Electrospinning of ultrafine cellulose acetate fibers: Studies of a new solvent system and deacetylation of ultrafine cellulose acetate fibers

Electrospinning of cellulose acetate (CA) in a new solvent system and the deacetylation of the resulting ultrafine CA fibers were investigated. Ultrafine CA fibers (∼2.3 μm) were successfully prepared via electrospinning of CA in a mixed solvent of acetone/water at water contents of 10–15 wt %, and more ultrafine CA fibers (0.46 μm) were produced under basic pH conditions. Ultrafine cellulose fibers were regenerated from the homogeneous deacetylation of ultrafine CA fibers in KOH/ethanol. It was very rapid and completed within 20 min. The crystal structure, thermal properties, and morphology of ultrafine CA fibers were changed according to the degree of deacetylation, finally to those of pure cellulose, but the nonwoven fibrous mat structure was maintained. The activation energy for the deacetylation of ultrafine CA fibers was 10.3 kcal/mol. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 5–11, 2004     

Preparation of antimicrobial poly(vinyl alcohol) nanofibers containing silver nanoparticles

Polyvinyl alcohol (PVA) nanofibers containing Ag nanoparticles were prepared by electrospinning PVA/silver nitrate (AgNO₃) aqueous solutions, followed by short heat treatment, and their antimicrobial activity was investigated for wound dressing applications. Since PVA is a water soluble and biocompatible polymer, it is one of the best materials for the preparation of wound dressing nanofibers. After heat treatment at 155 °C for 3 min, the PVA/AgNO₃ nanofibers became insoluble, while the Ag⁺ ions therein were reduced so as to produce a large number of Ag nanoparticles situated preferentially on their surface. The residual Ag⁺ ions were reduced by subsequent UV irradiation for 3 h. The average diameter of the Ag nanoparticles after the heat treatment was 5.9 nm and this value increased slightly to 6.3 nm after UV irradiation. It was found that most of the Ag⁺ ions were reduced by the simple heat treatment. The PVA nanofibers containing Ag nanoparticles showed very strong antimicrobial activity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2468–2474, 2006     

Preparation of Antimicrobial Ultrafine Cellulose Acetate Fibers with Silver Nanoparticles

Summary: A feasible method for the preparation of antimicrobial ultrafine fibers with silver nanoparticles was developed by direct electrospinning of a cellulose acetate (CA) solution with small amounts of silver nitrate followed by photoreduction. Silver nanoparticles in ultrafine CA fibers were stabilized by interactions with carbonyl oxygen atoms in CA. Ultrafine CA fibers with silver nanoparticles showed very strong antimicrobial activity.

TEM image of an ultrafine CA fiber electrospun from 10 wt.‐% CA solution with 0.5 wt.‐% AgNO₃.     

Fourier-domain low-coherence interferometry for differential mode delay analysis of an optical fiber

We propose a novel mode analysis and differential mode delay measurement method for an optical fiber using Fourier-domain low-coherence interferometry. A spectral interferometer based on a Mach-Zehnder interferometer setup was used with a broadband source and an optical spectrum analyzer to detect relative temporal delays between the guided modes of a few-mode optical fiber by analyzing spectral interference signals. We have shown that experimental results of the proposed method agree well with those results obtained by using a conventional time-domain measurement method. We have demonstrated that this new mode analysis technique has high sensitivity (<60 dB) and very good resolution (<1 ps/m).     

Convenient asymmetric synthesis of both enantiomers of 3,4-disubstituted 3,4-dihydro-1,4-benzoxazin-2-ones

Both enantiomers of N-substituted 3-arylated 3,4-dihydro-1,4-benzoxazin-2-ones were conveniently synthesized up to 93:7 er based on the dynamic kinetic resolution of either (R)-pantolactone- or l-mandelate-derived α-bromo arylacetates in nucleophilic substitution with N-alkylated 2-aminophenols.     

Synthesis and characterization of biodegradable poly(?-caprolactone-co-β-butyrolactone)-based polyurethane

Poly(?-caprolactone-co-β-butyrolactone) (PCLBL)-based polyurethane (PCLBL-PU) was synthesized and its tensile properties and hydrolytic degradability were investigated in an attempt to improve the degradability of poly(?-caprolactone)-based polyurethane (PCL-PU). PCLBL was synthesized by the ring-opening polymerization of ?-caprolactone (CL) and β-butyrolactone (BL) with stannous octoate as a catalyst. The introduction of a small amount of BL units significantly decreased the crystallinity of PCLBL. The crystallinity of the soft segment of PCLBL-PU also decreased with increasing BL content, and thus its hydrolytic degradation rate was dramatically increased. PCLBL-PU polymerized with PCLBL containing 5.7 mol% of BL units showed very similar tensile properties to PCL-PU, but its hydrolytic degradation rate increased by 100% at 45 °C.     

Encapsulation of nanomaterials using an intermediary layer cross‐linkable ABC triblock copolymer

For the preparation of core‐shell nanoparticles containing functional nanomaterials, a photo‐cross‐linkable amphiphilic ABC triblock copolymer, poly(ethylene glycol)‐b‐poly(2‐cinnamoyloxyethyl methacrylate)‐b‐poly(methyl methacrylate) (PEG‐PCEMA‐PMMA), was synthesized. This triblock copolymer was then used to encapsulate Au nanoparticles or pyrene. The triblock copolymer of PEG‐b‐poly(2‐hydroxyethyl methacrylate)‐b‐PMMA (PEG‐PHEMA‐PMMA) (M_n = 15,800 g/mol, M_w/M_n = 1.58) was first synthesized by activators generated by electron transfer atom transfer radical polymerization. Its middle block was then functionalized with cinnamoyl chloride. The degrees of polymerization of the PEG, PHEMA, and PMMA blocks were 45, 13, and 98, respectively. PMMA‐tethered Au nanoparticles (with an average diameter of 3.0 nm) or pyrene was successfully encapsulated within the PEG‐PCEMA‐PMMA micelles. The intermediary layers of the micelles were then cross‐linked by UV irradiation. The spherical structures of the PEG‐PCEMA‐PMMA micelles containing Au nanoparticles or pyrene were not changed by the photo‐cross‐linking process and they showed excellent colloidal stability. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4963–4970, 2009     

One‐step synthesis of block copolymers using a hydroxyl‐functionalized trithiocarbonate RAFT agent as a dual initiator for RAFT polymerization and ROP

A range of well‐defined block copolymers were synthesized using 4‐cyano‐4‐(dodecylsulfanylthiocarbonyl)sulfanylpentanol (CDP) as a dual initiator for reversible addition‐fragmentation chain transfer (RAFT) polymerization and ring‐opening polymerization (ROP) in a one‐step process. Styrene, (meth)acrylate, and acrylamide monomers were polymerized in a controlled manner for one block composed of vinyl monomers, and δ‐valerolactone (VL), ε‐caprolactone (CL), trimethylene carbonate (TMC), and L ‐lactide (LA) were used for the other block composed of cyclic monomers. Diphenyl phosphate was used as a catalyst for the ROP of VL, CL, and TMC, and 4‐dimethyamino pyridine for the ROP of LA. These catalysts did not interfere with RAFT polymerization and the synthesis of various block copolymers proceeded in a controlled manner. CDP was found to be a very useful dual initiator for a one‐step synthesis of various block copolymers by a combination of RAFT polymerization and ROP. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis and micellar characterization of thermosensitive amphiphilic poly(ε-caprolactone)-b-poly(N-vinylcaprolactam) block copolymers

Poly(ε-caprolactone)-b-poly(N-vinylcaprolactam) (PCL-b-PVCL) block copolymers were synthesized as new biocompatible, thermosensitive, amphiphilic block polymers by a combination of ring-opening polymerization and reversible addition–fragmentation chain transfer (RAFT) polymerization, and their thermosensitive micellar behavior was examined. The PCL macro-chain-transfer agent was first synthesized by converting the end group of PCL-OH to O-ethyl xanthate, which was subsequently used for the RAFT polymerization of N-vinylcaprolactam. The critical micelle concentration of PCL-b-PVCL (M _n,NMR?=?56,300?g/mol, polydispersity index?=?1.18) was 0.026?mg/mL. The mean diameter of the PCL-b-PVCL micelles determined by transmission electron microscopy was 55?±?25?nm. The PCL-b-PVCL micelles exhibited repetitive aggregation and dispersion during reversible cooling and heating cycles between 20 and 40?°C due to the thermosensitive behavior of the PVCL shell. Overall, the PCL-b-PVCL block copolymers have potential applications in thermosensitive drug delivery applications.     

Synthesis of poly(vinyl acetate)-b-poly(4-vinylpyridine) block copolymers by a combination of cobalt-mediated radical polymerization and RAFT polymerization and their use in dispersion polymerization under UV radiation

Well-defined poly(vinyl acetate)-block-poly(4-vinylpyridine) (PVAc-b-P4VP) block copolymers were synthesized for the first time by a combination of cobalt-mediated radical polymerization (CMRP) and reversible addition–fragmentation chain transfer (RAFT) polymerization, and were used to prepare PVAc-b-P4VP hairy polystyrene (PSt) particles. PVAc end-capped by a cobalt(II) acetylacetonate complex was first synthesized by the CMRP of vinyl acetate, after which the cobalt complex was modified into a dithiobenzoate group for the RAFT polymerization of 4-vinylpyridine. The hairy PSt particles were synthesized by the dispersion polymerization of St using the PVAc-b-P4VP as both a macro-initiator and a colloidal stabilizer under UV radiation. The average size of PSt particles synthesized with 20 wt.% of PVAc-b-P4VP (M _n = 39,500 g/mol) was 136 nm (CV = 19.2%). Very small Au nanoparticles were successfully immobilized on the surface of the PSt particles.