Search

We exploited organic photo-redox-catalyzed atom transfer radical polymerization (O-ATRP) to synthesize a thermo-responsive polymer with a narrow molecular weight distribution. Poly(methyl methacrylate) (PMMA) chains were polymerized from a hydroxypropyl cellulose (HPC)-based macroinitiator using metal-free O-ATRP under visible-light irradiation. This O-ATRP is mediated by 1,2,3,5-tetrakis (carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), a photoredox catalyst with a substantial excited-state reduction potential, low cost, and ease of preparation. The synthesis of a series of PMMA-grafted HPC (PMMA-g-HPC) was characterized by various analytical methods, including FTIR spectroscopy, NMR spectroscopy, TGA, and GPC analysis. The lower critical solution temperature (LCST) of the polymers was determined by measuring the transmittance of the polymer solution as a function of the temperature at various pH values. Consequently, we expanded the LCST window of the HPC-based polymers and generated the opposite pH dependency of the LCST by forming PMMA-g-HPCs. Our "grafting-from" synthetic approach and thermo-responsive polymers, which are controllable in full range of physiological conditions, are promising in a variety of biological, electronics, and biosensor applications, particularly in drug delivery systems. [ABSTRACT FROM AUTHOR]

Oxime grafted polyacrylonitrile (OX-g-PAN) nanofibers (NFs) membrane was prepared by combining electrospinning and chemical grafting techniques. The membrane was extensively characterized with field emission scanning electron microscopy (FE-SEM) and Fourier transforms infrared (FT-IR) spectroscopy. High percent grafting (79 %) with no change in the physical nature was confirmed by FT-IR spectra. The adsorption kinetics of methylene blue (MB), rhodamine B (RB) and safranin T (ST) onto OX-g-PAN NFs membranes followed a pseudo-second-order model and no change in the intraparticle diffusion pattern was observed. The order of adsorption capacity ((q) at equilibrium time) was; MB (102.15 mg/g) < ST (118.34 mg/g) < RB (221.24 mg/g). The adsorption data for the dyes fitted well to Langmuir ( r values and varied from 0.950 to 0.985 and Freundlich ( r values varied from 0.988 to 0.996) equations. The increased adsorption by OX-g-PAN NFs membrane could be attributed to the increased exposed surface and number of active sites on the membranes. The good fitting to adsorption equations showed that beside condensation (physical adsorption) monolayer adsorption has also occurred. The adsorption capacity values of the present system were higher as compared to the values reported in the literature for conventional adsorbents. [ABSTRACT FROM AUTHOR]

Random and highly aligned bead-free chitosan nanofibers (NFs) were successfully prepared via electrospinning by keeping the applied voltage (22 kV), flow rate (0.4 mL h), needle diameter (0.8 mm), and needle to collector distance (100 mm) constant while varying the solution concentration and collector rotation speed. No electrospinning was observed for lower solution concentrations, i.e., 1-3 wt% (w/v), whereas a decrease in the number and size of beads and microspheres, and bead-free NFs were obtained when the concentration of solution was increased from 4 to 6 wt%. Increase in the polymer concentration increased the solution viscosity (from 3.53 to 243 mPa s) and conductivity (from 29.80 to 192.00 μs cm) to critical values, which led to beadless NFs. The optimized conditions (i.e., concentration of solution 6 wt%, applied electrical potential 22 kV, flow rate 0.4 mL h, needle diameter 0.8 mm, and needle to collector distance 100 mm) were further used for the alignment of chitosan NFs. The alignment of the NFs increased from 35.6 to 94.4 % and the diameter decreased from 163.9 to 137.4 nm as the rotation speed of the cylindrical collector drum was increased from 2.09 to 21.98 m s. The aligned and small diameter chitosan NFs might find potential applications in biomedical, environmental, solar fuel cell applications, etc. Several target devices and polymer systems in the literature have been used to obtain aligned NFs; however, almost no work has been reported on individual chitosan alignment. [ABSTRACT FROM AUTHOR]