TABLE 227.— PROPERTIES OF GR-1 (BUTYL RUBBER, ISOBUTENE 



COPOLYMER) 



237 



ISOPRENE 



Unit 



Density g cm" 3 



Expansivity (1/V) (dV/dT) (deg C)" 1 



Thermal 



Second-order transition temperature deg C 



Optical 



Refractive Index nD 



Electrical 



Dielectric constant 



Mechanical 



Shear modulus 



Initial slope of stress-strain curve dynes cm~ : 



Ultimate elongation percent 



Tensile strength kg cm" 2 



Complex dynamic shear modulus (60 cps), 

 v'+ia" 

 e 



Real part G', — dynes cnT ! 



e 



Imaginary part G", — dynes cm" 



Resilience (ball rebound) percent 



Unvulcanized 



.92 



-67 to —73 



1.5091 



Pure-gum 

 vulcanizate 



.93 

 57X10" 5 



Vulcanizate 

 containing 

 about 339Ji 



carbon black 



1.13 



46X10" 5 



2.1-2.6 



7-15X10 8 



750-950 



180-210 



4-10X10° 

 2-3X10 6 



18X10° 

 30-40X10° 

 650-850 

 180-210 



36X10° 



16X10° 

 7 



TABLE 228.— COMPRESSION OF RUBBER 73 



Commercial soft-packing, black, density about 1.9 g/cm 3 and Vo = 1 cm 3 



AV 



73 Bridgman, P. W., Proc. Amer. Acad. Arts and Sci., vol. 74, p. 50, 1940. 



SMITHSONIAN PHYSICAL TABLES 



