bluuebunny/crossref_metadata_2025 huggingface dataset:
Calorimetric determination of head‐to‐head defect in poly(vinylidene fluoride)
Authors: Millich F. , Hauber B. F.
Published: April 2003

Differential scanning calorimetric analyses were conducted on samples of poly(vinylidene fluoride) polymerized in an autoclave by tributylborane‐oxygen by free‐radical initiation at low temperature (‐70‐0°C). The peak melting points and the percent head‐to‐head defect in each polymer sample were determined by a reported calorimetric method. A commercial sample showed a melting temperature in the range 157–162°C and a percent head‐to‐head defect of 7.7%; whereas two experimental samples showed melting temperatures in the range 172–179°C with a percent head‐to‐head defect of 4.4 and 4.9%. The calorimetric procedure was modified by reducing annealing times to only 2 h, which saves time and, as shown in this study, avoids thermal polymer degradation.
Crystallinities of copolymers of ethylene and 1‐alkenes
Authors: Clas S.‐D. , Heyding R. D. , McFaddin D. C. , Russell K. E. , Scammell‐Bullock M. V. , Kelusky E. C. , St‐Cyr D.
Published: April 2003

Random copolymers of ethylene with 1‐butene, 1‐octene, and 1‐octadecene have been prepared using a homogeneous vanadium‐based catalyst system. Comonomer contents determined by 13C‐NMR analysis of polymer solutions are in the range 1–10 mol%. Crystallinities were estimated by means of density measurements, x‐ray diffraction, differential scanning calorimetry, laser Raman spectroscopy, and CPMAS 13C‐NMR spectroscopy. The results are compared with those obtained for heterogeneous copolymers of ethylene containing 1–4 mol% 1‐butene. As the comonomer content is increased, the crystallinity decreases. The dimension perpendicular to the 110 plane in orthorhombic crystallites decreases linearly with crystallinity. This decrease in crystallite size is accompanied by an increase in the size of the orthorhombic unit cell. For copolymers containing large amounts of 1‐octene and 1‐octadecene, a second crystalline form appears. Differences in estimates of crystallinity are discussed in terms of looser packing in highly branched copolymers and the extent to which the second crystalline form participates in the phase structure.
Composition of vinylidene chloride/phenylacetylene (VDC/PA) copolymers and vinylidene chloride/methyl acrylate/phenylacetylene (VDC/MA/PA) terpolymers from analysis by 13C‐NMR spectroscopy
Authors: Howell B. A. , Smith P. B.
Published: April 2003

13C‐NMR spectroscopy has been utilized to characterize Saran polymers containing polyene segments generated by incorporating phenylacetylene (PA) units into either poly(vinylidene chloride) (PVDC) or a typical Saran copolymer of 91% vinylidene chloride (VDC) and 9% methyl acrylate (MA). The incorporation of PA could not be defined in the usual statistical way because the presence of the PA double bond in the polymer backbone appeared to cause the dehydrohalogenation of units next to it. Thus, sequences of PA next to VDC were not observed. Rather, sequences of olefinic units next to VDC units were present at a level equal to the level of PA incorporation. The level of unsaturation in the PA copolymers is approximately four times the level of PA incorporation. These observations are consistent with the random incorporation into the copolymer of PA which then initiates the dehydrohalogenation in adjacent VDC units. This dehydrohalogenation reaction appears to propagate from one unit to the next along the backbone of the polymer such that polyene segments containing the PA unit are formed.
Miscibility of polyester/nitrocellulose blends: A DSC and FTIR study
Authors: Jutier Jean‐Jacques , Lemieux Even , Prud'homme Robert E.
Published: April 2003

The miscibility of polyester/nitrocellulose blends was investigated by differential scanning calorimetry and Fourier‐transform infrared (FTIR) spectroscopy. Two nitrocelluloses (NC) derived from wood and having different nitrogen contents (12.62 and 13.42%) were used. On the basis of the glass transition temperature criterion, poly(ϵ‐caprolactone) (PCL), poly(valerolactone), poly(ethylene adipate), and poly(butylene adipate) are miscible with nitrocellulose, whereas poly(α‐methyl α‐propyl β‐propiolactone) and poly(α‐methyl β‐proiolactone) are immiscible. The Tg versus composition curves of PCL/NC blends do not follow a monotone function but exhibit a singular point at a critical PCL volume fraction of 0.51 for NC‐1342 and 0.45 for NC‐1262 in agreement with Kovacs' theory. A shift of 17 cm‐1 of the carbonyl stretching band was observed with PCL/NC blends and is taken as evidence for hydrogen bonding interaction between the PCL carbonyl group and NC hydroxyl group. The frequency difference between the free hydroxyl absorbance and the absorbances of the hydrogen‐bonded species was found to be 85 cm‐1 in pure NC and 125 cm‐1 in PCL/NC blends; it indicates that the average strength of this interaction is stronger than the corresponding self‐associated hydrogen bonding in pure NC. The presence of a dipole‐dipole interaction between the nitrate‐ester groups of NC and the carbonyl groups of the polyesters is reported. The relative strength of the hydrogen bonding and dipole‐dipole interactions is discussed and correlated with polymer miscibility.
Energy storage in polymer chains under stress
Authors: Cook Robert
Published: April 2003

The local conformation and storage of energy in individual polymer chains during a deformation of a bulk polymer sample are examined by the computer simulation of a relatively simple model. It is shown that as the interaction between the chain atoms and surrounding medium increases, rotational angle motion is suppressed during the deformation, and large amounts of energy are stored in backbone bond angle and bond length distortions. The relationship of this phenomena to Tg and the implications for chain relaxation are discussed.
Isothermal crystallization of poly(vinylidene fluoride) in the presence of high static electric fields. I. Primary nucleation phenomenon
Authors: Marand H. L. , Stein R. S. , Stack G. M.
Published: April 2003

Primary nucleation of poly(vinylidene fluoride) (PVF2) γ‐phase crystals from the melt is affected by the presence of an electric field. Crystallization under the electric field is studied by polarized optical microscopy, thermal analysis, and wide‐angle x‐ray diffraction. Preliminary results indicate that the γ‐phase crystal nucleation rate and content are enhanced by the electric field.

A modification of the classical theory of homogeneous nucleation of a crystalline phase is proposed to account for the experimental observations. Electrostatic interaction between the nucleus total polarization and the electric field contributes to the free energy of nucleation to a very large extent at low undercooling. Theoretical predictions indicate that a static electric field will increase the nucleation rate of a polar phase and will decrease the nucleation rate of a nonpolar phase. Confirmation of the former fact is observed experimentally.
Ionic miscibility enhancement in poly(tetrafluoroethylene)/poly(ethyl acrylate) blends. I. Dynamic mechanical studies
Authors: Murali R. , Eisenberg A.
Published: April 2003

It is shown that ion‐ion interactions resulting from a proton transfer induce considerable miscibility in blends of functionalized poly(tetrafluoroethylene) with ethyl acrylate copolymers containing 4‐vinyl pyridine. Dynamic mechanical measurements, in conjunction with transparency of the samples, are used to evaluate miscibility. It is shown that mixing conditions exert a profound effect on the properties of the final blend. The glass transition of the blend is shown to be strong function of the blend composition, as is characteristic of highly miscible systems.
Sorptive dilation of poly(vinyl benzoate) and poly(vinyl butyral) by carbon dioxide
Authors: Kamiya Yoshinori , Hirose Takuji , Mizoguchi Keishin , Terada Katsuhiko
Published: April 2003

Dilation of poly(vinyl benzoate) and poly(vinyl butyral) accompanying sorption of carbon dioxide is measured with a cathetometer under pressures up to 50 atm at 25°C. Sorption isotherms for carbon dioxide in these polymers were also determined gravimetrically. Each dilation isotherm plotted versus pressure, as well as the sorption isotherm, showed an inflection point corresponding to the glass transition of the polymer‐gas system. The dilation isotherms changed their form at that point from concave to convex to the pressure axis or to a straight line. Dilation and sorption isotherms exhibited time‐dependent hysteresis below the inflection point but not above the point. Partial molar volumes of carbon dioxide in polymers, which were determined from dilation and sorption data above the point, were found to be independent of concentration and larger than those below the point. The latter volumes depended on concentration. Based upon the extended dual‐mode sorption concept, which takes account of plasticization of polymer by sorbed gas, a dilation model was developed. Dilation data were described well by the model.
Polarized reflection spectrum and molecular orientation in uniaxially drawn poly(ethylene terephthalate)
Authors: Kaito Akira , Nakayama Kazuo , Kanetsuna Hisaaki
Published: April 2003

The polarized electronic spectrum of oriented poly(ethylene terephthalate) (PET) sheets was obtained from the specular reflection spectrum using the Kramers‐Kronig relationship. The surface orientation function of drawn and drawn/annealed PET sheets was determined from the dichroic ratio of the second π* ← π transition observed at 41,000 cm‐1. The bulk orientation functions in the crystalline and amorphous regions were evaluated from wide‐angle X‐ray diffraction and sonic modulus measurements. On annealing of drawn PET sheets, the crystalline orientation and crystallinity were much improved, but the amorphous orientation function showed a minor decrease. The overall molecular orientation in the surface of the drawn PET sheet was shown to be approximately equivalent to the molecular orientation in the bulk.
Plastic deformation of poly(tetramethylene oxide). II. Molecular orientation as measured by x‐ray diffraction and NMR measurements
Authors: Kretz M. , Meurer B. , Spegt P. , Weill G.
Published: April 2003

The orientation of the crystalline and amorphous phases in uniaxially drawn samples of polytetramethylene oxide has been studied by x‐ray and NMR methods. Pole figure measurements give the orientation of the crystalline phase. Its dependence on the draw ratio does not obey the pseudoaffine model. The crystalline fraction is derived from NMR measurements at temperatures between Tg and Tm, where the free induction decay (FID) of the unoriented sample can be analyzed in terms of a rigid (crystalline), a constrained, and an amorphous phase. Low temperature (T < Tg) measurements of the NMR second‐moment anisotropy in protonated and deuterated samples give a mean orientation of the chains higher than that corresponding to the crystalline phase. The lack of anisotropy in the tail of the FID at temperatures between Tg and Tm indicates no appreciable anisotropy in the truly amorphous interlamellar phase. From this and from the ratio of the P4/P2 orientations, factors which obey the “most probable distribution,” it is concluded that the amorphous orientation is due to the layer of constrained chains at the surface of the lamellae.
Characterization of the surface hydrolysis of kevlar‐49 fibers by diffuse reflectance FTIR spectroscopy
Authors: Chatzi E. G. , Tidrick S. L. , Koenig J. L.
Published: April 2003

A modified diffuse reflectance technique is used to characterize the surface hydrolysis of Kevlar‐49 fibers. Treatment with 10 wt% NaOH solution produces carboxylate groups on the surface which increase rapidly up to treatment times of about 20 min at room temperature or 50 min in boiling solution. After this maximum the carboxylate groups decrease and then level out. This behavior can be explained by considering the increase as due to hydrolysis of the surface amide groups, competing with the decrease due to removal of the extensively hydrolyzed, fragmented molecules into the treatment solution. Our results shows that mild conditions (10 wt% NaOH and room temperature) as well as relatively small treatment times (less than 20 min) can be used for modifying the surface of the Kevlar‐49 fiber without destroying the skin and thus deteriorating the mechanical properties of the fiber.
On the distribution of dye molecules in stretched poly(vinyl alcohol)
Authors: van Gurp M. , van Ginkel G. , Levine Y. K.
Published: April 2003

The symmetry of the orientational distribution function of dye molecules in stretched PVA films is studied using polarized fluorescence. The different symmetries are monitored by a simple experimental technique in which angle‐resolved fluorescence depolarization ratios are measured. A uniaxial distribution of rhodamine 6G molecules is obtained on stretching the film at temperatures above 60°C. In contrast a biaxial distribution of trypaflavine molecules is found for stretch temperatures in the 50–115°C range. It is suggested that the hydrogen bonding between the PVA chains, and between the dye molecules and the PVA chains, influences the symmetry of the distribution upon stretching.
Edge‐excitation red shift of the fluorescence of flexible solute molecules in a poly(methyl methacrylate) polymer matrix
Authors: Al‐Hassan Khader A.
Published: April 2003

An excitation wavelength dependence of the fluorescence of tert‐butyl and methyl esters of 9‐anthroic acid and of tetraphenylbutadiene and tetraphenylmethylbutadiene in a poly(methyl methacrylate) (PMMA) polymer matrix is explained in terms of the presence of conformers that experience different free volumes at 77 K relative to room temperature.
A study of surface dynamics of polymers. II. Investigation by plasma surface implantation of fluorine–containing moieties
Authors: Yasuda T. , Okuno T. , Yoshida K. , Yasuda H.
Published: April 2003

Macromolecules at the surface of a polymeric solid have considerable mobility, and the specific arrangement of functional groups of macromolecules at the surface is dictated by the environmental conditions in which the surface is placed. Consequently, the change of environmental conditions, such as immersion in water or placement in a biological surrounding, could cause a cosiderable degree of change in the surface characteristics of a polymer from those evaluated in the laboratory against ambient air. The mobile nature of a polymer surface can be investigated by surface‐implanting fluorine‐containing moieties, mainly—CF3, by the plasma implantation technique and following the disappearance and reappearance of fluorine atoms on the surface. The disappearance rates (based on the immersion time in water at room temperature) of ESCA F1s signals, the decay rates of (advancing) contact angle of water, and the recovery of these values on heat treatment of water‐immersed samples were measured as a function of crystallinity of polymer samples (at three levels of crystallinity) for poly(ethylene terephthalate) and nylon 6.
On the nature of the free volume in amorphous polymers
Authors: Brather A.
Published: April 2003

In a previous publication1 it was shown that the free volume in amorphous polymers cannot consist of empty sites according to the quasilattice model. In this paper it is demonstrated why theories which are based on the assumptions of this model are nevertheless partly successful. It is even possible to calculate all three jumplike alterations in the second derivatives of Gibbs free energy at the glass transition in accordance with the experimental results. As far as we know, this is the first time that, in addition to the steplike changes in the thermal expansion coefficient Δα and the specific heat Δcp, the analogous change in the compressibility Δχ can also be described correctly by a theory. The parameters for accommodation however reveal, that the quasilattice model does not apply. Consequently better‐founded equations are derived, which despite their simplicity, give excellent agreement with the experimental data. One conclusion is that if the free volume consists of cavities in the material, their mean size has to be at least ten times smaller than that of a segment of the chainlike polymer molecules.
Melt spinning of thermotropic liquid‐crystal polyesters to form ultrahigh‐modulus filaments
Authors: Itoyama Kuniyoshi
Published: April 2003

The properties and structure of ultrahigh‐modulus filaments were investigated for wholly aromatic copolyesters (WACPs) containing 60 and 70 mol% p‐oxybenzoate, based on p‐hydroxybenzoic acid, p,p′‐biphenol, terephthalic acid, and isophthalic acid and for poly(ethylene terephthalate co‐p‐oxybenzoate) containing 60 mol% p‐oxybenzoate. As‐spun filaments with varying degrees of molecular orientation were spun from melts by taking the spin‐extension ratio as a variable at given temperatures. The as‐spun filaments were further subjected to thermal annealing. Changes in the structural ordering with the extension ratio were monitored by wide‐angle x‐ray scattering, scanning electron microscopy, viscoelastic properties, and measurements of the thermal expansion coefficient. The increase in modulus is correlated well with the crystallite orientation at a relatively low extension ratio. However, for extension ratios above 10, the modulus of as‐spun filaments is almost independent of the crystallite orientation. Modulus values as high as 100 GPa are obtained for WACP filaments spun at extension ratios above 500. It is suggested that ultrahigh‐modulus values can be reached in highly oriented noncrystalline chains. Furthermore, the results for annealed filaments indicated that the relaxation of molecular orientation occurs partially in the oriented noncrystalline regions during the stage of long‐time annealing above Tg, leading to depression of the modulus.
Coextrusion drawing of reactor powder of ultrahigh molecular weight polyethylene
Authors: Pawlikowski Gregory T. , Mitchell Donald J. , Porter Roger S.
Published: April 2003

Certain nascent polymers have been shown to have unusual thermal and morphological properties that are irretrievably lost once the polymer has been melted or otherwise reduced to the isotropic state. We show further that nascent ultrahigh molecular weight polyethylene “reactor powder” exhibits a remarkable ductility when uniaxially drawn by coextrusion techniques after initial compaction in film form at 100°C. When drawn at a temperature of 110°C, draw ratios of 56 have been obtained, resulting in an enhanced tensile modulus of 58 GPa. Thermal analyses and dynamic mechanical measurements were also made towards understanding the initial and final morphologies.
The observation of a sub(gel‐sol) transition in PVC/DOP gels
Authors: Gallego F. , Muñoz M. E. , Peña J. J. , Santamaría A.
Published: April 2003

Dynamic viscoelastic measurements on poly(vinyl chloride)/dioctyl phthalate gels have been carried out in parallel‐plate shear mode. Two transitions are observed: the well‐known gel‐sol transition at temperature Tf, which probably corresponds to the beginning of fusion of crystalities, and a transition, at a temperature below Tf, denoted as Ts and corresponding to phase separation. The sub(gel‐sol) Ts temperature is manifested as the transition from the first plateau zone to a second plateau in log G' versus temperature plots. Other techniques like polarizing microscopy and DSC measurements are not adequate for the detection of Ts.
Composition analysis of an ethylene–propylene block copolymer by fractionation and turbidity measurements at the lower critical solubility gap
Authors: Besombes Michel , Menguel Jean‐Francois , Delmas Genevieve
Published: April 2003

The composition of an ethylene‐propylene block copolymer with a nominal 15% content of ethylene by weight (EP−B15%) has been investigated through fractionation near the lower critical solution temperature (LCST). Observation of the solution heated above the boiling point of the solvent indicated that some polymer was phase separating, apparently continuously, between the LCSTs of polyethylene (PE) an polypropylene (PP) of similar molecular weight. IR and DSC analysis of three fractions obtained by twice separating the concentrated phase from the dilute phase gave the following result: EP−B15% consists of an ethylene‐rich block copolymer (93% E), an EP copolymer of intermediate composition, and a propylene‐rich copolymer (94% P). The three fractions constitute respectively 12%, 12%, and 76% of the total weights. In order to choose a suitable temperature for fractionation, a turbidity analysis of the solution of the initial polymer is made continuously during phase separation. The trace of turbidity against temperature shows three peaks of turbidity at temperatures T0, T1 and T2, which can be associated with the above fractions. A mixture of PE, PP, and a 33% E random copolymer gives a turbidity trace with characteristic temperatures very similar to that of EP‐B15% in the same solvent. Fractionation from several solvents or mixtures of solvents indicated that the composition of the fractions did not depend significantly on the nature of the solvent. Conditions for obtaining a quantitative analysis of a mixture from a thermogram are discussed. Turbidity analysis during phase separation and fractionation at the LCST can be a useful tool in analyzing and separating complex mixtures before use of powerful analytical techniques such as NMR or IR spectroscopy.
Statistics of polymer chains in orienting fields
Authors: Walasek Janusz
Published: April 2003

The theory of a freely jointed polymer chain is modified by introduction of interactions between dipole chain segments and an orienting field. Such a field results either from external forces (e.g. external electric or magnetic fields) or represents interactions between dipole segments of chains (molecular mean‐field). The distribution of orientations of chain segments and the free energy of a chain in such orienting fields are calculated and discussed.
Calorimetric relaxation and glass transition in poly(propylene glycols) and its monomer
Authors: Johari G. P. , Hallbrucker Andreas , Mayer Erwin
Published: April 2003

The glass transition temperature Tg of propylene glycol (PG) and poly(propylene glycols) (PPGs) of molecular weight up to 4000 has been measured by differential scanning calorimetry, and the activation energy and change in heat capacity ΔCp have been determined in the glass transition range. The activation energy increases with an increase in the molecular weight of the polymer, and ΔCp measured at a fixed heating rate decreases. The increase in Tg with molecular weight is remarkably more rapid for poly(propylene glycols) than for other polymers, and a limiting value of Tg is reached for a chain containing 20 monomer units. These results are discussed in terms of the Fox‐Flory and the entropy theories. The calorimetric relaxation times are comparable with the extrapolated dielectric relaxation times. The initial increase of ΔCp from PG to PPG 200 is attributed to the decrease of H‐bonding sites from 12 in 3 monomers to 4 on polymerization to PPG 200 and further decrease with increase in molecular weight to an increasingly large amplitude of the β‐process at T < Tg.
Single‐crystal‐like orientation of ultrahigh‐molecular‐weight polyethylene by uniaxial stretching
Authors: Seoul Chang , Kim Sang Yong
Published: April 2003

Dried gel film of ultrahigh‐molecular‐weight polyethylene (UHMW PE) can be drawn to 370 times its original length at 135°C. Single‐crystal mats and dried gel film of UHMW PE develop double orientation despite uniaxial stretching. This is unique for preferentially oriented UHMW PE systems. To elucidate the origin of this single‐crystal‐like orientation, precursors with different aspect ratios were prepared and drawn uniaxially. The degree of double orientation was measured by infrared spectroscopy. The origin of single‐crystal‐like orientation seems to reside in the necking region. The stacked lamellar structure is transformed into a fibrillar structure in a two‐dimensional fashion. This condition is easily provided when UHMW PE single‐crystal mat or dried gel film is drawn uniaxially. A draw ratio of 40 and aspect ratio of 40 are the optimal conditions to obtain a doubly oriented structure from UHMW PE single‐crystal mat or gel film at 135°C.
A 13C CP‐MAS NMR study of irradiated polyethylene
Authors: Pérez E. , Vanderhart D. L.
Published: April 2003

Solid‐state 13C‐NMR was used to analyze several polyethylene samples, irradiated at room temperature with gamma rays in vacuum or with electrons in air up to a maximum dose of 200 Mrad. The main observed events were the formation of methyl ends and interior double bonds (vinylenes), as well as the disappearance of the initial vinyl ends. No signals associated with “H” or “Y” crosslinks were found in any of the samples.

The partitioning of methyl ends and interior vinylenes between the crystalline and noncrystalline regions was determined only for the irradiated ultrahigh‐molecular‐weight polyethylene (UHMWPE) samples. Although concentration of methyl ends in the crystalline regions was approximately half that in the noncrystalline regions, the vinylenes had very similar concentrations in the two phases. Although some evidence for both cis and trans vinylenes appears in the spectrum of the noncrystalline regions, only one configuration (trans) seems to exist in the crystalline regions. No appreciable effect on the partitioning was detected after annealing the electron‐irradiated UHMWPE samples for 16 h at 130°C.
Kinetic analysis of curing of tetraepoxides and diamines in the presence of etherification side reactions
Authors: Tsou Andy H. , Peppas Nikolaos A.
Published: April 2003

The theory of branching processes is used to describe the polymer network formation resulting from the reaction of tetraepoxides with diamines using various initial compositions. Differences in reactivities of primary and secondary amine groups and the reaction between the epoxide groups and reaction‐generated hydroxyl groups are taken into account; however, intramolecular reactions in the pregel stage are neglected. Expressions are derived for the critical epoxide conversion at the gel point, molecular weight in the pregel stage, changes in sol and gel fraction in the post‐gel stage, and the concentration of elastically active network chains as a function of reaction conditions. The analysis of the simulation results shows that etherification reactions significantly raise the concentration of elastically active network chains of the mixture under stoichiometric excess of epoxide groups.
A study of surface dynamics of polymers. III. Surface dynamic stabilization by plasma polymerization
Authors: Yasuda T. , Yoshida K. , Okuno T. , Yasuda H.
Published: April 2003

As demonstrated in Part II of this series of studies, the hydrophobic character of CF4 plasma‐treated Nylon 6 and poly(ethylene terephthalate) (PET) decay with time of water immersion, and the rate of decay can be used as a measure for the surface mobility of (substrate) polymers. The same method of using fluorine‐containing moieties introduced by CF4 plasma treatment as surface labeling is applied to investigate the influence of a thin layer of plasma polymer of methane applied onto the surface of those polymers. An ultrathin layer of plasma polymer provides a barrier to the rotational and diffusional migration of the introduced chemical moieties from the surface into the bulk of the film. The influence of operational parameters of plasma polymerization on the surface dynamic stability are examined by measuring the decay rate constants for (subsequently) CF4 plasma‐treated samples. The rate constant was found to decrease sharply with increasing value of plasma energy input manifested by J/kg monomer, and no decay was observed as the energy input reached a threshold value (about 6.5 GJ/kg for PET, about 7.0 GJ/kg for Nylon 6), indicating that unperturbable surfaces can be created by means of plasma polymerization.
Copolymerization of ethylene and butadiene with supported titanium catalyst
Authors: Sun Lixin , Lu Zejian , Lu Yun , Lin Shangan
Published: April 2003

The copolymerization of ethylene and butadiene with a supported titanium catalyst (TiCl4/MgCl2/EB/Φ2SiCl2/AlEt3) is described. The resulting products were characterized by IR, 13C‐NMR, x‐ray diffraction, differential thermal analysis, electron microscopy, and solvent extraction. It was found that the butadiene units are substantially in trans‐1,4 configuration and blocked sequences. Both ethylene and butadiene blocks form crystalline phases. The presence of unsaturated bonds made it possible to graft MMA and maleic anhydride. The influences of monomer composition, temperature, Al/Ti ratio, catalyst concentration, and solvents on the copolymerization were investigated.
Radiation hardening of polytetrafluoroethylene against chemical etching
Authors: Rye R. R.
Published: April 2003

Exposure of polytetrafluoroethylene (PTFE) to MgKα x‐rays (1253.6 eV) for times as short as 10 min is observed to lead to permanent radiation hardening toward chemical etching. X‐ray‐dosed surfaces are visibly less etched, and the loss of F is over a factor of 2 smaller. For PTFE itself, the x‐ray photoelectron spectrum shows only slight changes for x‐ray exposures up to several hours, but thermal desorption spectroscopy yields a direct correlation between the desorption of low‐molecular‐weight fluorocarbons and x‐ray exposures down to the order of minutes. Irradiation of PTFE is know to lead to molecular weight degradation and branching and/or crosslinking through free radical reactions. The degradation reactions are the source of the low‐molecular‐weight fluorocarbons which desorb at elevated temperatures. Branching and/or crosslinking, which produce a more rigid, thermally stable structure, are proposed as the mechanism for resistance to chemical etching. Similar resistance to chemical etching, in the absence of x‐rays, is observed for the fluorinated ethylene‐propylene copolymer which contains intrinsic fluorinated methyl group side chains.
The effect of morphology on the transport of dichloromethane in poly(aryl‐ether‐ether‐ketone)
Authors: Grayson Michael A. , Wolf Clarence J.
Published: April 2003

A study of the transport of the dichloromethane in neat poly(aryl‐ether‐ether‐ketone) (PEEK) samples with thicknesses from 0.08 to 3.0 mm with different morphologies was conducted at 35°C. Both sorption and desorption of the solvent were studied. Thermal annealing was used to vary the sample morphology, and density measurements were used to determine the crystallinity of the samples. The equilibrium concentration of solvent and rate of solvent sorption were found to vary with sample morphology. The density of the dichloromethane when in the PEEK resin was found to be 1.65 g/cm3. Solvent desorption was independent of sample morphology or any previous sample treatment and depended only upon desorption temperature. Solvent sorption appears to alter the morphology of amorphous samples by increasing the crystallinity to about 20% after one sorption/desorption cycle. Small amounts of the solvent, less than 0.5 wt.%, remain trapped in fully desorbed samples. The micromorphology of solvent‐induced crystallization appears to be different from that induced by thermal treatment.
Elastomer reinforcement from a glassy polymer polymerized in situ
Authors: Fu F.‐S. , Mark J. E.
Published: April 2003

Cross‐linked networks of poly(dimethylsiloxane) were swelled with styrene containing benzoyl peroxide. Polymerization of the styrene in situ, by increasing the temperature, gave novel elastomeric composites. Scanning electron micrographs suggest that low concentrations of styrene (∼ 14 wt.%) gave primarily low‐molecular‐weight polystyrene (PS), which acted merely as a diluent in the networks. Larger amounts gave PS which phase separated into glassy particles having diameters in the approximate range 0.05–1.5 μm. In these cases, an increase in wt.% PS gave networks showing large increases in ultimate strength, which was to be expected. Surprisingly, there were also increases in maximum extensibility, which usually decreases in response to modifications which increase the ultimate strength.
Blends of poly(vinyl methyl ether) with styrenic copolymers
Authors: Min K. E. , Paul D. R.
Published: April 2003

Blends of poly(vinyl methyl ether) (PVME) with styrene/acrylonitrile (SAN), with styrene/maleic anhydride (SMA), and with styrene/acrylic acid (SAA) copolymers were examined for glass transition and lower critical solution temperature behavior. These copolymers were found to be completely miscible with PVME at levels of 3% or less of AA; below 10–11% AN, and below 15% MA (w%). Small amounts of the comonomers raised the temperature at which blends with PVME undergo phase separation on heating. This effect was greatest in the order AA > AN > MA. An interpretation of these results is given in terms of recent theories for homopolymer‐copolymer blends, and the extent to which solubility parameter theory can be useful is considered.
Rheology and phase separation in polystyrene/poly(vinyl methyl ether) blends
Authors: Ajji A. , Choplin L. , Prud'homme R. E.
Published: April 2003

Blends of monodisperse polystyrene and poly(vinyl‐methyl‐ether) of various compositions were prepared from solution in benzene. Dynamic rheological properties of these blends were studied at different temperatures below, near, and above Ts, the temperature of phase separation, and in a frequency range from 0.05 to 100 rad/s. A flattening in the storage modulus and an initial plateau for the complex viscosity were observed near and above Ts in the low‐frequency region; in contrast, below Ts the behavior of the blends was similar to that of the homopolymers. The WLF superposition principle applies only at temperatures below Ts, i.e., in the miscible and homogeneous region. G″ versus G′ representations for the blends were found to be independent of temperature and to vary with composition in the miscible region but are temperature and composition‐dependent in the immiscible region. It is also shown that the η″ versus η′ representation is a useful tool for characterizing phase separation of blends and is more sensitive than the classical frequency dependence of the material functions.
Network architecture and modulus of miscible heteropolymer blends
Authors: Tsenoglou Christos
Published: April 2003

The architecture and entanglement density of a multicomponent polymer network composed of miscible, flexible chains is related to the corresponding properties and concentrations of the pure components. It is assumed that the coupling frequency between different chain species is proportional to their fractional participation in the blend and that the entanglement ability of polymers can be affected by the presence of heteropolymer neighbors. The theory, equally applicable to temporary and permanent networks, estimates the molecular weight between entanglements and their total number along a chain in the blend. This information is used in establishing a mixing law for the rubbery plateau modulus of a fluid polymer blend and in deriving a relationship for the equilibrium modulus of an interpenetrating polymer network containing trapped entanglements and dangling segments. The theoretical predictions are compared with experimental results from the literature on several miscible polymer blends.
Thermal cycling of glasses. II. Experimental evaluation of the structure (or nonlinearity) parameter x
Authors: Hutchinson J. M. , Ruddy M.
Published: April 2003

The structure parameter x (also known as the nonlinearity parameter), which in the KAHR model determines the relative contributions of temperature and structure to the retardation times of polymers in the glass transition region, is evaluated experimentally for a narrow molecular weight fraction of atactic polystyrene by the peak‐shift method. This method is based on the dependence on heating rate and annealing time of the endothermal peak temperatures Tp, obtained by differential scanning calorimetry during the heating stage of well‐defined three‐step thermal cycles. The results obtained from the shifts of Tp, with both heating rate and the amount of isothermal recovery during the annealing stage before reheating, are consistent with the theoretical predictions of the KAHR model. The appropriate analysis of the data for a polystyrene fraction of molecular weight 30,100 leads to a value of x = 0.46 ± 0.02. Furthermore, this value of x is constant for a wide range of annealing times and heating rates and for two different annealing temperatures, in full agreement with the theoretical model. The advantages of the peak‐shift method over that used by most other workers, the curve‐fitting method, are critically discussed.
Computer simulation of a binary polymer mixture in three dimensions
Authors: Cifra P. , Karasz F. E. , MacKnight W. J.
Published: April 2003

The behavior of a binary polymer mixture was simulated on a cubic lattice over both the miscibility and immiscibility regions. The number and distribution of interactions in the mixture were found to be different from the mean‐field picture; however, the observed phase behavior agrees with that predicted by the mean‐field theory and is not affected by the observed concentration fluctuations. The relationship between the phenomenological χ parameter and the heterosegmental interaction energy was investigated. Polymer chains show nearly ideal behavior, even for strongly interacting mixtures; this simplifies the theoretical treatment of polymer mixtures analogous to homopolymer melts.
Relaxation processes and structure of ultradrawn polyethylene
Authors: Failla M. D. , Carella J. M. , De Micheli R.
Published: April 2003

Solid‐state extruded polyethylene fibers have been prepared, with a wide range of draw ratios and constant processing temperature. The draw ratios vary from 4 up to 30, and the processing temperature was always 398 K. The extruded material behaves anisotropically, owing to the high degree of chain orientation in the drawing direction. The modulus and linear expansion coefficients in the fiber axis direction have been measured, over a wide temperature range, from 140 K up to 320 K. These two properties are closely related to the degree of structural continuity of the fibers. A fibrous structure model is proposed to explain the temperature effects and the values obtained for the modulus and expansion coefficients, in terms of crystallinity and volumetric fraction of extended‐chains structure. At least three relaxation processes can be identified which cause the structural continuity of the fibers to change with temperature.
Strain and temperature accelerated relaxation in polycarbonate
Authors: Yee A. F. , Bankert R. J. , Ngai K. L. , Rendell R. W.
Published: April 2003

The nonlinear viscoelastic behavior of glassy polymers and its relationship to ductile yielding is studied by single‐ and double‐step stress relaxation experiments. In the latter case a small stress relaxation step is superimposed on a specimen at an elevated state of temperature or strain. The results show that the changes in the relaxation behaviors in the two cases closely parallel each other. The relaxation behavior at strains near yield closely approximates that at low strain but near Tg. The small strain relaxation response can be described well by a Kohlrausch‐Williams‐Watts (KWW) type function. The interpretation of these data in terms of a coupling model which includes the KWW form is discussed.
NMR Approach to the kinetics of polymer crystallization. II. Polydimethylsiloxane solutions
Authors: Feio G. , Buntinx G. , Cohen‐Addad J. P.
Published: April 2003

The dilution effect on the crystallization kinetics of PDMS/toluene solutions, ranging from a polymer volume fraction of ϕ = 1.00 (pure PDMS) to ϕ = 0.32, was studied using 1H high‐power NMR. Spin‐spin magnetic response was analyzed into relaxation components, arising from the different phases of the semicrystalline sample, through a spin‐echo technique. The intensity and shape of the amorphous component provide relevant information concerning (1) the global crystallization process and (2) the state of hindrance of the amorphous chains induced by the growing crystalline domains. It was shown that, in solutions, the main effect on the crystallization kinetics of changing concentration is to depress the equilibrium melting temperature of the system. However, a radically distinct crystallization rate between the pure and the more concentrated system must be explained in terms of the activation energy for interphase chain transport. Thermodynamic parameters of PDMS crystallites were also deduced from a model. Comparison between the isothermal development of the overall crystallinity and the variation of a characteristic relaxation time of the amorphous PDMS proton response gives an insight into the relative predominance of nucleation or growth rates in the crystallization mechanisms.
Infrared study of phase transitions in thermotropic liquid crystal polyesters
Authors: Benedetti Enzo , Galleschi Franco , Chiellini Emo , Galli Giancarlo , Lenz Robert W.
Published: April 2003

Three samples of semiflexible thermotropic liquid‐crystalline polyesters based on mesogenic aromatic triads and a decamethylene spacer have been investigated by IR spectroscopy at various temperatures between room temperature and 290°C. The crystal‐to‐liquid crystal (either nematic or smectic) phase transition was accompanied by fairly strong spectral variations, whereas slight, but significant, changes in the IR profiles were detected at the liquid crystal‐to‐isotropic transition. By comparing the results obtained with the spectral behavior recorded for corresponding structural analogs of low molar mass, it was possible to attribute the spectral variations observed in the polymer samples to a decrease in intermolecular interactions rather than to conformational changes. The thermal transitions indicated by IR spectra were in good agreement with the analogous data obtained by calorimetric or optical microscopy techniques.
The transport of oxygen through oriented poly(ethylene terephthalate)
Authors: Slee J. A. , Orchard G. A. J. , Bower D. I. , Ward I. M.
Published: April 2003

The transport of oxygen through oriented PET at 25 and 60°C has been studied using the dynamic diffusion method. It did not prove possible to determine the diffusion and solubility coefficients with reasonable accuracy, and only the permeability coefficients are discussed in terms of the structure of the samples. The results suggest that the lowering of the oxygen permeability on drawing is related to the production of additional material with the trans conformation of the glycol residue, either in crystallites or in amorphous regions, rather than solely to the overall development of orientation or crystallinity.
Stochastic concepts in the study of size effects in the mechanical strength of highly oriented polymeric materials
Authors: Wagner H. D.
Published: April 2003

A study of size effects in the ultimate mechanical properties of crystalline and semicrystalline polymeric materials (fibers, single crystals) is conducted. The concept of size effect and its importance are discussed. A statistical/stochastic approach is adopted and is shown to yield analytical predictions which are at least as accurate as other modeling schemes (mainly based on fracture mechanics theory) previously proposed in the literature. Within this framework, we propose a possible scheme for simultaneous interpretation of both longitudinal (gauge length) and transversal (diameter) size effects, which provides some interesting information regarding the type of flaw population present in a given polymeric material. The statistical scheme used is based on the Poisson/Weibull model, and variants of it, since this model is relatively well established from both physical and experimental viewpoints. Some unsolved problems inherent to the Weibull/weakest link model for failure are discussed, and a new distribution function for the strength of solids is derived. This is illustrated through an analysis of available experimental data for ultrahigh‐molecular‐weight polyethylene, poly‐p‐phenylene terephthalamide (Kevlar), polydiacetylene, and polyoxymethylene. A maximum likelihood approach is used for the first time for interpreting the effect of diameter variability on the mechanical strength of polymeric fibers. We propose a procedure by which the Weibull shape parameter is maximized over a continuous range of values of the size exponent. Finally, we conjecture on the relative roles of defect populations distributed over the boundary and in the bulk.
On the diffusion of gases in partially crystalline polymers
Authors: Horas J. A. , Rizzotto M. G.
Published: April 2003

The diffusion of gases through partially crystalline polymers is studied. The effective diffusion coefficient Deff is obtained as the result of the averaged superposition of two fundamental mechanisms, namely, diffusion through the crystallites is considered to be zero, and diffusion through the rubbery fraction of the polymer obeys a Fujita‐like free‐volume theory. The predicted Deff is compared with experimental data of Kreituss and Frisch. The behavior of the diffusion coefficient in terms of concentration and crystalline fraction is satisfactorily explained through the model.
The effect of plasticization on the transport of gases in and through glassy polymers
Authors: Zhou S. , Stern S. A.
Published: April 2003

The effects of plasticization on the transport of gases and vapors in and through glassy polymers are examined from the viewpoint of the “dual‐mode” sorption model with partial immobilization. The analysis assumes the existence of two penetrant populations with different mobilities in the Henry's law and Langmuir domains of the glassy polymers. These mobilities are characterized by their mutual diffusion coefficients DD and DH. The plasticization of the polymer by penetrant gases is reflected in the concentration dependence of DD and DH. Expressions for the effective (apparent) diffusion and permeability coefficients are derived assuming that DD and DH are exponential functions of the penetrant concentration in the polymers. The results of this study are compared with a similar analysis which assumed the existence of a single mobile penetrant population. The present analysis provides information on the effects of plasticization on the penetrant transport in the Henry's law and Langmuir domains separately. The effects of antiplasticization or clustering of penetrant molecules on the effective diffusion and permeability coefficients are also examined.
Fourier transform infrared study of conformational changes occurring at the yield point in uniaxially drawn polymers
Authors: Xu Z. , Jasse B. , Monnerie L.
Published: April 2003

Fourier‐transform infrared measurements on atactic and amorphous isotactic polystyrenes have been made during application of strain. On passing through the yield point, spectra indicate an increase of the amount of higher‐energy conformation. In atactic polystyrene it corresponds to an increase of gauche conformations whatever the state may be: pure or plasticized samples, blend with another compatible polymer, or styrene‐acrylonitrile copolymer. In amorphous isotactic polystyrene an increase of higher‐energy trans conformation is observed. These results strongly support the theory developed by Robertson to explain plastic deformation of polymers.