摘要:

AbstractThe thermal behavior of random copolyamides which are used as model polymers with hydrogen bonds has been investigated by differential scanning calorimetry (DSC), x‐ray diffraction, and infrared spectroscopy. The quenched copolyamides have only halo patterns in their x‐ray diffraction photographs. A random copolymer of nylons 6, 66, and 610 (in a composition ratio of 3: 4: 3) was found to have 20% of unbonded amide groups immediately after quenching. When the sample was kept at the glass transition temperature (20°C), no change in x‐ray diffraction was observed after the treatment. The free amide band in the infrared spectrum at 3450 cm‐1, however, was decreased in intensity by keeping the sample at the glass transition temperature. The transition peak height observed in a DSC curve also increased in the same experiment. Large glass transition peaks were found in DSC curves after annealing of the random copolyamides in the vicinity of the glass transition temperature. It is probable that the free amide groups in the amorphous chains were rearranged and formed new hydrogen bonds during the heat treatment at the glass transition temperature. Packing and restriction of the amorphous chains due to the increase in hydrogen bonding seemed to increase the height of the transition peak in a DSC curve. It is inferred from the above results that in the case of the random copolyamide, structures corresponding to a given enthalpy of the glassy state can be related to the number of hydrog

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110501

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThe most stable conformations of typical isotactic helical polymers, polypropylene (PP), poly‐4‐methyl‐1‐pentene (P4MP), poly‐3‐methyl‐1‐butene (P3MB), polyacetaldehyde (PAA), and poly(methyl methacrylate) (PMMA), were analyzed without fixing the fiber identity period by taking into account the intramolecular potential energy due to the internal rotation barriers, and van der Waals and electrostatic interactions. According to the results of the calculations, the number of chemical units per turnNin the stable conformations is 2.91 for PP (value determined by x‐ray diffraction: 3.0), 3.52 for P4MP (3.5), 4.17 for P3MB (4.0), and 3.94 for PAA (4.0). This indicates that the molecular conformations of these four polymers are governed primarily by intramolecular interactions, i.e., steric hindrance of side chains, and are additionally modified by the intermolecular interactions in the crystal. For PMMA, the lowest minimum in the potential map corresponds toN= 12, but the energy difference between the minima ofN= 12 andN= 5 (corresponding to the actual one) is only 3 kcal/mole of monomer unit. The (5/1) helix of PMMA may be reasonably interpreted in terms of the intermolecular interactions mainly due to the polar and bulky side groups. The intermolecular interaction energy of isotactic PAA in the crystal lattice is also calcula

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110502

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThe rate of peroxy radical accumulation as a function of strain at various temperatures in AC1220 high molecular weight polyethylene has been determined by EPR spectroscopy. The results of isothermal radical decay experiments are used, where appropriate, to correct the apparent accumulation rate to the actual rate. An exponential dependence of radical concentration [R], on true strain is observed at all temperatures investigated in the range from 160 to 294°K. For constant effective strain, measured from the approximate strain at which radical accumulation initiates, it is found thatd[R]/de exhibits two sharp transitions as a function of temperature. One of these, at low temperature, is believed to be associated with the glass transition of the amorphous phase of the material; the other, at higher temperature, is believed to occur as a result of a change in the rate‐controlling mechanism of deformati

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110503

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThe sensitivity of the light‐scattering method for the determination of the composition heterogeneity of copolymers is discussed in terms of the accuracy of measurements of the intensity of scattered light. When the composition is independent of molecular weight, a nomographic solution has advantages. The nomograph is used to investigate the feasibility (a) of the determination of heterogeneity by a single measurement at zero refractive index increment of the copolymer and (b) of the determination of the heterogeneity from two measurements. The results show that in the case of low heterogeneities the light‐scattering method can be used only at higher molecular weights. By using the heterogeneities calculated elsewhere, the possibility of determining them for the individual types of copolymers is discussed. It appears that reported discrepancies between measured and calculated heterogeneities are mostly found in cases where the sensitivity of the light‐scattering method for the determination of the composition heterogeneity i

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110504

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractHeat capacities of molten polyethylene, polypropylene, poly‐1‐butene, polystyrene, and poly(methyl methacrylate) were measured over a wide range of temperature by using a differential scanning calorimeter. The upper limit of temperature was established for each polymer at about 10°K below the beginning of thermal decomposition. For poly‐1‐butene and poly(methyl methacrylate) the solid‐state heat capacity was also measured starting from room temperature. Several samples of each polymer were used so that average values of heat capacities could be established (reported in 10°K intervals). The data revealed for all polymers a nearly linear increase of heat capacity with increasing temperature over the whole temperature range i

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110505

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractPoly(vinylidene chloride) (PVDC) separates from the reaction mixture during the free‐radical polymerization of vinylidene chloride. The morphology of the “as‐polymerized” powder is determined by the degree of undercooling existing in the reaction medium at the time of crystallization. Crystallization occurs simultaneously in the process of polymerization and subsequently by the precipitation of polymer which formed in solution. As the medium becomes more favorable, an increasing portion of the polymer forms in solution and then crystallizes. The morphology developed by polymerization in borderline solvents such as dioxane can be nearly duplicated by recrystallization under similar conditions. The simultaneous occurrence of solution and solid phase polymerization leads to a double DTA endotherm. The upper peak at ca. 200°C represents the melting point of PVDC. The size and temperature of the lower peak vary with polymerization conditions. The results can be correlated with the degree of under‐cooling as estimated by the difference between the polymerization temperature and the temperature at which the crystalline polymer dissolves in the reacti

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110506

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThe sedimentation of an unperturbed polymer chain in dilute solution is reformulated by using Burgers' method, in which the no‐slip boundary condition on the surface of each chain element is taken into account approximately. It is shown that the forcevelocity proportionality relation employed so far as the basis of theoretical developments in polymer hydrodynamics can be justified as a first approximation to the no‐slip condition. The derived expression for the translational friction coefficientftis a complex function ofnanda/b, wherenis the number of chain elements in a single molecule anda/bis the ratio of the Stokes radius of a chain element to the effective bond length. Three special cases corresponding mathematically tob= ∞ (no hydrodynamic interaction),a≪b(Kirkwood‐Riseman theory), andb= 2a(touching‐sphere model) are examined in detail. Finally, it is shown that whena/b= 0.2360, ourftvaries linearly withn1/2over the entir

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110507

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractOver the last decade, empirical evidence has indicated that the effective surface energy γ associated with the fracture of noncrystalline is a linear function of the reciprocal of the viscosity–average molecular weight:\documentclass{article}\pagestyle{empty}\begin{document}$ \gamma = \gamma _\infty - b\bar M_v ^{ - 1} $\end{document}. For poly(methyl methacrylate), data of J. P. Berry, G. C. Berry and Fox show that gamma; ∼ 0 at about the same value ofM̄vthat corresponds to the polymer chain‐entanglement length. From this fact, we have developed an entanglement network model for fracture, that bears a resemblance to F. Bueche's entanglement model for the melt viscosity of bulk polymers. Our model allows for the expression of the previously empirical constants, γ∞andb, in terms of molecular parameters:\documentclass{article}\pagestyle{empty}\begin{document}$ {{\gamma _\infty = \gamma _{\rm s} A_{\rm s} Z_{\rm c} \rho _{\rm c} N_A } \mathord{\left/ {\vphantom {{\gamma _\infty = \gamma _{\rm s} A_{\rm s} Z_{\rm c} \rho _{\rm c} N_A } {\bar M_{\rm s} }}} \right. \kern-\nulldelimiterspace} {\bar M_{\rm s} }} $\end{document}and\documentclass{article}\pagestyle{empty}\begin{document}$ b = 2({{\bar M_v } \mathord{\left/ {\vphantom {{\bar M_v } {\bar M_n }}} \right. \kern-\nulldelimiterspace} {\bar M_n }})\gamma _\infty M_{\rm f} $\end{document}whereM̄nandM̄fare the number‐average molecular weights of the polymer and of the free chain ends,M̄vis the viscosity‐average molecular weight, γsis the average fracture‐energy per entanglement in the craze volume,Asis the average cross‐sectional area of the polymer chain,Zcand ρcare the thickness and density of crazed material on the fracture surface, respectively;M̄sis the average strand molecular weight between entanglements, a

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110508

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThe unit cell of an alternating copolymer of ethylene and tetrafluoroethylene was determined by x‐ray diffraction. In spite of uncertainties due to irregularities in the chain structure and a low level of crystallinity, a reasonable unit cell and structure was derived which gives a calculated crystalline density of 1.9 g/cm3. The unit cell is believed to be either orthorhombic or monoclinic with the following parameters:a= 9.6 Å,b= 9.25 Å,c= 5.0 Å, (γ = 96°). The molecular conformation is that of the extended zigzag, and the molecular packing appears to be orthorhombic, each molecule having four nearest neighbors with the CH2groups of one chain adjacent to the CF2groups of th

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110509

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractBy means of an extrusion technique, a uniformly oriented macrolattice based on an alternating sequence of polystyrene and polybutadiene lamellae has been obtained. This is confirmed by the techniques of low‐angle x‐ray diffraction, electron microscopy, and electron diffraction. Layer thicknesses and spacings have been derived, and good quantitative agreement exists between the values obtained by the different methods. In addition, the electron micrographs exhibit many singular features which are of potential importance both in their own right and for the macroscopic propert

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110510

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY