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Thermoresponsive polymers have shown great potential in applications such as bioseparation, drug delivery and diagnostic. Only few thermoresponsive polymers that present an upper critical solution temperature (UCST) in a relevant temperature range, i.e. phase separate from solution upon cooling, have been reported so far. Moreover, the most studied UCST type polymers namely polybetaines are difficult to use under physiological conditions, which significantly restricts their potential applications. Therefore, UCST polymers with sharp and robust phase transition in physiological conditions (in the presence of salts, ions etc.) are highly needed in order to extend the range of applications of this class of polymers. Herein, a robust UCST-type copolymer of acrylamide (AAm) and acrylonitrile (AN) (poly(AAm-co-AN)) was prepared by reversible addition fragmentation chain transfer (RAFT) polymerization and its thermo-induced aggregation behavior in aqueous media was studied. At temperature below the UCST, the copolymer chains were aggregated together. The aggregate size was found to be larger with increasing AN contents and became smaller upon dilution of the copolymer solutions. While above the UCST, the copolymer chains were expanded and weekly associated in solution. The association between the copolymer chains formed smaller aggregates with increasing the AN contents or the dilution of the solutions. A model is proposed to explain such aggregation-association behavior of the Fig. 1.
Figure 1. Schematic illustration of the proposed thermos-induced aggregation behavior of the poly(AAm-co-AN) in aqueous solution.
The molecular dynamics of linear poly(N-isopropylacrylamide) (pNIPAM) in aqueous media at temperatures below and above the lower critical solution temperature (LCST) are investigated using broadband dielectric relaxation spectroscopy in a frequency range from 10–1 to 1011 Hz. Below the LCST, two relaxation processes are observed in the megahertz and gigahertz region assigned to the reorientation of dipoles of the solvated polymer segments (p-process) and water molecules (w-process), respectively. Both relaxation processes are analyzed using the Havriliak–Negami (HN) function, taking special attention to the w-process. Above the LCST, the dielectric spectra of the pNIPAM solutions resemble that of pure water, showing only the high frequency relaxation process of the water molecules with a more or less Debye-type behavior. The non-Debye behavior of the w-process below the LCST is mainly induced by the interactions between water and pNIPAM chains via hydrogen bonding. The relaxation time and strength of the w-process is studied with dependence on the concentration, temperature, and the polymer chain length (molecular weight). The information obtained is useful for a deeper understanding of the dehydration behavior at the phase transition. The suggestion of dehydration of the pNIPAM chains at the LCST is confirmed by calculating a dehydration number.
Thermoresponsive polymers have shown great potential in applications such as bioseparation, drug delivery and diagnostic. Only few thermoresponsive polymers that present an upper critical solution temperature (UCST), i.e. phase separate from solution upon cooling, in a relevant temperature range have been reported so far. Moreover, the most studied UCST type polymers namely polybetaines are difficult to use under physiological conditions, which significantly restricts their potential applications. Therefore, UCST polymers with sharp and robust phase transition in physiological conditions (in the presence of salts, ions etc.) are highly needed in order to extend the range of applications of this class of polymers.
Herein, a robust UCST-type copolymer of acrylamide (AAm) and acrylonitrile (AN) (poly(AAm-co-AN)) was prepared by reversible addition fragmentation chain transfer (RAFT) polymerization[4] and its thermo-induced aggregation behavior in aqueous media was studied. At temperature below the UCST, the copolymer chains were aggregated together. The aggregate size was found to be larger with increasing AN contents and became smaller upon dilution of the copolymer solutions. While above the UCST, the copolymer chains were expanded and weekly associated in solution. The association between the copolymer chains formed smaller aggregates with increasing the AN contents or the dilution of the solutions. A model is proposed to explain such aggregation behavior.
Combining experiments and all-atom molecular dynamics simulations, we study the conformational behavior of polyacrylamide (PAM) in aqueous alcohol mixtures over a wide range of temperatures. This study Shows that even when the microscopic interaction is dictated by hydrogen bonding, unlike its counterparts that present a lower critical solution temperature (LCST), PAM shows a counterintuitive tunable upper critical solution temperature (UCST)-type phase transition in water/alcohol mixtures that was not reported before. The Phase transition temperature was found to be tunable between 4 and 60 1C by the type and concentration of alcohol in the mixture as well as by the solution concentration and molecular weight of the polymer. In addition, molecular dynamics simulations confirmed a UCST-like behaviour of the PAM in aqueous alcoholic solutions.
Additionally, it was observed that the PAM is more swollen in pure alcohol solutions than in 80% alcoholic solutions due to y-like behaviour. Additionally, in the globular state, the size of the aggregates was found to increase with increasing solvent hydrophobicity and polymer concentration of the solutions. Above ist Phase transition temperature, PAM might be present as individual polymer chains in the coil state (r10 nm). As PAM is a widespread polymer in many biomedical applications (gel electrophoresis, etc.), this finding could be of high relevance for many more practical applications in high performance pharmaceuticals and/or sensors.
Dual orthogonal functionalities in a single material is highly desirable in many fields such as bio-imaging, sensing, coating or diagnostic and therapy. However, a precise and controlled approach to prepare two different functionalities is still a challenging task. Herein, we show the simple preparation method for the synthesis of dual-functional hybrid core/shell/shell nanoparticles consisting of a silica core with a fluorescent and a thermoresponsive polymeric layer. Silica core particles were first coated by a fluorescent layer using surface- nitiated reversible addition-fragmentation chain transfer (RAFT) polymerization. The fluorescent silica nanoparticles were then completely enclosed within a switchable protective coating made of thermoresponsive poly(N-isopropylacrylamide) via RAFT polymerization. Thermoresponsive poly(N-isopropylacrylamide) is known to change its properties according to the surroundings temperature in a reversible and controllable way (LCST behavior). The successful preparation of well-defined dual-functional hybrid core/shell/shell nanoparticles was shown by scanning electron microscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy, while their fluorescence and thermoresponsive properties were confirmed by fluorescence spectroscopy and dynamic light scattering measurements, respectively.
Thermoresponsive polymers have shown great potential in applications such as bioseparation, drug delivery and diagnostic. Only few thermoresponsive polymers that present an upper critical solution temperature (UCST) in a relevant temperature range, i.e. Phase separate from solution upon cooling, have been reported so far. Moreover, the most studied UCST type polymers namely polybetaines are difficult to use under physiological conditions, which significantly restricts their potential applications. Therefore, UCST polymers with sharp and robust phase transition in physiological conditions (in the presence of salts, ions etc.) are highly needed in order to extend the range of applications of this class of polymers.
Herein, a robust UCST-type copolymer of acrylamide (AAm) and acrylonitrile (AN) (poly(AAm-co-AN)) was prepared by reversible addition fragmentation chain Transfer (RAFT) polymerization and its thermo-induced aggregation behavior in aqueous media was studied by turbidity and dynamic light scattering measurements. At temperature below the UCST, the poly(AAm-co-AN) copolymer chains were aggregated together. The aggregate size was found to be larger with increasing AN contents and became smaller upon dilution of the copolymer solutions. While above the UCST, the poly(AAm-co-AN) copolymer chains were expanded and weekly associated in solution. The association between the copolymer chains formed smaller aggregates with increasing the AN Contents or the concentration of the solutions. A model is proposed to explain such aggregationassociation behavior of the poly(AAm-co-AN) copolymer depending on the AN Contents and concentration of the solutions.
A novel cop olyme r based on supramolecular motif2,6-diaminopyridin e and water-soluble acrylamide, poly[N-(6-ace tamidopyridin-2-yl) acrylamide-co-acrylamide], was synthe-size d via rev ersible addi tion–fragmentation chain transfer (RAFT)polymerization with various monomer compositions. The thermo-respon sive behavior of the copolymers was studied by turbidime-try and dynamic light scattering (DLS). The obtained copolymersshowed an upper critical solution temperature (UCST)-typ e phasetransition behavior in water and electrolyte solution. The phasetransition temperature was found to increase with decreasingam ount of acrylamide in the copolymer and increasing concentra-tion of the solution. Furth ermore, the phase transition temperatureva ried in aqueous solutions of electrolytes according to the naturean d concentration of the electrolyte in accordance with theHoffmeister series. A dramatic solvent isotope effect on thetransition temperature was o bserved in this study, as the transitiontemperature was almost 10–12C higher in D2OthaninH2Oatthesame concentration and acrylamide co mposition. The size of theaggregates below the transition temperature was larger in D2Ocompared to that in H2O that can be explained by deuterium iso-tope effect. The thermoresponsive behavior of the copolymers wasalso investigated in different cell medium and found to be exhibitedUCST-type phase transition behavior in different cell medium.Such behavior of the copo lyme rs can be useful in many a pplica-tions including biomedical, microfluidics, optical materials, and indrug delivery.
Functional polymer based on 2,6-diaminopyridine with tunable UCST behaviour in water/alcohol mixture
(2017)
Thermoresponsive polymers are of great importance in numerous applications such as bioseparation, drug delivery, diagnostic and microfluidic applications.[1-2] Only a few thermoresponsive polymers have been reported that present an Upper Critical Solution Temperature (UCST), i.e. phase separate from solution upon cooling, in a relevant temperature range and “green” solvents such as water or ethanol.[3] Indeed, polymers with UCST behavior below 60°C in alcohol or water/alcohol mixtures are extremely promising for the preparation of “smart” materials for sensing.
In this work, two novel functional polymers of based on a 2,6-diaminopyridine motif were synthesized by free-radical polymerization. Their UCST-type transition temperature is tunable by varying either their concentration in solution or the type of solvent. Insights into this phenomenon are investigated using turbidimetry and temperature dependent dynamic light scattering.
Fluorescent nanoparticles that “light up”/”dim down” by applying external stimuli are of particular interest in the fields of sensing, diagnostics, photonics, protective coatings and microfluidics. The current challenge for these materials is to combine for instance fluorescence and its response to a stimulus such as temperature in a precise manner. Here we present such a system based on a core/shell/shell architecture consisting of a silica core with a fluorescent layer and a thermoresponsive shell.
The silica core nanoparticles were first coated with a fluorescent shell using surface initiated reversible addition-fragmentation chain transfer (RAFT) polymerization. The fluorescent nanoparticles were then completely engulfed by a switchable protective coating made of thermoresponsive poly(N-isopropylacrylamide). The fluorescence of the nanoparticles could be “switched on” at room temperature and “switched off” with increasing environmental temperature because of the presence of the thermoresponsive layer. Insights into this phenomenon will be given based on temperature dependent fluorescence measurements and dynamic light scattering.
An UCST-type copolymer of acrylamide (AAm) and acrylonitrile (AN) (poly(AAm-co-AN)) was prepared by reversible addition fragmentation chain transfer (RAFT) polymerization and its temperature-induced phase transition and aggregation behaviour studied by turbidimetry, static and dynamic light scattering, small angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM) measurements. The phase transition temperature was found to increase with increasing AN content in the copolymer, concentration of the solutions and copolymer chain length. A significant effect was observed onto the phase transition temperature by addition of different electrolytes into the copolymer solution. The copolymer chains were aggregated below the phase transition temperature and disaggregated above it. The size of the aggregates increases with increasing AN contents and concentration of the copolymer solutions below the phase transition temperature. The copolymer chains were expanded and weekly associated in solution above the phase transition temperature. A model is proposed to explain such association–aggregation behaviour of poly(AAm-co-AN) copolymers depending on AN contents and concentration of the copolymer solutions as a function of temperature.