bluuebunny/crossref_metadata_2025 huggingface dataset:
The chemistry of poly(vinyl chloride) stabilization. III. Organotin stabilizers having radioactively tagged alkyl groups
Authors: Frye Alfred H. , Horst Raymond W. , Paliobagis Marko A.
Published: April 2003

The stabilizing action of a representative group of organotin compounds of the formula Bu2Sn Y2 has been studied by a radioactive tracer technique, the tags (14C) being located in the butyl group's C1‐position. The Y groups of the chosen organotin compounds were: monomethyl maleate, oxoöctyl thioglycolate, β‐mercaptopropanoate, and 2‐ethylhexanoate. It was found that after a sequence of two dissolution and precipitation cycles (using tetrahydrofuran and methanol) an appreciable portion of radioactivity is retained by the resin, the resins having been previously admixed with the tagged stabilizer, milled into films and then subjected to carefully controlled heat treatments. Under these conditions it was found that the amount of radioactivity retained by the resin was determined by the nature of the Y group and the duration of the heat treatment. Further, it was found that for a given Y group, the amount of retention first increases with increase in the duration of the heat treatment, reaches a maximum, and then drops off. However, the amount of radioactivity retained by such a resin was not found to be constant when the sample was subjected to further dissolution–precipitation cycles, but, within the limits of the present experiments, to decrease markedly with each successive cycle. It is suggested that the major portion of this retention is due to the formation of an associative link between the polymer and the organotin compound and that this linkage is partially ruptured by the tetrahydrofuran–methanol treatment. It is also shown that only a very minor portion of the radioactivity retained by the precipitated resin can be due to actual butylation of the resin as preposed by Kenyon, and that it is unlikely that it could contribute appreciably to the resin's stabilization. It is suggested that the formation of an associative complex between the resin and the organotin compound functions as a precursor wherein certain relatively labile centers in the polymer chain can be altered, possibly by a displacement reaction involving the organotin compound's Y group, and int his way retard or inhibit the zipperlike elimination of hydrogen chloride which is the initial phase of the polymer's degradation.
Viscoelastic behavior of plasticized polyvinyl chloride at large deformations. III. The effect of filler
Authors: Sabia Raffaele , Eirich F. R.
Published: April 2003

The behavior of filled and plasticized samples is similar in many ways (such as creep, critical strain for the onset of a permanent deformation, etc.) to plasticized polyvinyl chloride. The presence of small amounts of CaCO3 as filler was found to result in improved mechanical response, while high amounts produced stiffening effects of the nature of an inert filler. At larger deformations, the polymer ceases to wet the filler and the volume of the filled resin increases with strain by crazing, the more so the more highly filled. Filler wetting by the resin is influenced by plasticizer content. In stress relaxation, the dewetting time, very short for the highly filled samples, increases appreciably with decreasing filler content while depending at the same time on plasticizer content. Because of this, equilibrium and delayed moduli increase with filler content at low strain and decrease variously at higher strain.
Molecular weight of poly(vinyl chloride)
Authors: Freeman M. , Manning P. P.
Published: April 2003

A number of fractionated and unfractionated poly(vinyl chlorides) have been characterized by light scattering, osmometry, and solution viscometry. From the results on fractions it is concluded that the larger molecules contain long branches. For linear fractions the relation between intrinsic viscosity in tetrahydrofuran at 25°C. and weightaverage molecular weight measured by light scattering is: [η] = 1.63 × 10−4Mw0.766 dl./g.
Absolute propagation rate constants for the radical polymerization of substituted styrenes
Authors: Paoletti K. P. , Billmeyer F. W.
Published: April 2003

Absolute propagation rate constants were determined by application of the Smith‐Ewart kinetic theory to the emulsion polymerization of styrene, o‐methylstyrene, p‐methylstyrene, and “vinyltoluene” (Dow, 60:40 m‐:p‐methylstyrene). Conversion during polymerization was followed by dilatometry, and weight‐average molecular weights of the latex particles were determined by light scattering. The monomer–polymer equilibrium ratio was determined both dynamically as the inflection point of the rate curve and statically by equilibrating monomer with polymer. For styrene, the propagation rate constant (300 l./mole sec. at 50°C.) and its activation energy (17.6 kcal./mole) are in good agreement with literature values. Both rates and activation energies are lower for the other monomers (o‐methylstyrene, 60 l./mole sec. and 13.9 kcal./mole; p‐methylstyrene, 140 l./mole sec. and 7.7 kcal./mole; vinyltoluene, 220 l./mole sec. and 13.4 kcal./mol, all at 50°C.). The differences are attributed to increased radical stability from methyl group contributions to resonance structures and to steric hindrance of the ortho‐methyl group.
Photodegradation of poly(methyl acrylate)
Authors: Fox R. B. , Isaacs L. G. , Stokes S. , Kagarise R. E.
Published: April 2003

Thin films of poly(methyl acrylate) at room temperature have been photodegraded in air and in vacuum by radiation from a low‐pressure mercury source. Changes in intrinsic viscosities, ultraviolet absorption, and volatile products were followed as a function of the energy absorbed. Crosslinking occurs in both air and vacuum, but at a slower rate in air. The apparent quantum yield for random scission in air was 0.013 scissions per quantum absorbed. In air, carbonyl groups are formed along the backbone chain. Most of the volatile products studied appear to orginate from the ester groups in the polymer; formaldehyde, methanol, and methyl formate evolved at a constant rate for doses up to at least 2 × 1020 quanta/g.; quantum yields for each were determined. Carbon dioxide forms in amounts increasing exponentially with dose. Small amounts of carbon monoxide, methane, and hydrogen were detected qualitatively, but monomer was not observed. A mechanism compatible with these findings is suggested.
Polyesters of 1,4‐cyclohexanedimethanol1
Authors: Kibler Charles J. , Bell Alan , Smith James G.
Published: April 2003

A series of polyesters of trans‐1,4‐cyclohexanedimethanol was prepared and the melting points compared with those of the analogous series of polyesters prepared from p‐xylylene glycol. Only slight differences in melting points were noted between the corresponding pairs of polyesters prepared from a single aliphatic dicarboxylic acid and from the two glycols. However, polyesters derived from aromatic dibasic acids and trans‐1,4‐cyclohexanedimethanol melt at a higher temperature than the corresponding polymer from p‐xylylene glycol. The probable molecular configuration of polyesters based on trans‐1,4‐cyclohexanedimethanol is discussed. It is suggested that the diol moiety in the polyester can adopt a slightly contracted conformation so that the oxygen‐oxygen distance is less than in polyesters derived from p‐xylylene glycol. This, together with the similar degree of rigidity and symmetry of the trans‐1,4‐cyclohexylene and p‐phenylene ring systems, is employed to explain the observed melting points. Polyesters prepared from cis‐1,4‐cyclohexanedimethanol are also described. As expected from the lower degree of symmetry of the diol, these polyesters have lower melting points than the analogous compositions prepared from trans‐1,4‐cyclohexanedimethanol. Polyesters of cis‐1,4‐cyclohexanedimethanol and trimethylene glycol have similar melting points. It is suggested that a cis‐1,4‐cyclohexylene ring and a methylene group have a similar effect on the melting point of a polyester. Copolyesters of cis‐ and trans‐1,4‐cyclohexanedimethanol with terephthalic acid do not form a minimum melting composition. Instead, they show a continuous change of melting point from that of the polyester prepared from one stereoisomer to that of the polymer prepared from the other isomer.
On the relation between long spacings, molecular length, and orientation in long chain compounds with reference to the possibility of chain folding. Part I. Oligomeric amides
Authors: Calleja F. J. Baltá , Keller A.
Published: April 2003

In this set of two papers the possibility of chain folding occurring in chain molecules not much longer than the presumed fold length was examined. The present paper deals with oligomeric amides. Following up the preceding work on the relation between long spacing and chain length by Zahn and Pieper on the same compounds, the relation between long spacings and chain orientation was examined in order to assess how far oblique structures could present alternatives to chain folding. It could be concluded that they cannot, the chains remaining straight up to a certain length only (80 A.), beyond which chain folding offers the most probable explanation. The preparation and examination of oriented aggregates required for this conclusion to be reached are discussed. In addition the dependence of the long spacings on the crystallization temperature, and relation between melting point and long spacing are demonstrated, and examples of annealing behavior are given all of which have their corresponding counterpart in the chain‐folded high polymers.
On the relation between long spacings, molecular length, and orientation in long chain compounds with reference to the possibility of chain folding. Part II. Poly(ethylene oxide)s
Authors: Calleja F. J. Baltá , Keller A.
Published: April 2003

Poly(ethylene oxide)s, including low molecular weight Carbowaxes and high molecular weight Polyox resins were examined as regards their long period chain length relationship with reference also to chain inclination with respect to the long spacings. The results show that the chains can only be straight up to a certain length (100–150 A.), beyond which chain folding needs to be invoked. Reference is made to single crystals required for these experiments. The long spacings (fold length) depend on the solvents, presumably by their effect on the crystallization temperature and on the heat treatment (annealing) of the samples, this providing the continuity between the behavior of the waxy low molecular weight compounds and that of typical high polymers. The general conclusion (based on Part I and II) is reached that in the light of present concepts there seems to be no acceptable alternative to chain folding beyond a certain critical length (dependent on physical factors) to account for the observations.
Fractionation of polymers of higher α‐olefins
Authors: Flowers D. L. , Hewett W. A. , Mullineaux R. D.
Published: April 2003

Fractionation of 1–10 g. samples of a series of poly‐α‐olefins in a glass bead column has been studied. A thermal gradient was found to decrease fractionation efficiency relative to that obtained at constant (ambient) temperatures. A “stepwise‐continuous” solvent gradient technique was developed to improve fractionation of the high molecular weight material. Fractionation efficiency decreased with increasing bead loading but was still good at polymer to bead ratios of 0.1 compared to the ratio of 0.01 usually used; efficiency is poorer in the absence of a column, even when the latter is operated at constant temperature. The Kuhn‐Mark‐Houwink equation was used to correlate intrinsic viscosities to light‐scattering molecular weights. Values of the constants were K = 2.1 × 10−4 and α = 0.61. Molecular weight distribution correlations show these polymers to have very high Mw/Mn.
Negative spherulite of poly‐γ‐methyl‐L‐glutamate and effect of aging polymer solution on spherulite growth
Authors: Ishikawa Saburo , Kurita Toshio , Suzuki Eikichi
Published: April 2003

Poly‐γ‐methyl‐L‐glutamate was obtained by the NCA method in a chloroform solution using trimethylamine as initiator. After polymerization, the solution was left alone for a long time at room temperature before spherulites formed. A film was casted very slowly from this aged solution in a desiccator at room temperature. We could then obtain spherulites in these thin films. This aging treatment was one of the main factors in making the spherulites. The morphological structure, optical properties, and the molecular orientation of the spherulites were examined by infrared spectroscopy, the x‐ray method, and electron microscopy. After short aging periods (1–6 months), we could obtain positive spherulites. After much longer aging periods (6–10 months), negative spherulites were obtained. The conformation of the molecules in both spherulites was the same—the so‐called α‐helical conformation, but the orientation of the α‐helical axis in the spherulites was just the opposite. In the positive spherulites, the helical axes oriented along the radius, but in negative spherulites, the helical axes oriented along the tangential direction. These positive and negative spherulites were constructed with microfibriles the diameters of which were about 45–67 A. The orientation of these microfibriles in the spherulites was just the same as the α‐helical axes' orientation. These microfibriles oriented by side‐by‐side association in making the layer structure in the spherulites so that the α‐helical axes were aligned parallel to these layers. Also, no evidence was observed of the presence of the so‐called folding orientation of these α‐helical molecules or microfibriles, as was pointed out in the case of polyethylene. From these results, we know that the crystallization habits of helical molecules, such as polypeptides, were different from those of polyethylene. The helical axes of the polypeptide molecules were not oriented perpendicular to the layer surface of the spherulites, but parallel to the layer surface. The crystallization mechanism of polypeptide was not by the so‐called folding mechanism, but by the side‐by‐side crystallization mechanism.
Acrylic anhydrides and polymers derived therefrom
Authors: Hwa Jesse C. H. , Fleming William A. , Miller Leon
Published: April 2003

The free‐radical polymerization of four acrylic anhydrides—methacrylic anhydride, acrylic anhydride, acrylic methacrylic anhydride, and acrylic propionic anhydride—under a variety of conditions has been studied. The polymers and their polyacid and polyester derivatives were characterized by solubility, infrared spectroscopy, and x‐ray diffraction. Methacrylic anhydride could be polymerized in bulk and in hydrocarbon solvents from −50°C. to 80°C. to give soluble, linear cyclopolymers in high conversions. In a polar solvent such as dimethyl sulfoxide, gelation would result at high monomer concentrations and at high conversions. Acrylic anhydride, however, appeared to become crosslinked more readily; soluble polymers could be obtained only by polymerization in nonpolar solvents. Most of the previous and somewhat conflicting results on the cyclopolymerization of these two monomers can now be reconciled by the present findings. The physical properties of cast poly(methacrylic anhydride) suggest that it has a stiff backbone with hindered functional groups and that the monomer itself was perhaps intramolecularly associated. Some improvements in the aqueous hydrolysis of poly(methacrylic anhydride) and in the esterification of the derived polyacid by diazomethane were described. By these refinements, poly(methyl methacrylate), derived from a −50°C. poly(methacrylic anhydride), had previously been shown to possess a novel, mixed syndiotactic and syndioduotactic (++−−++−−) configuration. Acrylic methacrylic anhydride could be cyclopolymerized very much like methacrylic anhydride. The polyacid and polyester derived from this unsymmetrical anhydride are expected to have unique structures; the acrylic or methacrylic units in the derivatives do not occur more than twice in succession. Acrylic propionic anhydride, when homopolymerized, readily changed to a soluble polymer and an unidentified, immiscible liquid. Its soluble copolymer with methyl methacrylate, however, could be crosslinked by heating. An intramolecular and intermolecular disproportionation reaction was postulated to explain these two interesting observations, respectively.
Electron exchange polymers. XXI. Polymerization behavior of 2,5‐dimethoxystyrene
Authors: Kamogawa Hiroyoshi , Cassidy Harold G.
Published: April 2003

It was shown that 2,5‐dimethoxystyrene polymerizes under free‐radical, cationic, and anionic initiation. The less bulky character of the ortho substituent in the benzene ring makes the behavior of this monomer more normal than that of the previously reported vinylhydroquinone dibenzoate. Thus, a linear relationship is observed between specific extinction coefficients of copolymers in the ultraviolet absorption spectra and copolymer compositions. Q‐e values are also normal (Q = 1.76, e = −1.04). The copolymerization behavior is well understood through these values.
Decomposition of asymmetric peranhydrides
Authors: Smets G. , Van Rillaer W.
Published: April 2003

The synthesis of a peranhydride copolymer was carried out in three steps: (a) copolymerisation of acrylyl chloride with methyl methacrylate, (b) reaction of the acid chloride copolymer with perbenzoic acid, (c) treatment with aqueous methanol and methylation with diazomethane, in order to avoid free carboxylic groups. The polymer contained 18.1 wt.‐% peranhydride groups. The stability of this peranhydride copolymer (PerBzO2) has been compared to that of acetylbenzoic peroxide AcBzO2; the overall energies of activation of thermal decomposition in toluene solution are 24.6 and 33.2 kcal./mole, respectively. The relative importance of first‐order decomposition with respect to the induced decomposition has been determined. The first‐order rate constants are 3.8 × 10−4 sec.−1 for PerBzO2 at 59.7°C. and only 5.8 − 10−5 sec.−1 for AcBzO2; consequently the peranhydride copolymer is much less stable than the low molecular weight anhydride. This unexpected result must be related to chain structural effects.
Graft copolymerization with peranhydride side groups
Authors: Van Rillaer W. , Smets G.
Published: April 2003

Several copolymers of methyl acrylate, methyl methacrylate, and acrylyl perbenzoate of different peranhydride contents (5.35, 9.24, 12.6, 20.2, and 33.9 wt.‐%) were prepared and used for initiating the graft polymerization of styrene. The overall rate of polymerization and the grafting rate are proportional to the square root of the peranhydride concentration, while they are practically first order with respect to the monomer concentration. The graft copolymers were separated from both homopolymers by precipitation with methanol from the chloroform solution of the copolymer; the styrene content of the graft copolymer increases with monomer concentration e.g., 32.4 and 51.1% for monomer concentrations of 2.6 and 6.1 mole/l., respectively. The ratio of Rg/Rh, i.e., the weight of styrene bonded as graft to that as homopolystyrene has been taken as a conventional measure of the graft efficiency. At 80°C. this ratio never exceeds 0.46, independent of the composition of the initiating copolymer. It increases, however, markedly with decreasing grafting temperature; for a styrene concentration of 6.1 mole/l. it is equal to 0.64 and 1.27 at 72.1 and 55.6°C., respectively. The ratio Rg/Rh depends also strongly on steric effects: when the copolymer contains only methyl acrylate and acrylyl perbenzoate units with exclusion of methyl methacrylate, Rg/Rh is much larger than unity: at 74.9°C. it is equal to 1.68 and 2.31 for monomer concentrations of 2.6 and 4.35 mole/l., respectively, in the presence of a polymer containing 23.9 wt.‐% of peranhydride. This ratio is also enhanced by the viscosity of the solution. The results are compared to those obtained with similar copolymers containing tert‐butyl perester side groups.
Distribution of molecular weight and of branching in high molecular weight polymers from bisphenol a and epichlorohydrin
Authors: Myers G. E. , Dagon J. R.
Published: April 2003

The molecular weight distributions and long‐chain branching distributions of three samples of Bisphenol A poly(hydroxy ether) have been investigated. The samples were fractionated and the fractions characterized by solution viscosity and light‐scattering measurements. A log‐log plot of intrinsic viscosity and M̄w for fractions of all three resins yields a straight line up to molecular weights of about 70,000 (approximately 80% by weight of each polymer) described by [η] = 1.48 × 10−4 M̄w. Beyond this molecular weight the viscosities fall increasingly below the straight line whose constants are representative of those expected for linear fractions in a good solvent. It is evident that long‐chain branching does not occur appreciably in the lower fractions but does begin abruptly at 70,000 molecular weight and increases continuously above that point. Comparison of both the branching and molecular weight distributions with those predicted from Beasley's random branching mechanism confirms the nonrandom nature of the branching mechanism in these poly(hydroxy ethers). The numbers of branches calculated using the Zimm‐Kilb theory reach impossibly high values, while those calculated from the Zimm‐Stockmayer theory appear more reasonable. No correlation was found between the Huggins' k′ and molecular weight or branching. The highest molecular weight sample possesses a longer and more highly branched high molecular weight tail, which is reflected in differences in physical properties.
Free radical‐catalyzed reaction of the acrylamidomethyl ether of cotton
Authors: Gardon J. L.
Published: April 2003

A limited number of acrylamidomethyl ether groups can be introduced into cotton. We can assume that the reactive groups form a lattice and that when two or more adjacent sites are occupied, these neighboring vinyl groups will react with each other when a free radical catalyst is applied to them. A monomer group isolated from others by empty neighboring sites will remain unconverted. If each site has Z neighbors, Z being the coordination number, the conversion can be calculated as a function of the fractional site occupancy and of Z. The expression derived from the lattice model is mathematically equivalent to an expression which is based on an excluded volume model. In the latter, it is assumed that each reactive monomer has a reactive shell around it. If another monomer is placed within this shell, the two can react with each other. In terms of this model the parameter Z is defined as the ratio between the volume of the reactive shell and of the volume occupied by the monomer. The latter model offers some mathematical advantages and allows the calculation of both conversion and degree of polymerization from Z and the fractional site occupancy. It is shown that the ultimately achievable conversion and the degree of polymerization increases with Z and with site occupancy. Acrylamidomethylated cotton samples were treated with increasing amounts of ammonium persulfate and the conversion was determined. The data could be extrapolated to infinite initiator concentration and Z was found to have a value of 3.5–4. Since the reaction between double bonds on neighborings sites of a single cellulose chain would have a coordination number equal to 2, the fact that Z > 2 indicates that reaction between double bonds attached to different cellulose chains must occur. The fraction of links which are intermolecular is (Z‐2)/Z, being 43–50%. This result is an excellent agreement with previous data showing that only 42% of the crosslinks contribute to the increased resilience of cotton. It is likely that the termination of the polymerization reaction involves the combination of two radicals. Consequently, each polymeric or oligomeric chain contains two sulfate groups when ammonium persulfate is used as initiator. The molecular weight of these chains can be calculated from the mole ratio between the converted monomers and sulfur. The molecular weights determined this way agreed reasonably well with the molecular weight values calculated from the theory with Z = 4.
Redox polymerization of unsaturated polyester resins. III. Catalytic properties of tertiary amine N‐oxides. Redox polymerization with the system, dimethylaniline N‐oxide with vanadyl acetyl acetonate
Authors: Svoboda Glenn R.
Published: April 2003

Catalytic activity has been shown for both trialkyl and aryl dialkyl amine N‐oxides. Of the series, unsaturated polyester resins catalyzed with dimethylaniline N‐oxide exhibited complete polymerization in a practical length of time (24 hr.), when promoted with vanadyl acetyl acetonate. Such a resin system may also be heat cured without the addition of any promoter. A unique property of dimethylaniline N‐oxide‐catalyzed resins is the extraordinary stability exhibited by these resins systems. Up to two years precatalyzed resin and catalyst stability has been noted with resins stored at normal ambient temperatures. Lower storage temperatures are recommended.
Rubber elasticity in highly crosslinked systems: Crosslinked styrene, methyl methacrylate, ethyl acrylate, and octyl acrylate
Authors: Tobolsky A. V. , Katz D. , Takahashi M. , Schaffhauser R.
Published: April 2003

Styrene, methyl methacrylate, ethyl acrylate, and octyl acrylate were each copolymerized with tetraethylene glycol dimethacrylate (TEGDM) over the complete range of copolymer compositions. Modulus‐temperature curves of these polymers were constructed and compared. The equation of state for rubber elasticity was applied to the rubbery plateau regions of these polymers.
Crystallization of polyethylene from o‐xylene
Authors: Wunderlich Bernhard , James Edward A. , Shu Tsao‐Wen
Published: April 2003

The upper limit of platelike growth of polyethylene from a 0.1% solution by weight in o‐xylene can be represented by the equation T′ = M × 103/(2.747M + 170.6). This equation was derived on kinetic and thermodynamic arguments. Dendritic growth occurs 8–10°C. below T′. Higher molecular weights give more irregular and more branched dendrites. The ratio of heterogeneously nucleated hedgehog dendrites is constant for any one preparation crystallized at different temperature. Polymethylene can crystallize in a different morphology above T′. Interference microscopy was used as a main tool in this research.
Carriers and unpaired spins in some organic semiconductors
Authors: Pohl Herbert A. , Chartoff Richard P.
Published: April 2003

Semiconduction and electron spin resonance studies on a number of conjugated polymers representative of the polyacetylenes, the polybenzimidazoles, and the polyacene quinone radical polymers were made. Observed resistivities ranged from 270 to 1016 ohm‐cm. at room temperature. These and the spin concentrations, the relaxation times, and the energies of activation of conductance and spin concentration were found to be functions of the molecular structure. It was considered impressive evidence that impurity effects on the electronic properties of molecular solids are far less than those commonly observed with the covalently bonded semiconductors such as Ge and Si, for example. A detailed analysis was made of the carrier and free radical formation and life‐times in these ekaconjugated molecular solids using a simple model.
Incorporation of hydroxyl endgroups in vinyl polymer. Part II. Aqueous polymerization of methyl methacrylate initiated by salts or complexes of some metals in their higher oxidation states
Authors: Ghosh Premamoy , Mukherjee Ashish R. , Palit Santi R.
Published: April 2003

Hydroxyl endgroups have been incorporated in polymers of methyl methacrylate obtained by initiation with salts or complexes of Mn4+, Ce4+, Co3+, and Ag3+ with the monomer in aqueous solution. Hydroxyl and carboxyl endgroups in the respective polymer samples have been estimated with the help of the dye interaction technique. Initiation with Mn4+ and Ce4+ ions in dilute H2SO4 medium in the dark at room temperature has been found to incorporate an average of about 2 hydroxyl endgroups per polymer chain. Initiation with potassium trioxalato cobaltate (III) complex has been carried out both in the dark and in the presence of ultraviolet light at room temperature, and both carboxyl and hydroxyl endgroups have been characterized in the polymers formed. An average total of 1 endgroup (both COOH and OH combined) per polymer chain has been obtained in case of photoinitiation, and about 2 per polymer chain in the case of thermal initiation in dark. Polymerization in the dark at room temperature has been carried out in neutral medium with ethylene dibiguanidinium nitrate complex of tripositive silver as the initiator, and an average of 2 hydroxyl endgroups per polymer chain has been found to be incorporated in the process.
Radiation crosslinking of polyethylene–polyfunctional monomer mixtures
Authors: Odian George , Bernstein Bruce S.
Published: April 2003

Polyfunctional monomers such as allyl methacrylate, allyl acrylate, and diallyl maleate have been found to greatly enhance the radiation crosslinking of polyethylene. The radiation dose for incipient gelation is decreased by a factor of approximately 25 by the presence of small amounts of these monomers. The ultimate scission/crosslinking ratio is unchanged by the presence of these monomers and the swelling behavior of the gels follows the Flory‐Rehner equation. The monomer‐crosslinking process is compared to the monomer‐free process as regards the physical properties (tensile strength, elongation, modulus) of the crosslinked materials. A mechanism is presented for the enhancement of polyethylene crosslinking by polyfunctional monomers.
Mechanisms of thermal degradation of phenolic condensation polymers. I. Studies on the thermal stability of polycarbonate
Authors: Lee Lieng‐Huang
Published: April 2003

Bisphenol‐A polycarbonate gradually degrades at temperatures above 310°C. as detected by differential thermal analysis. The first stage of degradation of the dry and purified resin is induced by oxygen. In connection with oxidation, zinc stearate causes a notable degradation. This compound may act partly as an oxidation catalyst. The initial site attacked by oxygen is presumably the isopropylidene linkage of the polymer. The second stage of degradation shows a characteristic endothermic peak between 340 and 380°C. This stage is chiefly associated with depolymerization since only a small amount of volatiles is detectable. Depolymerization can be caused by hydroperoxide cleavage, hydrolysis, alcoholysis and bisphenol cleavage. Bisphenol‐A can decompose in the presence of acid into phenol and isopropenylphenol. The latter compound is a color‐forming material. As temperature increases above 400°C., volatilization rate gradually increases. The last stage of degradation becomes uncontrollable above 500°C. At this stage, decarboxylation, dehydration, hydrolysis, hydrogen abstraction, ether cleavage, crosslinking as well as chain scission interact to yield aromatic hydrocarbons, phenolic compounds, and tar. The quantity of aromatic hydrocarbons is determined by the intensity of the thermal degradation.
Some graft copolymerizations at high pressure
Authors: Lamb J. A. , Weale K. E.
Published: April 2003

Some graft copolymerizations of monomers with substrates previously irradiated in air to form polymeric peroxides have been studied at pressures up to 8000 atm. In the heterogeneous system styrene‐irradiated polyethylene, the rate of grafting increases considerably with pressure up to about 3000 atm. At higher pressures the reaction is retarded, and this is attributed to diffusion control of the propagation reaction. The rate of homopolymerization increases exponentially with pressure over the range 1‐4000 atm. Irreproducible results were obtained when methyl methacrylate was used in place of styrene, possibly because the substrate is not swollen by this monomer. No grafting was observed between five different chloro‐substituted ethylenes and irradiated polyethylene at pressures up to 5000 atm. The rate of grafting in the homogeneous system vinyl acetate‐irradiated polystyrene increases considerably with pressure up to 8000 atm., and there is no indication of diffusion control of the propagation reaction.
Some aspects of the photosensitivity of poly(vinyl cinnamate)
Authors: Tsuda Minoru
Published: April 2003

A theoretical investigation of the relationships between the photosensitivity of poly‐(vinyl cinnamate) and various factors—the degree of esterfication, the average molecular weight, and the concentration of sensitizers—was made under the assumption that the main response of the polymer to light is the production of crosslinking by the dimerization of cinnamoyl groups. The obtained equations are S = k16C2 for the degree of esterification, S = k22M̄ for the average molecular weight, and S = k33 (1 − e) + k34 for the concentration of sensitizers, where S is the photosensitivity of the polymer, C is the degree of esterification, M̄ is the average molecular weight, c is the concentration of sensitizers, and kij is a constant. It was shown that these equations agree well with the experimental data obtained by other authors.
Peroxide crosslinking of ethylene–propylene rubber
Authors: Loan L. D.
Published: April 2003

The crosslinking of ethylene–propylene rubber by means of dicumyl peroxide has been followed in detail. The overall crosslinking efficiency has been found to be about 0.4 crosslinks per peroxide molecule, and this result has been shown by stress relaxation and permanent set experiments to result from a mixture of both scission and crosslinking reactions. The results obtained with two different rubbers are consistent with the view that scission results from abstraction of a tertiary hydrogen atom while crosslinking arises from attack at a secondary hydrogen. Such a scheme allows a relative reactivity of tertiary :secondary of 6:1 to be calculated. The action of sulfur in peroxide cures has been shown to be to introduce labile, presumably sulfur‐containing, crosslinks. Such labile crosslinks explain the increased tensile strength of such vulcanizates. Allyl compounds are effective in increasing the crosslinking efficiency of the peroxide.
Irradiation of polyethylene crystals: Gas evolution studies
Authors: Salovey R. , Malm D. L. , Beach A. L. , Luongo J. P.
Published: April 2003

Equal radiation yields of hydrogen are obtained from bulk polyethylene and thin films of solution crystallized polyethylene, with a G value of 4.6. The corresponding value for very thick mats of the solution crystallized material is 3.4. Reasoning from material balance considerations indicates that the yield of radiation‐induced crosslinking for bulk and thin films is about twice that for thick mats of polyethylene. It is suggested that thin films and thick mats differ only in fold surface contact, and that crosslinking is preferential at the folds. The retention of xylene between fold surfaces following crystallization is compatible with the effect of irradiation on trapped solvent.
Carborane polymers. II. Cyclic and polymeric formals
Authors: Green Joseph , Mayes Nathan , Kotloby Anatole P. , Cohen Murray S.
Published: April 2003

Cyclic and linear formals containing a unique polycycloborane named carborane were prepared. The treatment of carborane glycols with formaldehyde or dipropyl formal yielded cyclic formals, linear polyformals, a mixture of linear and cyclic formals or no formal product depending upon the reaction conditions and the particular carborane glycol used. It was demonstrated that two of the carborane diols have a great tendency to form cyclic formals in solution or bulk‐type reactions. In the reaction with 1,2‐bis‐(hydroxymethyl)carborane, the tendency to cyclize is greater than might be expected for a seven‐membered ring. This propensity to form cyclic structure has been attributed to the short carbon–carbon bond and the relatively acute external angle of the group attached to the carborane nucleus. The stability of these cyclics has been demonstrated by failure to open the formal cyclics to form linear polymer. Polymer was obtained with bis(2‐hydroxyethyl‐1‐carboranylmethyl) ether, however, neither cyclic nor polymer products were obtained with bis(2‐hydroxymethyl‐1‐carboranylmethyl) ether. The failure to obtain the desired products have been attributed to the steric requirements of the carborane group.
Evaluation of rate constants from thermogravimetric data
Authors: Fuoss Raymond M. , Salyer Ival O. , Wilson Harry S.
Published: April 2003

A method has been derived whereby the characteristic constants of the rate equation may be derived directly from the thermogravimetric analysis curve. The method described, in contradistinction to previously described methods, does not require transformation to a time scale, nor pointwise graphical differentiation, and no mathematical approximations are made. The method is applicable to any reaction showing one or more successive thermogravimetric inflection points, requiring only that the location of the inflection point and the slope of the curve at that point be determined. It is demonstrated that the constants derived apply to the whole curve as well as the vicinity of the inflection point.
Packing density of polymer melts near the glass transition temperature
Authors: Bondi A.
Published: April 2003

The reduced or packing density ρ*  Vw/V of polymer melts coincides with a general curve of ρ* versus reduced temperature T* at high temperatures. However, the reduced density of the polymer melt is much higher than that of monomeric liquids as Tg is approached. The density information is converted to the number of external degrees of freedom per repeating unit frozen in as the polymer melt contracts. This loss of degrees of freedom begins at Tg* + 0.2, which is about the temperature below which the WLF shift relation becomes valid. The wide range covered by the numerical values Tg* and the relation of Tg to molecular structure is briefly discussed. The density data suggest that the fractional expansion volume (V − V0)/V(V0 = Vcryst. at T = 0°K.) at Tg is the only form of free volume as constant as required by the WLF relation.
Stereoregular diene polymerization with inorganic catalysts. I. cis 1,4‐Polymerization of 1,3‐butadiene with a cobaltous chloride–aluminum chloride complex
Authors: Scott Harvey , Frost Robert E. , Belt Roger F. , O'Reilly D. E.
Published: April 2003

The polymerization of 1,3‐butadiene with several catalytic CoCl2–AlCl3 compositions is described. Blue solid products of the reaction of CoCl2 with AlCl3 in which Co is coordinated in an octahedral configuration, are ineffective as stereospecific catalysts, unless they are treated with an aromatic hydrocarbon to yield a solution of a mixture of a green catalytic Co(AlCl4)2 complex, in which the Co coordination has a square planar configuration, and AlCl3 which is comparatively inert under polymerization conditions. This mixture forms regardless of the resulting (and frequent varying) molar ratio of Al to Co in solution, and regardless of whether the solid products contain AlCl3 that is not complexed with Co. Similar solutions result from the reaction of CoCl2 with AlCl3 in an aromatic hydrocarbon. In the absence of a modifier a benzene solution of a Co(AlCl4)2 complex catalyzes stereoregular and nonstereoregular polymerizations to about an equal extent. However, the addition of thiophene favors cis polymerization at the expense of the nonstereoregular polymerization, and a quantitative yield of polybutadiene with 94–99% of its unsaturation in the cis configuration and a sulfur content corresponding to one thiophene endgroup per polymer molecule was thereby obtained. Cis content and conversion reached a maximum at thiophene levels of 300 mole‐% based on AlCl3. At lower thiophene levels, conversion, unlike cis content, passed through a minimum before reaching a maximum. Polymers with a similarly high cis content were also obtained in the absence of thiophene by preparing oily catalyst compositions in toluene or xylene in the presence of traces of aluminum, magnesium or zinc powders which are believed to serve mainly as proton scavengers. The stereospecificity of the catalytic solutions was essentially independent of the ratio of Al to Co in solution. A possible mechanism consistent with polymerization data is discussed. It is suggested that stereoregular polymerization involves the attachment of thiophene and butadiene to one aluminum atom of the Co(AlCl4)2 complex in which Co is coordinated in a square planar configuration, by displacement of chloride ions from this aluminum atom to vacant coordination positions about the cobalt atom, resulting in an octahedral configuration about cobalt, followed by a cycloalkylation reaction between the coordinated thiophene and butadiene and subsequent insertion of butadiene into the polymer chain by a sequence of similar cycloalkylation reactions.
Stereoregular diene polymerization with inorganic catalysts. II. Magnetic resonance optical and x‐ray study of catalysts containing cobalt
Authors: O'Reilly D. E. , Poole Charles P. , Belt Roger F. , Scott Harvey
Published: April 2003

Complexes formed between aluminum and cobaltous halides have been studied by means of nuclear magnetic resonance, electron paramagnetic resonance, optical spectra, and x‐ray diffraction. Solutions of aluminum chloride and cobaltous chloride in benzene exhibit two separate Al27 NMR signals: one arising from dissolved AlCl3 and another, shifted by 316 ppm to higher magnetic field, due to Al27 complexed with cobaltous chloride. Shifts and intensity changes in the Al27 resonance occurring upon the addition of LiAlCl4, thiophene, and butadiene to such solutions are described. EPR spectra of the cobalt aluminum complex at 77°K. were obtained and are interpreted by means of the theory of Abragam and Pryce. Optical spectra of cobaltous compounds in the visible and ultraviolet regions are given and related to the coordination symmetry of the compounds. X‐ray diffraction data on the fusion product of AlCl3 and CoCl2 indicate that a compound is formed with the composition Co(AlCl4)2 containing four molecules in a monoclinic cell unit. The results of the various methods are interpreted in terms of a complex of composition AlCl3·CoCl2·AlCl3 which forms charge‐transfer type compounds with butadiene and thiophene. A calculation of the chemical shift of Al27 in the model complex is given which is in good agreement with the experimental shift.
1,3‐Cyclohexadiene polymers. Part I. Preparation and aromatization of poly‐1,3‐cyclohexadiene
Authors: Lefebvre G. , Dawans F.
Published: April 2003

Polymerization of 1,3‐cyclohexadiene was carried out in the presence of initiator systems such as titanium tetrachloride, organoalkali compounds, and Ziegler‐type catalysts. The best results as regards conversion rate and molecular weight, were those obtained with the use of organolithium compounds as initiators. When polymerization is performed in noncomplexing medium, all polycyclohexadienes are comparable, no matter what the initiator system used. They are composed mainly of 1,4‐substituted cyclohexene units and the double bond configuration is cis and trans. The cis–trans isomerization of the double bond seems to be independent of the polymerization mechanism. Complexing or highly polar reaction media favor the 1,2‐linking between cycles. The microstructure of the polymers was determined by infrared spectrometry and nuclear magnetic resonance analysis. Aromatization or partial dehydrogenation of polycyclohexadiene was achieved either by reaction with tetrachloro‐p‐benzoquinone or by bromination followed by dehydrobromination. An increase of the bromination temperature results in the direct formation of an aromatized polymer through the evolution of hydrogen bromide as soon as the bromine is fixed to the polymer. Infrared spectral analysis of the aromatized polymers give a further confirmation of two different types of substitution in polycyclohexadiene.
Homogeneous anionic polymerization. V. Association phenomena in organolithium polymerization
Authors: Morton Maurice , Fetters L. J.
Published: April 2003

A study has been carried out of the association phenomena which occur during the polymerization of styrene, isoprene, and butadiene by organolithium initiation. This has been done by means of viscosity measurements of these systems after the conclusion of the polymerization reaction. It has been found that, in general, the polymerlithium species, in hydrocarbon systems, are associated in pairs. This applies to the styrene system in benzene and to the isoprene and butadiene systems in n‐hexane. In tetrahydrofuran solution, none of these systems show any polymer association. For the polyisoprenyl lithium in n‐hexane, the equilibrium constant for the dissociation of the associated pairs at 30°C. is of the order of 10−6, and the heat of dissociation is about 37 kcal./mole. By means of this viscosity technique, it has also been found possible to show that tetrahydrofuran forms a monosolvate with the polyisoprenyl lithium (RMiLi · THF) and that the heat of solvation is about 18 kcal./mole. These findings are in accord with the proposed mechanism in which the active species, in hexane, is represented by the unassociated polymer‐lithium, RMi,Li, while, in THF, it is the solvated species, RMiLi · THF. On this basis the following propagation rate constants have been deduced for isoprene polymerization: kp(hexane) = 3.4 × 103 exp {−4100/RT} = 8.9 at 60°C.; kp(THF) = 1.5 × 104 exp{ −6800/RT} = 0.4 at 60°C.
Cyclopolymerization of α,ω‐polymethylene diisocyanates
Authors: Iwakura Yoshio , Uno Keikichi , Ichikawa Kiyoshi
Published: April 2003

The study of polymerization of α,ω‐polymethylene diisocyanates, tetramethylene, trimethylene, ethylene, and methylene diisocyanate, was carried out by the use of basic catalysts and polar solvents. Soluble polymers were obtained. Structures of the polymers were determined on the basis of solubility, infrared absorption, x‐ray diffraction, and chemical reactions, especially aminolysis of the polymers. It was shown that these polymers contained heterocyclic recurring units (imidazolidone and imidazoline) in each polymer chain. Finally, a possible mechanism of this kind of cyclopolymerization is described.
Study of epoxy compounds. Part VI. Curing reactions of epoxy resin and acid anhydride with amine, acid, alcohol, and phenol as catalysts
Authors: Tanaka Yoshio , Kakiuchi Hiroshi
Published: April 2003

The curing reaction of an epoxy resin and acid anhydride with an amine and/or acid, alcohol, and phenol was studied kinetically by using commercial epoxy resins and acid anhydrides. No etherification reaction occurred at 70–140°C., even in the case of epoxide/acid anhydride/HA (acid, alcohol, or phenol) and of epoxide/acid anhydride tertiary amine/HA, and the initial reaction rate was proportional to the concentrations of epoxide, acid anhydride, and catalysts such as tertiary amine, acid, alcohol, and phenol. The apparent activation energy of the reaction system of Epikote 828/methyl‐bicyclo(2,2,1)heptene‐2,3‐dicarboxylic anhydride/triethanol amine/HA was obtained as about 14.7 kcal./mole, and the low frequency factors and large negative entropies of activation for the reaction might confirm that the curing reaction of epoxy resins and anhydrides belongs to the type of nucleophilic bimolecular displacement reaction. The effects of the substituents, R, of acid, alcohol, and phenol as cocatalyst on the curing reaction of epoxy resin/acid anhydride/tertiary amine/HA were studied. The reaction constants, p, obtained positively for HA's, indicate that electron‐withdrawing substituents of HA increase the rate of curing reaction of system of epoxide/acid anhydride/amine/HA. Differences in the catalytic and cocatalytic effects among benzoic acid, benzyl alcohol, and phenol in these reaction systems might be considered to depend on the donating power of hydrogen bond which is the important role rather than a general electrostatic interaction effect as solvent effects in nucleophilic substitution reactions. These results supported the proposed mechanisms reasonably.