Kuk Ro Yoon

Synthesis of monodisperse spherical silica particles with solid core and mesoporous shell: mesopore channels perpendicular to the surface

Both particle monodispersity and mesopore orientation have been considered in this work. Monodisperse spherical silica particles with a solid core and a mesoporous shell featuring mesopore channels perpendicular to the core surface were synthesized for the first time by adopting silica particles as the core component and by employing Cn-TAB (n = 12, 14, 16, 18), the structure-directing agent for the mesoporous shell. Micelles on the surface of the silica particles are formed from the electrostatic interaction between the partially negatively charged silica particles and the positively charged surfactant molecules under basic conditions. The particles synthesized in this work have a uniformly coated thin mesoporous shell of about 28–61 nm in thickness over the silica core and possess a surface area of ca. 370–500 m2 g−1, pore volume of ca. 0.2–0.35 cc g−1, and narrow pore size distribution.

Surface-initiated, ring-opening polymerization of p-dioxanone from gold and silicon oxide surfaces

A polymeric thin film of a biodegradable poly(p-dioxanone) (PPDX) was grown from flat solid surfaces by a combination of formation of self-assembled monolayers terminating in hydroxyl groups and surface-initiated, ring-opening polymerization (ROP) of p-dioxanone (PDX). Tin(II) octoate [Sn(Oct)2] was used as a catalyst, and gold and silicon oxide surfaces were chosen as model surfaces. A molecularly-ordered film (self-assembled monolayer, SAM) was formed by immersing gold and silicon oxide substrates in a solution of alkanethiolates and in a solution of triethoxysilanes, respectively. The polymerization was achieved by heating a mixture of Sn(Oct)2, PDX, and the SAM-coated substrate in anhydrous toluene for 24 h at 55 °C (for a gold substrate) or 70 °C (for a silicon oxide substrate). The characteristic IR peaks of PPDX (C–H stretching at ∼2923 cm−1 and the CO ester at ∼1748 cm−1) were observed in polarized infrared external reflectance spectroscopy (PIERS) spectra, indicating the presence of a PPDX film on the gold and silicon oxide surfaces. The average thickness of the PPDX film was measured to be 90 nm on the gold substrate and 46 nm on the silicon oxide substrate by ellipsometry. The PPDX films were further characterized by X-ray photoelectron spectroscopy (XPS), contact angle measurement, and atomic force microscopy (AFM).

Formation of carbon nanotube/glucose-carrying polymer hybrids by surface-initiated, atom transfer radical polymerization

ConclusionsIn conclusion, we demonstrated that SI-ATRP could be utilized for generating CNT/glycopolymer hybrid nanocomposites. As a proof-of-concept, we grafted MAIpGlc, a monomer that carries protected glucose ring, onto s-MWCNTs. After coating s-MWCNTs with pMAIpGlc, the MAIpGlc moiety was deprotected to extrude the glucose group onto the surface of s-MWCNTs. LAMA (and its derivatives) would have advantages over MAIpGlc, because various monosaccharides and a sequence of saccharides could be incorporated into the polymer backbone and polymerization does not need protection/deprotection steps. Considering the biological importance of polysaccharides, the method described herein would be beneficial in many areas, such as pathogen detection and biosensors.

Patterning Si by using surface functionalization and microcontact printing with a polymeric ink

This paper describes a simple procedure for patterning Si substrate using a combination of surface functionalization and microcontact printing(ΜCP). The Si/SiO2 surfaces were chemically modified to present self-assembled monolayers (SAMs) of siloxanes terminating in reactive carboxylic anhydride groups and then patterned with poly(ethylene imine) (PEI) by, ΜCP We used the patterned thin films of PEI as etch resists on Si surfaces.

Surface-initiated atom-transfer radical polymerization of 3-O-methacryloyl-1,2:5,6-di- O-isopropylidene-α- D-glucofuranoside onto gold surface

A sugar-containing polymer was grown on gold surface by surface-initiated atom-transfer radical polymerization (SI-ATRP) of methacrylate monomer, 3-O-methacryloyl-1,2:5,6-di-O-isopropylidene-alpha-D-glucofuranoside (MAIpGIc), using 1,4,8,11-tetraaza-1,4,8,11-tetramethylcyclotetradecane (Me(4)Cyclam) as ligand, 2-bromopropionyl moiety attached on the gold surface as initiator, and Copper(I) bromide as catalyst, respectively, in tetrahydrofuran (THF) medium. The resultant sugar film was characterized by polarized infrared external reflectance spectroscopy (PIERS), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), ellipsometry, and contact angle goniometry. The IR peaks characteristics of poly(3-O-methacryloyl-alpha,beta-D-glucopyranoside) (PMAGlc), broad O--H stretch at approximately 3400 cm(-1), and C==O ester stretch at approximately 1748 cm(-1) observed in PIERS spectra demonstrate the formation of PMAGlc on the gold surface. The AFM and SEM images show the polymer growth away from the gold surface without visible domain boundaries, and it further confirms the formation of sugar coating. The method described in the article would be beneficial in many areas, such as pathogen detection and biosensors, considering the biological importance of carbohydrate polymers.

Mono- and Multi-layer Langmuir-Blodgett Films of Maleimide Polymers Possessing Nonlinear Optical-Active Side Chains

A copolymer P[OSA-MI] was synthesized by copolymerization of its corresponding monomers,N-phenyl maleimide (MI) and 2-octen-1-ylsuccinic anhydride (OSA). The polymer (poly[2-[1-(2,5-dioxo-1-phenylpyrrolidin-3-ylmethyl)heptyl]-succinic acid 4-(2-{ethyl-[4-(4-nitrophen-ylazo) phenyl]amino}ethyl) ester]) P[DR1MA-MI] was obtained from the reaction of P[OSA-MI] with 2-[4-(4-nitrophenylazo)-N-ethylphenylamino] ethanol (DR1). A stable monolayer of P[DR1MA-MI] was formed by spreading the solution of the polymer in chloroform. In Y-type Langmuir-Blodgett (LB) films prepared using this Langmuir-Blodgett method, the second harmonic waves generated from adjacent monolayers canceled each other out. In X- and Z-type LB films, the second harmonic intensity increased upon increasing the number of monolayers, but this increase was somewhat smaller than predicted by the square law. This phenomenon is due to defects or imperfect alignment of the dipoles in the LB film. The generation of second harmonic waves from Y-type LB films having an even number of monolayers supports this argument. The degree of imperfection seemed to increase as the number of layers increased. The second-order nonlinear optical properties of spin-cast films of these polymers were also measured. The largest second harmonic coefficient of the poled P[DR1MA-MI] film coated on a glass plate was 19 pm/V.

Synthesis of Symmetric Liquid Crystal Dimers Based on Azo and Imine Groups and Investigation of Phase Behaviour by Varying Alkoxy Terminal Chain Length

With the objective to study the effect of alkoxy terminal chain length on mesomorphic properties of liquid crystals, we have synthesized two (Azo and Imine) different series of dimesogens by varying terminal alkoxy chain length (n = 6–12) with a short spacer unit in between two mesogens. Transition temperatures and phase characterization were studied by DSC, POM and XRD analysis. It was found that all the dimers show mesomorphic properties and the change in terminal alkoxy chain length has pronounced effect on the smectic phase window. In the DSC cooling scan, the smectic phase window of azo compounds increased from 6.4°C (2A6) to 16.0°C(2A12), whereas in Schiff base compounds, it increased from 9.2°C (2S6) to 31.0°C(2S12). Further, the 2A11 dimer was found to undergo photo induced configurational changes.

Graft polymerization of p-dioxanone onto polyhydroxyethylaspartamide through ring-opening polymerization using organometallic and enzyme catalysts

The grafting of poly(p-dioxanaone) (PPDO) onto β-poly(N-2-hydroxyethyl)-DL-aspartamide (PHEA) was achieved, first, by synthesis of polysuccinimide (PSI) from DL-aspartic acid through thermal condensation polymerization, and then, followed by aminolysis of PSI to form PHEA with hydroxyl end groups, and finally the PPDO was grafted onto PHEA through these hydroxyl end groups by ring-opening polymerization (ROP) of PDO in the presence of tin octoate [Sn(Oct)2] and Candida Antarctica Lipase B (Novozyme 435) catalysts. Evidence of grafting was obtained by comparing Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD) analysis, polarized optical microscopy (POM), proton nuclear magnetic resonance (1H–NMR) spectroscopy, and solubility characteristics of PHEA with PPDO-grafted copolymers (PHEA-g-PPDO). The FT-IR spectroscopic analysis reveals the formation of ester linkage between PPDO and hydroxyl end groups of PHEA. TGA analysis shows a quite different thermal profile for grafted polymers. DSC and XRD results reveal the existence of graft copolymer in two different crystalline forms. POM shows banded spherulitic morphology for the graft copolymers. The grafting of PPDO was further confirmed by 1H–NMR. Eventhough, graft copolymer was obtained by both these methods, the graft copolymer obtained by enzyme catalyzed ROP shows higher crystalline order, better spherulitic morphology, and solubility characteristics than that of the graft polymer obtained by organometal catalyzed ROP.

Polycondensation of Sebacic Acid with Primary and Secondary Hydroxyl Groups Containing Diols Catalyzed by Candida antarctica Lipase B

Abstract The aliphatic polyesters are normally synthesized by ester interchange reactions or direct esterification of hydroxyacids or diacid/diol combinations. Biotransformation, utilizing the enzymes as catalysts, was accepted as an alternative route for the synthesis of aliphatic polyesters and offers various advantages compared with the conventional, metal-catalyzed polymerization reactions. Previous studies indicated that lipase-catalyzed polycondensation reactions between diols and diacids occurred preferentially at primary hydroxyl groups of diols, when diols contained both primary and secondary hydroxyl groups. In this work, we investigated lipase-catalyzed polycondensation of diacids and secondary hydroxyl group–containing diols, and successfully synthesized polyesters by polycondensation with secondary hydroxyl groups as well as primary hydroxyl groups. Various diols, glycerol, 1,2-propanediol, 1,3-butanediol, 2,3-butanediol, and 2,4-pentanediol were tested for the polycondensation. The polymerization was achieved by heating a mixture of lipase B, sebacic acid, and the diols in anhydrous toluene at 100 °C for 72 h. The resulting polymers were characterized by 1H and 13C NMR spectroscopy, Fourier transform–infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography. GRAPHICAL ABSTRACT

Construction of protein-resistant pOEGMA films by helicon plasma-enhanced chemical vapor deposition.

This paper describes the formation of protein-resistant, poly(ethylene glycol) methyl ether methacrylate (pOEGMA) thin films by helicon plasma-enhanced chemical vapor deposition (helicon-PECVD). pOEGMA was successfully grafted onto a silicon substrate, as a model substrate, without any additional surface initiators, by plasma polymerization of OEGMA. The resulting pOEGMA films were characterized by ellipsometry, FT-IR spectroscopy, X-ray photoelectron spectroscopy and contact angle goniometry. To investigate the protein-resistant property of the pOEGMA films, four different proteins, bovine serum albumin, fibrinogen, lysozyme and ribonuclease A, were tested as model proteins for ellipsometric measurements. The ellipsometric thickness change for all the model proteins was less than 3 Å, indicating that the formed pOEGMA films are protein-resistant.