Thermal Expansion and Second-Order Transition Effects in High Polymers. I. Experimental Results

1944 ◽  
Vol 17 (4) ◽  
pp. 802-812
Author(s):  
R. F. Boyer ◽  
R. S. Spencer
Keyword(s):  
Thermal Expansion ◽  
Second Order ◽  
Order Transition ◽  
Theoretical Treatment ◽  
Polymeric Systems ◽  
Crystalline Polymers ◽  
Brittle Point ◽  
Second Order Transition ◽  
Transition Effects ◽  
Point Determination

Abstract The results presented here on second-order transitions are in general accord with what has been known for other high polymeric systems. The value of the volume-temperature technique for investigating the nature of polymeric mixtures and the homogeneity of copolymers has been emphasized. In Part II a theoretical treatment of second-order transition effects, including the related brittle point determination, will be given. Finally, Part III will permit a more expanded treatment of the behavior of Saran and other crystalline polymers.

Ideal Copolymers and the Second-Order Transitions of Synthetic Rubbers. I. Noncrystalline Copolymers

1953 ◽  
Vol 26 (2) ◽  
pp. 323-335 ◽  
Author(s):  
Manfred Gordon ◽  
James S. Taylor
Keyword(s):  
Thermal Expansion ◽  
Transition Temperature ◽  
Small Molecules ◽  
Second Order ◽  
Order Transition ◽  
Kinetic Measurements ◽  
Practical Applications ◽  
Second Order Transition ◽  
Binary Copolymers ◽  
General Reduction

Abstract Theoretical and practical evidence is put forward to show that copolymers can be treated like solutions of small molecules in the interpretation of packing phenomena, and that ideal volume-additivity of the repeating units in copolymers is frequently realized. On this basis equations are derived for predicting θ, the second-order transition temperature, of binary copolymers from the two second-order transition temperatures of the pure polymers and their coefficients of expansion in the glassy and rubbery states. Previous mechanistic theories of the second-order transition temperature of such copolymers are thus superseded by a general reduction of the problem to the mechanism of thermal expansion. Practical applications to the choice of monomers in producing synthetic rubbers are outlined, and attention is drawn to the importance of second-order transitions in kinetic measurements on the reactions of polymers.

THE THERMAL CONDUCTIVITY OF ELASTOMERS UNDER STRETCH AND AT LOW TEMPERATURES

1950 ◽  
Vol 28a (6) ◽  
pp. 596-615 ◽  
Author(s):  
T. M. Dauphinee ◽  
D. G. Ivey ◽  
H. D. Smith
Keyword(s):  
Natural Rubber ◽  
Classical Theory ◽  
Heat Conductivity ◽  
Second Order ◽  
Rate Of Change ◽  
Order Transition ◽  
Hysteresis Phenomenon ◽  
Brittle Point ◽  
Second Order Transition ◽  
Hysteresis Phenomena

Heat conductivity of natural rubber and GR–S was studied in the range from + 50 °C. to − 170 °C. and from 0 to 100% stretch. The apparatus used was a greatly modified version of one designed by Schallamach. The conductivity of both types of rubber at 0% stretch lies in the range between 3.5 × 10−4 and 4.0 × 10−4 cal./sec. cm. deg. C. Stretching increases the rate of change of conductivity with temperature of both natural rubber and GR–S, and decreases the conductivity of the latter. On lowering the temperature and raising it again natural rubber exhibits a complicated hysteresis phenomenon, while GR–S shows a hysteresis loop caused by a second order transition near the brittle point. The hysteresis phenomena of both types of rubber near the second order transition temperature shows considerable similarity to the changes in specific heat observed by Bekkedahl and coworkers. Above and below the transition region the heat conductivity decreases approximately linearly with temperature as might be expected from classical theory. The variation through the second order transition does not agree with classical theory, but may be explained qualitatively on the basis of a diffuse lambda type transition.

The Amphorous and Crystalline Forms of Rubber Hydrocarbon

1937 ◽  
Vol 10 (1) ◽  
pp. 135-136 ◽  
Author(s):  
George S. Parks
Keyword(s):  
Heat Capacity ◽  
Thermal Expansion ◽  
Coefficient Of Thermal Expansion ◽  
Second Order ◽  
Crystalline Form ◽  
Order Transition ◽  
Heat Of Fusion ◽  
Warm Up ◽  
Volume Coefficient ◽  
Second Order Transition

Abstract The coefficients of thermal expansion and the heat capacities of rubber hydrocarbon, both in an amorphous and in a so-called crystalline form, have been recently reported in two papers by Bekkedahl and Matheson. According to these investigators, the amorphous form undergoes a transition of the second order in the neighborhood of 199° K. Above this temperature they found a rather abrupt increase of approximately 205 per cent in the volume coefficient of thermal expansion, and one of about 38 per cent in the heat capacity. These phenomena are strikingly similar to those found in numerous studies on glasses in this laboratory, and especially in the recent investigation on polyisobutylene by Ferry and Parks. Thus, with the particular sample of polymerized isobutene employed, the transition region centered around 197° K. and the subsequent increases in volume coefficient and heat capacity were 200 and 32 per cent, respectively. Bekkedahl and Matheson found that, by cooling the amorphous rubber hydrocarbon to about 230° K. and then permitting it to warm up slowly over a period of days, their material could be obtained in a “crystalline” form. These “crystals” melted at 284° K. with a heat of fusion of 4.0 calories per gram. They also exhibited the previously mentioned second-order transition at about 199° K., but with somewhat smaller subsequent increases with rising temperature, i. e., about 165 per cent increase in the volume coefficient of thermal expansion and 28 per cent in the heat capacity. Two facts appear surprising and highly significant with these “crystals”: (1) the value of the heat of fusion which is extremely low compared with the figures of 20 to 54 calories per gram hitherto reported for various aliphatic hydrocarbons melting near room temperature, and (2) the duplication of the second-order transition found previously for amorphous rubber hydrocarbon.

Crystallization and Second-Order Transitions in Silicone Rubbers

1951 ◽  
Vol 24 (2) ◽  
pp. 366-373 ◽  
Author(s):  
C. E. Weir ◽  
W. H. Leser ◽  
L. A. Wood
Keyword(s):  
Thermal Expansion ◽  
Volume Change ◽  
Silicone Rubber ◽  
Low Temperatures ◽  
Linear Thermal Expansion ◽  
Second Order ◽  
Order Transition ◽  
General Electric ◽  
Second Order Transition ◽  
Silicone Rubbers

Abstract In the course of an investigation to determine which rubbers might be suitable for use at low temperatures, interferometric measurements of the length-temperature relationships of silicone rubbers have been made. Crystallization was found between −60° and −67° C in Dow-Corning Silastic X-6160 and in General Electric 9979G silicone rubber, the latter of which contains no filler. Crystallization between −75° and −85° C was found in Silastic 250. Melting occurred over a range of temperature above the temperature of crystallization. The volume change on crystallization varied from 2.0 to 7.8 per cent. No crystallization or melting phenomena were observed in Silastic X-6073 between −180° and +100° C. All types of silicone rubber exhibited a second-order transition at about −123° C, the lowest temperature at which such a transition has been observed in a polymer. The coefficient of linear thermal expansion of silicone rubbers containing no filler was found to be about 40×10−5/degree C between −35° and 0° C.

Thermal Expansion Measurements and Transition Temperatures, First and Second Order

1959 ◽  
Vol 32 (4) ◽  
pp. 1005-1015
Author(s):  
Mark L. Dannis
Keyword(s):  
Thermal Expansion ◽  
Transition Temperature ◽  
Physical Properties ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Second Order ◽  
Rate Of Change ◽  
Order Transition ◽  
Abrupt Changes ◽  
Second Order Transition

Abstract When any pure material goes through a change in state, its physical properties change greatly. In each phase the physical properties are relatively constant or change slowly enough with temperature that the rate of change of a property such as volume is a constant. This rate of change of volume is the thermal expansion coefficient, (∂V/V)/∂T. The thermal expansion coefficient is almost constant, experimentally, as long as the temperature range over which measurements are made does not include a phase transition. At the transition temperature, abrupt changes in volume are found as illustrated in Figure 1. Polymeric materials often show changes in physical properties not necessarily accompanied by abrupt changes in volume, even though the expansion coefficient does change. Since the expansion coefficient changes, some change in internal structure is suspected, and the name second-order transition (Tg) has been adopted. This kind of change is roughly diagrammed in Figure 2. This latter change at the second-order transition temperature can be found in every known polymer, even though many polymers possess clear, first-order, crystalline transitions as well. Hevea rubber, for example, has a crystalline melting point of 28° C, compared to its Tg about −70°. These data are shown, copied from Boyer and Spencer, as Figure 3.

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