Crystallization Behaviors of Poly(ethylene 2,6-naphthalate) in the Presence of Liquid Crystalline Polymer

The crystallization behaviors and morphology of poly(ethylene 2,6-naphthalate) (PEN) in the presence of liquid crystalline polymer (LCP) Vectra RD501 have been studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), atomic force microscopy (AFM), and wide-angle X-ray diffraction (WAXD). It was found that the LCP in PEN/LCP blends accelerates the crystallization rate of PEN at both higher and low crystallization temperatures, which indicates that LCP acts as both nucleating agent and nucleation promoter for PEN crystallization. The crystallization of PEN was effectively improved with increasing LCP content up to 1 wt %, and then tended to level off with increasing LCP. The Avrami exponent n changed from 2.0−2.7 for pure PEN to <2 for PEN in the presence of LCP, which indicated that the nucleation mechanism of PEN crystallization was changed. The size of the PEN spherulitic crystals became smaller in the presence of LCP, but WAXD has shown that there is no change in the crystal modifications of PEN

Smart Assembly Behaviors of Hydroxypropylcellulose-<i>graft</i>-poly(4-vinyl pyridine) Copolymers in Aqueous Solution by Thermo and pH Stimuli

Thermo- and pH-sensitive graft copolymers, hydroxypropylcellulose-graft-poly(4-vinyl pyridine) (HPC-g-P4VP), were synthesized via atom transfer radical polymerization (ATRP) and characterized. The thermo- and pH-induced micellization and stimuli-responsive properties of HPC-g-P4VP graft copolymers in aqueous solution were investigated by transmittance, 1H NMR, dynamic light scattering (DLS), and so on. For the pH-induced micellization, the P4VP side chains collapse to form the core of the micelles, and the HPC backbones stay in the shell to stabilize the micelles. In the case of thermoinduced micellization, the HPC backbones collapse to form the core of the micelles that was stabilized by the P4VP side chains in the shell upon heating. What’s more, the cloud point of the HPC-g-P4VP copolymers in the aqueous solution could be finely tuned by changing the length of P4VP side chains or the pH values. In acidic water, the longer the side chains, the higher the cloud point. For those HPC-g-P4VP copolymers with short side chains, for example, HPC0.05-g-P4VP3, the lower pH correlates a higher cloud point. The thermo- or pH-induced micelles also have the pH- or thermosensitivity due to their P4VP or HPC shells

Isodimorphism in Polyamide 56/Polyamide 66 Blends with Controllable Thermal and Mechanical Properties

The crystallization behaviors of polyamide 56/polyamide 66 (PA56/PA66) blends are investigated. Isodimorphism is first found in PA56/PA66 blends. The melting point, crystallization temperature, and crystallinity of the blends first decrease and then increase with the increase of PA66 content in the blends at the pseudo-eutectic point with ϕ66 = 0.5. The crystalline structure follows the dominant component in the blends. That is, PA56 phase and PA66 phase are obtained in the PA56-rich and PA66-rich blends, respectively, upon cooling the blends from the melting state. Both PA56 phase and PA66 phase are formed in PA56/PA66 blends at the pseudo-eutectic point upon cooling from the melting state. Fourier transformation infrared spectroscopy results indicate that the isodimorphic behavior is attributed to the hydrogen bonding interactions between PA56 and PA66 chains in the blends. Mechanical properties of the blends indicate that the elongation at break of the blends is tremendously enhanced without scarifying the strength and modulus of the materials. The isodimorphism of PA56 and PA66 provides a simple and promising approach for fabricating polymeric materials with versatile applications

Dissolution Mechanism of Cellulose in <i><i>N,N</i></i>-Dimethylacetamide/Lithium Chloride: Revisiting through Molecular Interactions

Understanding the interactions between solvent molecules and cellulose at a molecular level is still not fully achieved in cellulose/<i><i>N,N</i></i>-dimethylacetamide (DMAc)/LiCl system. In this paper, cellobiose was used as the model compound of cellulose to investigate the interactions in cellulose/DMAc/LiCl solution by using Fourier transform infrared spectroscopy (FTIR), ¹³C, ³⁵Cl, and ⁷Li nuclear magnetic resonance (NMR) spectroscopy and conductivity measurements. It was found that when cellulose is dissolved in DMAc/LiCl cosolvent system, the hydroxyl protons of cellulose form strong hydrogen bonds with the Cl^–, during which the intermolecular hydrogen bonding networks of cellulose is broken with simultaneous splitting of the Li⁺–Cl^– ion pairs. Simultaneously, the Li⁺ cations are further solvated by free DMAc molecules, which accompany the hydrogen-bonded Cl^– to meet electric balance. Thereafter, the cellulose chains are dispersed in molecular level in the solvent system to form homogeneous solution. This work clarifies the interactions in the cellulose/DMAc/LiCl solution at molecular level and the dissolution mechanism of cellulose in DMAc/LiCl, which is important for understanding the principle for selecting and designing new cellulose solvent systems

Bacterial Cellulose Supported Gold Nanoparticles with Excellent Catalytic Properties

Amidoxime surface functionalized bacterial cellulose (AOBC) has been successfully prepared by a simple two-step method without obviously changing the morphology of bacterial cellulose. AOBC has been used as the reducing agent and carrier for the synthesis of gold nanoparticles (AuNPs) that distributed homogeneously on bacterial cellulose surface. Higher content in amidoxime groups in AOBC is beneficial for the synthesis of AuNPs with smaller and more uniform size. The AuNPs/AOBC nanohybrids have excellent catalytic activity for reduction of 4-nitrophenol (4-NP) by using NaBH₄. It was found that catalytic activity of AuNPs/AOBC first increases with increasing NaBH₄ concentration and temperature, and then leveled off at NaBH₄ concentration above 238 mM and temperature above 50 °C. Moreover, AuNPs with smaller size have higher catalytic activity. The highest apparent turnover frequency of AuNPs/AOBC is 1190 h^–1. The high catalytic activity is due to the high affinity of 4-NP with AuNPs/AOBC and the reduced product 4-aminophenol has good solubility in water in the presence of AuNPs/AOBC. The catalytic stability of the AuNPs/AOBC was estimated by filling a fluid column contained AuNPs/AOBC and used for continuously catalysis of the reduction of 4-NP by using NaBH₄. The column works well without detection of 4-NP in the eluent after running for more than two months, and it is still running. This work provides an excellent catalyst based on bacterial cellulose stabilized AuNPs and has promising applications in industry

Controllable Aggregation and Reversible pH Sensitivity of AuNPs Regulated by Carboxymethyl Cellulose

A pH-sensitive gold nanoparticle-cysteamine/carboxymethyl cellulose (Au-CA/CMC) dispersion system was prepared by a simple approach. Gold nanoparticles (AuNPs) were first synthesized by directly reducing chloroauric acid (HAuCl4) with sodium carboxymethyl cellulose (CMC). Then the AuNPs were decorated by an electrostatic compound of cysteamine hydrochloride (CA) and sodium carboxymethyl cellulose (CMC) through ligand exchange to get the assembly of Au-CA/CMC. The Au-CA/CMC dispersion system exhibits strongly reversible pH-responsive behavior with the aggregation of AuNPs caused by the combined action of the chain conformation change of CMC and electrostatic interactions between CA and CMC at different pH values. Finally, the reversible aggregation mechanism of AuNPs in the Au-CA/CMC dispersion system has been investigated by transmission electron microscopy (TEM) and ultraviolet−visible spectroscopy (UV−vis spectroscopy). This study provides a new method to fabricate a stimuli-responsive system free from complicated organic synthesis without using a toxic reducing agent

Osmium Bipyridine-Containing Redox Polymers Based on Cellulose and Their Reversible Redox Activity

Thermo-, pH-, and electrochemical-sensitive cellulose graft copolymers, hydroxypropyl cellulose-<i>g</i>-poly(4-vinylpyridine)-Os(bipyridine) (HPC-<i>g</i>-P4VP-Os(bpy)), were synthesized and characterized. The electrochemical properties of the resulting material were investigated via cyclic voltammetry by coating the graft copolymers on the platinized carbon electrode. The results indicated that the electrochemical properties of the graft copolymer modified electrode were responsive to the pH values of the electrolyte solution. The reversible transformation between the active and inactive state originated from the changes in the architecture of the HPC-<i>g</i>-P4VP-Os(bpy) graft copolymer at different pH values. At high pH (e.g., above the p<i>K</i>_a of P4VP), the chains of P4VP collapsed, and the electrochemical activity of the electrode was reduced. With immobilization of glucose oxidase (GOx) on the graft copolymer decorated electrode, a biosensor for glucose detection was prepared. The current of the biosensor depended on the glucose concentration in the detected solution and increased with the successive addition of glucose

Self-Assembly and Dual-Stimuli Sensitivities of Hydroxypropylcellulose-<i>graft</i>-poly(<i>N</i>,<i>N</i>-dimethyl aminoethyl methacrylate) Copolymers in Aqueous Solution

The self-assembly and pH- and thermo-sensitivities properties of hydroxypropyl cellulose-graft-poly(N,N-dimethyl aminoethyl methacrylate) (HPC-g-PDMAEMA) copolymers in aqueous solutions were investigated by transmittance, dynamic light scattering (DLS), and 1H NMR spectroscopy. Micelles with different structure can be formed by varying either pH value or temperature. At low pH, e.g., 3.0, the HPC backbone of the copolymer collapse to form the core of micelles stabilized with protonated PDMAEMA side chains on the surface of the micelles upon heating. At the medium pH, e.g., 8.1, both HPC backbone and PDMAEMA side chains collapse upon heating to form unstable aggregates. At high pH, e.g., 12.3, PDMAEMA side chains collapse first to form the core of micelles stabilized with HPC chains upon heating. Further heating the copolymer solution at this pH leads to the aggregation of the micelles due to the collapse of the shell HPC chains. The thermal sensitivity of the HPC-g-PDMAEMA copolymers is reversible

Dissolution and Metastable Solution of Cellulose in NaOH/Thiourea at 8 °C for Construction of Nanofibers

To develop a facile approach for the dissolution of cellulose, a novel solvent (9.3 wt % NaOH/7.4 wt % thiourea aqueous solution) was used, for the first time, to dissolve cellulose within 5 min at 8 °C. The results of NMR and Raman spectra demonstrated that stable thiourea···OH^– complexes were formed through strong hydrogen bonds in NaOH/thiourea at room temperature. Moreover, the strength of the hydrogen bonds in thiourea···OH^– complexes was much higher than that in urea···OH^– complexes, and the number of thiourea···OH^– complexes increased significantly in 9.3 wt % NaOH/7.4 wt % thiourea compared to that in 9.5 wt % NaOH/4.5 wt % thiourea, which dissolved cellulose at −5 °C, leading to the dissolution of cellulose at a relatively high temperature (8 °C). The cellulose that dissolved at such a high temperature was metastable. The results of dynamic light scattering and transmission electron microscope experiments confirmed that the extended cellulose chains and their aggregates coexisted in the dilute cellulose solution. Interestingly, stiff cellulose chains could be self-assembled in parallel to form nanofibers in the metastable cellulose solution, from which cellulose microspheres consisting of nanofibers could be easily produced by inducing heating. This work not only proposed a novel method for the dissolution of cellulose in aqueous system at temperatures over 0 °C but also opened up a new pathway for the construction of nanofibrous cellulose materials

Synthesis, Characterization, and In Vivo Biodistribution of ¹²⁵I-Labeled Dex-<i>g</i>-PMAGGCONHTyr

Dextran graft poly (N-methacryloylglycylglycine) copolymer–tyrosine conjugates (dextran-g-PMAGGCONHTyr) were synthesized and characterized. Dynamic light scattering (DLS) results indicated that the graft copolymers are soluble in pH 7.4 PBS and 0.9% saline solutions. The graft copolymers were labeled with 125I, and the labeling stability in 0.9% saline solution was investigated. Pharmacokinetics studies showed a rapid clearance of 125I-labeled graft copolymers from the blood pool. Biodistribution images confirmed the preferable liver and spleen accumulation within 1 h after injection and rapid clearance from all the organs over time. The graft copolymer with molecular weight of 9.8 kDa was eliminated from the kidney significantly faster than those with higher molecular weight. The effect of the numbers of −COOH groups on the graft copolymers on the biodistribution was also investigated. It was found that the graft copolymers with the average number of −COOH groups per glucopyranose unit (DS–COOH) of 0.57 and 0.18 are mainly distributed in liver and spleen at 1 h after injection, whereas the graft copolymer with DS–COOH of 0.07 is mainly accumulated in kidney