Showing papers in "Journal of Polymer Science Part A in 1972"

Chromocene catalysts for ethylene polymerization: Scope of the polymerization

Abstract: Chromocene deposited on silica supports of high surface area forms a highly active catalyst for polymerization of ethylene. Polymerization is believed to occur by a coordinated anionic mechanism previously outlined. The catalyst formation step liberates cyclopentadiene and leads to a new divalent chromium species containing a cyclopentadienyl ligand. The catalyst has a very high chain-transfer response to hydrogen which permits facile preparation of a full range of molecular weights. Catalyst activity increases with an increase in silica dehydration temperature, chromium content on silica, and ethylene reaction pressure. The temperature-activity profile is characterized by a maximum near 60°C, presumably caused by a deactivation mechanism involving silica hydroxyl groups. A value of 72 was estimated for the ethylene–propylene reactivity ratio (r1). Linear, highly saturated polymers are normally prepared below 100°C. By contrast with other commercial polyethylenes, the chromocene catalyst produces polyethylenes of relatively narrow molecular weight distribution. Above 100°C, unsaturated, branched polymers or oligomers are formed by a simultaneous polymerization–isomerization process.

Interaction of poly(styrene sulfonate) with polycations carrying charges in the chain backbone

Abstract: The interaction between sodium poly(styrene sulfonate) (NaSS) and side-chain charged polycation polymer (pendent type) or main-chain charged polycation polymer (integral type) has been studied. It was found that the polyion complex (the reaction product of these polyelectrolytes) of pendent–pendent type has an equimolar composition at any mixing ratio of two component polymers. However, a polyion complex of integral–pendent type can form a water-soluble complex with a ratio of [polycation]/[polyanion] = 1/3, in addition to a complex with a equimolar composition. The mechanism of formation of this specific complex is discussed.

Polymers having stable radicals. I. Synthesis of nitroxyl polymers from 4‐methacryloyl derivatives of 2,2,6,6‐tetramethylpiperidine

Abstract: Polymers having stable nitroxyl free radicals, poly-4-methacryloylamino- and poly-4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyls, were synthesized from their precursor polymers by oxidizing them in a methanolic solution of hydrogen peroxide. The precursor polymers were prepared by radical polymerization of 4-methacryloyl-amino/oxy-2,2,6,6-tetramethylpiperidines in various solvents. These polymerizations in acetic acid were found to yield polymers of high molecular weight. The copolymers of the precursor monomers with styrene and methyl methacrylate were also prepared as precursor copolymers. These precursor polymers of a piperidine type were converted to the polymers having stable nitroxyl free radicals by the hydrogen peroxide method. In this report, it was assumed that the post-oxidation reaction introduced a nitroxyl group smoothly and quantitatively at room temperature. Elucidations of the stable radical formation and the electron spin behavior of the stable radical polymers were made in terms of elemental analyses, infrared, ultraviolet, and ESR spectroscopy.

The nature of accessible surfaces in the microstructure of cotton cellulose

Abstract: The accessible regions in cotton cellulose were tagged by the introduction of diethyl-aminoethyl (DEAE) substituents at DS = 0.034 without other substantial changes in structure. Evidence from rates of hydrolysis of this DEAE cotton to hydrocelluloses and from the composition and structure of the solubilized and insoluble fractions provides the basis for considerable detail regarding two types of accessible regions in the cotton fiber; these are identified as accessible surfaces of elementary fibrils. One type of accessible surface is characterized by molecular chain segments which are distorted and disordered by tilt/twist strain that is concentrated in this segment of the elementary fibril; the second type of accessible surface is characterized by a relatively high degree of order which reflects the high level of crystallinity within the interior of this unstrained segment of the elementary fibril. Substantial differences between these accessible surfaces are discussed. It is estimated that chain segments on accessible surfaces of the first type are substantially disordered, i.e., approximately 60–90% of the D-glucopyranosyl units are dislocated from positions of perfect crystalline order. Accessible surfaces of the second type are quite highly ordered, i.e., only 5–30% of the D-glucopyranosyl units dislocated.

Polymerization of vinyl stearate multilayers

Abstract: A study was made of the solid-state polymerization of built-up monomolecular layers of vinyl stearate. Polymerization was initiated by exposing the samples to 60Co γ-radiation. The reactions were followed by multiple internal reflection infrared spectroscopy. The structure of the multilayer monomer and polymer was studied by x-ray diffraction. Surface properties of the multilayers were studied by contact-angle measurements. Results showed that, under the proper conditions, monomer multilayers of vinyl stearate could be polymerized to virtually 100% completion. Reaction was favored by higher irradiation temperatures, larger doses of radiation, and by higher reaction temperatures. The x-ray diffraction photographs indicated that both the monomer and polymer multilayers possessed some single crystal character. Contact-angle measurements indicated that the molecules in both the monomer and polymer multilayers were closely packed.

Surface changes during polypropylene photo-oxidation: A study by infrared spectroscopy and electron microscopy

Abstract: The surface oxidation of polypropylene films which occurs during ultraviolet irradiation in air was found to result in extensive surface restructuring. This restructuring was detected by changes in surface infrared spectra, as measured by attenuated total reflection spectroscopy, and by electron microscopy. The 997 cm−1/974 cm−1 absorbance ratio of the film surfaces increased steadily during ultraviolet degradation and was interpreted as an increase in helical ordering which resulted from backbone scission during irradiation. This scission probably also results in the increase in crystallinity detected by density changes. Electron microscopy of direct surface replicas and replicas of material detached from the oxidized film surfaces showed that surface cracking resulted during photo-oxidation, and that this oxidation penetrated selectively into the polymer structure. The replicas of detached, oxidized material showed periodic structures related to the interior morphology of the films. The observed restructuring is believed to be entirely responsible for the decrease in percentage elongation at break which results from photodegradation.

Preparation of polyethylene in solution

Abstract: Polyethylene was prepared in a homogeneous system at 120°C. Several catalytic systems were employed, all using a soluble vanadium compound. The first consisted of an alkylaluminum compound in conjunction with the vanadium compound and a “promoter.” This promoter, which is believed to act as an oxidizing agent to reactivate dead catalyst sites, was a polyhalo compound with esters of trichloroacetic acid preferred. The promoter was added continuously throughout the polymerization. Polyethylene so produced had a narrow Mw/Mn ratio close to the theoretical ratio of 2.0 for a single catalyst site. Up to 266 polymer chains were produced per vanadium atom. In the second system, the cocatalyst was an AlBr3(AlCl3)–(C6H5)4Sn[(C6H5)3Bi] combination. The continuous addition of a promoter such as methyl trichloroacetate was necessary, presumably to reactivate dead catalytic sites. By this procedure, yields up to 6.6 kg of polymer per millimole of vanadium and 30–60 chains per vanadium atom were achieved. The product had a narrow Mw/Mn ratio of 2.4 by gel-permeation chromatography (GPC). A study of the interactions of the catalyst compounds indicated that CCl3COOR does oxidize di- and trivalent vanadium.

Interaction of urea with poly(2‐hydroxyethyl methacrylate) hydrogels

Abstract: The interaction of poly(2-hydroxyethyl methacrylate) [poly(HEMA)] and other similar hydrogels with dilute urea solution has been studied by a variety of techniques, including swelling experiments, fluorescence quenching, near infrared spectroscopy and fundamental band infrared spectroscopy. The results obtained indicate that the anomalous swelling behavior of poly(HEMA) gels in the presence of such dilute urea solutions is probably not due to the disruption of a secondary hydrophobic bond structure as has been generally believed. Although poly(HEMA) gels do contain sites that can participate in hydrophobic bonding, the evidence gathered indicates that dilute urea solutions have no effect on such bonds. A plausible model that does fit all the data involves the interaction of urea with a secondary structure composed of hydrogen-bonded hydroxyl groups, stabilized by the exclusion of water molecules from the regions containing the bonds.

Ethylene polymerization with supported bis(triphenylsilyl) chromate catalysts

Abstract: Bis(triphenylsilyl) chromate is an active catalyst for ethylene polymerization without further treatment or additives. Catalytic activity is markedly increased when the compound is deposited on silica–alumina and is further increased if it is deposited on silica and then treated with an aluminum alkyl. Polymer molecular weight can be controlled by reaction temperature, hydrogen addition, support type, and reducing agent structure to give polymers ranging in melt index from essentially zero to > 100. In the supported catalysts the bis(triphenylsilyl) chromate appears to be bound to the support and to undergo a reduction step either by reaction with ethylene or with aluminum alkyl prior to polymerization. The active site is envisioned as chromium alkyl, bound to the support, with propagation occurring by insertion of the monomer into a CrC bond. Chain termination is by chain transfer to monomer.

Intramolecular cyclization of styrene–p‐divinylbenzene copolymers

Abstract: Styrene has been copolymerized at low conversion with minor quantities of p-divinyl-benzene (p-DVB) in (10–15%) solution in toluene and cyclohexane. Under these conditions the molecular weight of the polystyrene formed in the absence of p-DVB was controlled by chain transfer, and the copolymerization coefficients of the styrene and the p-DVB agreed with previous work. Polymer molecular weights were studied as a function of conversion. At very low conversions the number-average (2.2 × 105) and the weight-average (4.4 × 105) molecular weights were unaffected by substituting some of the styrene by p-DVB, but as the reaction continued Mn increased slowly and Mw much faster. On the other hand, even at the lowest conversions the intrinsic viscosity was drastically reduced by the introduction of p-DVB, and the radius of gyration, as measured by light scattering, fell. Infrared studies on the polymer show that the concentration of pendent double bonds in low-conversion copolymers is about half of the doubly substituted phenyl groups. It is concluded that the first polymer chains formed are extensively cyclized with the formation of a relatively large number of small rings.

Benzophenone/triethylamine‐photoinitiated polymerization of methyl acrylate

Abstract: Benzophenone-sensitized photopolymerization of methyl acrylate was shown to be remarkably enhanced by the addition of small amounts of triethylamine. This was attributed to the efficient formation of an electron-transfer complex between photoactivated benzophenone and ground-state amine. Ketyl and amine free radicals derived from this complex were postulated to be the chain-initiating species. Quantum yield experiments indicated that methyl acrylate itself was also a quencher of the benzophenone triplet state.

Gel-permeation chromatography. VII. Molecular weight detection of GPC effluents

Abstract: A detector system for GPC has been built consisting of a pressure cell and capillary viscometer, a constant-flow-rate pumping system, a concentration detector, and a computer interfacing system. This detector system provides two chromatograms; pressure drop (ΔP) versus retention volume and concentration (C) versus retention volume. Since at constant flow rate ΔP is proportional to the effluent viscosity η, the intrinsic viscosity of any effluent fraction can be computed from the equation, where subscripts 1 and 0 refer to the solution and solvent, respectively. The precision and accuracy of the above technique were evaluated using well characterized broad and narrow molecular weight distribution polymers. Both the precision and accuracy were found to be comparable to light scattering and other classical molecular weight measurement techniques. In its present form, the molecular weight detector system was found to be very sensitive to polymers with very high molecular weights, as expected, and also useful for molecular weights less than 50,000.

Mechanism of thermal degradation of poly(vinyl chloride)

Abstract: The mechanism of thermal degradation of poly(vinyl chloride) has been studied by pyrolysis up to 400°C in a thermobalance under four kinds of dynamic atmospheres: helium, oxygen, air, and hydrogen chloride. The gaseous product from the thermobalance was analyzed for hydrogen chloride by the argentometric determination of chloride ions by using Mohr's method. An attempt was made to analyze for other gases in the product stream by chromatography with the use of a glass column, but failed due to the accumulation irreversibly of hydrogen chloride on the column. The molecular weights of the samples were determined by measurements of viscosities at 25°C in cyclohexanone; their molecular weight distributions were studied by fractionation and gelpermeation chromatography (GPC). From the thermograms, the mechanism of degradation in different heating atmospheres, the rate, the heat effect, the energy of activation, and the order of decomposition were deduced.

Carbon-13 NMR of polybutadiene

Abstract: By using the carbon-13 NMR technique, it is shown that there are no cis-1,4–trans-1,4 linkages in a n-BuLi-catalyzed polybutadiene. The polymer consists of “blocks” of cis-1,4 units and trans-1,4 units separated by isolated vinyl units. Preliminary evidence suggests this might also be true for other types of 1,3-diene polymerization. Some of the implications of this finding on the mechanism of polymerization are discussed. Tacticity triad distributions are readily determined in polybutadienes with high 1,2 addition contents.

Vinyl polymerization by metal complexes. III. Vinyl polymerization initiated by oligoamide and cupric ion system

Abstract: Polymerization of methyl methacrylate and other vinyl monomers was studied in the presence of oligoamide (ϵ-aminocaproic acid, its dimer, trimer, tetramer, and pentamer) and cupric ion in aqueous media. The polymerization was found to be of free-radical character and selective for the type of vinyl monomer. Carbon tetrachloride can accelerate the polymerization. The initiation mechanism of the polymerization is discussed. Spectroscopic measurements were indicative of formation of 1:1 complex between oligoamides and cupric ion in aqueous NaClO4 solution. Some chemical and physical properties of the resulting polymers were measured.

Perfluoroalkylene-linked aromatic polyimides. I. Synthesis, structure, and some general physical characteristics

Abstract: This paper describes the preparation of a series of novel perfluoroalkylene- and ether-linked aromatic polyimides. Depending on the nature of the precursor diamine, the polyimides were prepared by either melt or solution techniques, the latter via the corresponding poly(amic acids). The polymers were characterized by a variety of methods, and their structure is discussed.

Grafting of acrylic acid onto radiation-peroxidized polypropylene film in the presence of ferrous ion

Abstract: Acrylic acid has been grafted from aqueous solution onto 70 μ isotactic polypropylene-film previously peroxidized by irradiating in air with both 400 keV electrons and γ-radiation from a 60Co source. Ferrous ion has been used to induce the redox decomposition of the macromolecular peroxy species at temperatures between 0 and 40°C. It has been shown that the effect of low [Fe2+] is to increase grafting rates, but that at [Fe2+] > 8 × 10−4 molal the retarding effect of the reducing ion becomes increasingly important. At constant [Fe2+] a pronounced maximum in rate is observed at around 50 wt-% of acrylic acid; this may be related to increased swelling of the polymer matrix at this point. The initial rate of grafting increases as the square root of the preirradiation dose and, in the preirradiation dose rate range, 1.6–8.0 Mrad/sec, is independent of the dose rate. The grafting rate during the later stages of the reaction, however, increases as the preirradiation dose rate decreases. In the temperature range 0–40°C, the overall activation energy is 19 kcal/mole; from this value, the activation energy of initiation has been estimated to be around 20 kcal/mole.

Photodegradation of urethane model systems

Abstract: The photo-oxidation products of ethyl N-phenyl-carbamate (EPC) were identified as ethyl o-aminobenzoate, ethyl p-aminobenzoate, aniline, water, carbon dioxide, azo compounds, and other colored material. The ethylaminobenzoates, formed by intramolecular rearrangement of EPC, were precursors of the azo and colored products. Diethyl 4,4′-azobenzenedicarboxylate was produced by the ultraviolet irradiation of the precursor, ethyl p-aminobenzoate, in the presence of oxygen. Benzophenone and anthraquinone, as the triplet donors, sensitized the photo-oxidation of EPC. Quantum yields of photolysis of EPC were measured. The photorearrangement reaction was inhibited by the polar solvent (ethanol). The presence of metal ions and phenyl isocyanate in EPC showed no effect on the oxygen consumption rate.

Perfluoroalkylene‐linked aromatic polyimides. II. Further property studies

Abstract: The synthesis and general physical characteristics of the perfluoroalkylene-linked aromatic polyimides have been discussed in Part I. In this paper the hydrolytic, oxidative, and thermal stabilities of these polymers are compared with those of certain wholly aromatic polyimides. Comparative studies are also made on the effect of the fluoroalkylene chain on the glass transition temperatures. The polymer from di-(4-aminophenyl) ether and 1,3-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride has been studied in most detail and various mechanical and electrical properties of this polymer in film and solid molded form are discussed.

Some physical properties of polyorganosiloxanes. I. Linear polyorganosiloxanes

Abstract: Some physical properties of linear polydimethylsiloxanes have been studied. The states and transitions in polydimethylsiloxanes have been investigated by using the method of dynamic heat capacity and a thermomechanic method in the temperature range from −150 to +200°C. The temperature dependence of primary and secondary crystallization has been studied by optical, calorimetric, and x-ray methods.

Copolyesters of glycols and bisphenols: A new preparative process

Abstract: A new process for the preparation of copolyesters of glycols and bisphenols is described. Employing a preformed polyester, an acid, and a bisphenol diacetate, the procedure is useful for a variety of copolyesters. It is illustrated with the preparation of copolyterephthalates of ethylene glycol and 4,4′-isopropylidenediphenol. The reaction is proposed to proceed by an initial cleavage of the polyester, followed by polymerization of the acid- and acetate-terminated products. Intermediate heterogeneous structures then equilibrate.

Effect of amines on the ceric ion‐initiated polymerization of vinyl monomers. II. Polymerization of acrylonitrile by ceric ion in presence of various substituted amines

Abstract: The effect of various substituted amines on the polymerization of acrylonitrile initiated by ceric ammonium sulfate has been studied in aqueous solution at 30°C. It was found that the secondary and tertiary amines considerably increased the rate of polymerization, whereas the primary amines seemed to have no effect at all. From the kinetic studies it was found that the overall polymerization rate Rp is independent of ceric ion concentration and can be expressed by the equation: Rp = k1 [amine] [monomer] + k2[monomer]2, where k1 and k2 are constants (involving different rate constants). The accelerating effect of the amines was attributed to a redox reaction between the ceric ion and the amine involving a single electron transfer, the relative activity of the different amines being thus dependent on the relative electron-donating tendency of the substituents present in the amine. The mechanism of the polymerization is discussed on the basis of these results, and various kinetic constants are evaluated.

Graft modification of poly(vinyl chloride) and related reactions

Abstract: Cationically polymerizable olefins can be efficiently grafted onto poly(vinyl chloride) in the presence of alkylaluminum compounds. The substitution of labile chlorines in PVC by various branches yields a product of improved thermal stability as compared with unmodified PVC. Thus the grafting of a few per cent of polyisobutylene or poly-butadiene onto PVC gives graft copolymers superior in thermal stability to the PVC backbone, as determined by thermogravimetric and differential thermal analyses as well as color development of molded films. At advanced stages of thermal degradation the thermal stability of poly(vinyl chloride)-g-isobutylene) (PVC-g-PIB is some 40°C superior to the unmodified PVC. In addition to grafting of polymer chains onto the PVC backbone, other methods are also available to achieve improved thermal stability. In pentane suspension, alkylaluminum compounds efficiently alkylate labile chlorines in PVC, and the product exhibits improved thermal stability. Alternatively, PVC carbonium ions can alkylate aromatic compounds, and these products also exhibit high heat stability. Based on the assumption that certain alkylaluminums quantitatively react with labile chlorines in PVC, it was estimated that 2–3% of the chlorines present in suspension-grade PVC are labile.

Side-chain crystallinity. V. Heats of fusion and melting temperatures on monomers whose homopolymers have long side chains

Abstract: Heats of fusion and melting temperatures were obtained for selected monomeric n-alkyl acrylates, N-n-alkylacrylamides, and vinyl esters. The corresponding thermodynamic parameters for homopolymers, derived from these monomers, had been reported previously from this laboratory. The α-hexagonal crystal modification was indicated near the melting point for the higher n-alkyl acrylates, but a β form was stable at low temperatures for the entire series. The magnitude of the heats of fusion indicated β polymorphs for vinyl esters in support of x-ray diffraction analysis from the literature. Because hexagonal crystal geometry prevailed in all reported homopolymers having long side chains, greater emphasis was placed on thermodynamic data for monomers exhibiting this crystal modification. Accordingly, a convergence temperature was estimated statistically for the α-hexagonal crystal modification of these systems and appropriate literature values of the n-alkanes and ethyl esters. The convergence temperature was computed to be 135°C, uncorrected for the entropy of disorientation. The anomalously large interfacial end-packing-defect energy of the poly(n-alkyl acrylates) and the poly-N-n-alkylacrylamides was shown to be associated with a high energy barrier to molecular transport in the melt as the vitreous state was approached. In support of this conclusion, similarity of the glass and melting transition temperatures of these homopolymer homologs occurred near their critical side-chain lengths, below which the homopolymers are amorphous. A special critical requirement of nucleus length was not indicated from rough estimations of nucleation parameters for the poly(n-alkyl acrylates). These findings lent increased, but still not unqualified, support to an x-ray diffraction study from the literature. The latter had specified the inclusion of the entire side chain and the main-chain units in the crystal lattices of the higher poly(n-alkyl acrylates).

Anionic polymerization of caprolactam. XLIII. Relationship between osmometric molecular weight, viscosity, and endgroups of a polymer†

Abstract: For unfractionated anionic polymers, the following relationship between the osmometric molecular weight and intrinsic viscosity is valid: Mn = 13200[η]1.115 (cresol), or Mn = 13000[η]1.021 (93.8% H2SO4). A comparison of the osmometric and viscometric data with the number of endgroups of a polymer confirmed the finding that under certain conditions, moderately branched molecules can be formed; the above parameters depend on the type of the activator used.