Showing papers in "Journal of Polymer Science Part B in 1984"

Dynamic mechanical studies of α and β relaxations of polyethylenes

Abstract: Relaxations α et β d'une variete de polyethylenes etudiees en detail par des methodes mecaniques dynamiques a basse frequence

An analysis of the crystallization behavior of poly(ethylene oxide)/poly(methyl methacrylate) blends by spectroscopic and calorimetric techniques

Abstract: Cristallisation et changements microstructuraux du PEO dans ces melanges par spectroscopie IR et calorimetrie differentielle

The thermodynamic properties of polytetrafluoroethylene

Abstract: Polytetrafluoroethylenes of different crystallinity were analyzed between 220 and 700 K by differential scanning calorimetry. A new computer coupling of the standard DSC is described. The measured heat capacity data were combined with all literature data into a recommended set of thermodynamic properties for the crystalline polymer and a preliminary set for the amorphous polymer (heat capacity, enthalpy, entropy, and Gibbs energy; range 0–700 K). The crystal heat capacities have been linked to the vibrational spectrum with a θ3 of 54 K, and θ1 of 250 K, and a full set of group vibrations. Cv to Cp conversion was possible with a Nernst–Lindemann constant of A = 1.6 × 10−3 mol K/J. The glass transition was identified as a broad transition between 160 and 240 K with a ΔCp of 9.4 J/K mol. The room-temperature transitions at 292 and 303 K have a combined heat of transition of 850 J/mol and an entropy of transition of 2.90 J/K mol. The equilibrium melting temperature is 605 K with transition enthalpy and entropy of 4.10 kj/mol and 6.78 J/K mol, respectively. The high-temperature crystal from is shown to be a condis crystal (conformationally disordered), and for the samples discussed, the crystallinity model holds.

FT‐IR study of intermolecular interactions in polymer blends

Abstract: Application de cette technique d'un melange homogene chitosane-alcool polyvinylique afin d'elucider les mecanismes moleculaires impliques dans ses proprietes mecaniques

Creep behavior of ultrahigh‐modulus polyethylene: Influence of draw ratio and polymer composition

Abstract: The creep behavior of ultrahigh-modulus polyethylene monofilaments has been studied over the temperature range 20–70°C. A wide range of samples was examined in an attempt to determine the influence of draw ratio, molecular weight, copolymerization, and crosslinking by γ irradiation Prior to drawing. Results are also presented for a solution-spun fiber. It is proposed that the permanent flow creep arises from a combination of two creep processes, one of which is associated with the crystalline regions of the oriented structure and the other with a molecular network.

X-ray scattering from amorphous acrylate and methacrylate polymers: Evidence of local order

Abstract: X-ray scattering patterns from amorphous polymers frequently contain halos corresponding to distances significantly greater than that of van der Waals packing of carbon atoms. Regularities in the positions of such halos as a function of pendant group size have been reported, primarily for the “crystallizable” comb polymers. This work concerns n-alkyl acrylate, n-alkyl methacrylate, and cycloalkyl methacrylate polymers with small alkyl groups: regularities in halo position with alkyl group size are seen, but the behavior with size is quantitatively different from that of the comb polymers. A case is made for the existence of a moderate amount of intersegmental order as the normal condition in the condensed amorphous state. The behavior of poly(methyl methacrylate) is anomalous and studies on it may not be used to generalize about the structure of the amorphous state.

Crystalline order and melting behavior of isotactic polypropylene (α form)

Abstract: The dependence of the order in the orientation of the chains in the crystalline structure on the crystallization temperature is described for the α-form of isotactic polypropylene.

Phase segregation kinetics in segmented linear polyurethanes: Relations between equilibrium time and chain mobility and between equilibrium degree of segregation and interaction parameter

Abstract: The kinetics of phase segregation of segmented linear polyurethanes, from a homogeneous single-phase system into a two-phase one, have been studied by measuring the heat capacity change at the glass transition of the soft phase. The extent of phase segregation at equilibrium is a linear function of the Flory–Huggins interaction parameter χ. For χ lower than about 3, no segregation can take place. This value, higher than expected theoretically, indicates forced compatibility due to chemical links between soft and hard blocks of the segmented polyurethanes. The time required to attain equilibrium is not a function of thermodynamic parameters but of the chain mobility. A linear relation is proposed between the logarithm of equilibrium time and the viscosity of the pure soft phase.

The effects of morphology on 1H NMR spectra and relaxation in semicrystalline polyolefins

Abstract: Bref resume du role de l'heterogeneite structurale, des couplages magnetiques dipolaires, de la structure moleculaire et du mouvement moleculaire dans la determination des spectres RMN du proton et des proprietes de relaxation de solides heterogenes tels que les polymeres semicristallins. Mesures de la relaxation spin-reseau du proton en labo et en referentiel tournant pour du polyethylene cristallise en solution et au fondu, du polypropene isotactique recuit et trempe et du polybutene-1 isotactique

Morphological and structural changes in a copolymer of glycolide and lactide occurring as a result of hydrolysis

Abstract: The changes in the structure and morphology of a random copolymer containing 92 mol % glycolide units and 8 mol % lactide units as a function of in vitro hydrolysis have been studied. A number of techniques, such as wide-angle x-ray diffraction, small-angle x-ray scattering, density measurements, infrared spectroscopy, and viscometry were employed in this study. The results showed that the hydrolytic attack was initiated in the amorphous areas of the polymer. After 28 days in the in vitro medium most of the amorphous areas had been chemically converted to lower-molecular-weight species such as oligomers of poly(glycolide-co-lactide). These low-molecular-weight species become water solble and are removed rapidly after day 28. Thus the fiber takes on a Swiss cheese character as the amorphous matter is hydrolyzed and eventually dissolved. As hydrolysis proceeds further, the crystalline areas of the polymer are attacked and eventually removed from the fiber by solubilization. The resulting voids in the fiber are eventually filled by a “collapse” of the structure. The role of the amorphous areas of the polymer in controlling the tensile strength of the suture is discussed.

A small‐angle X‐ray scattering study of an aromatic polyimide

Abstract: The morphology of isotropic films of poly[N,N'-bis(phenoxyphenyl)-pyromellitimide] was investigated by means of small-angle x-ray scattering. A significantly different morphology was found to develop in these films as compared to that in films possessing as in-plane molecular orientation. It was found that morphology could be described by a damped periodic modulation in the electron density characteristic of a chain segment aggregation. An increase in the initial imidization temperature resulted in an overall increase in the lateral packing of the chains and a reduction in the amplitude of the density modulation. Evidence was also found for segmental aggregation in the precursor polyamic acid which contained up to 35% solvent.

Self-diffusion in polymer-solvent-solvent systems

Abstract: Les donnees d'autodiffusion ternaire de Ferguson et von Meerwall sont analysees en utilisant une forme generalisee de la theorie du volume libre proposee par Vrentas et Duda

Shear‐induced coalescence in two‐phase polymeric systems. I. Determination from small‐angle neutron scattering measurements

Abstract: It has been found that flow-induced coalescence occurs at a very rapid rate during the mixing of polymeric fluids. Furthermore, the rheological properties of the dispersed and continuous phases, as well as the nature of the flow field used in their blending, can greatly influence this coalescence. The significance of these findings is that in the development of a mixing scheme to obtain a desired morphology with minimum expenditure of time or energy, attention is usually focused only on the particle breakup aspects of the blending process. The competing coalescence can, however, be accelerated by the same conditions often employed to facilitate particle breakup (e.g., higher shear rates, reduced dispersed-phase viscosity). A better understanding of the mechanism for coalescence of viscoelastic fluids is clearly required. In this manner optimal blending of immiscible polymers can be achieved with respect to both the nature of the final material and the ease with which it is obtained.

Selective permeation of CO2 and CH4 through kapton polyimide: Effects of penetrant competition and gas-phase nonideality

Abstract: Sorption isotherms for pure CO2 and pure CH4 in Kapton H® polymide films at 60°C are reported for pressures up to 20 atm and are analyzed in terms of the dual-mode sorption model An experimental scheme for the measurement of steady-state permeabilities of both pure and mixed gas feeds is described Permeabilities of Kapton to the individual components at 60°C are presented for a mixture comprised of 322% CO2 in CH4 as functions of feed pressure up to 590 psi (absolute) The permeabilities for the individual penetrants in the mixed feed are lower than the respective purecomponent values at the corresponding partial pressures Furthermore, the permeabilities of both penetrants drop as the feed pressure is increased at constant composition The dual-mobility transport model used to analyze the data postulates that the observed pressure and composition dependence of the permeabilities is due to competition between penetrants for a limited microvoid sorption capacity in the glassy polymer It is demonstrated that in addition to flux depressions due to dual-mode effects, nonideality of the gas phase must be accounted for to explain the substantial flux depressions observed for the CO2/CH4 mixtured used in this study

Crazing and shear deformation in crosslinked polystyrene

Abstract: Thin films of polystyrene (PS) are bonded to copper grids and crosslinked with electron irradiation. When the films are strained in tension regions of local plastic deformation, either crazed or plane stress deformation zones (DZs), nucleate and grow from dust particles. the nature of the local deformation, as well as the local extension ration λ, is determined by transmission electron microscopy. The behavior of the PS glass is consistent with its being a network of molecular strands of total density v = vE + vX, where vE is the entangled strand density inferred from melt elasticity measurements of uncrosslinked PS and vX is the density of crosslinked strands determined from the ratio of the applied electron dose to the electron dose for gelation. when v is less than 4 × 1025 m−3 ( 20% in PS with v = 33 × 1025 m−3 (v = 10vE); crosslinking to still higher crosslink densities, e.g., v = 14vE, results in cracks which propagate in a catastrophic manner at low applied strains. An optimum v thus exists, one not too high to suppress local shear ductility but high enough to suppress crazes which can act as crack nucleation sites. these results are compared with previous results on a variety of linear homopolymers, copolymers, and polymer blends that are characterized by a wide range of v (v = vE). The transitions from crazing to crazing plus shear and from crazing plus shear to shear only take place at almost identical values of v. In addition the correlation between λ in the crazes and DZs and λmax for a single network strand is the same for both classes of polymers. This agreement implies that chain scission is the major mechanism by which strands in the entanglement network are removed in forming fibril surfaces. Craze suppression, by either increasing v in the crosslinked polymer or vE in the uncrosslinked ones, is due to the extra energy required to break more main-chain bonds to form these surfaces.

Morphology of conducting organic polymers: Polythiophene and poly(3‐methyl thiophene)

Abstract: Polythiophene and substituted polythiophene can be electrochemically generated as very adhesive thin films or as thick powdery deposits. The homogeneity of the thin films is very high, but it decreases when the film thickness is increased. Scanning electron microscopy shows that the nature of the dopant strongly influences the film morphology. Transmission electron microscopy reveals mainly a fibrillar structure, with a fibril diameter of 200 A in the undoped state, and 800 A in the doped conducting state.

The dependence of yield behavior on temperature, pressure, and strain rate for linear polyethylenes of different molecular weight and morphology

Abstract: The temperature, strain-rate, and pressure dependences of the yield stress have been determined for two polyethylene homopolymers of differing molecular weights and for a polyethylene copolymer. Samples were prepared by slowly cooling from the melt, and also by quenching in order to assess the effects of morphology on the yield behavior. The data have been analyzed on the basis of two Eyring processes acting in parallel. Comparison of all data sets reveals the existence in general of three distinct activated processes each with its own temperature, strain-rate, and pressure dependences. The relative contribution of each process is dependent on the molecular weight, morphology, etc. Also discussed is the relation of these three yield processes to the well-known loss processes of linear viscoelasticity.

Hard‐segment polymorphism in MDI/diol‐based polyurethane elastomers

Abstract: X-ray analyses of methylene-bis(4)phenyl isocynate(MDI)/diol/poly(tetramethylene adipate) polyurethane elastomers prepared using hexanediol (HDO), butanediol (BDO), and propanediol (PDO) point to the development of a second crystalline structure in the hard segments as a result of thermal elongation and annealing. The HDO polymer crystallizes initially in the fully extended conformation, but a second crystal structure, a contracted form, develops with stretching and annealing at 130°C. In contrast, the BDO and PDO polymers crystallize initially in contracted conformation, but fully extended forms develop as a result of elongation and annealing. Only a contracted conformation has been seen so far in hard segments prepared using ethylene glycol (EDO) as the chain extender. These results correlate very well with DSC data for the same polymers. The development of the new crystal structures is accompanied by the appearance of new hard-segment melting peaks in the DSC traces. For the HDO polymer, the new peak for the contracted form appears at a higher temperature than that for the original extended form; for the BDO and PDO polymers the new peaks for the extended forms appear at lower temperatures than those for the contracted forms. Only a single peak is seen for the EDO polymer, for which only one crystal structure has been detected for the hard segments. These results indicate that the development of polymorphic crystal structures must be taken into account in interpreting the multiple melting phenomena seen for the hard domains in polyurethane elastomers.

The effect of crystallinity and crosslinking on the depression of the glass transition temperature in nylon 6 by water

Abstract: The influence of crystallinity and crosslinking on the depression of the glass transition temperature in nylon 6 by water has been investigated by dynamic mechanical methods. Radiation crosslinking by high-energy electrons was effective in preventing morphological changes during the measurement of the incremental change in heat capacity (ΔCp) at Tg, which was performed by differential scanning calorimetry. The experimentally determined value of ΔCp, when normalized to account for the crystalline phase, was found to deviate from a linear two-phase relation and was reduced further than would be expected based on this model. It is proposed that nylon 6 is best described by a three-phase model which consists of a crystalline domain, a wholly amorphous domain, and an “intercrystalline” region. The importance of this in explaining the relatively large depression of Tg by small quantities of water is illustrated by applying equations derived to account for the compositional dependence of Tg in polymerdiluent mixtures, based on a classical thermodynamic interpretation of the glass transition phenomenon.

Isobaric thermal behavior of glasses during uniform cooling and heating. III. Predictions from the multiparameter KAHR model

Abstract: The behavior of the multiparameter KAHR model (put forward by Kovacs, Aklonis, Hutchinson, and Ramos) has been investigated using a single-box retardation spectrum to describe the kinetics of volume and enthalpy recovery of glasses in three-step thermal cycles involving colling, isothermal annealing, and subsequent reheating. It has been shown that during the heating stage, the system may display up to three peaks in the expansion coefficient and the specific heat. The shifts of the peak temperatures Tp with respect to each of the four experimental variables Yi defining the thermal history are analyzed systematically in terms of a set of reduced variables, scaled by two of the material constants of the system. These shifts, from which the various partial derivatives (∂Tp/∂Yi)j≠i are estimated, are determined for five values of another material parameter x, which characterizes the relative contributions (O ≤ x ≤ 1) of temperature and structure to the retardation times. the results show that the upper peak is always small and is insensitive to the characteristics of the spectrum and to the value of x, while the relevant peak temperature depens only slightly on the cooling and heating rates. On the Other hand, the magnitude and the shifts of the main peak depend on all the experimental variables and the material constants in a rather complex manner. It is shown, however, that in limiting situations, involving fast heating of well-stabilized glasses, the shifts of the relevant peak temperature Tall reduce to a linear function of x−1. since this relationship is rather insensitive to the shape of the spectrum, the experimental determination of any one of the nonzero partial derivatives of T provides a simple means for an independent estimate of the value of the important material constant x. Finally, the shifts of the upper and main peaks relative to each other will be analyzed in terms of the pertinent experimental variables and compared with actual data reported in the literature for polymer glasses.

Complex formation between enantiomeric polyesters

Abstract: Proprietes d'un racemique fait de poly-S et poly-R poly(α-methyl α-ethyl β-propiolactone) isotactiques (PMEPL). Etude du comportement de melanges poly-S/poly-R PMEPL contenant un exces de poly-S ou de poly-R (melanges binaires). Comportement de melanges ternaires de PMEPL racemique, poly-S PMEPL et poly-R PMEPL. Fusion et proprietes morphologiques de ces melanges et nombre limite de donnees cristallographiques

Optical studies of pyrolyzed polyacrylonitrile

Abstract: The results of measurements of the optical absorption spectra, IR absorption spectra, thermogravimetric analysis, and elementary analysis of pyrolyzed polyacrilonitrile are presented as a function of the pyrolysis temperature Tp and of the duration of pyrolysis. At Tp ∼ 200°C, an intermediate phase was discovered, containing conjugated CN sequences and a completely unreacted carbon backbone. The optical absorption data imply that the resulting polymer is a semiconductor with a delocalized π-electron system and an energy gap Eg ⋍ 2.5 eV. For Tp > 260°C, the weight loss rapidly increases, and the absorption edge gradually broadens and shifts to lower energies. The resulting polymer (after higher-temperature pyrolysis) contains CN and CCC conjugation sequences, but appears to be a complex structure consisting of a mixture of different chemical species.

Regularities in x‐ray scattering patterns from amorphous polymers

Abstract: It is known that the x-ray scattering pattern of an amorphous polymer may contain one or more halos corresponding to van der Waals spacings or larger. In this work we found that (i) the halo positions (and equivalent Bragg spacings) vary systematically with the cross-sectional area of the polymer chain in the crystal and (ii) there are at least two families of such halos with spacings larger than that of van der Waals contacts of atoms. From the wide variety and nature of the polymers considered, this behavior is believed to be representative of the amorphous state existing in polymeric samples. This work indicates that there is a degree of packing regularity in amorphous polymers that should be considered in models and theories of polymer chain conformation.

Drawing of ultrahigh‐molecular‐weight polyethylene single‐crystal mats

Abstract: Preparation de mâts de ces monocristaux, proprietes mecaniques dynamiques, chaleur et point de fusion par DSC, diagrammes de diffraction RX

Dependence of the elastomeric properties of bimodal networks on the lengths and amounts of the short chains

Abstract: Bimodal elastomeric networks were synthesized by tetrafunctionally end-linking very short and relatively long hydroxyl-terminated chains of poly(dimethylsiloxane) Decrease in the molecular weight of the short chains (from 880 to 660 to 460 g mol−1) generally results in significant increases in ultimate strength and energy for rupture Decrease in the number of short chains, however, causes these two quantities to go through a maximum Too many short chains gives essentially a brittle thermoset, and this precludes any upturn in the modulus from the limited extensibility of the short chains Having too few short chains makes their limited extensibility irrelevant since the entire macroscopic deformation can then be taken up by the long chains present in the network

Copolymers of 1,1‐difluoroethene with tetrafluoroethene, chlorotrifluoroethene, and bromotrifluoroethene

Abstract: Copolymers of 1,1-difluoroethene with tetrafluoroethene, chlorotrifluoroethene, and bromotrifluoroethene have been prepared by emulsion polymerization, and their crystallinity has been investigated by means of x-ray diffraction. The results are discussed in relation to copolymer composition and structure.

Heterogeneous nucleation of poly(ethylene terephthalate)

Abstract: The effect of various metal salts as nucleating additives for poly(ethylene terephthalate) (PET) has been investigated. In the case of sodium benzoate and probably for all other effective nucleating additives, the nucleation process can be divided into a “heterogeneous particle nucleation” performed by the unreacted salt and a “homogeneous nucleation” due to the polymer–sodium (metal) salt formed during the extrusion. This polymer–sodium (metal) salt is the major nucleating agent in these systems. We have also shown the fundamental difference between the concept of a nucleating additive and that of a nucleating agent.

The heat of fusion of 66 nylon

Abstract: The heat of fusion ΔHf of 66 nylon has been determined by use of the Clapeyron equation. Measurements of ΔHf and the unit-cell parameters on molding pellets show that this material contains the α2 crystal phase, which is less dense than the α1 phase obtained by crystallization from solution. The value of ΔHf-45–46 cal/g, is in good agreement with earlier reports.

Piezoelectric properties and molecular motion of poly(β‐hydroxybutyrate) films

Abstract: Mesures des proprietes piezoelectriques, elastiques et dielectriques de ce polymere naturel optiquement actif en fonction de la frequence et de la temperature