bluuebunny/crossref_metadata_2025 huggingface dataset:
Macromolecular models for branched PVC. II. Reactivity of chlorine bound to a tertiary carbon atom in the copolymer vinyl chloride–isopropenyl chloride
Authors: Caraculacu Adrian A.
Published: April 2003

The selectivity of the phenolysis reaction of a chlorine atom bound to a tertiary carbon ClT on a macromolecular model, i.e., the copolymer of vinyl chloride–isopropenyl chloride, was verified. The phenolysis reaction can be used as a chemical method to determine ClT in the copolymers. Phenolic polyelectrolytes are obtained as products. The increase of the ClT content leads to an appreciable decrease of the thermal stability of the polymer. The thermal decomposition by dehydrochlorination is a chain reaction. The γ and ultraviolet radiolysis processes did not reveal a remarkable influence of ClT; the samples with an increased ClT content showed a decreased stability towards sunlight. One concludes that when ClT is present in PVC it can initiate the decomposition reaction at lower temperatures than would be expected.
Preparation and characterization of syndiotactic polypropylene
Authors: Boor J. , Youngman E. A.
Published: April 2003

The preparation and characterization of syndiotactic polypropylene are reported. The influence of polymerization variables on the syndiotactic regulating capacity of the VCl4–AlEt2Cl catalyst were investigated. Vanadates could be substituted for VCl4, and Al(C6H5)2Cl or AlEt2Br for AlEt2Cl under suitable conditions. Hydrogen functioned as a chain transfer agent for the AlEt2Cl–VCl4 catalyst, and polymerizations which were terminated with tritiated alcohols yielded polymers containing bound tritium. The syndio‐regulating capacity of the AlEt2Cl–VCl4 catalyst was increased under specific conditions when cyclohexene, oxygen, or tert‐butyl perbenzoate was incorporated. A polymerization mechanism is proposed. According to this mechanism, preference for a monomer complexing mode which minimizes steric repulsions between methyl groups of the new and last added monomer unit is responsible for syndiotactic propagation. Characterization included determination of infrared syndiotactic indices, melting points (65–131°C.), glass transition temperature, densities (0.859 to 0.885 g./cc.), nuclear magnetic resonance spectra, birefringence, differential thermal analysis spectrograms, solubility, and heat of fusion (∼450 cal./mole).
Studies on Ziegler‐Natta catalysts. Part IV. Chemical nature of the active site
Authors: Rodriguez L. A. M. , van Looy H. M.
Published: April 2003

The determination of the number of sites active in the polymerization of ethylene on the surface of α‐TiCl3–Al(CH3)3 dry catalysts leads to the conclusion that this number is small in comparison to the total surface of the catalyst. Qualitatively this conclusion is also reached by two other independent methods. Infrared spectra of the catalyst before and after polymerization do not show a change in the type of bonds present in the surface. Electron microscopy proves that no active sites are formed on the basal plane of the α‐TiCl3 which constitutes 95% of the total surface. The results strongly favor the lateral faces of α‐TiCl3 as the preferred location of active centers. The lateral faces contain chlorine vacancies and incompletely coordinated titanium atoms. This must then be the essential conditions for the formation of active centers. The propagation of the polymer chain has been repeatedly shown to follow an insertion mechanism. The active site, therefore, necessarily contains a metal–carbon bond. The study of catalysts derived from TiCl3CH3 leads to the conclusion that a TiC bond on titanium of incomplete coordination is the active species in these cases. The alkylation of surface titanium atoms was proven to be an intermediate step in the catalyst formation from TiCl3 and AlR3. Survival of titanium–alkyl bonds on the lateral faces, where titanium atoms are incompletely coordinated explains best, in the light of our data, the activity of Ziegler‐Natta catalysts. Coordination of aluminum alkyl compounds in or around the active center probably complicates the structure of the active centers.
New high‐temperature polymers. II. Ordered aromatic copolyamides containing fused and multiple ring systems
Authors: Dobinson Frank , Preston J.
Published: April 2003

Symmetrical diamines, containing preformed carbonamide linkages, were prepared by reacting nitrobenzoyl chlorides with aromatic diamines and reducing the dinitro intermediates. The diamines were polymerized with aromatic diacid chlorides to give wholly aromatic ordered copolyamides of exceptionally high thermal stability. Ordered diamines were prepared containing only phenylene units as the aromatic portion, and others containing phenylene and naphthylene or biphenylene groups. Low‐temperature solution polymerization of these diamines with isophthaloyl chloride, 4,4′‐bibenzoyl chloride, or 2,6‐naphthalenedicarbonyl chloride, gave thirteen ordered copolyamides, each containing a naphthylene and/or biphenylene group in its repeating unit. Differential thermal analyses and thermogravimetric analyses showed these polymers to have melting points or decomposition temperatures of from 420 to over 500°C. Films of one of the polymers had a breakdown voltage of 3000 v./mil at 180°C. Fibers of the same composition had tenacities of up to 8 g/den.; a 5.5 g/den. sample retained 85% of its tenacity after 17 hr. at 300°C. and 21% after 9 days.
Correlation of cationic copolymerization parameters of cyclic ethers, formals, and esters
Authors: Yamashita Yuya , Tsuda Tetsuo , Okada Masahiko , Iwatsuki Shouji
Published: April 2003

Carefully determined cationic copolymerization parameters of cyclic ethers, formals, and esters are collected. Relative reactivity correlates with basicity and free energy. Further correlations of the copolymerization parameters for styrene, the effect of promoters, and the known mechanism of hydrolysis permitted a decision between the carbonium ion (including acylium ion) or the oxonium ion as the active intermediate of the propagation. Structural features which promote depropagation are identified. Equations describing these possibilities were derived and briefly discussed. Catalyst and solvent effects limited the correlation possibilities.
Flow rates of polymer solutions through porous disks as a function of solute. II. Thickness and structure of adsorbed polymer films
Authors: Rowland Fred W. , Eirich Frederick R.
Published: April 2003

The thickness of films of poly(methyl methacrylate) (PMMA), poly(vinyl acetate) (PVAc), and polystyrene (PS) adsorbed on Pyrex glass was studied by measuring the flow rates of polymer solutions and the corresponding pure solvents through sintered filter disks. Adsorption isotherms were in agreement with those reported by other workers and showed saturation adsorption equivalent to 2–8 condensed monolayers of monomer units. Film thicknesses were of the order of magnitude of the free coil diameters in solution and were directly proportional to the intrinsic viscosity of the polymer, except for PS in benzene where the thicknesses leveled off as molecular weight increased. It was concluded that polymers adsorb from solution in monolayers of compressed or interpenetrating coils; that below some critical molecular weight which varies with polymer and solvent, a much larger fraction of the segments lies directly in the interface; that adsorbed films may consist of a dense layer immediately adjacent to the surface and a deep layer of loops extending into the solvent; and that it is the segment—solvent interaction rather than the segment—surface interaction which dominates the conformation of the adsorbed chain.
Crystalline polymers of bis(β‐chloroethyl) vinylphosphonate
Authors: Marktscheffel Fritz , Turbak A. F. , Wilchinsky Z. W.
Published: April 2003

The polymerization of bis(β‐chloroethyl) vinylphosphonate to a crystalline solid was carried out with a Ziegler‐Natta catalyst. A confirmation of the crystalline nature of the polymers was carried out by x‐ray diffraction. The polymers would not melt even at temperatures up to 620°C., but instead began to char. However, they were soluble in dimethylformamide and acrylonitrile.
Rates of copolymerization of acrylonitrile and ethylenesulfonic acid
Authors: Alfrey Turner , Pfeifer Charles R.
Published: April 2003

Use was made of differential absorption in the near‐infrared region to follow the rates of copolymerization of acrylonitrile (AN, M1) with ethylenesulfonic acid (ESA, M2) in aqueous zinc chloride solution. The concentrations of the monomers were followed separately and simultaneously. It was found experimentally that the ratios d log [M1]/dt and d log [M2]/dt were each constant. This was interpreted to mean that the product of the reactivity ratios of the two monomers (r1,r2) is unity and that the ratio of termination rate constants is equal to the propagation reactivity ratio. It was found that d log [M1]/d log [M2] = r1 = 4.52. This value is in fair agreement with polymer composition data obtained independently. In the Q—e system the equality r1r2 = 1 is equivalent to the monomers having equal e values. Thus, in the AN—ESA system, P1/P2 = k11/k21 = k12/k22 = k1T/k2T, where P1 is the resonance constant of polymer radicals ending in units of M1; and k11, k12, and k1T are the rate constants involving the reaction of this radical with M1, M2, and T (terminating agent), respectively. A gel effect was not observed even at M1 conversions as high as 88%.
Thermal volatilization analysis: A new method for the characterization of polymers and the study of polymer degradation
Authors: McNeill I. C.
Published: April 2003

In a continuously evacuated system in which volatile products are passing from a heated sample to the cold surface of a trap some distance away, a small pressure will develop which varies with the rate of volatilization of the sample. If this pressure (measured by Pirani gage) is recorded as the sample temperature is increased in a linear manner, a TVA thermogram showing one or more peaks is obtained. TVA thermograms for a number of polymers and copolymers are presented and briefly discussed. The technique has some advantages over TGA for characterizing polymers or studying qualitative aspects of polymer degradation.
Polymerization in the crystalline state. IX. Relation between the velocity of radiation‐induced in‐source polymerization and post‐polymerization
Authors: Morawetz Herbert
Published: April 2003

A general relation is derived between the polymerization velocities to be expected for crystalline monomers during irradiation at a polymerization temperature and the post‐polymerization observed in samples irradiated at very low temperatures and subsequently warmed outside the irradiation source. For acrylamide, the experimental data are in satisfactory agreement with the theoretical relationship. The possible reasons for a deviation from this relationship are discussed.
Polymers derived from fluoroketones. I. Preparation of fluoroalkyl acrylates and methacrylates
Authors: Pittman A. G. , Sharp D. L. , Lundin R. E.
Published: April 2003

The preparation and physical properties of some perhaloalkyl acrylate and methacrylate esters are discussed. In the synthetic route to the perhaloalkyl esters, acryloyl or methacryloyl chloride is made to react with a metal fluoride—perhaloketone adduct. A side reaction which accompanies esterification is the formation of acryloyl or methacryloyl fluoride. Possible mechanisms for the formation of acyl fluoride and ester are considered. Evidence is presented which suggests that acyl fluoride formation may occur by a breakdown of the fluoroalkyl esters through an intramolecular fluorine shift.
Studies on addition polymerization in mixed solvent system. Part I. Chain transfer of water in polymerization of methyl methacrylate
Authors: Bhattacharyya Bhupati Ranjan , Nandi Umasankar
Published: April 2003

The role of water as a chain‐transfer agent in addition polymerization of methyl methacrylate and acrylamide in a mixed solvent system was studied. Water does not have any transfer with the growing polymer radical. The degree of polymerization is found to increase with increasing water concentration. This is probably due to a reduced termination rate resulting from coiling of the polymer chain in the presence of a nonsolvent like water.
Mechanism of ozone attack on α‐methyl glucoside and cellulosic materials
Authors: Katai Andrew A. , Schuerch Conrad
Published: April 2003

Ozone attack on cellulose and related substances was investigated and appears to involve a twofold mechanism. One is a free‐radical chain mechanism involving oxygen in the propagating step. This slow reaction is highly indiscriminate, showing very little, if any, specificity as to the site of attack and resulting in the formation of peroxide, carbonyl, carboxyl, and presumably lactone groups. In the presence of oxygen, kinetic chain lengths of over 100 were measured, but in nitrogen atmosphere the total oxidation of substrate was equivalent to the amount of ozone consumed. The second process appears to be an electrophilic attack which liberates the anomeric carbon of glycosides via an ozone‐catalyzed hydrolysis of glycosidic linkages. This reaction, analogous to a nitronium or chloronium ion‐ or proton‐catalyzed hydrolysis, is postulated since chain degradation of polysaccharides is equally severe in the presence or absence of oxygen, and occurs in buffered solutions or suspensions even in the neutral pH range, and because the main product of ozone attack on α‐methyl glucoside is glucose. Brightness improvement in cellulose involves an electrophilic attack on double bonds and therefore is a direct function of the quantity of ozone used, like chain degradation. It is therefore not surprising that we have found no method of enhancing the specificity of ozone attack on the colored material relative to chain degradation. Because of the topochemical and diffusion‐controlled character of the reaction on cellulose, the use of a different temperature range will cause only a trivial difference in the relative rates of attack.
Effect of thiourea on the radical polymerization of vinyl monomers. Part II. Effect of diphenyl thiourea on the polymerization of methyl methacrylate with benzoyl peroxide as initiator
Authors: Minoura Yuji , Sugimura Takaaki
Published: April 2003

The polymerization of methyl methacrylate (MMA) initiated by benzoyl peroxide (BPO) in the presence of diphenyl thiourea (DPTU) has been studied. It was found that the BPO–DPTU catalyst system was not an effective accelerating system but showed a relatively strong retarding effect. With DPTU derivatives, the polymerization rate was found to decrease with the increase in the electron‐attracting forces of substituents attached to the phenyl groups of DPTU. In the polymerization of MMA initiated by AIBN, the addition of DPTU to the reaction systems affected neither the polymerization rate nor the degree of polymerization. From this fact, it might be concluded that DPTU itself serves as a radical scavenger. It seems most probable from the results of kinetic studies, iodometric titration, and from the effect of an oxidation product of DPTU (diphenyl formamidine disulfide) that the retardation effect observed is attributable to the action of the disulfide (DPFDS). By extending the Alfrey‐Price scheme for the copolymerization reactions to the chain‐transfer reactions, the Q and e values of DPFDS were determined. The apparent chain‐transfer constants for DPTU and its derivatives were calculated by means of rate measurements and were correlated with substituent constants. The mechanism of the polymerization is discussed on the basis of these results.
Effects of polysulfides on the polymerization of methyl methacrylate
Authors: Sugimura Takaaki , Ogata Yayoi , Minoura Yuji
Published: April 2003

The effect of organic sulfur compounds on the radical polymerization of methyl methacrylate initiated by azobisisobutyronitrile at 50°C. has been studied. The sulfur compounds used were benzene‐type polysulfides (C6H5CH2SnCH2C6H5; n = 0–4), benzyl mercaptan, and sulfur (S8). All sulfur compounds studied, except dibenzyl, dibenzyl monosulfide, and dibenzyl disulfide, were found to behave as retarders under these experimental conditions. Chain‐transfer constants of these compounds were determined from rate measurements and from the conventional method based on numberaverage degree of polymerization. Chain‐transfer constants of benzyl‐type polysulfides were less than those of mercaptan and sulfur and increased with increasing sulfur. The correlation of the reactivities of sulfur compounds as transfer agents and their molecular structures is discussed.
Ionic polymerization under an electric field. III. Cationic polymerizations of α‐methylstyrene and styrene
Authors: Sakurada Ichiro , Ise Norio , Tanaka Yoshinobu , Hayashi Yuzuru
Published: April 2003

Cationic polymerizations of α‐methylstyrene and styrene were carried out in an electric field with iodine as a catalyst and ethylene dichloride as the solvent. The effects of the field on the rate of polymerization and the degree of polymerization were studied. It was found that the field increased the rate of polymerization of α‐methylstyrene and, also slightly increased the degree of polymerization, whereas the field had no influence on these quantities in the case of styrene. The expressions for the rate of polymerization and the degree of polymerization, which were derived in a previous paper and refined in the present paper, show that these quantities are generally a function of the degree of dissociation of ion pairs at growing chain ends. For a comparatively large degree of dissociation, these expressions can account for the field effect as was observed on α‐methylstyrene, if one assumes that the degree of dissociation in the presence of an electric field is larger than that in its absence, and that the free‐ion propagation proceeds much faster than the ion‐pair propagation. For a small degree of dissociation, however, these expressions become practically independent of the degree of dissociation so that a possible increase due to the presence of an electric field gives rise to no observable effect on the polymerization. This situation may be interpreted as corresponding to the case of styrene. In other words, the polymerization of α‐methylstyrene has more free ionic character than that of styrene.
Copolymerization of styrene and methyl methacrylate. Reactivity ratios from conversion–composition data
Authors: Meyer Victor E.
Published: April 2003

A method for the determination of reactivity ratios from conversion–composition data has been outlined. The conversion–composition changes during the copolymerization of styrene (M1) and methyl methacrylate (M2) have been studied at 60°C. By a method of graphical intersection, the integrated form of Skeist's equation has been used to determine the reactivity ratios (r1 = 0.54 ± 0.02 and r2 = 0.50 ± 0.06) in reasonably good agreement with values reported in the literature. The area of intersection was used as a measure of the precision of the data.
Solution Polymerization of Acrylonitrile Catalyzed by Sodium Triethylthioisopropoxyaluminate: A Polyacrylonitrile with High Structural Regularity
Authors: Chiang R. , Rhodes J. H. , Evans R. A.
Published: April 2003

A new catalyst for the polymerization of acrylonitrile has been found by reacting sodium aluminum tetraethyl with a stoichiometric amount of oxygen, alcohols, or mercaptans, etc. The catalyst prepared by reacting NaAlEt4 with RSH remains active at temperatures as low as −78°C., polymerizing acrylonitrile into high molecular weight polymers with high conversions. At −78°C., the propagating chain remains active over a period of days, and the chain length increases with time or conversion. At high conversions the molecular weight of the polymer is directly proportional to the concentration of the monomer, the catalyst concentration being kept constant. The efficiency of the catalyst expressed as the ratio of the number of the polymer molecules produced to the number of the sulfur atoms used is in excess of 80%. The weight‐average molecular weight of the polymer measured by light scattering is roughly equal to the number‐average molecular weight determined by sulfur analysis assuming only onesulfur atom in each polymer molecule. Although the data given here are only qualitative in nature, it is nevertheless evident that this system bears great resemblances to anionic polymerizations resulting in “living polymers.” The polymer obtained with the NaAlEt3S(i‐Pr) catalyst at −78°C. differs from free‐radical polyacrylonitrile in exhibiting substantially lower solubility, higher melting point, and higher rate of crystallization than that for the free‐radical polymer. The polymer is also free from structural mpurities; it does not cause fluorescence in dilute solutions and has no absorption peak at 265 mμ; both these effects are produced by impurities in free‐radical polyacrylonitrile. It is concluded that the polymer reported here is more regular in structure than free‐radical polyacrylonitrile.
Mechanism of fracture in glassy polymers. II. Survey of crazing response during crack propagation in several polymers
Authors: Kambour Roger P.
Published: April 2003

Of nine glassy polymers so far investigated, eight yield evidence that fracture propagation involves the formation and breaking of craze material. All eight produce fracture surfaces exhibiting interference colors to one extent or another and even the colorless areas cause low angle x‐ray scattering. Ranked in terms of decreasing ease of colored surface formation, these polymers are poly(methyl methacrylate), poly(ethyl methacrylate), polystyrene, acrylonitrile—styrene copolymer, poly‐α‐methylstyrene, poly(vinyl acetate), a polyhydroxy ether, and polycarbonate. Only rigid poly(vinyl chloride) has failed to show evidence of precrack craze formation.
Thermodynamics of crystalline linear high polymers. V. Extended‐chain copolymers of polyethylene
Authors: Arakawa Tamio , Wunderlich Bernhard
Published: April 2003

Ethylene—propylene and ethylene—butene‐1 copolymers with up to 1.7 side groups per 100 carbons have been crystallized at 227°C. and under 4100–4900 atm. pressure. The resulting crystalline polymers are at least partially of extended‐chain crystal morphology. Comparison with the same polymers crystallized at atmospheric pressure, which gives folded‐chain crystal morphology, revealed: (1) a density higher by 0.008–0.019 g./cm.3 depending on copolymer content; (2) a similar decrease of crystallinity with side group concentration; (3) a similar decrease of the beginning of melting from 125°C. for homopolymer to 65°C. for 1.7 side groups per 100 carbons; (4) a higher (138 ± 0.8°C.) experimental maximum melting point which, in contrast, is independent of copolymer content and seems to vary only with the fraction of low molecular weight material; (5) a decreasing amount of high‐melting crystals with increasing copolymer content (72–8%) and an increasing amount of low‐melting crystals (27–53%) with increasing copolymer content. In addition, superheating, which reached 5.5°C. for 50°C./min. heating rates, was detected. It was concluded that high‐pressure crystallization leads, at least for part of the crystals, to solid solution formation, while atmospheric pressure crystallization does not. Which mode of crystallization is achieved seems kinetically determined. Experimental techniques were dilatometry, DTA, and calorimetry.
Single crystals of amylose V complexes. II. Crystals with 71 helical configuration
Authors: Yamashita Yuhiko , Hirai Nishio
Published: April 2003

It has been shown that lamellar crystals of amylose V complexes with 71 helical configuration can be obtained by using complexing agents larger in cross section than n‐butanol. The electron diffraction studies indicated a new unit cell for the unheated lamellar crystals which are composed of molecules with 71 helical configuration and hold water molecules on the exterior of the helix. Furthermore, from a throughly dried specimen at 100°C. in vacuo we obtained a pattern which showed only three Debye rings. Its spacings were explained by a two‐dimensional hexagonal unit cell having a = b = 14.7 A. proposed by Zaslow. It was also found that when the crystals were dispersed in methanol at room temperature, their electron diffraction pattern was the same as that of the anhydrous amylose V complex of n‐butanol.
Intercrystalline links in polyethylene crystallized from the melt
Authors: Keith H. D. , Padden F. J. , Vadimsky R. G.
Published: April 2003

Intercrystalline links in polyethylene have been revealed by crystallizing from the melt mixtures of fractionated polymer and the linear hydrocarbon n‐C32H66, the latter constituent being removed later by washing at room temperature in an organic solvent. These fibrous links measure up to 15,000 A. in length and are 30–300 A. in thickness. Molecular chains are oriented parallel to the lengths of the links, and apparently nucleate on tie molecules formed by the simultaneous crystallization of different parts of the same molecule on the surfaces of different, and often widely separated, crystals. The maximum length of the links found in a given polymer varies as the square root of molecular weight, and there are indications that molecules in the melt are much more extended than is predicted by conventional configurational statistics. The links are under tension and presumably exert a significant influence on physical properties.
Specific volume studies of γ‐irradiated polytetrafluoroethylene from 40 to 150°C
Authors: Licht W. R. , Kline D. E.
Published: April 2003

The effect of γ‐irradiation and post‐irradiation heat treatment on the specific volume versus temperature relationships of polytetrafluoroethylene (PTFE) samples (1/2‐in. diameter rods) have been studied over the 40–150°C. temperature range for radiation doses up to 8.9 X 108 rad. At low doses the specific volume at any temperature decreased with dose, but above about 108 rad it increased with dose. Similarly, the rate of volumetric expansion initially decreased with dose, while, at very high doses (8.9 X 108 rad) the rate of expansion at temperatures above 100°C. exceeded that of the unirradiated PTFE. Heating at 150°C. for 100 hr. produced a substantial decrease in the specific volume and a decrease in the rate of expansion for the irradiated samples. Irradiation effects in PTFE are considered to be a result of such factors as radiation‐induced chain scission, increased crystallinity, and increased void content. Changes resulting from post‐irradiation heat treatment can be attributed to increased crystallinity, decreased void content, and weight loss.
Internal motion in some aromatic polyesters and linear aromatic chains
Authors: Mattes Rainer , Rochow Eugene G.
Published: April 2003

Low‐temperature internal motions of the following polyesters have been investigated by broad line nuclear magnetic resonance: poly(methylene terephthalates) (2–6 methylene groups), poly[1,4‐(dimethylene)cyclohexylene terephthalate], poly(diethyleneglycol terephthalate), poly(1,2‐propylene terephthalate), poly(1,4‐phenylene terephthalate), poly(2,2,3,3,4,4‐hexafluoropentamethylene terephthalate), poly[1,4‐phenylenebis(dimethyl) siloxane], and poly(2,6‐dimethylphenylene oxide). No complex line structure was found for any of the samples. Molecular motions in the polyesters appear to be restricted by polar forces arising from the ester groups. Above—196°C. the line width decreases smoothly with increasing temperatures for all polymers except poly[1,4‐(dimethylene)cyclohexylene terephthalate] and poly[1,4‐phenylenebis(dimethyl)siloxane]. These two show a definite transition in line width at −20°C. and +12°C., respectively, caused by the onset of considerable internal motion. At −196°C. the lattices are rigid except for polymers containing methyl groups: poly(1,2‐propylene terephthalate), poly[1,4‐phenylenebis(dimethyl) siloxane], and poly(2,6‐dimethylphenylene oxide). Internal motion that can be ascribed to be a reorientation of the methyl groups is present at −196°C. for these three polymers, as is demonstrated by comparison of experimental second moments and those calculated on the basis of various models.
Sizes and interfacial free energies of crystallites formed from fractionated linear polyethylene
Authors: Mandelkern L. , Price J. Michael , Gopalan M. , Fatou J. G.
Published: April 2003

Replicas of fracture surfaces of fractions of linear polyethylene, which were crystallized at elevated temperatures for extended time periods, were examined by electron microscopy. Striated. lamella‐type crystallites were observed for all molecular weights over the range 3.2 × 103−5.7 × 105. In agreement with Anderson's previous report, for molecular weights of 12,000 or less, the crystallite thicknesses were comparable to the extended chain length. As the molecular weight increased above this level, however, the crystallite sizes increased only slightly and hence at high molecular weights were very much smaller than the extended chain length. From the measured melting temperatures, crystallite interfacial free energies were calculated from the theory for the melting of finite size crystals comprised of chains of finite length. The crystallite interfacial free energy was found to increase with molecular weight. Based on these results, a crystallization process is outlined which allows for the formation of either extended chain crystallites, or crystallites whose size is much smaller than the extended chain length without any change in nucleation mechanism or arbitrary adjustment in growth mechanism with molecular weight.
Free volumes in simple and polymeric liquids
Authors: Miller A. A.
Published: April 2003

Values of ε0ν0 the vaporization energy and volume in the hypothetical liquid state at 0°K., are derived for some simple polar and nonpolar molecules used as models for vinyl polymers. The following empirical relationship between the free volume fraction, f = (v − v0)/v, and the liquid compressibility coefficient β is demonstrated: −f2 ∝︁ This is applied to several vinyl polymer liquids near their glass transition temperatures, Tg, giving. fg ≃ 0.17, if the “hard‐core” volume v* is considered to be independent of pressure and temperature, (i.e., v* = v0); or, fg ≃0.12, if the P,T dependence of v* is considered to be the same as that of the glass. These agree with fg values derived by Simha and Boyer from thermal expansion coefficients for the two analogous cases. An empirical viscosity‐free volume equation of the Doolittle form: η = ATneb/f is applied to the glass transition, on assuming that this is an isoviscosity state and with the use of reported values for the expansion and compressibility coefficients and dTg/dP for three polymers: polystyrene, poly(methyl methacrylate), and poly(vinyl acetate). Reasonable values of b/n are thus obtained. This viscosity equation is critically examined in the light of molecular theories of liquid viscosity.
Effect of strain on the thermodynamic melting temperature of polymers
Authors: Krigbaum W. R. , Dawkins J. V. , Via G. H. , Balta Y. I.
Published: April 2003

X‐ray diffraction, sonic velocity, and birefringence measurements were used to study the variation of the apparent melting point of strained natural rubber and polychloroprene vulcanizates with elongation ratio and crystallization temperature. The procedure of Hoffman and Weeks was employed to obtain the thermodynamic melting point, tm, for each elongation ratio α. The parameter β relating to the distribution of fold lengths is unusually large for low elongation ratios and decreases into the usual range only at higher elongations. The observed variations of tm with α for these two polymers are compared with the theoretical predictions of Flory and Roe and Krigbaum. Although the predictions of the Flory theory depend somewhat upon the value assigned for the number of repeating units per statistical link, and this parameter is not well known for polychloroprene, we nevertheless conclude that his treatment offers a better representation of the melting point elevation for high elongations. Due to the approximations introduced, the treatment of Flory is not valid for lower elongations. Any attempt to improve this treatment must begin by specifying the free energy of the semicrystalline system, which implies a knowledge of the distribution of crystallite orientations and how this distribution varies with strain and with the crystallization conditions.
Dynamic mechanical properties of crystalline, linear polyethylene
Authors: Penn Robert W.
Published: April 2003

Two sets of dynamic mechanical property data and some stress relaxation data for semicrystalline, linear polyethylene are treated by data reduction methods previously described. These data can be represented by a master plot of reduced modulus versus reduced frequency and two sets of temperature‐dependent shift factors. The first of these factors reflects the change of viscoelastic relaxation times with temperature. The second represents a separable change of modulus with temperature which applies over the entire time or frequency range of the experiments. This change is larger and in the opposite direction to that found applicable in the behavior of noncrystalline plastics and rubbers. The two sets of dynamic data show the same frequency–temperature dependence which can be represented by an activation energy of 22 kcal./mole. Small differences in the modulus–temperature dependence are attributed to differences in molecular weight or annealing conditions. The stress relaxation data superposes to a curve in good agreement with the dynamic data but with a factor of 20 difference in time scale. This difference is attributed to the finite strains used in the stress relaxation measurements. Such strains might be expected to increase free volume in simple extension deformations and so accelerate the relaxation.
NMR observations of drawn polymers. V. Sorption into drawn and undrawn polyethylene
Authors: Peterlin A. , Olf H. G.
Published: April 2003

NMR measurements on undrawn polyethylene (PE) samples in contact with a solvent such as C2Cl4 indicate an increase in the mobility of the mobile chain segments as compared to dry samples. Highly drawn PE shows no such effect. This is because Sa, the sorption per unit mass of noncrystalline material present, decreases from 20.9 wt.‐% (dry basis), found for undrawn quenched PE, to 0.63 wt.‐% after drawing (Sa determined at 25°C. and 0.80 vapor activity). Drawing also reduces the segment mobility according to the NMR spectrum. It is shown that these effects are caused by considerable structural changes occurring in the noncrystalline regions of PE upon drawing. Annealing of drawn PE samples at successively higher temperatures leads to a gradual relaxation of the noncrystalline regions towards the state characteristic of undrawn PE. With increasing annealing temperature Sa as well as the mobility approach values found with undrawn PE.
Narrow molecular weight distribution poly(styrenesulfonic acid). Part I. Preparation, solution properties, and phase separation
Authors: Carroll William R. , Eisenberg Henryk
Published: April 2003

A method is described for the conversion of polystyrene to poly(styrenesulfonic acid) without change in the molecular weight distribution; the reaction is performed at room temperature in 100% H2SO4 and uses Ag+ catalyst. The resulting polyelectrolyte has solubility and other characteristics significantly different from those of previously investigated poly(vinylsulfonic acid). This permits a study of the influence of the aromatic group on the local and long range interactions in solution. The barium salt of poly(styrenesulfonic acid) is unusual in showing both upper and lower consolute temperatures in solution.
Epitaxial crystallization of homopolymers on single crystals of alkali halides
Authors: Koutsky J. A. , Walton A. G. , Baer Eric
Published: April 2003

Epitaxial deposition of homopolymers from solution [polyethylene, isotactic polystyrene, poly‐3,3‐bischloromethyloxacyclobutane (Penton) and polypropylene] was found on the (001) faces of cleaved alkali halide single crystals. Electron and optical microscopy studies have shown that the polymer usually grew from small, rodlike crystallites which were oriented in (110) directions of the halide crystal. Large oriented, four‐leaved, “rose” structures also were observed for polyethylene. Electron diffraction studies indicate that the polymer chain axes for polyethylene, isotactic polystyrene, and Penton generally lie parallel to the (001) faces of the halide crystal and are also oriented in the 〈110〉 directions of the crystal face. Investigations on the effect of various halide substrates upon the epitaxial crystallization habit of polyethylene inferes that lattice matching does not play the major role in orientation. Two possible explanations are offered for this epitaxial behavior.
Wideline NMR studies of oriented nylon 66
Authors: McMahon P. E.
Published: April 2003

Wideline NMR techniques have been applied to both singly and doubly oriented specimens of nylon 66. Variations in the spectra obtained are observed for different orientations of the specimens relative to the applied field. These variations demonstrate that the zigzag chain axis is essentially parallel to the draw direction and that motion occurs in all of the sample. The motion is of two types: random in the mobile regions and rotation of segments about the chain axis in the rigid regions.
Persistent polarization in polymers. II. Depolarization currents
Authors: Miller M. L. , Murray J. R.
Published: April 2003

Depolarization currents were used to study the persistent polarization induced in polystyrene and poly(methyl methacrylate) by cooling with flow under pressure. These studies showed that the charge on electrets made by flow under pressure consists in part of a surface charge which leaks off rapidly in moist air and in part of a charge due to volume polarization which decays more slowly. The volume polymerization produced in poly(methyl methacrylate) by flow under pressure is of the same order as that produced by cooling under a voltage drop, but flow under pressure produces a larger surface charge.
Effect of stereosequence length on crystallization kinetics of propylene oxide polymers
Authors: Aggarwal S. L. , Marker Leon , Kollar W. L. , Geroch R.
Published: April 2003

Crystallization kinetics of crystalline fractions of propylene oxide polymers made with different catalysts have been studied by isothermal dilatometric and microscopical measurements. Isothermal microscopical measurements indicate that spherulite growth in these polymers proceeds from predetermined nuclei. The half time for spherulitic appearance is less than, but of the same order as, the half time for complete crystallization. Only by taking this factor into account can the dilatometric data be represented by the Avrami equation. The deviation of the crystallization isotherm from that predicted from the microscopical data using the Avrami theory is attributed to a secondary crystallization process taking place within the spherulite. Crystallization continues long after spherulites completely occupy the available volume in the polymer. By assuming that the secondary crystallization proceeds as a first‐order process in the uncrystallized, but crystallizable, portions of the melt, it is shown that the crystallization isotherms can be completely described in terms of four parameters. These are: (1) the time constant for the primary crystallization process; (2) the time constant for nucleation; (3) the time constant for the secondary crystallization process, and (4) the extent of secondary crystallization. The important conclusions of these studies are: the rates of nucleation and of spherulitic growth are far more dependent on temperature than on stereoregularity; the ratio of the rate of the secondary crystallization process to that of the primary crystallization process is almost independent of temperature, but increases with increasing stereoregularity of the polymer.
Orientation behavior of stereoregular poly(vinyl alcohols)
Authors: Nomura Shunji , Kawai Hiromichi
Published: April 2003

The orientation behavior of stereoregular poly(vinyl alcohols) was investigated during stretching and after releasing the stress on the bulk polymers at relatively high humidity (80% R. H.) A structural model, differing from polyethylene, was proposed in which the crystallites were embedded in a considerably swollen amorphous matrix without any definite physical interaction so as to form an aggregation of crystallites, a superstructure. The crystal orientation followed, in principle, “the first borderline case” of Kratky, but with some difference from theory in orientation, while the noncrystalline orientation was represented by the freely jointed equivalent chain model of Kuhn and Grün with a value of N/γ as small as around 5. The difference between crystal orientation found and the theorietical orientation is discussed and some factors which prevented the crystal orientation are considered.
Molecular weight determination of polyamides by vapor pressure osmometry
Authors: Ohama Mariko , Ozawa Takeo
Published: April 2003

The vapor pressure osmometry method for determining the molecular weight of polyamides has been studied by use of the newly developed solvents. Polymers used were polycaprolactams, polyenanthamides, and polypelargonamides. The measurements were carried out with 2,2,3,3‐tetrafluoro‐1‐propanol and 2,2,3,3,4,4,5,5,6,6,7,7‐dodecafluoro‐1‐heptanol as solvents at 50 and 130°C., respectively. Endgroup determinations on samples were also done in m‐cresol by 0.1 N‐hydrochloric acid. Reduced resistance differences (ΔR/C)0 obtained by vapor pressure osmometry at 50°C. were found to be in linear relation with the reciprocal of the number‐average molecular weight determined by endgroup titrations; but anomalous results were obtained when dodecafluoroheptanol was used as the solvent at 130°C.
Second virial coefficient of amylose acetate
Authors: Patel C. K. , Patel R. D.
Published: April 2003

The second virial coefficients of amylose acetate fractions have been determined at different temperatures and have been analyzed according to recent theories of second virial coefficient.
Configurational entropy of polyethylene and other linear polymers
Authors: Smith Richard P.
Published: April 2003

The configurational entropy of the polyethylene chain at the melting points calculated in two ways. In both calculations, tetrahedral angles and discrete trans and gauche arrangements of all bonds are assumed, and trans bonds are assumed more stable than gauche by energy U1. First, calculations are made on chains of up to N = 18 bonds, disallowing all configurations having overlapping atoms, and the result is extrapolated to large N. Second, a calculation is made directly for long chains, with overlaps excluded only over every short chain segment. The results are in almost exact agreement, suggesting that the second method can be safely used with other molecules. The calculated configurational entropy is in line with that suggested by the entropy of fusion, assuming the chains to acquire a configurational freedom in the melt which approaches that of independent chains.
Crystallographic studies of nylon 4. I. Determination of the crystal structure of the α polymorph of nylon 4
Authors: Fredericks Robert J. , Doyne Thomas H. , Sprague Robert S.
Published: April 2003

The crystal structure of the α polymorph of nylon 4 has been determined from the x‐ray diffraction patterns of uniaxially oriented monofilaments. In general the crystal structure of α nylon 4 is similar to that of α nylon 6. The unit cell is monoclinic with the following dimensions: a = 9.29 ± 0.05 A., b = 12.24 ± 0.05 A., c = 7.97 ± 0.05 A., and β = 114.5 ± 1.0°. There are eight monomeric units in the unit cell. The theoretical density is 1.37 g./cc. and the observed density 1.25 g./cc. The space group is P21. The nylon 4 chains are of the extended planar zigzag type, with the plane of the zigzag approximately parallel to the a axis of the unit cell. Along the a axis, every other chain is inverted—an antiparallel arrangement of chains—thus permitting complete hydrogen bonding and the formation of sheets of nylon 4 chains. Along the c axis of the unit cell, the second sheet is displaced by3/10 of the b axis, thus leading to a staggered arrangement of sheets. The sheets are held in place by van der Waals forces.
Crystallographic studies of nylon 4. II. On the β and δ polymorphs of nylon 4
Authors: Fredericks Robert J. , Doyne Thomas H. , Sprague Robert S.
Published: April 2003

In addition to the α polymorph, two crystalline forms of nylon 4, the β and δ polymorphs, have been observed and studied.

The β polymorph of nylon 4, which has not been found in a pure condition, appears to be similar to the β polymorph of nylon 6. The extended planar zigzag conformation of chains, found in the α polymorph, is present also in the β polymorph. Three models have been proposed to explain the observed data. In model 1, the staggered shear of van der Waals bonded sheets found in the α polymorph is abandoned; in model 2, the sheets are displaced by 1/2 the b axis, and in model 3 the chains are arranged in a parallel array. The β polymorph is converted to the α form in air upon heating for 11 min. at 227°C. and upon immersion in water for 2 hr. Models 1 and 2 would be converted to the α polymorph by a slippage of the van der Waals bonded sheets while the conversion from model 3 would involve a rupture of hydrogen bonds, a rotation of the chains through 90°, and the reformation of hydrogen bonds. The δ polymorph is formed by rapidly quenching extruded nylon 4 against chilled rolls. It is a metastable form which has only been observed in an unoriented condition. Upon orientation it is completely converted to the α polymorph. In addition to this, its conversion to the α form occurs under conditions similar to the β–α transition. The observed diffraction pattern can be indexed on the basis of a hexagonal packing of chains. High‐temperature x‐ray diffraction studies of the α polymorph suggest that the δ form, or a structure similar to it, is the high‐temperature form of nylon 4.
Mechanical properties and transition temperatures for copolymers of N‐n‐alkylacrylamides and acrylonitrile
Authors: Jordan Edmund F. , Riser George R. , Parker Winfred E. , Wrigley A. N.
Published: April 2003

Random copolymers of N‐n‐butyl‐, N‐n‐octyl‐, or N‐n‐octadecylacrylamide with acrylonitrile were prepared in tert‐butanol at 60°C. to test the effect of amide homologs as internal plasticizers. At room temperature under high deformations all samples showed brittle failure; at 100°C. flexible and resilient copolymers were obtained. At low deformations, torsional stiffness values Tf followed the equations of Wood, Fox, and Dimarzio and Gibbs, the latter two modified by use of mole fraction instead of weight fraction. Mole fraction appeared to function better than weight fraction for these special cases where wi > 2mi and where modulus‐temperature curves were broad. Because literature values for the glass (or brittle) temperatures of homologs of poly‐n‐alkyl acrylates, methacrylates, n‐alkyl styrenes and alkenes, and estimated values for poly‐N‐n‐alkylacrylamides, plotted as a function of the logarithm of the number of single bonds in repeat units, extrapolate to an average value of −111°C. at a chain length of eighteen carbon atoms, and because side‐chain melting points of linear eighteen carbon side‐chain homologs appear to have a common value of 48–50°C. regardless of structure, it was concluded that similar glass and melting transitions are obtained when the side chain reaches eighteen carbon atoms in any series of homologs. Transitions for longer side‐chain lengths then approach the limit of a polyethylene graft, where Tg is −81°C. and Tm is 137°C.