C-15 0.6 0.8 1.0 1.2 1.4 1.6 MO /P205 ratio Fig. 3. Composition dependence of free volume in glasses of the system MO-P,O, (M =Be, Zn).calcium phosphate and barium phosphate glasses has a constant value of =O. 1 but V , for magnesium phosphate glasses is ~0 . 3 , which is much higher than piwiously reported. All investigations were almost independent of the MO/P,O, ratio. In contrast to the data of Fig. 2, V, of beryllium and zinc phosphate glasses depends on the MO/P,O, ratio and shows a minimum at MO/P,O, = 1 ( Fig. 3). Figure 4 gives V, for a (1 -x)MO.P,O,-xAl,O,. 3P20, quasi-binary metaphosphate system where M is Ca and Ba, indicating a maximum V , ( ~0 . 2 ) atx =0.5; V, for M = & as shown in Fig. 5 does not have a maximum nor minimum, and V f changes monotonously with x .Weyl and MarboeR assumed that abrupt change in expansivity at T , for silicate glasses is due to asymmetry in Si04 tetrahedra. They pointed out that glasses containing no nonbridging 0'-ion, such as vitreous silica, Li,O. Al,O,.xSiO,, MgO. Al,O,~xSiO,, etc. did not show the increase in expansivity prior to the softening point. Hence, V , for their glasses will be close to zero. In contrast, our V, for B,O, glass is very high (==0.3) which is comparable to MgO-P,O, glasses.Thus, it is apparent that V, is not a universal constant for all glasses and that glass transition does not occur at an iso-free volume state. The writers support the assumption that glass transition takes place at an iso-viscosity state (1013 to 1014) rather than at an iso-free volume state. We believe for V , to vary with the degree of the threedimensional asymmetry of the glass backbone structure (SiO,, PO,, B04, BO,, etc.), the smaller the V,, the mole symmetrical the backbone. Experimental V , of glasses was =O to 0.3. ReferencesIT. G . Fox, Jr. and P. J . Flory, "Second-Order Transition Temperatures and Related Properties of Polystyrene, 1," J . A/?/?/. Phys., 21, 581-91 (1950).
The primary purpose of this paper is to summarize some of the general relationships between chemical structure and transition temperatures for polymers. In addition to the two primary transitions, the melting point Tm, and the glass transition TG, other transitions occurring either below TG or between TG and Tm are discussed. A secondary purpose of this paper is to make a preliminary attempt at some rational nomenclature and classification scheme for polymer transitions, especially in the case of polymers having multiple transitions. This article is not intended to be a complete review of the literature on transitions in polymers. Our paper was inspired by a comprehensive lecture on multiple transitions presented by Dr. Karl Wolf in Midland, Michigan, during the summer of 1960. The substance of this lecture has recently been published. Willbourn has also been concerned with the classification of multiple transitions. A recent comprehensive report by Saito, Okano, Iwayanagi and Hideshima called “Molecular Motion in Solid State Polymers” also considers in elaborate detail many of these same problems.
Considerable progress has been made in the past 20 years in the synthesis, characterization and fabrication of plastics. Previous SPE Award winners, such as Mark, Natta, and Marvel dealt largely with synthesis; Flory with characterization; Alfrey and Du Bois with fabrication. One of the still unsolved problems lies in the realm of relating mechanical properties, such as impact strenght and creep to molecular structure. The design enginner who wishes to use a plastic part is concerned primarily with how some property such as impact strenght varies with temperature, speed of test, test method, etc. The polymer scientist must know why. Through knowing why, he may be able to design better plastics. This paper attempts to survey some of the world‐wide progress made in this area in the past 10 years. The ultimate goal is to understand these mechanical properties in terms of internal molecular motions which occur in solid polymers. Internal motion can be detected by electrical, electromagnetic and dynamic mechanical measurements. When these three methods are applied on a given polymer over a range of temperatures, insights can be gained as to the variation of impact strength and other properties with temperature and frequency for that same polymer. These three fundamental methods, which require very small samples (less than 50 grams), can provide insight into the practical behavior of plastic materials over the wide range of temperatures and frequencies encountered in the real world.
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.
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