Ultrathin, Biomimetic, Superhydrophilic Layers of Cross-Linked Poly(phosphobetaine) on Polyethylene by Photografting

Ultrathin, biomimetic, superhydrophilic hydrogel layers, composed of cross-linked poly­(2-methacryloyloxyethyl phosphorylcholine), are formed on low-density polyethylene films via ultraviolet-initiated surface graft polymerization. The layers are 19–58 nm thick as revealed by electron microscopy and have three-dimensional networks; the unique network structure, along with its zwitterionic nature, rather than surface roughness results in superhydrophilicity, that is, the water contact angle around 5°. This superhydrophilicity depends on a variety of factors, including the concentration of the monomer and cross-linker, the type of reaction solvents, the reaction and drying time, the intensity of UV light, and the way of measurement of water contact angles. Superhydrophilicity is obtained under a fixed ratio (e.g., 1/1) of the monomer to cross-linker, a reaction time over 120 s, a short drying time, (75%) ethanol as the reaction solvent, and low-intensity UV light, largely because these factors together generate optimal three-dimensional networks of cross-links

Effects of Poly(vinyl butyral) as a Macromolecular Nucleating Agent on the Nonisothermal Crystallization and Mechanical Properties of Biodegradable Poly(butylene succinate)

To improve the crystallization and mechanical properties of poly­(butylene succinate) (PBS), a series of poly­(vinyl butyral) (PVBs) with various degrees of polymerization, have been synthesized as macromolecular nucleating agents. Nonisothermal crystallization kinetics of PBS nucleated by the PVBs has been examined via polarized optical microscopy and differential scanning calorimetry, followed by detailed analysis with theoretical models. The PVBs are found to significantly increase the number of spherulites and crystallization temperatures by 11 °C, and to reduce the spherulite size from 80 to 3 μm and the activation energy from 133 to 53 kJ/mol. Only Avrami and Tobin’s models are capable of well characterizing the crystallization kinetics. The effects of the PVBs depend on their concentration and the degree of polymerization, coupled with their miscibility/immiscibility with PBS. Meanwhile, the nucleated PBS exhibits a significant enhancement in mechanical properties: 69% in Young’s modulus, 26% in tensile strength, and 14% in impact strength

Effects of Polyoxymethylene as a Polymeric Nucleating Agent on the Isothermal Crystallization and Visible Transmittance of Poly(lactic acid)

In this work, use of polyoxymethylene (POM) as a polymeric nucleating agent for poly­(lactic acid) (PLA) was studied. The compounding was performed using a twin-screw extruder. Effects of POM on isothermal crystallization of PLA at temperatures ranging from 106 °C to 111 °C and visible transmittance of PLA were examined in detail with various techniques, including polarized optical microscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD), and ultraviolet–visible (UV-vis) spectroscopy. Banded spherulites were noted when the POM content exceeded 5 wt %. The presence of POM generally resulted in effective reductions in the half time of crystallization and the spherulite size of PLA. However, 1% POM was a threshold for the nucleating effect: at ≤1% POM, no nucleating effect was observed. Fourier transform infrared (FTIR) spectroscopy revealed the strong interaction between the two polymers. The Avrami modeling suggested a three-dimensional crystal growth at all temperatures and loading levels of POM. Although POM does not accelerate the crystallization of PLA as fast as some of the inorganic nucleating agents such as talc, it imparts PLA the nucleating effect without sacrificing transparency

Role of Molecular Chemistry of Degradable pHEMA Hydrogels in Three-Dimensional Biomimetic Mineralization

Three-dimensional (3D) biomimetic mineralization is highly desired for soft biomaterials such as collagen to create useful hybrid biomaterials for orthopedic tissue engineering. Here, we apply an approach of current-mediated ion diffusion, as a feasible means of 3D biomimetic mineralization, to a series of generic, hydrolytically degradable poly­(2-hydroxyethyl methacrylate) hydrogels with various molecular structures, imparted by the introduction of the comonomers, acrylic acid and 2-hydroxyethyl methacrylamide. This approach enables us to create a wide range of nanoscale single crystals of calcium phosphate within the hydrogels as characterized by high-resolution transmission electron microscopy (TEM). Molecular chemistry of the hydrogels, coupled with pH and gel strength, plays a crucial role in formation of the minerals. Both brushite (CaHPO₄·2H₂O) and octacalcium phosphate (Ca₈H₂(PO₄)₆·5H₂O) are observed in pHEMA homo hydrogel. Both octacalcium phosphate and monetite (CaHPO₄) are seen in a copolymer hydrogel, poly­(2-hydrogelethyl methacrylate-co-acrylic acid). In another copolymer hydrogel (poly­(2-hydroxyethyl methacrylate-co-2-hydroxyethyl methacrylamide), both hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) and monetite (CaHPO₄) are observed. All these nanocrystals are essential to bone regeneration. They organize themselves primarily as nanoscale fibers, sheets, needles, and clusters. These nanoarchitectures are important to bone-cell attachment, proliferation, migration, and differentiation, and dictate the ingrowth of new bone tissues

A Turn-On Fluorescent Probe for Detection of Sub-ppm Levels of a Sulfur Mustard Simulant with High Selectivity

A new type of fluorescent probe capable of detecting a sulfur mustard (SM) simultant at a concentration of 1.2 μM in solution and 0.5 ppm in the gas phase has been developed. Owing to its molecular structure with a thiocarbonyl component and two piperidyl moieties integrated into the xanthene molecular skeleton, this probe underwent a highly selective nucleophilic reaction with the SM simultant and generated a thiopyronin derivative emitting intensive pink fluorescence. The distinct difference in electronic structure between the probe and thiopyronin derivative generated a marked shift of the absorption band from 445 to 567 nm, which enabled an optimal wavelength propitious for exciting the thiopyronin derivative but adverse to the probe. Such efficient separation of the excitation wavelength and tremendous increase in fluorescence quantum yield, from less than 0.002 to 0.53, upon conversion from the probe to the thiopyronin derivative, jointly led to a distinct contrast in the beaconing fluorescence signal (up to 850-fold) and therefore the unprecedented sensitivity for detecting SM species