Search

Stress relaxation measurements have been made on a series of wool+polyacrylonitrile graft copolymers containing up to 90% by weight of polymer. To minimise the effect of variations in the equilibrium water regains of the copolymers on the mechanical properties measurements have been made at 83% R. H. and 35 °C. Under these conditions the water content is independent of copolymercomposition. Two rate constants are identified one of which shows a linear correlation with copolymer composition.

Gels cross-linked to various degrees and containing various amounts of nitrile, amide and carboxylic groups were prepared by polymerizing acrylonitrile at various concentrations in aqueous 70 per cent ZnCl2 solution and by hydrolysis of polymers for various times in HCl vapours. Chemical characteristics of gels, concentration membrane potentials, membrane functions and permselectivities in KCl solutions were determined. It was proved that under the conditions used (pH close to 7, content of acrylic acid in the copolymer only 1·4–3·9 mole %). cross-linking is the decisive factor for permselectivity and ideality of the membrane functions. Cross-linking yielded almost 100 per cent permselectivity values and a slope of the membrane function of about 55 mV/decade. Further hydrolysis impairs the ideality of membranes, since the increase in swelling outweighs the effect of the increase in concentration of the active groups. Variability of the density of the ionizable groups is not sufficient to explain differences in the behaviour of the membranes under investigation.

This paper refers to an analytical technique by a tandem DTA-GC-MS combined system and describes our experiments to analyze polyacrylonitrile(PAN)resin and Nylon6in different atmospheres of air and inert gases. The DTA-GC-MS tecnique not only provides informations on the behaviors of samples under heating but also qualitatively determines the gases evolved during the process of heating. The GC-MS identified HCN evolved from the PAN resin samples and HCN and NH, evolved from a Nylon6sample using a Chromosorb103column, and acetonitrile, vinyl-acetonitrile, methylbutene, cyclohexane, toluene, pro panenitrile and2-methyl-propanenitrile evolved from the PAN resin sample, using a PEG-20M column.

Viscometric, mechanical and electron microscope investigations were carried out on mixtures of polyacrylonitrile (PAN) with its copolymers containing methyl methacrylate (MMA) and vinyl sulphate (VS) units. It was found that the compatibility of the components in solutions is reduced when the number of MMA and VS units in the copolymers is increased, as was also found in the case of differences in the molecular weight of the PAN. The tensile strength of films prepared from a mixture of PAN and its copolymers, containing up to 20% of the latter, is reduced as the number of MMA and VS units rises, while the number of double bends (in the case of the AN-MMA copolymer) is increased. It is shown that if the copolymer content of the mixtures exceeds 20%, the molecular weight of the PAN is the factor that has the most influence on the mechanical properties of the films.

The morphology and physicomechanical properties of carbonized PAN fibers (oxidized and heat-treated to 1500, 2000, and 2750°C) have been studied. It is shown that surface and internal structural defects sharply reduce the values of the physicomechanical characteristics of the carbonized fibers. The scanning electron microscope reveals the nonuniformities of the fiber over the fracture surface and makes it possible to take into account the effect of macro- and microdefects in studying fiber strength.

Thermal and alkaline cyclization of modified polyacrylonitrile (PAN) containing thioamide groups was studied. The presence of thioamide groups initiates thermal cyclization of PAN and reduces the initial temperature of cyclization to 130–150°; the activation energy of this reaction is 20 kcal/mole. The addition of thioamide groups to a PAN macromolecule also promotes alkaline cyclization of PAN under mild conditions, where unmodified PAN does not undergo cyclization. As a result of treatment with ammonium hydroxide of PAN fibres containing thioamide groups cyclized fibres were obtained of high heat resistance and elasticity modulus at increased temperatures.

The swelling of polyacrylonitrile (PAN) film in aqueous I2/KI (or I3 −) solutions of different concentrations up to 2.0 molal has been investigated, using both biaxially oriented and unoriented film. The absorption curve (equilibrium absorption vs concentration) for oriented film shows three distinct steps, at concentrations of 0.25, 0.65, and 1.6 molal, leading to weight increases of the sample of approximately 250%, 2000%, and 3200%, respectively. In unoriented film, smooth progressive increases of absorption are observed in place of the first and third steps; only the second abrupt step remains. A significant difference in desorption behavior is seen in extraction experiments carried out above and below the second step. It is hypothesized that the first and third steps of swelling correspond to the penetration of two different “amorphous” phases in the polymer, which together with a crystalline phase would indicate a three-phase structure for PAN. The second step of swelling may represent a co...

The microstructure of stress-graphitized polyacrylonitrile-based carbon fibers has been studied through the measurements of magnetoresistance at 77K and by scanning electron microscopy. The carbon fibers were stretched throughout oxcidation, carbonization and graphitization (at 2700°C). The fibers were then annealed at 3000°C. The transverse magnetoresistance of the fibers was positive. The magnetoresistance changes linearly with increasing magnetic field strength above 3kG. The low field behavior of the magnetoresistance suggested the existence of the light minority carriers in the samples. The maximum transverse magnetoresistance at 10kG is 10.45%, which indicates the presence of the extensively grown crystallites with three dimensional crystallinity. Preferred orientation of the samples was determined by the anisotropy of the magnetoresistance as follows: (1) The c-axes of the crystallites are perpendicular to the fiber axis.(2) The c-axes of the crystallites are parallel to the radial direction in the cross-section of the fibers. The preferred orientation of the crystallites in the cross-section was confirmed by scanning electron microscopy. The average crystallite size of the samples was estimated by the scanning electron micrographs of the cross-section to be about 0.6-1.2μm in width and 500-700A in thickness.

Carbon fibres have been prepared from PAN fibres spun under clean conditions to avoid contamination with impurity particles. This has enabled carbon fibres with significantly higher tensile strengths to be produced. Clean PAN fibres yielded carbon fibres with a strength of 2·75 GN/m2 after heat-treatment to 2500°C whereas control fibres spun under normal laboratory conditions only gave a strength of 1·51 GN/m2 after the same heat-treatment. The average strength of carbon fibres from the clean precursor increased with heat-treatment temperature and was constant for gauge lengths of 1–5 cm after heating to 2500°C. This was in marked contrast to the control fibres which decreased in strength after heat-treatment. The results indicate that by working in clean conditions the average separation of severe flaws operative below 2 GN/m2 was about 20 cm. Examinations of fracture surfaces with the scanning electron microscope showed that failures were initiated at the surface in all cases.

The reaction of atomic oxygen and singlet oxygen molecules with films from various polymeric substrates was studied. The polymers used were poly(vinyl chloride), polyacrylonitrile, polystyrene, nylon 66, and poly(ethylene terephthalate). Atomic oxygen reacted readily with all of these polymers. The reaction was confined to the surface layers which results in the polymer films becoming more hydrophilic. No change was observed in the contact angle of water with films of poly(vinyl chloride) and polystyrene after they had been exposed to singlet oxygen molecules for several hours. Die Reaktion von atomarem und von Singulett-Sauerstoff mit Filmen aus verschiedenen Polymeren wurde untersucht an Polyvinylchlorid, Polyacrylnitril, Polystyrol, Nylon 66 und Polyathylenterephthalat. Atomarer Sauerstoff reagierte leicht mit den genannten Polymeren. Die Reaktion beschrankte sich auf die Oberflache, was dazu fuhrte, das die Polymeren hydrophiler wurden. Der Kontaktwinkel von Wasser mit Filmen von Polyvinylchlorid und Polystyrol zeigt nach mehrstundiger Einwirkung von Singulett-Sauerstoff keine Anderung.

The X-ray method was used in calculating the differential curves of radial distribution in investigations of short range order which were carried out for a number of amorphous rubbers (polybutadiene, butadiene-nitrile rubbers) and polyacrylonitrile. The effect of temperature and of side groups on the structure of the amorphous polymers was investigated. The temperature-dependence of short range order was investigated by analysing the ratios of the heights of intramolecular and intermolecular peaks proposed by the authors as additional parameters of the amorphous state. The validity of the latter parameters for describing changes taking place within the limits of the amorphous state is demonstrated, taking as examples polyethylene, polytrifluorochloroethylene and polybutadiene. In the investigations of polybutadiene, polyacrylonitrile and a number of butadiene-nitrile rubbers it was found that the incorporation of even 18% of nitrile groups as side substituents already leads to a marked increase in the distance between the molecules in the entire volume of the polymer.

Kuhn-Mark-Houwink-Sakurada relations were obtained in methyl ethyl ketone N,N-di-methylformamide and dichlorethane at 30 for (styrene acrylonitrile) alternating copolymer. The values of the unperturbed dimensions. [ K 0 or (r o −2 /M) 1/2 ] and conformational parameter σ have been determined, using several graphical and semiempirical methods, and the results were compared with the direct determinations in a θ solvent. The best values for K θ were obtained using the methods of Stockmayer-Fixman and Inagaki-Suzuki-Kurata. By comparing the values of σ for polystyrene, polyacrylonitrile, random and alternating (styrene-acrylonitrile) copolymers, it is to be concluded that the short-range interactions do not markedly influence the chain dimensions in solutions for random and alternating (styrene-acrylonitrile) copolymers.

A titrimetric method has been developed for following the removal of titanium-dimethylamine bonds during the polymerization of acrylonitrile by tetrakis(dimethylamido)titanium(IV) (T 4 ). The kinetics of the reaction of T 4 with monomer can be interpreted in terms of a sequence of insertion reactions in which dimethylamino ligands are successively removed from titanium. The calibration of a GPC instrument for measurement of the molecular weights of polyacrylonitrile is discussed. The results of initiator consumption and polymer molecular weight measurements are combined to allow the efficiency of initiation by T 4 to be assessed. Over the whole conversion range, titanium-dimethylamine bonds are broken in about 50 per cent excess over those used for polymerization. However, at high conversions more than one polymer chain is produced per titanium atom reacted.

The free formaldehyde content, both in parts per million (ppm) and in percentage, was determined by quantitative analysis on 112 fabrics obtained from American textile manufacturers and distributors. This fabric sampling included textiles of 39 different types of composition. All 112 samples, regardless of composition, contained some free formaldehyde. In an analysis of 15 samples of 100% polyester knit and eight samples of 100% polyacrylonitrile (Orlon), it appears that these fabrics, in general, contain less free formaldehyde than those made up of 100% rayon, 100% cotton, 50% polyester and 50% cotton, and fabric composed of 65% synthetic polyester fiber (Dacron) and 35% cotton. Formaldehyde content in this study of clothing samples ranged from 1 to 3,517 ppm.

Single crystals of polyacrylonitrile (PAN) were grown by the film formation method. Lamellar thickness was measured at different crystallization temperatures. Growth rates of single crystals were measured in a wide range of temperatures. It was possible to fit the experimental data in the WLF equation by substituting C 2 = 130. Concentration dependence of growth rate has been examined. Thermodynamic calculations were carried out and various parameters were evaluated which were compared with the data of other polymers. The present study indicates that PAN is a stiff chain molecule.

A study was made of the mechanical properties of graft copolymers of gelatin with polyacrylonitrile (PAN) and with polybutylacrylate (PBAC), and these were compared with those of pure gelatin. The experimental results show that the elasticity of the system is increased by grafting of the flexible chain PBAC, while the grafting of PAN leads to increased rigidity. For graft copolymers of gelatin with PBAC it was found that shrinkage in the course of heating to 120° is greatly reduced, and this reduction is attributed to the formation of a microheterogeneous structure, the disperse phase of the latter including gelatin and PBAC in its composition. Model mechanical mixtures consisting of these components with approximately the same degree of dispersion of PBAC show shrinkage behaviour during heating to 120° resembling that of pure gelatin.

Mass transfer in wet-spun acrylic fibers during drying process was studied for monofilaments with different polymer compositions. The relation between water transfer in fibers and fine structure of them was made clear.Equations of diffusion were solved under a boundary condition that radius of monofilament changes with time; the condition was experimentally fixed. The numerical solutions were obtained by electronic computer for a set of given coefficients of diffusion. The coefficients of diffusion for water at all stages of drying were obtained by comparing the experimental values with the calculated ones. The obtained results are as follows:(1) Diffusion coefficients of water are functions of polymer composition, drying temperature and time; they are in the range of 5 × 10-7_??_5 × 10-6 cm2 /sec.(2) For the samples composed of such polymers as polyacrylonitrile (PAN), copolymer of acrylonitrile and methyl acrylate (P (AN-MEA)) and terpolymer of acrylonitrile, methyl acrylate and allyl sulfonate (P (AN-MEA-SAS)), the diffusion coefficients decrease with time until the water content in the fiber becomes less than 5_??_10%, but thereafter they increase. This behavior of water transfer during drying process corresponds well with the facts that the fine structure collapses at first stage and the fiber temperature rises at final stage.(3) In fiber of copolymer of acrylonitrile and allyl sulfonate (P (AN-SAS)), the increase in the diffusion coefficient at final stage is not observed. This is presumably due to the presence of SAS which is the strong hydrophilic component, and suppress the water transfer.(4) For the compact fibril-void structure like P (AN-SAS) fiber, the water transfer takes place more slowly than for the coarse structure like P (AN-MEA) fiber.Apparent activation energy of diffusion is about 3 to 5 Kcal/mol for all tested fibers.

The copolymerization constants for the radically initiated system acrylonitrile (AN)/α-methyleneglutaronitrile (MGN) in bulk were determined by means of IR spectra using a base-line technique and independently by means of NMR spectra. The constants obtained from the IR spectra were whereas those from the NMR measurements were The IR spectrum of polyacrylonitrile, obtained by anionic polymerization and initiation with the electrochemically generated nitrobenzene radical anion in sulfolane (tetrahydrothiophene 1,1-dioxide), has been established to correspond to an AN-MGN copolymer structure having on an average 4 to 6 s-cyanoethyl units per 10 backbone acrylonitrile units. A competitive addition-prototropy mechanism is suggested to explain the formation of cyanoethyl groups. Die Copolymerisationsparameter der radikalisch initiierten Substanzpolymerisation des Systems Acrylnitril (AN)/α-Methylenglutaronitril (MGN) wurden mit Hilfe von IR-Spektren mittels einer Basislinientechnik und unabhangig davon aus NMR-Spektren ermittelt. Die aus den IR-Spektren erhaltenen Parameter waren whereas those from the NMR measurements were Das IR-Spektrum von Polyacrylnitril, das durch anionische Polymerisation mit einemelektrochemisch hergestellten Radikalanion des Nitrobenzols in Sulfolan (Tetrahydrothio-phen-l,l-dioxid) hergestellt wurde, weist die Struktur eines AN-MGN-Copolymers auf,welches im Durchschnitt 4 bis 6 P-Cyanoathyleinheiten auf 10 Acrylnitrileinheiten enthalt.Ein konkurrierender Additions-Prototropie-Mechanismus wird zur Erklarung der Bil-dung von Cyanoathylgruppen vorgeschlagen.

Acrylonitrile (AN) was graft-polymerized onto gelatinized cationic starch (CS) possessing diethylaminoethyl ether groups by cerium (IV) initiation to give stable latexlike copolymer dispersions. Dispersions of the latex copolymers, having up to 50% grafted polyacrylonitrile (PAN), air- and heat-dry on glass to clear, adhesive films. Sonification of up to 8% dispersions at 20 Khz reduced their viscosities from 1500–3000 cP to 15–40 cP. Scanning electron microscopy revealed that both nonsonified and sonified dispersions consist of ball-like particles measuring about 0.05–0.15 μ in diameter when dry. The films are formed by coalescence of these particles. The degree to which AN grafts onto CS at ambient temperature is related to the nitrogen content of CS, gelatinization time of CS at 95°C, sequence of AN and cerium(IV) addition, concentration of cerium (IV), concentration of AN, and severity of reaction agitation. Number-average molecular weight values of PAN were about 106 when grafting was conducted under stirring and about 5 × 105 when conducted under shaking action.

A study was made of the distribution of graft polymer in fibre in the case of graft polymerization of acrylonitrile in ultra thin chlorinated PVC fibres with accelerated electrons in doses of 0·1–0·8 Mrad/min. It was shown that the theoretical distribution of graft polymers is characterized by a dimensionless parameter α, which depends on the diffusion coefficient, kinetic constants, rate of initiation and fibre radius. With parameters α ⩽ 0·5, when graft polymerization takes place in the kinetic range, the graft polymer is evenly distributed in the fibre. When parameter α ⩾ 10, grafting is limited by monomer diffusion into the fibre and the rate of grafting depends on the specific surface of the fibre and dose to the extent of 0·25. Grafting takes place in this case mainly in the superficial region of the fibre. Distribution of graft polyacrylonitrile in fibre affects the surface micro-relief, kinetics of monomer adsorption and the properties of modified fibres.

A purified preparation of tissue plasminogen activator was obtained from acetone-dried pig heart powder, principally based on the methods described by Bachmann et al. (1) and Rickli & Zaugg (2). The preparation exhibited the following properties; (i) the molecular weight similar to egg albumin, (ii) the relative thermal stability at neutral pH, (iii) inhibition by EACA and t-AMCHA, (iv) inhibition by DFP and (v) stability to iodoacetamide and TLCK. An additional study indicated that the tissue plasminogen activator was well adsorbed to polyacrylonitrile fiber and eluted with aqueous ammonia.

Cationic and nonionic dyes in polyacrylonitrile fiber are determined spectrophotometrically by dissolving the dyed fiber in dimethylsulfoxide (DMSO) acidified with p-toluene-sulfonic acid. The absorptivity and stability of the cationic dye dissolved in DMSO depend upon the acidity of the solvent and exhibit a maximum in the pH range of 2.4-4.0. In the absence of acid some cationic, e.g., triarylmethane, dyes fade rapidly in DMSO or dimethylformamide (DMF). The fading is not always reversible upon acidification. The lightfastness of cationic dyes is higher in DMSO than in DMF containing the same amount of p-toluenesulfonic acid.

TGA, DTA, IR- and ESR-spectroscopy were used to study the thermal reactions of polyacrylonitrile (PAN) grafted on Aerosil. No thermal polymerization by the nitrile groups took place with the surface of the mineral support. An exothermal formation of imine structures occurred at 240–280°C during the nitrile group reactions with the hydroxyls at the surface of the support. Isomerization of ketimine to enamine structures was found to take place above 300°C and the sample also became discoloured. The colours is due to the formation of a conjugated system of CC bonds as a result of the dehydrogenation of the polymer chains.

Polyacrylonitrile (PAN) has been prepared by a free-radical mechanism using azobisisobutyronitrile as the initiator. Fibres were produced by extruding a solution of this polymer into dilute sodium thiocyanate. Wide-angle X-ray analysis showed that the resulting fibres exhibited a moderate degree of crystalline order. An orthorhombic unit-cell has been proposed to account for the observed reflections, the cell constants are: a = 21·48 ± 0·02 A ; b = 11·55 ± 0·03 A ; c = 7·096 ± 0·003 A . A helical structure has been proposed for PAN with four monomer units per crystallographic repeat. The probability of a syndiotactic configuration has been suggested to account for the meridional reflections; the calculated density of the proposed cell (1·199 g cm−3) was found to agree very well with values quoted in the literature.

High and low density polyethylene films were modified by radiation graft polymerization of acrylonitrile, vinylidene chloride and methacrylic acid. The structures, strength and deformation properties of the grafted films were investigated in relation to various factors in the temperature range — 196 to 180° which covers alll the states of PE. It was found that in the high elastic and the viscous flow states the strength and the initial elastic modulus of PE are increased as the graft polymer content in the PE rises. It is shown that peculiarities in the behaviour of the grafted films may all be accounted for through a mechanism of PE reinforcement by the graft structures acting as active particles preventing the relaxation of the PE oriented structures.

The fatigue properties of a number of different types of fibers have been investigated and failure under cyclic loading conditions compared to that caused by simple tensile loading. Polyamide, polyester, and polyacrylonitrile fibers have been studied and all have been found to fail by fatigue mechanisms. The loading conditions have been monitored by a fiber fatigue apparatus developed for this purpose and the fracture morphologies inspected by scanning electron microscopy. In all of the cases which are considered in detail, fatigue failure of the fibers has been found to occur when cycling from zero load to a maximum load of about 60% of the tensile strength. Fatigue failure is accompanied by a distinctive fracture morphology, clearly different from the tensile fracture morphology and involving crack propagation along the fiber at a slight angle to its axis, although the mechanism which causes this in the acrylic fiber is probably different from that for the polyamide and polyester fibers.

In evaluating the effects of chain mobility, stress concentration and growth of hydrogen bond in amorphous part, elongation fatigue tests are performed for rubber and some model tire yarns which contain titanium oxide or foreign polymers in amorphous part. The results obtained are as follows:(1) Molecular chains are broken down by repeating elongating and fatigue phenomena are observed even in the material such as rubber with good mobility and not causing the permanent set arrangement.(2) When tire yarn contains foreign materials, such as titanium oxide, polyacrylonitrile and polymethyl acrylate, in amorphous part, cellulose chains in some part suffer stress concentration and fatigue is accelerated.These results suggest that the homogeneous mobility of cellulose chains is more significant for fatigue life of tire yarns than mobility itself in amorphous part. When the hydrogen bonds arise between oriented chains during fatiguing, force per molecular chain will distribute more evenly, then fatigue resistance will be elevated.

ポリアクリロニトリルは加熱することによって,比較的高い電気伝導性を持つ物質を生ずる。この加熱生成物の電気抵抗率を最高60kbarまでの高圧力下において,15°～100℃の温度範囲で測定した。加圧は六面体アンピル型超高圧装置によって行なった。この物質の電気伝導度は圧力の増加,および温度の増加にともなっていちじるしく増加する。高圧力下においても通例の電気伝導度を表わす式:σ=σ0exp(-E/kT)がなり立つ。伝導の活性化エネルギー,Eは圧力の増加にともなって減少する傾向を持つ。またこの物質の加熱変質機構についても赤外吸収スペクトル測定によって検討した。高い電気伝導性は炭素と窒素の連なる共役二重結合系によることを確認した。

Electron microscopical observations of radiation-induced rayon–styrene graft copolymers were published by Kaeppner and Huang in 1965. The present paper reports electron microscopical investigations on the relationship of the structure of vinyl–cotton graft polymers to the original morphology of the cotton fiber and into the distribution of the grafted vinyl polymer in the cotton fiber structure. The grafted vinyl monomers investigated in this study were acrylonitrile, styrene, methyl methacrylate, and vinyl acetate. Two radiation-induced procedures were used: simultaneous irradiation grafting and post-irradiation grafting. Ceric ion grafting of acrylonitrile to cotton was included for purposes of comparison. Distribution of the vinyl polymer within the cotton fiber is illustrated by a series of electron micrographs, selected as typical of the particular grafted species under consideration. Results indicate that the diffusion rate of monomer into the cellulose fiber plays an important role in the final distribution of polyacrylonitrile grafts within the fiber. Uniform distribution of polyacrylonitrile in the fiber was achieved by simultaneous irradiation grafting of acrylonitrile on a highly substituted cyanoethylated cotton. In samples of low degree of cyanoethylation the distribution of graft polymer was non-uniform. In grafting initiated by ceric ion the acrylonitrile graft polymer was evenly distributed. Polystyrene–cotton copolymers from grafts, made by simultaneous irradiation of cotton in methanol solutions of the styrene monomer, were uniform throughout the fiber but showed opening of structure associated with the amount of graft formed. Grafting of methyl methacrylate occurred only in the peripheral regions of the fiber; by contrast, grafting of vinyl acetate was uniform throughout the fiber wall. Important factors governing the successful irradiation grafting in cotton fibers are choice of solvent, ratio of monomer to cellulose, nature of prior chemical modification of the cellulose, and total irradiation dosage.

An improved method of utilizing bis(acetyl acetonato) copperII complexes as catalysts for grafting polyacrylonitrile in wool fibres has been found. The effects of variation of temperature and of the concentrations of copper, acrylonitrile, water, and additional co-catalysts on the grafting rate are described. On the basis of these results, it is suggested that polymerization may be brought about by a combination of ionic and free-radical mechanisms.

Poly-α-deuteroacrylonitrile and poly-α,β,β-trideuteroacrylonitrile were synthesized. α-Deuteroacrylonitrile was prepared by the deuterium exchange reaction of acrylonitrile with D2O in the presence of CaO. α,β,β-Trideuteroacrylonitrile was prepared by the addition reaction of C2D2 and DCN. The infrared spectra of polyacrylonitrile, the deuterated polyacrylonitriles, and the intermediate products of the syntheses were measured in the 4000–400 cm.-1 region and discussed. The polarized spectra of the oriented polymer samples were also measured. The bands of PAN in the CH stretching region exhibit reasonable shifts in the spectra of the deuterated polymers, while the C≡N stretching band shows no appreciable shift. The bands in the region lower than 1400 cm.-1 exhibit complicated behavior in deuteration. The calculation of the normal vibrations of polyacrylonitrile has been made, assuming a syndiotactic planar zigzag chain as a most simple model for calculation. The assignments of the bands are discussed.

The oxidative thermal degradation of polyacrylonitrile has been examined using infrared spectroscopy. It was found that the generally accepted mechanism for the thermal degradation of polyacrylonitrile in air, which involves direct interaction of neighboring nitrile groups, and alternate proposals, involving azomethine crosslinks through reaction of the nitrile group and a neighboring tertiary hydrogen atom, do not satisfactorily represent an initial degradation scheme accounting for the observed infrared spectral changes. Rather, it must be concluded that these reactions take place after the initial degradation, to produce highly complex pyridinoid systems, and are not observable under the experimental conditions employed here. By detailed interpretation of the spectral changes using, in part, a difference spectral examination technique, an alternate route for the oxidative degradation involving the introduction of double bonds in the polymer chain could be formulated. This reaction can best be visualized as occurring via the attack of molecular oxygen at the activated tertiary carbon–hydrogen bond adjacent to the electron-withdrawing nitrile group. The nitrile group was shown to remain unreacted during the course of the initial oxidation. After the introduction of the double bond, a number of secondary degradative reactions, of which the previously proposed routes of degradation are representative, take place; these include degradation reactions of the nitrile groups to form acid and amide groups. It was observed that the accumulation of oxygenated intermediates on the surface of the polymer film is a rapid reaction and that the initial degradation process is controlled by the concentration of these species.

The reasons for the interest of the Royal Aircraft Establishment in carbon are given and a problem and possible solution in the structure of low density pyrolytic graphite outlined. Work on the thermal accommodation coefficients of some gases on a pyrolytic graphite surface and on nuclear applications is described. The chemistry of the formation of high modulus carbon fibres from polyacrylonitrile fibres is discussed and it is concluded that the pyrolysis of polyacrylonitrile resembles that of fused ring heterocyclic compounds, the nitrogen incorporated in the ladder polymer formed at about 220°C being slowly evolved as elemental nitrogen above 600°C. It is shown that the present strength of carbon fibres from PAN fibres is limited by macro defects such as voids. Finally activation of the surfaces of carbon fibres by oxidative etching to increase the interlaminar shear strength of carbon fibre resin composites is described.

Melting point depressions were determined by dilatometric and microscopic measurements for polyacrylonitrile in dimethylformamide and in γ-butyrolactone. These data give for the glass transition and melting point of the pure polymer 104 and 317°C., respectively. Both the heat and entropy of fusion are low. This suggests that the high melting point of polyacrylonitrile is due to its extended molecular conformation rather than to strong attractions between the molecules in the crystalline state. Average crystallization rates measured dilatometrically indicate that the optimum temperature for crystallization from solutions in the concentration range 17–27% is only 21°C. above the glass transition temperature. On either side of the optimum temperature the rate decreases sharply, and although crystallization then continues for a longer time the amount of crystallinity finally developed is less. For 15–20% solutions the viscosity increases abruptly as the glass transition is approached, and decreases rapidly at about 25°C. below the true melting point. The shear dependence is large at low temperatures but appears to vanish at 25°C. below the melting point. As the temperature is raised a narrow region is observed for each concentration in which the viscosity exhibits an anomalous increase. These temperatures stand in good agreement with the optimum temperature for crystallization as determined dilatometrically. The foregoing observations suggest the presence of molecular aggregates which are held together by regions of small and imperfect crystallites. In addition to the low entropy of fusion, additional evidence for the extended shape of polyacrylonitrile molecules is provided by estimates based on dilute solution measurements. The interaction between nearest-neighbor nitrile dipoles was investigated in an attempt to correlate large unperturbed dimensions with the molecular structure. This dipolar interaction is repulsive, and its magnitude depends upon the rotational position of the two nitrile groups. By adding a further contribution representing the steric repulsion the total rotational potential is estimated for isotactic and syndiotactic sequences. The dipolar interaction is much larger than the steric repulsion, and the rotation about successive chain bonds must be cooperative to avoid certain high energy conformations. This requirement probably explains the low flexibility and high extension of polyacrylonitrile molecules. The total rotational potential for an isotactic sequence favors the same helical conformation observed in crystalline isotactic polyolefins, while for a syndiotactic sequence some type of helical conformation appears to be preferred rather than the extended planar zigzag.

The starch–polyacrylonitrile graft copolymer prepared from gelatinized wheat starch with ceric ammoninm nitrate as the initiator has been freed of ungrafted polyacrylonitrile and separated into fractions by extraction with dimethylformamide, γ-butyrolactone, and dimethyl sulfoxide. The copolymer fractions obtained differed appreciably in level of add-on, molecular weights of grafted chains, and grafting frequency. To determiue the molecular weights of grafted chains, the starch part of the copolymer was effectively removed by hydrolysis with α-amylase. It was necessary to dissolve or swell the polymer in dimethyl sulfoxide and freshly precipitate it by addition to water before enzymatic hydrolysis. In studying the effect of reaction medium on copolymer composition, there was less ungrafted homopolymer formed and a higher yield of graft copolymer possessing more frequent grafts with water than with aqueous dimethylformamide or aqueous ethylene glycol. Polymer solubility, the results of control polymerizations of acrylonitrile in the absence of starch, and the detection of glucose endgroups on the polyacrylonitrile liberated from the fractionated polymer by hydrolysis are presented as evidence that the copolymers obtained are true grafts rather thau intimate mixtures.

The analytical characterization of synthetic fibers has not kept pace with their development and production. Whereas the “second-generation” fibers have already conquered the market, the chemical investigation methods used until now for the three classical fiber polymers of the polyester, polyamide, and polyacrylonitrile types are still frequently unsatisfactory. Though they satisfy the requirements of production supervision and quality control, they do not supply enough information to enable us to understand and to explain the degradation of and damage to the polymers under hydrolytic, thermal, or thermooxidative influences. This report presents methods of chemical analysis that open up new possibilities for investigations of this nature on synthetic fibers. The results reported for commercial products must not be taken as an assessment of quality. They are simply intended to show the diversity to be expected in the chemical properties and to emphasize the practical basis of the chemical analysis of synthetic fibers.

An attempt has been made to evaluate the velocity coefficients for the propagation and termination reactions in the bulk polymerization of acrylonitrile using the thermocouple non-stationary-state method. The reaction has been studied at 25 °C, and 1. 1'-azo-bis- cyclo -hexane carbonitrile has been employed as a photosensitizer. In the very early stages of the reaction (< 0.1 % conversion) when there is very little dead polymer present, the intensity exponent is 0.5, which indicates that the termination reaction proceeds by the interaction of growing polymer chains. The values obtained for the propagation and termination velocity coefficients (namely, 52 and 5.0 × 10 6 1. mole -1 s- 1, respectively) are lower than those reported in the literature for the polymerization of acrylonitrile in dimethylformamide solution. The difference has been attributed to environmental factors. Measurements of rates and lifetimes of the kinetic chain have also been made in the region of 1 to 7% conversion. By means of a suitably designed dilatometer which could be centrifuged, the effects of polyacrylonitrile on the polymerization reaction was studied. It was shown that the presence of polymer produced an enormous increase in the lifetime of the kinetic chain, while the rate decreased a little probably due to the scattering of initiating irradiation by the precipitated polymer. The intensity exponent appeared to increase to a value of 0.7, but this may not have been a true effect, as errors in the determination of the rate may have arisen due to difficulties in maintaining adiabatic conditions throughout the non-stationary state. The results in general are in keeping with the occlusion theory suggested by previous workers to explain some peculiar characteristics of the bulk polymerization of acrylonitrile.

Experiments were carried out for the preparation of polyacrylonitrile (PAN) emulsions using isopropyl alcohol as a regulator and anionic, cationic or nonionic surface active agent as an emulsifier Optimal conditions as emulsions for the mixed spinning were found. When the ratio PAN: PVA were 2:8 filaments could be spun most smoothly. The tenacity of the filaments were as high as that of the pure PVA filament.

The acrylonitrile 4-(beta-vinylsulfonyl)-2-aminoanisole copolymer (I) (PANV) fiber was modified by graft copolymn. with Me acrylate (II), Bu acrylate (III), or acrylic acid (IV) in the presence of a redox system composed of HVO3 plus H2SO4. The graft copolymerization kinetics was markedly affected by fiber orientation. Smaller degree of drawing and higher reaction temp. brought about increased polymn. rate. The grafted copolymers-exhibited higher loop strength, wear resistance, and in the case of I-IV graft copolymer, also increased flexural strength.