Rubbery amorphous polymers

Rubbery amorphous polymers behave this way, and not like liquids, because their chains are not entirely free to slide past one another. The principal factors that limit long range... 

Rubbery amorphous polymers do not hold their shape well unless they are permanently crosslinked. If automobile tires were not crosslinked, they would be a soft sticky mess that would flow under the weight of the car. For this reason, we rarely encounter rubbery amorphous polymers that are not crosslinked. 

The properties of a rubbery amorphous polymer form a continuum ivith those of the polymer in its molten state. Rubbery amorphous polymers exhibit the same range of motions as molten polymers, but they happen much slower, due to reduced thermal motion and the associated decrease in free volume. 

The elongation at break of a sample is the strain at which at which it breaks. This value varies widely depending on polymer type and processing conditions. Glassy amorphous polymers typically exhibit low elongations at break because their chains cannot slide past one another. In rubbery amorphous polymers the situation is somewhat different. High molecular weight... 

Styrene co-butadiene is a rubbery amorphous polymer with a glass transition temperature well below room temperature. Polystyrene co-butadiene is an important component of several commercial families of plastic that contain polystyrene blocks. 

D. W. van Krevelen, Properties of Polymers, 3rd ed., Elsevier, New York, 1972, pp 44—54. (The data used here, Table 4.3 on p. 44, are titled Molar volumes of rubbery amorphous polymers at 25° C. They need not necessarily represent crosslinked elastomers. We are making an... 

TABLE 4.6 Molar volumes of rubbery amorphous polymers at 25 °C... 

The decrease of En with increasing T may be explained by the extra free volume created by thermal expansion. This was suggested by Batchinski in 1913 already. Several attempts have been made to formulate a joint temperature function for polymer melts and rubbery amorphous polymers on this basis. Doolittle (1951) formulated the equation ... 

The factors (298 Tg) and (Tg 298) are the "thermal distances" of Tg from room temperature for rubbers and glasses respectively. The influence of these "thermal distances" is probably connected with the fractional free volume of the polymer in rubbery amorphous polymers this f.f.v. increases with decreasing Tg, in glassy amorphous polymers the f.f.v. increases with increasing Tg (increasing formation of micro-voids), hence lowering of the activation energy. 

Polymers, specifically rubbery, amorphous polymers, have several inherent advantages as chemically sensitive sensor coatings diey can be deposited as thin, adherent, continuous films of fairly uniform thickness by solvent casting or spray coating techniques they are nonvolatile and of homogeneous composition and their chemical and physical properties can be modified to some extent by judicious choice of monomers and synthetic procedures. 

A final advantage of rubbery, amorphous polymers is that their sorption isotherms are often linear over relatively large ranges in penetrant concentration. Appendix C lists some common polymers that have been used as sensor coatings along with their Tg, Tfn, and monomer repeat unit structure. 

Table 8.1. Stress-optic coefficients Ca of glassy and rubbery amorphous polymers, and of melts of semicrystalline polymers, in Brewsters (=1(H2 Pa). T denotes the measurement temperature. 

As was noted above, the conformations of polymer chains in solution under 0 conditions are essentially identical to the random coil conformations of chains in glassy and rubbery amorphous polymers [5,6], where interactions of polymer chains with solvent molecules are replaced by interactions between the polymer chains. Knowledge of the "unperturbed dimensions" of polymer chains in solution therefore also plays an important role in predicting the physical properties of glassy and rubbery amorphous polymers. For example ... 

Then, the 3D power-law constitutive relation which is proposed for the rubbery amorphous polymer becomes... 

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