Youn-Sik Lee

Degradable polyurethanes containing poly(butylene succinate) and poly(ethylene glycol)

Abstract Biodegradable polyurethanes may be used in the fabrication of plastic films which can replace common films prepared from nondegradable polymers such as polyethylene and polypropylene. Prepolymers were synthesized from poly(butylene succinate) polyol (PBS, M n 1650), poly(ethylene glycol) (PEG, M n 1000), and 4,4′-dicyclohexylmethane diisocyanate, and reacted with 1,4-butanediol chain extender to obtain polyurethanes. Their number-average molecular weights and melting temperatures are in the range of 30,000–38,000 and 99–101°C, respectively. The tensile strengths (2.0–2.4 kg/mm 2 ) of the polymers were somewhat greater than the reported value (1.6 kg/mm 2 ) of PBS with a comparable molecular weight ( M n 20,000). However, their elongations at break (230–330%) were significantly greater than that of the PBS (42%). They were hydrolytically degradaded very rapidly in 3% NaOH solutions at 37°C such that their weight loss was approximately 30–60% within 2 days, depending on the content of PEG and hard segment. On the other hand, polyurethanes containing only PBS as soft segments showed a much slower degradation rate under the identical conditions.

Studies on metal-containing copolyurethanes

Metal-containing copolyurethanes having ionic linkages in the main chain were synthesized by the polyaddition reaction of hexamethylene diisocyanate (HMDI) or toluene 2,4-diisocyanate (TDI) with 1:1 mixtures of divalent metal salts of mono(hydroxypentyl)phthalate, [M(HPP)]2 (where M=Ca2+, Cd2+, Pb2+ and Zn2+), and diethylene glycol (DG) by using di-n-butyltin dilaurate (DBTDL) as catalyst. The prepared coployurethanes were characterized by FT-IR, 1H-NMR, 13C-NMR, elemental analysis, solubility, viscosity and X-ray diffraction studies. Thermal properties of the polymers were also studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The antibacterial activity of these polymers has also been investigated by agar diffusion method.

Mechanistic Study and Characterization of 3C-SiC(100) Grown on Si(100)

Single crystal cubic SiC(100) thin films were grown on Si(100) from thermal cracking of tetramethylsilane (TMS) as a function of growth temperature reactor pressure, source gas flow rate, and Si/C atomic ratio in a radio frequency-inductive chemical vapor deposition reactor. The orientation of as-grown SiC films mostly followed that of the Si substrate. However, the growth of SiC( 111) was detected in the films grown at high TMS flow rates and high Si/C atomic ratios. The thickness of the SiC film was increased with the growth temperature, reactor pressure, TMS flow rate, and Si/C atomic ratio. Voids were formed in the silicon side of the SiC/Si interface, hut disappeared when the reactor pressure TMS flow rate, and Si/C ratio were increased. The formation of voids was attributed to the outdiffusion of Si atoms from the Si substrate. The stresses and strains generated in the grown films were also investigated in terms of the growth conditions. The formation mechanism of voids at the SiC/Si interface was discussed on the basis of the experimental observations.

Introduction of next-generation 3D AFM for advanced process control

To fulfil advanced process control requirements for 1X node production, the semiconductor industry must cope with multiple parallel metrology requirements such as resolution, precision and accuracy enhancement in all directions to answer to new 3D integrated circuit fabrication methods. At the 1D and 2D levels, CDSEM and Scatterometry techniques are the workhorse techniques for production and process control. However, for process control of 3D devices and high resolution patterning such as direct self-assembly lithography, reference metrology is necessary to maintain a global process control uncertainty that is sufficient for production standards. CD-SEM and Scatterometry have intrinsic limitations that limit their utility for these cases, and new characterization methods are needed. Among the industrial reference techniques currently available, TEM and CD-AFM are generally employed to address this issues but both of these techniques have their own limitations for 1X node production. Nevertheless, they are also very useful for engineers to calibrate production CD metrology techniques and for more accurate process window and process development definition at the R&D level. Thus, there is a critical need to develop new technologies that build upon these capabilities while overcoming the limitations.

A new polymer containing confined phenylenevinylene segments: synthesis and photoluminescence

Abstract Poly[bis(4,6-di- tert -butyl-1,2-phenylene-1,2-ethenylene)-1,4-phenylene-4,4′-ethylenebis(11-oxyundecanylphenyl urethane)] (PV-PU) consisting of alternating a confined phenylenevinylene segment and a nonconjugated urethane segment in the main chain was synthesized. Photoluminescence (PL) of PV-PU is emitted in the blue region with a maximum intensity at about 440 nm. PV-PU blended with 2-(4-biphenylyl)-5-(4- tert -butylphenyl)-1,3,4-oxadiazole (PBD)–polystyrene (1:2, wt/wt) in weight ratio of 1:10 and 1:15 also show PL spectra similar to that of pure PV-PU but with enhanced intensity, suggesting that the photo-excited PBD donor transfers its energy to PV-PU in the ground state and subsequently the excited PV-PU acceptor emits the blue light.

Synthesis of 4-vinylpyridine–divinylbenzene copolymer adsorbents for microwave-assisted desorption of benzene

Reports on the development of polymer adsorbents for microwave-assisted desorption of nonpolar volatile organic compounds (VOCs) are rare. In this study, we synthesized macroporous polymeric adsorbents with hydrophilic methyl pyridinium units for microwave-assisted desorption of nonpolar VOCs. The benzene adsorption and desorption properties of the adsorbents were investigated under both dry and humid conditions. Under humid conditions, as the content of the hydrophilic methyl pyridinium units in the adsorbents increased from 0 to 20%, the adsorption capacity of benzene decreased from about 21 to 7 mg/g, while the desorption efficiency of benzene increased significantly from 48 to 87%. The maximum concentration of desorbate also increased significantly as the content of the hydrophilic units was increased under humid conditions. We attributed the enhanced desorption efficiency mainly to more adsorbed moisture, which indirectly allowed heating of the polymer adsorbents to higher temperatures upon irradiation with 600 W microwaves.

Carbazole-thieno[3,4-b]thiophene polymers: Synthesis and photovoltaic applications

AbstractTwo novel conjugated polymers consisting of alternating thieno[3,4-b]thiophene and either carbazole (PCTT1) or carbazole with two thiophene spacers (PCTT2) were synthesized. PCTT1 (Mn 44,000) showed a bandgap of 2.14 eV but a significantly deep highest occupied molecular orbital level of -5.52 eV. PCTT1-based photovoltaic devices showed promising power conversion efficiency of 2.53% under AM 1.5 G illumination at 100 mW/cm2.

Inductively Coupled Plasma Etching of Doped GaN Films with Cl2 / Ar Discharges

The inductively coupled plasma etching of undoped n- and p-type GaN films was carried out with Cl 2 /Ar discharges using different radio frequencies of 100 kHz and 13.56 MHz, in which the chuck power source operates. The etch rates with lower frequency of 100 kHz were greater than those with higher frequency of 13.56 MHz due to higher ion bombarding energy. The etch rates of the GaN films with 100 kHz frequency increased substantially with increasing pressure, while the etch rates with 13.56 MHz increased up to 20 mTorr and then decreased at higher pressures. The n-GaN showed somewhat faster etch rates than undoped and p-type GaN films. The surface of the etched GaN films showed quite smooth morphology, and the n-GaN showed some depletion of nitrogen from the etched surface.

Preparation of Tunable Emissive Poly(ethylene oxide) Nanofibers by Doping with TPP and DCM

AbstractPoly(ethylene oxide) (PEO) nanofibers that were doubly-doped with a donor, 1,3,5-triphenyl-2-pyrzoline (TPP), and an acceptor, 4-(dicyanomethylene)-2-methyl-6-(p-dimethyl-aminostyryl)-4H-pyran (DCM), were prepared by electrospinning to be 200–300 nm in diameter. Fluorescence from DCM was caused by non-radiative Forster-type fluorescence resonance energy transfer from photo-excited TPP to DCM. The color of the fluorescence from the PEO-TPP/DCM nanofibers was controllable through variation of the TPP:DCM molar ratio and ranged from blue to orange to white.

PREPARATION OF MEROCYANINE SALTS BY TREATMENT OF ACIDS ON SPIROPYRANS AND INVESTIGATION ON THEIR PHOTOCHROMIC BEHAVIORS

Merocyanine salts were prepared and their photochromic behavior investigated. The salts were prepared from a solution of spiropyrans in the presence of acids such as toluenesulfonic acid and dodecylbenzene sulfonic acid under irradiation of UV light and heat. The 1H NMR spectrum confirmed the chemical structure of the merocyanine salts. The salt showed an absorption peak at 422 nm, which was blue-shifted as compared with the absorption peak at 578 nm of the merocyanine form of spiropyran. The salt form was quite stable and virtually exhibited a negative photochromism. The salt showed better fatigue resistance than the spiropyran. The photoinduced refractive index change for the salt films by a prism coupler method was estimated to be as large as 0.0055.