摘要:

AbstractMost organic polymers show a complex array of transition and/or multiple relaxation phenomena in addition to the classical glass transition and the melting point. An amorphous hydrocarbon backbone polymer such as an equimolar, random copolymer of ethylene and propylene, can exhibit, four types of relaxation regions: (1) motion of the entire chain as a unit; (2) motion of a chain segment of perhaps 50–100 carbon atoms, i.e., the glass transition; (3) motion of a 2, 3, or 4 carbon atom moiety about the chain axis, i.e., the γ transition: (4) motion of a side group, such as CH3in a propylene unit. A moderately crystalline hydrocarbon backbone polymer, i.e., polypropylene, can show all of the loss peaks noted above but in addition may exhibit peaks as follows: (1) melting point; (2) a first‐order transition from one crystal type to another; (3) motion of side groups such as CH3within the crystallites; (4) interactions between crystallites and amorphous regions; (5) frictional losses within crystallites. Single crystals of linear polyethylene show several loss peaks related to loss peaks in partially crystalline polyethylene. Additional types of loss mechanisms arise in polymers such as polyethylene glycol terephthalate, polycarbonates, cellulose derivatives, and nylon, in which different types of moieties alternate along the chain. Different teat methods varying in specificity toward molecular groups in frequency and in sensitivity are needed to elucidate the full spectrum of loss mechanisms. Brief comment is made on the dielectric data of Kheir showing two clearly resolved loss peaks for 5% cellulose acetate in dio

ISSN:0449-2994    

DOI:10.1002/polc.5070140103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

ISSN:0449-2994    

DOI:10.1002/polc.5070140104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractThe phenomenon of diffuse phase transitions occurs widely in simple inorganic and organic systems, such as the solid‐solid transitions in ammonium chloride and in methane. It is known that in a finite temperature interval centered around the transition temperature, both the low temperature phase A and the high temperature phase Bcoexist.The most renowned manifestations of this phenomenon are the unusual specific heat curve (the lambda point anomaly); the appearance of x‐ray lines of two distinct phases, A and B, in the temperature interval of transition; and a gradual rather than a discontinuous change of volume in the transition interval. A statistical thermodynamic model of the Ising type was developed which describes all of these seemingly diverse phenomena in a unified and quantitative manner. The central feature of the theory is that it postulates the existence of a geometrically simple boundary phase which coexists with phase A and phase B. The theory introduces only a simple constant to describe a diversity of experimental results, the constant being the free energy of formation of the boundary phase, denoted as ΔGk. The theory was applied to the diffuse phase transitions in such solids as (NH4)2SiF6, Ag2H3IO6, KH2AsO4, KH2PO4, NH4Cl, and CH4, as well as to the diffuse melting of polymers, such as polyethylene, and to the helix‐coil transition in polypeptides and in polynucleotides. By use of a single constant, ΔGk, for each substance a very good fit of the experimental heat capacities versus temperature is generated for (NH4)2SiF6, Ag2H3IO6, KH2PO4, KH2Aso4, NH4Cl, and CH4. For diffuse solid‐solid transitions, the width of the x‐ray lines in the coexistence regions was predicted‐ Since such experimental data are not yet available, this prediction is offered as a very severe experimental test of the theory. In this paper we present very simple approximate equations of the Gaussian form which represent an excellent fit to the exact theory and

ISSN:0449-2994    

DOI:10.1002/polc.5070140105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractIt has long been recognized that the detailed selection rules describing the dielectric loss spectrum of a macromolecule in solution depend on the manner in which the individual polar groups are attached to the structure. As many as three distinct loss peaks may appear, due to contributions respectively from (1) long‐range dipoles whose magnitude and direction are proportional to the overall dimensions of the molecule; (2) dipoles rigidly attached to the chain but without long‐range correlation; and (3) dipoles on flexible side chains. In addition, there is the Kirkwood‐Shumaker mechanism of “proton polarizahility.” Theoretical and experimental examples of the above generalities are

ISSN:0449-2994    

DOI:10.1002/polc.5070140106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractNuclear magnetic resonance (NMR) spectroscopy has become a valuable method of studying motions of chain segments and substituents in polymer molecules, since it views motion in away that, complements the information from other methods of measurement and since it extends the range of accessible frequencies to a region (∼108cycles/sec.) that is beyond the usual range of dielectric and mechanical studies. In this report, a brief survey is given of the NMR relaxation processes and their significance to the understanding of thermal motions in solid polymers. The occurrence of multiple relaxation processes is discussed for a series of poly(n‐α‐olefins), poly(alkyl methacrylates), and some important elastomers, including natural rubber, polyisobutylene, and polybutadiene. Correlations are drawn with results in the literature on dynamic mechanical and dielectric relaxation in po

ISSN:0449-2994    

DOI:10.1002/polc.5070140107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractSpecific heat studies of polymers are reviewed within the framework of Buyer's classification: (a) melting transition (Tm); (b) glass transition (Tg); (c) subglass relaxation (T

ISSN:0449-2994    

DOI:10.1002/polc.5070140108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractIn the last several years, studies of the dynamic behavior of polymers have shown that many, if not all, polymers exhibit more than one transition region when the investigation covers a sufficiently wide temperature or frequency range. The purpose of this paper is to discuss, for a few selected polymers, those multiple transitions which have been found by using dynamic mechanical methods, with particular emphasis on those exhibited by certain olefinic polymers and copolymers. In addition to work published in the literature, this paper also covers some unpublished results based on measurements made in our laboratory. Although attempts have been made to relate secondary transitions with such types of motion as the rotation and/or oscillation of short side chains, subgroups, and short segments of the main polymer chain, there are few polymers for which secondary transitions have been definitely assigned to a particular motion of a specific group. For the most part, the results to be discussed in this paper are based on measurements made with a torsion pendulum, vibrating reed, or transverse vibration apparatus.

ISSN:0449-2994    

DOI:10.1002/polc.5070140109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractResults of dynamic mechanical investigations for various polymers in the temperature region from 4.2–77°K. or above are reviewed, and the mechanisms believed to be responsible for the various loss maxima are discussed. Dynamic mechanical data, obtained at ∼104cps with a longitudinal vibrational apparatus, are presented for an un‐annealed polypropylene sample, for a commercial poly(methyl methacrylate) specimen, for a sample of purified poly(methyl methacrylate) containing 1% water, for three poly(vinyl toluene) samples (in the 200–300°K. range), and for a 76% styrene‐24% acrylonitril

ISSN:0449-2994    

DOI:10.1002/polc.5070140110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractThe α‐dispersion in many polymer systems is the process to be associated with the glass transition temperature where many physical properties undergo drastic changes. We have measured and analyzed the complex dielectric behavior of the α‐dispersions for five polymers [i.e., polycarbonate and polyisophthalate esters of bisphenol A, isotactic poly‐(methyl methacrylate), poly(methyl acrylate), and a copolymer of phenyl methacrylate and acrylonitrile] and have found that the usual methods of analysis cannot be used to represent the data. However, it is possible to represent the relaxation process as the sum of two dispersions but there is no evidence to support this contention. An empirical expression is proposed to represent the data. This expression which takes the form of\documentclass{article}\pagestyle{empty}\begin{document}$$ [\varepsilon ^* (\omega) - \varepsilon _\infty]/[\varepsilon _0 - \varepsilon _\infty] = [1 + (\iota \omega \tau _0)^{1 - \alpha}]^{ - \beta} $$\end{document}appears to be a general representation for the three known dispersions, i.e., Debye, circular arc, and skewed semicircle. The complex dielectric constants calculated with the aid of this expression and the parameters for each polymer system which was determined graphically were found to be in excellent agreement with the experimental complex dielectric constants. This method of representation was extended to sixteen α‐dispersions reported in the literature always with excelle

ISSN:0449-2994    

DOI:10.1002/polc.5070140111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

ISSN:0449-2994    

DOI:10.1002/polc.5070140112

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY