Phase separation of poly(N-isopropylacrylamide) in water: a spectroscopic study of a polymer tagged with a fluorescent dye and a spin label

Thermo-pH-Salt Environmental Terpolymers Influenced by 2-((Dimethylamino)methyl)-4-methylphenyl Acrylate: A Comparative Study for Tuning Phase Separation Temperature

This study offers a comparison between three different types of thermoresponsive (TR) and thermo-pH-salt (TPR) multiresponsive polymers including homopoly(N-isopropylacrylamide) (PNIPAAm), copolymers with three different monomers, 2-hydroxyethyl methacrylate (HEMA), N,N-dimethylacrylamide (DMAAm), and styrene (S) at three different concentrations (5, 10, and 20 mol %), and a PNIPAAm terpolymer with 5, 10, and 20 mol % 2-((dimethylamino)methyl)-4-methylphenyl acrylate (DMAMCA) and 10 mol % HEMA, DMAAm, and S monomers. All polymers were chemically analyzed with 1H NMR and Fourier transform infrared spectroscopy (FT-IR) as well as gel permeation chromatography (GPC) for the molecular weights and dispersity and differential scanning calorimeter (DSC) for the glass transition temperatures. The cloud point, also known as the phase separation temperature (Cp), was determined for all polymers by a turbidity test using a UV-vis spectrophotometer; a micro-differential scanning calorimeter was used for measuring the cloud point in deionized water. The influence of a tertiary amine cationic group of DMAMCA changed the behavior of TR copolymers into TPR by shifting the cloud point of the TPR to higher values in acidic solutions (lower pH) and to lower values in alkaline solutions. The Cp was measured at different concentrations of Hofmeister kosmotropic and chaotropic anion salt solutions in a range of pH solutions for the terpolymers. It demonstrated the same behavior as mentioned in pH solutions besides the effect of salt ions. By measuring the Tc and Cp of these polymers, we can exploit various applications of stimuli-responsive materials for sensors and biomedical technology.

Chemical design and synthesis of macromolecular profluorescent nitroxide systems as self-reporting probes

The objective of this mini-review article is to highlight the importance of the chemical design towards the synthesis of polymeric profluorescent nitroxides applicable as self-reporting probes.

Hydrophobic Interaction-Induced Coassembly of Homopolymers and Proteins

Studies on the fabrication of polymer-protein hybrid self-assemblies have aroused great interest over the past years because of a broad range of applications of the materials in drug/protein delivery, biosensors, and enhancement of protein stability. The hybrid assemblies are usually fabricated from polymer-protein bioconjugates, which may suffer from the damages to the protein structures and the loss of functionalities in the synthesis. Herein, we report a simple and efficient approach to the fabrication of vesicle-like structures based on coassembly of homopolymer chains and protein molecules. At room temperature, poly(N-isopropylacrylamide) (PNIPAM) and bovine serum albumin (BSA) are able to form complexes through hydrophobic interactions in aqueous solution. Upon heating to a temperature above the cloud point of PNIPAM, vesicle-like structures with collapsed PNIPAM in the walls and BSA at the surfaces are formed. The size and membrane thickness of the assemblies can be tuned by the molar ratio of PNIPAM to BSA. The hydrophobic interaction between PNIPAM and BSA plays a key role in the complex formation and self-assembly process. The complexes and assembled structures are analyzed by using micro differential scanning calorimetry, light scattering, and transmission electron microscopy. BSA in the assemblies retains over 90% of its activity, and the protein stability is enhanced because of the hydrophobic interaction between proteins and polymers. This approach allows us to prepare polymer-protein assemblies without bioconjugate synthesis. Meanwhile, possible damages to the protein structures and the loss of bioactivities of proteins can be avoided.

Design and synthesis study of the thermo-sensitive poly (N-vinylpyrrolidone-b- N, N-diethylacrylamide)

The reversible addition fragmentation chain transfer (RAFT) polymerization method was adopted here to prepare a series of thermo-sensitive copolymers, poly (N,N-diethyl- acrylamide-b-N-vinylpyrrolidone). Their structures, molecular weight distribution and temperature sensitivity performances were characterized by the nuclear magnetic resonance (1HNMR), the gel permeation chromatography (GPC) and the fluorescence spectrophotometer, respectively. It has been identified that the synthesis reaction of the block copolymer was living polymerization. The thermo-sensitivity study suggested that N-vinylpyrrolidone (NVP), played a key role on the lower critical solution temperature (LCST) performance.

Thermo-responsive fluorescence of AIE-active poly(N-isopropylacrylamides) labeled with highly twisted bis(N,N-dialkylamino)arenes

A thermo-responsive fluorescent polymer materials were synthesized fromN-isopropylacrylamides with AIE-active 9,10-bis(N,N-dialkylamino)arene monomers.

Spin fluorescence silencing enables an efficient thermally driven self-reporting polymer release system

A self-reporting profluorescent release system driven by the thermo-reversible dynamic covalent ligation of chromophores to polymer chain, whose fluorescence is silenced by unpaired spins of nitroxides prior to release is introduced.

Influence of the Near Molecular Vicinity on the Temperature Regulated Fluorescence Response of Poly(N-vinylcaprolactam)

A series of new fluorescent dye bearing monomers, including glycomonomers, based on maleamide and maleic esteramide was synthesized. The dye monomers were incorporated by radical copolymerization into thermo-responsive poly(N‑vinyl-caprolactam) that displays a lower critical solution temperature (LCST) in aqueous solution. The effects of the local molecular environment on the polymers' luminescence, in particular on the fluorescence intensity and the extent of solvatochromism, were investigated below as well as above the phase transition. By attaching substituents of varying size and polarity in the close vicinity of the fluorophore, and by varying the spacer groups connecting the dyes to the polymer backbone, we explored the underlying structure⁻property relationships, in order to establish rules for successful sensor designs, e.g., for molecular thermometers. Most importantly, spacer groups of sufficient length separating the fluorophore from the polymer backbone proved to be crucial for obtaining pronounced temperature regulated fluorescence responses.

Aqueous polymeric sensors based on temperature-induced polymer phase transitions and solvatochromic dyes

This feature article provides, for the first time, an overview of the research that guided the way from fundamental studies of the thermo-responsive phase separation of aqueous polymer solutions to polymeric sensor systems. The incorporation of solvatochromic dyes into thermoresponsive polymers as well as the concepts of polymeric sensors are presented and discussed in detail.

Parallel effects of cations on PNIPAM graft wettability and PNIPAM solubility

Stimuli-responsive surfaces grafted with thermoresponsive polymers switch from hydrophilic to hydrophobic thermally, making these surfaces attractive in applications such as in microfluidics devices, as antifouling surfaces, and in cell culture and tissue engineering. These materials exhibit changes in wettability as the polymer undergoes a phase transition above its lower critical solution temperature (LCST). Because the presence of salts affects LCSTs in accordance to the Hofmeister series, salt effects on the wettability of these thermoresponsive surfaces will dramatically impact device performance. Prior studies of such effects have focused on the influence of anions. Detailed studies of the effects of cations have not been carried out. Here, the influence of varying cation identity in a series of mono-, di-, and trivalent sulfate salts on the wettability of a stimuli-responsive grafted surface was investigated by measuring advancing water contact angle (Theta(a)) changes. The cation-induced changes in Theta(a) were correlated with corresponding changes in surface morphology examined by AFM. The results showed that the effects of varying cations on surface wettability are as large as the effects of varying anion identity and concentration (i.e., Theta(a) changes of up to 90 degrees). Parallel studies of the effects of varying the cation identity and concentration for these same cation sulfate salts in solution show that cation variation also has a large effect on the LCST of PNIPAM, the stimuli responsive polymer component of the nanocomposite grafts that were studied. Moreover, analyses of the Theta(a) and LCST data using activity showed that the Theta(a) or LCST versus cation activity/concentration could be readily grouped by charge. Such differences are not seen in similar studies where anion identity, charge, and concentration are changed.

Temperature-sensitive water-soluble hybrid organic/inorganic nanoparticles formed through complexation of Cu2+ ions with poly(sodium acrylate)-g-poly(N-isopropylacrylamide) comb-type copolymers in aqueous solution

The preparation of temperature-sensitive water-soluble hybrid organic/inorganic nanoparticles, exploiting the complexation of Cu2+ ions with PANa-g-PNIPAMx comb-type copolymers, is presented. These copolymers consist of a Cu2+-complexing poly(sodium acrylate) backbone, PANa, and thermosensitive poly(N-isopropylacrylamide), PNIPAM, side chains. UV-vis spectrophotometry verified that the polymer/Cu2+ complexation follows a charge neutralization process, while turbidimetry revealed that the complexes formed can indeed be stabilized in water, provided that copolymers with a sufficiently high PNIPAM content (x approximately 80 mol % in monomer units) are used. Dilute solution viscometry and dynamic light scattering indicated that the hydrodynamic dimensions of the hybrid polymer/Cu2+ nanoparticles decrease substantially upon heating, reflecting the lower critical solution temperature behavior of the PNIPAM side chains. However, when the net negative charge of the hybrid polymer/Cu2+ nanoparticles decreases, interparticle aggregation and, eventually, phase separation may take place. In semidilute aqueous solution, the complexation of the polymer backbone with Cu2+ ions effectively controls the thermothickening properties of the thermosensitive comb-type PANa-g-PNIPAM copolymers. Finally, the temperature-induced formation of a compartmentalized hydrophilic-hydrophobic nanocontainer, where the hydrophilic and the hydrophobic compartments can be loaded with Cu2+ ions and hydrophobic substances, respectively, was evidenced through pyrene fluorescence probing.

Surface plasmon resonance study of the interaction of a beta-cyclodextrin polymer and hydrophobically modified poly(N-isopropylacrylamide)

Surface plasmon resonance (SPR) technique is used to follow, both in real time and in situ, the association between a physically adsorbed polymer of beta-cyclodextrin (pbetaCD) and different hydrophobically modified poly(N-isopropylacrylamide) (PNIPAM) copolymers containing either adamantyl or dodecyl groups. This association is due to the complex formation between the hydrophobic groups and the betaCD cavities. Therefore, the adsorbed amount of PNIPAM onto the pbetaCD layer depends on the substituent and on its substitution level. The association and dissociation rate constants are evaluated from the kinetics of PNIPAM adsorption. An estimation of the association constants leads to values higher than 10(4) M(-1), reflecting the strong interaction between these polymers.