Total Amount Of Monomers Research Articles

Effect of synthesis conditions on properties of covalently cross‐linked thermosensitive hydrophilic gels

AbstractGel synthesis conditions have a considerable influence on the characteristic properties of the polymerized gel system. Under variation of total amount of monomer, cross‐linker concentration and synthesis temperature, different covalently cross‐linked hydrophilic gels based on N‐isopropylacrylamide were synthesized.The shear modulus, the phase transition temperature and ‐enthalpy and the swelling degree of the hydrophilic gels were measured. Synthesis conditions had a significant influence on the shear modulus and the swelling degree. An influence on the phase transition temperature and ‐enthalpy could only be found in some special cases.

Effects of crosslinking and temperature on the dose response of a BANG polymer gel dosimeter

The effects of varying the weight fraction (%C) of the crosslinker N,N'-methylene-bisacrylamide (bis) per total amount of monomer (6% w/w), and the NMR measurement temperature, on the dose response of the transverse relaxation rate of bis-acrylamide-nitrogen-gelatin (BANG) aqueous polymer gel dosimeters have been investigated. The gel samples were irradiated in test tubes with 250 kV x-rays, and the water proton NMR transverse relaxation rates were measured at 0.47 T using a Carr - Purcell - Meiboom - Gill multiecho pulse sequence. Both the dose sensitivity (slope of the linear portion of an -dose response) and the maximum rate at which the -dose response saturated , were found to depend strongly on the crosslinker fraction and on the temperature of the measurement. The dose sensitivity peaked at approximately 50% C, and, for this composition, varied from at to at . The maximum transverse relaxation rates ranged from at 33% C and to at 83% C and . These results suggest that water proton transverse relaxation in the gel is controlled by an exchange of magnetization between the aqueous phase and the semi-solid protons associated with the polymer, and that the latter experience spectral broadening from immobilization which increases with crosslinking or cooling. Theoretical and practical implications of the above findings are discussed in the paper.

Methylmethacrylate sulfopropylmethacrylate copolymer nanoparticles for drug delivery. Part I: Preparation and physicochemical characterization

Methylmethacrylate (MMA) sulfopropylmethacrylate (SPM) copolymer nanoparticles were prepared by free radical polymerization. The conditions of preparation were varied with regard to the concentration of initiator and monomer, and copolymer composition. Nanoparticles with a yield greater than 80% were produced. The particles were characterized in terms of particle size, size distribution, particle charge (zetapotential) and molecular weight. The data were compared to pure polymethylmethacrylate (PMMA) nanoparticles. The copolymer composition was shown to influence particle size and particle charge. The influence of the total monomer amount in the polymerization medium on the particle size was characteristic up to a concentration of 2% depending on the solubility of MMA in water at the temperature of reaction. An increasing amount of total monomer led to particle sizes of 60–130 nm for low monomer concentrations (0.5%), depending on the proportion of SPM (0–10%), to 120–280 nm for higher total monomer concentrations (greater than 2%). Surface charge as well as particle size were influenced mainly by the proportion of the comonomer SPM in the copolymer. The negative surface charge increased from - 52 mV for pure PMMA nanoparticles to − 80mV for the copolymer particles with an SPM content of 10%. In the same range of 0–10%), SPM of the total monomer, the particle sizes decreased from 187 to 100 run. The concentration of the initiator up to a concentration of 0.3% showed no effect on the particle size of the resulting nanoparticle suspension. Higher concentrations led to intolerably large variability in the polymerization process.

Formation of novel poly(hydroxyalkanoates) from long-chain fatty acids.

Poly(hydroxyalkanoates) (PHAs) were isolated from Pseudomonas aeruginosa 44T1 cultivated on euphorbia oil and castor oil. With the aid of 2-D proton NMR spectra and proton-detected multiple bond coherence NMR spectra the structures of the PHAs were determined. In addition to the usual PHA constituents (C6-C14 3-hydroxy fatty acids), PHAs formed from euphorbia oil contained delta 8,9-epoxy-3-hydroxy-5c-tetradecenoate, and probably delta 6,7-epoxy-3-hydroxydodecanoate and delta 4,5-epoxy-3-hydroxydecanoate. These novel constituents account for approximately 15% of the total amount of monomers and are clearly generated via beta-oxidation of vernolic acid (delta 12,13-epoxy-9c-octadecenoic acid), the main component of euphorbia oil. In PHAs formed from castor oil, 7% of the monomers found were derived from ricinoleic acid (12-hydroxy-9c-octadecenoic acid). The presence of 3,8-dihydroxy-5c-tetradecenoate was clearly demonstrated. Furthermore, NMR analysis strongly suggested the presence of 3,6-dihydroxydodecanoate, 6-hydroxy-3c-dodecenoate, and 4-hydroxydecanoate.

Model prediction of batch emulsion copolymerization as a function of conversion: A sensitivity analysis

AbstractRecently a model has been developed capable of predicting absolute monomer concentrations and their ratios in the polymer, aqueous, and monomer droplet phases as a function of conversion in batch emulsion copolymerizations without using any adjustable parameters. In this article the sensitivity of model predictions of composition drift toward deviations of 10% in all model parameters (maximum swellabilities of monomer in the polymer phase, water solubilities, reactivity ratios, and monomer and polymer densities) was estimated using the monomer combination methyl methacrylate‐styrene as an example. From the sensitivity analysis it can be concluded that the reactivity ratios are the most important parameters affecting composition drift. The effects of deviations in maximum swellabilities and monomer and polymer densities on composition drift can be neglected, while the water solubility is important only in those cases where the amount of monomer in the aqueous phase cannot be neglected as compared with the total monomer amount. © 1994 John Wiley & Sons, Inc.

The composition of the cutin of the caryopses and leaves ofTriticum aestivum L.

The outer layers (bran) of white wheat (Triticum aestivum L. cv. Jubilar) caryopses contain several layers of lipophilic materials. It was the objective of the present work to establish the nature, composition and amounts of the lipid polymers of wheat bran and to compare it with leaf cutin. Prior to analysis, the bran was isolated and divided into two fractions: (i) the inner bran containing the remnants of the nucellus, the seed coat and the inner layers of the pericarp, and (ii) the outer bran consisting of the peripheral layers of the pericarp. Following depolymerization, a total number of 14 long-chain monobasic, dibasic, ω-hydroxymonobasic, α-hydroxymonobasic, dihydroxymonobasic, trihydroxymonobasic and epoxyhydroxymonobasic alkanoic acids have been identified as constituents of bran lipid polymeres. The most abundant single constituent was 9,10-epoxy-18-hydroxyoctadecanoic acid. The qualitative and quantitative compositions of depolymerisates from the inner and outer bran fractions were similar except for the absence of 9,10,18-trihydroxyoctadecanoic acid and of long-chain (C22-C26 ω-hydroxyalkanoic acids in the outer bran. The composition of bran depolymerisates closely resembled the constitution of the BF3/CH3OH susceptible fraction of wheat leaf cutin. Only less than 2% of the total amount of monomers released from inner bran were indicative for the presence of suberin. The total cutin content of wheat bran amounted to 4.2 g per kg of dry caryopses. Most of it (96.6%) was contributed by the cuticles of the seed coat and the nucellus while the cuticle of the pericarp made up only 3.4%.

Incorporation of macromolecules in microparticles: preparation and characteristics.

Macromolecules can easily be incorporated in microparticles of polyacrylamide by copolymerization with acrylamide in a water-in-oil emulsion. The microparticles preferably arount 1-3 mum in diameter, will have a macroporous structure formed by the polymeric network. The amount of incorporation of the macromolecules will depend on the structure of the network, which, in turn, will depend on the total amount of monomer (T) and the relative amount of cross-linking agent (C) in the monomeric solution. Two mechanisms are responsible for the incorporation; all macromolecules are, independently of the size, fixed in the threads of polyacrylamide and large ones are entrapped within the network formed by the threads. The amount entrapped will depend on the size of the macromolecule and the mean pore radius of the gel. In microparticles with a total concentration of monomers of 8% and a cross-linking of 25% (T-C=8-25) the biological properties of incorporated macromolecules are retained, due to the macroporous structure, as found in binding studies with albumin. The density of the particles will also depend on C and T and, to some extent, on the protein concentration. Due to the fixation in the polyacrylamide threads, some of the incorporated macromolecules will be exposed on the surface, allowing them to react with, for instance, cells, which cannot penetrate the particles. The optimal conditions for the incorporation of macromolecules in the microparticles are investigated.

Copolymerization of propylene and complexed acrylonitrile by TiCl3–AlEt3 catalyst system

AbstractIt was found that an equimolar complex is formed from acrylonitrile with triethylaluminum. The complex formation was verified by infrared spectroscopy. The original bands of acrylonitrile at 2235 cm−1 shifted and the new bands appeared at 2225 and 2275 cm−1. Copolymerization of acrylonitrile with propylene was proved to be possible with a TiCl3–AlEt3 catalyst system.Kinetic studies on copolymerization of propylene with acrylonitrile showed that composition of the starting monomer mixture markedly influenced the course of the reaction and the acrylonitrile content of the copolymer.Optimum conditions of the copolymerization reaction were as follows: temperature, 70°C; reaction time, 30 min; molar ratios of acrylonitrile to the metal alkyl and Al to Ti, 1:1 and 2;1, respectively, concentration of the total amount of monomers. Conversion is influenced by the aging time of the acrylonitrile‐metal alkyl complex; the yield is a linear function of the aging time. Composition of copolymers was determined by chemical analysis.

Grafting vinyl monomers to starch by ceric ion. I. Acrylonitrile and acrylamide

AbstractStudies were carried out on the grafting of acrylonitrile (AN) and acrylamide (AA) to starch by ceric ion. The variables affecting the grafting of AN and AA were investigated with granular wheat starch dispersed in aqueous N,N‐dimethylformamide and ceric ammonium nitrate as catalyst. Results showed that the concentrations of monomer and catalyst are the major factors influencing the grafting of AN; thus the monomer content of the grafts can be regulated by these variables. The grafting of AA is also influenced by these variables, but to a much less degree. Increasing concentrations of monomer promote homopolymerization and increasing concentration of catalyst inhibit grafting. The extent of grafting of this monomer can best be controlled by reaction time. Under the most favorable conditions, maximum grafting efficiency (ratio of amount of grafted monomer to total amount of monomer converted to polymer) was 87% for AN and 43.8% for AA. Although the monomer content of the AN grafts was higher than that of AA grafts prepared under identical conditions, the number of branches in the grafts was almost the same; only the length of the branches was different. The AN‐starch grafts have branches of higher molecular weight.

Vinyl acetate emulsion polymerization

AbstractVinyl acetate emulsion polymerization at 70°C. using potassium peroxydisulfate as initiator and a partially hydrolyzed polyvinyl acetate as emulsifying agent has been studied. In agreement with the Smith and Ewart scheme for emulsion polymerizations, the polymerization rate was found to be independent of the total monomer amount present and approximately dependent on the 3/5 power of the emulsifier concentration. Instead of a 2/5 power dependence on initiator concentration for the rate of polymerization, a 0.7 power dependence was found. From surface tension measurements an “apparent critical micelle concentration” was determined for aqueous solutions of the emulsifier. However, light scattering studies gave no indication that aggregates of the emulsifier exist in aqueous solutions.