INTERACTION OF POLYMERS AND MECHANICAL WAVES 



345 



Here, F. = effective volume per molecule (and hence as determined by 

 chain configuration), M = moic'cular weight, a represents change in 

 linear extcMil of molecule l)ec:iuse of mutual interference of segments 

 and s? expresses [\\v hydrodynamics int(M'action of solvent and molecular 

 coil (including \'aryiiig degrees of "straining tiu'ough" the coil). ' '*■' '' ' 

 Interpretation of the mechanical properties of chains in tlilute solution, 

 with reference to the rough concepts of Fig. K), arouses particular in- 

 terest in the factor a'\ For a high molecular weight polyisobutylene, 

 intrinsic xiscosily theory""'^ indicated that a the ratio for volume of 

 actual coil dividetl by volume for ideal random flight coil was 3.81 in 

 cyclohexane but only 1.42 in benzene, both at 30°C. This strikuig alter- 

 ation in equilibrium chain configuration, a variable which is not readily 

 introduced into polymer liciuids or solids, appears in the inherent vis- 

 cosity vs c curves in cyclohexane, Fig. 21, and benzene. Fig. 22. The 

 lai'ge difference in [r}] at 25°C, 6.00 in cyclohexane vs '^l.S in benzene, 

 indeed emphasizes the different soh'ent powers. " Likewise, the large in- 

 crease of [77] with temperature in Fig. 22 accents the poor solvent qual- 

 ities of benzene. Too, empirically, polymer molecules which are either 

 tight coils or are actually chemically cross-linked to form microgel mole- 

 cules characteristically show positive slopes of inherent viscosity vs c 

 plots. Accordingly, all this evidence for large changes in the conforma- 

 tion of chain molecules in "good" vs "poor" solvents should show up 

 in dynamics of dilute solutions. Also, technically, Ciiiite different physical 

 properties are found for polymer-plasticizer compounds where compat- 

 ibility is high (good solvent) than where it is low (poor solvent). Here, 



6.00 f 



0.250 0.500 0.750 1.000 



CONCENTRATION IN GRAMS PER 100 ML. OF SOLUTION 



Fig. 21 — Inherent viscositv of ])olvisol)ut vlenc (.1/^ = 3.87 X lO") in cyclo- 

 hexane at 25°C. 



