344 



THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1952 



j\ 1 000 



10 



45 



50 



15 20 25 30 35 40 



TEMPERATURE IN DEGREES CENTIGRADE 



Fig. 20 — Temperature variation of rigidity of 1 per cent solution of polyiso- 

 butylene (M„ = 1.18 X lO^) in cyclohexane. 



dynes/cm" from the entangled segments stiffness, ms ; and only 3 dynes/ 

 cm^ from the intra-cham stiffness, m . Thus, chain configuration me- 

 chanics, including the associated viscosities, can be well enough thought 

 of in the foUowmg paragraphs, in terms of mb , ^b and r\A ■ 



The exponential decrease of m with temperature familiar for polymer 

 solids and liquids is much suppressed in the /xs vs T curve of Fig. 20. 

 While the in , internal rotation, mechanism for single poljasobutylene 

 molecules probably has a considerable activation energy, that for the 

 JU2 , configurational, rigidity should be very small. Then, without re- 

 tardation, the mtrinsic chain modulus would rise with rismg tempera- 

 ture. These influences seem to combine to give the modest declme of /xb 

 appearing m Fig. 20. If these rigidities are plotted against 1/T, the 

 temperature coefficient is 2.3 kcal. This is much less than the familiar 

 values for the stiffening of rubbery solids, and emphasizes that inter- 

 chain action reigns then. 



Solvent Variation 



Effects of solvents of different (mostly positive) heats of mixing on 

 state of polyisobutylene molecules in solution have been nicely estab- 

 lished by Fox and Flory. Especially, this work has clarified principal 

 factors in the intrinsic viscosity expression 



w = ri 



100 



= luM 



1/2 3 



