macroinitiators terminated with chlorine should be used. The corresponding macroinitiators with bromine as a transferable group did not yield well- defined copolymers. Diblock copolymers of tBMA and DEAEMA were also successfully synthesized by one-pot strategy via ATRP. Kinetic results clearly demonstrated the controlled/“living” character of the polymerization.
Chapter Four describes the aggregation behavior of a novel zwitterionic AB diblock copolymer of poly(methacrylic acid-b-DEAEMA). The poly(MAA-b-DEAEMA), obtained by hydrolysis of poly(tBMA-b-DEAEMA), showed pH-dependent reverse micellization behavior. Micellar aggregates formed from poly(MAA30-b-DEAEMA71), poly(MAA68-b-DEAEMA55) and poly(MAA64-b-DEAEMA44) had fairly low polydispersity index at both solutions of low pH of 2 ) and high pH of 12. Micelles formed at pH 2 were larger (Rh ~ 40 - 61 nm) with looser core due to hydration of the MAA. In the presence of simple electrolyte (0.3 mol dm-3 NaCl solutions), the size of the micelles reduced by almost half while the aggregation number was little changed. This is attributed to the draining of the hydrated micellar core due to osmotic pressure. On the other hand, DEAEMA-core micelles formed at pH 12 were compact and much smaller (Rh ~ 14 – 22 nm). Addition of NaCl had only a small effect. The micellar size reduced only slightly due to the electrostatic screening effect and the aggregation number was almost unchanged. Amphiphilic block copolymers exhibiting these versatile reversible micellization behaviors have been hailed as “polymeric surfactants for the new millennium”. The micellization behavior in aqueous solution at room temperature and different pH values were studied in detail by potentiometric and conductivity titration, UV-Visible spectrophotometry, 1H NMR, static and dynamic laser light scattering.
Chapter Five describes the polymerizations of DEAEMA and DMAEMA in aqueous and methanolic solutions via ATRP. Poly(DMAEMA) and poly(DEAEMA) of low polydispersity index (PDI) of ~ 1.07 were obtained using the p-TsCl/CuCl/HMTETA system. Excellent control of polymerization was achieved even in methanol. This is in contrast with the very poor control of DMAEMA ATRP in methanol reported previously using a different initiator/catalyst/ligand system. The initiator p-TsCl underwent hydrolysis reaction in aqueous methanolic solutions with a second-order rate constant of 6.1×10-4dm3mol-1s-1 at 25 °C. Well-defined hydrophilic block copolymers of DEAEMA and DMAEMA were successfully obtained by starting with either macroinitiator of DEAEMA or DMAEMA. Poly(DMAEMA) with very high molar masses has also been successfully synthesized. The detailed kinetic studies demonstrated the polymerization was very well-controlled and exhibited the living characteristic of the process. The molecular weights achieved were by far the largest ever reported for the polymerization via ATRP technique.
The synthesis of a novel stimuli-responsive amphiphilic block copolymer of DMAEMA and 3-(trimethoxysilyl)propyl methacrylate (TMS) is described in Chapter Six. The homopolymerization of TMS was carried out at p-TsCl/CuCl/HMTETA and ethyl 2-bromoisobutyrate (EBrIB)/CuCl/HMTETA system respectively. However, only EBrIB/CuCl/HMTETA system could offer a controlled process for TMS ATRP. The diblock copolymer, poly(DMAEMA-b-TMS) self-assembled into vesicles in methanol/H2O mixed-solvent. Interestingly, the structure of the vesicles could be fixed through the crosslinking via polycondensation after hydrolysis by the –Si-(OCH3)3 groups of TMS. The vesicles are temperature and pH- sensitive. They can easily be redissolved and reprecipitated by merely changing the temperature or pH of the solution. The structures of the vesicles were fully characterized by LLS, SEM and TEM analysis. These novel stimuli-responsive organic/inorganic hybrid particles could potentially be used for various applications such as for the isolation and purification of protein/DNA and as packing materials for analytical columns.
Polymerization of 2-(diethylamino)ethyl methacrylate (DEAEMA) via homogeneous ATRP and its block copolymers with tertiary butyl methacrylate (tBMA) are described in Chapter Three. For both monomers polymerization under various reaction conditions, the effects of the initiators and solvents were examined. With 1,1,4,7,10,10-hexamethyl triethylenetetramine/copper(I) chloride/p-toluenesulfonyl chloride as the ligand/catalyst/initiator system in methanol, the polymers with a polydispersity index as low as 1.07 were synthesized. Kinetic studies demonstrated the polymerization was very well controlled and exhibited the living characteristic of the process. Well-defined block copolymers of DEAEMA and tBMA were successfully synthesized. The copolymers could be synthesized with equally good results by starting with either poly(DEAEMA) or poly(tBMA) as the macroinitiators. However, only the macroinitiators terminated with chlorine should be used. The corresponding macroinitiators with bromine as a transferable group did not yield well- defined copolymers. Diblock copolymers of tBMA and DEAEMA were also successfully synthesized by one-pot strategy via ATRP. Kinetic results clearly demonstrated the controlled/“living” character of the polymerization.
Chapter Four describes the aggregation behavior of a novel zwitterionic AB diblock copolymer of poly(methacrylic acid-b-DEAEMA). The poly(MAA-b-DEAEMA), obtained by hydrolysis of poly(tBMA-b-DEAEMA), showed pH-dependent reverse micellization behavior. Micellar aggregates formed from poly(MAA30-b-DEAEMA71), poly(MAA68-b-DEAEMA55) and poly(MAA64-b-DEAEMA44) had fairly low polydispersity index at both solutions of low pH of 2 ) and high pH of 12. Micelles formed at pH 2 were larger (Rh ~ 40 - 61 nm) with looser core due to hydration of the MAA. In the presence of simple electrolyte (0.3 mol dm-3 NaCl solutions), the size of the micelles reduced by almost half while the aggregation number was little changed. This is attributed to the draining of the hydrated micellar core due to osmotic pressure. On the other hand, DEAEMA-core micelles formed at pH 12 were compact and much smaller (Rh ~ 14 – 22 nm). Addition of NaCl had only a small effect. The micellar size reduced only slightly due to the electrostatic screening effect and the aggregation number was almost unchanged. Amphiphilic block copolymers exhibiting these versatile reversible micellization behaviors have been hailed as “polymeric surfactants for the new millennium”. The micellization behavior in aqueous solution at room temperature and different pH values were studied in detail by potentiometric and conductivity titration, UV-Visible spectrophotometry, 1H NMR, static and dynamic laser light scattering.
Chapter Five describes the polymerizations of DEAEMA and DMAEMA in aqueous and methanolic solutions via ATRP. Poly(DMAEMA) and poly(DEAEMA) of low polydispersity index (PDI) of ~ 1.07 were obtained using the p-TsCl/CuCl/HMTETA system. Excellent control of polymerization was achieved even in methanol. This is in contrast with the very poor control of DMAEMA ATRP in methanol reported previously using a different initiator/catalyst/ligand system. The initiator p-TsCl underwent hydrolysis reaction in aqueous methanolic solutions with a second-order rate constant of 6.1×10-4dm3mol-1s-1 at 25 °C. Well-defined hydrophilic block copolymers of DEAEMA and DMAEMA were successfully obtained by starting with either macroinitiator of DEAEMA or DMAEMA. Poly(DMAEMA) with very high molar masses has also been successfully synthesized. The detailed kinetic studies demonstrated the polymerization was very well-controlled and exhibited the living characteristic of the process. The molecular weights achieved were by far the largest ever reported for the polymerization via ATRP technique.
The synthesis of a novel stimuli-responsive amphiphilic block copolymer of DMAEMA and 3-(trimethoxysilyl)propyl methacrylate (TMS) is described in Chapter Six. The homopolymerization of TMS was carried out at p-TsCl/CuCl/HMTETA and ethyl 2-bromoisobutyrate (EBrIB)/CuCl/HMTETA system respectively. However, only EBrIB/CuCl/HMTETA system could offer a controlled process for TMS ATRP. The diblock copolymer, poly(DMAEMA-b-TMS) self-assembled into vesicles in methanol/H2O mixed-solvent. Interestingly, the structure of the vesicles could be fixed through the crosslinking via polycondensation after hydrolysis by the –Si-(OCH3)3 groups of TMS. The vesicles are temperature and pH- sensitive. They can easily be redissolved and reprecipitated by merely changing the temperature or pH of the solution. The structures of the vesicles were fully characterized by LLS, SEM and TEM analysis. These novel stimuli-responsive organic/inorganic hybrid particles could potentially be used for various applications such as for the isolation and purification of protein/DNA and as packing materials for analytical columns.
Date Issued
2005
Call Number
QD281.P6 Mao
Date Submitted
2005