Stabilizer Molecular Weight Research Articles

현탁중합을 이용한 레졸형 구형 페놀입자의 합성

암모니아수 또는 트리에틸아민(TEA)을 촉매로 사용하여 페놀과 포름알데히드로부터 구형 페놀수지를 페놀:포름알데히드=1:1~1:4의 몰 비로 <TEX>$98^{\circ}C$</TEX>에서 현탁중합을 통해 합성하였고, 이를 <TEX>$700^{\circ}C$</TEX>의 질소 환경에서 탄화시켜 구형 탄소입자를 형성하였다. 현탁중합으로 형성된 구형 페놀수지의 열적 특성으로부터 후경화가 필요함을 확인하였다. 현탁중합의 최적조건을 결정하기 위하여 페놀/포름알데히드(P/F)의 몰 비, 촉매의 pH, 안정제의 분자량이 구형 페놀입자의 크기와 수율에 미치는 영향을 나머지 변수를 고정시킨 상태에서 조사하였다. P/F 몰 비에 따라 형성되는 입자 크기는 증가하는 반면 수득율은 감소하는 것을 확인하였고, 촉매의 pH가 클수록 큰 입자가 형성되며, 또한 안정제의 분자량은 입도분포보다는 수득율에 더 큰 영향을 미치는 것을 확인하였다. 또한 후경화를 거쳐 얻어진 구형 페놀수지의 열안정성을 TGA를 통하여 조사하였으며, P/F 몰 비가 높은 경우는 dibenzyl ether의 존재로 인하여 후경화 이후에도 <TEX>$220^{\circ}C$</TEX>의 중량감소가 여전히 존재하며, 반면에 P/F 몰 비가 낮은 경우는 <TEX>$220^{\circ}C$</TEX> 이후 <TEX>$400^{\circ}C$</TEX>에 걸쳐 꾸준한 중량감소가 일어나는 것으로부터 P/F 몰 비가 1:2인 경우가 열안정성이 가장 우수함을 확인하였다. The phenolic beads in macrosize range were obtained by suspension polymerization at <TEX>$98^{\circ}C$</TEX> from phenol and formaldehyde in the presence of basic catalyst with a phenol to formaldehyde (P/F) range of 1:1~1:4, and they were carbonized to spherical carbon beads under nitrogen at <TEX>$700^{\circ}C$</TEX>. Thermal analysis on spherical phenolic beads obtained by suspension polymerization showed that the postcuring process is essential. In order to optimize the suspension polymerization, the effects of the P/F molar ratio, the pH of catalyst, and the molecular weight of stabilizer on the size distribution and yield of spherical phenol beads were examined separatively. The particle size was increased whereas the yield was decreased with P/F molar ratio. The increasing basicity of catalyst made the particle size to increase, while the molecular weight of stabilizer had more effect on the yield rather than on the particle size distribution. The thermal stability of the spherical phenolic beads obtained through postcure was also examined by TGA. The phenol beads of high P/F ratio still showed the weight loss at <TEX>$220^{\circ}C$</TEX> even after postcure due to the high possibility of dibenzyl ether, while those of low P/F ratio showed the steady decrease in weight during <TEX>$220^{\circ}C$</TEX> to <TEX>$400^{\circ}C$</TEX>, which showed that the optimal P/F ratio was 1:2.

The Micromorphology of Anionic Polyacrylamide Dispersions

Anionic polyacrylamide dispersions were prepared by dispersion polymerization in aqueous salt solutions. The effects of reaction conditions, such as salt concentration, molecular weight of stabilizers, on the micromorphology of the dispersions were investigated systematically by using biological photomicroscope. The results showed that the particle shape in stable dispersions were more regular, basically spherical or ellipsoidal. Stable anionic polyacrylamide dispersions could be obtained on condition that salt concentration was between 26%~30%, molecular weight of stabilizers between 1.760×106~2.317×106 g•mol-1.

Dispersion Polymerization of Acrylamide and Acrylic Acid in Aqueous Media

Dispersion polymerization of acrylamide and acrylic acid was successfully carried out in aqueous salt solutions using anionic polyelectrolytes as stabilizers. The influences of aqueous solution of salt concentration, molecular weight and concentration of the stabilizers on the apparent viscosity and stability of the dispersions, and on the molecular weight of the polymers prepared were investigated. The results showed that stable dispersions could be obtained on condition that salt concentration was between 26%~30%, concentration of stabilizers between 8%~12%, and intrinsic viscosity of stabilizers between 2.977~3.740 dL/g. With salt concentration ranging from 26% to 30%, molecular weight of products increased first and then decreased. Molecular weight of products was hardly changed when concentration of stabilizer was between 8%~12%. When intrinsic viscosity of stabilizer was between 2.977~3.740 dL/g, increase of the molecular weight of stabilizer resulted in a decrease in the molecular weight of the products.

Preparation and characterization of novel cationic pH-responsive poly( [formula omitted]-dimethylamino ethyl methacrylate) microgels

Novel monodisperse cationic pH-responsive microgels were successfully prepared by dispersion polymerization in ethanol/water mixture using N , N ′ -dimethylamino ethyl methacrylate (DMAEMA) as the monomer, poly(vinyl pyrrolidone) (PVP) as the steric stabilizer and N , N ′ -methylenebisacrylamide (MBA) as the cross-linker. The effects of various polymerization parameters, such as medium polarity, concentration of cross-linker, concentration of monomer, and concentration and molecular weight of stabilizer on the final diameter and monodispersity of poly( N , N ′ -dimethylamino ethyl methacrylate) (PDMAEMA) microgels were systematically studied. The pH-responsive characteristics of PDMAEMA microgels were also investigated. The experimental results showed that these microgels exhibited excellent pH-responsivity and significantly swelled at low pH values. The maximum ratio of volume change of the prepared microgels in response to pH variation was more than 11 times. It was found that the prepared microgels completely aggregated at the isoelectric point (IEP) around pH 6. On the other hand, the microgels were stable in aqueous solution at both low and high pH values. The results can be used for effectively controlled separation of particles.

Poly( N-vinylisobutyramide)-stabilized platinum nanoparticles: synthesis and temperature-responsive behavior in aqueous solution

Colloidal platinum nanoparticles in the size range of 10–30 Å were prepared in ethanol–water mixture with an ethanol volume fraction of 0.8 via the reduction of PtCl 6 2− by ethanol in the presence of poly( N-vinylisobutyramide) (PNVIBA). The formation of PNVIBA–Pt colloidal dispersion was followed by UV-visible spectroscopy. The PNVIBA–Pt nanoparticles can be easily transferred into distilled water, and then TEM and AFM studies of the nanoparticles have been performed. The particle size and size distribution are dependent on the monomeric unit/Pt molar ratio and the molecular weight of stabilizer, PNVIBA. The colloidal PNVIBA–Pt nanoparticles exhibit inverse temperature solubility and a cloud-point temperature of 38.9°C in water. The catalytic behaviors of PNVIBA–Pt nanoparticles were studied for the hydrogenation of allyl alcohol in water. At temperatures lower than the cloud-point, the temperature dependence of reaction rate follows normal Arrhenius behavior. Above 40°C, however, the catalyst's activity is abruptly decreased owing to the phase separation of PNVIBA–Pt from the continuous phase containing the substrate. On cooling the reaction solution below the cloud-point, the catalyst redissolves and its activity is renewed to the original level.