Abstract

ABSTRACT

Abstract

Poly(N-isopropylacrylamide)-block-poly{6-[4-(4-methylphenyl-azo) phenoxy] hexylacrylate} (PNIPAM-b-PAzoM) was synthesized by successive reversible addition-fragmentation chain transfer (RAFT) polymerization. In H₂O/THF mixture, amphiphilic PNIPAM-b-PAzoM self-assembles into giant micro-vesicles. Upon irradiation of light at 365 nm, fusion of the vesicles was observed directly under an optical microscope. The real-time fusion process is presented and the derivation is preliminarily due to the perturbation by the photoinduced trans-to-cis isomerization of azobenzene units in the vesicles.

A new synthetic approach to prepare Ag nanoparticles protected side-chain liquid crystalline (LC) azobenzene polymers was reported. It is based on the reduction of silver ions in presence of a LC polymer polymerized by RAFT. The formation of Ag colloidal nanoparticles was confirmed by TEM and UV analysis. At the same time, according to the results of DSC, XPS, and FTIR spectra, Ag nanoparticles were protected by the side-chain LC azobenzene polymers through surface attachment interactions between thiol groups and Ag. The out-plane orientation of side-chain LC is confirmed by surface-enhanced Raman spectra analysis and scanning near-field optical microscope, resulting from the large electromagnetic field arising from the excitation of surface plasmon polariton of Ag nanoparticles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5380–5386, 2007

Side-chain azobenzene-containing liquid crystalline polymer (ALCP) of Poly(6-[4-(4-cyanophenylazo)phenoxy] x-methylene methacrylate)(Px, x is 2 or 6) was synthesized and used to study its photoinduced alignment behavior irradiated by a linearly polarized laser at room temperature. The relationships between transmittance and irradiation time as well as transmittance and various incident angles were studied in detail. The oversaturation phenomenon of P₂ film was found to be higher than 1 mW/cm² under irradiation energy density. A model of the biaxial orientation was introduced to explain the phenomenon: it is the rigid short spacer that makes it possible for mesogen to coexist in a way of out-of-plane and in-plane orientation (biaxial orientation), in which the type of photoinduced motions is a single mesogen motion in the film of P₂, whereas in the film of P₆ with longer spacer, the motion is a microdomain motion. The whole domain motion restricted the out-of-plane orientation, which shows a slow orientation rate and all mesogens aligned within the film plane. A novel dynamic fitting was also presented to describe the orientation of P₂, which was discussed in terms of the fitting parameters. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1378–1384, 2006

A series of optically active methacrylic homopolymers, poly[(4-{4′-[(S)-2-methyl-1-butyloxycarbonyl]phenylazo}phenoxyl)x-methylene methacrylate] (x = 0, 2, 6, or 11), were synthesized. The structures of the polymers were characterized by IR, ¹H NMR, UV, differential scanning calorimetry, and gel permeation chromatography. The chiroptical properties of the polymers in films were investigated with circular dichroism (CD) measurements. The CD and UV spectra of the films suggested that CD absorptions occurred in the films of the polymers with long spacers (x = 6 or 11) but not in the films of the polymers with short spacers (x = 0 or 2). After irradiation with linearly polarized light at 442 nm, the CD values were amplified in all the polymeric films. The amplificatory values of the CD bands in the absorption region (260–360 nm) of azobenzene chromophores suggested that the spacer length had an effect on both the transfer of chirality and photoinduced chirality in the polymeric films. The largest level of photoinduced chirality was induced in the polymer containing six methylene units. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3210–3219, 2006

A step-index polymer optical fiber (SI POF) containing Rhodamine B in poly(methyl methacrylate) (PMMA) has been fabricated by a preform technique. Fluorescence of different fiber lengths were observed and discussed. A high gain (23 dB) for a SI POF with 60-cm length, 400-μm diameter was obtained. The Rhodamine B content of the doped SI POF is 5 ppm-wt. The signal wavelength providing the highest gain for a 60 cm SI POF is around 630 nm, and the optimum fiber length is about 60 cm at 10 kW launched pump power. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 681–685, 2004

Emulsifier-free emulsion polymerization was adopted to synthesize rare earth containing submicron polymer particles under microwave irradiation. To control the size and distribution of the particle, the relationship between reaction time, monomer content, and particle radius was studied for the polymerization of methyl methacrylate (MMA) in the absence and presence of rare earth ions, in which water was used as solvent, and potassium persulfate was used as initiator. In the latter polymerization, the solution of MMA and europium octanoate (EOA) was used instead of MMA itself as EOA can be dissolved in MMA within certain concentrations, and the result shows that the polymerization process is affected by existence of EOA except when the amount of MMA is 2 ml. For particles containing rare earth ions, characterization shows that mole percentage of Eu(III) ion in the surface layer with a thickness of 5 nm, which is estimated from X-ray photo electron spectroscopy (XPS), is always larger than the value estimated by inductively coupled plasma atomic emission spectrometer (ICP-AES) for the whole particle, indicating that surface enrichment of rare earth ions took place during the polymerization. Further characterization by XPS depth measurement after Ar⁺ sputtering shows the same result. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1124–1131, 2003

A theoretical model has been established to describe the dynamic temperature distribution during the alignment of an azobenzene liquid crystalline polymer irradiated by a linearly polarized laser beam. The dynamic heat diffusion equations are used, and the relationship between heat source item and time is introduced, based on experimental results. With the model, the contours of the temperature distribution at different time have been worked out. It can be found from the theoretical model that there is a maximum temperature rise during the photo-induced alignment, which is coincident with the analysis of experimental observations. The existence of a minimum laser power and an offset photo-alignment temperature T_off required to carry on photo-induce alignment are explained based on the theoretical model.

A new model is established to infer a ratio of multipleted ions to the total ions (ρ) based on rate equations of ionic transferring between excited and unexcited states, which is designed for rare earth containing polymer optical fiber (POF) with low ion concentration ranging from 30 to 200 ppm. A step-index (SI) Nd³⁺-doped POF was made from a preform which was prepared by using bulk polymerization of methyl methacrylate (MMA) with a certain amount of neodymium octanoate (NOA) as a dopant, 2,2-azoisobutyronitrile (AIBN) as an initiator, and n-butyl mercaptan as a chain-transfer agent. The measurement of transmission at 810 nm of the Nd³⁺-doped POF was made by fitting experimental data and by using the theoretical model, the values of ρ at different Nd³⁺ concentration could be obtained. The result showed that the ratio is 0.03, 0.08, and 0.3 for Nd³⁺-doped POF at Nd³⁺ concentrations of 70, 100, and 200 ppm, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2033–2040, 2002