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ABSTRACT:Mean-square radii of gyration and viscosities of polystyrene samples covering a broad range of molecular weight M in cyclohexane were measured at temperatures above and below the theta temperature () in order to see how the coil of a linear flexible polymer collapses to a globule as T is lowered. The data for either the radius expansion factor or the viscosity expansion factor as a function of T and M gave a composite curve when plotted against (Tie-I)M 1 1 2 or (l-eiT)M 1 1 2 In the range of the abscissa values studied, this curve did not reach the asymptote for globular behavior. Thus, the coil-to-globule transition of a linear flexible polymer should be a very gradual process.KEY WORDS Coil-Globule Transition I Polystyrene I Cyclohexane I Radius of Gyration I Intrinsic Viscosity I Much still remains te be investigated theoretically and experimentally in regard to the chain dimensions and flow properties of a linear flexible polymer in a poor so.lvent below the theta temperature e. Long ago Stockmayer 1 suggested that a random coil might eventually collapse to a globule as the temperature Tis lowered below e. This coilglobule transition should manifest itself as a change in molecular weight dependence of (S 2 ) from the type (S 2 )a;:Mto the type (S 2 )ocM 213 , where (S 2 ) is the mean-square radius of gyration at infinite dilution and M is the molecular weight of the polymer.By extending Flory's mean-field theory to include a term associated with the ternary cluster integral {J3 and assuming that the binary cluster integral {J 2 is proportional to r and {J3 is independent of T, de Gennes 2 showed that as a coil shrinks to a globule, the dependence of (S 2 ) on M and Tasymptotically approaches the form (1) where r is a reduced temperature defined by r=(T-e)je (2)
ABSTRACT:Mean-square radii of gyration and viscosities of polystyrene samples covering a broad range of molecular weight M in cyclohexane were measured at temperatures above and below the theta temperature () in order to see how the coil of a linear flexible polymer collapses to a globule as T is lowered. The data for either the radius expansion factor or the viscosity expansion factor as a function of T and M gave a composite curve when plotted against (Tie-I)M 1 1 2 or (l-eiT)M 1 1 2 In the range of the abscissa values studied, this curve did not reach the asymptote for globular behavior. Thus, the coil-to-globule transition of a linear flexible polymer should be a very gradual process.KEY WORDS Coil-Globule Transition I Polystyrene I Cyclohexane I Radius of Gyration I Intrinsic Viscosity I Much still remains te be investigated theoretically and experimentally in regard to the chain dimensions and flow properties of a linear flexible polymer in a poor so.lvent below the theta temperature e. Long ago Stockmayer 1 suggested that a random coil might eventually collapse to a globule as the temperature Tis lowered below e. This coilglobule transition should manifest itself as a change in molecular weight dependence of (S 2 ) from the type (S 2 )a;:Mto the type (S 2 )ocM 213 , where (S 2 ) is the mean-square radius of gyration at infinite dilution and M is the molecular weight of the polymer.By extending Flory's mean-field theory to include a term associated with the ternary cluster integral {J3 and assuming that the binary cluster integral {J 2 is proportional to r and {J3 is independent of T, de Gennes 2 showed that as a coil shrinks to a globule, the dependence of (S 2 ) on M and Tasymptotically approaches the form (1) where r is a reduced temperature defined by r=(T-e)je (2)
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