Addition Of Nonsolvent Research Articles

Molecular weight distribution of an unsaturated polyester

AbstractA precipitation fractionation was carried out by the nonsolvent addition method of 60 g of an unsaturated polyester. The polyester was prepared by the generally known melt condensation of maleic anhydride, phtalic anhydride, ethylene glycol, and cyclohexanol. Number‐average molecular weights of fractions were determined by vapor pressure osmometry in acetone at 36°C. Polydispersities of fractions were evaluated by gelpermeation chromatography (GPC) measurements with tetrahydrofuran as solvent. They seem to be wider for fractions of higher molecular weights. By infrared spectroscopy the fractions were found not to have marked differences in chemical compositions. The obtained molecular weight distribution curve of the unsaturated polyester was found to be in good agreement with that expected from the theory of polycondensation kinetics. The small differences appear only in the low molecular weight range.

Polyisobutylene: fractional precipitation from binary solvent induced by non-solvent addition

Large fractions of polyisobutylene chains may be obtained from precipitation induced by acetone added to solutions of polymer in a binary mixture (chloroform and dichloromethane). Fractions were characterized by weight average molecular weights, M ̄ w , and average radii of gyration, R ̄ 2 G , obtained from light-scattering measurements performed on a good solvent (cyclohexane); the product M ̄ w × R ̄ 2 G was found to vary according to the formula: M w × R 2 G = 1.33 × M m w with m = 2.22; while the intrinsic viscosity of fractions was found to vary as: [keta;] = 1.11x10 -4 × M m w with n = 0.76. Considering that m = 2 v + 1 and n = 3 v − 1, where v is the critical exponent associated with the description of properties of polymer chain solutions; values of v derived from m and n were found to be 0·61 or 0·58, respectively; the theoretical value is known to be 0·588. Polydispersity indices, l, were obtained from g.p.c. measurements: 1.1 < l < 1.3.

Sustained release of sulfamethizole, 5-fluorouracil, and doxorubicin from ethylcellulose-polylactic acid microcapsules.

The preparation of ethylcellulose-polylactic acid microcapsules with long release half-lives of chemotherapeutic agents was investigated. The microcapsules were prepared by means of coacervation-phase separation of ethylcellulose from ethyl acetate solution by nonsolvent addition in the presence of polylactic acid. In the case of sulfamethizole microcapsules, longer release half-life was obtained with larger amounts of polylactic acid in the preparation. The release rate of sulfamethizole was not very dependent on the pH of the release media. 5-Fluorouracil and doxorubicin hydrochloride were similarly microencapsulated. 5-Fluorouracil microcapsules were sieved prior to release studies. A release half life of 2.6 hr was obtained with the 5-fluorouracil microcapsules. In the case of doxorubicin microcapsules, the drug was released with a half-life of 84 min, whereas uncoated doxorubicin dissolved completely within 15 min.

Preparation and Evaluation of Microencapsulated Ion-Exchange Resin Beads

Ion-exchange resin beads in the benzoate form were coated by several microencapsulation techniques to alter and improve characteristics, especially the control of drug release, of this type of drug delivery system. The most successful techniques included polymer-polymer interaction, temperature change, and nonsolvent addition. The microencapsulated beads then were studied with respect to the release rate of the organic anion to determine the effects of microencapsulation. The release rate of the organic anion could be controlled over a wide range, depending on the encapsulating material characteristics. Factors affecting the extent and rate of release as a result of microencapsulation are discussed.

Precipitation of polymers from solution in the presence of an electrical field

AbstractSome polymers and copolymers were precipitated from solutions by nonsolvent addition with and without stirring as well as by temperature lowering. It turned out that the precipitate is charged in all these cases. Stirring yields an increase of the charge quantity. The charging of the precipitate in experiments without stirring being a result of electron transfer between the solvent and polymer rich precipitate phase is probably due to the density fluctuations. The precipitation by stirring was used for preparative purposes to remove the precipitated drops from solution by fractionation. Deviation in composition observed in different fractions of copolymers could influence the molecular weight and molecular weight distribution measurements.

Mechanical denaturation of high polymers in solutions

In order to clarify the mechanism of crystallization under molecular orientation, the rates of precipitation of poly(vinyl alcohol) (PVA) from aqueous solutions under shearing force were measured under various conditions. The fractionation was carried out by separating the precipitates at time intervals. The shearing force was brought about in the solutions by stirring. The rate of precipitation was found to depend not only on the thermal motion of molecules, but also on the fluidity of the solution. In other words, at temperatures above 45°C, the initial rate of precipitation became smaller with increasing temperature, but at 45 °C it was higher than that at the lower temperature than 40°C. The rate of precipitation at 35°C decreased with the increase of the polymer concentration. At the constant polymer concentration, the maximum of the rate of precipitation was recognized at a certain chain length. The molecular weight of fractions decreased in the order of fractionation. As compared with the non-solvent addition method, the difference in the s-(diad) % of the initial fraction and the last fraction was large in the case of stirring fractionation. Therefore, the stirring fractionation of PVA depends not only on the molecular weight, but also on the tacticity.

Flocculation studies of non-aqueous sterically stabilized dispersions of polymer

The incipient instability of non-aqueous sterically stabilized dispersions of polymer particles has been investigated. Flocculation was induced by decreasing the solvency of the dispersion medium for the stabilizing moieties, either by non-solvent addition or by cooling. The influence of such factors as the nature of the dispersion medium, the temperature, the non-solvent, the stabilizing moieties, the anchor polymer, the disperse phase, the particle size and the surface coverage has been examined. Flocculation occurs in dispersion media which are of better solvency for the stabilizing moieties, in free solution, than the corresponding theta-solvents. It is apparently governed by the component of the soluble moieties for which the given flocculating dispersion medium is of least solvency. The results support Fischer' s general approach to steric stabilization.

Photochromic polymers

AbstractPhotochromic spiropyran copolymers have been prepared by radical copolymerization of 5‐methacrylamino‐3,3′‐diméthyl‐6′‐nitrobenzthiazo‐linospiropyran (R is CH2=C(Me)‐CO‐NH) with different vinyl monomers, as methyl methacrylate, methacrylonitrile, styrene, and 2‐vinylnaphthalene. Their solution behavior has been examined in different solvents and compared to that of the corresponding 5‐isobutyraminoderivatives (R is i‐C3H7‐CO‐NH). magnified image In a strong solvating medium the copolymers display a strong negative solvatochromism and behave similarly to the model substance; their decoloration reaction kinetics follow a first‐order relationship. The decoloration activation energy in DMF varies from 24.9 to 25.6 for the different copolymers instead of 22.1 for the model. In less polar solvents, the λmax of the copolymers show a large hypsochromic shift when compared to the model, while the decoloration reactions deviate strongly from first‐order kinetics. These deviations are interpreted by assuming the existence in the copolymers of two photocolored isomeric components, in slow equilibrium with each other, and with optical densities a and b and agree with following equation where the optical density can be related to the time of decoloration t. The ratio a/b i s equal to 0.57, 2.00, and 2.06 in acetone, dichloromethane, and tetrahydrofuran, respectively. It is assumed that the steric hindrance resulting from the macromolecular environment raises the potential barriers between these different stereoisomers. On addition of a polar nonsolvent as t‐butanol, first‐order kinetics are, however, restored up to a degree of conversion of 60%. The rate of decoloration of methyl methacrylate copolymers decreases with increasing spiran content. Finally, it was observed that an increase of the solution viscosity also provokes a deviation from first‐order kinetics.

A new molecular weight distribution technique for polystyrene

AbstractThe molecular weight distribution of a heterogeneous polystyrene can be obtained in principle by observing the cumulative volume of precipitate which corresponds to increasing additions of nonsolvent to a dilute solution of the polymer in question. This paper is concerned with experimental aspects of the method: size of container, initial concentration of polymer, choice of solvents and nonsolvent, manner of adding the nonsolvent. reequilibration of existing precipitate after each nonsolvent addition, and experimental difficulties. The initial concentration of polymer should be 0.1 to 0.2% by weight. The only system studied was polystyrene‐benzene‐methanol. Preliminary calibration data are presented, as well as a number of experimental distribution curves on fractions, mixed fractions, and heterogeneous polymers. The method has been applied to one polymer of known distribution. While the method is simple and seemingly reliable it becomes very slow when the concentration of polymer is reduced to 0.1%. About 2 months are required for a detailed distribution curve. Means of speeding up the process are indicated.