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Development of novel well-defined functional polymers and surface modification via atom transfer radical polymerization
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Type
Thesis
Author
Li, Xiaoshi
Supervisor
Gan, Leong Huat
Abstract
The thesis describes the development of stimuli-responsive polymeric materials, active ester polymers, and surface modifications via atom transfer radical polymerization (ATRP).
Polymerizations of 2- dimethylamino ethyl methacrylate (DMAEMA) via ATRP under various reaction conditions are described and the effects of initiators and solvents are studied. By using 1, 1, 4, 7, 10, 10-hexamethyltriethylenetetramine (HMTETA)/p-toluene sulfonyl chloride (p-TsCl)/CuCl as the ligand/initiator/catalyst system in methanol, poly(DMAEMA) with polydispersity as low as 1.07 is obtained. In water, the polymerization rate is greatly enhanced. Almost 100% monomer conversion could be achieved within 0.25 h of reaction at ambient temperature. The fast polymerization, however, increases the polydispersity slightly to ~1.20.
Unlike the extensively studied poly(N-isopropyl acrylamide), the lower critical solution temperature (LCST) of poly(DMAEMA) is highly dependent on its molar mass, decreasing with increasing Mn. The LCST ranges from 30 ºC to 50 ºC in correspondence to Mn from 5,000 to 45,000.
Well-defined block copolymers of DMAEMA and methyl methacrylate (MMA) were successfully synthesized using poly(DMAEMA) as macroinitiator. The LCST of poly(DMAEMA-b-MMA) decreases with increasing MMA content as expected, owing to the hydrophobic nature of MMA.
Two active ester polymers were successfully synthesized. ATRP of Nhydroxysuccinimide methacrylate (NHSM) using ethyl 2-bromoisobutytate (EBrIB) as initiator and CuBr as the catalyst in DMSO were investigated. By using 2, 2’-bipyridine as ligand, the polymerization did not yield well-defined poly(NHSM) due to excessive radical-radical coupling reactions. The polymerization improved greatly when N-benzyl2-pyridylmethanimine (NBPM) was used as ligand instead. The polymerization was well controlled with high monomer conversion and low polydispersity (Mw/Mn = 1.28). The polymerization is first order with respect to the monomer, and the Mn is in good agreement with the target values. Diblock copolymer of NHSM with DMAEMA was synthesized successfully using poly(NHSM) as macroinitiator.
Polymerization of 2, 3, 5, 6-tetrafluorophenyl methacrylate (TFPM) using EBrIB/CuBr/HMTETA system resulted in an uncontrollable polymerization owing to strong radical-radical coupling. However, well-controlled polymerization was achieved with the addition CuBr2 as a deactivator. The controlled/“living” behavior is reflected from the good agreement between the experimental Mn with the target values and low polydispersity (Mw/Mn = 1.29). It was further confirmed by the kinetic results. The end groups of poly(TFPM) synthesized via ATRP retained almost full bromine functionality as chain extension of the second DMAEMA block to produce well-defined poly(TFPMb-DMAEMA) could be easily achieved.
Well-defined poly(NHSM) and poly(TFPM) can be used as precursors for polymer library synthesis. The active ester groups react with a variety of amines to produce a range of well-defined poly(methacrylamides), some of which are difficult to obtain from direct polymerizations of the methacrylamide monomers. Poly(NHSM) is slightly more reactive than poly(TFPM) when allowed to react with benzylamine. The second order rate constants in DMF are (1.56 ± 0.04) × 10-4 M-1 s-1 for poly(NHSM) and (1.16 ± 0.02) × 10-4 M-1 s-1 for poly(TFPM). For the reactions with secondary amines and primary amines with bulky groups, only poly(NHSM) yields substituted products while poly(TFPM) was unreactive and no substitution occurred.
As a proof-of-concept study, UV-induced grafting of poly(DMAEMA) on glass surface was carried out. The glass surface was first treated in 3-glycidoxypropyl trimethoxysilane (GPS) solution. The silanized glass surface was then subjected to argon plasma treatment, followed by air exposure and UV- induced graft polymerization of poly(DMAEMA). The results from X-ray photoelectron spectroscopic analysis revealed that the growth of poly(DMAEMA) from the glass surface was successful.
Well- defined poly(DMAEMA) and poly(NHSM) brushes on gold surfaces were prepared by the “grafting-from” approach. The gold surfaces were first attached to 2-bromo-2-methyl-propionic acid 6-[6-(2-bromo-2-methyl- propionyloxy)hexyldisulfanyl]hexyl ester (BMPHE) as the initiator. Controlled polymerizations were then carried out on the initiated gold surface via ATRP. The attached poly(NHSM) was cleaved from the surface and its Mn determined by 1H NMR. The results reveal that the ATRP of NHSM initiated from the gold surface proceeded in the same manner as that in solution. The growth of poly(NHSM) was also confirmed by ATR- FTIR. Furthermore, 6-nitro-3-aminocoumarin (NAC) molecules were successfully attached to the grafted polymer chains via aminolysis reaction. The fluorescent intensity of the modified surface increases with increasing molecular weight of poly(NHSM). The results indicate that the NHS groups on the solid surface are available nearly as freely as those in solution for the reaction with amino groups to form amide linkages. The modified gold surface could thus be used as sensors for biomolecules containing amino groups.
Polymerizations of 2- dimethylamino ethyl methacrylate (DMAEMA) via ATRP under various reaction conditions are described and the effects of initiators and solvents are studied. By using 1, 1, 4, 7, 10, 10-hexamethyltriethylenetetramine (HMTETA)/p-toluene sulfonyl chloride (p-TsCl)/CuCl as the ligand/initiator/catalyst system in methanol, poly(DMAEMA) with polydispersity as low as 1.07 is obtained. In water, the polymerization rate is greatly enhanced. Almost 100% monomer conversion could be achieved within 0.25 h of reaction at ambient temperature. The fast polymerization, however, increases the polydispersity slightly to ~1.20.
Unlike the extensively studied poly(N-isopropyl acrylamide), the lower critical solution temperature (LCST) of poly(DMAEMA) is highly dependent on its molar mass, decreasing with increasing Mn. The LCST ranges from 30 ºC to 50 ºC in correspondence to Mn from 5,000 to 45,000.
Well-defined block copolymers of DMAEMA and methyl methacrylate (MMA) were successfully synthesized using poly(DMAEMA) as macroinitiator. The LCST of poly(DMAEMA-b-MMA) decreases with increasing MMA content as expected, owing to the hydrophobic nature of MMA.
Two active ester polymers were successfully synthesized. ATRP of Nhydroxysuccinimide methacrylate (NHSM) using ethyl 2-bromoisobutytate (EBrIB) as initiator and CuBr as the catalyst in DMSO were investigated. By using 2, 2’-bipyridine as ligand, the polymerization did not yield well-defined poly(NHSM) due to excessive radical-radical coupling reactions. The polymerization improved greatly when N-benzyl2-pyridylmethanimine (NBPM) was used as ligand instead. The polymerization was well controlled with high monomer conversion and low polydispersity (Mw/Mn = 1.28). The polymerization is first order with respect to the monomer, and the Mn is in good agreement with the target values. Diblock copolymer of NHSM with DMAEMA was synthesized successfully using poly(NHSM) as macroinitiator.
Polymerization of 2, 3, 5, 6-tetrafluorophenyl methacrylate (TFPM) using EBrIB/CuBr/HMTETA system resulted in an uncontrollable polymerization owing to strong radical-radical coupling. However, well-controlled polymerization was achieved with the addition CuBr2 as a deactivator. The controlled/“living” behavior is reflected from the good agreement between the experimental Mn with the target values and low polydispersity (Mw/Mn = 1.29). It was further confirmed by the kinetic results. The end groups of poly(TFPM) synthesized via ATRP retained almost full bromine functionality as chain extension of the second DMAEMA block to produce well-defined poly(TFPMb-DMAEMA) could be easily achieved.
Well-defined poly(NHSM) and poly(TFPM) can be used as precursors for polymer library synthesis. The active ester groups react with a variety of amines to produce a range of well-defined poly(methacrylamides), some of which are difficult to obtain from direct polymerizations of the methacrylamide monomers. Poly(NHSM) is slightly more reactive than poly(TFPM) when allowed to react with benzylamine. The second order rate constants in DMF are (1.56 ± 0.04) × 10-4 M-1 s-1 for poly(NHSM) and (1.16 ± 0.02) × 10-4 M-1 s-1 for poly(TFPM). For the reactions with secondary amines and primary amines with bulky groups, only poly(NHSM) yields substituted products while poly(TFPM) was unreactive and no substitution occurred.
As a proof-of-concept study, UV-induced grafting of poly(DMAEMA) on glass surface was carried out. The glass surface was first treated in 3-glycidoxypropyl trimethoxysilane (GPS) solution. The silanized glass surface was then subjected to argon plasma treatment, followed by air exposure and UV- induced graft polymerization of poly(DMAEMA). The results from X-ray photoelectron spectroscopic analysis revealed that the growth of poly(DMAEMA) from the glass surface was successful.
Well- defined poly(DMAEMA) and poly(NHSM) brushes on gold surfaces were prepared by the “grafting-from” approach. The gold surfaces were first attached to 2-bromo-2-methyl-propionic acid 6-[6-(2-bromo-2-methyl- propionyloxy)hexyldisulfanyl]hexyl ester (BMPHE) as the initiator. Controlled polymerizations were then carried out on the initiated gold surface via ATRP. The attached poly(NHSM) was cleaved from the surface and its Mn determined by 1H NMR. The results reveal that the ATRP of NHSM initiated from the gold surface proceeded in the same manner as that in solution. The growth of poly(NHSM) was also confirmed by ATR- FTIR. Furthermore, 6-nitro-3-aminocoumarin (NAC) molecules were successfully attached to the grafted polymer chains via aminolysis reaction. The fluorescent intensity of the modified surface increases with increasing molecular weight of poly(NHSM). The results indicate that the NHS groups on the solid surface are available nearly as freely as those in solution for the reaction with amino groups to form amide linkages. The modified gold surface could thus be used as sensors for biomolecules containing amino groups.
Date Issued
2006
Call Number
QD281.P6 Li
Date Submitted
2006