Showing papers in "Journal of Polymer Science Part A in 1970"
TL;DR: In this article, the curing reactions of epoxy resin with aliphatic diamines and the reaction of phenyl glycidyl ether with butylamine were investigated with a differential scanning calorimeter (DSC) operated isothermally.
Abstract: The curing reactions of epoxy resin with aliphatic diamines and the reaction of phenyl glycidyl ether with butylamine as a model for the curing reactions were investigated with a differential scanning calorimeter (DSC) operated isothermally. The heat of reaction of phenyl glycidyl ether with butylamine is equal to 24.5 ± 0.6 kcal/mole. The rate of reaction was followed over the whole range of conversion for both model and curing reactions. The reactions are accelerated by the hydrogen-bond donor produced in the system. The rate constants based on the third-order kinetics were determined and discussed for the model reaction and for the chemically controlled region of curing reactions. The activation energies for these rate constants are 13-14 kcal/mole. At a later stage of conversion, the curing reactions become controlled by diffusion of functional groups. The final extent of conversion is short of completion for most isothermally cured and even for postcured samples because of crosslinking. It was quantitatively indicated that the final conversion of isothermal cure corresponds to the transition of the system from a viscous liquid to a glass on the basis of the theory of glass transition temperature of crosslinked polymer systems.
436 citations
243 citations
TL;DR: In this article, a general oxidation mechanism for polypropylene is presented and the overall functional group distribution is found to differ from that found in a polyethylene sheet, which is an indication of the importance of an intramolecular backbiting process.
Abstract: The nonvolatile products in thermal-oxidized polypropylene sheet have been quantitatively identified by infrared analysis and chemical reaction. The molecular weight changes with oxidation have been studied by gel-permeation chromatography. It was determined that there is a functional group at each end of a chain. A general oxidation mechanism scheme for polypropylene is presented. The discovery of γ-lactone is an indication of the importance of an intramolecular backbiting process. The overall functional group distribution is found to differ from that found in a polyethylene sheet.
162 citations
96 citations
TL;DR: In this article, the authors conducted a study of cerium (IV) oxidations of model compounds for the hydroxylic functional groups of cellulose in 1.0M perchloric acid.
Abstract: Cerium (IV) oxidations of model compounds for the hydroxylic functional groups of cellulose were conducted in 1.0M perchloric acid. Glucose, the model selected for the reducing end group, was oxidized 360 times faster than Schardinger β-dextrin, the model for anhydro-D-glucose repeating units. In the presence of a fourfold excess of glucose, stoichiometry indicated specific conversion to arabinose; the competitive oxidation of arabinose produced is insignificant. Specific C1–C2 bond cleavage was also indicated for 2-O-methyl-D-glucose, galactose, 2-O-methyl-D-galactose, and cellobiose. Anhydro-D-glucose units were oxidized predominantly by C2–C3 bond cleavage as shown by the identification of erythrose and glyoxal in hydrolyzates of cerium (IV) oxidized Schardinger β-dextrin and cellulose. Kinetic studies showed that chelate complexes were involved in oxidations of glucose, methyl β-D-glucopyranoside, 1,5-anhydro-D-glucitol, and Sahardinger β-dextrin. The oxidations of glucose derivatives which differed with respect to substituents on C1 and C2 demonstrated the importance of the hemiacetal group and the presence of oxygen on C2. For example, the relative rates of oxidation at 15°C for methyl β-D-glucopyranoside, 1,5-anhydro-D-glucitol, 2-deoxy-D-glucose, glucose, and 2-O-methyl-D-glucose are 1:1:12:360:1860, respectively. The mechanism of glucose oxidation is thought to involve formation of a chelate complex, disproportionation of the complex to form a free radical at either C1 or C2 and further rapid oxidation to 4-O-formyl-D-arabinose which is hydrolyzed in the reaction medium. General implications of the experimental results pertaining to initiation of vinyl graft polymerization on cellulose are discussed.
86 citations
TL;DR: The nonvolatile oxidation products of photodegraded polypropylene have been analyzed by infrared spectroscopy and chemical reactions as discussed by the authors, and the major functional group is ester followed by vinyl alkene, then acid.
Abstract: The nonvolatile oxidation products of photodegraded polypropylene have been analyzed by infrared spectroscopy and chemical reactions. The major functional group is ester followed by vinyl alkene, then acid. In comparison, thermally oxidized polypropylene contains relatively more aldehyde, ketone, and γ-lactone and much less ester and vinyl alkene. Photodegraded polyethylene contains mostly vinyl alkene followed by carboxylic acid. Gel-permeation chromatography (GPC) determined the decrease in polypropylene molecular weights with exposure time. A calculation determined that there is one functional group formed per chain scission; in thermal oxidation there are two groups formed per scission.
83 citations
TL;DR: In this paper, the curing reaction of polyester fumarate with styrene was investigated with a differential scanning calorimeter (DSC) operated isothermally, and the change in rate of cure was followed over the whole range of conversion.
Abstract: The curing reaction of polyester fumarate with styrene was investigated with a differential scanning calorimeter (DSC) operated isothermally. The change in rate of cure was followed over the whole range of conversion. The rate of cure is accelerated by the gel effect to about ten to fifty times the rate of model copolymerization of diethyl fumarate with styrene. This autoacceleration is much enhanced for systems with higher crosslinking densities and at lower temperatures. The results confirm that both termination and propagation steps of the curing reaction are controlled by diffusion of polymeric segments and monomer molecules over almost the whole range of conversion. The final extent of conversion is short of completion for isothermal cure and even for postcure of polyester fumarate with styrene because of crosslink formation. The final conversion of isothermal cure decreases with increasing crosslinking density and shows a maximum with increasing reaction temperature. This temperature dependency of the final conversion is caused by the difference in the activation energies for two propagation rate constants kpf and kps, which were evaluated to be 7–10 and 5–8 kcal/mole, respectively, for the intermediate stage of the curing reaction.
80 citations
TL;DR: In this paper, Diethylene glycol (DEG) is formed in a side reaction during the ester interchange of dimethyl terephthalate (DMT) with feed-forward glycol or during direct esterification of Terephthalic acid with ethylene gels, and to a smaller extent during polycondensation of the low-molecular material.
Abstract: Polymers of poly(ethylene terephthalate) (PET) always contain a certain amount of incorporated diethylene glycol (DEG), substituting the incorporated glycol. DEG is formed in a side reaction during the ester interchange of dimethyl terephthalate (DMT) with ethylene glycol or during direct esterification of terephthalic acid with ethylene glycol, and to a smaller extent during the polycondensation of the low-molecular material. DEG is formed via an unusual type of reaction: ester + alcohol → ether + acid. Some evidence of this type of reaction is given by the formation of dioxane in low molecular PET and of methyl Cellosolve and methyl carbitol during the ester interchange of DMT with ethylene glycol and diethylene glycol, respectively. The strongest support for this type of reaction, however, was obtained from kinetic data. Polyesters of low molecular weight with OH group contents ranging from 3 to 0.5 mole/kg were heated at 270°C in sealed tubes for 1–7 hr. The kinetic equation for the proposed reaction is: d[DEG]/dt = k[OH] [ester]. With the aid of one rate constant the formation of DEG in all esters could be described.
71 citations
62 citations
TL;DR: In this paper, the breakdown mechanism of an aromatic polyamide and four polyimides has been studied under vacuum in the temperature range of 375-620°C, by using techniques described earlier, involving collection and analysis of volatile products as well as analyses of residues at different temperatures.
Abstract: The breakdown mechanism of an aromatic polyamide and four polyimides has been studied under vacuum in the temperature range of 375–620°C, by using techniques described earlier, involving collection and analysis of volatile products as well as analyses of residues at different temperatures. The decomposition of the polyamide up to 375°C yielded predominantly carbon dioxide, while between 375 and 450°C about equal amounts of carbon dioxide and carbon monoxide formed. Hydrogen is the major product between 450 and 550°C, along with hydrogen cyanide, methane, and carbon monoxide. The major reaction at the lower temperatures seems to be the cleavage of the linkage between the carbonyl group and the ring, with subsequent formation of a carbodiimide linkage via isocyanate intermediates, and liberation of carbon dioxide. Alternatively, cleavage between the carboxyl and the NH-group leads to the formation of carbon monoxide. Carbon dioxide and carbon monoxide are also the major volatile decomposition products of the polyimides at the lower temperatures. The primary cleavage reaction is believed to be the rupture of the imide ring between a carbonyl and nitrogen, with subsequent formation of isocyanate groups. The latter react with each other to form carbodiimide linkages and carbon dioxide, while the remaining benzoyl radical is the source for carbon monoxide.
61 citations
TL;DR: In this article, a pyrolysis-gas chromatographic mass spectrometric technique for analyzing the products of poly(vinyl chloride) homopolymer and a series of PVC plastisols is described.
Abstract: A pyrolysis–gas chromatographic–mass spectrometric technique for analyzing the pyrolysis products from polymers in an inert atmosphere is described. Initial studies encompassing the pyrolysis of poly(vinyl chloride) homopolymer and a series of PVC plastisols (based on o-phthalate esters) have provided a complete qualitative and semi-quantitative analysis of the pyrolysis products from these materials. PVC resin yields a series of aliphatic and aromatic hydrocarbons when pyrolyzed at 600°C; the amount of aromatic products is greater than the amount of aliphatic products. Benzene is the major organic degradation product. A typical PVC plastisol [PVC/o-dioctyl phthalate (100/60)] yields, upon pyrolysis, products that are characteristic of both the PVC matrix and the phthalate plasticizer. The pyrolysis products from the plasticizer dilute those from the PVC portion of the plastisol and are, in turn, the major degradation products. There are no degradation products resulting from an interaction of the PVC with the plastisol. The pyrograms resulting from pyrolysis of the various plastisols of PVC can be used for purposes of “fingerprinting.” Identification of the major peaks in a typical plastisol pyrogram provides information leading to a precise identification of the plasticizer. The pyrolysis data from this study were related to a special case of flammability and toxicity.
TL;DR: In this article, the volume increases of rubber samples as a function of their length were found to be considerably larger than predicted by the molecular theory, contrary to common belief, the values of (∂E/∂L)V,T might not be related solely to changes in intramolecular interactions with extension.
Abstract: The molecular theory of rubber elasticity assumes the free energy to consist of two parts: a liquidlike free energy that is governed by intermolecular interactions and is independent of strain at constant volume and an intramolecular interaction free energy equal to the sum of the free energies of the chains making up the network. The volume increases of rubber samples as a function of their length were found to be considerably larger than predicted by the molecular theory. Therefore, contrary to common belief, the values of (∂E/∂L)V,T might not be related solely to changes in intramolecular interactions with extension. Also, the usual procedure to obtain values of (∂E/∂L)V,T from measurements of (∂f/∂T)p,L with the aid of the molecular theory is not correct.
TL;DR: In this article, the structure of the copolymer from methyl methacrylate complex and styrene was examined by NMR spectroscopy and the formation of a charge transfer complex of styrene with a monomer coordinated to zinc atom was inferred from the ultraviolet spectra.
Abstract: The 1:1 or 2:1 complex of acrylonitrile, methacrylonitrile, or methyl methacrylate with ZnCl2 was copolymerized with styrene at the temperature of 0–30°C without any initiator. The structure of the copolymer from methyl methacrylate complex and styrene was examined by NMR spectroscopy. The complexes of acrylonitrile or methacrylonitrile with ZnCl2 gave a copolymer containing about 50 mole-% styrene units. The complexes of methyl methacrylate yielded an alternating copolymer when the feed molar ratio of methyl methacrylate to styrene was small, but with increasing feed molar ratio the resulting copolymer consisted of about 2 moles of methyl methacrylate per mole of styrene. The formation of a charge-transfer complex of styrene with a monomer coordinated to zinc atom was inferred from the ultraviolet spectra. The regulation of the copolymerization was considered to be effected by the charge-transfer complex. The copolymer resulting from the 2:1 methyl methacrylate–zinc chloride complex had no specific tacticity, whereas the copolymer from the 1:1 complex was richer in coisotacticity than in cosyndiotacticity. The change of the composition of the copolymer and its specific tacticity in the polymerization of the methyl methacrylate complex is related to the structure of the complex.
TL;DR: In this article, the ESR spectrum obtained at 77°K is a broad singlet and assigned to phenoxy-type free radicals, phenyl radicals, and polyenyl type free radicals.
Abstract: Paramagnetic species produced in polycarbonate (PC) by γ- or ultraviolet irradiation were investigated by ESR. In γ-irradiation, scissions of carbonate groups in the main chain occur. ESR spectra (g = 2.0034) composed of a sharp singlet, some broad singlets, and a small signal with hyperfine structure are obtained, and they are assigned to trapped electrons, positive radical ions, phenoxy-type free radicals, phenyl radicals, and OC6H4C(CH3)2 radicals. The G value for total yields of paramagnetic species at 77°K is 1.8. The percentage of CO and CO2, the dominant gases evolved, is 65.4 and 33.8%, respectively. In ultraviolet irradiation, energy is absorbed selectively at the surface region. The surface region becomes insoluble in methylene chloride because of crosslinking of phenyl groups. The ESR spectrum obtained at 77°K is a broad singlet and assigned to phenoxy-type free radicals, phenyl radicals, and polyenyl-type free radicals. Some differences in effects of γ- and ultraviolet irradiation of PC are discussed.
TL;DR: In this article, samples of polypropylene particles at progressively higher yield levels (grams polymer/gram catalyst) were sliced and examined by electron microscopy and two apparently equivalent statistical models were developed on the basis of this concept.
Abstract: Samples of “as produced” polypropylene particles at progressively higher yield levels (grams polymer/gram catalyst) were sliced and examined by electron microscopy. In the polymerization of propylene with the TiCl3–(C2H5)2AlCl catalyst system the catalyst breaks up immediately into basic 100–1000 A particles. As the yield increases, the catalyst particles gradually disappear and finally become completely dispersed in the polymer particle. These results are compatible with a theory which views the catalyst as a porous crystal containing a single species of active sites uniformly distributed. As polymerization progresses, all sites should eventually initiate a polymer chain whose length should be inversely proportional to the depth of the site below the surface of the particle. Two apparently equivalent statistical models were developed on the basis of this concept. Both models predict a slow increase in the Xw/Xn ration (Q) with increasing molecular weight, after an initial rapid increase. The most useful of these models states that Q is equal to the sum of Xw terms of the simple harmonic series, and that a complete spectrum of x-mers should be present in the product. This agrees satisfactorily with analytically determined values.
TL;DR: In this article, the effect of the degree of swelling of polyethylene on the rate of grafting was investigated by diluting the styrene with methanol and with n-octane.
Abstract: The radiation-induced grafting of low-density polyethylene in contact with styrene solution was studied. The effect of the degree of swelling of the polymer on the rate of grafting was investigated by diluting the styrene with methanol and with n-octane. For styrene-methanol solution, the rate of grafting was found to increase with degree of swelling, passing through a maximum when the sorbed solvent reaches 6.2 wt-% (70 vol-% methanol in the outside solution) and decreasing therafter. The methanol fraction of the sorbed liquid is far too small to cause precipitation of the grafted chains and inhibition of their termination rate. The dilution of styrene by octane has no effect on the swelling of polyethylene, but it decreases the grafting rate over the entire concentration range. The results are explained in terms of the concentration of sorbed monomer and the viscosity of the amorphous region of the polyethylene swollen by nonpolar liquids. Supporting evidence for the mechanism is presented in the form of grafting kinetic data as a function of dose rate (2.8 × 102−9.5 × 104 rad/hr), and post-irradiation grafting measurements for polyethylene in methanol-styrene (70/30, v/v). The data indicate that at the maximum grafting rate an optimum is achieved between a high concentration of sorbed monomer and a low viscosity for the poorly swelled polymer matrix.
TL;DR: In this paper, the authors have synthesized various monometallic nickel coordination catalysts for polymerization of diolefins by transition metal derivatives, and they have shown the strong influence of the nature of the counteranion used on the stereospecificity and the polymerization rate.
Abstract: In the course of investigations of polymerization of diolefins by transition metal derivatives, we have synthesized various monometallic nickel coordination catalysts. The complexes were prepared by reacting 2,6,10-dodecatriene-1,12-diyl nickel with protonic acids; they were shown to initiate the stereospecific polymerization of 1,3-butadiene. The study of these catalysts showed the strong influence of the nature of the counteranion used on the stereospecificity and the polymerization rate. Moreover, by adding various ligands, we were able to modify the behavior of the catalytic systems and to prepare either pure cis-1,4 or pure trans-1,4 or cis–trans equibinary polybutadienes, starting from the same complex and keeping a high 1,4 specificity. Some of these modifications were shown to be reversible.
TL;DR: In this article, a new macromolecular model for branched PVC was synthesized by copolymerization of vinyl chloride with 2,4-dichloropentene-1.
Abstract: A new macromolecular model for branched PVC was synthesized by copolymerization of vinyl chloride with 2,4-dichloropentene-1. The composition and the properties of this new copolymer were studied and the phenolysis reaction to determine the content of chlorine atom bound to the tertiary carbon atom (ClT) was carried out. The presence of a longer branch, of PVC type, does not impede the reaction. It is concluded that there are no chlorine atoms at the branching sites in PVC.
TL;DR: In this article, the authors derived a rate constant for the bimolecular reactions between two radical chain ends and a primary radical and a radical chain end at a thermal energy equal to the coulombic energy of interaction of the net charges.
Abstract: A rate constant is generally derived by using Fick's equation corresponding to the spherical interdiffusion of particles. By using this rate constant, chain and primary radical termination rate constants can be approximated to rate constants for the bimolecular reactions between two radical chain ends, and primary radical and radical chain end, respectively. The former is given by ks = 8πNLDsLs exp { − Ls/Rs} × 10−3 1./mole-sec. The latter is given by ksi = 4πNL(Ds + Di)Lsi exp { − Lsi/Rsi} × 10−3 1./mole-sec. Here, NL is Avogadro's number; Ds and Di are the diffusion constants of radical chain end and primary radical, respectively; Ls and Lsi are, respectively, the distances between two radical chain ends and between a primary radical and a radical chain end at a thermal energy equal to the coulombic energy of interaction of the net charges; and Rs and Rsi are, respectively, the average distances between two radical chain ends and primary radical on a collision.
TL;DR: In this article, a theory is developed which states that the (unactivated) stereospecific fraction of the catalyst consists of molecules containing eight TiCl3 units which are separated from each other by AlCl3 in solid solution.
Abstract: Polypropylene produced by the TiCl3–diethylaluminum chloride catalyst system was separated into two kinds of polymers, a minor atactic fraction with little or no steric order and a major fraction with a high degree of steric order. Each fraction had a wide molecular weight distribution. The relative amounts, the molecular weights and the molecular weight distributions of the fractions responded differently to changing reaction conditions. This indicates that the fractions are produced by separate catalysts and by different reaction mechanisms. Polymer/catalyst mole ratios from polymerizations at various conditions showed that a least one-half of the TiCl3 content of a catalyst may become directly involved in the polymerization process. A theory is developed which states that (1) the (unactivated) stereospecific fraction of the catalyst consists of molecules containing eight TiCl3 units which are separated from each other by AlCl3 in solid solution; (2) two chlorine atoms in this molecule are replaced with alkyl groups in the first step of activation; (3) the molecule contains two active sites, one d- and the other l-orienting; (4) the molecules are crystallized in an open structure which has equally reactive sites uniformly spaced; and (5) the AlCl3 component is not an inherent part of the stereospecific catalytic structure but it contributes to high activity by opening the crystal structure.
TL;DR: In this article, it was shown that only the cis-and trans-PBDs were susceptible to oxidation by singlet oxygen and no chain scission was involved in the attack of cis- and trans PBDs.
Abstract: In recent years much evidence has been accumulated to implicate electronically excited oxygen (1Δg) molecules as the agent responsible in photosensitized oxidations for the formation of allylic hydroperoxides from olefins and of endoperoxides from 1,3-dienes. Little regarding the mechanistic aspects of the photo-oxidative degradation of polybutadiene (PBD) is known, however. To determine if electronically excited oxygen (1Δg) molecules can oxidize PBD, the ABS polyblend and standard samples of PBD's containing high trans, high cis, and high vinyl content were treated in homogeneous solution at low temperature with chemically produced singlet oxygen in situ. The source of the singlet oxygen was the triphenylphosphite-ozone adduct. Studies by spectroscopy, elemental analysis, viscosity determinations, and gel measurements showed only the cis- and the trans-PBD were susceptible to oxidation; no chain scission was involved in the attack of cis- and trans-PBD by singlet oxygen; the oxidation of the cis PBD involved the initial formation of hydroperoxides which on thermal decomposition yielded gel. The trans-PBD was found to oxidize but apparently by a mechanism different from that of cis-PBD. Initial singlet oxygen attack of ABS proceeds by oxidation of the PBD portion of the polyblend. It was also observed that when only a small amount of the double bonds in the cis-PBD polymer had been oxidized to hydroperoxides, subsequent thermal treatment of this sample resulted in gross structural changes in the whole polymer.
TL;DR: In this paper, a new class of high molecular weight polyarylsulfones is described, which are prepared by Friedel-Crafts type polycondensation of aromatic sulfonyl chlorides with aromatic hydrocarbons.
Abstract: A new class of high molecular weight polyarylsulfones is described. Polymer synthesis and structure–property relationships are discussed. The polymers are prepared by Friedel-Crafts type polycondensation of aromatic sulfonyl chlorides with aromatic hydrocarbons. A number of Lewis acids in small quantities are useful as catalysts for the polymerization. The polymerization reaction is carried out at elevated temperatures in the melt or in solution. Inert, nonbasic solvents which are compatible with the Lewis acid catalysts such as nitrobenzene and dimethyl sulfone are useful for conducting the polymerization. Many of the polyarylsulfones are amorphous, rigid thermoplastics with unusually high softening points, having glass transition temperatures in the range of 200–350°C. Outstanding resistance to air oxidation at high temperatures is derived from incorporation of the deactivating sulfone groups in the aromatic polymer backbone. Melt stability and solubility in selected solvents are emphasized as basis for processibility by conventional solution casting and molding techniques. The combination of properties, which in addition to thermal stability includes a high level of mechanical and electrical properties, chemical inertness, and hydrolysis resistance makes these new arylsulfone polymers useful over a wide temperature range and in severe and corrosive environments.
TL;DR: In this article, the uses of electron paramagnetic resonance (EPR) in studying aspects of polymer fracture are discussed and a discussion of the difference between the tensile fracture of drawn polymer fibers, in which strong signals are obtained, and cast and molded materials is given.
Abstract: The uses of electron paramagnetic resonance (EPR) in studying aspects of polymer fracture are discussed. The sensitivity of EPR is such that all phases of fracture are not amenable to investigation by these means. This paper attempts to define those areas where the authors' experience would indicate that success might or might not be expected. A discussion of the difference between the tensile fracture of drawn polymer fibers, in which strong signals are obtained, and cast and molded materials is given.
TL;DR: The thermal responses of various polyurethane elastomers in the form of changes in heat capacity, linear expansion, and tensile strain have been examined in this article, and most of the change which can be attributed to the backbone of polyethylene adipate, found in several modes of thermal analysis, are still apparent, though shifted somewhat, among most diisocyanate extended elastomer used in this study.
Abstract: The thermal responses of various polyurethane elastomers in the form of changes in heat capacity, linear expansion, and tensile strain have been examined. Most of the change which can be attributed to the backbone of polyethylene adipate, found in several modes of thermal analysis, are still apparent, though shifted somewhat, among most of the diisocyanate extended elastomers used in this study. Tolylene diisocyanate extension changes the modulus properties markedly, low modulus properties being observed at ambient temperatures. Both hydrogenated MDI and MDI elastomers show comparable expansion and modulus response, whereas the hydrogenated TDI elastomer does not have the same characteristics as TDI-based elastomers. The thermal properties of the hydrogenated TDI elastomer resemble more those exhibited by the polyol mixture extended with hexamethylene diisocyanate, and in addition this latter elastomer exhibits more crystallinity, as shown by the large endotherm in the specific heat measurement. The structure of the diisocyanate naturally changes the behavior of the hard segment.
TL;DR: In this article, a cyclohexane solution of low density polyethylene and polystyrene with anhydrous aluminum chloride was used to form graft copolymers, and the intrinsic viscosities of the polymers dropped from initial values of 2.4-6.5 to 0.55-0.85 in 5 min, followed by a slower decline over the next 2 hours.
Abstract: Treatment of a cyclohexane solution of low density polyethylene and polystyrene with anhydrous aluminum chloride causes chemical reaction between the two polymers which results in the formation of a graft copolymer. The initial copolymer-forming reaction is very rapid, and prolonged contact of the polymers with aluminum chloride causes subsequent degradation in molecular weight. Treatment of separate solutions of polyethylene, isotactic polypropylene, and ethylene–propylene copolymers with aluminum chloride was studied as a function of time. The intrinsic viscosities of the polymers dropped from initial values of 2.4–6.5 to 0.55–0.85 in 5 min, followed by a slower decline over the next 2 hr. In the case of polypropylene, the low molecular weight fragments largely retained the isotactic structure, which demonstrates that stereochemical isomerization is not a major reaction.
TL;DR: In this paper, a preliminary experimental survey of the thermal degradation of styrene-acrylonitrile copolymers was conducted using thermal volatilization analysis (TVA).
Abstract: By the use of thermal volatilization analysis (TVA), 292°C was chosen as a suitable temperature for a preliminary experimental survey of the thermal degradation of styrene–acrylonitrile copolymers. TVA also indicated that there is no fundamental change in reaction mechanism as the acrylonitrile content of the polymer is increased from zero to 33.4% although there is a progressive increase in the rate of volatilization. The increase in the rate of volatilization over that of polystyrene is directly proportional to the acrylonitrile content of the copolymer. From the changes in molecular weight which occur during the reaction it is clear that the primary effect of the acrylonitrile units on stability is to cause an increased rate of chain scission, but there is a small proportion of “weak links” which are associated with the styrene units and which are broken instantaneously at 292°C. The number of monomer molecules liberated per chain scission, the zip length, is about 40 for polystyrene in the initial stages of degradation and decreases only to the order of 20 even in copolymer containing 24.9% acrylonitrile. Thus the unzipping process is not severely affected by the acrylonitrile units; this is borne out by the fact that acrylonitrile appears among the products in very much greater concentrations than from pure polyacrylonitrile. The proportion of larger chain fragments (dimer, trimer, etc.) also increases with acrylonitrile content.
TL;DR: In this paper, the authors investigated depolymerization and consumption of catalyst in the polymerizing system of ϵ-caprolactam by using NaAl(Lac)4 catalyst at 255°C.
Abstract: Depolymerization and consumption of catalyst in the polymerizing system were investigated in the polymerization of ϵ-caprolactam by using NaAl(Lac)4 catalyst at 255°C. In the first stage of depolymerization, marked consumption of catalyst was observed. The relationship between the degree of polymerization of resulting polymer and the catalyst concentration, during the polymerization time from 10 min to 3 hr, was different from that observed for the final polymer in the case of sodium phenylacetate or sodium catalyst, and follows the equation, Pn ∞ 1/[Lac].0.4 This behavior is ascribed to the peculiar catalytic behavior of Al(Lac)3, which is a component of this catalyst.