Showing papers in "Journal of Polymer Science Part A in 1973"
TL;DR: In this article, the core binding energies of the homopolymers of ethylene and fluoroethylenes were measured using ESCA and interpreted in terms of semi-empirical all-valence electron SCF MO calculations in the CNDO/2 formalism in conjunction with the charge potential model.
Abstract: Molecular core binding energies have been measured by ESCA for the homopolymers of ethylene and the fluoroethylenes. The data are interpreted in terms of semiempirical all-valence electron SCF MO calculations in the CNDO/2 formalism, in conjunction with the charge potential model. The results are used as a basis for interpreting the measured core binding energies of some Viton and Kel F type polymers. The routine application of ESCA to the determination of copolymer compositions is described.
126 citations
TL;DR: In this paper, a detailed investigation of the condensation of aromatic amines and maleimide compounds was conducted by the use of model compounds, and strong Bronsted acids were found to have a marked catalytic effect on the reaction.
Abstract: A detailed investigation of the condensation of aromatic amines and maleimide compounds was conducted by the use of model compounds. Weak Bronsted acids were found to have a marked catalytic effect on the reaction. By using glacial acetic acid as the reaction medium, a number of model aspartimide compounds were prepared. Aromatic diamines and bismaleimide compounds were condensed to high polymers in cresol containing a small amount of a protonic acid catalyst. Polymers having a variety of novel backbone structures were prepared and their physical properties studied.
111 citations
100 citations
TL;DR: The chromocene catalyst for ethylene polymerization shows a high response to hydrogen which leads directly to highly saturated polyethylenes containing methyl groups as the major terminal functionality in the polymers as discussed by the authors.
Abstract: The chromocene catalyst for ethylene polymerization shows a high response to hydrogen which leads directly to highly saturated polyethylenes containing methyl groups as the major terminal functionality in the polymers. At a polymerization temperature of 90°C the ratio of termination rate constants for hydrogen (kH) and ethylene (kM) is kH/kM = 3.60 × 103. The ratio of kH to the chain propagation constant (kp) is kH/kp = 4.65 × 10−1 A simple relation that can be derived from polymerization kinetics and the Quackenbos equation exists between melt index and hydrogen–ethylene ratio. A deuterium isotope effect (kH/kD) = 1.2 was calculated for the termination reaction. The overall polymerization process has an apparent activation energy of 10.1 kcal/mole. Oxygen addition studies show catalyst activity is proportional to initial divalent chromium content.
93 citations
TL;DR: In this paper, the effects of crystallinity, orientation and degree of polymerization on the vacuum pyrolysis of cellulose have been investigated and the initial weight loss and subsequent reaction rate were dependent upon the crystallinity of the sample.
Abstract: The effects of crystallinity, orientation and degree of polymerization on the vacuum pyrolysis of cellulose have been investigated. Natural, modified and manmade celluloses were characterized and the kinetics of their pyrolysis at 251°C studied. The high-temperature pyrolysis of these samples was also investigated by means of DSC and TGA. At 251°C all of the samples showed a rapid, initial weight loss followed by a linear (weight loss)1/2 versus time dependency. Both the initial weight loss and the subsequent reaction rate were dependent upon the crystallinity of the sample. The reaction rate was shown to be inversely proportional to (DP)1/2 and related to the orientation. Effects of crystallinity and orientation could also be seen in the DSC thermograms and in the apparent energies of activation. Results are interpreted in terms of probable mechanisms of the uncatalyzed pyrolysis of cellulose.
90 citations
TL;DR: In this paper, the gamma-initiated oxidations of thin films of high-and low-density polyethylene, atactic and isotactic polypropylene, and of three ethylene-propylene copolymers were determined.
Abstract: Rates of oxygen absorption and formation of oxidation products were determined in gamma -initiated oxidations of thin films of highand low-density polyethylene, atactic and isotactic polypropylene, and of three ethylene-- propylene copolymers. Radiation yie1ds G for O/sub 2/ absorbed and formation of hydroperoxides depend on dose rates and decrease sharply with increasing ethylene content of the copolymers and moderately with increasing crystallinity of any base polymer. G values for dialkyl peroxide and carbonyl formation, and therefore for chain initiation and termination, do not change much with polymer composition and crystallInity and not at all with dose rates. A few experiments with atactic polypropylene and an amorphous ethylene--propylene copolymer, initiated by ditert-butylperoxy oxalate, indicate that 37 mole% of ethylene in the polymer increases the efficiency of initiation and the tendency toward crosslinking. (auth)
89 citations
TL;DR: In this article, the authors investigated the dependence of rate of formation of each product on rate of initiation, and showed that PP hydroperoxide, formed in a half-order reaction, can inhibit all noncage propagation and all formation of polymeric dialkyl peroxide.
Abstract: Oxidations of bulk atactic polypropylene (PP) have been carried out at 22 and 45°C, and the dependence of rate of formation of each product on rate of initiation has been determined. The principal product is PP hydroperoxide, formed in a half-order reaction. One termination product is polymeric dialkyl peroxide, formed in a first-order reaction. Other termination and propagation products, alcohols and carbonyl compounds, are formed in reactions that are mostly first-order in initiation. At 22°C, G is 9–63. G is about three times as great at 45°C as at 22°C. Experiments with 2,6-di-tert-butyl-p-cresol shows that it can inhibit all non-cage propagation and all formation of PP hydroperoxide, but that it does not affect cage reactions of initiating radicals and their successors. Only about 16% of the initiating PPO2· radicals escape the cage at 45°C. Oxidations of PP, n-hexane, and their mixture with both peroxide and γ-ray initiation show that nearly all the initiating radicals escape the cage in solution but that the concentration of PPO2· radicals is much less than in bulk because of a much faster chain termination. Both the propagation and termination constants for PP oxidation are much faster in solution, but the changes compensate so that kp/(2kt)½ is about the same in solution as in bulk.
85 citations
TL;DR: In this paper, the properties of block polymers and blends of the styrene-containing block copolymers were examined, especially in regard to their suitability as reverse osmosis desalination membranes.
Abstract: Copolymer containing 2-vinylpyridine–trimethylsilyl methacrylate, styrene–2-vinylpyridine, and styrene–trimethylsilyl methacrylate blocks as well as terpolymers containing the styrene2–vinylpyridine–trimethylsilyl methacrylate blocks were synthesized by initiation of the appropriate monomers sequentially both with butyllithium and sodium. These polymers were subjected to hydrolysis by which the acrylate ester segment is converted to the free acid and to the reaction with methyl iodide, which quaternizes the pyridine segment; finally the hydrolyzed and quaternized polymers were subjected to dehydrohalogenation with external base. The properties of these block polymers and blends of the styrene-containing block copolymers were examined, especially in regard to their suitability as reverse osmosis desalination membranes.
70 citations
66 citations
63 citations
TL;DR: In this article, the authors used high-resolution magnetic resonance spectroscopy to investigate three areas of novolac resin chemistry: first, the lifetimes of glycol species in formalin under acid and base conditions and the reactivity of methylene glycol towards alcohols.
Abstract: High-resolution magnetic resonance spectroscopy has been used to investigate three areas of novolac resin chemistry: first, the lifetimes of glycol species in formalin under acid and base conditions and the reactivity of methylene glycol towards alcohols; second, the in situ identification of novolac resin intermediates; third, the novolac–hexamethylenetetramine cure mechanisms. It is shown that the mean lifetime of a given glycol species is an order of magnitude shorter under basic conditions than under an acid of equal normality. The ratio of the equilibrium constants for the addition of methylene glycol to methanol, benzyl alcohol, and phenol was measured as 70:20:1. New reactive intermediates were discovered while monitoring the reaction of phenol and formalin. The reactions of various phenols with hexamethylenetetramine were studied, and short-lived benzoxazines were detected at 100–120°C whenever ortho hydrogen was available on the phenolic nucleus. The NMR peak assignments in the reaction sequence: benzoxazine, dibenzylamine, tribenzylamine, diphenylmethane are presented. Spectra of the very elusive p-benzylamines of 2,6-xylenol were recorded at 100–155°C. At 170°C, the lifetimes of these p-benzylamines are too short to afford proton resonance spectra. No evidence of hexahydrotriazine or (CH2 = N-CH2)3N type structures was found in 100 MHz NMR spectra of reaction mixtures of a phenol and hexamethylene-tetramine.
TL;DR: In this article, the stable trihydrochloride salt of 2,3,5,6-tetraaminopyridine (TAP) has been found to be a versatile intermediate to a variety of thermally stable polymers such as polybenzimidazoles (PBI), polyimidaxopyrrolones (pyrrones), and polybenzmanidazobenzophenanthroline (BB polymer).
Abstract: The stable trihydrochloride salt of 2,3,5,6-tetraaminopyridine (TAP) has been found to be a versatile intermediate to a variety of thermally stable polymers such as polybenzimidazoles (PBI), polyimidazopyrrolones (pyrrones), and polybenzimidazobenzophenanthroline (BB polymer). The controlled reactivity of two of the four amino sites of TAP · 3HCl towards diacid halides and dianhydrides makes possible the preparation of high molecular weight, soluble polyamide prepolymers at mild temperatures. PBI, pyrrones, and BB polymer are obtained from the linear polyamide precursors by heating at 150–375°C. Unoptimized cyclized polymers were aged isothermally in air at 600°F (316°C) and found to be superior to analogous polymers described in the literature. Weight retentions of up to 97% were observed after 500 hr in air at 600°F.
TL;DR: In this paper, the pyrolysis of purified celluloses in air at 251°C was studied, and the results were interpreted in terms of an oxygen-catalyzed decomposition, with the accessibility of oxygen to the cellulose determining the rate of pyroolysis.
Abstract: The pyrolysis of purified celluloses in air at 251°C was studied. The pyrolysis was found to obey first-order kinetics, and the rate constants correlated with the crystallinities, orientations and accessibilities of the samples. The results are interpreted in terms of an oxygen-catalyzed decomposition, with the accessibility of oxygen to the cellulose determining the rate of pyrolysis. The production of levoglucosan under conditions approaching combustion was shown to be a function of the crystallinity and orientation of cellulose. Some levoglucosan appears to be produced from the less ordered regions.
TL;DR: In this paper, the rate constants of polyurethanes and poly(urethane-ureas) were obtained in aqueous pyridine solution at 110°C.
Abstract: Alkaline hydrolysis of model carbamates, polyurethanes, and poly(urethane-ureas) has been investigated. The model carbamates were based upon phenyl, benzyl, and cyclohexyl isocyanates. The polyurethanes and poly(urethane-ureas) were prepared from tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), and 4,4′-dicyclohexylmethane diisocyanate (H12MDI) and a poly(oxyethylene)glycol of 6000 molecular weight. Pseudo-first-order rate constants of hydrolysis were obtained in aqueous pyridine solution at 110°C, and second-order rate constants were obtained in aqueous KOH solution for the model biscarbamates. Pseudo-first-order rate constants of hydrolysis were obtained in alcoholic KOH solution for the polyurethanes and poly(urethane-ureas). The hydrolysis of the model carbamates showed that the stability increased in the following manner: phenyl < benzyl < cyclohexyl. The pseudo-first-order rate constants were dependent upon the pKb of the corresponding amines. The hydrolysis of the polyurethanes and poly(urethane-ureas) showed that the stability increased in the following manner: aromatic < aralkyl < cycloaliphatic. It was shown that polyurethanes are more susceptible to alkaline hydrolysis than to acidic hydrolysis.
TL;DR: The long-wave photo-oxidation of polystyrene in solution at 25°C has been studied osmometrically as discussed by the authors, and two types of chain scission have been observed: a purely photo process which occurs completely independently of oxygen and which is attributed to fission of photolabile groups in the polymer, and another process associated with random photolyses of the products of oxidation scavenger experiments with 131I2.
Abstract: The long-wave (λ < 3000 A) photo-oxidation of polystyrene in solution at 25°C has been studied osmometrically. Two types of chain scission have been observed: a purely photo process which occurs completely independently of oxygen and which is attributed to fission of photolabile groups in the polymer, and another process associated with random photolyses of the products of oxidation Scavenger experiments with 131I2 have shown that approximately two iodine atoms are incorporated per chain scission when photolysis is carried out in solution (benzene, hexafluorobenzene, methylene chloride) under high vacuum conditions in the presence of 131I2. No iodine incorporation or chain scission occurs when ionically prepared polystyrenes are treated similarly. The nature of the photolabile bond has been discussed, and there is some evidence for a peroxidic linkage arising from oxygen copolymerization in the chains. It is suggested that fission of the photolabile groups contributes to the initiation of the long-wave photooxidation of the polymer.
TL;DR: In this article, the second-generation polymer overcoats the seed polymer in a core-shell fashion, rather than swelling the particle uniformly as has always been envisioned, and the encapsulation phenomena is governed by the microscopic thermodynamic environment of the latex particles which has, in turn, a profound effect upon the conformational behavior of the long-chain polymer molecules as they interact with the particle-water interface.
Abstract: We have performed a series of seeded styrene emulsion polymerizations in which the second stage of growth was initiated only after the second-stage monomer charge had achieved equilibrium saturation with the seed particles. The final particles were observed in the electron microscope by using two means of distinguishing between the first- and second-generation polymer: (a) butadiene tagging and osmium tetroxide staining coupled with ultramicrotomy and (b) tritiated-styrene tagging coupled with autoradiographic detection. We find that the first- and second-generation polymer chains are not uniformly mixed throughout the final latex product; rather, the second-generation polymer overcoats the seed polymer in a core–shell fashion. In order to explain these results, we present the viewpoint that monomer actually concentrates at the periphery of the swollen particle to form a monomer-encapsulated structure, rather than swelling the particle uniformly as has always been envisioned. We believe the encapsulation phenomena to be governed by the microscopic thermodynamic environment of the latex particles which has, in turn, a profound effect upon the conformational behavior of the long-chain polymer molecules as they interact with the particle–water interface.
TL;DR: In this article, poly(phenylene sulfides) were synthesized from m-benzenedithiol and aromatic dibromides in a basic medium of potassium carbonate in dimethylformamide or dimethylacetamide.
Abstract: Poly(phenylene sulfides) were synthesized from m-benzenedithiol and aromatic dibromides in a basic medium of potassium carbonate in dimethylformamide or dimethylacetamide. The products obtained were slightly off-white with relatively low melting ranges and had inherent viscosities in the 0.2–0.4 dl/g range in hexamethylphosphoric triamide. Similar poly(phenylene sulfides) containing pendant cyano groups along the polymer chains were obtained by the use of 5 mole-% of either 2,4-dichlorobenzonitrile or 3,5-dichlorobenzonitrile. The products were similar to the pure polyphenylene sulfides, except that they showed lower melting ranges and gave insoluble products when heated alone or in the presence of zinc chloride.
TL;DR: The successful initiation of styrene polymerization is strongly dependent upon the type of solvent employed as mentioned in this paper, such as diethyl ether, tetrahydrofuran, or 1,2-dimethoxyethane.
Abstract: Lithium diethylamide has been found to be an active initiator for the polymerization of isoprene both in hydrocarbon media and in a variety of polar solvents, such as diethyl ether and tetrahydrofuran. The successful initiation of styrene polymerization is, however, strongly dependent upon the type of solvent employed. Thus no polymerization is observed in hydrocarbon media or in diethyl ether solution, but polymerization occurs rapidly in either tetrahydrofuran or 1,2-dimethoxyethane solution. These polymerization processes are anionic in nature and are characterized by sigmoidal conversion–time plots, indicating that the initiation reactions are relatively slow compared to chain propagation.
TL;DR: A series of phenylated polydihydrophthalimides has been synthesized by the Diels-Alder reactions of 3,3′-(oxydi-p-phenylene)bis(2,4,5-triphenylcyclopentadienone) and 3, 3′-(p)-phenylene), with N,N′-o-, -m-, and p-phenylenedimaleimide as mentioned in this paper.
Abstract: A series of phenylated polydihydrophthalimides has been synthesized by the Diels-Alder reactions of 3,3′-(oxydi-p-phenylene)bis(2,4,5-triphenylcyclopentadienone) and 3,3′-(p-phenylene)bis(2,4,5-triphenylcyclopentadienone) with N,N′-o-, -m-, and -p-phenylenedimaleimide. The polydihydrophthalimides were soluble in dimethylformamide (DMF) and had intrinsic viscosities that ranged from 0.33 to 1.01, the polymers were dehydrogenated thermally and chemically to afford the corresponding phenylated polyphthalimides. The totally aromatic polyimides were also soluble in DMF but had intrinsic viscosities only as high as 0.41. The thermogravimetric analyses of the polyphthalimides showed breaks near 530°C in air and in nitrogen atmospheres.
TL;DR: In this paper, the synthesis details of solution polymerization in benzene and bulk polymerization of vinylferrocene are reported, with azobisisobutyronitrile (AIBN) as the initiator.
Abstract: The synthetic details of solution polymerization in benzene and bulk polymerization of vinylferrocene are reported. In benzene solutions, with azobisisobutyronitrile (AIBN) as the initiator, small yields of low-polydispersity low molecular weight (Mn ≃ 5000) polyvinylferrocene is obtained. However, high yields can be obtained by continuous or multiple AIBN addition. Higher molecular weight polymers and binodal polymers can be obtained as the monomer concentration is increased. In bulk polymerizations, yields of 80% can be obtained. The molecular weight increases as temperature decreases from 80 to 60°C in bulk polymerizations, and an increasing amount of insoluble polymer results. The soluble portion is often binodal, the higher molecular weight node consisting of an increasingly branched structure. Lower molecular weight polymer was readily fractionated into narrow fractions from benzene–methanol systems, but higher molecular weight polymer proved impossible to fractionate into narrow fractions due to branching.
TL;DR: In this paper, a copolymer with dimethylsilane units alternating with dioxysilphenylene and diorganosilane units was investigated as a source of high-temperature elastomers for the aerospace industry.
Abstract: Copolymers with alternating dioxysilphenylene and diorganosilane units were investigated as a source of high-temperature elastomers for the aerospace industry. A copolymer with dimethylsilane units alternating with dioxysilphenylene had a glass transition temperature of −63°C and exceptional thermal stability; a polymer with diphenylsilane units alternating with dioxysilphenylene had a glass transition temperature of 0°C and slightly higher thermal stability. Both were cured to elastomers at room temperature with ethyl silicate in combination with dibutyltin diacetate. Both had tensile strengths (ultimate) above 4000 psi even without reinforcing fillers. Reinforced elastomers of the dimethyl copolymer had tensile strengths (ultimate) up to 16,000 psi.
TL;DR: In this paper, the effect of ultrasound on the steady-state operation of a stirred tank polymerization vessel was investigated, and it was shown that the ultrasound breaks polymer chains, giving polymeric free radicals which increase in size while increasing the rate of polymerization.
Abstract: Methyl methacrylate has been continuously polymerized in toluene solution with AIBN as an initiator at 60°C in a jacketed steel vessel of 890 ml volume with holding times of several hours. Provision was made for good mixing and introduction of a steady stream of monomer, solvent, and initiator. The effluent stream was analyzed for polymer content and molecular weight distribution by gel-permeation chromatography. After the reactor had been operating for three holding times, an ultrasonic probe in the reactor was turned on, and the effect of the ultrasound on the steady-state operation of the reactor was observed. The ultrasound caused a rapid increase in the conversion level. A small, concomitant increase in the degree of polymerization was also noted. It is proposed that the ultrasound breaks polymer chains, giving polymeric free radicals which increase in size while increasing the rate of polymerization. Simulation of the polymerization in the stirred tank reactor has been achieved by using a digital computer, and a quantitative treatment of the effect of ultrasound has been developed.
TL;DR: In this paper, the role of electronically excited singlet (1Δg) oxygen molecules in photooxidation of polymers has received increased attention in recent years, but little information regarding the interaction of ultraviolet stabilizers with singlet oxygen is known.
Abstract: The role of electronically excited singlet (1Δg) oxygen molecules in the photooxidation of polymers has received increased attention in recent years. Little information regarding the interaction of ultraviolet stabilizers with singlet oxygen is known, however. In this study, singlet oxygen was produced by a microwave discharge in a flow system and rate constants were obtained for quenching by ultraviolet stabilizers. It was found that some nickel chelate stabilizers are effective quenchers of singlet oxygen and their quenching behaviors can be correlated with ultraviolet stabilization effectiveness in thin polypropylene and polyethylene films. The best oxygen quenchers of those examined are nickel chelates with sulfur donor ligands.
TL;DR: The photochromic effect has been investigated for three compounds of the benzospiran group dissolved in amorphous polymers: poly(methyl methacrylate), poly(n-butyl methacyl), poly (vinyl acetate), and poly(vinyl n-butyrate).
Abstract: The photochromic effect has been investigated for three compounds of the benzospiran group dissolved in amorphous polymers: poly(methyl methacrylate), poly(n-butyl methacrylate), poly(vinyl acetate), and poly(vinyl n-butyrate). The kinetics of the thermal bleaching reaction above Tg of the matrix follow a first-order equation due to the averaging of free volume distribution related to the diffusion of segments in viscoelastic state. A more complex mechanism of decolorization below Tg has been considered from the point of view of unequal, discrete distribution of environments in which the photochromic molecules exist in the glassy matrix. A change of the activation energy and the mechanism of color decay on passing through Tg is not a rule (PVB), which shows, that for a polymer having long, flexible chains, secondary glass transition phenomena play a decisive role. In the case of glassy polymers (PMMA), the photochromic effect of benzospirans may be employed to determine Tβ. It seems, that in addition to steric restrictions for trans–cis isomerization in the decolorization process one must consider the interactions of photochromic molecules with the matrix as well as their chemical nature.