Graft polymerization of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid onto starch

Mixtures of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid (AASO₃H) were graft polymerized onto starch by cobalt-60 irradiation, and the water absorbency and water solubility of the resulting products were determined. The conversion of monomers to polymer was nearly quantitative when pregelatinized wheat starch and a water solution of the two monomers were simultaneously irradiated (simultaneous irradiation conditions). Products with high water absorbency were obtained with equal weights of starch and total monomers when acrylamide:AASO₃H ratios ranged from 9:1 to 1:3. Water solubility of these polymers was over 50%. Neither of the two monomers gave absorbent polymers when graft polymerized individually onto starch. Although highly absorbent products were also obtained at a total monomer:starch ratio of 2:5, ratios of 1:5 and lower gave products with poor absorbency. Neutralization of AASO₃H with sodium hydroxide before graft polymerization drastically reduced both the water solubility and absorbency of the final products. A reaction with granular starch was also carried out under simultaneous irradiation with a total monomer:starch ratio of 2:5 and with equal weights of the two monomers. Conversion of monomers to polymer was once again nearly quantitative. To obtain good water absorbency from this granular product, it was necessary to first neutralize the AASO₃H portion with alkali, then disperse the polymer in hot water, and finally dry the resulting water dispersion. Graft copolymers with good water absorbency were also obtained by adding preirradiated starch to a water solution of acrylamide and AASO₃H, although only partial conversions of monomers to polymer were realized. Selected products from the various graft polymerizations were fractionated by extraction with either water or a 1% solution of sodium chloride. The synthetic polymer content of the resulting fractions and the percentage of AASO₃H in the synthetic portion of each polymer were determined. The M _n of some of the synthetic polymers was also determined after removal of carbohydrate by enzymatic hydrolysis.     

Graft copolymers of starch with mineral acid salts of dimethylaminoethyl methacrylate. Preparation and testing as flocculating agents

Mineral acid salts of dimethylaminoethyl methacrylate (DMAEMA) have been graft polymerized onto starch with ferrous ammonium sulfate–hydrogen peroxide initiation. The nitric acid salt was used in most reactions, and graft polymerizations were run in both water and aqueous–organic solvent systems. Increased monomer concentration in water led to an increase in both the percentage of poly(DMAEMA · HNO₃) in the graft copolymer (percent add-on) and the molecular weight of grafted branches. Variations in initiator concentration altered the percent add-on only slightly but affected the molecular weight of grafted polymer significantly. When swollen starch, in contrast with unswollen starch was used in graft polymerization reactions run in water, the product had a higher per cent add-on and a larger number of grafted branches of lower molecular weight. The efficiency of starch–poly(DMAEMA · HNO₃) graft copolymers as flocculants for diatomaceous silica increased with per cent add-on; however, variations in grafting frequency and graft molecular weight had less effect on the behavior of these materials as flocculants.     

Graft copolymers of polysaccharides with thermoplastic polymers. A new type of filled plastic

A series of starch graft copolymers and one cellulose graft copolymer were prepared containing 40-50 percent synthetic polymer. The monomers used (styrene, methyl methacrylate, methyl acrylate, and butyl acrylate) were chosen to give grafted synthetic polymers with varying glass transition temperatures (T_g). These graft copolymers were extruded, in the absence of any added thermoplastic homopolymer, to give strong, continuous polysaccharide-filled plastics which are biodegradable and which exhibit little or no die swell. Properties of plastics varied with the T_g of the thermoplastic portion. Starch-g-polystyrene and starch-g-poly(methyl methacrylate) were hard and brittle, while graft copolymers prepared from methyl and butyl acrylate were more flexible and leathery. The graft Uopolymers with lower T_g grafts required less torque and could be extruded at lower temperatures. In the methyl acrylate series, a graft copolymer prepared from gelatinized starch was more easily extruded than one prepared from granular starch, and addition of water produced a water-filled extrudate of excellent quality. The surprising feature of these results is that the matrix polymers, starch and cellulose, are rigid, nonsoftening materials. Grafting of a thermoplastic polymer to these matrix polymers would not be expected to give an extrudable product. The results are explained as powder flow followed by fusion or sintering of the graft polymers under the temperature and pressure conditions in the die.     

APPLICATION AND USE OF THE ATR,FT-IR METHOD TO ASPHALT AGING STUDIES

ABSTRACT

Infrared analysis is an extremely valuable tool for investigating the chemical functionality of asphalts. The attenuated total reflection (ATR) FT-IR method is especially useful for the study of this intractable material. Quick and easy sample preparation, natural state analysis, and clean and reproducible spectra are advantages of the ATR method over conventional transmission methods. Comparisons of this procedure to potassium bromide pellet and solution methods support the method's use. Asphalt oxidative and solvent aging studies employed the ATR method to track hardening of asphalt in various solvents as indicated by increased carbonyl absorbances. Also. standard laboratory tests for simulating the hot-mix aging of asphalts, compared using this method as well as other chemical and physical properties, sbow significant differences from actual hot-mix aging     

Diffraction efficiency of volume gratings with finite size: Corrected analytical solution

Abstract

In order to correct errors in a previously published work on a treatment of two-dimensional coupled-wave theory, a complete derivation of the two-dimensional ‘overlap grating’ coupled wave equations is given. By using the Riemann method, a corrected solution to the equations in closed mathematical form is obtained. On the basis of this solution a brief investigation of the diffraction properties of finite-sized gratings, and in particular the dependence of diffraction efficiency on the geometric size of gratings, is given.     

Electric field stimulation of excitable tissue

The authors consider the determination of conditions when an excitable membrane can be considered linear and steady-state. The following topics are dealt with: threshold for a space-clamped fiber; threshold for a fiber stimulated by a point current source; subthreshold response; passive vs. active response; defibrillation stimulus-response time-constant; the transient intracellular current; the transient transmembrane potential due to junctional resistance     

The thiocyanogen value of linolenic acid

Ethyl linolenate (Wijs iodine number 247.3; theory 248.5) was prepared by the debromination of purified hexabromostearic acid. The thiocyanogen value determined exactly as recommended by the Committee on Analysis of Commercial Fats and Oils, [Ind. Eng. Chem. Anal. Ed.8: 234 (1936)] was found to be 151.2, corresponding to a corrected value of 167.3 for the free linolenic acid, rather than the theoretical value of 182.5. Data are presented to show the effects of time, excess and concentration of reagent. The thiocyanogen number of linolenic acid is proved to be an empirical value which, however, is reproducible under carefully controlled conditions. Several improvements of technique found to insure reproductibility of results are discussed in detail. Aided by grants from the Hormel Foundation, the National Livestock and Meat Board, the Rockefeller Foundation, and the Graduate School of the University of Minnesota.     

Identification of the Tirandamycin Biosynthetic Gene Cluster from Streptomyces sp. 307‐9

The structurally intriguing bicyclic ketal moiety of tirandamycin is common to several acyl‐tetramic acid antibiotics, and is a key determinant of biological activity. We have identified the tirandamycin biosynthetic gene cluster from the environmental marine isolate Streptomyces sp. 307–9, thus providing the first genetic insight into the biosynthesis of this natural product scaffold. Sequence analysis revealed a hybrid polyketide synthase–nonribosomal peptide synthetase gene cluster with a colinear domain organization, which is entirely consistent with the core structure of the tirandamycins. We also identified genes within the cluster that encode candidate tailoring enzymes for elaboration and modification of the bicyclic ketal system. Disruption of tamI, which encodes a presumed cytochrome P450, led to a mutant strain deficient in production of late stage tirandamycins that instead accumulated tirandamycin C, an intermediate devoid of any post assembly‐line oxidative modifications.     

Calculation of the Sampling Distribution of the Range

Two dynamic programming models are developed for a class of production-inspection problems. The two models correspond to two different levels of information and result in fixed-point and adaptive inspection policies respectively. Choice of the “optimal” model can then be made via comparison of expected benefits obtained versus the costs of deriving and implementing the solutions.