Synthesis and characterization of fluorocarbon‐modified poly(N‐isopropylacrylamide)

Poly(N‐isopropylacrylamide) copolymers (PNIPAMs) containing pendent perfluoroalkyl (R_F) or dodecyl groups have been synthesized by copolymerization of NIPAM with small amounts of R_R‐acrylates or ‐methacrylates containing a sulfonamido moiety between the acrylate and R_F groups or with dodecyl acrylate. Evidence for strong intermolecular hydrophobic association of the fluorocarbon groups is provided by large viscosity increases with copolymer concentration and upon addition of NaCl and surfactants. These interactions appear to be much stronger than that of the corresponding copolymers of poly(N,N‐dimethylacrylamide) with similar comonomer contents. Hydrophobic association between the R_F groups is found to be much stronger than that of the corresponding dodecyl groups. The viscosity of some of the copolymer solutions, particularly in the presence of perfluorocarbon surfactants, was unusually temperature sensitive, decreasing by a factor of at least 1000 upon increasing the temperature from 10 to 20 °C. This large decrease is most probably related to the collapse of the copolymer coils near the lower critical solution temperature. This is in sharp contrast to the corresponding polyacrylamide or poly(N,N‐dimethylacrylamide) R_F‐acrylate copolymers that show viscosity increases with increasing temperature in the 40–60 °C range. The NIPIAM copolymers were also found to be different from the acrylamide or N,N‐dimethylacrylamide perfluorocarbon acrylate copolymers in that they were found to be Newtonian at a low R_F content but dilatant at a higher comonomer content. © 2000 Society of Chemical Industry     

Synthesis and solution properties of fluorocarbon‐modified poly(N,N‐dimethylacrylamide)

Poly(N,N‐dimethylacrylamide) (PDMA) containing perfluoro‐octyl pendent groups was prepared by solution polymerization of N,N‐dimethylacrylamide in benzene with 0.16 –1.25 mol% 2‐(N‐ethylperfluoro‐octane sulfonamido) ethyl acrylate (FX‐ 13®) or 2‐(N‐ethylperfluoro‐octane sulfonamido) ethyl methacrylate (FX‐14®). The copolymer intrinsic viscosity strongly decreases with increasing comonomer content due to intramolecular association. However, the Huggins constant increases more than 40‐fold with increasing comonomer content, indicating that intermolecular association increases with increasing comonomer content. Strong Brookfield viscosity enhancements are observed above a critical copolymer concentration varying between 0.5 and 2.0 wt% depending on comonomer type and content. Some of the copolymers show pseudoplastic behaviour whereas others show shear‐thickening or both types of behaviour. These observations are consistent with competing inter‐ and intramolecular micellar association. Fluorescence studies using a perfluorocarbon‐substituted pyrene as a probe indicate the formation of hydrophobic microdomains formed by the association of perfluorocarbon groups. © 2001 Society of Chemical Industry     

A study on solution properties of poly(N,N‐diethylacrylamide‐co‐acrylic acid)

Poly(N,N‐diethylacrylamide) (PDEA), poly(acrylic acid) (PAA), and a series of (N,N‐diethylacrylamide‐co‐acrylic acid) (DEA‐AA) random copolymers were synthesized by the method of radical polymerization. The measurement of turbidity showed that the phase behaviors of the brine solutions of the copolymers changed dramatically with the mole fraction of DEA (x) in these copolymers. Copolymers cop6 (x = 0.06) and cop11 (x = 0.11) in which acrylic acid content was higher presented the upper critical solution temperature (UCST) phase behaviors similar to PAA. Copolymer cop27 (x = 0.27) presented the lower critical solution temperature (LCST) behavior similar to PDEA. While copolymer cop18 (x = 0.18) in which acrylic acid content was moderate presented both UCST and LCST behaviors. The solution properties of the polymers were investigated by measurements of viscosity, fluorescence, and pH. It is reasonable to suggest that the sharp change of the phase behavior may be attributed to the interaction between acrylamide group and carboxylic group in the (DEA‐AA) copolymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Temperature‐sensitive switch from composite poly(N‐isopropylacrylamide) sponge gels

Thermally sensitive polymers change their properties with a change in environmental temperature in a predictable and pronounced way. These changes can be expected in drug delivery systems, solute separation, enzyme immobilization, energy‐transducer processes, and photosensitive materials. We have demonstrated a thermal‐sensitive switch module, which is capable of converting thermal into mechanical energy. We employed this module in the control of liquid transfer. The thermally sensitive switch was prepared by crosslinking poly(N‐isopropylacrylamide) (PNIPAAm) gel inside the pores of a sponge to generate the composite PNIPAAm/sponge gel. This gel, contained in a polypropylene tube, was inserted into a thermoelectric module equipped with a fine temperature controller. As the water flux through the composite gel changes from 0 to 6.6 × 10² L m⁻² h, with a temperature change from 23 to 40°C, we can reversibly turn on and off the thermally sensitive switch. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75:1735–1739, 2000     

Poly(N‐isopropylacrylamide) grafted to a strongly charged backbone: Thermoresponsive behavior in aqueous solution

The thermoresponsive properties in aqueous solution of the graft copolymer poly(acrylic acid‐co‐2‐acrylamido‐2‐methyl propane sulfonic acid)‐g‐poly(N‐isopropylacrylamide) [P(AA‐co‐AMPSA)‐g‐PNIPAM] were studied and compared to the corresponding behavior of the poly(acrylic acid)‐g‐poly(N‐isopropylacrylamide) (PAA‐g‐PNIPAM) graft product. Both products contain about 40% (w/w) of PNIPAM, whereas the backbone, P(AA‐co‐AMPSA), of the first copolymer contains about 40% of AMPSA mole units. The strongly charged P(AA‐co‐AMPSA)‐g‐PNIPAM graft copolymer was water soluble over the whole pH range, whereas the PAA‐g‐PNIPAM copolymer precipitated out from water at pH < 4. As a result, the first product exhibited a temperature‐sensitive behavior in a wide pH range, extended in the acidic region, whereas in semidilute aqueous solutions, an important thermothickening behavior was observed, even at low pH (pH = 3.0). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3466–3470, 2004     

Thermogelling of highly branched poly(N‐isopropylacrylamide)

Highly branched poly(N‐isopropylacrylamide) (PNIPAM) has been synthesized by a reversible addition‐fragmentation chain transfer (RAFT) copolymerization of NIPAM and a vinyl contained trithiocarbonate RAFT agent. ¹H‐NMR measurements revealed that the degrees of branch (DB) are in the range of 0.032–0.105. Laser light scattering (LLS) measurements gave the hydrodynamic radii (R_h) of the polymers to be 3.6–5.7 nm with molecular weight in the range of 1.3 × 10⁴ g/mol–2.3 × 10^?4 g/mol. Highly branched PNIPAM with terminal thiol groups were obtained by aminolysis the polymers, and the product can be oxidized by air to form disulfide bonds (? S? S? ) among chains and resulting in the formation of nanoparticle in aqueous solution. Interestingly, the nanoparticle in size of R_h ? 80 nm showed a thermogelling behavior to form bulk hydrogel when the temperature was increased up to 25°C due to the thermo‐induced association of the PNIPAM chains among the nanoparticles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Amine‐derivatized poly(diallyldimethylammonium chloride) from N‐vinylformamide copolymerization

The reactivity ratios for the aqueous free‐radical copolymerization of diallyldimethylammonium chloride and N‐vinylformamide were found to be 0.13 and 1.92, respectively, from a Fineman–Ross analysis of a series of batch polymerizations. Because batch polymerization could not give a uniform product in a high yield with two monomers of such different reactivities, a semibatch procedure was developed in which the more reactive N‐vinylformamide was added in 10 steps over the course of the copolymerization. The poly(diallyldimethyl‐ ammonium chloride‐co‐N‐vinylformamide) copolymers were hydrolyzed to give poly(diallyldimethylammonium chloride‐co‐vinylamine). The utility of the vinylamine/diallyldimethylammonium chloride copolymers was demonstrated by the preparation and characterization of three derivatives: (1) a copolymer with coupled dansyl groups for fluorescence detection; (2) a copolymer with coupled dabsyl groups for ultraviolet–visible detection; and (3) an ultra‐high‐molecular‐weight (1.6 × 10⁶ Da) poly(diallyldimethylammonium chloride) by chain extension (coupling) with glycerol diglycidyl ether. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1068–1075, 2007     

Phase separation of poly(N‐isopropylacrylamide) solutions and gels using a near infrared fiber laser

We used a tunable near infrared fiber laser in the wavelength range of 1533–1573 nm to induce photothermal phase changes in poly(N‐isopropylacrylamide) (PNIPAM) aqueous solutions and hydrogels. The laser induces the hydrophilic to hydrophobic transition of the polymer by heating the surrounding water. We report our observations of the phase changes based on using a novel fiber backreflectance method coupled with visual cloud point measurements. At 1533 nm the phase transition was induced at the end of a single mode optical fiber with 9 mW of power at an ambient temperature of 24°C. We found that the power required to reach the lower critical solution temperature was inversely proportional to the absorption spectrum of water. In addition, phase changes in both solutions and gels occurred very rapidly (<1 s) as the laser was turned on and off. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Boron removal by liquid‐phase polymer‐based retention technique using poly(glycidyl methacrylate N‐methyl D‐glucamine)

The removal of boron was analyzed by liquid‐phase polymer based retention (LPR) technique using washing and enrichment method. The extracting reagents were water‐soluble polymers (WSPs) containing quaternary ammonium salts and N‐methyl‐D ‐glucamine (NMG) groups. The removal experiments of boron using the washing method were conducted at 1 bar of pressure by varying pH, polymer:boron molar ratio, and concentrations of interfering ions (chloride and sulfate). The results showed higher retention capacity for boron (60%) at pH 10 with the polymer containing NMG group. The optimal polymer:boron molar ratio was 40 : 1. Selectivity experiments showed that the presence of interfering ions did not affect the boron removal capacity. The maximal boron retention capacity was determined by the enrichment method, obtaining a value of 12 mg B/g‐polymer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Influence of the coagulation‐bath temperature on the phase‐separation process of poly(vinylidene fluoride)‐graft‐poly(N‐isopropylacrylamide) solutions and membrane structures

A poly(vinylidene fluoride)‐graft‐poly(N‐isopropylacrylamide) (PVDF‐g‐PNIPAAm) copolymer was synthesized, and flat‐sheet membranes were prepared via the phase‐inversion method with N,N‐dimethylformamide (DMF) as the solvent and water as the coagulation bath. The effects of the coagulation‐bath temperature on poly(vinylidene fluoride) (PVDF)/DMF/water and PVDF‐g‐PNIPAAm/DMF/water ternary systems were studied with phase diagrams. The results showed that the phase‐separation process could be due to the hydrophilicity/hydrophobicity of poly(N‐isopropylacrylamide) at low temperatures, and the phase‐separation process was attributed to crystallization at high temperatures. The structures and properties of the membranes prepared at different coagulation‐bath temperatures were researched with scanning electron microscopy, porosity measurements, and flux measurements of pure water. The PVDF‐g‐PNIPAAm membranes, prepared at different temperatures, formed fingerlike pores and showed higher water flux and porosity than PVDF membranes. In particular, a membrane prepared at 30°C had the largest fingerlike pores and greatest porosity. The water flux of a membrane prepared in a 25°C coagulation bath showed a sharp increase with the temperature increasing to about 30°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Flourescent probe and ESEM morphologies of a acrylamide‐based terpolymer in aqueous solution

The terpolymer (PASA) of acrylamide with butyl styrene and sodium 2‐acrylamido‐2‐methylpropane sulfonate was synthesized. The composition and molecular structure were characterized by elemental analysis, UV, FTIR, and ¹H NMR. The aggregation behaviors of PASA were studied by means of the fluorescent probe analysis and environmental scanning electron microscope (ESEM). The flourescent probe analysis indicates that the PASA molecules form excellent hydrophobically associating structures in pure water and with the increase in PASA concentration at low concentrations, the nonpolarity of hydrophobic microdomains and the degree of intermolecular hydrophobic association increase in aqueous and brine solution. ESEM measurements show that gigantic aggregates have been formed in the PASA aqueous solution at the polymer concentration of 0.05 g dL^?1, which is the critical association concentration of the polymer, and excellent solution properties of PASA are attributed to integrated network‐structures formed by PASA in aqueous solution, which are collapsed by the addition of salt, resulting in the decrease in apparent viscosity of PASA in brine solution. However, with the increase in the NaCl concentration or the PASA concentration, the number and size of aggregates increase, leading to the remarkable increase in the apparent viscosity of PASA in brine solution. These results are consistent with the AFM and viscosity study results. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:277–286, 2007     

Lower critical solution temperatures of thermo‐responsive poly(N‐isopropylacrylamide) copolymers with racemate or single enantiomer groups

BACKGROUND: Thermo‐responsive copolymers with racemate or single enantiomer groups are attracting increasing attention due to their fascinating functional properties and potential applications. However, there is a lack of systematic information about the lower critical solution temperature (LCST) of poly(N‐isopropylacrylamide)‐based thermo‐responsive chiral recognition systems. In this study, a series of thermo‐responsive chiral recognition copolymers, poly[(N‐isopropylacrylamide)‐co‐(N‐(S)‐sec‐butylacrylamide)] (PN‐S‐B) and poly[(N‐isopropylacrylamide)‐co‐(N‐(R,S)‐sec‐butylacrylamide)] (PN‐R,S‐B), with different molar compositions, were prepared. The effects of heating and cooling processes, optical activity and amount of chiral recognition groups in the copolymers on the LCSTs of the prepared copolymers were systematically studied. RESULTS: LCST hysteresis phenomena are found in the phase transition processes of PN‐S‐B and PN‐R,S‐B copolymers in a heating and cooling cycle. The LCSTs of PN‐S‐B and PN‐R,S‐B during the heating process are higher than those during the cooling process. With similar molar ratios of N‐isopropylacrylamide groups in the copolymers, the LCST of the copolymer containing a single enantiomer (PN‐S‐B) is lower than that of the copolymer containing racemate (PN‐R,S‐B) due to the steric structural difference. The LCSTs of PN‐R,S‐B copolymers are in inverse proportion to the molar contents of the hydrophobic R,S‐B moieties in these copolymers. CONCLUSION: The results provide valuable guidance for designing and fabricating thermo‐responsive chiral recognition systems with desired LCSTs. Copyright © 2008 Society of Chemical Industry     

Water‐soluble fluorescent nanoparticles without distinct aggregation of conjugated polymer chains

In a previous study, we reported water‐soluble light‐emitting nanoparticles with distinct interchain aggregation states of the constituent conjugated polymers. These interchain states usually result in strong self‐quenching, dramatically reducing the quantum efficiency of fluorescence. In the work reported in the present study, we developed new water‐soluble fluorescent nanoparticles without distinct aggregation of the conjugated polymer chains, which demonstrated distinctive morphologies and optical properties. ‘Strawberry’ morphologies of the nanoparticles were directly observed using transmission electron microscopy. The conjugated polymers were dispersed in the individual cores of the nanoparticles and the majority of the core diameters were in the range 8–12 nm. The primary optical properties of the conjugated polymers in tetrahydrofuran still remained in the nanoparticles. The results suggest that the conjugated polymer chains formed a possible unimolecular structure without distinct aggregation in the nanoparticles. Copyright © 2010 Society of Chemical Industry     

Thermodynamic study of a pressure‐temperature phase diagram for poly(N‐isopropylacrylamide) gels

The volume change, ΔV_h,_, accompanying the hydrophobic hydration associated with the volume phase transition in Poly(N‐isopropylacrylamide) gels was measured by a simple method. The hydration accompanies a negative ΔV_h′?2.5 cm³/mol. The P‐T phase diagram, the coexistence curve, for the gels was determined from the swelling ratio‐pressure curves up to 350 MPa for various constant temperatures. The contour of the coexistence curve is shaped like an ellipsoid on the P‐T plain, which is a feature peculiar to the reversible pressure‐temperature denaturation of a protein. The thermodynamic analysis of the Clausius–Clapeyron relation for the measured ΔV_h elucidates that the obtained coexistence curve represents the phase boundary between thermodynamic different phases like the two phases, native and denatured, of a protein and gives the transition enthalpy, ΔH, 5.2kJ/mol by estimate, which well coincides with the transition heat measured by a calorimetric method. Considering the volume‐dependent free energy, Δv_mi · P, for the mixing free energy of the gel, we can fit the calculated curve to the measured swelling ratio‐pressure curve of PNIPA gels. The value of Δv_mi changes the sign from negative to positive above around 100MPa. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 405–412, 2005     

Hydrophobic association and temperature and pH sensitivity of hydrophobically modified poly(N‐isopropylacrylamide/acrylic acid) gels

Hydrophobically modified poly(acrylic acid/N‐isopropylacrylamide) gels were synthesized by the radical copolymerization of acrylic acid/N‐isopropylacrylamide with a small amount of the hydrophobic comonomer 2‐(N‐ethylperfluorooctanesulfoamido)ethyl acrylate, stearyl acrylate, or lauryl acrylate in tert‐butanol with ethylene glycol dimethacrylate as a crosslinker. Swelling kinetics and fluorescence measurements showed that the hydrophobic association ability of fluorocarbon groups was stronger than that of hydrocarbon analogues in modified hydrogels that contained both physical and chemical crosslinking networks. The effects of the fractions and the species of the hydrophobe on the gel swelling and pH and temperature sensitivity were studied. The results indicated that the swelling behavior and pH and temperature sensitivity of the gels were affected by the degree of hydrophobic modification. A hydrogel with a suitable 2‐(N‐ethylperfluorooctanesulfoamido)ethyl acrylate content (0.349 mol %) showed good pH and temperature sensitivity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2406–2413, 2003     

Synthesis of water‐soluble and conducting polyaniline by growing of poly (N‐isopropylacrylamide) brushes via atom transfer radical polymerization method

Polyaniline‐graft‐Poly(N‐isopropylacrylamide) copolymers were synthesized by atom‐transfer radical polymerization (ATRP) of N‐isopropylacrylamide using polyaniline macro‐initiators. Polyaniline‐chloroacetylchloride and polyaniline‐chloropropionylchloride macroinitiators were obtained by the reaction of amine nitrogens of polyaniline with chloroacetyl chloride and 2‐choloropropionyl choloride, respectively. Both macroinitiators and graft copolymers were characterized by FT‐IR and ¹H‐NMR spectroscopy. The cyclic voltammetry (CV) and UV‐Vis spectroscopy studies showed that these copolymers are electroactive. The solubility test revealed that the polyaniline‐graft‐poly (N‐isopropylacrylamide) copolymers are water soluble or water/methanol soluble. The Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) images showed the growing of poly (N‐isopropylacrylamide) chains on polyaniline backbone. Investigation of thermal behavior of graft copolymers by thermal gravimetry analysis (TGA) confirmed the results obtained from AFM and SEM images. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and solution properties of single‐chain microgels from poly(N‐isopropylacrylamide) copolymer

“Single‐chain” microgels were synthesized successfully from the cross‐linkable poly(N‐isopropylacrylamide) (PNIPAM) copolymer. This type of microgel has the exact chemical structure, molecular weight and molecular weight distribution of its precursor. It provides a direct way to compare the properties of linear polymers with those of their networks. The viscosity properties show that the microgels have lower critical solution temperatures (LCST) that are even higher than those of the corresponding linear copolymers. This can be attributed to the crosslinking points, which retard the change of the conformation of the network chains. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2179–2183, 2003     

Antimicrobial poly(N‐vinyl‐2‐pyrrolidone‐alt‐maleic anhydride)/poly(ethylene imine) macrocomplexes

The antimicrobial polymer/polymer macrocomplexes were synthesized by radical alternating copolymerization of N‐vinyl‐2‐pyrrolidone with maleic anhydride [poly(VP‐alt‐MA)] with 2,2′‐azobis‐isobutyronitrile as an initiator at 65°C in dioxane solutions under nitrogen atmosphere, and interaction of prepared copolymer with poly(ethylene imine) (PEI) in aqueous solutions. The susceptibility of some Gram‐negative (Salmonella enteritidis and Escherichia coli) and Gram‐positive (Staphylococcus aureus and Listeria monocytogenes) bacteria to the alternating copolymer and its PEI macrocomplexes with different compositions in microbiological medium was studied using pour‐plate technique. All the studied polymers, containing biologically active moieties in the form of ionized cyclic amide, and macrobranched aliphatic amine groups and acid/amine complexed fragments, were more effective against L. monocytogenes than those for Gram‐positive S. aureus bacterium. This fact was explained by different surface layer structural architectures of biomacromolecules of tested bacteria. The resulting polymeric antimicrobial materials are expected to be used in various areas of medicine and food industry. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5841–5847, 2006     

Thermodynamic investigation of thermoresponsive xanthan‐poly (N‐isopropylacrylamide) hydrogels

Polysaccharide‐based hydrogels, such as xanthan maleate/poly(N‐isopropylacrylamide) (PNIPAAm) interpenetrated polymer networks, are thermostimulable materials of interest for the controlled release of biologically active components due to conformation changes at the low critical‐solution temperature (LCST) PNIPAAm phase transition. The phase transition of these interpenetrated polymer network hydrogels, where PNIPAAm is in a ‘confined’ environment, was examined by high resolution magic angle spinning nuclear magnetic resonance and differential scanning calorimetry. High resolution magic angle spinning nuclear magnetic resonance spectroscopy allows the accurate determination of LCST and an evaluation of the corresponding thermodynamic data. More particularly, the evolution of these data as a function of the composition of the hydrogel, and of the external parameters such as pH and ionic strength, was considered. LCST shows a minimal value with increasing xanthan content. Moreover, it was possible to calculate, as a function of temperature, the fraction of NIPAAm which remains uncollapsed. The data obtained for pure PNIPAAm hydrogels are in good agreement with recently published results. The phase transition of PNIPAAm in a diphasic hydrogel is broader when PNIPAAm is ‘confined’ within an interpenetrated polymer network than in a pure PNIPAAm crosslinked network. The widening of the transition with increasing xanthan content indicates a reduction of the PNIPAAm interchain aggregation in a network structure. Copyright © 2011 Society of Chemical Industry     

Rheology of poly(N‐vinyl pyrrolidone)–poly(ethylene glycol) adhesive blends under shear flow

The rheological properties of adhesive miscible blends of high‐molecular‐weight poly(N‐vinyl pyrrolidone) (PVP) with short‐chain poly(ethylene glycol) (PEG) under oscillatory and steady‐state shear flow have been examined with dynamic mechanical and squeezing‐flow analysis. The latter allows the rheological characterization of adhesive blends under conditions modeling adhesive‐bond formation as a fixed compressive force is applied to an adhesive film. The most adhesive PVP blend with 36 wt % PEG has been established to flow like a viscoplastic (yield stress) liquid with a power‐law index of about 0.12. The study of the apparent yield stress as a function of the PVP–PEG composition, content of sorbed water, molecular weight of PVP, and temperature shows that the occurrence of a yield stress in the blends results most likely from a noncovalent crosslinking of PVP macromolecules through short PEG chains by means of hydrogen bonding of both terminal OH groups of PEG to the complementary functional groups in PVP monomer units. A molecular mechanism of PVP–PEG interaction was established earlier by direct and independent methods. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 522–537, 2006