Thermo-responsive Poly(methyl methacrylate)-block-poly(N-isopropylacrylamide) Block Copolymers Synthesized by RAFT Polymerization: Micellization and Gelation (original) (raw)
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European Polymer Journal, 2009
A reversible addition-fragmentation chain transfer (RAFT) agent, the methyl-2-(n-butyltrithiocarbonyl)propanoate (MBTTCP) has shown to be efficient in controlling the polymerization of N,N-dimethylacrylamide (DMA), N-isopropylacrylamide (NIPAM) and N-acryloyloxysuccinimide (NAS). Two different strategies have been studied to synthesize block copolymers based on one PNIPAN block and the other a random copolymer of DMA and NAS. When a PNIPAM trithiocarbonate-terminated is used as macromolecular chain transfer agent for the polymerization of a mixture of NAS and DMA, well-defined P(NIPAM-b-(NAS-co-DMA)) block copolymers were obtained with a low polydispersity index. These thermoresponsive block copolymers dissolved in aqueous solution at 25°C and self-assembled into micelles when the temperature was raised above the LCST of the PNIPAM block. The micelle shell containing NAS units was further crosslinked using a primary diamine in order to get shell-crosslinked nanoparticles. Upon cooling below the LCST of PNIPAM this structure may easily reorganize to form nanoparticles with a water filled hydrophilic core.
Journal of Applied Polymer Science, 2008
Well-defined triblock copolymer poly(ethylene oxide)-b-poly(2-(diethylamino)ethyl methacrylate)-b-poly (N-isopropyl-acrylamide) (PEO-b-PDMAEMA-b-PNIPAAm) was synthesized via sequential reversible additionfragmentation chain transfer polymerization (RAFT) of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and Nisopropylacrylamide (NIPAAm) using a-methoxy-x-S-1dodecyl-S-a-(a,a 0-dimethyl-a 00-acetate) poly(ethylene oxide) (mPEO-DDAT) as macro-RAFT agent, AIBN as initiator in dioxane at 808C. The polymerization data indicated that the both RAFT processes were well controlled. The molecular weights of macro-RAFT agents showed the influence on the RAFT polymerization process. The final PEO-b-PDMAEMA-b-PNIPAAm triblock copolymer can form uniform micelles in aqueous media above the lower critical solution temperature (LCST) due to containing temperature-sensitive PNIPAAm block. The micelle size and D h were dependent on the composition of triblock copolymer and the pH value of the solution. The PEO-b-PDMAEMAb-PNIPAAm triblock copolymer showed dual temperatureand pH-sensitive property in aqueous media.
European Polymer Journal, 2014
We report on the synthesis of poly(N-isopropyl acrylamide)-block-poly(n-butyl acrylate) (PNIPAm-b-PnBA) amphiphilic block copolymers and their temperature-responsive selfassembly behavior in aqueous solution. Well-defined PNIPAm-b-PnBA copolymers have been synthesized by a two-step RAFT polymerization scheme. The self-assembly behavior was studied by means of static and dynamic light scattering, 1 H NMR and fluorescence spectroscopy and transmission electron microscopy. The results show that already below the lower critical solution temperature (LCST) of PNIPAm, association of the PNIPAm blocks with hydrophobic dodecyl end groups of the charge transfer agent leads to the formation of loose aggregates of PNIPAm-b-PnBA micelles, the size and density of which increase with the increasing length of the PNIPAm block. The collapse of the PNIPAm blocks above the LCST leads to the decrease of the aggregates' size and the increase of their density, but the collapsed PNIPAm chains do not allow for interpenetration of the micellar shells and no further aggregation occurs.
Block Copolymer Nanoparticles Prepared by RAFT Aqueous Polymerisation
2017
vi Abstract This thesis describes the reversible addition-fragmentation chain transfer (RAFT) polymerisation of block copolymer nanoparticles in water. Firstly, a water-soluble poly(glycerol monomethacrylate) (PGMA) macromolecular chain-transfer agent (macro-CTA) was synthesised via RAFT solution polymerisation in ethanol. The PGMA macro-CTA is then chain-extended with 2-hydroxypropyl methacrylate (HPMA) via RAFT aqueous dispersion polymerisation. Polymerisation-induced self-assembly (PISA) occurs under these conditions, where the miscible HPMA monomer polymerises to form an insoluble poly (2-hydroxypropyl methacrylate) block, thus driving in situ formation of spheres, worms or vesicles. These PGMA-PHPMA diblock copolymers are then chain-extended with benzyl methacrylate (BzMA) via ‘seeded’ RAFT aqueous emulsion polymerisation to prepare PGMA-PHPMA-PBzMA triblock copolymers. In Chapter Two, a series of model framboidal PGMAPHPMA-PBzMA triblock copolymer vesicles are synthesised with...
Polymer, 2009
Atom transfer radical polymerization (ATRP) was used to prepare thermosensitive cationic block copolymers of (3-acrylamidopropyl)-trimethylammonium chloride (AMPTMA) and N-isopropylacrylamide (NIPAAM) with different block lengths. By using ethyl-2-chloropropionate (ECP) as initiator and CuCl/ CuCl 2 /tris(2-dimethylaminoethyl)amine (Me 6 TREN) catalytic system in DMF:water 50:50 (v/v) mixtures at 20 C the polymerization was controlled. The association properties in NaCl aqueous solution were studied as a function of temperature and polymer concentration by dynamic light scattering, NMR spectroscopy, fluorescence spectroscopy and energy filtered-transmission electron microscopy. The block copolymers formed micellar aggregates above the lower critical solution temperature (LCST) of pNIPAAM. The LCST is strongly influenced by the relative length of the two blocks and is significantly higher than that of pure pNIPAAM. The size of core and shell of the micelles is discussed in terms of block copolymer composition.
Designed Monomers and Polymers, 2017
Sharply thermo-and pH-responsive pentablock terpolymer with a core-shell-corona structure was prepared by RAFT polymerization of N-isopropylacrylamide and methacrylic acid monomers using PEG-based benzoate-type of RAFT agent. The PEG-based RAFT agent could be easily synthesized by dihydroxyl-capped PEG with 4-cyano-4-(thiobenzoyl) sulfanylpentanoic acids, using esterification reaction. This pentablock terpolymer was characterized by 1 H NMR, FT-IR, and GPC. The PDI was obtained by GPC, indicating that the molecular weight distribution was narrow and the polymerization was well controlled. The thermo-and pH-responsive micellization of the pentablock terpolymer in aqueous solution was investigated using fluorescence spectroscopy technique, UV-vis transmittance, and TEM. The LCST of pentablock terpolymer increased (over 50 °C) compared to the NIPAM homopolymer (~32 °C), due to the incorporation of the hydrophilic PEG and PMA blocks in pentablock terpolymer (PNIPAM block as the core, PEG the block and the hydrophilic PMA block as the shell and the corona). Also, pH-dependent phase transition behavior shows at a pH value of about ~5.8, according to pKa of MAA. Thus, in acidic solution at room temperature, the pentablock terpolymer self-assembled to form core-shell-corona micelles, with the hydrophobic PMA block as the core, the PNIPAM block and the hydrophilic PEG block as the shell and the corona, respectively.
Synthesis and Properties of Novel Cationic, Temperature-Sensitive Block-Copolymers
Facile, one-step synthesis of self-assembling, cationic block copolymers of poly(2-N-(dimethylaminoethyl) methacrylate) (pDMAEMA) and PEO-PPO-PEO (Pluronic®) is developed. The copolymers are obtained via free-radical polymerization of DMAEMA initiated by Pluronic-radicals generated by cerium (IV). The copolymers possess surface activity, are polycationic at pH<7.1, and self-assemble into micelle-like aggregates when neutralized. Potential applications of the novel copolymers for DNA transfection in gene therapy are discussed.
Journal of Polymer Science Part a Polymer Chemistry, 2011
This study synthesized thermo-sensitive amphiphilic block-graft PNiPAAm-b-(PaN 3 CL-g-alkyne) copolymers through ring-opening polymerization of a-chloro-e-caprolactone (aClCL) with hydroxyl-terminated macroinitiator poly(N-isopropylacrylamide) (PNiPAAm), substituting pendent chlorides with sodium azide. This was then used to graft various kinds of terminal alkynes moieties by means of the copper-catalyzed Huisgen's 1,3-dipolar cycloaddition (''click'' reaction). 1 H NMR, FTIR, and gel permeation chromatography (GPC) was used to characterize these copolymers. The solubility of the block-graft copolymers in aqueous media was investigated using turbidity measurement, revealing a lower critical solution temperature (LCST) in the polymers. These solutions showed reversible changes in optical properties: transparent below the LCST, and opaque above the LCST. The LCST values were dependant on the composition of the polymer. With critical micelle concentrations (CMCs) in the range of 2.04-9.77 mg L À1 , the block copolymers formed micelles in the aqueous phase, owing to their amphiphilic characteristics. An increase in the length of hydrophobic segments or a decrease in the length of hydrophilic segments amphiphilic block-graft copolymers produced lower CMC values. The research verified the core-shell structure of micelles by 1 H NMR analyses in D 2 O. Transmission electron microscopy was used to analyze the morphology of the micelles, revealing a spherical structure. The average size of the micelles was in the range of 75-145 nm (blank), and 105-190 nm (with drug). High drug entrapment efficiency and drug loading content were observed in the drug micelles.
Polymer, 2004
Series of amphiphilic diblock copolymers with poly(N-isopropylacrylamide) as a hydrophilic block and a hydrophobic block consisting of either polystyrene or poly(tert-butyl methacrylate) were synthesised using RAFT polymerisations. Differential scanning calorimetry showed the chemically different blocks being phase separated in dry polymers. Light scattering and microcalorimetry studies were performed on aqueous solutions to investigate the phase behavior of the diblock copolymers. By carefully transferring the polymers from an organic solvent to water, either micellar particles or large aggregates were obtained depending on the relative lengths of the blocks. Large aggregates collapsed upon heating, whereas collapse occurred slowly within a broad temperature range in the case of micelle like structures. However, microcalorimetrically the collapse of the PNIPAM chains was observed to take place in all samples, suggesting that the shells of the micellar particles are crowded in a way which hinders the compression of the poly(N-isopropylacrylamide) chains.