bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase structure, morphology and phase boundary diagram in an aromatic polyimide (BPDA–PFMB)/m‐cresol system
Authors: Park Jae‐Young , Kim Doyun , Harris Frank W. , Cheng Stephen Z. D.
Published: April 2003

An organo‐soluble aromatic polyimide has been synthesized from 3,3′, 4,4′‐bis(phenyltetracarboxylic) dianhydride (BPDA) and 2,2′‐bis (trifluoromethyl)‐4,4′‐diaminobiphenyl (PFMB) via a one‐step polymerization in m‐cresol. The phase boundary diagram for this system has been established by differential scanning calorimetry, polarized light microscopy (PLM) and wide angle X‐ray diffraction (WAXD) experiments. A crystallosolvate form I has been found over the entire concentration region at low temperatures. When the temperature is increased, an isotropic phase has been observed below concentrations of about 40%. In the relatively high concentration region between 45 and 95%, a transition from the crystallosolvate from I to a crystallosolvate form II has been observed. Form II exhibits a different WAXD pattern. In a narrow concentration region between the isotropic and the crystallosolvate form II (40–45%), a biphase behavior has been found. The birefringence of this region may be an indication of a liquid crystalline phase. The BPDA–PFMB polymer crystal has been found in the very high concentration region (>95%) for temperatures >250°C. The morphologies of these phases have been investigated via PLM and transmission electron microscopy. Above the gel/sol transition temperature, the form I shows negative birefringent spherulites consisting of thin lamellae. The form II exhibits a tendency of positive birefringent spherulites. Possible mechanisms of the formation of the metastable phase morphology and their associations with the mechanical gel/sol transition are also discussed.
On the triple melting behaviour of poly(ethylene succinate)
Authors: Al‐Raheil Ismail A. , Qudah Ali M. A.
Published: April 2003

The morphology of melt‐crystallized poly(ethylene succinate) (PES) was investigated by optical microscopy and scanning electron microscopy, and the melting behaviour of PES was studied by differential scanning calorimetry (DSC). At low crystallization temperature imperfect crystals were formed which could melt and recrystallize during the DSC scan. Triple melting peaks were observed, and the melting behaviour was strongly dependent on crystallization time and scan rate. It was observed that crystallization at high temperature perfected the crystals (dominant and subsidiary lamellae in the spherulitic structure). Increasing the scan rate reduced the chance for reorganization. However, at high crystallization temperature two melting peaks were observed. The material formed was much more perfect, so that the melting process was not dominated by recrystallization. Accordingly, the cause of dual melting is the existence of two kinds of crystal perfection.
Effect of high temperatures on the dielectric behaviour of viscose fibres at low frequency
Authors: Moteleb M. M. Abdel , Saad G. R.
Published: April 2003

Commercial and purified viscose fibres exhibit dielectric dispersion and a loss peak within the frequency range 0.05–1 k c/s and at temperatures of 80–140°C. Such high temperature relaxation is local in nature and is attributed to side group motion. The characteristics of the absorption bands of these samples are compared and the results obtained are interpreted. The variation of the dielectric constant with temperature showed a second order transition at about 110°C with these samples, which disappears on hydrolysis.
H‐complex formation and influence on the radical copolymerization of acrylic acid and 1‐vinyl‐2‐pyrrolidone in tetrahydrofuran
Authors: Georgiev George S. , Koseva Nely S. , Christov Latchezar K.
Published: April 2003

The association constant of the H‐complex formation between acrylic acid and 1‐vinyl‐2‐pyrrolidone in tetrahydrofuran at 22°C (K1 = 1350 mol 1−1) was determined by means of 1H NMR spectroscopy. A detailed equation for the copolymer composition, accounting for the participation in the chain propagation of the above complex and that between acid and solvent molecules, was derived. It was used for evalution of the relative reactivities of the complexes discussed and of the uncomplexed 1‐vinyl‐2‐pyrrolidone molecules.
Polyurethanes from renewable resources. IV–properties of linear, crosslinked and segmented polymers from polytetrahydrofuran diols and their glucosides
Authors: Donnelly Michael J.
Published: April 2003

Various types of polyurethanes were synthesised from two classes of polyols: (i) 1,4‐butane diol or selected polytetrahydrofuran (PTHF) diols of different average molecular weights in the range ∼300–2300; (ii) mono‐ or bisglucosides derived from each of these diols. Linear or crosslinked polymers were prepared by reaction with diphenylmethane diisocyanate (MDI) and the properties of polymers from each class of polyol were compared. Higher PTHF molecular weights produced better properties for the diol based materials whereas lower (parent) PTHF molecular weights favoured the glucoside based materials. Segmented polymers were prepared from reaction with MDI and the chain extender ethylene glycol (EG). Manipulation of the cure conditions and hard block concentration produced materials of widely differing properties. At certain hard block concentrations and using rapid (high temperature) curing the glucoside based materials were (i) superior in properties to the diol based materials and (ii) had similar properties to commercial reaction injection moulding polyurethanes.
Studies on the process and products of multimethacrylate polymerisation
Authors: Jantas Roman , Połowiński Stefan , Strobin Grażyna
Published: April 2003

Free‐radical polymerisation of multimethacrylate‐poly(2‐methacryloyloxyethyl methacrylate)—in dilute dioxan solutions was examined. The effects of the multimethacrylate molecular weight and the multimonomer concentration on the polymerisation rate and molecular weight distribution and molecular weights of the polymerisation products were determined. The extent of conversion of double bonds in multimethacrylate was determined by FTIR spectrometry, while the molecular weight distributions were determined by gel permeation chromatography. The effect of the parameters under investigation on the template mechanism of the multimethacrylate polymerisation is discussed.
Studies on permeation through polymer latex films, III. Modification using soluble polymeric additives
Authors: Steward Paul A. , Hearn John , Wilkinson Michael C.
Published: April 2003

The influence of two distinct types of water leachable polymeric additives upon the transport properties across polymer latex films is considered. Hydroxypropyl methylcellulose, added as an aqueous solution, and a methyl methacrylate–methacrylic acid copolymer, added as latex particles, are both shown to be more effective than lower molecular weight rapidly water soluble additives, typified by sucrose, in enhancing solute transport and creating pathways for convective diffusion.
Sorption and desorption of water vapour by membranes of the polyelectrolyte complex of chitosan and carboxymethyl cellulose
Authors: Peniche‐Covas C. , Argüelles‐Monal W. , San Román J.
Published: April 2003

Sorption of water vapour by chitosan/carboxymethyl cellulose polyelectrolyte complex membranes prepared at two different pHs was studied. A linear dependence of the water uptake (W) on time was observed for W values lower than 0.5 g of water per gram of membrane. For higher values of W diffusion becomes controlled by the relaxation of the chains, and second‐order kinetics is observed. An equation that satisfactorily reproduces this behaviour is proposed. Desorption experiments were carried out at different temperatures and the W versus time curves obtained exhibited the same general pattern and were also adjusted by this equation. The approximate average diffusion coefficients were evaluated at each temperature and the apparent activation energy for the diffusion process is reported.
Investigation of pH‐sensitive drug delivery system of chitosan/gelatin hybrid polymer network
Authors: Yao Kang De , Yin Yu Ji , Xu Mei Xuan , Wang Yu Feng
Published: April 2003

A novel hydrogel based on a crosslinked chitosan/gelatin with glutaraldehyde hybrid polymer network was prepared. The gel swells in acidic medium and deswells in alkaline medium. A comparative study of the pH‐dependent release of levamisole, cimetidine and chloramphenicol was carried out.
Surface plasticisation of nylon 6,6 by water
Authors: Stuart Barbara , Briscoe Brian
Published: April 2003

Tribological studies have been carried out on Nylon 6,6 with particular emphasis placed on the examination of the effect of water on this polymer. An examination of the sliding frictional behaviour of Nylon 6,6 against a steel substrate shows that the friction decreases with increasing load, probably due to the formation of thermally softened interfaces in the contact. After exposure of this polymer to water, dramatic changes to the frictional behaviour of the Nylon are observed; the friction increases with increasing load. From the application of the adhesion model of friction it is postulated that the observed changes are caused by extensive plasticisation of the Nylon and, as a consequence, an increase in the contact area. This proposition is confirmed by the reported scratch hardness data. After treatment with water the scratch friction mechanism changes significantly and a notable reduction in the hardness of Nylon is observed.
Direct radiation grafting of acrylic acid to nylon‐6 fabric and the behaviour of the resulting graft copolymer
Authors: El‐Naggar A. M. , El‐Salmawi K. , Ibraheim S. M. , Zahran A. H.
Published: April 2003

The role of certain cations as homopolymer inhibitors in the direct radiation grafting of acrylic acid to nylon‐6 fabric was investigated. The grafting solution was methanol and water at a ratio of 30 : 70 vol%. The maximum graft yield was obtained at 0·08 wt% when using Fe2+ and at 0.7% for Fe3+. In addition, the graft yield obtained with the latter ion was higher than that for the former. Moreover, the presence of Na+ and K+ salts in concentrations as low as 0·1 wt% caused an increase in the graft yield. The hydrophilic properties investigated indicated that the water absorption of nylon‐6 fabric after 9 days increased by 44 times after grafting with poly(acrylic acid) at 166% graft yield. This ratio became 123 times, when this graft copolymer was transformed to the sodium salt. These ratios became 105 and 490 times for the corresponding recrystallized forms, respectively. A study was made to gain a better understanding of the observed super water absorption using SEM and DSC analysis. SEM micrographs of the recrystallized copolymer indicated the formation of large pores with a dendritic structure. Moreover, DSC showed a decrease in both the heat of fusion and melting point. The grafted nylon‐6 fabric showed a noticeable affinity for different dyestuffs.
Transient and thermally stimulated depolarization currents in polyvinyl formal films
Authors: Khare P. K. , Chandok R. S.
Published: April 2003

Transient currents in double‐sided vacuum aluminized polyvinyl formal (PVF) film samples of thickness 40 μm were investigated in the charge and discharge modes at different temperatures and fileds. The results observed suggest that the transient currents are governed by charge injection processes leading to space charge effects. Comparative studies of the isochronal characteristics (i.e. current–temperature plots at fixed times) with the thermally stimulated discharge current (TSDC) indicated a strong resemblance between the two techniques. These studies suggest that the simultaneous mechanism of movement of charges through microscopic distances coupled with dipolar orientation may be responsible for the TSDC peak observed at 100°C.
Kinetic study of a radical scavenging effect of hyaluronic acid
Authors: Tokita Yuichi , Sakashita Hiroshi , Okamoto Akio , Kubota Kenji
Published: April 2003

The rate of the scavenging reaction of hyaluronic acid with hydroxyl radicals was investigated by means of competitive reaction with 4‐nitrosodimethylaniline. It was found that the reactivity of hyaluronic acid with hydroxyl radicals depends on both the molecular weight and the concentration of hyaluronic acid. These features were accounted for by the characteristic molecular properties of hyaluronic acid in solution.
Tear and processing behaviour of short sisal fibre reinforced styrene butadiene rubber composites
Authors: Kumar R. Prasantha , Thomas Sabu
Published: April 2003

The tear failure and processing characteristics of short sisal fibre reinforced styrene butadiene rubber (SBR) composites were investigated. Tear strength was examined with special reference to the effects of fibre length, fibre orientation, fibre concentration and bonding agent. It was observed that the tear strength depends on all the above factors. The tear failure mechanism was analysed from fractographs taken using a scanning electron microscope (SEM). During tear testing, the composites failed by a shearing process. Microscopic examination of cracks propagating in SBR composites revealed that the amorphous SBR matrix developed cracks, leaving ligaments of rubber attached to the broken fibres. The rubber particles were stretched as the crack opened and failure occurred at large critical extensions. It was observed that an increase in the concentration of fibres increased the tear strength in both longitudinal and transverse directions. The tear strength values were almost three to four times higher than those of the unfilled vulcanizates under similar conditions. In order to analyse the processing behaviour, the green strength, mill shrinkage and Mooney viscosity of the compounds were determined. Finally, the polymer–filler interaction was studied using the Lorenz–Park and Kraus equations.
Curing of novolac–lignocellulosic composites
Authors: Simitzis J. , Karagiannis K. , Zoumpoulakis L.
Published: April 2003

Novalac resin (N) with hexamethylenetetramine (HTA) was cured with biomass (B) or Kraft lignin (KL) or hydroxymethylated Kraft lignin (KLH) or cellulose (CEL). The agricultural/industrial by‐product of olive stones was used as biomass. Kraft lignin, hydroxymethylated Kraft lignin and cellulose were isolated from the biomass. The cure was followed by DSC and IR spectroscopy. Based on the IR spectra of cured materials and their characteristic bands, the proportion of N/B = 50/50 was chosen for the preparation of novolac mixtures with other components. Only N–KLH exhibited values of ΔH higher than ΔHm, calculated from the law of mixtures, indicating that KLH participates in the cure reaction. The kinetic parameters E and K0 of the total cure reactions, calculated by DSC scans, increased in the order N < N–KLH < N–B < N–KL < N–CEL. The incorporation of KLH in the mass of N–HTA led to a slight increase in E and k0. On the other hand, KL, CEL and B acted as diluents in the mass of novolac. Generally, the cure of all materials was a first order reaction, indicating that the cure mechanism of novolac remains the same.
Radical homopolymerization and copolymerizations of ring‐methoxy substituted α‐cyanostyrenes
Authors: Tanaka H. , Teraoka Y. , Yoshida S.
Published: April 2003

Radical homopolymerization and copolymerizations of ring‐methoxy substituted α‐cyanostyrenes were studied using benzoyl peroxide and dimethyl 2,2′‐azobisisobutylate at 60°C. It was found that the cyanostyrenes containing 2‐methoxy cyanostyrene gave homopolymer in moderate yield and they were also copolymerized with vinyl monomers such as styrene and vinyl acetate. The relative reactivity of the cyanostyrenes towards a polystyryl radical (1/r2) in the copolymerization of cyanostyrenes (M1) and styrene (M2) was correlated with the Hammett and Taft substituent constants of the methoxy groups and the 13C NMR chemical shift of the β‐carbon of the cyanostyrenes. The enhancement of the radical polymerization reactivity by introducing a nitrile group in the captodative α‐position of styrene was considered to be due to the suppression of the termination reaction and the activation of the propagation reaction. In addition, thermal properties such as glass transition and degradation temperatures of the cyanostyrene polymers obtained were also examined.
Study on phase behavior–impact strength relationship of unsaturated polyester/polyurethane hybrid polymer network
Authors: Xu Mei Xuan , Liu Wen Guang , Guan Yun Lin , Bi Zuo Peng , Yao Kang De
Published: April 2003

The phase behavior of a hybrid polymer network (HPN) composed of poly[(propylene glycol maleate)‐co‐(propylene glycol phthalate)] crosslinked with styrene and polyester–urethane crosslinked with methylene‐bis‐ortho‐chloroaniline was examined. The correlation between phase separation and impact strength of the HPNs is discussed. The composition of HPNs has an effect on their properties.
Analysis of Fizeau fringes crossing fibres with trilobal shaped cross‐section having skin–core structure
Authors: Fouda I. M. , El‐Nicklawy M. M. , Hassan A. F. , Kelany A. M.
Published: April 2003

A mathematical formula is derived for the shape of multiple‐beam Fizeau fringes crossing a trilobal fibre having a core surrounded by multiple skins. Fizeau fringes in transmission crossing the fibre were obtained experimentally to calculate their optical parameters. Microinterferograms are given for illustration.
Determination of the width of the transition layer between the crystalline and amorphous zones in nylon 1010 by SAXS
Authors: Meng Chaofu , Lin J. S.
Published: April 2003

The width of the transition layer between the crystalline and amorphous zones in nylon 1010 was determined by SAXS with point collimation and long‐slit collimation, respectively. The width of the transition layer, E, was found to be 1.7 nm. The results show that the width of the transition layer is independent of crystallinity.
Monomer sequence length distributions of hard segments of linear segmented poly(urethane–urea)s 1: chromatographic study
Authors: Hanahata Hiroyuki , Kamide Kenji
Published: April 2003

An attempt was made to determine, by the chromatographic method, monomer sequence length distributions of the hard segments in segmented poly(urethane–urea)s (PURs) synthesised in a two‐step process: (1) a prepolymer formation reaction of an excess of methylenebis(4‐phenylisocyanate) (MDI) with poly(tetramethyleneoxide) (PTMO) and (2) a polymerisation reaction of the prepolymer containing unreacted MDI with ethylenediamine, giving PUR. The monomer sequence length of the hard segment was found to become longer and its distribution to broaden as the initial concentration ratio of MDI to PTMO increased. This result is attributable to an increase of the concentration ratio of the unreacted MDI to the prepolymer, leading to gelation of the polymer solution. By comparing the chromatographic results with the theoretical data calculated in the simple case of the equal reactivity of the reactants in the prepolymerisation and polymerisation reactions, respectively, the existence of unequal reactivities of the reactants in both reactions, is predicted.
Controlled release of diltiazem hydrochloride
Authors: Xu Ping , Mark James E. , Wang Song‐Bo , Nathan Paul , Korol Bernard
Published: April 2003

A new type of complex reservoir–matrix system for the controlled delivery of diltiazen hydrochloride was developed. This capsule‐type device was designed for oral administration to humans and/or animals. It contained (i) an appropriate amount of the drug in a compartment; (ii) a swelling‐controlled membrane which was prepared by mixing polymeric materials with another appropriate amount of the drug; and (iii) a water‐soluble gelatin capsule as container. The swelling‐controlled membranes were prepared from poly(2‐hydroxyethyl methacrylate) hydrogels. The effect of pH on the swelling of the hydrogels was studied. In‐vitro dissolution testing was carried out to evaluate the release of the drug using a continuous‐flow method. Zero‐order release kinetics was obtained over a period of 12 h.
Using a water‐insoluble amphoteric starch to simultaneously adsorb heavy metal ions/phenol from solutions
Authors: Chan Wu‐Chung
Published: April 2003

An investigation was undertaken regarding the adsorption of heavy metal ions (CrO2−4 or Pb2+) and phenol from solution with a highly crosslinked amphoteric starch containing the phosphate anionic group and the tertiary amine cationic group. The adsorption process was found to be dependent on initial pH and concentration for both metal ions, and to be concentration‐independent for the phenol organic substance. The adsorption follows the Langmuir adsorption isotherm for CrO2−4, and the Freundlich adsorption isotherm for Pb2+. The adsorption mechanism confirms that the Na+ of the sodium phosphate group and the Cl− of the tertiary amine group are used to exchange Pb2+ and CrO2−4 ions, respectively, and the tertiary amine group is used to adsorb phenol.
Toughening of aromatic diamine‐cured epoxy resins by modification with hybrid modifiers composed of N‐phenylmaleimide–styrene copolymers and N‐phenylmaleimide–styrene–p‐hydroxystyrene terpolymers
Authors: Iijima Takao , Suzuki Norio , Fukuda Wakichi , Tomoi Masao
Published: April 2003

Hybrid modifiers composed of N‐phenylmaleimide–styrene copolymers (PMS), and N‐phenylmaleimide–styrene–p‐hydroxystyrene terpolymers (PMSH) containing pendent p‐hydroxyphenyl groups as functionalities, were used to improve the toughness of bisphenol‐A diglycidyl ether epoxy resin cured with p,p′‐diaminodiphenyl sulphone. The hybrid modifiers were effective in toughening the epoxy resin. When using the modifier composed of 10 wt% PMS (M̄w 313000) and 2.5 wt% PMSH (2.5 mol% p‐hydroxystyrene units, M̄w 316000), the fracture toughness (KIC) for the modified resins increased 100% with no deterioration in the flexural properties and the glass transition temperature. The improvement in toughness of the epoxy resins was attained because of the co‐continuous phase structure and the improvement in interfacial adhesion. The toughening mechanism is discussed in terms of the morphological characteristics of the modified epoxy resin systems.
Isothermal cure of an epoxy/cycloaliphatic amine system. Vitrification and gelation
Authors: Barral L. , Cano J. , López A. J. , López J. , Nogueira P. , Ramírez C.
Published: April 2003

Times to gelation and times to vitrification during isothermal curing for the epoxy system diglycidyl ether of bisphenol A and 1,3‐bisaminomethyl‐cyclohexane were measured at different curing temperatures between 50 and 100°C. Gelation occurs around 56% conversion. Vitrification was determined from data curves of glass transition temperature, Tg, versus curing time obtained from DSC experiments. The minimum and maximum Tg determined for this epoxy system were Tgo = −37°C and Tg∞ = 150°C. Values of activation energy of the epoxy/amine cure reaction of 58 kJ/mol and 49.5 kJ/mol were obtained from Tg versus time shift factors and gel time measurements respectively. The isothermal time–temperature–transformation diagram has been established.
Polypyrrole–poly(heptamethylene p,p′‐bibenzoate) conducting materials. Synthesis and characterization
Authors: de la Plaza M. A. , González‐Tejera M. J. , de la Blanca E. Sánchez , Jurado J. R. , Hernández‐Fuentes I.
Published: April 2003

Polypyrrole–poly(heptamethylene p,p′‐bibenzoate) conducting materials, PPy–P7MB/ClO4, were obtained by anodic coupling of pyrrole into a polybibenzoate inert matrix, using perchlorate anions as dopant agent. P7MB is a main‐chain liquid crystalline polybibenzoate with adequate mechanical properties and elastic modulus of 1.4GPa at room temperature. The method of synthesis, galvanostatic or potentiostatic electrodeposition, is responsible for differences in the PPy–P7MB/ClO4 films electrochemical response. FTIR spectra show the complex structures of P7MB and the composite conducting material.

The conductivity of PPy–P7MB/ClO4 films maintains a relatively high value, σ = 13.74Scm−1, in spite of the insulating effect of polybibenzoate. Film micrographs reveal the typical cauliflower morphology exhibited by polypyrrole and the evolution of film growth with time.
An improved osmotic balance
Authors: Enoksson Bertil
Published: April 2003

The construction and operation of the osmotic balance has been described. Because of the damping effect of the cell immersed in the solvent the sensitivity of the balance is diminished. This can be avoided if a suitable weight is placed above the central knife‐edge of the beam of the balance. A way to calculate the dimensions of a cell which gives the lowest possible temperature sensibility has been discussed. The disadvantage of a thick cell wall with respect to reference point adjustments has been pointed out. The measurements made with the balance have shown that osmotic pressures of the magnitude 0.011 ± 0.001 g./cm.2 can be measured. An example of the use of the balance has been given for three samples of nitrocellulose.
Polymerization‐degradation of styrene in solution
Authors: Spodheim Hilda W. , Badgley Wilfrid J. , Mesrobian Robert B.
Published: April 2003

The changes in the viscosity–average size distribution of polystyrene under conditions of simultaneous degradation and polymerization in toluene solutions have been observed. The appearance of the differential distribution curves for the degraded polymers and the polymerized monomer in the steady‐state viscosity region are nearly identical. Osmotic pressure data on fractions of the degraded polymers do not show evidence for the occurrence of chain branching.
Depolarization of light scattered from dilute macromolecular solutions. I. Theoretical discussion
Authors: Doty Paul
Published: April 2003

This paper represents an attempt to review the general interpretation of the phenomenon of depolarization of light scattered from colloidal solutions and to combine this with other recently acquired knowledge in order to predict the qualitative behavior of the depolarization ratios, as well as the individual components which make up these ratios, with respect to concentration, solute–solvent interaction, and the characteristics of the macromolecules. The ratio ρv depends inversely on the turbidity of the solution, the behavior of which is now understood due to the investigations of the light scattering method relative to molecular weight determinations. If allowance is made for turbidity changes and the effects of intramolecular interference ρv reflects the optical anisotropy of the segments of polymer molecules and of rigid molecules as a whole. The values of ρh will generally diminish from a value of unity as the size of the scattering particle increases. Sniall rodlike particles appear to be an exception to this behavior according to the works of Gans and Neugebauer but experimental confirmation is lacking notwithstanding recent claims to the contrary.
Heat of crystallization of cellulose
Authors: Calvet E. , Hermans P. H.
Published: April 2003

The measurement of the heats of dissolution of cellulose of diverse percentages of We crystallization has permitted us to find the heat of crystallization of the cellulose. We have found 4100 cal./mole. This number is about 25% less than the heat of crystallization of the beta‐glucose and it is very near that which had been found by one of the authors by means of the heats of wetting. The knowledge of the heats of crystallization of the cellulose and the determination of the heats of dissolution make possible the determination of the percentage of crystallization of a sample of cellulose when the composition of the sample in reference is known.
Photochemistry of proteins. XVII. Inactivation of enzymes with ultraviolet light and photolysis of the peptide bond
Authors: McLaren A. D. , Gentile Philip , Kirk David C. , Levin Norman A.
Published: April 2003

Ribonuclease and carboxypeptidase are inactivated by ultraviolet light (2537 A.) with quantum yields of 0.03 and 0.001–0.005 respectively. The quantum yields for low molecular weight proteins are of the order of 0.03 and are higher than those for splitting peptide bonds in typical peptides (0.004–0.0004 or less). It is postulated that the primary process of inactivation involves modification of aromatic residues in proteins. A possible reason for the inverse relationship between quantum yields and molecular weights of enzymes and proteins is discussed.
Oxidation of butadiene popcorn polymer
Authors: Miller Glenn H.
Published: April 2003

Butadiene popcorn polymer reacted readily with oxygen to produce a yellow to orange colored product. The apparent over‐all activation energy for the reaction averaged 16.7 kcal. Using the reaction with oxygen as a measure of the degree of unsaturation, the glassy type butadiene popcorn polymer was found to be more saturated that the earlier generation popcorn from which it was grown. The induction period which precedes the logarithmic growth of the polymer when placed in the presence of monomer increased as the oxygen content of the seeds increased. No increase in growth activity was ever attained by exposing the seeds to oxygen. Short exposures of the seeds to oxygen up to three hours at room temperature had no effect on the growth activity of the seeds. No correlation could be found between the seed growth activity and the degree of unsaturation as determined by the oxidation reaction.
Rheology of polyisobutylene. I. Theory and experimental procedures
Authors: Leaderman Herbert
Published: April 2003

A formulation is given of the response of a body manifesting linear viscoelastic behavior in shear to arbitrary simple shear stress history. A description is given of procedures for the measurement of the retarded elasticity function and of the viscosity by means of experiments under constant shear stress and following removal of stress. The non‐Newtonian flow of polymers is considered. Existing information on the viscosity of polyisobutylene as a function of temperature and molecular weight is reviewed. The applicability of the kinetic theory of rubberlike elasticity to a system of linear molecules is discussed. The use is described of the concentric cylinder rotational viscometer for the measurement of non‐Newtonian flow and of linear viscoelastic behavior.
Ionic chlorination of polystyrene
Authors: Teyssié Ph. , De Wilde M. C. , Smets G.
Published: April 2003

The structure of the ionically chlorinated polystyrenes has been investigated by both chemical and infrared spectrometric analyses. The chlorination reaction, performed in the total darkness and in the presence of iodine as catalyst, proceeds only by a substitution mechanism, both in the aromatic nucleus and in the main polymeric chain. The catalyst concentration exercises a determining effect on the over‐all rate of the reaction. The aliphatic chlorine content has been determined by reaction with aniline; indeed preliminary experiments have shown that the aromatic chlorinated isomer has been determined by infrared quantitative spectrometry, by comparison with reference polymers: polystyrene, poly‐para‐ and poly‐ortho‐chlorostyrenes, poly‐3,4‐, ‐2,4‐, ‐2,5‐, and ‐2,6‐ dichlorostyrenes. The chlorine is preferentially oriented in the para, secondarily in the ortho position. From about 37% total chlorine content, nearly all the phenyl groups have reacted and the amount of para‐ and ortho‐chloro units decreases rapidly in favor of dichlorophenyl units. Some evidence is found of a trichloro substitution in samples of about 41% Cl or more. To elucidate the problem of the dichlorophenyl units, some samples of poly‐para‐ and poly‐ortho‐chlorostyrenes were also chlorinated: the second chlorine atom is directed into the phenyl ring mainly in the 3 position for poly‐para‐chlorostyrene, and in the 5 position for poly‐ortho‐chlorostyrene. However, a certain amount of the 2,4‐isomer is also obtained in both cases. By adding the amount of halogen (calculated from infrared analysis) to the aliphatic chlorine content (obtained from aniline analysis), a value has been found which agrees with the total chlorine content determined by the method of Wurzschmitt. The decrease of the degree of polymerization, due to the chlorination, has been followed by osmotic measurements and found to be favored by both a high degree of substitution and a polar character of the catalyst.
Emulsifier‐free polymerization in aqueous media
Authors: Whitby G. S. , Gross M. D. , Miller J. R. , Costanza A. J.
Published: April 2003

The polymerization in solution of a variety of water‐soluble monomers with a variety of water‐soluble redox initiators is described and a detailed study is reported on the polymerization, in aqueous solution, of methyl vinyl ketone and of methyl methacrylate under the influence of potassium sulfate‐silver nitrate. Keeping the persulfate concentration constant and varying the silver nitrate or, conversely, keeping the silver nitrate constant and varying the persulfate, it is found that, except at very high concentration of catalyst, both the rate of polymerization and the molecular weight of the polymer bear a linear relation to the square root of the catalyst concentration, in harmony with the general theory of catalyzed bulk and emulsion polymerization. The molecular weight of the polymer formed diminishes with increase in the temperature of polymerization. The study of redox polymerization in water, without emulsifier, has been extended to the case of a mixture of a water‐soluble and a water‐insoluble monomer, and it has been found that copolymerization proceeds at a reasonable rate and frequently forms a stable latex. The copolymerization of styrene and 5 or 10 per cent of its weight of methacrylonitrile in water under the influence of a water‐soluble persulfate‐bisulfite redox pair has been examined with some closeness. Polymerization is apparently initiated in the aqueous solution, since, contrary to the state of affairs in emulsion polymerization, water‐soluble retarders are more effective than oil‐soluble ones, when the retarder is added at the outset. If the retarder is added at a later stage of polymerization, oil‐soluble reagents are more effective than water‐soluble ones. The water‐soluble monomer enters into the polymer at a greater rate than the water‐insoluble one, but it appears that, even at the earliest stage at which it is practicable to take samples co‐polymerization occurs. The influence of catalyst concentration on the rate of polymerization, the molecular weight of the polymer, and the latex particle size was examined.
Enzyme models and their relation to inclusion compounds
Authors: Lautsch W. , Broser W. , Biedermann W. , Gnichtel H.
Published: April 2003

Syntheses of high polymers with active groups of the hemin and chlorophyll series and their optical properties, the shifts of the band maxima, and the change of the acid dissociation constants of the active groups are discussed. This touches upon the question of the existence of inclusion compounds in solution. The existence of true compounds in solution was proved by applying the law of mass action to several known inclusion systems. The acid dissociation constants of some dyes and their cyclodextrin inclusion compounds were determined by means of prototropy equilibria. The system serum albumin/methyl orange and macromolecular compounds with active groups of the hemin and chlorophyll series show a similarity to true inclusion compounds in solution, which suggests the existence of inclusion regions in the high polymers in question. Furthermore, syntheses of D‐, L‐, and DL‐forms of polyphenylalanines substituted by active groups, their optical and catalytic properties, and first experiments regarding a synthesis of cytochrome c models are discussed.
Thermal initiation of vinyl polymerization by ceric solutions
Authors: Saldick Jerome
Published: April 2003

Acid solutions of ceric perchlorate, nitrate, and sulfate initiated vinyl polymerization in the dark, via a normal free‐radical mechanism.
On the determination of methyl content in polyethylenes
Authors: Slowinski E. J. , Walter H. , Miller R. L.
Published: April 2003

A method for the quantitative determination of the degree of branching (methyl content) in ethylene polymers is described. This method involves the use of a calibration curve prepared from hydrocarbons of known methyl content. Because of the importance to the calibration of having hydrocarbon with a methyl content roughly that of the polymers to be measured, the hydrocarbon, n‐C58H118, was prepared and its synthesis is given. The methyl contents of a series of polyethylenes, both commercial and experimental, were determined, and the results correlated with some physical properties of the polymers. A quantitative relationship was shown between the crystallinity of a polymer, as measured by the density, and the degree of branching. Qualitative relationships between molecular weight and branching and between mechanical properties and branching were also shown.
Polymers and group interactions. II. Friedel‐Crafts reactions on polyvinyl chloride, a route to poly‐1,3‐methyleneindans1
Authors: Teyssié Ph. , Smets G.
Published: April 2003

Polyvinyl chloride was condensed with a series of aromatic compounds (benzene, toluene, m‐xylene, pseudocumene, and mesitylene) in the presence of aluminum chloride. These condensation reactions were carried out in several reaction media, in heterogeneous or semihomogeneous systems. The catalyst concentration exercises a determining effect on the over‐all rate of the reaction. The degree of substitution of the polymers obtained was evaluated by chemical determination of the residual chlorine content. The condensation proceeds through a two‐step reaction scheme: an alkylation reaction of the aromatic ring, according to the classical orientation rules (except for pseudocumene and mesitylene), followed by a fast intramolecular cyclization reaction yielding 1,3‐methyleneindan units. Nevertheless some “abnormal” substituted products were also detected in the end products. The structure of these polymers determined from their infrared absorption spectra by comparison with the spectra of the following reference compounds: polystyrene, poly‐m‐methyl‐ and poly‐p‐methylstyrenes, poly‐2,4‐dimethyl‐ and poly‐3,5‐dimethylstyrenes, poly‐2,4,6‐trimethylstyrene, 1,3‐dimethyl‐, 1,3,6‐trimethyl‐, and 1,1,3,3,4,6‐hexamethylindans. The condensation reactions of this type are always accompained by a strong decrease of the degree of polymerization, which was followed by both viscometric and osmotic measurements; this decrease of the degree of polymerization depends mostly on the amount of aromatic substitution on the polymers.
Diffusion and gelation in polyadditions. IV. Statistical theory of ring formation and the absolute gel point
Authors: Gordon Manfred , Roe Ryong‐Joon
Published: April 2003

In the model nonlinear polyaddition system methyl methacrylate/ethylene dimethacrylate (MMA/EDMA), the plot of the critical conversion against the rate of polymerization is a straight line. This is in accord with the classical theory of gelation, whose vindication is completed in this paper. To account quantitatively for the slope of the line, internal cyclization within the primary polymerization chains must be extensive. Thus of the order of half the pendent vinyls on such a chain fall to the radical on the same chain, in agreement with theoretical prediction on the basis of molecular models. The intercept of the critical conversion plot at zero rate can also be explained in terms of the internal cyclization reaction, while chain transfer makes at most a small contribution. The dependence of the gel point on the proportion ρ of EDMA unsaturation, over a 250‐fold range, is satisfactorily accounted for by the classical gelation theory. A statistical theory of internal cyclization suggests that a steady state is approached in the growth of a given radical chain. Pendent vinyls are then lost by cyclization as fast as they are added by polymerization. The limiting number of pendent vinyls on a primary chain is about 1000 ρ. A statistical theory of multiple crosslinking (cyclization involving more than one primary chain) suggests that it is unimportant. The number of pendent vinyls on a giant molecule grows proportionately to the number of primary chains of which it is comprised. Thus multiple crosslinking has little effect on the classical network theory of gelation, but makes a contribution to the parameter introduced into the theory to correct for internal cyclization. The interplay of kinetic and gelation measurements is useful in mechanistic studies of nonlinear polymerization.
Electron exchange polymers. VIII. The redox potentials of polymeric hydroquinones
Authors: Luttinger Lionel , Cassidy Harold G.
Published: April 2003

The redox potentials of linear and crosslinked polymeric hydroquinones were studied under a variety of experimental conditions. For aqueous systems a sulfonated copolymer was employed. The main features of these titrations were: (1) In aqueous solution the potentials were up to 200 mv. higher than that of a comparable monomer. (2) These potentials fell to about the expected value when the titration was carried out in 1 M KCI. (3) Titrations of the unsulfonated copolymer in 90% dioxane‐water indicated that a small but measurable enhancement of the potential (about 10–50 mv. over that of a comparable monomer) exists in this case. (4) Both the linear and crosslinked polymers yielded substantially the same results. (5) A smaller enhancement of the potential was observed when bromine rather than ceric sulfate was used as oxidant. (6) The reactions were very slow, but in the case of the oxidations with ceric sulfate the reaction rate was increased tenfold in the presence of 1 M KCl. The potentials are discussed in the light of current polyelectrolyte theory, which gives a plausible explanation of much of the observed effect, but direct experimental confirmation was not forthcoming. Various possibilities with regard to the catalysis by KCl are discussed. These polyelectrolyte phenomena are also shown to have important consequences for redox enzyme and other protein systems.
A rational measure for the heterogeneity of polymeric homologous substances
Authors: Hultin Eskil
Published: April 2003

A rational measure of the heterogeneity of high molecular substances is obtained by comparison of their molecular weight distribution with the theoretical distribution arrived at if infinitely large molecules are depolymerized in such a way that all linkages between the basic molecules are broken with equal ease. This distribution differs noticeably from the error function, which was used by Lansing and Kraemer in measuring heterogeneity. A table is given, by which the distribution curve can be transformed to a straight line. These table values, called “dist” values, are logarithms of the degrees of polymerization in the theoretical distribution, expressed in per cent of the median degree of polymerization. For a fractionated sample, the table values corresponding to the various percentages of substance at which the fractions were obtained are plotted versus the logarithms of the molecular weights. If the molecular weight distribution of the sample is similar to that in depolymerization, a straight line fits the points. The inverse value of the inclination of this line is a measure of the heterogeneity, for which the name heterogeneity quotient is suggested.
Chain scission efficiency in the oxidation of natural rubber vulcanizates
Authors: Veith A. G.
Published: April 2003

The efficiency of the oxidative chain scission in natural rubber vulcanizates has been measured for a simple MBTS vulcanizate with and without antioxidants. This was accomplished by making concurrent measurements of the chain scission velocity and oxidation rate. The chain scission velocity was obtained from stress relaxation measurements which were corrected for the relaxation not due to oxygen by means of relaxation in vacuo. The reciprocal scission efficiency, defined as the number of molecules of O2 per chain scission, was found to be 1.5 as a mean for six vulcanizates both with and without antioxidant. The decrease in network chains was found to be first order. From the theoretical analysis by Bueche such behavior has been interpreted to indicate a nonrandom scission process with the scission occurring at the crosslinked site. The form of the dependence of the reciprocal scission efficiency on time, in vulcanizates with and without antioxidant, is consistent with nonrandom scission. Experiments on Butyl vulcanizates and the known effect of crosslink density or combined sulfur on oxidation rate further strengthen the concept of scission at the crosslinked site.
Anionic polymerization of isoprene: Effect of ionic character of the growing ion pair on polymer structure
Authors: Tobolsky A. V. , Rogers C. E.
Published: April 2003

The styrene content of styrene‐isoprene copolymers initiated by alkali metals in different solvents is correlated with the total 1,4‐adduct content of isoprene homopolymers initiated in the same manner. A very good linear relationship is obtained over the whole range which is dependent on the ionic character of the propagating species highly ionic systems (i.e., Na in ethers) give high styrene and low 1,4‐adduct contents, while less ionic systems, i.e., butyllithium in aromatic ethers and in hydrocarbons, give progressively lower styrene and higher 1,4‐adduct contents.
The apparent specific volume of polymers in dilute solution
Authors: Horth A. , Patterson D. , Rinfret M.
Published: April 2003

Apparent specific volumes φ2 of polymers in dilute solution (<5%) have been obtained with a magnetic float type densitometer for the following systems: polyvinyl acetate–chlorobenzene, polyisobutylene–benzene and –chlorobenzene, and polystyrene–chlorobenzene and –chloroform. Large variations of φ2 with concentration in very dilute solution have been reported in the literature, but could not be detected; preliminary results did show a variation, but this was found to be a nonequilibrium effect. The difference between φ2 and the specific volume of the pure polymeric liquid is found to be roughly proportional to the calorimetrically determined heat of mixing of polymer and solvent.
High pressure polymerization of ethylene. A kinetic study of polymerization initiated by 2,2′‐azobisisobutyronitrile
Authors: Kodama Shinjiro , Matsushima Yoshinori , Ueyoshi Akihito , Shimidzu Takeo , Kagiya Tsutomu , Yuasa Sachio , Fukui Kenichi
Published: April 2003

The polymerization of ethylene initiated by 2,2,‐azobisisobutyronitrile in water was studied at 70–120° C. and at 100–1500 kg./cm.2 pressure. The following relations between the reaction conditions and the properties of polyethylene produced were obtained (1) the density decreases with temperature, and (2) the molecular weight increases with pressure, independent of the amount of initiator. The reaction begins with an incubation period for which the overall rate Ri is represented by Ri = const. × I0P0, in which I0 and P0 are the amount of initiator used and the initial pressure, respectively. In the main period of reaction the overall rate was found to be R = k′I0 exp {−αt}P1.8. A reaction mechanism is proposed from which this rate equation can be derived. The proposed mechanism implies that the deactivation and the termination of radicals is first order with respect to the radical concentration.
Characterization of polyolefins by differential thermal analysis
Authors: Ke Bacon
Published: April 2003

Differential thermal analysis has been used to study the solid‐liquid transitions of four polyethylenes, an isotactic polypropylene, a series of ethylene‐propylene copolymers, and a physical mixture of polyethylene and polypropylene. The thermograms obtained directly yield the transition temperatures. By calibration, heats and entropies of fusion were also derived from the thermograms. From the heats of fusion, the degree of crystallinity of these polymers has been calculated. Differential thermal analysis can detect a physical mixture of polymers that melt sufficiently wide apart. The thermogram‐peak areas are proportional to the amounts of material present. Convenience and speed make differential thermal analysis a useful tool for characterizing polymeric materials when uniform conditions are maintained.