The study focuses on the characterization of the superparamagnetic microspheres of poly(methyl methacrylate) (PMMA) prepared by the modified suspension polymerization. The nano-sized oleic acid-coated magnetite particles (OMP) mixed with methyl methacrylate (MMA) monomers and divinylbenzene were employed to produce the nonporous superparamagnetic PMMA microspheres. The morphology, composition and magnetic properties of the magnetic PMMA microspheres were characterized with the scanning electron microscopy, particle size analyzer, transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, and superconductor quantum interference device. As a result, the obtained PMMA microspheres had the average particle size of 1.8-6.8 lm and magnetite content of 4.74-10.85 wt %. The corresponding saturation magnetization of the PMMA microspheres was in the range of 2.04-8.51 emu/g. The diameter of the PMMA microspheres showing the polydispersity significantly decreased with the higher weight ratio of OMP to MMA. On the contrary, the magnetite content and saturation magnetization of the PMMA microspheres would increase with the higher weight ratio of OMP to MMA. Furthermore, the distinct relationships between the characteristics of magnetic PMMA microspheres and the weight ratio of OMP to MMA have been proposed. The magnetic PMMA microspheres show the good stability in the solution with the pH region of 2.1-12.9.
Kydroxyl-terminated liquid crystalline bis[4-(5-hydroxypentyloxycarbonyl)phenylene] terephthalate (BHT) was prepared and compared with its non-hydroxylated analog, bis [ 4-( pentyloxycarbonyl)phenyIene] terephthalate (BPT). BHT, with the possibility to form intermolecular hydrogen bonding (H-bonding), has higher thermal transition temperatures (T, and 7;) than BPT. Infrared spectroscopy was applied to prove the existence of H-bonding for BHT. An X-ray diffraction study suggests that the smectic A (S,) phase is the only phase existing for BPT but for BHT, an interdigitated layered structure was found to be mixed with the SA phase. The formation of this interdigitated layered structure is mainly due to the intermolecular H-bonding between the terminal hydroxyl and the external ester groups in BHT.
A novel and general kinetic rate equation combining ultraviolet-induced (UV-induced) curing and thermal curing was successfully derived from the conventional thermal-kinetic rate equation. This proposed novel kinetic rate equation can be applicable to the curing system either simultaneously or individually by UV-induced and thermal cure methods. This general kinetic rate equation is composed of the reaction order n, activation energy E a , curing temperature T, energy barrier of photoinitiation E Q , intensity of UV radiation Q, concentration of photoinitiator [I], and a few other parameters. The proposed equation was supported by experimental data based on the curing systems of 4,4 0 -bismaleimidodiphenylmethane (BMI) and 2,2-bis(4-(4 maleimido phenoxy) phenyl propane (BMIP). The BMI and BMIP systems were isothermally cured at various temperatures, or simultaneously cured with varying intensity of UV radiation (wavelength 365 nm). Conversion levels for the various cured samples were subsequently measured with a FTIR spectrometer. The reaction order n ¼ 1.2, activation energy E a ¼ 40,800 J/mol, and E Q ¼ 7.5 mW/cm 2 were obtained for curing BMI system. The reaction order n ¼ 1.3, activation energy E a ¼ 53,000 J/mol, and E Q ¼ 9.1 mW/cm 2 were obtained for curing BMIP system. The values of n and E a in the same curing system (BMI or BMIP) are irrespective of the curing method (either simultaneously or individually by UV-induced and thermal cure methods). The salient results of this study show that UV radiation only enhances the initiation rate and UV ration do not influence the activation energy E a . The experimental results are reasonably well represented by these semi-empirical expressions.
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