bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism of phosphite stabilizers in polyolefins subjected to ultraviolet irradiation
Authors: Hutson G. V. , Scott G.
Published: June 2010

The effect of thermal‐oxidative processing on the stability to ultraviolet irradiation of high density polyethylene containing a catechol hindered‐phenyl phosphite has been studied by periodic observation of carbonyl index by infrared spectrometry and by recording embrittlement times.

Certain of the possible thermal‐oxidative reaction products of catechol hindered‐phenyl phosphite, catechol hindered‐phenyl phosphate and mono‐(σ‐hydroxyphenyl)phosphoric acid have also been studied. The results are consistent with the theory previously developed that the latter or its dehydration product, catechol hydroxy phosphate, is the effective antioxidant produced during processing.
Changes in concentration of some stabilizers during the photooxidation of polypropylene films
Authors: Vink P.
Published: June 2010

The changes in concentration of 2‐hydroxy‐4‐octyloxybenzophenone, Cyasorb UV‐1084, and Tinuvin P during the photooxidation of films of polypropylene, stabilized by these compounds, is determined. The change in concentration of the benzophenone derivative obeys zero‐order kinetics, while that of Cyasorb UV‐1084 tends to be first order. The concentration of both compounds has strongly decreased at the end of the induction period. The concentration of Tinuvin P decreases strongly only after the induction period. The implications of these results for the mechanism of UV stabilization are discussed.
Three‐dimensional anionic polymerization of oligoesteracrylates
Authors: Lipatova T. E. , Shapoval G. S. , Basilevaskaya N. P. , Shevchuk E. S.
Published: June 2010

The mechanism of the formation of soluble and network polymers during the process of anionic polymerization of oligoesteracrylates (OEA) was investigated.

It was shown that the network polymer was built from charged branching macromolecules. The anionic polimerization of OEA establishes the equilibrium in the process of electron distribution between functional groups of OEA and equilibrium between soluble and network polymers and residual OEA. Both types of equilibria are determined by the temperature and the ratio of concentration of OEA and catalyst. The equilibrium in the system of network and soluble polymers and residual OEA is established both by the interaction of catalyst with OEA and with “dead” network polymer which may be “vitalized” in this way.
Some features of radical polymerization of acrylic and methacrylic acid salts in aqueous solutions
Authors: Kabanov V. A. , Topchiev D. A. , Karaputadze T. M.
Published: June 2010

The kinetics of radical polymerization of acrylic and methacrylic acids and their salts in aqueous solutions have been studied. A considerable increase in the polymerization rate at an increase in pH in the alkalinity area has been detected, the general trend of the rate‐enhancement being specifically dependent on the type of cation present in the solution. On the basis of the set of the experimental data an assumption was made on the kinetic role of ion pairs in the radical polymerization of ionizable monomers. Formation of ion pairs results in the increase of the elementary propagation rate constant Kp. Rotating sector measurements for individual kinetic constant confirmed the advanced hypothesis. The importance of the conformational state of polyelectrolyte growing chains in the kinetics of radical polymierzation of ionizable monomers has been shown. Participation of ion pairs in the propagation step leads to marked stereochemical effects and, in certain cases, to the formation of practically stereospecific polymers.
Unsaturated polymers from aliphatic nitriles
Authors: Wöhrle D. , Helling G.
Published: June 2010

Nitrile groups of fumaronitrile, succinonitrile, and polyacrylnitrile were polymerized with the anion of DMSO. Dark‐colored polymers with conjugated CN‐bonds were obtained with high yield. A reaction mechanism is discussed. The polymerization of succinonitrile with Ziegler catalysts such as Al(C2H5)2 Cl/TiCl4 also gave dark‐colored polymers with high yield.
Studies on the emulsion polymerization of vinyl chloride by seed polymerization
Authors: Ugelstad J. , Fløgstad H. , Hansen F. K. , Ellingsen T.
Published: June 2010

Kinetic experiments with homodisperse seeds of various particle size verified the previous results as to the effect of particle number, degree of conversion, and initiator concentration on the rate of polymerization. Also, experiments with mixed seeds consisting of two sets of homodisperse particles of different sizes were carried out and the relative growth of the particles was measured. A mathematical model involving desorption and reabsorption of radicals into particles was developed for such competitive growth experiments and applied to describe the experimental results. Experiments with mixed emulsifier systems consisting of an anionic emulsifier and different fatty alcohols in seed polymerization supported previous results regarding the effect of fatty alcohol on the rate of reaction. The application of certain systems of anionic emulsifier and fatty alcohol led to a much more effective emulsification of the monomer. It is suggested that in this case the monomer droplets may serve as loci for initiation and polymerization.
Morphology of segmented polyester thermoplastic elastomers
Authors: Cella Richard J.
Published: June 2010

The morphology of a new family of copolyester thermoplastic elastomers is described and the physical properties of these polymers are interpreted in terms of their unusual two‐phase domain structure. The elastomers were synthesized by the equilibrium melt transesterification of dimethyl terephthalate with 1, 4‐butanediol and poly (tetramethylene ether) glycol, resulting in a molecule in which crystallizable tetramethylene terephthalate (4GT) segments and amorphous poly (tetramethylene ether) glycol terephthalate segments are randomly distributed along the backbone. The 4GT sequences were found to crystallize as lamellar domains measuring approximately 100 Å in width and up to several thousand angströms in length. These crystalline regions are not discrete as are the polystyrene domains in the typical polystyrene‐polybutadiene‐polystyrene (SBS) triblock polymers, but rather are continuous and highly interconnected. Like the glassy regions in the SBS polymers, however, they serve as intermolecular tiepoints for the amorphous portions of the molecules and lead to the formation of a three‐dimensional network structure. At temperatures below the crystallite melting point, the material exhibits many properties characteristic of conventionally cured elastomers, but at elevated temperatures the melting of these thermally labile noncovalent junctures allows the material to flow and be processed as a thermoplastic. The stress‐strain behavior of these polymers is discussed in terms of their morphology, and thermal analysis, electron microscopy, and x‐ray diffraction results are presented.
TR: A new characteristic temperature for thermoplastic polymers
Authors: Aharoni Shaul M.
Published: June 2010

Treatment of thermal data of fluids at their critical point Tc and of 31 polymers at their Tg according to a modified Goldhammer equation indicates that at these points they have a fractional free volume (FFV) averaging 0.113 magnified image and yields TR′S characteristic of each polymer. The FFV values obtained from magnified image showed small deviations from 0.113. These were in the direction and order of magnitude of chemically similar fluids at their Tc. When TR = 2Tg, eq. (2) reduces to FFV = (aL – aG) Tg. Plots of FFV versus TR – 2Tg show similarities in polymeric homologs behavior. A modified WLF equation with C1 = 3.85, C2 = 0.113/(aL – aG), and T – Tg = TR – Tg places all the data on a single curve. The stress concentration coefficient γ of long‐term polymeric strength is temperature dependent. magnified image
The influence of charged groups in gel permeation chromatography of polyelec‐trolytes
Authors: Forss K. G. , Stenlund B. G.
Published: June 2010

When polyelectrolytes (lignosulfonates) with a broad molecular weight distribution are eluted from Sephadex gels with water, the fractionation is affected by steric exclusion, polyelectrolyte expansion, ion exclusion, and ion inclusion effects. The ion inclusion effect is due to interaction of charged sites in the macro‐ions which are more or less excluded from the gel with charged sites in more permeable macro‐ions. The ion inclusion effect depends on the cation of the lignosulfonates in such a way that the elution of lignosulfonates with a univalent cation is affected to a greater extent than the elution of lignosulfonates with a divalent cation. This is due to the existence of a higher density of free charges in the lignosulfonates with a univalent cation owing to a lesser tendency to form ion pairs. By choosing suitable eluents, it is possible to alter the retention volumes of lignosulfonates of different sizes and thus optimize the resolution.
Solution and bulk flow properties of linear and branched styrene–butadiene rubbers
Authors: Mieras H. J. M. A.
Published: June 2010

The solution and bulk flow properties of various styrene‐butadiene rubbers have been investigated. Bulk flow properties were measured with the Instron capillary rheometer, while the Weissenberg rheogoniometer was used to measure to steady‐state and oscillatory flow properties of 15% wt solutions in decalin.

A comparison of the rheological information obtained from the solution and bulk behavior with GPC and intrinsic viscosity data makes it possible to distinguish between different forms of branching and between the effects of molecular weight distribution and branching.

Branching decreases the hydrodynamic volume of a polymer coil relative to its molecular weight, so that branched polymers have lower solution viscosities at the same molecular weight than linear polymers. This effect is more pronounced for short‐chain and dendritic forms of branching than for star‐shaped long‐chain branching. At higher concentrations and especially for bulk polymers, however, star‐shaped long‐chain branching will give rise to much higher viscosities, which is hardly, if at all, found for short‐chain or dendritic forms of branching.

Star‐shaped branching greatly affects the shear sensitivity of the bulk viscosity, whereas it has relatively little effect on polymer fluid elasticity either in bulk or in solution, this elasticity being mostly determined by the width of the molecular weight distribution Mz/Mw.
Investigation of anisotropic light scattering by solutions of polymers and copolymers
Authors: Ehrenburg E. G. , Piskareva E. P. , Poddubnyi I. Ya.
Published: June 2010

The intensity of depolarized components of light scatered by polymer solutions has been measured in solvents of different refractive indexes. It has been found that the dependence of the Rayleigh ratio (RHv/c) on the solvent refractive index (n0) for polymer solutions significantly differs from the corresponding dependence (RHv/c) = f (n0) for solutions of low molecular weight compounds. The interpretation of the observed relations (RHv/c) = f (n0) is given and the equation relating RHv/c with the polarizability tensor anisotropy 〈γ2〉 of dissolved macromolecules proposed. The equation differs from the corresponding equation applicable to low molecular weight compounds by the use of Λ in a medium. Values of 〈γ2〉 for atactic polystyrene determined by the equation given are compared with calculation reported by Flory and co‐workers.

The difference between the statistical segment principal polarizabilities calculated from the anisotropic light scattering data has been also compared with that determined from birefringence data. All the results obtained are in agreement with the equation proposed. It is shown that the intensity of the anisotropic light scattering by block copolymer solutions is sensitive to disturbances in the regular block structure and, hence, the anisotropic scattering method can be used to characterize the alternating of monomer units in copolymer chains.
On the combinatorial entropy of athermal polymer solutions
Authors: Bellemans A. , De Vos E.
Published: June 2010

A computer simulation of the lattice model of an athermal polymer solution shows that the Huggins formula for the combinatorial entropy is a rather good approximation. It also appears that the mean dimension of the chains decreases as the concentration of the solution increases.
Investigation of chemical behavior of anthracene derivatives as monomers and reagents in synthesis of macromolecules containing anthracene groups
Authors: Skorokhodov S. S. , Krakovjak M. G. , Anufrieva E. V. , Shelekhov N. S.
Published: June 2010

Methods for obtaining polymers with various content and position of anthracene groups in macromolecules (in the main chain, in the side radicals, or at the chain end) have been worked out. The methods are based on the copolymerization and on the reaction of synthetic and natural polymers with the participation of anthracene‐containing monomers or reagents. The pecularities of the anthracene group reactivity in these reactions were investigated. Investigation of free radical copolymerization of 9‐vinyl‐anthracenes has shown that the reaction center can shift from the α‐carbon of 9‐anthrylmethyl system to the 10th position. This permits the preparation of polymers with anthracene groups in the main chains. We established the structure and content of the anthracene groups in the polymers obtained (polyacrylic and polymethacrylic acids and their esters, polystyrene, polymethylene, polyvinylic ethers, some biopolymers) by UV‐spectroscopy and by measurements of their luminescent parameters (spectra, lifetime of excitation, and polarization of fluorescence). The polymers with very low amount of anthracene groups “luminescent marks” (one per more than thousand of monomeric units), differently placed in macromolecules, have been used for investigating intramolecular motion of macromolecules by the method of polarized luminescence.
Studies in heterocyclic polymers. III. A comparison of the thermal stability of some linear and related ladder polymers
Authors: Hodd K. A. , Holmes‐Walker W. A.
Published: June 2010

Static and dynamic thermogravimetry in an inert atmosphere and in air have been used to assess the thermal and oxidative stability of the ladder structured macrocyclic polymers and the related linear polymers the poly(benzobis (aminoiminopyrrolenes)) and their N‐substituted derivatives in the range 200–450°.

The results of these weight loss studies have been analyzed using the methods discussed by Audebert and Aubineau,5 and by Zsako. The activation energies of polymer degradation derived by these analyses suggest that for this particular polymer system, contrary to the generally accepted theory, the ladder polymers are not significantly more thermally stable than the linear polymers. This deviation is explained in terms of macrocyclic strain and chain stiffness.
Determination of the crystalline fold period in poly(ethylene terephthalate)
Authors: Overton J. R. , Haynes S. K.
Published: June 2010

The morphological characteristics of poly(ethylene terephthalate) (PET) have been inferred from the selective chemical degradation of amorphous regions, including chain folds, and subsequent analysis of the molecular weight distribution of the reaction products. Bulk PET of known thermal and orientation history was reacted with 40% aqueous methylamine at 35°C and the reaction products examined by gel permeation chromatography. It was determined that the average crystalline fold period increased from six to nine monomer units over the crystallization temperature range of 126°C to 229°C. Evidence for the existence of a paracrystalline form at the lower crystallization temperatures was suggested by the presence of residual high molecular weight polymer in the reaction products. Samples crystallized at the lower temperatures exhibited multiple melting during DSC analysis. Results obtained by heating such samples in the DSC to a temperature between the two endotherms and quenching, followed by aminolysis and GPC, lead one to conclude that the first endotherm represents the initiation of melting and recrystallization. The second endotherm at ∼255°C, characteristic of PET, represents the melting of folded chain lamellae containing nine repeat units between folds. This material is formed during the DSC run as a result of melting and thermally compensatory recrystallization.
Structural data on crystalline polymers by thermal analysis
Authors: Wunderlich Bernhard
Published: June 2010

Linear marcromolecules in the solid state may assume different macroconformations. While x‐ray diffraction and electron microscopy have been the prime instruments for the analysis of the highly ordered state, difficulties exist in the evaluation of less ordered portions. The enthalpy changes connected with changes in order can be determined by thermal analysis. Furthermore, modern instrumentation allows thermal measurements as a function of heating rate. Such mode of analysis can give kinetic information and data on metastable states. The macroconformations, thermal analyses, experimental techniques, and recent applications of thermal analysis to structural analysis giving information on folds, tie molecules, loops, and ciliae of poly(ethylene terephthalate), polyparaxylylene, selenium, and polyethylene are discussed.
Techniques used in applying regularization to the ill‐posed problem of determining a molecular weight distribution from sedimentation equilibrium.
Authors: Wiff D. R. , Gehatia Matatiahu
Published: June 2010

Inferring the Molecular Weight Distribution (MWD) of a polymer in solution from ultracentrifuge sedimentation equilibrium data has been a problem of major concern during the past decades. Recently, it has been shown that this problem is of itself mathematically ill‐posed, i.e., leads to unstable and unreliable results. To combat this difficulty, a technique of regularization applicable to the sedimentation equilibrium equation has been formulated which casts this into a well‐posed problem. This paper discusses the criteria for calling a problem mathematically ill‐posed; a regularization technique for circumventing this ill‐posedness; a regularization incorporated into linear programming technique; and a recent method for incorporating regularization into a quadratic programming algorithm. All examples are presented using arbitrarily assumed MWD. Good results were obtained by applying this technique to a unimodal through a pentamodal distribution.
Polyvinylimidazolium salts of varying hydrophilic‐hydrophobic character
Authors: Salamone J. C. , Israel S. C. , Taylor P. , Snider B.
Published: June 2010

The homopolymerizations of a series of 3‐n‐alkyl‐1‐vinylimidazolium iodides are described in which the length of the quaternizing alkyl group was varied from methyl to n‐propyl to n‐hexyl to n‐heptyl to n‐dodecyl to n‐hexadecyl. The preparations of these cationic monomers have previously been reported through reaction of 1‐vinylimidazole with the corresponding n‐alkyl iodide. All polymerizations were performed in aqueous solution at the same molar concentration of monomer using the free radical initiator 4,4′‐azobis‐4‐cyanopentanoic acid. It was found that the short side‐chain polyions (methyl and n‐propyl) were water soluble, whereas the more hydrophobic intermediate side‐chain polyions (n‐hexyl and n‐heptyl) were water insoluble. The long side‐chain polyions (n‐dodecyl and n‐hexadecyl), on the other hand, being highly hydrophobic, appeared to form polysoaps and remained in aqueous solution. The solution behavior of these polyions in water, in aqueous salt solution, and in chloroform is discussed as well as is the critical micelle concentration of a long side‐chain polyion and its corresponding monomer.
Applications of extracellular micro‐bial polysaccharide‐polyelectrolytes: Review of literature, including patents
Authors: Jeanes Allene
Published: June 2010

Hydrophilic macromolecular polysaccharides, selected for their distinctive constitution and unusual properties, are produced industrially from common sugars by nonpathogenic microorganisms. The α‐(1–6)‐linked D‐glucan dextran and fractions of defined lower molecular‐weight produced from it are derivatized chemically to a variety of ionogenic substances for uses such as: anticoagulant, antilipemic, and peptic‐ulcer alleviating agents; to enhance the sensitivity and covering power of x‐ray and photographic emulsions; and separations of sensitive biochemical products by two‐phase liquid distribution and ion‐exchange and affinity chromatography. The polyanionic heteropoly‐saccharide xanthan is used in many industries (such as agriculture, abrasives, ceramics, food, paint, petroleum production, and textile) for its thickening and suspending ability even in the presence of high salt concentrations, reversible shear thinning, synergistic interaction with galactomannans, and excellent stability to heat and to acidic and basic conditions. Other water‐soluble polysaccharide‐polyelectrolytes, produced in liquid cultures unattached to the microbial cells, have potentially useful properties.
Reactions of N‐methylolacrylamide in radiation‐chemical modification of cotton fabrics
Authors: Dziedziela W. M. , Rosiak J.
Published: June 2010

The reactions of N‐methylolacrylamide (NMA) occurring in the individual steps of the radiation‐chemical finishing of cotton fabric were investigated both qualitatively and quantitatively.

Cotton fabric (poplin) was padded with an aqueous solution containing NMA, with zinc nitrate as an acid catalyst and a wetting agent. After being dried, the samples were gamma irradiated at ambient conditions and heat treated. In some experiments only irradiation or heating was used. Conclusions concerning the reactions of NMA were drawn on the basis of gravimetric measurements, nitrogen, double bonds, formaldehyde content, and from DTA and DTG of pure NMA and acrylamide.

It has been noticed that during drying of padded fabric, NMA was decomposed with the evolution of free formaldehyde. The yield of decomposition depends mainly on the temperature of drying. Irradiation of a fabric containing NMA leads to the grafting of the latter onto cellulose and its homopolymerization, while the grafting is the predominant process. In the step of heat treatment, the fabric undergoes further decomposition of the methylol groups and condensation of the remaining ones with each other and with the OH groups of cellulose and thermal polymerization of NMA. The stability of the links between NMA and cellulose to acid hydrolysis has been examined.
Nonisothermal membrane phenomena through charged membranes
Authors: Tasaka Masayasu , Nagasawa Mitsuru
Published: June 2010

Applying nonequilibrium thermodynamics, a theory of nonisothermal membrane phenomena through charged membranes is described. Agreement between theory and observed thermal membrane potential is satisfactory. In thermo‐osmosis, the effective temperature difference across the membrane is determined by measuring the thermal membrane potential. A qualitative explanation based on nonequilibrium thermodynamics is presented for the experimental results.
The significance of incompatible polymer systems
Authors: Battaerd H. A. J.
Published: June 2010

A short review of multiphase polymer composites is given, biased towards some as yet unexplained observations. It is proposed that the interface between the two phases of such polymers has an important influence on the properties observed. It is also suggested that careful study of the interface may lead to improved polymer properties. Some methods that may be applied for such studies are listed and briefly discussed.
The chemical reactivities of macromolecules attached to an interface
Authors: Went Peter M. , Evans Robert , Napper Donald H.
Published: June 2010

The rates of alkaline hydrolysis of polyacrylamide chains attached to polystyrene latex particles have been measured and compared with the corresponding values in free solution. The attached chains exhibited a significant reduction in rate. The magnitude of this reduction increased with decreasing molecular weight. Consequently, the rates of hydrolysis of attached chains were a function of their molecular weight; this contrasted with the apparent second‐order rate constants for the chains in free solution, which were insensitive to the molecular weight. The reduction in rate was attributed to the decreased accessibility of the amide groups to the hydroxyl anions when the polymer chains were attached to an impenetrable interface.
Cyclopolymerization
Authors: Solomon D. H.
Published: June 2010

Diallylamines readily undergo free‐radical polymerization to form polymers which contain cyclic structures. Five‐membered rings predominate, and this conclusion is supported by ESR spectroscopy of the radicals formed in a flow system, by chemical characterization of the compounds formed under nonpropagating conditions, and by NMR spectroscopy of the polymers. The presence of substituent groups in the diallylamine molecule has an important bearing on the cyclization reaction. For example, methyl groups in the β‐position, (dimethallylamines) form a mixture of 5‐ and 6‐membered rings, and the presence of bulkier groups, as in methyl bis‐2‐tert‐butyl allylamine, can prevent reaction with certain free‐radical initiators. Similarly, increasing temperature results in an increase in the amount of 6‐, relative to 5‐, membered ring structures with N‐methyldimethallylamine. These results are generally similar to those obtained with the carbon analogues.

From a theoretical viewpoint, the formation of the 5‐membered ring structure indicates that the generally accepted less stable primary radical is formed in preference to the 6‐membered structure which would contain a secondary radical. This apparent conflict is explained by the kinetics of the reaction and particularly the stereo‐electronic effects which operate in the transition state. Thus, the reaction can be under kinetic control and lead predominantly to 5‐membered ring structures, but when thermodynamic control starts to operate, e.g., at higher temperatures, the more stable 6‐membered ring structures may become significant. Changing the polymer structure from a predominantly 5‐membered one to one containing 6‐membered rings can be expected to alter the properties of the polyelectrolyte. Thus, differences in the titration curves have been noted, and the possibility exists of relating these differences to the polymerization conditions and, hence, to polymer structure.
The use of magnetic polymers in water treatment
Authors: Bolto B. A. , Dixon D. R. , Eldridge R. J. , Swinton E. A. , Weiss D. E. , Willis D. , Battaerd H. A. J. , Young P. H.
Published: June 2010

Magnetic polymers, originally conceived in ion‐exchange form as a means of handling microbeads in a thermally regenerable desalination process, have now been prepared in a variety of configurations for use in a number of water purification procedures. Processes have been devised which employ magnetic polymers in filtration, in oil slick removal, and in the adsorption of metal ions.

Suitably shaped particles, when magnetized, form a filter bed of high voidage volume. Tests have been run on a variety of turbid waters. The particles give considerably better performance as filter aids than the diatomaceous earth normally used. An extremely important advantage is that the magnetic filter aids can be recovered and reused after washing.

Vesicular forms of magnetic hydrophobic polymers float on water and have application in the removal of oil spills from water surfaces. The oil becomes trapped in the voids between the particles; the resulting mass is readily removed from the water by magnetic means, after which the oil is separated from the particles simply by centrifugation. The particles and residual oil are then recycled.

Magnetic ion exchangers, smaller in size than conventional resins, can be employed in continuous contacting systems, such as fluidized and semifluidized beds. When compared with normal continuous ion‐exchange systems, the same removal of ions can be accomplished using considerably less resin in a plant which is smaller, simpler, and much cheaper to construct.
The photodegradation of poly 2,2′–(m–phenylene)–5,5′–bibenzimidazole
Authors: Brown J. R. , Burchill P. J. , George G. A. , Power A. J.
Published: June 2010

Poly(2,2′‐(m‐phenylene)‐5,5′‐bibenzimidazole) (PBI) shows outstanding properties of low flammability, good abrasion resistance, and high moisture regain; but it is susceptible to degradation by sunlight. The chain‐scission quantum yield of 10−5 indicates a fundamentally stable structure. Degradation is related to the very intense light absorption in the solar region. Results also show that the degradation route is one of photooxidation. Limitations of traditional methods for preventing photodegradation are discussed, and the possibility of stabilization by a protective coating is explored.
Chemical reactions for the investigation of structure and properties of macromolecules
Authors: Braun Dietrich
Published: June 2010

Chemical reactions are a useful tool in the investigation of structure and properties of macromolecules. They can be used to prove the tacticity of noncrystallizable polymers. The chain conformation of polymers and helix‐coil transformations in solution can be studied by spin labeling, introducing stable free radical groups into the polymers. Competition of inter‐ and intramolecular reactions of macromolecules gives information on interpenetration of coils. The structure of crosslinked polymers can be studied by chemical cleavage of the network.
Recent developments in alternating copolymerization
Authors: Furukawa Junji
Published: June 2010

Alternating copolymers exhibit several characteristic types of behavior. Their glass points Tg are sometimes derived from the mean of two homopolymers. It was found that Tg of copolymers of different degree of alternation can be expressed as a molar mean of each diad involved in the copolymer. The melting points are not clear except for some polymers of extremely high degree of alternation. High orientation was observed on stretching and greatly enhanced tensile property is exhibited. Alternating copolymers constitute versatile material such as rubber, functional polymer. etc.

There have been developed several methods for the preparation of alternating copolymers. For the copolymerization of olefin and diolefin a modified Ziegler catalyst was developed. By controlling the number of coordination sites of the catalyst, the alternating coordination of olefin and diolefin is. made possible. The polymerization mechanism was established by determining the polymer structure using ozonolysis.

For the copolymerization of an electron‐donating monomer and an electron‐accepting monomer two mechanisms are considered, one involving the donor‐acceptor intermediate complex and the other without such complex. The discrimination of these mechanisms is very difficult because there is little difference in the stereoregularity as well as sequence regularity according to the mechanisms.

In the copolymerization of butadiene and acrylic monomer complexed with EtA1Cl2 and VOC13, there exists a maximum rate of polymerization at a definite monomer composition which is not changed by the amount of EtA1Cl2. This fact can be explained only by the complex mechanism.

Other interesting methods for the preparation of the alternating copolymer, such as copolymerization through a zwitterion intermediate and ring‐opening polymerization, are reviewed.
Structure and properties of pharmacologically active polymers
Authors: Ringsdorf Helmut
Published: June 2010

Although the concept of using pharmacologically active macromolecular compounds as drugs is still regarded with much skepticism for both theoretical and practical reasons, interest in this field has grown in recent years because of the opportunity to take advantage of the specific properties of polymeric materials. For low molecular weight drugs, changes in structure often lead to a loss of specific activity. On the other hand, the properties of macromolecular drugs depend on the structure of the polymer used and this can be varied over a wide range by the incorporation of comonomer units, by the application of polymer‐analogous reactions, or by related structural changes. A new model is presented for pharmacologically active polymers which incorporates the possibility for continuous variation in (a) solubility and toxicity, (b) fixation and removal of active material, and (c) body distribution. Using the new model as a guide, examples of the synthesis and study of the biological activity of various macromolecular drugs are presented in order to emphasize the importance of this cooperative effort between polymer research and therapeutic problems.
Conditions of gelation in the anionic divinylbenzene‐styrene copolymerization
Authors: Eschwey Helmut , Burchard Walther
Published: June 2010

The anionic copolymerization of p‐ and m‐divinylbenzene (DVB) with varying amounts of styrene (St) was studied. The molecular weights of the samples before gelation and of the sol fraction were followed according to their dependence on the applied ratio R′ = [St] [DVB]. Gelation occurred at critical values of R′c = 2.08 for the p‐DVB/St and of R′c =2.80 for the p‐DVB/St copolymers. The results are tentatively interpreted using Stockmayer's theory of the crosslinking of chains. A good agreement between theory and experiment was obtained for the polymers in the pregel state. The molecular weights of the polymers in the sol of the gel can be described by an equation that is similar to the Stockmayer equation, except the crosslinking probability is multiplied by the extinction probability, v. As v is closely related to the sol fraction, this fraction can be calculated from the applied R′ values and the experimentally observed molecular weights of the products. The sol fraction thus obtained was compared with the experimentally observed sol fraction. The differences between both sol fractions are discussed in some detail.
Dependence of crystallization capability of polyurethanes upon the degree of cross‐linking
Authors: Slowikowska Irena , Daniewska Irena
Published: June 2010

The investigation of crystallization capability of polyurethanes has been carried out on two series of polyurethanes, in which the degree of crosslinking was systematically changed. These tests included the light depolarization method, optical microscopy, and differential thermal analysis. Accurate dependence of the crystallization capability of crosslinked polyurethanes on the degree of crosslinking was found.
Wood fiber‐synthetic polymer composites. I. Laminates of paper and polyethylene
Authors: Michell Anthony J. , Vaughan Janet E. , Willis Donald
Published: June 2010

Wood fiber‐synthetic polymer composites are being studied with a view to using, in building or packaging, residues from the production of sawlogs and wood resources which are unsuitable for timber, pulp, or paper production. The structure of wood fibers and the properties required in a fiber intended for use as a reinforcing agent are described briefly.

Laminates comprising 67% by weight of cellulose fibers have been produced by hot‐pressing sheets of paper coated with low‐density polyethylene. Mechanical properties of the laminates have been studied with particular attention to the effects of exposure to moisture. The flexural properties of the laminates at low relative humidities compared favorably with those of glass‐filled high‐density polyethylene and of paper‐phenolic resin laminates but declined more at high relative humidities.
Cationic polymerization of N‐vinylcarbazole by triphenylmethyl hexafluoroantimonate
Authors: Rooney J. M.
Published: June 2010

The polymerization of N‐vinylcarbazole (NVC) in methylene dichloride initiated by triphenylmethyl hexafluoroantimonate has been studied at 0 and 20°C.

Experiments in an adiabatic calorimeter showed the rates of polymerization to be rapid (t1/2 ∼ 3 sec at [M]0 = 0.050M and [I]0 = 10−6 M), attaining first‐order with respect to monomer concentration after 30–50% conversion. The observed rate constants of propagation decreased with increasing initiator concentration to a constant value after [I]0 ∼ 10−5 M, which was not further reduced by the presence of excess SbF6− anions [from PhCH2(CH3)3NSbF6]. This behavior suggests propagation by both unpaired and paired ions and permits estimates of kp+ = 6 × 105 M−1 sec−1 at 20°C; 4.5 × 105 M−1 sec−1 at 0°C; and kp± = 5 × 104 M−1 sec−1 at both temperatures.

Molecular weights (Mn) ranged between 30,000 and 100,000 according to conditions. The degree of polymerization was always < [M]0/[I]0, indicating that transfer reactions govern this chain length. Excess common anion reduced the molecular weights.

A stopped‐flow apparatus was employed to monitor initiator consumption and values of ki, estimated at 130 M−1 sec−1 at 20°C and 34 M−1 sec−1 at 0°C.
The nature of the double bond in low molecular weight polyisobutylenes and “polybutene” copolymers
Authors: Puskas Imre , Banas Emil M. , Nerheim A. Glenn
Published: June 2010

Olefin types were quantitatively determined by PMR and infrared spectroscopic analyses in polyisobutylenes and commercial polybutenes of Mn ranging from 500 to 2000. The catalyst and the polymerization conditions were found to have a great influence on the olefin type produced. In polyisobutylenes produced with BF3, the terminal vinylidene formed initially can diminish under the isomerizing influence of the catalyst. In polyisobutylenes synthesized with AlCl3, the major olefin type is °C(R)=CH(CH3). Its formation is explained by a multistep termination which involves tail‐to‐tail coupling. Internal vinyl‐idenes were also identified in most of the samples. Their formation can be explained by a skeletal rearrangement either in the termination step, or during polymer double‐bond isomerizations. In most polymers, the spectroscopically measured unsaturation was lower than that determined by hydrogenation. The difference is attributed to the presence of tetrasubstituted olefins.
The thermal‐mechanical degradation of high density polyethylene
Authors: Rideal G. R. , Padget J. C.
Published: June 2010

The changes in molecular structure of high density polyethylene which can take place during processing have been studied using a nitrogen blanketed Brabender plastograph to simulate processing conditions. At high melt temperatures (> 290°C) decreases in melt viscosity and a narrowing of molecular weight distribution were observed, while at lower melt temperatures an increase in melt viscosity was observed. The increase in melt viscosity arises from a molecular enlargement reaction which is mainly attributable to the formation of long chain branches (LCB) which were detected using intrinsic viscosity measurements as well as by a novel method involving the measurement of melt elasticity on a Weissenberg rheogoniometer. The scission and enlargement reactions are not mutually exclusive but competitive, and a basic reaction scheme is proposed to explain the experimental results. The effect on this basic reaction scheme of mechanical shear, polymer unsaturation, and oxygen content has been investigated. The presence of excess oxygen promoted the scission reaction, the extent of molecular weight reduction increased with decreasing temperature as would be expected for a shear induced reaction. However, it was found that under nitrogen the effect of mechanical shear at low melt temperature (<290°C) was to increase the melt viscosity and extent of LCB when compared to the corresponding reactions performed at the same melt temperatures but in the absence of shear; an explanation of this effect which involves the breakdown by shear of a radical cage is proposed. The observation that polymers having a high vinyl content undergo extensive increases in melt viscosity and LCB at all melt temperatures and in the presence or absence of shear has also been explained on the basis of the proposed reaction scheme.
Simple kinetic model diffusion controlled decay of free radical in highly crystalline polyolefins
Authors: Kryszewski M. , Nadolski B. , Zujewicz M.
Published: June 2010

A simple kinetic model for the diffusion controlled decay of radicals in two‐phase high crystalline polyolefins is proposed. The analysis of the kinetic system was carried out taking into consideration a structural unit model containing all the structural properties of the macroscopic system. Radical decay in the amorphous phase and on the surface of lamellae has been discussed taking into account Wait's theory of diffusion controlled reactions, radiation boundary conditions, and the flux of radicals through lamellae surfaces.

A rough computer calculation using the derived equation and the experimental data of Kashiwabara on radical decay in γ‐irradiated polyethylene was carried out leading to DA values equal to 10−9 cm2/sec, which favors the interchain hydrogen atom “hopping” mechanism of radical migration.
Antioxidants and stabilizers. LXII. Transformations of antioxidants: Thermal properties of alkylperoxycyclohexadienones
Authors: Buben I. , Pospíšil J.
Published: June 2010

The behavior of a number of alkylperoxycyclohexadienones investigated by differential scanning calorimetry and thermal gravimetric analysis has been described. The relationship between thermal behavior and the participation in the autoxidation process has been discussed.
The effect of transition metal N,N‐diethyl diselenocarbamates on the photooxidation of polyethylene
Authors: Osawa Zenjiro , Nakano Kosaku
Published: June 2010

The effect of transition metal (Co, Ni, Cr, and Zn) N,N‐diethyl diselenocarbamates over the range of 0.01 to 1.0 part per hundred resin (abbreviated as phr) on the photooxidation of a high density polyethylene film was examined, particularly by changes in the carbonyl IR absorption of the samples.

The photooxidation of the polymer was remarkably affected by the kind of metal and concentration of the carbamates, and by the wavelength of irradiated light. Zn and Cr carbamates behaved as oxidation accelerators at lower concentrations over the range of 0.01 to 0.1 phr and as oxidation retarders at concentrations above the range of 0.5 to 1.0 phr. Co and Ni carbamates merely enhanced oxidation and the effect of both these carbamates increased with increasing concentration.

Neat polymer gave an emission spectrum at ca. 350 nm which gradually decayed, and a new emission appeared at 470 nm following photooxidation of the samples. The presence of metal carbamates remarkably changed the emission spectra of the polymers, e.g., the disappearance of emission at ca. 350 nm.

The roles of these metal carbamates are discussed on the basis of the luminescence and ultraviolet spectral data.
Some aspects of the photolysis and photooxidation of polyethylene containing ketone groups
Authors: Sitek F. , Guillet J. E. , Heskins M.
Published: June 2010

Studies of the photodegradation of polyethylene containing 2 wt % methyl vinyl ketone (MVK) and methyl isopropenyl ketone (MIPK) show that the relative quantum yields of Norrish type I and II photolysis are strongly dependent on the structure of the ketone carbonyl. The type 1 process, leading to free radical formation, is particularly efficient in the MIPK copolymer, somewhat less so in the MVK copolymer, and very low in ethylene‐carbon monoxide copolymers where the carbonyl group is in the chain backbone. In the presence of oxygen, this difference shows up strongly in the rate of photooxidation. Backbone carbonyl groups have very low efficiency in initiating photooxidation of solid polymer films, while the side chain ketone groups initiate rapid photooxidation.
The role of interfibrillar tie molecules in drawing of polymers
Authors: Marikhin V. A. , Myasnikova L. P.
Published: June 2010

A structural‐mechanical study of the orientation process in some flexible‐chain semicrystalline polymers has been conducted. By their deformation properties, such polymers may be conditionally divided into two groups: the ultimate draw ratio is 20‐25 for the first group and 6‐10 for the second one, the transformation of the original structure into a microfibrillar one being completed at a draw ratio (λ) of 8‐10 in the polymers of the first type and at a draw ratio of 2‐4 in those of the second type. The low draw ratios characterizing the moment of a virgin neck propagation in the polymers of the second type are considered to be due to a large number of tie molecules in the original su‐permolecular structures. When microfibrils are formed, these molecules are supposed to be included between fibrils.

It is shown that a further increase of λ results from the microfibrillar slip. In the polymers of the first type, the slip is, however, relatively easy and is not accompanied by significant changes in the internal structure of microfibrils, because the interfibrillar tie molecules are almost absent in them. In the polymers of the second type, a significant change in the internal cture of microfibrils, associated with a large number of interfibrillar tie molecules, is observed (obliquity of crystallites and an increase of the long period attributed to an increase in the length of the amorphous intrafi‐brjjlar layer).

The microfibrillar slip leads to their more dense packing, which results in a sharp increase in the orientation load required for further drawing. This reduces significantly the lifetime of the specimens in high temperature drawing and leads to their fracture by a thermal fluctuation mechanism.
Drawing behavior and mechanical properties of highly oriented polycarbonate fibers
Authors: Falkai B. , Hinrichsen G.
Published: June 2010

Fibers from bisphenol‐A polycarbonate are typical representatives of the less crystallizing synthetic fibers. Because of the high glass transition temperature, textiles produced from these fibers have outstanding laundry‐resistance and noncreasing properties. Polycarbonate fibers can be produced both by the dry or wet‐spin and by the melt‐spin process. The stretching of the fibers is carried out in accordance with the proposed textile characteristics below or above the glass transition temperature or by a special swelling–drawing process, in the course of which fibers of particularly high tenacity and elastic modulus can be obtained. The fibers produced by the latter process were investigated by a number of physical measurements of their morphological structure (density, birefringence, X‐ray wide‐ and small‐angle scattering, differential calorimetry, thermo‐mechanical analysis). These measured values of density, birefringence, and heat of fusion show that these fibers have a higher degree of crystallinity than the fibers produced by a melt or dry spinning process. Whereas with dry‐spun fibers an increase in tenacity can be obtained by raising the molecular orientation up to a limited tenacity value, it is possible with fibers produced by the swelling‐drawing process to virtually double the tenacity due to the higher crystallinity and improved crystal structure (creation of a large number of physical linkages). By means of X‐ray small‐angle scattering on annealed swollen‐drawn polycarbonate fibers, we were able to detect, for the first time, a marked two‐phase structure consisting of crystalline and noncrystalline regions with a long‐period of about 120 Å. With other crystalline polymers, a period of this kind has been known for many years.
Natural and artificial heterogeneous nucleation in polymer crystallization
Authors: Binsbergen F. L.
Published: June 2010

An outline is given of heterogeneous nucleation as the main starting point for crystallization of unoriented polymer melts and solutions. The influence of temperature history on nucleation is discussed. As little is known about naturally occurring nucleants, the nature of several types of artificial nucleating agents is described. Potential mechanisms of heterogeneous nucleation are discussed against the background of various theoretical models. Experimental methods of measurement of nucleation density or of nucleation frequency may give some indication as to which mechanism is operative. The main conclusion is that heterogeneous nucleation is governed by “active sites” in the surface of the nucleants.