Showing papers in "Journal of Polymer Science in 1952"

Method of colloid titration (a new titration between polymer ions)

Abstract: A general discussion about the method of colloid titrations is given in this report. A new titration method is based on the stoichiometric combination of positive and negative colloid ions. The end point is decided by indicators (known as metachromatic coloring matters) like toluidine blue. The standard colloid reagents are P.V.S.-K (potassium salt of polyvinyl alcohol sulfate) and Macramin (N-polymethylated chitosan derivatives). The typical operations of this method are described briefly: the direct, indirect, and differential titration methods. The colloid titration curve is somewhat different from the acid-base titration curve obtained potentiometrically, but it is characteristic and reproducible under definite conditions and so it is useful in quantitative and qualitative analysis. This titration may be carried out even under extraordinary dilute conditions (5 × 10−4N) and the entire process is quite similar to the usual acid-alkali titration. The precision is below ±ca. 5% if the method is carefully followed.

Molecular distribution in condensation polymers

Abstract: The theory of molecular distribution in condensation polymers has been extended to include systems of a rather general type. Equations for the distribution and the weight-average molecular weight are given.

The p-phenylene linkage in linear high polymers: Some structure–property relationships†

Abstract: The high crystallite melting point of polyethylene terephthalate (Terylene) compared with the melting points of the aliphatic polyesters emphasizes the significance of the p-phenylene linkage as an important factor determining polymer properties. A consideration of other polymer structures containing the p-phenylene linkage shows that its influence is independent of any polar groups which may be present. X-ray examination of the crystallite structure of polyethylene terephthalate and related substances has revealed no evidence of strong intermolecular forces. From a study of co-polyesters based upon polyethylene terephthalate with aliphatic dibasic acids it is shown that the melting point of compositions containing more than 40 mole per cent of ethylene terephthalate is essentially independent of the aliphatic di-basic acid employed. The Flory relationship between crystallite melting point and mole fraction of the units forming the crystallites shows fair agreement with the results obtained. The calculated latent heat of fusion of polyethylene terephthalate approaches closely to that of the corresponding aliphatic polyesters, and suggests that the high melting point induced by the p-phenylene linkage is due to chain rigidity rather than to strong interchain attraction. This rigidity is consistent with the second order transition temperatures of such polyesters. It is shown that second order transition temperature is a linear function of the number of p-phenylene linkages per unit chain length. The p-phenylene linkage reduces the possibilities of change of shape available to a given length of chain, so accounting for the low entropy of crystallization and high melting point of polyethylene terephthalate. Evidence is advanced for the isomorphism of adipyl and terephthalyl linkages in linear polyamides. The absence of isomorphism in polyethylene adipate/terephthalate copolymers is ascribed to the weakness of the interchain forces.

Rates of thermal degradation of polystyrene and polyethylene in a vacuum

Abstract: When heated in a vaccum at 325° to 375°C., polystyrene yields mainly the monomer and some dimer, trimer, tetramer, etc., indicating that the breaks in the molecular chains occur largely at the ends. Polyethylene, under similar conditions, but at a some-what higher temperature, yields fragments of an average molecular weight of about 700, indicating that the molecular chains break, mostly at random positions. A study was made of rates of thermal degradation of these two polymers by measuring rates of loss of weight of samples by means of a very sensitive tungsten spring balance enclosed in a vaccum. The samples were limited to 5–6 mg. in order to avoid spattering during degradation. Rate curves plotted against per cent loss of weight by volatilization indicate that in the case of polystyrene the process is intermediate between a zero and first order reaction, while in the case of polyethylene, the process approximates a first order reaction. Activation energies were calculated on the basis of rates of degradation at various temperatures. The values thus obtained for polystyrene and polyethylene are 58 and 68 kilocalories, respectively.

Mastication of rubber, I. Mechanism of plasticizing by cold mastication

Abstract: A mechanism is proposed for the degradation of natural rubber by the cold mastication process. The rubber hydrocarbon is considered to be ruptured into free radicals by the deformation of the rubber. These recombine, or react with oxygen or other suitable reactant, and thereafter do not necessarily recombine. Experimental evidence supporting this mechanism is reported, mainly the masticating or rubber in an atmosphere of nitrogen after incorporation of substances likely to interact with the radical ends of the ruptured chains. Forty-seven substances functioning in this way are listed. A more detailed study has been carried out with one of these, benzoquinone, varying separately concentration, time of mastication, temperature, and mean chain length of rubber. A similar mechanism is shown to apply to the synthetic rubbers tested. The probable chemical reactions occuring and the correlation of cold mastication with other freeradical systems are discussed. The role of oxygen in cold mastication is considered in detail. The possible significance and practical application of the work is suggested.

Rates of initiation in vinyl polymerization

Abstract: The rates of initiation Ri of polymer chains in styrene and methyl methacrylate have been measured for four different catalysts. The results for styrene at 60°C are: Ri = 1.28 × 10−5[azo]; Ri = 2.96 × 10−6[Bz2O2]; Ri = 6.12 × 10−7[CHP]; Ri = 9.96 × 10−5[BHP]. Azo, Bz2O2, CHP, and BHP refer to 2-azobisisobutyronitrile, benzoyl peroxide, cumene hydroperoxide, and tert-butyl hydroperoxide, respectively. Rates are expressed in moles per liter per second. The corresponding results for methyl methacrylate at 60° are: Ri = 1.42 × 10−5[azo]; Ri = 6.62 × 10−6[Bz2O2]; Ri = 3.92 × 10−7[CHP]; Ri = 7.30 × 10−8[BHP]. Catalyst efficiencies for azo and Bz2O2 are shown to be nearly unity in both monomers. Chain transfer constants were calculated for all catalysts in both monomers. Photopolymerization was shown to proceed via chains growing in one direction only. The polymerizations were all carried out in the pure monomers (bulk polymerization) with exclusion of oxygen and other inhibitors.

Studies concerned with the structure of collagen. II. Stress-strain behavior of thermally contracted collagen

Abstract: Thermally contracted collagen, when swollen in appropriate media, obeys rubber elasticity theory. On the basis of the measurements which were made, it was possible to establish that the material behaves as if it were a network polymer crosslinked by covalent bonds. However, the chemical nature of these crosslinks is not known. The molecular weight of the chain between points of crosslinking is approximately 55,000. This corresponds to the molecular weight calculated for collagen from x-ray data (60,600), assuming the c axis of the unit cell to be the characteristic 625 A. spacing.

Structure of copolymers from polymerization of ethylene of polyvinyl acetate

Abstract: The formation of “grafted” vinyl copolymers by polymerizing one monomer in the presence of a preformed vinyl polymer has been extended to a new monomer-polymer combination and one point of attachment of the lateral (grafted) polymer chain has been shown precisely. When ethylene was polymerized in the presence of polyvinyl acetate under a variety of conditions, modified polyvinyl acetates having lateral polyethylene chains were formed. Alkaline methanolysis of such modified polymers yielded mixtures of long-chain fatty acids and ethylene-modified polyvinyl alcohols (which were inseparable from any unmodified polyvinyl alcohol that may have been present). The hydrolysis to long-chain acids shows that polyvinyl acetate acts as a chain transfer agent and that one point of lateral growth of polyethylene chains is the CH3 in the acetoxy group of polyvinyl acetate. The second hydrolysis product, the ethylene-modified polyvinyl alcohol, shows that chain transfer, and subsequent growth of polyethylene chains, can also occur on the chain carbons of polyvinyl acetate. Oxidation of the ethylene-modified polyvinyl alcohols yielded a mixture of oxalic acid and long-chain fatty acids. At the low ethylene pressures studied (300 to 1200 p.s.i.) only traces to small amounts of low molecular weight polyethylene waxes were formed.

The number-average molecular weight of polythene

Abstract: Direct determinations of the number average molecular weights of a variety of British and American polythenes have been made making use of two experimental techniques: (1) ebulliometry and (2) high temperature osmometry. An intrinsic viscosity-molecular weight relation has also been obtained which covers the range 1.3 × 103 to 76 × 103 and includes representative samples of Alkathene. The Huggins constants k' and μ have been evaluated from viscosity and osmotic pressure data and their bearing on polythene structure discussed.

The effect of chemical composition on selected physical properties of linear polymers

Abstract: A review of the data available in the literature and new data reported in this paper show that in any homologous series of condensation polymers there is a uniform change in the melting point as the hydrocarbon content of the polymer is increased. If all such series are treated as copolymers of the simplest modifying element and polyethylene and the composition expressed on a mole fraction basis, the data when presented graphically show that the melting points of any such series passes through a minimum at some intermediate composition. The position of the minimum as well as the depth of the minimum is dependent on the polarity of the modifying group. This survey has included aliphatic polyesters, aromatic polyesters, polysulfides, cellulose derivatives, and polyamides. Some of the series are complete enough to show a definite minimum with compositions on either side of the minimum with higher melting points. In some compositions based on the very highly polar groups, such as amides, the series is not complete enough to establish the complete shape of the curve, but the indications are strong that the minimum does exist.

Absolute propagation rates in emulsion polymerization. III. Styrene and isoprene

Abstract: The study of the rate of polymerization per particle in emulsion systems has been extended to include the following monomers and initiator systems: Text Table Text. Monomer Initiator System Styrene Persulfate Styrene CHP-TETA Isoprene DIBHP-TEPA In all cases, linear rates of polymerization were obtained in the region where the number of particles can be considered as remaining constant (30–60% conversion). Furthermore, the addition of catalyst in this region did not affect the rate of polymerization, so that a rate per particle could be calculated. From the rates per particle, the following absolute propagation rates were calculated for styrene and isoprene, and are compared with values obtained for styrene from photoinitiation studies: Text Table Text. Monomer Catalyst system Eact. A kp at 60°C. Styrene Persulfate 7.4 4.1 × 107 277 Styrene CHP-TETA 8.4 3.3 × 107 221 Styrene Photoinitiation 7.8 2.2 × 107 176 Isoprene DIBHP-TEPA 9.8 1.2 × 108 50

Control of dust in solution for turbidimetry

Abstract: Dust-free polymer solutions have been prepared with the aid of special equipment which is described.

X‐ray diffraction studies of addition compounds of amylose with inorganic salts

Abstract: Many salts in aqueous alcohol solution can be exchanged for the alkali in oriented filaments of alkali amylose. If the filaments are held taut during exchange, orientation is retained, and excellent fiber patterns are produced. By this method, compounds of amylose were obtained with the iodide, bromide, formate, acetate, and propionate of potassium and with sodium bromide and ammonium fluoride. In addition, potassium bicarbonate–amylose was formed by the action of carbon dioxide on moist filaments of potassium hydroxide–amylose. Data on the composition of the amylose–potassium salt filaments indicate stoichiometric compound formation between amylose and salt, the ratio of salt molecules to glucose residues being 1:2 for the iodide, bromide, formate, and tetragonal form of the acetate, and 1:1 for the propionate and the orthorhombic form of the acetate. As shown by x-ray diffraction patterns, the potassium salts crystallized in two structures. One, based on a tetragonal unit cell, was common to the iodide, bromide, formate, acetate, and bicarbonate; the other, based on an orthorhombic unit, was the stable structure for the acetate and the propionate. Dimensions of the tetragonal unit cells of air-dried filaments of the iodide and bromide were identical, with a0 = 10.7 and c0 (fiber axis) = 16.1 A. Corresponding dimensions for the formate and acetate were 10.8 and 16.1 A., and those for the bicarbonate were 10.8 and 15.8 A. The orthorhombic structures of the potassium acetate and propionate addition compounds with amylose appeared to be isomorphous, unit cells having a0 = 11.0, b0 = 18.1, c0 (fiber axis) = 17.9 A. for the acetate, and a0 = 11.4, b0 = 18.0, c0 = 17.6 A. for the propionate. The tetragonal structural modification is of particular interest. Observed diffraction maxima were consistent with the enantiomorphous space groups, P4121 and P4321, and this, together with composition and density data, demands that the amylose chains posses fourfold screw symmetry, with four glucose residues corresponding to the fiber repeat period of 16.1 A. Succesive residues in the amylose chain must, therefore, be identical. This is the first x-ray evidence which has demonstrated the identity of successive residues in the amylose chain. From a Patterson projection of potassium bromide amylose, the positions of the inorganic ions were determined. The Fourier projection, ρz(x,y), computed from Fhk0 with signs determined by the bromide ion, confirmed the location of the inorganic ions and gave a general outline of the packing of the amylose chains.

Study of degradation of polystyrene by means of mass spectrometry

Abstract: The degradation of polystyrene by heat and ultraviolet radiant energy was followed by mass spectrometric analysis of the gaseous products evolved. Oxygen content, discoloration, and insolubility of the treated polymer were also investigated. The degradation of polystyrene involves two different processes: (1) the breakdown of thermolabile groups formed in the polymer prior to degradative treatment; this breakdown is caused by exposure to heat at 120°C. in vacuo and 115°C. in oxygen and to ultraviolet radiant energy at 120°C. in vacuo and 118°C. in oxygen; it is accompanied by the removal of residual materials such as solvent; and (2) the oxidation of the polymer caused by exposure to ultraviolet radiant energy in the presence of oxygen. The evolution of benzene, methyl ethyl ketone, dimethylbenzenes, and alcohols is associated with the first stage involving the breakdown of thermolabile groups and the removal of residual materials. Compounds such as formaldehyde, formic acid, and acetic acid are produced as a result of oxidation of the polymer. The oxygen content of the polymer was decreased from 0.33 to approximately 0.1 percent by heating at 120°C. in vacuo and at 115°C. in oxygen, and by exposure to ultraviolet radiant energy at 120°C. in vacuo. Ultraviolet treatment at 118°C. in oxygen for 250 hours quadrupled the original oxygen concentration. Discoloration of the polystyrene was definitely noted only on exposure to ultraviolet radiant energy in oxygen and is associated with oxidation of the polymer. The material became insoluble as a result of all heat and ultraviolet treatments. The amount of insoluble material increased with severity of exposure conditions.

A new tool for determination of the stage of polymerization of thermosetting polymers

Abstract: Studies of the change of attenuation and velocity of longitudinal ultrasonic waves with proceeding polymerization of thermosetting plastics have revealed that this new technique may permit rapid determination of the stage of polymerization under various conditions. The ultrasonic equipment used for these tests is described in detail. On the basis of results so far obtained, future possibilities for the application of this new technique in studying polymerization reactions are outlined.

Intrinsic viscosity–molecular weight relation for polymethyl methacrylate: Effect of size distribution

Abstract: Polymethyl methacrylate samples were prepared by bulk polymerization at 60° initiated by benzoyl peroxide and 2-azobisisobutyronitrile. Osmotic measurements and intrinsic viscosities were made in chloroform solutions at 20°, using unfractionated polymers of varying number-average molecular weights. The relation between number-average degree of polymerization and intrinsic viscosity was obtained and compared with reported relationships for fractionated polymers under the same conditions. Inferences were drawn regarding the size distribution in the unfractionated polymers.

Light scattering studies on some muscle proteins

Abstract: A light scattering investigation of actin and actomyosin gives the following information. The weight average molecular weight of 80,000 is found for G-actin. The average molecular weight and length of F-actin decrease upon increasing concentration of electrolyte, the effect being especially pronounced in the case of KI. The average molecular weight and length of F-actin decrease with increasing of pH of polymerization. The average length and molecular weight of F-actomyosin increase with decreasing ionic strength. The average length and molecular weight of F-actomyosin decrease with decreasing size of the F-actin component.

Solubility and fractionation of polyvinylpyrrolidone

Abstract: Polyvinylpyrrolidone (PVP) can be conveniently fractionated from water by successive precipitation with acetone, from chloroform with ether, or from ethanol with benzene. The major part (60–70%) of the common PVP has the intrinsic viscosity of 0.12–0.30. The fractions can be liberated from the low molecular components by extraction of the solid polymer with acetone. Precipitability with ammonium sulfate is a very convenient means of characterizing the fractions. The amount of ammonium sulfate needed to produce turbidity decreases with increasing mean molecular weight of the fractions, with the increasing concentration of the polymer, and with increasing temperature. The molar concentration of ammonium sulfate that produces turbidity is a linear function of the logarithm of the mean molecular weight of the fractions. The amount of ammonium sulfate which produces turbidity decreases linearly with increasing temperature.

Molecular weight degradation of polyvinyl acetate on hydrolysis

Abstract: When the acetate groups of polyvinyl acetate are removed and subsequently restored, the viscosity of the polymer is usually decreased. It is found that after such processing, vinyl acetate polymers prepared at a given temperature approach a maximum viscosity regardless of the viscosity of the original resins. This maximum is increased by lowering the temperature of polymerization and is different for other vinyl esters. The extent of degradation is negligible at low conversions. It is concluded that this phenomenon is characteristic of the monomer. The chemical bond responsible for the degradation has many of the properties of ester linkages. The resins degrade with both bases and acids although the latter catalyst sometimes requires the presence of water. They also degrade when heated in a solution of pyridine, acetic acid and acetic anhydride. The extent of degradation closely parallels the degree of hydrolysis. It is suggested that these ester linkages are formed during polymerization as a result of transfer with the carbon-hydrogen bonds of the acetate groups of both monomer and polymer. Evidence of another transfer reaction involving the vinyl group, but having no bearing on the degradation, is also advanced. If polyvinyl acetate is alcoholized with an acid catalyst, in the absence of water, the processed resin may have a higher viscosity than would be the case with an alkaline catalyst. How much higher is governed by the type of initiator used in the polymerization. This suggests that polymer molecules may be united under these conditions, but the nature of the reaction is obscure.