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A low-density polyethylene was shear modified by repeated extrusions. These operations resulted in no detectable changes in the polymer molecular weight distribution. The apparent melt viscosity and elasticity decreased after extrusion, as is commonly observed in shear modification. These rheological effects were fully reversible by annealing the melt. Transverse proton relaxation measurements showed the existence of four identifiable different regions in the polymer melt. The range of relaxation times encompassed two orders of magnitude. These reflect the existence of regions with different degrees of conformational order. Shear modification results in the breakup of a minor proportion of the most constrained regions, which have the shortest relaxation times. The apparent “entanglements” that are inferred from rheological measurements probably reflect the coexistence of segments of more than one macromolecule in chain-folded domains, as indicated by molecular dynamics calculations. These results are evidence that the equilibrium state of LDPE is not a chain-entangled, highest entropic condition, but rather a lowest free energy state in which chain folding is favored. They are consistent with other longstanding observations, such as the failure of experiments to produce amorphous polyethylene and the apparent lack of mixing of HDPE and LDPE on a molecular level.

Reported here is a novel technique, based on inverse gas chromatography (IGC), to measure the three-dimensional solubility parameters of nonionic surfactants—nonyl phenol ethoxylates—with different ethylene oxide chain lengths at two different temperatures. These solubility parameters can then be used to characterize the relative oil and water affinities of the surfactant. The three-dimensional solubility parameters of these surfactants were determined on the basis of the measured interaction parameters and known three-dimensional solubility parameters of the solvents (probe molecules) used in the IGC experiments. In particular, it was assumed, based on the regular solution theory, that the occurrence of a zero or negative interaction parameter is evidence of thermodynamic compatibility of the particular probe and surfactant. The three-dimensional solubility parameters of the surfactant are obtained by averaging the corresponding values of the compatible low-molecular-weight probe substances. In this way, combination of the lattice model of solutions (which allows negative enthalpies of solution) and the solubility parameter theory (which accounts for endothermic solutions only) is not required. As a result, measured negative interaction parameters are not a stumbling block for obtaining Hildebrand and three-dimensional solubility parameters. The method described is applicable to measurement of three-dimensional solubility parameters of all materials. Surfactants were used here as a convenient illustration only.

Matrix assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) is used to mass characterise several low molecular weight, commercially available PS, PMMA and PEG samples. In addition, the utility of the technique for the study of polymer synthesis is demonstrated; different initiation and termination mechanisms leave dead chains with characteristic end groups which, in many cases, can be rapidly identified mass spectrometrically. There is broad agreement between MWDs derived from MALDI spectra and those obtained from conventional GPC analysis, but in some instances the differences are significant. Polydispersities obtained mass spectrometrically are invariably lower than those determined by GPC.

In emulsion polymerization processes it is important to control the surfactant level to avoid secondary nucleation (too much surfactant) and coagulation (too little). Persulfate initiators generate two types of surface active sulfate-containing species; anchored sulfate groups (10-20%) and mobile in situ surfactant (ISS; 50-70%). This paper examines the significance of the competition between these two species and an added surfactant, sodium dodecylbenzene sulfonate (SDBS). SDBS soap titrations were performed on five uncleaned methyl methacrylate/butyl acrylate latexes with particle sizes from 500 nm to 3.25 μm at volume fractions from 1 to 30%. Not surprisingly, traditional Langmuir adsorption analyses were unsatisfactory, even after correction for finite volume fraction of solids. We develop a Langmuir site adsorption model to describe the competitive adsorption of ISS and SDBS in the presence of anchored sites and fit the surface tension data from 84 data points to obtain three parameters: the adsorption equilibrium constants for SDBS ( K s = 760 ± 30 liter mol -1 ) and ISS ( K 1 = 50 ± 12 liter mol -1 ) and the limiting area per molecule (APM = 0.37 ± 0.01 nm 2 ). These parameters are quite consistent with literature values determined in noncompetitive situations. The anchored groups were most significant on smaller particles, and the mobile ISS adsorption was most significant on smaller particles at high volume fraction. The relatively weak attraction of the ISS to the particle surface is due to its low molecular weight (∼400 Da per sulfate group) and results in desorption upon latex dilution.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to characterize nonionic, anionic and cationic surfactants. Rapid mass analyses can be achieved with proper choice of matrix material. The technique is suitable for development as a routine analytical tool.

Low-density polyethylene (LDPE) and also linear low-density polyethylene (LLDPE) resins can be characterized by the degree of strain hardening and down-gaging during elongation. A new method for the determination of the apparent elongational flow characteristics is presented. In a small scale apparatus, a molten monofilament is stretched under nonisothermal conditions similar to those found in tubular film extrusion. Measurement of resistance to elongational flow and apparent elongational strain rates permit the comparison of the process-ability of different resins under specified conditions. The effect of melt temperature and extension ratio are examined. The importance of the molecular structure of both LDPE and LLDPE resins on these properties is also outlined.

In this paper we address the aspects associated with shear modification of low density polyethylene by extrusion. By successive passes of the polymer through an extruder it can be shown that both the melt viscosity and melt elasticity are reduced by shear modification. These reversible variations are not accompanied by significant changes in molecular weight distribution. The major effects of extrusion are to decrease the amount of elastically effecitve material. Study of proton relaxation times at 150°C shows that the melt comprises regions of relatively ordered, entangled, and unentangled polymer. Shearing reduces the proportion of more ordered material. The elastically effective anchors that are reduced by shearing are regions with restricted segmental mobility rather than conventional entanglements or intermolecular knots. Successive extrusions produce a relatively small decrease in the number of such constraints to molecular motion. Repeated shearing has a diminishing effect on the proportion of more ordered material in the polyethlene melt. This parallels observations of the effects of repeated shear modification on the properties of polyethylene films and other extrudates.

The influences of initiator concentration, ionic strength of the aqueous phase and styrene sulfonic acid sodium salt comonomer on the average particle size and particle uniformity of latexes generated via emulsifier-free emulsion polymerization of styrene has been studied. It was found that the average particle size increased with increasing initiator concentration in reactions where the ionic strength was not controlled. The uniformity of the latex particles decreased as the initiator concentration increased. It was also found that at a minimum initiator concentration of 1.5 × 10−3 M at a temperature of 80°, adequate conversion could not be obtained. This limited the range of particle sizes which could be produced without adding additional surfactants. It was also found that smaller particles, 0.135 μm diameter, could be formed by copolymerizing styrene sulfonic acid sodium salt with styrene. The effects of ionic strength on particle size was also investigated and it was found that the particle size increased with increasing ionic strength. At constant ionic strength, it was found that particle size decreased with increasing initiator concentration as expected theoretically.

A major stream of post-consumer plastics is a commingled blend of polyethylenes and polypropylenes, which usually exhibits lower performance compared with that of the homopolymers due to the incompatible nature of polyethylenes and polypropylenes. Various studies have been carried out to characterize the structure, morphology, mechanical, thermal, and rheological behavior of this blend. The effect of processing, modification, and compatibilization have also been studied by various workers. This article is a review of the work done on polyethylene–polypropylene blends to help in the understanding of this important blend. © 1994 John Wiley & Sons, Inc.

The viscoelastic responses of some molten polymers, and particularly of low density polyethylene (LDPE), are known to vary with processing history. Reasons for the variations include the effects of shear history on morphological states of the polymer, or on its molecular weight parameters. A typical low density polyethylene has been used to test the shear-history dependence concept following a variety of processing steps. The polymer was sheared in single-screw and twin-screw extruders, and in a high speed melter / mixer (Gelimat). Samples also were precipitated from very dilute solutions in trichlorobenzene and in p-xylene. GPC analyses showed that, in general, these procedures did not affect the various moments of molecular weight. An exception was the Gelimat-mixed sample, for which mild reductions in Mn and Mw were noted. In contrast, melt viscosity and elasticity readings, the former from low shear evaluations and the latter from extrudate swelling, were affected by the various procedures. A drop in melt viscosity and in elasticity was observed, being most pronounced for precipitated and twin-screw extruded versions of the LDPE. Reductions also were observed in the specimen sheared in the Gelimat instrument. Following conditioning at the test extrusion temperature (170°C), viscous and elastic responses tended to revert to those of the unsheared control sample, the exception again being the sample sheared in the Gelimat melter / mixer. Of the various mechanisms proposed in the literature to account for transient property changes such as those reported, temporary changes in the degree of chain entanglement appear the most satisfactory explanation. Irreversible alterations in viscoelastic properties may be associated with changes in molecular weights due to processing at high shear.

The rheology and morphology of thermotropic liquid crystalline (TLC) polyesters are greatly dependent on the shear and thermal history of the sample. In this paper, the results of the time‐dependent melt rheology of a main chain, low‐melt TLC polymer with two flexible spacers are presented. Factors which have an effect on the viscoelastic properties such as temperature, frequency, and strain amplitude are discussed. It is shown that the increase in η* at constant strain amplitude and temperature, depends only on time and not shear. X‐ray diffraction patterns indicate that shear causes the polymer molecules to orient in the shear direction. Both frequency and strain amplitude seem to induce a gradient of crystallinity in the bulk of the samples and the crystalline fraction is predominant near the surface.

Direct grafting of polystyrene onto polyethylene has been carried out in a twin screw extruder with an organic peroxide and a crosslinking co-agent. The reaction extruded blends exhibited enhancement in impact properties at an optimum level of peroxide and co-agent. Further improvement was achieved by introducing styrene monomer into the system during reactive extrusion. The structure and morphology of the blends were studied using differential scanning calorimetry, scanning electron microscopy, infrared spectroscopy, and size exclusion chromatography

The surface energetics of poly(methyl methacrylate-co-butyl acrylate) emulsion polymer films was investigated using dynamic contact angle (DCA) analysis. From a series of Wilhelmy plate experiments using several probe liquids, the dispersive and polar components of the surface energy were determined to be 20.6 and 3.4 mJ · m−2, respectively. The surface energy was calculated from these values to be 24 mJ · m−2. It was found that addition of molecular weight modifiers (ethylene glycol dimethacrylate crosslinking agent and carbon tetrabromide chain transfer agent) during polymer synthesis had no effect on the surface tension of the polymer. The surface energy measured here was lower than expected for a poly(methyl methacrylate-co-butyl acrylate) system. This result was attributed to the exudation of oligomeric or polymeric pseudosurfactant to the surface of the films. The sulfate ion terminated pseudosurfactant is produced from the ammonium persulfate initiator used during the emulsion polymerization. The presence of these groups at the film surface was confirmed by attenuated total reflectance Fourier transform infrared spectroscopy. In addition to the measurement of the polymer surface energy, the effect of water inhibition on the polymer—water contact angles was studied. The reduction of the contact angles after water exposure times of 1 week and 1 month indicated progressive orientation of the hydrophilic functionalities toward the water phase.

A model, developed to account for the concentration dependence of the dimensions of dissolved polymers over a wide concentration range, has been combined with very simple hard sphere statistical mechanical relations to predict transport properties of polymer solutions. Diffusion and sedimentation coefficients are estimated accurately and Newtonian solution viscosity can also be predicted up to fairly high concentrations.

The effects of molecular structure on the dicumyl peroxide crosslinking of two low density polyethylenes have been studied. Peroxide efficiency was determined largely by the content of terminal vinyls in the two polymers. Differences in molecular weight distribution and branch content had comparatively little influence on the gel content but hot creep resistance of the vulcanized materials was affected. Scorching was affected, also, by the presence of vinyl unsaturations in the polymer.

A model, developed to account for the concentration dependence of the dimensions of dissolved polymers over a wide concentration range, has been combined with very simple hard sphere statistical mechanical relations to predict thermodynamic properties of the polymer solutions. Estimated values of reduced osmotic pressures, second virial coefficients and Flory-Huggins interaction parameters agree very well with experimental data for a variety of polymers and solvents.

In this paper we report the estimation of the cohesive energy density and three-dimensional solubility parameters for a common nonionic surfactant (alkyl phenol ethoxylate) using atomistically detailed models of the glassy phase and a classical force field. Energy minimization and constant temperature molecular dynamics methods were used to estimate the solubility parameters for quenched systems as well as systems with kinetic energies corresponding to 300 and 400 K. The relative effects of temperature on the energy contributions due to dispersive, electrostatic, and hydrogen bonding interactions found in these simulations are consistent with the known phase behavior of these materials. The advantages of this approach over group contribution methods are discussed.

A series of ethylene-vinyl acetate copolymers has been examined by 13 C-NMR spectroscopy and DSC. These polymers are products of high pressure free radical copolymerizations and contain 1–40% vinyl acetate by weight. Such copolymers are random and almost all the vinyl acetate units are isolated between ethylene units. All copolymers were branched, but total branching decreased with increasing vinyl acetate content. This effect arises mainly because the vinyl acetate residues inhibit the formation of cyclic intermediates that are involved in the productions of short branches. A decrease of about one short branch per 1000 ethylene carbons is observed for every increase of 2 mol% vinyl acetate. About 10% of the vinyl acetate units are branched at main chain carbons. Copolymers that have been cooled slowly from the melt exhibit multiple melting peaks. The lower melting, minor peaks are believed to reflect crystallization of lower molecular weight, branched molecules. The melting temperature of the copolymers is a function of the average sequence length of crystallizable ethylene units, when allowance is made for vinyl acetate units and short branches.

Linear low density polyethylenes are manufactured by copolymerizing ethylene with 1-alkenes, yielding a linear polyethylene backbone with short side chains. Due to the nature of the catalyst used in the polymerizaton, multimodal branching distributions are typically obtained. In this report, we have investigated the processability of four 1-octene linear low density polyethylenes as a function of the short chain branching distribution. Analytical techniques such as 13C nuclear resonance spectroscopy, size exclusion chromatography, differential scanning calorimetry, and temperature rising elution fractionation, in particular were used to elucidate the molecular structure. Processability measurements were made using various extrusion techniques and dynamic mechanical analyses.It was determined that in the absence of any variations in molecular weight, the polymers with the higher proportions of linear polyethylene showed inferior processability In terms of onset of surface imperfections at lower extrusion rates. Polymers with worse processability characteristics also exhibited higher zero shear viscosities.

A co-rotating twin screw extruder was employed in melt mixing and reactive extrusion of polystyrene/linear low density polyethylene (PS/PE) blends. Blends of PS/PE in the ratio of 9: 1 were prepared under different conditions of shear mixing and with different concentrations of dicurnlyl peroxide (DP) and triallyl isocyanurate (TALC) coupling agent. The Charpy impact strength of unnotched samples of melt blends was found to be lower than that of the polystyrene and was not affected much by the different conditions of melt mixing at different rates of extrusion, screw speeds, and screw configurations. In the case of reaction-extruded blends, the impact strength initially deteriorated with small addition of TAIC/DP, but improved with further increase in the level of TAIC/DP, exceeding that of polystyrene at an optimum concentration. With even further increase in TAIC/DP concentration, the impact strength again decreased. This was attributed to the different extents of coupling reactions of PE-TAIC-PE, PE-TAIC-PS, and PS-TAIC-PS with different levels of TAIC/DP. The interfacial adhesion of the incompatible PS-PE was postulated to be improved by the graft copolymers formed during reactive extrusion. This observation was supported by melt rheology, thermal characterization, molecular weight, and fracture surface morphology studies.

A series of commercial polystyrenes was tested using an instrumented impact tester to determine the fracture toughness Kc and critical strain energy release rate Gc. Over the range of Mw, 201,000 to 336,000, Kc increased from 1.38 MN/m3/2 to 1.76 MN/m3/2and Gc from 0.92 kJ/m2 to 1.60 kJ/m2. A linear correlation for Kc and Gc was seen with melt index, and an inverse relationship was obtained against molecular weight. Examination of the fracture surfaces revealed the presence of crack growth bands corresponding to the crack tip plastic zone size. It is suggested that these bands are the consequence of variations in crack growth along crazes that form in the crack tip stress field. As the crack propagates, the stress is relaxed locally, decreasing the growth rate allowing a new bundle of crazes to nucleate along which the crack advances. The spacing of these bands corresponds to the craze length formed in the plastic zone, and the band spacing increases with molecular weight.

The use of N,N'-dimethyldiazenecarboxamide as an initiator for the emulsion polymerization of methyl methacrylate is described. Polymerization was achieved with 85-90% conversion of monomer in both batch and semi-batch modes with no coagulation noted. Particle diameters were in the range 120-130 nm with a polydispersity of 1.05

The feasibility of inducing beneficial changes to polystyrene/polyethylene (PS/PE) blends via reactive extrusion processes is considered. Experiments have been conducted on 50:50 wt.% PS/PE blends that were treated with different levels of dicumyl peroxide and triallyl isocyanurate coupling agent. Both a low molecular weight and a high molecular weight blend series have been investigated. A “more reactive” polystyrene was synthesized by incorporation of a minor amount of ortho-vinylbenzaldehyde. Blends containing this modified polystyrene were subjected to identical processing' conditions on a counter-rotating twin screw extruder. Examination of the tensile properties of the extrusion products suggested that a judicious level of peroxide and coupling agent additives would be beneficial to the ultimate physical properties. The quantity of styrenic phase becoming chemically grafted to the polyethylene matrix was influenced most strongly by the level of the chosen coupling agent. As determined by scanning electron microscopy, the phase morphologies of the tensile test fracture surfaces were strongly dependent upon the reaction extrusion process; those extruded blends that had been exposed to the additive pre-treatment displayed substantially finer microstructure. The enthalpy of fusion of the polyethylene melting endotherm was likewise influenced by both the presence or absence of the additives as well as the molecular weight nature of the blend series.

A 5-inch diameter disc extruder was operated with a commercial polypropylene polymer to provide comparison data and the model predictions were compared to machine performance as a function of extrusion conditions and polymer characteristics. The mathematical model used for comparison has been described previously by the authors.

The hydrodynamic volumes of solvated polymers shrink with increasing concentrations in solution until a concentration (cx) is reached at which the effective dimensions are the same as those in a Flory theta solvent. Further increases beyond cx result in progressively greater overlapping of separate macromolecules. Several theories are available for the prediction of cx but none is entirely satisfactory. A semi-empirical method is described here for the estimation of cx, using intrinsic viscosities as input parameters. The magnitude of cx is shown to be solvent dependent; its lower limit is zero, in a theta solvent.

Effect of Solvent on Concentration Dependence of Hydrodynamic Volumes and GPC Elution Volumes

Size exclusion chromatography (SEC) and 13C-NMR analyses have been used to measure long chain branching indices in low density, free radical-polymerized polyethylenes. Calculation of long chain branching frequency from SEC data requires the assumption of a molecular model. Generally, a randomly branched polymer is assumed, with branches originating at trifunctional branch points. Long chain branch concentrations determined by SEC analysis alone appear to be valid only in a relative sense. The parameters used in the model assumptions vary from polymer to polymer. Despite these limitations, SEC analyses appear to be internally consistent when applied to polyethylenes made by a single manufacturer and process. Comparisons of absolute values of long branch frequency between products from different reactor types require NMR as well as SEC data.

The flow of polymer melts in a rotating disc extruder is analyzed with the development of a mathematical model for drag flow in a contoured rotating disc. The model assumes a fully melted material which exhibits Newtonian flow behavior under isothermal conditions. Flow is evaluated in successive sections of the flow path, and the drag flow component is calculated by assuming a zero pressure gradient by analogy to the analysis of single screw extruder performance. The final expression involves a computer-assisted numerical solution. Results of the drag flow model are presented for three different disc geometries. A mathematical model of negative flow, and a comparison of the results with experimental data will be presented in followup papers.

Copolymers of styrene and ortho -vinylbenzaldehyde ( o -VBA) have been polymerized to high conversion by free radical methods. Those polymers polymerized at 423°K formed thermoplastic materials over the entire composition range with onset glass transition temperatures varying from 363° to 410°K as the o -VBA content was increased from 0 to 100%. Similar high conversion copolymers synthesized at lower polymerization temperatures tended to display markedly less solubility and thermoplasticity, especially for those compositions rich in the o -VBA substituent.

Blends of polycarbonate/polystyrene (PC/PS), polycarbonate/polypropylene (PC/PP) and ternary blends of the three components (PC/PS/PP) were studied. Extrudate swell of the molten blends increased with increasing concentrations of the minor components and leveled off at characteristic blend compositions. These compositions corresponded to the limits of compatibility as judged by the onset of brittleness in tensile tests. Both PS and PP appear to have some limited practical compatibility with PC. The change in extrudate swell behavior with concentration may be a rapid and convenient test for the effective concentration limits of partially miscible polymers.

Poly(ethylene terephthalate) and polypropylene are considered, to be incompatible by the usual criteria for polymer blends. Sheath/core filaments of these polymers could not be oriented because of poor adhesion of the base polymers. Melt blends of the two polymers with 30 and 50 weight percent polypropylene produced useful, oriented monofilaments. Tensile and dynamic mechanical properties of these filaments indicate that the structures consist of interlocked microfibrillar domains of the polyester and polyolefim. The glass transition region of poly(ethylene terephthalate) is not affected by admixture with polypropylene. A fine mutual dispersion of the two polymers was possible because the melt viscosities of the ingredients were reasonably well matched under the conditions of mixing. The melt viscosity and elasticity of blends were lower than those of either component as expected if the two polymers are immiscible. Monofilament extrusion and melt flow measurements were made with a one-half inch single screw extruder.

Time dependence of recovery from shear history effects in polymer liquids can be used advantageously to modify the properties of macromolecules. The net result of shearing is a reduction in elasticity and possibly in viscosity of the polymer fluid. The material may be processed subsequently in a transient, less elastic, and less viscous state if the diffusion-related rate of recovery of a more fully entangled equilibrium state is not too rapid. Shear-induced changes in entanglement density are manifested in variations in die swell, die entrance pressure losses, normal stresses, melt strength, flow defects such as melt fracture and sharkskin surfaces, haze of extruded films, application properties of coatings liquids and, other properties. Evidence for shear-modification effects is reviewed in this article. The polymer species that are most amenable to this treatment are identified in general terms; shear modification processes that have been used are summarized. Methods for augmenting the efficiency of mechanical shear modification include addition of plasticizers, fillers, and incompletely miscible polymers. The expedient mentioned last can be particularly effective. Assessments of the degree of shear modification are reviewed and applications to coatings mixtures are also summarized. The time-dependent behavior of the type reviewed in this article limits the success of theoretical approaches, as in the application of constitutive equations to describe polymer-liquid behavior. Attempts to relate Newtonian viscosities and other rheological parameters to polymer characteristics are similarly hindered when shear history effects are not taken into account.

Purified, gel free butadiene-styrene copolymers were prepared by emulsion polymerization with butadiene contents of 80, 55 and 30 weight %. Radiation behavior of these materials at 30°C was independent of dose rate in the range 0.04-0.46 Mrad/hour and the scission-crosslinking ratio was about 0.40 for all copolymers and was independent of total dose. Extrapolated sol fractions at infinite dose, intrinsic viscosities of irradiated polymers and Mn in the pre-gel region gave mutually consistent estimates of this ratio. G(crosslink) was 3.4. At the relatively low doses studied, intra-molecular crosslinking was evident only with the high styrene content polymer. Active sites for intermolecular crosslinking are thought to be allylic to chain double bonds, whereas vinyl groupings may be involved in intramolecular crosslinking. On a prepare des copolymeres du mutadiene et du styrene purifies et exempts de gel, au moyen d'une polymerisation par emulsion avec des teneurs de 80,55 et 30% en poids de butadiene. Le comportement des dits copolymeres, lorsqu'ils etaient exposes aux radiations a 30°C, s'est avere independant du taux de la dose, pour une echelle de 0.04 a 0.46 megarad a l'heure; en outre, le rapport entre la scission et les liaisons croisees a ete d'environ 0.40 pour tous les copolymeres et il a ete independant de la dose totale. Les fractions de sols extrapolees a une dose infinie, les viscosites intrinseques des polymeres irradies et la valeur Mn dans la zone pre-gel ont fourni des estimations dudit rapport qui concordaient bien les unes avec les autres: G (liaison croisee) etait 3.4. Compte tenu des doses de radiation relativement faibles qu'on a etudiees, les liaisons croisees entre les molecules ne sont apparues clairement que dans le cas du polymere a forte teneur en styrene. Il y a lieu de croire que les sites actifs pour les liaisons croisees entre les molecules sont les radicaux allyliques pour les chaǐnes a double liaison et les groupes vinyles pour les liaisons croisees intramoleculaires.

The flow of polymer melts in a rotating disc extruder is analyzed with a mathematical model for pressure flow and leakage flow (termed neg ative flow). It is assumed that the material is fully melted and exhibits Newtonian flow behavior under isothermal conditions for each element. Flow is evaluated in successive sections of the flow path and the final expression involves a computer-assisted numerical solution. Pressure flow, which is negative, is calculated by analyzing the situation in which the pressure gradient causes the extrudable material to flow back across the stationary disc. A simplified geometrical model is developed for numerical solution, assuming incompressible flow. Leakage flow is between the contours of the disc and the engaging interior face of the housing. The flow is also directed opposite to the drag component and is estimated by using parallel plate flow equations.

An optimized experimental procedure has been developed for the 13C-NMR analysis of polyethylenes. These analyses were performed at 62.5 MHz in 60–80 (w/w)% mixtures in trichlorobenzene. Signal sensitivity is enhanced by operating at 100°C rather than higher temperatures. Solutions were prepared by holding the polymer-solvent mixtures at 155–160°C before cooling to the analysis temperature. This solution procedure, which is used also in size exclusion chromatography of polyethylenes, reduces NMR line widths and increases carbon spin-spin relaxation times. Spin-lattice relaxation times (T1) under these experimental conditions are similar to those reported earlier at higher temperatures. The longest T1 is 7.0 sec, indicating a minimum 35 sec delay time during accumulation of the spectrum. The long analysis time results in some decrease of polymer molecular weight during the NMR data acquisition. In low density polyethylenes, ethyl branches occur usually as 1–3 pairs, rather than as isolated branches. Some ethyl (and presumably other) branches occur at quaternary main chain carbons. Branch concentrations measured here are qualitatively similar but quantitatively different from those in earlier reports where shorter NMR delay times were employed.

Quasi-elastic light scattering was used to measure the concentration dependence of diffusion coefficients of anionic polystyrenes in butanone. This system has been studied previously by other workers whose results do not entirely agree. The present data are used to resolve this discrepancy. The predictions of a recent theory of Vrentas and Duda gives predictions which coincide quite well with experimental values.

The assumptions involved in the analysis of flow of polymer melts in a closed end falling coaxial cylinder viscometer(1–3) are examined and it is shown that true values of shear rate and shear stress at the wall of the moving cylinder can be obtained by assuming classical Poiseuille flow. Flow curves obtained with a variety of apparatus geometries, driving loads and polymers are consistent with those of other measurement techniques. This apparatus, which is a simple modification of a capillary extrusion rheometer, provides measurements of apparent viscosity at much lower shear rates than can be obtained with the former viscometers. A quantitative measurement of end correction effects is provided by the present analysis. End effects, which are formally similar to those in capillary extrusion, were measured for several polystyrenes and polyethylenes. On a examine les hypotheses qu'implique l'analyse de l'ecoulement de polymeres en fusion dans un viscosimetre comprenant un cylindre coaxial a extremites fermees et tombant; on a constate qu'on peut obtenir les vraies valeurs du taux de cisaillement et de l'effort de cisaillement sur la paroi du cylindre en mouvement en supposant qu'il s'agit de l'ecoulement classique de Poiseuille. Les courbes d'ecoulement qu'on a obtenues, en employant differentes formes geometriques de l'appareil et charges de poussee ainsi que divers polymeres, ont bien concorde avec celles qui resultent de l'utilisation d'autres methodes de mesure. Ledit appareil, qui est un simple modification d'un rheometre a extrusion capillaire, permet d'obtenir des mesures de la viscosite apparente a des taux de cisaillement bien plus faibles que dans le cas des viscosimetres prealablement employes. L'analyse actuelle fournit une mesure quantitative des effets finals de correction; on a mesure, dans le cas de plusieurs polystyrenes et polyethylenes, les effets finals qui sont formellement semblables a ceux qu'on rencontre dans le cas de l'extrusion capillaire.

The two main flow defects which appear to originate in the processing machine or die are melt fracture and sharkskin. Both are associated with the elastic nature of the polymer melt. Processing variations that decrease the elastic nature of the melt diminish the severity of the effects of melt fracture. These include increased die length and temperature and shear at temperatures at which polymer segmental mobility is not too high. The sheared, less elastic melt structure may sometimes be stabilized by polymeric additives. A simple model is presented to account for this behavior, which is illustrated with examples of polyethylene and plasticized PVC.

An inexpensive, accurate falling coaxial cylinder viscometer is described. Viscosities can be measured at shear stresses at least as low as 103 dynes per cm2 and flow curves can be obtained with shear thinning fluids. Data for a polystyrene and a polyethylene polymer coincide with those from other techniques and with corresponding literature values. The lower Newtonian viscosities pf both polymers were experimentally accessible, and it is shown that estimation of ηo by extrapolation from viscosities in the non-Newtonian region may be subject to errors of uncertain magnitude. Shear history of the sample affects the Newtonian and low shear viscosities of high molecular weight polymer melts. On decrit un viscosimetre non-coǔteux dans lequel on peut determiner avec exactitude le temps de chute d'un cylindre coaxial dans un fluide. On peut mesurer des viscosites correspondent a des efforts de cisaillement aussi faibles que 103 dynes au centimetre carre et peut obtenir des courbes d'ecoulement pour des fluides dont la viscosite est reduite par le cisaillement. Les resultats obtenus dans le cas de deux polymeres (polystyrene et polyethylene) concordent avec ceux qui proviennent d'autres methodes et avec les valeurs correspondantes qui ont ete publiees. On a pu determiner experimentalement les viscosites newtoniennes plus faibles des deux polymeres et demontre que l'estimation de ηo par extrapolation des viscosites dang le secteur non-newtonien peut ětre sujette a des erreurs dont l'importance est aleatoire. Le degre de cisaillement auquel ont ete soumis les echantillons affecte les viscosites newtoniennes et a cisaillement faible des polymeres fondus qui possedent un poids molceulaire eleve.

This article considers possible erxors in experiment or analysis and alternative methods of data treatment for a falling coaxial cylinder viscometer. The viscometer uses a weighted rod falling into a polymer melt contained in a closed end concentric cylinder. Flow relations can be solved for non-Newtonian fluid response in steady, simple shearing flow. Although the rod fall is found not to be steady, as assumed, this produces negligible error in the computed flow curves. Consistent flow curves which were independent of apparatus geometry were obtained by a method in which instantaneous rod velocities were estimated graphically from raw data and an end correction was taken into account. On considere, dans le present travail, les erreurs qui peuvent se glisser dans les experiences ou analyses et la methodes alternatives du traitement des donnees dans le cas d'un viscosimetre base sur la chute d'un cylindre coaxial. Dam le dit viscosimetre, on laisse tomber une tige alourdie par un poids dans un polymere en fusion qui se trouve dans un cylindre ferme et concentrique. On peut resoudre les equations d'ecoulement relatives a la reaction d'un fluide non-newtonien engage dans un ecoulement stable et a cisaillement simple. Bien qu'on constate que la chute de la tige n'est pas aussi reguliere qu'on le supposait, l'erreur resultante dans les courbes d'ecoulement calculees est negligeable. On a obtenu des courbes consistantes d'ecoulement, qui ne dependaient pas de la geometrie de l'appareillage, en utilisant une methode dans laquelle on a evalue graphiquement les velocites instantanees de la tige, a partir de donnees brutes, et tenu compte d'une correction finale.

The free radical copolymerization of methacrylonitrile, styrene, and α-methylstyrene was studied at 60 °C in toluene solution. Copolymer composition was calculated from the composition of the unreacted monomers, as measured by g.l.c. Reactivity ratios measured previously for the three monomer pairs involved were used with the simple terpolymerization equation to predict polymer composition. Agreement between predicted and experimental polymer compositions was satisfactory. The behavior of α-methylstyrene can be described by a simple model without reference to ceiling temperature or penultimate effects because sequence lengths of this monomer in the terpolymers are short.A true azeotropic feed composition was not investigated, but several monomer mixtures produced copolymers with compositions which varied so little from that of the feed that the systems could be considered to be azeotropic for practical synthetic purposes. This behavior is in accord with expectations.Analytical accuracy of the gas chromatographic techniques was examined and means are suggested to make the best use of this method in copolymerization studies.

A falling coaxial cylinder viscometer was used to measure the melt flow behaviour of a commercial polystyrene with Mw 260,000. The shear stress region extended down to 0.6 × 104 dynes/cm2 and shear rates were as low as 3 × 10−2 sec−1 at 186°C. The shear rate-shear stress plots were linear at low shear stresses with slopes (differential viscosities) of 3.3 × 105 poises at total shear less than 120 units and decreasing differential viscosity with higher total shear. The flow curves at relatively low total shear were initially dilatant and became pseudoplastic with increasing shear stress. The inflection point represents a Newtonian apparent viscosity, which agrees fairly well with literature values for polystyrenes of the same Mw. Newtonian apparent viscosity is characteristic of a point value of shear stress and shear rate and is not necessarily a plateau region. Observation of a Newtonian region with decreasing shear stress or shear rate does not prove that this flow regime persists unchanged to zero values of the experimental parameter. The existence and magnitude of the Newtonian apparent viscosity reflects shear history of the polymer as well as its constitution and molecular weight distribution.

Variation of the second virial coefficient as a function of polymer composition for three pairs of polystyrene mixtures in 2-butanone has been studied using static light scattering. The results are better represented by the simple method of taking the geometric mean of the second virial coefficients of the separate polymer species rather than by the two-parameter theory. In one of the three combinations studied, the presence of a minimum in the second virial coefficient-composition plot supports similar observations by previous workers.