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Macromolecular Internal Viscosity. The Role of Stereoregularity
Author(s) -
Allegra Giuseppe
Publication year - 2004
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.200451410
Subject(s) - macromolecule , polymer , viscosity , polystyrene , rotational energy , internal rotation , materials science , kinetic energy , thermodynamics , chemical physics , chemistry , polymer chemistry , organic chemistry , physics , classical mechanics , mechanical engineering , biochemistry , engineering
Abstract Macromolecular dynamics at the scale of a few chain bonds is largely controlled by the “internal viscosity” effect if the energy barriers hindering the skeletal rotations are sufficiently large. In an extensive spin‐echo neutron scattering analysis, Richter and co‐workers (A. Arbe, M. Monkenbusch, J. Stellbrink, D. Richter, B. Farago, K. Almdal and R. Faust, Macromolecules , 2001 , 34 , 1281) investigated the dynamic properties of polyisobutylene (PIB) and polydimethylsulfoxide (PDMS) in toluene solution, the latter polymer being currently assumed to have very small rotational barriers. Analysis of the data according to a theory proposed by this author enabled them to obtain realistic values both of the rotational barrier around C‐C bonds (∼3kcal/mol) and of the natural frequency of the rotational jumps. ‐ A problem related to chain internal viscosity concerns the iso ‐ and syndio ‐tactic forms of polystyrene (respectively i‐PS and s‐PS): After a careful conformational analysis it is shown that i‐PS has very large effective energy barriers due to interactions between phenyl rings (S. Br¨ckner, G. Allegra and P. Corradini, Macromolecules , 2002 , 35 , 3928). This effect is compounded with that of the intrinsic rotational barrier and helps explaining the kinetic difficulty to crystallise of i‐PS as compared with s‐PS.