Syntheses and self‐assembly of poly(benzyl ether)‐b‐poly(N‐isopropylacrylamide) dendritic–linear diblock copolymers

This article describes the syntheses and solution behavior of model amphiphilic dendritic–linear diblock copolymers that self‐assemble in aqueous solutions into micelles with thermoresponsive shells. The investigated materials are constructed of poly(benzyl ether) monodendrons of the second generation ([G‐2]) or third generation ([G‐3]) and linear poly(N‐isopropylacrylamide) (PNIPAM). [G‐2]‐PNIPAM and [G‐3]‐PNIPAM dendritic–linear diblock copolymers have been prepared by reversible addition–fragmentation transfer (RAFT) polymerizations of N‐isopropylacrylamide with a [G‐2]‐ or [G‐3]‐based RAFT agent, respectively. The critical micelle concentration (cmc) of [G‐3]‐PNIPAM₂₂₀, determined by surface tensiometry, is 6.3 × 10^?6 g/mL, whereas [G‐2]‐PNIPAM₂₃₅ has a cmc of 1.0 × 10^?5 g/mL. Transmission electron microscopy results indicate the presence of spherical micelles in aqueous solutions. The thermoresponsive conformational changes of PNIPAM chains located at the shell of the dendritic–linear diblock copolymer micelles have been thoroughly investigated with a combination of dynamic and static laser light scattering and excimer fluorescence. The thermoresponsive collapse of the PNIPAM shell is a two‐stage process; the first one occurs gradually in the temperature range of 20–29 °C, which is much lower than the lower critical solution temperature of linear PNIPAM homopolymer, followed by the second process, in which the main collapse of PNIPAM chains takes place in the narrow temperature range of 29–31 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1357–1371, 2006     

Synthesis and characterization of core–shell‐type polymeric micelles from diblock copolymers via reversible addition–fragmentation chain transfer

A method was developed to enable the formation of nanoparticles by reversible addition–fragmentation chain transfer polymerization. The thermoresponsive behavior of polymeric micelles was modified by means of micellar inner cores and an outer shell. Polymeric micelles comprising AB block copolymers of poly(N‐isopropylacrylamide) (PIPAAm) and poly(2‐hydroxyethylacrylate) (PHEA) or polystyrene (PSt) were prepared. PIPAAm‐b‐PHEA and PIPAAm‐b‐PSt block copolymers formed a core–shell micellar structure after the dialysis of the block copolymer solutions in organic solvents against water at 20 °C. Upon heating above the lower critical solution temperature (LCST), PIPAAm‐b‐PHEA micelles exhibited an abrupt increase in polarity and an abrupt decrease in rigidity sensed by pyrene. In contrast, PIPAAm‐b‐PSt micelles maintained constant values with lower polarity and higher rigidity than those of PIPAAm‐b‐PHEA micelles over the temperature range of 20–40 °C. Structural deformations produced by the change in the outer polymer shell with temperature cycles through the LCST were proposed for the PHEA core, which possessed a lower glass‐transition temperature (ca. 20 °C) than the LCST of the PIPAAm outer shell (ca. 32.5 °C), whereas the PSt core with a much higher glass‐transition temperature (ca. 100 °C) retained its structure. The nature of the hydrophobic segments composing the micelle inner core offered an important control point for thermoresponsive drug release and the drug activity of the thermoresponsive polymeric micelles. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3312–3320, 2006     

Self‐assembly of thermo‐ and pH‐responsive poly(acrylic acid)‐b‐poly(N‐isopropylacrylamide) micelles for drug delivery

Self‐assembled thermo‐ and pH‐responsive poly(acrylic acid)‐b‐poly(N‐isopropylacrylamide) (PAA‐b‐PNIPAM) micelles for entrapment and release of doxorubicin (DOX) was described. Block copolymer PAA‐b‐PNIPAM associated into core‐shell micelles in aqueous solution with collapsed PNIPAM block or protonated PAA block as the core on changing temperature or pH. Complexation of DOX with PAA‐b‐PNIPAM triggered by the electrostatic interaction and release of DOX from the complexes due to the changing of pH or temperature were studied. Complex micelles incorporated with DOX exhibited pH‐responsive and thermoresponsive drug release profile. The release of DOX from micelles was suppressed at pH 7.2 and accelerated at pH 4.0 due to the protonation of carboxyl groups. Furthermore, the cumulative release of DOX from complex micelles was enhanced around LCST ascribed to the structure deformation of the micelles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5028–5035, 2008     

Rheology and phase behavior of thermo‐reversible pentablock terpolymer hydrogel

Thermo‐reversible phase behaviors and rheological properties of a pentablock terpolymer solution, poly(N‐isopropylacrylamide)‐b‐poly(ethylene oxide)‐b‐poly(propylene oxide)‐b‐poly(ethylene oxide)‐b‐poly(N‐isopropylacrylamide) (PNIPAM₁₅₀‐PEO₁₃₆‐PPO₄₅‐PEO₁₃₆‐PNIPAM₁₅₀), are investigated in comparison with its precursor, PEO₁₃₆‐PPO₄₅‐PEO₁₃₆ (F108). It is found that the critical gelation concentration of the terpolymer solution is only about 11 wt %, which is significantly lower than that of F108 solution (～22 wt %). The 11 wt % terpolymer solution displays higher viscosity, stronger gel strength, and fast thermo‐responsive behavior compared with the 22 wt % F108 solution. The 11 wt % terpolymer solution shows a typical Newtonian fluid behavior at 30 °C due to the presence of individual spherical micelles, and presents an elastic gel property at 41 °C because of the formation of the close‐packed micelle aggregates. Cryogenic transmission electron microscopy (cryo‐TEM) and variable‐temperature ¹H NMR results demonstrate that the sol–gel phase transition mechanism is mainly related to the hydrophilic/hydrophobic transition of PPO and PNIPAM groups by external temperature stimulus. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1335–1342     

Temperature‐Responsive Mixed‐Shell Polymeric Micelles for the Refolding of Thermally Denatured Proteins

We have fabricated a mixed‐shell polymeric micelle (MSPM) that closely mimics the natural molecular chaperone GroEL? GroES complex in terms of structure and functionality. This MSPM, which possesses a shared PLA core and a homogeneously mixed PEG and PNIAPM shell, is constructed through the co‐assembly of block copolymers poly(lactide‐b‐poly(ethylene oxide) (PLA‐b‐PEG) and poly(lactide)‐b‐poly(N‐isopropylacryamide) (PLA‐b‐PNIPAM). Above the lower critical solution temperature (LCST) of PNIPAM, the MSPM evolves into a core–shell–corona micelle (CSCM), as a functional state with hydrophobic PNIPAM domains on its surface. Light scattering (LS), TEM, and fluorescence and circular dichroism (CD) spectroscopy were performed to investigate the working mechanism of the chaperone‐like behavior of this system. Unfolded protein intermediates are captured by the hydrophobic PNIPAM domains of the CSCM, which prevent harmful protein aggregation. During cooling, PNIPAM reverts into its hydrophilic state, thereby inducing the release of the bound unfolded proteins. The refolding process of the released proteins is spontaneously accomplished by the presence of PEG in the mixed shell. Carbonic anhydrase B (CAB) was chosen as a model to investigate the refolding efficiency of the released proteins. In the presence of MSPM, almost 93 % CAB activity was recovered during cooling after complete denaturation at 70 °C. Further results reveal that this MSPM also works with a wide spectrum of proteins with more‐complicated structures, including some multimeric proteins. Given the convenience and generality in preventing the thermal aggregation of proteins, this MSPM‐based chaperone might be useful for preventing the toxic aggregation of misfolded proteins in some diseases.     

Facile synthesis of dumbbell‐shaped dendritic‐linear‐dendritic triblock copolymer via reversible addition‐fragmentation chain transfer polymerization

We report the first instance of facile synthesis of dumbbell‐shaped dendritic‐linear‐dendritic triblock copolymer, [G‐3]‐PNIPAM‐[G‐3], consisting of third generation poly(benzyl ether) monodendrons ([G‐3]) and linear poly(N‐isopropylacrylamide) (PNIPAM), via reversible addition‐fragmentation chain transfer (RAFT) polymerization. The key step was the preparation of novel [G‐3]‐based RAFT agent, [G‐3]‐CH₂SCSSCH₂‐[G‐3] (1), from third‐generation dendritic poly(benzyl ether) bromide, [G‐3]‐CH₂Br. Due to the bulky nature of [G‐3]‐CH₂Br, its transformation into trithiocarbonate 1 cannot go to completion, a mixture containing ～80 mol % of 1 and 20 mol % [G‐3]‐CH₂Br was obtained. Dumbbell‐shaped [G‐3]‐PNIPAM₃₁₀‐[G‐3] triblock copolymer was then successfully obtained by the RAFT polymerization of N‐isopropylacylamide (NIPAM) using 1 as the mediating agent, and trace amount of unreacted [G‐3]‐CH₂Br was conveniently removed during purification by precipitating the polymer into diethyl ether. The dendritic‐linear‐dendritic triblock structure was further confirmed by aminolysis, and fully characterized by gel permeation chromatography (GPC) and ¹H‐NMR. The amphiphilic dumbbell‐shaped triblock copolymer contains a thermoresponsive PNIPAM middle block, in aqueous solution it self‐assembles into spherical nanoparticles with the core consisting of hydrophobic [G‐3] dendritic block and stabilized by the PNIPAM central block, forming loops surrounding the insoluble core. The micellar properties of [G‐3]‐PNIPAM₃₁₀‐[G‐3] were then fully characterized. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1432–1445, 2007     

Dispersion of polystyrene inside polystyrene‐b‐poly(N‐isopropylacrylamide) micelles in water

The addition of mixture of polystyrene‐b‐poly(N‐isopropylacrylamide) (PS‐b‐PNIPAM) and polystyrene homopolymer (h‐PS) in tetrahydrofuran dropwise into water leads to nanoparticles with a PS core and a thermally sensitive PNIPAM shell. The effects of the ratio of the homopolymer to copolymer and temperature on the formation and stabilization of the dispersion were investigated by using a combination of static and dynamic laser light scattering. PNIPAM shell continuously collapses as temperature increases in the range 20–40 °C. Such formed particles are stable even at temperatures much higher than lower critical solution temperature (LCST ～ 32 °C) of PNIPAM. Our results reveal that the area occupied per hydrophilic PNIPAM chain on the hydrophobic PS core remains nearly a constant regardless of the amount of h‐PS in the polymer mixture. This clearly indicates that the surface area occupied per hydrophilic group is a critical parameter for stabilizing particles dispersed in water. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 749–755, 2010     

Thermoresponsive Polymer Brush Modulation on the Direction of Motion of Phoretically Driven Janus Micromotors

We report a thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM) brush functionalized Janus Au–Pt bimetallic micromotor capable of modulating the direction of motion with the change of the ambient temperature. The PNIPAM@Au–Pt micromotor moved along the Au–Pt direction with a speed of 8.5 μm s^?1 in 1.5 % H₂O₂ at 25 °C (below the lower critical solution temperature (LCST) of PNIPAM), whereas it changed the direction of motion (i.e., along the Pt–Au direction) and the speed decreased to 2.3 μm s^?1 at 35 °C (above LCST). Below LCST, PNIPAM brushes grafted on the Au side were hydrophilic and swelled, which permitted the electron transfer and proton diffusion on the Au side, and thus the motion is regarded as a self‐electrophoretic mechanism. However, PNIPAM brushes above LCST became hydrophobic and collapsed, and thus the driving mechanism switched to the self‐diffusiophoresis like that of Pt‐modified Janus silica motors. These motors could reversibly change the direction of motion with the transition of the hydrophobic and hydrophilic states of the grafted PNIPAM brushes. Such a thermoresponsive polymer brush functionalization method provides a new strategy for engineering the kinematic behavior of phoretically driven micro/nanomotors.     

Novel thermo‐responsive self‐assembly micelles from a double brush‐shaped PNIPAM‐g‐(PA‐b‐PEG‐b‐PA)‐g‐PNIPAM block copolymer with PNIPAM polymers as side chains

A novel double brush‐shaped copolymer with amphiphilic polyacrylate‐b‐poly(ethylene glycol)‐b‐poly acrylate copolymer (PA‐b‐PEG‐b‐PA) as a backbone and thermosensitive poly(N‐isopropylacrylamide) (PNIPAM) long side chains at both ends of the PEG was synthesized via an atom transfer radical polymerization (ATRP) route, and the structure was confirmed by FTIR, ¹H NMR, and SEC. The thermosensitive self‐assembly behavior was examined via UV‐vis, TEM, DLS, and surface tension measurements, etc. The self‐assembled micelles, with low critical solution temperatures (LCST) of 34–38 ^°C, form irregular fusiform and/or spherical morphologies with single, double, and petaling cores in aqueous solution at room temperature, while above the LCST the micelles took on more regular and smooth spherical shapes with diameter ranges from 45 to 100 nm. The micelle exhibits high stabilities even in simulated physiological media, with low critical micellization concentration (CMC) up to 5.50, 4.89, and 5.05 mg L^?1 in aqueous solution, pH 1.4 and 7.4 PBS solutions, respectively. The TEM and DLS determination reveled that the copolymer micelle had broad size distribution below its LCST while it produces narrow and homogeneous size above the LCST. The cytotoxicity was investigated by MTT assays to elucidate the application potential of the as‐prepared block polymer brushes as drug controlled release vehicles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Doubly thermoresponsive brush‐linear‐linear ABC triblock copolymer nanoparticles prepared through dispersion RAFT polymerization

Doubly thermoresponsive ABC brush‐linear‐linear triblock copolymer nanoparticles of poly[poly(ethylene glycol) methyl ether vinylphenyl]‐block‐poly(N‐isopropylacrylamide)‐block‐polystyrene [P(mPEGV)‐b‐PNIPAM‐b‐PS] containing two thermoresponsive blocks of poly[poly(ethylene glycol) methyl ether vinylphenyl] [P(mPEGV)] and poly(N‐isopropylacrylamide) (PNIPAM) are prepared by macro‐RAFT agent mediated dispersion polymerization. The P(mPEGV)‐b‐PNIPAM‐b‐PS nanoparticles exhibit two separate lower critical solution temperatures or phase‐transition temperatures (PTTs) corresponding to the linear PNIPAM block and the brush P(mPEGV) block in water. Upon temperature increasing above the first and then the second PTT, the hydrodynamic diameter (D_h) of the triblock copolymer nanoparticles undergoes an initial shrinkage at the first PTT and the subsequent shrinkage at the second PTT. The effect of the chain length of the PNIPAM block on the thermoresponsive behavior of the triblock copolymer nanoparticles is investigated. It is found that, the longer chains of the thermoresponsive PNIPAM block, the greater contribution on the transmittance change of the aqueous dispersion of the triblock copolymer nanoparticles. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2266–2278     

Effects of graft length and density of well‐defined graft polymers on the thermoresponsive behavior and self‐assembly morphology

A series of well‐defined thermoresponsive graft polymers with different lengths and graft densities, poly(glycidyl methacrylate)‐graft‐poly(N‐isopropylacrylate) (PGMA‐g‐PNIPAM), were successfully prepared by combination of controlled/living free radical polymerization and click chemistry. Effects of grafting length and density on the thermoresponsive behavior, aggregating mean diameter, and self‐assembly morphology are systematically investigated. The thermosensitive characteristics of graft polymers in aqueous solution prove that the length and graft density had positive co‐relationship with the lower critical solution temperature value and mean diameter of micelles as well as the size distribution, while the effect of graft length of polymers is more significant than that of density. Transmission electron microscopy analysis shows that the conformations of PGMA₄₅‐g‐PNIPAM₂₀ and PGMA₄₅‐g‐PNIPAM₄₆ with longer length and bigger grafting density in aqueous solutions are spherical nanoparticles with the increasing trend of the diameters, while that of PGMA₄₅‐g‐PNIPAM_{(73, 50%)} shows a spherical‐like morphology, which indicates that the graft length and density have a significant effect on the mean diameter of micelle but not on the self‐assembly morphology. These results reveal that to obtain desired thermoresponsive behavior and self‐assembly morphology of functional polymers, it is essential to design and fabricate the structure of graft polymers with proper length and graft density. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2442–2453     

Thin films of PS/PS‐b‐pnipam and ps/pnipam polymer blends with tunable wettability

We developed thin films of blends of polystyrene (PS) with the thermoresponsive polymer poly(N‐isopropylacrylamide) (PNIPAM) (PS/PNIPAM) and its diblock copolymer polystyrene‐b‐poly(N‐isopropylacrylamide) (PS/PS‐b‐PNIPAM) in different blend ratios, and we study their surface morphology and thermoresponsive wetting behavior. The blends of PS/PNIPAM and PS/PS‐b‐PNIPAM are spin‐casted on flat silicon surfaces with various drying conditions. The surface morphology of the films depends on the blend ratio and the drying conditions. The PS/PS‐b‐PNIPAM films do not show an increase in their water contact angles with temperature, as it is expected by the presence of the PNIPAM block. All PS/PNIPAM films show an increase in the water contact angle above the lower critical solution temperature of PNIPAM, which depends on the ratio of PNIPAM in the blend and is insensitive to the drying conditions of the films. The difference between the wetting behavior of PS/PS‐b‐PNIPAM and PS/PNIPAM films is due to the arrangement of the PNIPAM chains in the film. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 670–679     

Synthesis of a thermoresponsive shell‐crosslinked 3‐layer onion‐like polymer particle with a hyperbranched polyglycerol core

A novel thermoresponsive shell crosslinked three‐layer onion‐like polymer particles were prepared using hyperbranched polyglycerol (PG) as parents compound, the periphery hydroxyl groups of PG were transformed into trithiocarbonates (? SC(S)S? ) first; then, it was used as chain transfer agent to prepare star‐like block copolymer of N‐isopropyl acrylamide (NIPA) and N,N‐dimethylaminoethyl acrylate (DMA) in sequence via reversible addition fragmentation chain transfer (RAFT) process. Thus, a three‐layer polymer, PG? [SC(S)S? (DMA)? b? (NIPA)]_n, was obtained. The middle layer of poly(DMA) was then crosslinked with 1,8‐diiodoctane, and the resulting onion‐like three‐layer polymer showed a lower critical solution temperature (LCST) in water because of the outer layer of poly(NIPA). The LCST value only slightly depended on the crosslinking degree. Finally, the ? SC(S)S? were transformed into thiols by sequential treating with sodium borohydride and formic acid; thus, the core molecule was chemically detached from the crosslinked shell and a novel shell crosslinked polymer particle was obtained. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5652–5660, 2005     

Synthesis and self‐assembly of thermoresponsive block‐graft fluoropolymer as well as its tunable wettability surface

Thermo‐responsive block‐graft fluoropolymer is synthesized and investigated the self‐assembly morphology and the tunable wettability surface on cotton fabric by dip‐coating into the micelles with different temperatures. Well‐defined block‐graft copolymer is prepared by click chemistry with poly(hexafluorobutyl methacrylate)‐block‐poly(glycidyl methacrylate) (PHFBMA‐b‐PGMA) and homopolymer poly(N‐isopropylacrylate) with alkyne on main chain (Alkynyl‐PNIPAM) to synthesize final block‐graft polymer PHFBMA‐b‐(PGMA‐g‐PNIPAM). The thermo‐responsive behaviors of block‐graft polymer prove that the diameter for fluoropolymer micelle is about 50–70 nm with uniform sphere shape at room temperature and bigger and broader at 40 °C. The surface of cotton fabric processed in micelle solution at room temperature is smooth and has good hydrophobic property, while it has the hydrophilic property dipped in high temperature micelle solution. This work may give valuable guidance for fabricating a facile strategy to establish controllable wettability surfaces on different substrates, which is a promising candidate for the coating materials and industrial fields. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 992–1002     

One‐pot synthesis of composite microspheres with core‐shell structure

One‐pot synthesis of thermoresponsive magnetic composite microspheres with a poly(N‐isopropylacrylamide) (PNIPAM) shell and a Fe₃O₄ core is demonstrated. Temperature sensitivity of PNIPAM was adopted to design the novel synthesis pathway. The as‐prepared composite microspheres have an obvious core‐shell structure with a mean size of approximately 250 nm. The Fe₃O₄ core is approximately 5 nm and the thickness of the PNIPAM shell is approximately 10 nm. The content of Fe₃O₄ in the composite microspheres can be controlled by this method. The composite microspheres experience a swelling and shrinking process in water by adjusting the temperature below and above the lower critical solution temperature (LCST) around 32 °C. These microspheres also show fine response to an external magnetic field. This work presents a platform to synthesize organic/inorganic composite microspheres in a facile and efficient approach. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2702–2708     

Molecular dynamics simulations of PNIPAM‐co‐PEGMA copolymer hydrophilic to hydrophobic transition in NaCl solution

Classical molecular dynamics simulations were carried out to investigate the hydrophilic to hydrophobic transition of PNIPAM‐co‐PEGMA close to its lower critical solution temperature (LCST) in 1 M NaCl solution. PNIPAM‐co‐PEGMA is a copolymer of poly(N‐isopropylacrylamide) (PNIPAM) and poly(ethylene glycol) methacrylate (PEGMA). The copolymer consists of 38 monomer units of NIPAM with two PEGMA chains attached to the PNIAPM backbone. The PNIPAM‐co‐PEGMA was observed to go through the hydrophilic?hydrophobic conformational change for simulations at temperature slightly above its LCST. Na⁺ ions were found to bind strongly and directly with amide O, even more strongly with the O atoms on PEGAMS chains, whereas Cl^? ions only exhibit weak interaction with the polymer. Significantly a novel caged stable metal‐organic complex involving a Na⁺ ion coordinated by six O atoms from the copolymer was observed after the PNIPAM‐co‐PEGMA copolymer went through conformational transition to form a hydrophobic folded structure. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

AB2‐type amphiphilic block copolymers composed of poly(ethylene glycol) and poly(N‐isopropylacrylamide) via single‐electron transfer living radical polymerization: Synthesis and characterization

Novel AB₂‐type amphiphilic block copolymers of poly(ethylene glycol) and poly(N‐isopropylacrylamide), PEG‐b‐(PNIPAM)₂, were successfully synthesized through single‐electron transfer living radical polymerization (SET‐LRP). A difunctional macroinitiator was prepared by esterification of 2,2‐dichloroacetyl chloride with poly(ethylene glycol) monomethyl ether (PEG). The copolymers were obtained via the SET‐LRP of N‐isopropylacrylamide (NIPAM) with CuCl/tris(2‐(dimethylamino)ethyl)amine (Me₆TREN) as catalytic system and DMF/H₂O (v/v = 3:1) mixture as solvent. The resulting copolymers were characterized by gel permeation chromatography and ¹H NMR. These block copolymers show controllable molecular weights and narrow molecular weight distributions (PDI < 1.15). Their phase transition temperatures and the corresponding enthalpy changes in aqueous solution were measured by differential scanning calorimetry. As a result, the phase transition temperature of PEG₄₄‐b‐(PNIPAM₅₅)₂ is similar to that in the case of PEG₄₄‐b‐PNIPAM₁₁₀; however, the corresponding enthalpy change is much lower, indicating the significant influence of the macromolecular architecture on the phase transition. This is the first study into the effect of macromolecular architecture on the phase transition using AB₂‐type amphiphilic block copolymer composed of PEG and PNIPAM. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4420–4427, 2009     

Synthesis and micellization of PSt‐PNIPAM‐PDMAEMA hetero‐arm star polymer with double thermo‐responsibility

A hetero‐arm star polymer, polystyrene‐poly(N‐isopropylacrylamide)‐ poly(2‐(dimethylamino)ethylmethacrylate) (PSt‐PNIPAM‐PDMAEMA), was synthesized by “clicking” the alkyne group at the junction of PSt‐b‐PNIPAM diblock copolymer onto the azide end‐group of PDMAEMA homopolymer via 1,3‐dipolar cycloaddition. The resultant polymer was characterized by gel permeation chromatography, proton nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy. PSt‐PNIPAM‐PDMAEMA micelles with PSt block as core and PNIPAM and PDMAEMA blocks as shell were formed when adding the copolymer solution in THF into 10 folds of water. Lower critical solution temperature (LCST) of PNIPAM and PDMAEMA homopolymer is 32 °C for PNIPAM and 40 to 50 °C for PDMAEMA, respectively. Upon continuous heating through their LCSTs, PSt‐PNIPAM‐PDMAEMA core‐shell micelles exhibited two‐stage thermally induced collapse. The first‐stage collapse, from 20 to 34 °C, is ascribed to the shrinkage of PNIPAM chains; and the second‐stage collapse, from 38 to 50 °C, is due to the shrinkage of PDMAEMA chains. Dynamic light scattering was used to confirm the double phase transitions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 786–796, 2009     

Synthesis and self‐assembly of thermoresponsive poly(N‐isopropylacrylamide)‐b‐poly(oligo ethylene glycol methyl ether acrylate) double hydrophilic block copolymers

We report on the synthesis of novel poly(N‐isopropylacrylamide)‐b‐poly(oligo ethylene glycol methyl ether acrylate) (PNIPAM‐b‐POEGA) thermoresponsive block copolymers using reversible addition–fragmentation chain transfer polymerization methodologies. The synthesized block copolymers are characterized by gel permeation chromatography, nuclear magnetic resonance, Fourier transform infrared (FTIR) techniques in terms of molecular weight and composition. Their thermoresponsive self‐assembly in aqueous media is investigated using dynamic and static light scattering. The PNIPAM‐b‐POEGA thermoresponsive block copolymers formed aggregates in water by increasing the temperature above the lower critical solution temperature value of PNIPAM block. Solution pH seems to affect the self‐assembly behavior in some cases due to the presence of ? COOH end groups. Therefore, the copolymers were utilized as “smart” nanocarries for the hydrophobic drug indomethacin, implementing a novel encapsulation protocol taking advantage of the thermoresponsive character of the PNIPAM block. The empty and loaded self‐assembled nanocarriers systems were studied by light scattering techniques, ultraviolet–visible, and FTIR spectroscopy, which gave information on the size and structure of the nanocarriers, the drug loading content and the interactions between the drug and the components of the block copolymers. Drug loaded nanostructures show stability at room temperature, due to active drug/block copolymer interactions. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1467–1477     

Poly(3‐hexyl thiophene)‐b‐poly(N‐isopropyl acrylamide): Synthesis and its composition dependent structural,solubility, thermoresponsive,electrochemical, and electronic properties

Conjugated block copolymers consisting of poly(3‐hexyl thiophene) (P3HT) and a thermoresponsive polymer poly(N‐isopropyl acrylamide) (PNIPAM) with varying composition have been synthesized by facile click reaction between alkyne terminated P3HT and azide terminated PNIPAM. The composition‐dependent solubility, thermoresponsive property in water, phase behavior, electrochemical, optical, and electronic properties of the block copolymers were systematically investigated. The block copolymers with higher volume fraction of PNIPAM form thermoresponsive spherical micelles with P3HT‐rich crystalline cores and PNIPAM coronas. Both X‐ray and atomic force microscopic studies indicated that the blocks copolymers showed well‐defined microphase separated nanostructures and the structure depended on the composition of the blocks. The electrochemical study of the block copolymers clearly demonstrated that the extent of charge transport through the block copolymer thin film was similar to P3HT homopolymer without any significant change in the band gap. The block copolymers showed improved or similar charge carrier mobility compared with the pure P3HT depending on the composition of the block copolymer. These P3HT‐b‐PNIPAM copolymers were interesting for fabrication of optoelectronic devices capable of thermal and moisture sensing as well as for studying the thermoresponsive colloidal structures of semiconductor amphiphilic systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1785–1794