Increase In Degree Of Polymerization Research Articles

Capillary Flow Properties of PVC Melts

The effects of degree of polymerization and temperature on flow properties of PVC melts have been studied by using a Koka Flow Tester. Each flow curve is expressed by two straight lines of different slopes which meet at a breaking point. The critical shear rate γ′wc at the breaking point increases as the degree of polymerization decreases or the temperature increases. The critical shear stress τc at γ′wc increases as the degree of polymerization decreases, being almost independent of the temperature. The end correction coefficient ν shows a minimum or begins to increase around γ′wc. The coefficient ν increases as the degree of polymerization increases or the temperature decreases. The extrudate is soomth on the surface at low shear rates, shows a small wavy roughness (shark skin) at shear rates just below γ′wc, becomes fairly smooth again beyond γ′wc, and then shows intensive irregular roughness (melt fracture) at higher shear rates. The die swell becomes notable as degree of ploymerization decreases or the temperature increases. The die swell takes a maximum at a shear rate just below γ′wc, where a shark skin appears on the extrudate. Differing from usual thermpolastic resin melts, PVC melts shows a negative correlation between the die swell ratio and the end correction coefficient. This seems to be due to the following reason: PVC melts have high viscosities and have long relaxation times for strain recovery, and thus the extrudates solidify without being fully relaxed. This tendency of solidification without relaxation is more noticeable as the degree of polymerization increases or the temperature decreases.

Effects of condensed tannins prepared from leaves of fodder plants on digestive enzymes in vitro and in the intestine of rats

1. Of the nineteen plants screened, six were found to contain large quantities of condensed tannins. Black locust (Robinia pseudo-Acacia), bush clover (Lespedeza bicolor), wistaria (Wistaria floribunda) and Japanese knotgrass (Reynoutria japonica) were used for the present experiment. Tannins of the investigated plants were fractionated into three or four molecular forms, according to the degree of polymerization, by chromatography on a column of Sephadex LH-20. 2. The protein-precipitating capacity of the fractionated tannins increased with the increase in degree of polymerization. The inhibitory effect of tannins on trypsin (EC 3.4.21.4), alpha-amylase (EC 3.2.1.1) and lipase (EC 3.1.1.3) activities in vitro also increased with the increase in degree of polymerization. The digestion of tannin-bovine serum albumin complex by trypsin was related to the degree of polymerization of tannins complexed. 3. Inclusion of black locust tannins in the diet (10 g/kg) depressed the activities of trypsin and alpha-amylase in the upper, middle and lower parts of the intestine of the rats, but the lipase activity was increased in the middle part and remained unaffected in the upper and lower parts. It is presumed that the tannins have little affinity for lipase. 4. Digestion trials, when the microflora level of the alimentary canal of rats was reduced by dietary antibiotic treatment, revealed that the inclusion of tannins in the diet (20 g/kg) depressed the digestibilities of proximate constituents, except crude fat, and increased faecal bile acid excretion.

Effects of dimethylsiloxane diluents on the optical properties of poly(dimethylsilmethylene) networks

Low molecular weight cyclic and linear molecules of highly flexible dimethylsiloxane (DMS) units [-Si(CH3)2O-] were used to swell elastomeric networks of poly(dimethylsilmethylene) [-Si(CH3)2CH2-]. Strain birefringence measurements in elongation at 10°C showed the birefringence to decrease regularly with increase in degree of polymerization of the DMS diluent, with three of the four diluents having the unusual effect of increasing the birefringence. Therefore, if correlative effects are the origin of the increase, they do not seem to require high geometric asymmetry in the diluent molecules.

Ein Einfaches Verfahren zur Bestimmung des Umsetzungsverhaltens organischer Primärsubstanz (OPS)

Summary Presented procedure is based on the hypothesis of raising stability of organic matter (OM) with increasing polymerization degree (increasing C content in OM). Large investigations of various crops of different origin showed a strong correlation between C content of primary organic matter (POM) in regard of its OM content and both the percentage decay of the plant material after 35 d of incubation and the compulsory reproduction factors which are a criterion of the stability of POM.

Distribution of Cyclic and Linear Macromolecules in the Polymerization of Cyclic Monomers with Simultaneous Backbiting and End biting Reactions

Abstract A system is discussed in which two kinds of cyclic macromolecules, without and with the active center located on the ring, are formed from linear ones (and vice versa) by two discrete processes: backbiting and endbiting, respectively. Thus, the probability of cyclization is not a function of the distance between one kind of the reacting groups, as in the Jacobson-Stockmayer (J-S) theory, but there are two sets of groups that can react and lead to cyclization. The proportion of the end- to-end process in the linear ⇄ cyclic macromolecule equilibration decreases with an increase in the average degree of polymerization of the macromolecules, as was assumed, but it differs from the J-S theory. The present treatment gives a quantitative solution of this new system; equations describing the equilibrium distribution of cyclic and linear oligomers are formulated. These equations are solved numerically, and the dependence of the fraction of macrocyclics, the dependence of the number-average degrees of pol...

Binding of zinc cations to pectin and its oligomeric fragments

The activity of Zn2+ ions bound to carboxyl groups of pectin of esterification degree E 0 to 90% and to oligomeric potassium galacturonates of polymerization degree 1 to 7 was estimated by the metallochromic indicator (tetramethylmurexide) method. The zinc ions are stoichiometrically bound to pectin, one Zn2+ cation to two free carboxyl groups. The stability constant K of zinc pectinates strongly decreases with the increasing esterification degree in a relationship close to a linear logarithmic function, log K = f(E) similarly, as with the binding of Ca2+ ions to pectin. Pectin reveals a little higher selectivity to Zn2+ ions when considering this couple of cations. The zinc ions are bound to the monomeric D-galacturonic acid to a very low extent in contrast to some toxic cations as e.g. Pb2+, Cu2+, and Cd2+. A continuous increase of the degree of association of Zn2+ ions with carboxyl groups of oligomers takes place with the increasing polymerization degree. The validity of the increment additivity of terminal and inner uronic acid units to the final activity of zinc counterions bound to these oligomers was proved. The results are discussed from the standpoint of application of pectin as an active component of prophylactic diets against poisoning with cations of toxic metals with respect to the excretion of Zn2+ ions from the human body. Findings concerning the interaction of Zn2+ ions with pectin in dependence on its esterification degree (E) constitute a theoretical basis for a potential application of pectin as a useful ligand of Zn2+ ions in medical treatment of zinc deficiency in the human body.

Binding of lead cations to oligogalacturonic acids

The activity of Pb2+ ions in solutions of lead oligogalacturonates of polymerization degree DP 1 to 5 (starting concentration of the investigated solutions 3.00 mmol (COOPb0.5) l-1, the ionic strenght of the solution I = 0.01 mol l-1, electrolyte KNO3, was determined by lead specific ion electrodes. The activity aPb2+ is independent on the kind of anion in very diluted solutions of lead perchlorate and nitrate. Ions of lead become bound quite firmly even to the monomeric D-galacturonic acid (association degree of Pb2+ ions to carboxyl groups of uronic acid β = 0.43). The increase of polymerization degree is associated with a strong decrease of the lead oligogalacturonate solubilities on one hand, and increase of the bond strenght of the Pb2+ ions to these oligomers on the other. The association degree of Pb2+ ions to carboxyl groups of the pentamer (β = 0.96) almost reaches the value found for the polymeric chain of pectate molecule (D-galacturonan); here, the stoichiometric binding of Pb2+ to two carboxyl groups takes place with a great deal of probability. Lead has been found to bind highly preferentially to oligogalacturonates even in the presence of calcium ions. Results presented in this paper help to clear the mechanism of elimination of lead from the human body through pectin and its oligomeric fragments.

PHOTOPHYSICS AND IONIC PHOTODISSOCIATION OF POLYESTERS WITH PENDANT 1‐PYRENYL GROUPS IN SOLUTION

Abstract—Primary photoprocesses of polyesters with pendant pyrenyl groups in solution were studied by means of nanosecond laser flash photolysis method. The intrapolymer process of the Sl Sl annihilation was observed. Intense laser excitation brings about dense population of several fluorescent states in a polymer chain, and their mutual interaction leads to efficient deactivation. This process is confirmed by excitation intensity dependence of fluorescence spectra and fluorescence intensity. It was also confirmed that the T‐T absorption intensity decreases as the degree of polymerization increases. This low formation yield of the triplet state in the polyesters is ascribed mainly to the above Sl Sl interaction. In addition the polymer effect on the ionic photodissociation yield of the polyester‐electron acceptor was investigated. The yield decreases as the degree of polymerization increases. This effect is due to slow solvation processes, which may be due to low micropolarity and high microviscosily around the polymer chain.

Cobalticenium‐Bridged polybenzazoles. Part II: High‐temperature. Solution polymerization in ethylated polyphosphoric acid

AbstractThe polycondensation of 1,1′‐diearboxycobalticenium hexafluorophosphate with 3,3′‐diaminobenzidine in ethylated poly phosphoric acid at 100‐240°C furnishes linear, soluble polymeric intermediates for the most part composed of cobalticenium‐1,1′‐diyl and bibenzimidazoline‐2,2′‐diyl units alternating along the chain. Heating of the primary products in the solid state at 300°C results in aromatization, giving polyheterocyclics essentially composed of alternating cobalticenium‐1,1′‐diyl and bibenzimidazole‐2,2′‐diyl units. The analogous reaction of the cobalticenium salt with 3,3′dimercaptobenzidine produces primary polymers containing benzothiazoline in lieu of benzimidazoline ring systems, which, by a heat treatment as before, convert to the corresponding polymeric benzothiazoles. The primary condensation products of both reaction types are of low molecular mass (ηinh, 5‐13 ml/g) vlien prepared at temperatures not exceeding 150°C. The degree of polymerization increases (ηinh, 20‐60 ml/g) at temperatures in the 200‐250°C range; however, Lewis acid‐induced cobalt‐ring bond cleavage proceeds as a significant side reaction under these conditions, leading to random chain scission and alteration of the polymer structure by alicvclic hydrocarbon groups. In addition, the benzimidazole polymers are to a variable extent contaminated with phosphate groups stemming from the medium. These structural defects, paired with distinct reactivity of the PF6‐ anion at higher temperatures, result in a thermogravimetric analysis performance not quite equal to that of common phenylene‐bridged Polybinzazoles.

The effects of pre-irradiation annealing on the track-development properties of solid-state nuclear track detectors

The effects of pre-irradiation annealing on the track registration and development properties of various cellulose-nitrate and polycarbonate plastic track detectors have been studied. The results show that, as the pre-irradiation annealing temperature is raised, the track-registration efficiency of most of the detectors at first shows a marked increase and then a slight decrease. Also, pre-irradiation annealing results in a significant decrease in the background etch pits. There are indications that, as the temperature is raised gradually, the degree of polymerization increases which, in turn, hardens the material and thus decreases the general etching velocity, V g. There seems to be very little effect on V t, the velocity along the damage trail produced after annealing; but due to a decrease in V g, the ratio V t/ V g increases, and a net gain in efficiency and maximum etched track length is achieved. At higher temperatures, some sort of a breakdown takes place which results in an increase in V g, thus decreasing the detection efficiencies and the maximum etched track lengths.

The synthesis and circular dichroism of a series of peptides possessing the structure (L-tyrosyl-L-alanyl-L-glutamyl)n.

A series of peptides possessing the structure (l‐Tyr‐l‐Ala‐l‐Glu)n, with n = 1,2,3,4,7,9, and 13 was synthesized. The oligomers up to n = 4 were prepared by stepwise synthesis using the N‐hydroxysuccinimide ester of the tripeptide derivative for the elongation of the chain. The oligomers with n = 7,9, 13 were prepared by a polycondensation technique, followed by gel filtration.The circular dichroism spectra of the above oligopeptides were measured in the wavelength range 200–330 nm in a solution of 0.15 M sodium chloride –0.02 M sodium phosphate, pH 7.4, conditions at which the high molecular weight polytripeptide (Tyr‐Ala‐Glu)n exists in a helical conformation. The circular dichroic spectrum of the high molecular weight polymer exhibits two negative ellipticity bands: an intense band at 220 nm ([Θ]max= 8700) and a weak band at 273 nm ([Θ]max= 360). The tripeptide (n = 1) exhibits a positive ellipticity band at 227 nm ([Θ]max= 4000) and a broad, positive, weak band at 270 nm ([Θ]max= 115). The other oligopeptides (n = 2 to 13) exhibit positive bands in the 227 nm region, with ellipticity values that decrease as the degree of polymerization increases. Except for (Tyr‐Ala‐Glu)13, which has a negative peak centered at 216 nm, circular dichroic spectra of the other oligomers (n = 1 to 9) in the 200–210 nm region resemble that of random coils. In the 260–290 nm region, the circular dichroic curves of the oligopeptides gradually approach the 272 nm band of the polypeptide (Tyr‐Ala‐Glu)n, as the degree of polymerization increases. Under physiological conditions, only the (Tyr‐Ala‐Glu)13 shows an indication of helical content.

Steric structure of L-proline oligopeptides. II. Far-ultraviolet absorption spectra and optical rotations of L-proline oligopeptides.

AbstractThe results of the measurement of the far‐ultraviolet absorption spectra of L‐proline oligomers in water and acetonitrile are summarized as follows. The monomer has an absorption maximum at 182.5 mμ in acetonitrile. The absorption maximum of the dimer is found at 185 mμ and a shoulder appears around 200 mμ, that is, splitting of the absorption spectrum is observed in the dimer. As the degree of polymerization increases, the position of the shoulder shifts toward the wavelength of the absorption maximum of poly‐L‐proline II, with an accompanying increase in intensity. We may describe the absorption peak around 203 mμ of poly‐L‐proline II as identical with the shoulder with an increased intensity. By measurements of optical rotatory dispersion and circular dichroic spectra, it was also confirmed that the appearance of the helical conformation commences at the tetramer. When the number of residues is five or greater, the conformation of the helical structure of poly‐L‐proline II seems to be completed.

Biological behavior of rabbit 131I-albumin polymers

Electrophoretically separated rabbit serum albumin is essentially in a monomeric form, whereas old freeze-dried albumin or fresh albumin oxidized by chloramine T, at pH 5.1, shows a number of polymers. The monomer, the dimer, the trimer, the tetramer, and the polymers of old freeze-dried rabbit serum 131I-albumin have been separated by gel filtration on Sephadex G-200 and, by determining the relative specific activities, a decrease of radioactivity has been shown in the polymeric albumin. The albumin components have been characterized by agar and starch gel electrophoresis and by double diffusion in agar gel in order to ascertain the purity and the identity with the monomeric albumin. Having excluded depolymerization of 131I-albumin aggregates in vivo, the biological behavior of rabbit 131I-albumin, either in monomeric or in polymeric form, was examined. The results indicate a progressive shorter half-life and an increase in the eliminated radioactivity as the degree of polymerization increases.

Crystallite orientation in regenerated cellulose filaments. II. Effect of degree of polymerization and stretch

AbstractMeasurements of the degree of orientation in cellulose filaments prepared from fractions of secondary cellulose acetate having a very limited range of degree of polymerization have shown that the degree of orientation produced by a given effective stretch increases as the degree of polymerization increases. The orientation distributions of the (101) and (020) planes have been compared with those predicted by Kratky's theory for the deformation of a material containing rod‐shaped crystallites, and it has been shown that the shapes of the observed and theoretical distributions are the same if the appropriate value of the degree of stretch is used. This value is always less than that calculated from the changes in the dimensions of the filaments produced by stretching. Kratky's theorv cannot however account for the variation with degree of polymerization and does not account for the observed shape of the curves for orientation as a function of stretch. Consideration of the process by which the filaments were produced shows that the filaments were subjected to stretches additional to those intentionally applied to them. The results of the orientation measurements are compared with published figures for the birefringence and tenacity of similar filaments, and linear relations are found between birefringence and orientation and between tenacity and orientation.

The Mutual Solubility of Polymers. IV. The Effect of the Packing Density of Polymer Molecules on Their Mutual Solubility

Abstract 1. It is pointed out that the decrease in volume plays an important part in the mixing of polybutadiene rubber (SKB) with butadiene-styrene rubber (SKS-30) and of polybutadiene rubber with polystyrene. In this connection it is emphasized that the assumption of volumes being additive in the mixing of polymers is limited in application. 2. It was shown that the heat effects of the mixing of polymers does not depend on the degree of polymerization, provided that no contraction takes place in mixing, and that the sign of the heat effects can even be changed if the packing of the molecule becomes more loose as the degree of polymerization increases. 3. From a theoretical analysis of experimental data found in the literature the opinion was advanced that the critical mixing temperatures for the systems polybutadiene rubber-butadiene-styrene rubber and of polybutadiene rubber-polystyrene are low, being somewhat above the vitrification temperature of polystyrene. The existence of lower critical mixing temperatures here is caused by a decreased packing density in the molecules of polystyrene and of butadiene-styrene rubber at temperatures below the vitrification temperature of polystyrene.