bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of thiourea on the radical polymerization of vinyl monomers. Part III. Effect of diphenyl thiourea on the polymerization of methyl methacrylate with various organic peroxides as initiator
Authors: Sugimura Takaaki , Minoura Yuji 
Published: April 2003

AbstractThe effect of diphenyl thiourea (DPTU) on the radical polymerization of methyl methacrylate (MMA) has been studied in benzene solution at 50°C. with the use of cumene hydroperoxide (CHP), p‐menthane hydroperoxide (PMHP), tert‐butyl perbenzoate (tBPBz), di‐tert‐butyl peroxide (DBP), and dicumyl peroxide (DCP) as initiators. In the CHP‐initiated polymerization, the rate of polymerization increased appreciably on addition of DPTU with a linear dependence on the square root of DPTU concentration up to a maximum which was observed when the ratio of the concentration of CHP to DPTU was 2.5. Then the rate decreased gradually with increasing DPTU concentration in the range greater than the above ratio. It was found from kinetic studied that the overall polymerization rate Rp was expressed by the equation: Rp = K[peroxide]1/2 [DPTU]1/2[MMA], where K is the rate constant, α = 1.2 for CHP and α = 1.0 for tBPBz. It was thought that the acceleration effect observed was due to a redox reaction caused by the interaction of a peroxide–monomer and/or a peroxide–solvent complex with DPTU, and the decrease in the polymerization rate which was observed over a certain concentration of DPTU was due to the action of the oxidized product of DPTU as a transfer agent. The effect of substituents was studied by using para and meta‐substituted DPTU. It was found that the polymerization rate increased as electron‐donating substituents are added to the benzene ring of DPTU with considerable dependence on Hammett's equation (p = −0.36). The acceleration effect is also observed for PMPH‐and tBPBz‐initiated polymerizations, whereas the DCP‐ and DBP‐initiated systems show no effects on the polymerization rate.
Mechanism of stereospecific polymerization of propylene with titanium trichloride–aluminum alkyl catalysts
Authors: Ingberman A. K. , Levine I. J. , Turbett R. J. 
Published: April 2003

AbstractThe effect of various aluminum alkyls at varying concentrations on the rate and stereospecificity of propylene polymerizations with titanium trichloride was examined. It was concluded that dialkylaluminum halides were merely chemisorbed on the surface of the titanium trichloride while the trialkylaluminums reacted more extensively with the surface. In the case of diethylaluminum chloride standard chemisorption kinetics were observed. The rate of polymerization was also found to be a function of solvent, with certain aromatic solvents causing significant rate increases. With diethylaluminum chloride essentially no termination occurs; the polymers are “living polymers.”
Influence of catalyst depletion or deactivation on polymerization kinetics. II. Nonsteady‐state polymerization
Authors: Chiang R. , Hermans J. J. 
Published: April 2003

AbstractThe number‐average and weight‐average degrees of polymerization at the end of the polymerization process have been calculated in terms of the initial monomer concentration, initial catalyst concentration, and rate constants for various polymerization processes, all of which assume instantaneous initiation. The mechanisms differ among themselves in that there is either first‐order catalyst deactivation, or transfer to monomer, or both. The calculation is greatly simplified if only the molecular weights at the end of polymerization are considered. The method given is particularly useful for systems where the calculation of the distribution function as a function of time is complicated. The fact that the monomer concentration and catalyst concentration have a marked effect on the molecular weight provides a good test of the validity of the mechanism under consideration. A comparison of the calculated and observed molecular weights obtained for the homogeneous polymerization of acrylonitrile with an organometallic catalyst will be given in a later communication.
Polymerization of some sulfur‐containing oxetanes
Authors: Goethals E. J. , Du Prez E. 
Published: April 2003

AbstractPolymerization under the influence of boron trifluoride of 2‐oxa‐6‐thia[3,3]spiroheptane gives two products: a linear polyether containing oxetane groups and a crosslinked polyether polysulfide. When the polymerization was carried out at −3°C., up to 60% of soluble polysulfide is obtained. This does not prove that the thietane group polymerizes more rapidly than the oxetane group but rather that oxetane polymerization is inhibited by the presence of thietane groups. Polymerization under the influence of boron trifluoride etherate of 3,3‐bis(mercaptomethyl)oxetane leads to a polyether containing free thiol groups. The degree of polymerization of the polymer, however, is low. In order to obtain higher degrees of polymerization several compounds with masked thiol groups were polymerized. 2‐Oxa‐6,7‐dithia‐6‐thio[3,4]spirooctane and 2‐oxa‐6,8‐dithia‐7,7‐dimethyl[3,5]‐spirononane gave crosslinked products. The diacetate of 3,3‐bis(mercaptomethyl)oxetane gave a linear polyether containing thiolacetate groups. Hydrolysis of this polymer leads to poly‐3,3‐bis(mercaptomethyl)oxetane with a softening temperature of 125–135°C.
Hydrogels of poly(hydroxyethyl methacrylate) and hydroxyethyl methacrylate—glycerol monomethacry‐late copolymers
Authors: Yasuda H. , Gochin Michael , Stone William 
Published: April 2003

AbstractHydrophilic three‐dimensional polymer networks (hydrogels) were prepared from hydroxyethyl methacrylate (HEMA) and the copolymer HEMA and glycerol monomethacrylate (GMMA). The equilibrium water content of the hydrogels in water was investigated as a function of the initial dilution of the polymerization mixture, the type of solvent, and the hydrophilicity of the polymer. The initial dilution was found to have a decisive effect on the swelling or deswelling of hydrogels after the completion of the gel formation. With relatively less hydrophilic hydrogels, there is a critical initial dilution to produce the gel which does not swell or deswell in water after the gel formation. This “isovolumic” initial dilution shifts toward a higher dilution as the hydrophilicity of the hydrogels increases; however, when hydrophilicity of the polymer rises above a certain point, gels always swell in water. Permeability of oxygen through hydrogels was also studied.
Polymerization of Cyclosiloxanes. I. Kinetic Studies on Living Polymer—Octamethylcyclotetrasiloxane Systems
Authors: Lee C. L. , Johannson O. K. 
Published: April 2003

AbstractThe kinetics of the anionic polymerization of octamethylcyclotetrasiloxane (D4) initiated by α‐methylstyrene living polymer in tetrahydrofuran was studied. The following kinetic scheme was postulated:
Initiation:

equation image

Propagation:

equation image

where S‐ and M represent the initiator and D4, respectively. At a living end concentration of 0.0377 mole/l. and a monomer concentration of 1.5 mole/l. in tetrahydrofuran at 25°C. the following kinetic data were obtained: k1 = 2.3 × 10−4 l./mole‐sec., k2 < 2.3 × 10−5 sec.−1, k3 = 2.75 × 10−2l./mole‐sec. k4 ≈ 1.17 × 10−2 sec.−1, K1 > 10 l./mole and K2 ≈ 2.35 l./mole. The rate constants k1 and k3 were found to be dependent on the concentration of anions. This is attributed to the dissociation of ion pairs to free ions at lower concentration. Under the experimental conditions studied the majority of the anions were present in the form of ion pairs. The reactivity of the free ions is about 100 times greater than that of ion pairs. There is no temperature effect on K2, indicating zero ΔH and positive ΔS in the propagation reaction.
Application of Molecular Weight and Particle Growth Measurements in Continuously Uniform Latices to Kinetic Studies of Styrene Emulsion Polymerization
Authors: Williams D. J. , Bobalek E. G. 
Published: April 2003

AbstractIt is possible to generate, in specially formulated styrene emulsion polymerizations, latices in which the monomer—polymer particles are uniform through all stages of growth. These latices are kinetically similar to their polydispersed counterparts and can therefore be used as model systems in generalized kinetic studies of emulsion polymerization. The most important feature of these systems is the fact that the particles are uniform throughout the reaction with regard to all intrinsic properties and rate processes, and the particles can be characterized by this complete, continuous uniformity. Certain remarkably simple, but precise, relationships exist between the overall, measurable kinetic parameters and the individual particle kinetic parameters, thereby resulting in a heretofore unrealized analytic accessibility. Molecular weight kinetic analyses are an order of magnitude more accurate than in non‐uniform systems. Application of these continuously uniform systems in actual kinetic studies indicates an inconsistency in the current concepts of emulsion polymerization, i.e., the generation of polymer at a constant molecular weight is predicted while an increase of several fold is observed. Before the situation can be clarified, further studies with continuously uniform systems are needed to evaluate molecular weight development, molecular weight distribution, and molecular structure and also to re‐evaluate the rate and diffusion processes which control these structural features.
Diffusion of Methanol in Polydimethylsiloxane
Authors: Barrie J. A. 
Published: April 2003

AbstractThe permeation and sorption of methanol in polydimethylsiloxane at 10 and 30°C. has been measured and the results analyzed to determine the concentration dependence of the steady‐state diffusion coefficient D which is found to decrease as the total concentration C is increased. An analysis of the isotherms indicates that clustering of the methanol occurs in the polymer, becoming more predominant as the concentration is increased. A polymerization model used to describe the shape of the D versus C curve for water in polydimethylsiloxane has been modified and applied with some success to describe the shape of the isotherm and the D versus C curve for methanol. The linearity of the permeation rate with relative pressure in this and a number of water—polymer systems is briefly commented on.
Copolymerization of Styrene and Methyl Methacrylate with Lithium as Initiator
Authors: Overberger C. G. , Yamamoto Naoki 
Published: April 2003

AbstractCopolymers of styrene and methyl methacrylate prepared with lithium dispersion as initiator do not contain random sequences of both monomers. Fractionation of the copolymers with acetonitrile and the NMR spectra of the insoluble fractions show that these are block copolymers which consist of a polystyrene portion and a poly(methyl methacrylate) portion. When the copolymerization is stopped at low conversion the copolymer has a high styrene content, which sometimes exceeds the value expected for radical copolymerization. This fact would indicate that styrene is preferentially polymerized at the early stages of chain propagation. When the copolymerization is carried to high conversion some crosslinked polymer is formed which contains more styrene than the soluble part of the same experiment. When a piece of metallic lithium is used as initiator, it is found that the crosslinked polymer is formed on the surface of the metal. The addition of lithium phenoxide or β‐naphthoxide to the system eliminates the formation of crosslinked polymer. A possible mechanism is proposed.
Single‐crystal model for the bulk crystallization kinetics of poly(ethylene oxide) and polystyrene
Authors: Hillier I. H. 
Published: April 2003

AbstractApproximations in the Avrami treatment of impingement which arise when the growing crystalline bodies are rods or disks are discussed, with particular reference to the single‐crystal model. This model, previously fitted to the isolated primary crystallization of polymethylene, is extended to discuss the growth of the composite lamellar structures, axialites, and spherulites, and is here fitted to the crystallization of poly(ethylene oxide) and polystyrene. Both polymers are found to yield anomalous values of the Avrami exponent when analyzed in terms of the conventional Avrami equation. The new analysis reveals similarities in the behavior of all three polymers. The residual deviations remaining after the fit of the model to polymethylene and poly(ethylene oxide) follow the same pattern, and the temperature dependence of the rate constants associated with the model is similar for all three polymers.
Measurements of relaxation time of a polyethylene melt
Authors: Aloisio C. J. , Matsuoka S. , Maxwell B. 
Published: April 2003

AbstractA device for measuring the elasticity of polymer melts has been designed by one of us (B. Maxwell). The device was used to obtain the relaxation modulus in shear of a linear polyethylene melt. From these data a discrete relaxation spectrum was derived. The range of the obtained spectrum was confirmed to correspond to the terminal zone of the “entanglement plateau” of the spectrum. The limiting dynamic viscosity (as frequency approaches zero) was obtained by integrating the relaxation modulus with respect to time. The viscosity and its activation energy were found to agree closely with the flow viscosity and the flow activation energy, respectively, involved in capillary flow.
Rheological properties of polymer melts
Authors: Vinogradov G. V. , Ya. Malkin A. 
Published: April 2003

AbstractA new method of treating experimental data on the viscous and viscoelastic properties of various polymer melts is suggested. The dependence of the apparent viscosity on the molecular weight, temperature and shear stress can be represented as the product of three independent functions, each of them having a single argument. All three functions are universal, at least in first approximation, and the dependence of the apparent viscosity on the variables indicated is determined by two parameters (glass transition temperature and critical molecular weight), characteristic of each homologous polymer series. The viscoelastic characteristics (dynamic, relaxation, creep, as well as relaxation and retardation spectra) of polymer melts are universal in shape in the linear region and contain only one individual polymer parameter, viz., maximum Newtonian viscosity. It is shown that upon normalization of certain nonlinear characteristics with respect to the maximum Newtonian viscosity, they can also be represented in the universal form.
Morphology of polypropylene crystallized from the melt
Authors: Hock Charles W. 
Published: April 2003

AbstractPolypropylene was oxidized with nitric acid in a manner contrived to remove its amorphous component. Concurrent with the loss in weight there was an increase in crystallinity, a decrease in molecular weight, a drop in melting point, and a change in visible structure. The crystalline component, which survived from polymer which had orginally crystallized isothermally, consisted of separated spherulites. These spherulites could be broken apart into lamellae which gave electron diffraction patterns like those now associated with a variety of solution‐grown single crystals. As opposed to the high molecular weight of the unoxidized parents, the lamellae which survived the acid treatment consisted of short chains whose length depended on the temperature at which the parents had crystallized. If, as diffraction studies indicate, these short molecules are lined up in rank and file, then the length of the molecules and the height of the lamellae should correspond. The heights of the lamellae could not be measured precisely enough to establish an exact correlation, but the variations in average chain length calculated from viscosity data at least approximated the heights of the lamellae which were observed visually.
Infrared study of poly(vinyl fluoride)
Authors: Koenig J. L. , Mannion J. J. 
Published: April 2003

AbstractPoly(vinyl fluoride) polymers prepared at different polymerization temperatures have been examined in the melt, oriented, and solid state by infrared spectroscopy. Bands arising from the head‐to‐tail and head‐to‐head‐tail‐to‐tail portions of the polymer have been isolated and assigned. The head‐to‐head‐tail‐to‐tail portion of the polymer crystallizes in the head‐to‐tail unit cell except for a portion of the 1,2‐difluorethylene units which apparently have the gauche (out‐of‐plane) structure. The head‐to‐tail portion of the polymer is nearly atactic, but is somewhat rich in syndiotactic chain structure. Bands arising from local syndiotactic order are observed.
Effects of composition on the solution properties of styrene–acrylonitrile copolymers
Authors: Shimura Yuko 
Published: April 2003

AbstractShort‐range interactions between chain units of random copolymers in solution may be influenced by the composition or precisely by the distribution of sequence lengths of the same monomer units. Steric factors were derived for random copolymers of styrene and acrylonitrile with different compositions from the relation between the limiting viscosity number and the molecular weight. Mark‐Houwink relations were obtained in methyl ethyl ketone (MEK) or in N,N′‐dimethylformamide (DMF) at 30°C. for random copolymers containing 0.383 (Co‐1) and 0.626 (Co‐2) mole fraction of acrylonitrile, the expressions are: [η] = 3.6 X 10−4 Mw0.62, for Co‐1 in MEK; [η] = 5.3 X 10−4 Mw0.61, for Co‐2 in MEK; [η] = 1.2 × 10−4Mw0.77 for Co‐2 in DMF. With the Stockmayer‐Fixman expression, these correlations become, respectively: [η]/M1/2 = 1.24 × 10−3 + 8.0 × 10−7 M1/2; and [η]/M1/2 = 1.70 × 10−3 + 6.3 × 10−7 M1/2; and [η]/M1/2 = 1.68 × 10−3 + 31.3 × 10−7 M1/2. From the unperturbed mean‐square end‐to‐end distances, 〈L2〉0, determined from the first terms of the latter expressions, together with 〈L2〉0f calculated by assuming the completely free rotation, gives the steric factor σ = (〈L2〉0/〈L2〉0f)1/2 as 2.25 ± 0.05 for Co‐1, and 2.31 ± 0.10 for Co‐2. These values of σ are close to those for polystyrene (σ = 2.22 ± 0.05) and for polyacrylonitrile (σ = 2.20 ± 0.05). Therefore, it is concluded that the dimensions of random copolymers of styrene and acrylonitrile in solution are not significantly influenced by the composition. In other words, the unperturbed dimensions are not affected by a change in the alternation tendency between styrene units with phenyl side groups having a large molar volume and acrylonitrile units with nitrile groups responsible for the electrostatic interactions. On the other hand, the long‐range interactions reflect the effect of sequence length. The Huggins constant and the second virial coefficient obtained from the light‐scattering measurements have optimum values at about 0.5 mole fraction of acrylonitrile, where the greatest tendency for alternation seems to exist.
Crystallization in stretched polymer networks. II. Trans‐polyisoprene
Authors: Gent A. N. 
Published: April 2003

AbstractMeasurements are described of the rates of crystallization and crystal melting temperatures in stretched test pieces of trans‐polyisoprene, crosslinked to various degrees. The increase in rate with extension are attributed to the corresponding increases in melting temperature and hence degree of supercooling. The rise in the melting temperature of both the α‐ and β‐crystal forms is found to be in satisfactory agreement with Flory's treatment of oriented crystallization. The changes in tensile stress are also generally in accord with the formation of oriented crystallites. For the more lightly crosslinked materials, a pronounced rise in tensile stress occurred during the later stages of crystallization, at extensions below about 100%. Reasons are given for attributing this phenomenon primarily to the relatively large contraction in volume on crystallization, rather than to the formation of folded‐chain crystallites.
Polymerization of adsorbed monolayers. III. Preliminary structure studies in dilute solution of the insertion polymers
Authors: Blumstein Alexandre , Billmeyer Fred W. 
Published: April 2003

AbstractInsertion poly(methyl acrylate) and poly(methyl methacrylate) were prepared from monomers adsorbed in monolayers on the surface of montmorillonite clay, both in the presence and in the absence of bifunctional crosslinkers (ethylene glycol dimethacrylate and tetramethylene glycol dimethacrylate). The insertion poly(methyl acrylate) and the crosslinked insertion poly(methyl methacrylate) and dilute‐solution properties quite different from conventional polymers of these monomers, the differences including high light‐scattering molecular weights combined with low viscosities, low values of the second virial coefficient, unusually large variations of the Huggins' constant k′ with the time‐temperature history of the solutions, and low sedimentation velocities. These properties suggest that the insertion polymers have compact structures and are consistent with the postulate of sheetlike macromolecules. The dilute‐solution properties of insertion poly(methyl methacrylate) made without crosslinker, unlike those of similarly prepared poly(methyl acrylate), were similar to those of conventional poly(methyl methacrylate). This difference in behavior is attributed to the different tendencies of the two monomers to undergo branching or crosslinking during radical polymerization.
Specific heats of poly(vinyl chloride) compositions
Authors: Dunlap L. H. 
Published: April 2003

AbstractSpecific heats of plasticized poly(vinyl chloride) can be readily obtained by means of the thin foil calorimeter when the polymer is fabricated into sheet or film. The effects of temperature and plasticizer content on the specific heat and of the plasticizer content on the glass temperature are readily observed. The data may be used to estimate the glass temperatures of plasticizers where those temperatures are not readily reached by normal techniques. The specific heat at the glass temperature is approximately 0.255 for the ranges of 0–30 phr plasticizer. A definite glass transition is not observed with 60 phr plasticizer. No other transitions were observed between 200 and 400°K. The previous history of the polymer is important, as it can change the specific heat of the polymer noticeably, especially above the glass temperature. Comparison of the values listed here with those obtained by others should be made with the understanding that these samples were fabricated by extrusion and were free of observable strain. The degree of crystallinity of these polymers is very small, probably less than 10%, since none was found by x‐ray diffraction. The plasticizing effect of some stabilizers was noted.
Axial dispersion of polymer molecules in gel permeation chromatography
Authors: Hess M. , Kratz R. F. 
Published: April 2003

AbstractGel permeation chromatography is an elution chromatographic process depending on the permeation of the solute through a bed of gel particles. This process is used in the estimation of molecular weight distributions of polymers, since elution occurs in decreasing order of molecular size. The eluting species, however, are not perfectly fractionated, and apparent broadening of the distribution occurs. This broadening results from an axial (longitudinal) mixing of the eluting species. Consideration of the accessible bed volume for each species permits a correction to be made for this axial dispersion. The concept was applied to heterodisperse distributions by solving the resulting simultaneous equations. A least‐squares regression may be employed to utilize the experimental data most effectively. The experimental chromatogram can be described in terms of accessible bed volume and dispersion coefficient of each species together with flow rate, sample concentration, and chromatograph column geometry. The chromatogram corrected for the axial dispersion describes the molecular weight distribution more accurately than does the experimentally determined curve. The correction procedure was applied to a well‐characterized polystyrene; the results of the gel permeation chromatography show excellent confirmation of the results of fractionation and of other instrumental analyses.