Collapse Of Poly Research Articles

Coordinate bond breaking induced by collapse of poly(N-isopropyl acrylamide) as ligands of a rare Earth complex

A novel water-soluble luminescent complex consisting of Eu(ally-dbm)3-2Tppo and poly(N-isopropyl acrylamide) (PNIPAM) is synthesized through a series of chemical reactions. The structure of the complex is characterized by TGA, GPC, HNMR, and the thermal-responsive fluorescence of the complex in aqueous solution is investigated. It is found that PNIPAM collapse above the lower critical solution temperature causes the coordination bond breaking, leading to weakening of the fluorescence from Eu3+ and enhancing of the fluorescence from the ligands. When temperature decreases, the fluorescence from Eu3+ is found to boost up and the fluorescence from ligands weakens accordingly. It is deduced from this phenomenon that the ligands re-coordinate with europium ions again along with the temperature decreasing, which is further confirmed by IR measurements. This thermal-responsive fluorescence is of reversibility, which can be used as molecular probes for biological imaging and collapse studying of PNIPAM.A novel water-soluble luminescent complex consisting of Eu(ally-dbm)3-2Tppo and poly(N-isopropyl acrylamide) (PNIPAM) is synthesized through a series of chemical reactions. The structure of the complex is characterized by TGA, GPC, HNMR, and the thermal-responsive fluorescence of the complex in aqueous solution is investigated. It is found that PNIPAM collapse above the lower critical solution temperature causes the coordination bond breaking, leading to weakening of the fluorescence from Eu3+ and enhancing of the fluorescence from the ligands. When temperature decreases, the fluorescence from Eu3+ is found to boost up and the fluorescence from ligands weakens accordingly. It is deduced from this phenomenon that the ligands re-coordinate with europium ions again along with the temperature decreasing, which is further confirmed by IR measurements. This thermal-responsive fluorescence is of reversibility, which can be used as molecular probes for biological imaging and collapse studying of PNIPAM.

Resilient collapse of thermal sensitive polymer on the surface of the optical fiber taper

ABSTRACTIn this work, collapse of poly(N‐isopropyl‐acrylamide) (pNIPAM) grafted on the surface of the optical fiber taper is probed by measuring fluorescence of rhodamine B solution at various temperatures. It is observed that the fluorescence intensity through the taper shows a nonlinear response to temperature. According to the optical model for the special designed taper, it is realized that the nonlinear response results from changing in effective refractive index of interfacial layer between taper and solution. Analysis on relationship between signal change and collapse process reveals a springback process during the collapse of pNIPAM chains. Such a novel phenomenon is further investigated on method for fluorescence measurement and molecular weight of the polymer. These results have not only revealed details of the collapse, but also establish a novel technique for study the collapse of thermal sensitive polymers on the surface. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 778–785

Influence of the structure on the collapse of poly(N-isopropylacrylamide)-based microgels: an insight by quantitative dielectric analysis.

The collapse of poly(N-isopropylacrylamide)/poly(acrylic acid) semi-interpenetrating polymer network (PNIPAM/PAA SIPN) and poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AA)) microgel suspensions is studied by dielectric spectroscopy in a frequency range from 40 Hz to 110 MHz as a function of temperature. Dielectric measurements show that the structure affects the relaxation behavior of microgels: two relaxations (micro-Brownian motion and interfacial polarization at low frequency and counterion polarization at high frequency) are observed in the SIPN microgel whose charges mainly exist in domains and one relaxation (interfacial polarization) is observed in the copolymer microgel whose charges distribute in the whole network. A dielectric model is proposed to describe the collapsed microgel suspensions, from which some parameters, such as the volume fraction and the permittivity of microgels, were calculated using Hanai's equation. The temperature dependencies of these parameters show that the SIPN microgel has better low-temperature swelling properties and thermal responsiveness. This is caused by different polymer-solvent and electrostatic repulsion interactions in different microgels. Compared with pure PNIPAM, the relationship of volume phase transition temperature (VPTT) is VPTTP(NIPAM-co-AA) > VPTTPNIPAM/PAA SIPN > VPTTPNIPAM, and it is explained from the viewpoint of interaction. Besides, the activation energy data prove that the structure influences the electrical properties of microgels, which is consistent with the results obtained from quantitative dielectric analysis.

Probing the Collapse Dynamics of Poly(N‐isopropylacrylamide) Brushes by AFM: Effects of Co‐nonsolvency and Grafting Densities

Collapse of poly(N-isopropylacrylamide) (PNIPAM) brushes in the mixed solvent system (water/methanol 50% v/v) is studied by in-situ atomic-force microscopy (AFM). PNIPAM brushes with three different grafting densities and similar chain lengths are synthesized via surface-initiated atom-transfer radical polymerization. By changing the solvent from water to a water/methanol (50% v/v) mixture, the polymer brushes switch from a swollen to collapsed state. AFM force measurements using a silica colloidal probe attached to the tip are employed to obtain the Young's moduli of the polymer brushes in different solvation states. The collapse dynamics of the brush is followed by monitoring the pull-off force (adherence) in situ. The modulus of the swollen high-density polymer brush is four times lower than that of the same brush in the collapsed state. It is shown that in the case of the high-density polymer brush with a thickness (t(in water) ) of 900 nm, the collapse takes place in a time scale of ~25 s, whereas the collapse occurs faster for the medium-density brush (t(in water) = 630 nm) and much more rapidly for the low-density brush (t(in water) = 80 nm). This difference in the response kinetics is primarily ascribed to the time needed for solvent exchange in the polymer brushes.

Collapse of Poly(methacrylic acid) Hydrogels in Response to Simultaneous Stimulation by an Electric Field and Complex Formation

Complex formation of poly(methacrylic acid) hydrogels with linear poly(ethylene glycol) has been studied at different pH values and in the presence of an electric field. The fastest contraction of the gel sample was observed under simultaneous action of electric field and complex formation.

Collapse of Poly(methacrylic acid) Hydrogels in Response to Simultaneous Stimulation by an Electric Field and Complex Formation

Collapse of Poly(methacrylic acid) Hydrogels in Response to Simultaneous Stimulation by an Electric Field and Complex Formation

Fluorescence and EPR studies on the collapse of poly( N-isopropyl acrylamide)- g-poly(ethylene oxide) in water

Studies on the thermal behaviour of copolymers, poly( N-isopropyl acrylamide), PNIPA, grafted with different amounts of poly(ethylene oxide), PEO, were conducted in aqueous solutions by fluorescence and EPR spectroscopies. The grafting reaction had been conducted under various reaction conditions and the number of PEO grafts per a PNIPA chain varied from 6 to 10. A fluorescence probe, 4-(dicyano methylene)-2-methyl-6-( p-dimethyl amino styryl)-4H-pyran (4HP) was observed to localise in the hydrophobic parts of the polymers. The changes in the polarity and microviscosity in the surroundings of 4HP upon the collapse of PNIPA depended in general on the amount of PEO in the polymer, polymer concentration, and sample-heating rate. However, fluorescence data revealed differences between the polymers, owing to the varying distribution of the PEO grafts along the PNIPA main chain. The polymer grafted in water at an elevated temperature ( T∼LCST) differed clearly from the others, those synthesised either in cold water or in an organic solvent. This particular polymer formed dense local hydrophobic domains inside the collapsed globule. Two ways of preparing the samples for EPR measurements resulted in a different localisation of a spin probe 5-doxyl stearic acid in the polymers. The probe resided either in the outer PEO shell close to the aqueous phase or in a less polar phase close to the PNIPA core of the polymer. The rate of the rotational diffusion of the radical increased discontinuously during the polymer collapse in the former case but in the latter, a typical linear activation of the thermal motion was observed. The results strongly suggest that the distribution of the PEO grafts along the PNIPA chains depends on the conformation of the functionalised PNIPA during the grafting, and this affects the behaviour of the graft copolymers.

Influence of temperature on the permeability of polyacrylamide hydrogels and semi-IPNs with poly( N-isopropylacrylamide)

Several polyacrylamide hydrogels and semi-interpenetrated polymer networks with poly( N-isopropylacrylamide) included were synthesised and characterised by their swelling ratio. Their permeability to Orange II was studied as a function of temperature in the range 25–45°C. In polyacrylamide hydrogels the permeability increases with temperature according to an Arrhenius relationship and the apparent activation energy for permeation decreases linearly as the swelling ratio of the hydrogel increases. In semi-interpenetrated polymer networks a more or less pronounced increase of the permeability to Orange II is observed above 32°C, the lower critical solution temperature of poly( N-isopropylacrylamide). Different values of the apparent activation energy for permeation were obtained below and above 32°C, the last one being always lower than the former one. The permeability of semi-interpenetrated polymer networks increases above 32°C though a slight shrinking of the gels is observed. This can be explained by the collapse of poly( N-isopropylacrylamide) chains resulting in an increase of the pore volume that facilitates the diffusion of the dye but simultaneously water is expelled and the swelling ratio of semi-interpenetrated polymer networks decreases.

Collapse of poly(methacryloylethyl trimethylammonium methylsulfate) on addition of acetone into an aqueous solution

The effect of the solvent composition on the conformation of a super high molar mass polyelectrolyte, M w=22–25×10 6, dissolved in a water–acetone mixture was investigated using static and dynamic light scattering. When increasing the concentration of acetone above 80 mass percent, a reversible conformational change of macromolecules occurs, which causes a sharp decrease in the viscosity, a rise in the light scattering intensity, and also a decrease in the radius of gyration, R g, the hydrodynamic radius, R h, as well as in the second virial coefficient A 2. The correlation function measured by dynamic light scattering changes from bimodal to unimodal indicating the formation of compact globular structures.

Conformational transitions in poly(methacrylic acid) gel/poly(ethylene glycol) complexes. Effect of the gel cross‐linking density

AbstractWe present results on the effect of the cross‐linking density on the collapse of poly‐(methacrylic acid) gels induced by the interaction with linear poly(ethylene glycol) and on their subsequent reswelling (reentrant transition). The abruptness and the amplitude of both transitions increase with decreasing cross‐linking density of the gel. A special feature of the reswelling transition for the PMAA gel/PEG system is the existence of a wide range of PEG concentrations where both collapsed and swollen states of the gel are stable. The conditions for the existence of such a region are easier realized for slightly cross‐linked gels. The corresponding theoretical explanation is given. The swelling degree of the collapsed gels increases with increasing cross‐linking density, which is explained by the presence of a certain amount of hydrophilic PEG loops in highly cross‐linked gels.