Showing papers in "Journal of Polymer Science in 1962"

Experimental determination of the elastic modulus of crystalline regions in oriented polymers

Abstract: The elastic modulus of the crystalline regions in some oriented polymers was determined. An x-ray diffractometer specially constructed for this purpose was used, and the lattice extension in the direction of the fiber axis was measured under application of a direct load. Usually a meridional reflection was used for the measurement of the lattice extension, but in the case where no strong meridional reflection exists a reflection from planes which are almost perpendicular to the fiber axis of the crystallites was used. The elastic modulus was calculated under the assumption of a simple series model. The values found are as follows: polyvinyl alcohol, 255 × 104 kg./cm.2; polyethylene, 240 × 104 kg./cm.2; polypropylene, 42 × 104 kg./cm.2; polyoxymethylene, 54 × 104 kg./cm.2; cellulose, 137 × 104 kg./cm.2; polyvinylidene chloride, 41.5 × 104 kg./cm.2.

Polyethylene unit cell variations with temperature

Abstract: The unit cell dimensions of a linear polyethylene are reported as determined by x-ray diffraction measurements at five-degree intervals from −70°C. to +130°C. and at −196°C. The relative expansion coefficient of the a dimension of the orthorhombic unit cell was found to increase from 1.1 × 10−5/°C. at −196°C. to 22 × 10−5/°C. at 30°C. to 58 × 10−5/°C. at 138°C., the melting point of the crystal. The coefficient of the b dimension was found to vary from −2.8 × 10−5/°C. at −196°C. (questionable) to +3.8 × 10−5/°C. at 30°C., and then to −7.3 × 10−5/°C. at 138°C. These values were obtained from series expansion analytical fits to the experimental points, and are less accurate at the ends of the temperature range; the 30°C. values are probably correct to a few per cent.

Preparation and properties of monodisperse branched polystyrene

Abstract: : Model branched polymers have been prepared by the reaction of relatively monodisperse polystyryl lithium with silicon tetrachloride. The branched molecules have been carefully characterized by light scattering and osmotic pressure measurements. A study of the dilute solution properties of the branched molecules has confirmed the theoretical development of the branching coefficient, g., by Zimm and Kilb. The second vi rial coefficient, Az , has been found to decrease with increased branching. In addition, the Huggins constant, k', has been found to be a poor measure of branching in molecules.

Thermal coloration and insolubilization in polyacrylonitrile

Abstract: The thermal coloration reaction in polyacrylonitrile is shown to be similar to that which occurs in polymethacrylonitrile, consisting essentially of the linking up of adjacent nitrile groups to form conjugated carbon-nitrogen sequences. Thus infrared spectral changes in both polymers consist of a decrease in CN absorption accompanied by the development of CN and conjugated CN absorption. The reactions are accelerated similarly, by nucleophilic reagents such as acids either copolymerized into or external to the polymer chains. There are, however, two major differences between the coloration behaviors of these two materials. Firstly, while polymethacrylonitrile remains color-stable below 200°C. in the absence of nucleophilic initiating agents, pure polyacrylonitrile colors at a finite rate which is not reduced by further attempts at monomer purification. This is due to the fact that the tertiary CH structures in polyacrylonitrile, absent in polymethacrylonitrile, are capable of initiating coloration. It seems more likely that this occurs intramolecularly than intermolecularly. Secondly, while polymethacrylonitrile remains soluble even when extensively colored, polyacrylonitrile rapidly insolubilizes. This is not due to crosslinking in an intermolecular self-initiation process; rather, it appears that the successive linking up of nitrile groups can move. from molecule to molecule in polyacrylonitrile owing to the more intimate packing of the chains, so that “propagation crosslinks” are produced. This theory of “propagation crosslinking” is supported by the observed influence of various comonomers in inhibiting crosslinking.

Phenylene sulfide polymers. III. The synthesis of linear polyphenylene sulfide

Abstract: Linear polyphenylene sulfide has been synthesized by the condensation polymerization of alkali metal salts of p-halothiophenols. The monomers investigated included the lithium, sodium and potassium salts of p-bromothiophenol and the sodium salts of p-fluoro-, p-chloro-, p-bromo-, and p-iodothiophenol. The mass polymerizations of these monomers were carried out below the melting points of the salts and appear to involve a solid state reaction. Rate measurements were made on the polymerization of these monomers in pyridine and on a model of the propagation reaction. In both cases, the order of reactivities of the sodium salts was I > Br > F ∼ Cl, and in the polymerization reaction, the order of reactivities of the alkali metal salts of p-bromothiophenol was K < Na < Li. Comparison of the rates of the polymerization and model reactions indicates that the reactivities of all functional groups were essentially identical for the iodo and bromo derivatives. However, this comparison indicated that for the chloro and fluoro derivatives, the polymer chain endgroups were more reactive than the monomers. This effect, termed preferential polymer formation, has been verified for the polymerization of sodium p-fluorothiophenoxide by the determination of unreacted monomer after the polymerization. Complete control of side reactions which lead to chain termination has not as yet been achieved for these condensation polymerization. Linear polyphenylene sulfide is kinetically stable in air and nitrogen up to 400°C. In nitrogen, a residue forms, representing approximately 50% of the original weight of the polymer, which is kinetically stable up to 900°C.

Precipitation of polyelectrolytes by salts

Abstract: Precipitation of poly(acrylic acid) by added salts has been investigated under various conditions. The PAA was neutralized to various degrees of ionization α by tetra-n-butyl ammonium hydroxide. The minimum salt concentration Cs at which precipitation occurs was determined at various polymer concentration Cp, temperature T, and α. The amount of bound cations to polyions, the change in ion hydration, and the polymer expansion near Cs were estimated by conductance, refractive index, and viscosity measurements, respectively. It is concluded that there are two kinds of precipitation; The L type which satisfies the relation Cs ≐ αCp and occurs at high α due to cation binding to the polyions, and the H type in which Cs is independent of Cp and which appears at low α with salts other than those having large ions. This classification of the precipitation is justified also by the Cs – T relation; in the L type, Cs is nearly independent of T, and in the H type Cs increases with T. At intermediate α-values pronounced specificities of salt ions are found in the precipitation; at α = 0.25, with Mg2+ the H type appears, while with Ba2+ or Ca2+ the L type appears, although all of these divalent cations are bound to polyions to the same degree. This is due to the difference in the hydration of the polyion-cation complexes. In the L-type the formation of cation bindings, such as salt bridge, makes the polymer hydrophobic, while in the H type highly concentrated salt ions render the polymer solution unstable by changing the arrangement of the water molecule.

Polymerization by oxidative coupling. II. Oxidation of 2,6‐disubstituted phenols

Abstract: Many 2,6-disubstituted phenols are readily oxidized with oxygen, a tertiary amine and a copper (I) salt being used as catalyst. The products are diphenoquinones (I) or 1,4-polyphenylene ethers (II): The effect of variation of the substituents on the phenol and the infrared spectra of the polymers is discussed. Amine complexes of copper salts are the only effective catalysts found for the polymer-forming reaction. The effect on the catalyst of varying the copper salt and the ligand is discussed.

Thermal conductivity of high polymers from −180°C. to 90°C.

Abstract: The thermal conductivity of plastics is relatively small and for this reason not easily measured. That is why the results in the literature vary sharply. Therefore measurements were made in the German Plastics Institute of the thermal conductivity of plastics with different methods and the results checked against each other. As the overall agreement is very good, we shall give the results only from a quasistationary method which works over a large temperature range. A good thermal contact at the surface of the sample is decisive. Therefore we had to abandon high vacuum as thermal insulation in favor of helium gas, which gives a good and exactly evaluated thermal contact. Thermal losses to the outside had to be prevented by guard rings. We deal first with amorphous high polymers. Their thermal conductivity varies only slightly with temperature even if one goes through the second-order transition region. However, a break in the curve of the thermal conductivity, is characteristic that is to say, a ...

Structural dependence of the electrical conductivity of polyethylene terephthalate

Abstract: The direct current conductivity of three different forms of polyethylene terephthalate was studied over a wide temperature and voltage range to determine the structural dependence of the conduction process. From the films in the amorphous, crystallized, and oriented and crystallized forms it was determined that crystallization reduces the conductivity by more than one order of magnitude. Orientation results in a sixfold decrease in conductivity. The conductivity does not change over a wide range of molecular weight or carboxyl end group concentration. As shown from model polymers and copolymers, disruption of chain symmetry and molecular packing, introduction of side chains, or any other modification which reduces the crystallinity and order, results in greater conductivity. The structural dependence of conductivity, the temperature dependence, and the current–voltage relationships of polyethylene terephthalate are consistent with a proposed ionic mechanism for the conduction process.

Polymer NMR spectroscopy. VI. Methyl methacrylate–styrene and methyl methacrylate–α‐methylstyrene copolymers

Abstract: The NMR spectra of methyl methacrylate–styrene and methyl methacrylate–α-methylstyrene copolymers exhibit, among other features of interest, an unexpected multiplicity in the 6.4–7.8 τ region, characteristic of methoxyl protons. This multiplicity is believed due to magnetic shielding by styrene units. By comparing the results of a statistical analysis of monomer sequence probabilities with the relative areas of the methoxyl peaks, it is shown that the degree of shielding of the methoxyl protons is dependent not only upon the presence of styrene units as nearest neighbors along the chain but also upon their stereochemical configuration with respect to the methyl methacrylate units. By means of reasonable assumptions it is possible to explain the copolymer spectra and to give a partial description of the stereochemical configuration of the methyl methacrylate–styrene copolymers. The NMR method should be valuable in the analysis of other copolymers, particularly block and graft copolymers.

Polymerization of methyl methacrylate by triethylboron–oxygen mixtures

Abstract: The effect of oxygen on the rate of polymerization of methyl methacrylate catalyzed by triethylboron has been investigated at temperatures in the range 0–52°C. In the absence of oxygen polymerization does not occur, but formation of polymer begins immediately on admission of oxygen. Polymerization is characterized by a decrease in rate with increasing conversion which is most pronounced when the concentrations of oxygen and triethylboron are greatly different. The initial rate of polymerization is proportional to the square root of the oxygen concentration and inversely proportional to the degree of polymerization of poly(methyl methacrylate) formed, confirming the radical nature of the polymerization. The apparent activation energy for the polymerization was unusually low, only 4 kcal./mole. A mechanism in which initiating radicals are produced by a sequence of reactions involving autoxidation of the boron alkyl to peroxide followed by induced decomposition of the peroxide by excess boron alkyl is suggested.

The swelling of polymer systems in solvents. I. Method for obtaining complete swelling–time curves

Abstract: A photometric method for measuring the swelling of polymers in solvents from zero time to equilibrium has been described. The method consists in following continually the growing “shadow” of the specimen as it imbides the solvent. Equipment details and method of operation are discussed. Typical swelling–time curves for butyl vulcanizates are reported. These serve as examples of the rapidity and reproducibility of the method and also as demonstrations of the completeness of solvent uptake. Essential agreement between the results on volume swelling at equilibrium obtained by the photometric method and by the conventional gravimetric method is observed. The new method is important in that the rate of swelling can be measured. Its use in this regard in studying the diffusion of liquids in polymers will be referred to subsequent papers in this series.

Microvoids in fibers as studied by small‐angle scattering of x‐rays

Abstract: Commercial and experimental fibers show diffuse small-angle x-ray scattering which varies in amount and shape, depending upon how the fibers were produced and also upon what aftertreatments they have received. Evidence is given showing that the amount of scattering should be interpreted in terms of the void content or microporosity in the fiber. These voids are too small to be seen by the light microscope, but are found to be measurable in the 15–200 A. range by present techniques. The spinning method greatly affects a fiber's void content. Wet-spinning and dry-spinning of a polymer solution produces fibers with a high void content. Melt-spinning produces yarns with relatively low void content. The cause of this difference is discussed. Voids are shaped by the spinning process in almost all cases. The fiber can be visualized as having longitudinal cracks, crevices, or ellipsoidal. voids in the as-spun condition, even though no molecular alignment is observed. This shaping was found to arise from a combination of (1) a shearing action of the spinneret and (2) tension on the windup. The voids are further elongated as the fiber is drawn.

Radiation‐induced solid‐state polymerization of ring compounds

Abstract: Ring compounds such as trioxane, β-propiolactone, diketene, and 3,3-bischloromethylcycloxabutane can be polymerized only in the solid state by γ-radiation. These ring compounds polymerize by a ring-opening, ionic mechanism to highly crystalline, high molecular weight, linear polymers. In general, the conversion vs. irradiation time curves reach a limiting value at relatively low yield. These saturation phenomena are due to the disruption of unreacted monomer lattice by the formed polymer. The polymers obtained from large-monomer crystals are found to have outward appearances of large crystals which suggest the monomer crystalline lattice has influenced that of the polymer. Moreover, the polymers from large crystalline monomer have higher polymerization rate and better orientation of the crystallites, as ascertained through x-ray diffraction and polarizing microscopic analyses. Polarizing microscopic photographs of the polymers show birefringence clearly. These facts indicate that the structure of the monomer lattice directly imposes order and orientation upon the polymer. X-ray diffraction analyses show that the polydiketene chain has a spiral configuration and poly-β-propiolactone has a planar zigzag chain. Some consideration of the propagation mechanism in the crystalline state of 3,3-bischloromethylcycloxabutene, γ-propiolactone, diketene, and trioxane is made. Investigations of the binary systems with β-propiolactone were carried out to determine the effects of additives upon the propagation mechanism.