摘要:

AbstractThe effect of elasticlike uniaxial tension on molecular mobility in polymers have been studied over a wide temperature range using the broad‐line NMR technique. The studies were carried out on oriented semicrystalline samples of nylon 6, poly(ethylene terephthlate), polypropylene, polyethylene, polyoxymethylene, poly(vinyl alcohol), and polytetrafluorethylene. Above the low‐temperature transition the NMR spectra are reversibly transformed under tension. Increases in the second moments of the spectra are attributed to weaker molecular motion in stressed polymers. The only exception is polypropylene, in which the reverse, i.e., enhancement of molecular mobility, can be observed in a certain temperature range. In the spectra of polymers stretched above the glass transition temperature the narrow component decreases, thus indicating inhibition of micro‐Brownian motion, a phenomenon we call “mechanical vitrification.” Such mechanical vitrification is proved to result from reduction in the number of possible tie‐chain conformations in the non‐crystalline regions and not from closer packing of chains. In discussing the results we use the experimental data on the reduction of the number ofgaucheisomers under tension (on average, one transition of agauchelink to thetransstate causes at least five methylene groups in the main chain to become immobile). The results of studies of molecular mobility in stretched polymers are used for more accurate definition of the mechanisms of molecular motion at different temperatures. A method for evaluation of the energy of intermolecular interactions which hinder small‐scale motion at low temperatu

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200701

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe technique of nitric acid etching followed by gel permeation chromatography has been used to determine the crystal length distribution in ultrahigh‐modulus polyethylenes. The crystal length distribution has been studied as a function of draw ratio, polymer molecular weight, processing conditions, and annealing. The results confirm that although there is a considerable broadening of the crystal length distribution on drawing, the majority of crystals have lengths less that 500 Å. There are detailed changes in the length distribution due to changes in draw temperature, molecular weight, and annealing which are not always reflected in corresponding changes in the long period determined from small‐angle x‐ray scattering. Possible reasons for these discrepancies are dis

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200702

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractCrazes have been grown from crack tips in thin films of the following five polymers: polytertbutylstyrene (PTBS), polystyrene (PS), poly(styrene‐acrylonitrile) (PSAN), poly(phenylene oxide) (PPO), and poly(styrene‐methyl methacrylate) (PSMMA). These polymers represent a wide range oflevalues, whereleis the chain contour length between entanglements. Quantitative transmission electron microscopy has been used to analyze the extension ratio λcrazeand displacement profiles for these crazes. From these measurements the craze surface stresses have been computed by using the method of distributed dislocations. This analysis also permits an accurate measure of the level of the applied stress σ∞. These measurements show that the stress necessary for crazing increases asledecreases and that the higher surface stresses present at crack tips generate crazes that have higher λs than isolated crazes in the same polymers. Surface drawing is shown to be the dominant mechanism for craze thickening in all five

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200703

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractPrevious studies on the dilute‐solution behavior of sulfonated ionomers have shown these polymers to exhibit unusual viscosity behavior in mixed solvents of low polarity. These results have been interpreted as arising from specific solvation effects by the solvents with the metal sulfonate groups which persist as ion pairs. The consequences of ion pair interactions and their solvation are exceptional thickening behavior at low polymer levels as compared to unfunctionalized polymers, and anomolous solution viscosities with varying temperature. These studies have now been extended to single‐component solvents which traverse a range of polarities. Using the sodium salt of lightly sulfonated polystyrene (S‐PS) as a model system, the authors found the solution behavior in low‐polarity solvents (tetrahydrofuran) to be consistent with that observed previously for mixed solvents; ion pair interactions predominated. However, in polar solvents such as dimethyl sulfoxide or dimethyl formamide, these polymers behave as classic polyelectrolytes even at sulfonate levels below 2 mol %. The behavior of the S‐PS acids is similar to that observed for the metal salts. To a first approximation these two behaviors, ion pair association and polyelectrolyte behavior, are dependent on solvent polarity. In some cases it is possible to induce polyelectrolyte behavior in a S‐PS/solvent combination exhibiting ion pair interactions by the addition of very low levels of a polar cosolvent, such as water. These results again demonstrate the selectivity of the solvent‐sulfonate

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200704

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractMixed crystals of polyethylene (PEH) and various‐molecular‐weight perdeuterated polyethylenes (PEDs) have been prepared at 80°C and their infrared spectra compared with those of samples grown at 55°C. Concentrations of 80 PEH/1 PED were required in the former case to eliminate segregation effects whereas 40 PEH/1 PED sufficed in the latter. Resolution of the observed CD2bend contour was most reasonably achieved with a crystalline singlet and two crystalline doublets, in addition to a contribution (ca. 15%) from the noncrystalline component. The singlet, comprising about 20% of the crystalline area, contains contributions from both isolated stems and (200) adjacent reentry folding. Random reentry folding is therefore not a predominant mode of chain organization in polyethylene single crystals. The inner of the two doublets arises from adjacent reentry folding along single (110) planes, and is present for all PED molecular weights. For low‐molecular‐weight fractions this splitting is consistent with the number of stems of one PED molecule allowed in the crystal. The outer doublet arises from multiple (110) plane adjacency, and is present for intermediate and high molecular weights. An analysis of both doublets suggests that at high molecular weights a single molecule can crystallize with noncontiguous regions of adjacent ste

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200705

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractShrinkage of unconstrained low‐density polyethylene samples and the retractive stress of samples with ends fixed have been investigated as a function of the annealing timetAand temperatureTAon material drawn at room temperature to draw ratios λ between 4 and 6. The shrinkage increases withtAandTA. The retractive stress on a sample annealed with ends fixed goes through a maximum as the sample is annealed and then drops to a limiting value which increases withTAas long asTAis at or below 80°C and rapidly decreases with higherTA. The drop from the maximum to the limiting retractive stress, slow at lowerTAand rapid at higherTA, seems to be a consequence of rapid pulling of chain segments out of crystal block in which interfibrillar tie molecules are anchored. This process is facilitated by the highTA, which softens the crystal matrix. At constant end‐to‐end distance, the contour length of the tie molecules is irreversibly increased, and this causes a reduction in the contribution of the affected tie molecules to the overall retraction stress. Hence one finds a substantially higher retraction stress during first heating than during subsequent cooling and heating of the drawn

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200706

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe birefringence of model structures of ultraoriented polyethylene has been calculated by using the point‐dipole concept and the polarizability tensor of the methylene group derived recently by Pietralla. For well‐oriented chains the birefringence is determined by the combination of a negative anisotropy of the polarizability tensor of the methylene group and a positive anisotropy of the Lorentz tensor, both with respect to the chain direction. As a consequence it decreases with increasing density. The results are in agreement with experimental values of Mead, Desper, and Porter. In the model the amorphous regions are regarded as a mixture of planar and helical segments arranged in nematiclike bundles which additionally may have a certain distribution of orientation. The birefringence is not much affected by defects which, on the other hand, strongly influence the ultimate mechanical propert

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200707

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe formation of cellulose fibers by coagulation of drops of cellulose solution in extensional flow was studied theoretically and experimentally. In the theory, which applies for slow‐motion conditions, homogeneity of the drop is assumed. The drop deforms according to a previously established deformation mechanism and becomes solid when a critical concentration of coagulant is reached at a certain position inside the drop. The theoretical predictions for the variation of fiber length with various parameters were tested experimentally in a four‐roller mill for cellulose/dimethyl sulfoxide/paraformaldehyde with glycerol as coagulant. In agreement with the theoretical predictions, it was found that fiber length increases with shear rate and original droplet size, but decreases with the diffusion coefficient of the coagulant in the cellulose solut

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200708

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe dynamic mechanical properties of a series of polyester resins made from a maleic/phthalic anhydride‐based unsaturated polyester crosslinked with each of styrene, 4‐methyl styrene, 4‐ethyl styrene, 4‐n‐butyl styrene, 4‐isopropyl styrene, tertiary butyl styrene, 4‐chlorostyrene, and 3,4‐dichlorostyrene were studied. The order of the α transition temperatures was as expected from that for the homopolymers, except in the case of the chlorostyrenes, for which dipolar interactions with the polyester chain may be important. The styrene bridges appeared to be involved in a steric interaction (and in the case of the chlorostyrenes, a dipolar interaction) with the β relaxing ester species. It is suggested that both the γ and γ′ relaxations involve similar interactions between the matrix and the relaxing moieties. For the 4‐n‐butyl styrene resin, an additional relaxation below −170°C was observed, and is ascribed to re

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200709

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThis article demonstrates that the neglect of nonlinear effects in the conventional counterion condensation theory for the double layer about a charged cylinder can be significant, especially for phenomena involving intramolecular or intermolecular interactions in dilute solutions. For concentrated solutions the Manning theory derives from a linearized superposition approximation for the potential, in contrast to the cylindrical‐cell model, which explicitly treats interactions within an ordered array of parallel cylinders. A new theory which treats interactions explicitly while permitting disorder in two dimensions is presented, and predictions for the osmotic pressure are compared with those from the Manning and cylindrical‐cell mod

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200710

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY