Iranian polymer journal
Volume:18 Issue: 12, 2009

Acommercial SiO2powder was treated with three different silane coupling agents,i.e., 3-aminopropyltriethoxysilane (KH-550), 3-glycidoxypropyltrimethoxysilane(KH-560), and 3-methacryloxypropyltrimethoxysilane (KH-570), respectively.The soap-free emulsion polymerization of methyl methacrylate (MMA) and hydroxyethyl methacrylate (HEMA, as stabilizing agent) was carried out in the presence of unmodified and modified SiO2particles. The polymerization rate andmonomer conversion of this system were investigated. The structure, particle size andparticle size distribution, morphology, surface tension, and ionic conductivity of theemulsion were determined by Fourier transform Infrared spectrometry (FTIR), dynamic light scattering (DLS), scanning electron microscopy (SEM), transmissionelectron microscopy (TEM), automatic interfacial tension and conductivity measurements, respectively. The results showed that silane modified SiO2particlesincreased the final monomer conversion, decreased the particle size, and narrowed theparticle size distribution of the poly(MMA-HEMA)/SiO2composite emulsion, in comparison to unmodified SiO2particles. Although, the former somewhat depressedthe polymerization rate at the early stage. The emulsion with KH-560 modified SiO2particles achieved the highest monomer conversion, the lowest coagulum, the smallestparticle size, the highest surface tension, and the maximum ionic conductively, whilethe emulsion with KH-550 modified SiO2particles produced little more coagulum. Bycompletion of polymerization process, the surface tension and ionic conductivity of theemulsion increased significantly and the aggregated SiO2powder formed the primaryparticles. SEM morphological study on the emulsion demonstrated that the shapes ofthe particles are spherical and their sizes are in agreement with those of the dynamiclight scattering measurement. TEM images confirmed that the SiO2particles have beenencapsulated inside the composite.

New formulations of microparticles for Tramadol HCl (TmH) controlled-releasewere developed and evaluated. These microparticles with controlled-release characteristics were prepared by non-solvent addition technique. Ethyl cellulose(EC) a hydrophobic polymer was employed to control and extend the drug releaseprocess. Dichloromethane (DCM) was employed as solvent for polymer and paraffin oilas non-solvent which induced phase separation. Microparticles of different polymerconcentrations M1(1:1), M2(1:2) and M3(1:3) were prepared. Among all these formulations, M3presented superior and desirable characteristics, i.e., 79% entrapment efficiency, good micromeritic properties, smooth morphology, and moresustained effect on cumulative release. Zero order, first order, Higuchi, Hixson-Crowell,and Korsmeyer-Peppas kinetic models were applied to assess the mechanism and pattern of drug release from microparticles. Release of TmH was best fitted to Higuchimodel because it presented highest values of correlation coefficient (R2= 0.981) followed by zero-order kinetic model (R2= 0.899). FTIR, XRD, and DSC analysesensured the chemical stability and integrity of TmH and EC in M3as no new bands weredetected in FTIR spectra. Moreover the XRD patterns of TmH showed its reduced crys-tallinity and endothermic peak was observed at the glass transition temperature of ECin DSC spectra. M3sample was kept at 40ºC/75% RH for three months and its stability was evaluated by determining sample''s in vitro release profile and drug assay.The effect of accelerated environment on its stability was not significant.

In this study polyacrylamide was prepared in various molar ratio contents of ethylacetate and ethanol at 60ºC by free-radical precipitated polymerization method. Theassignment of all stereosequences at pentad level of methine, hexad level of methylene, and triad level of carbonyl carbons of the polyacrylamide were observedusing 13C nuclear magnetic resonance spectroscopy (13C NMR) in deuterium oxide atroom temperature. Bernoullian and 1st-order Markov statistics were used for all carbons and the results were compared with experimental data by statistical method. Itwas shown that Bernoullian statistics model fit slightly better than 1st-order Markov statistics model for the assigned sequences. The results indicated that correspondingvalues of the probability (Pm) and length average (Nm) of meso addition were 0.443 and1.698, respectively and no significant differences were observed by changing the molarratios of the two solvents. By heteronuclear multiple quantum coherence (HMQC) astwo-dimensional NMR spectroscopy, the methylene and methine groups were assignedby triad sequences in which isotactic contour was thoroughly isolated from syndiotactic and atactic contours. Therefore, isotactic triad sequence could only be calculated by 1H NMR. In other words, isotactic placement value was calculated byusing the integration of areas of methylene and methine protons (mm = 0.21) peaks.

Aheterogenous polymeric form of N-bromosuccinimide as an efficient polymericN-halo reagent for oxidation of various types of organic compounds is introduced. Thus, cross-linked polymaleimides with different cross-linking densities were prepared from maleimide and divinylbenzene using benzoyl peroxide asan initiator by free radical polymerization reactions. The resulting cross-linked polymaleimide resin containing 7% of the cross-linking agent was chosen for further reactions. Cross-linked poly(N-bromomaleimide) (PNBM) was synthesized by thebromination of polymaleimide with bromine/potassium hydroxide, and then characterized. The capacity of PNBM was 6.4 mmol/g measured by gravimetric andiodometric methods. PNBM as a bromine-containing polymer supported reagent wasfound efficient in the oxidation of alcohols to their corresponding carbonyl compounds, synthesis of α-ketophosphonates from their α-hydroxyphosphonates, conversion of oximes to carbonyl compounds, coupling of thiols to their disulphides,and oxidation of sulphides to their sulphoxides. The reactivity of PNBM was found tobe much higher than poly(N-bromoacrylamide) or other similar structured polymers.The effect of various reaction conditions such as the temperature, organic solvent, andmolar concentration of the reagent on the efficiency of the reactions were examined inorder to find the optimum conditions for oxidation reactions. In addition, the efficiencyof PNBM was examined in water as a green solvent for oxidation of alcohols to theircorresponding carbonyl compounds. The spent polymeric reagent could be regenerated and reused for many times without appreciable loss in its efficiency. PNBMreagent offers several advantages including, high efficiency in oxidation reactions, longshelf life, elimination of hazards related to bromine containing compounds, and regeneration.

Ethylene/1-octene copolymerization over the SiO2-supported zirconocene/MMAOcatalysts was investigated. The silica support was modified by different batchesof 1.0 and 0.2 wt% Ga. It was found that Ga was well-dispersed all over the silica granules which cannot be detected by XRD. Based on the EDX measurement, itwas revealed that Ga-modification increased the adsorption ability of MMAO on the silica support after impregnation. Thus, Ga-modification showed a promising way toenhance the rate of ethylene/1-octene copolymerization. Based on TGAstudy, lowerinteractions between MMAO and support caused by Ga-modification was another reason for increase in catalytic activity. Moreover, the Ga-modification increased Lewisacid centres or active species on the catalytic system. In addition, a comparative studyof polymerization was also conducted with in situ and ex situ impregnation methods. Itwas found that the in situ impregnation method of the MMAO onto silica exhibitedremarkable (almost 3 times) activity compared to ex situ method which is attributed tolower deactivation effect of the catalyst. 13C NMR analysis, however, indicated that onlyrandom copolymers were produced in all systems. These results could be related to thehigh degree of 1-octene insertion and thus amorphous copolymers were produced inall systems.