| The intermolecular structure and dynamics in two, very different, systems has been investigated rheologically: (1) thermally reversible gel formation of atactic polystyrene (aPS) in mixed solvents of carbon disulfide (CS2) and tricresyl phosphate (TCP), and (2) a segmented block-copolymer comprising a crystallizable polyester and an amorphous poly(methyl acrylate), with blocks coupled through a thermally degradable moiety.; In the first project, the use of TCP as a cosolvent brought the relaxation times of the solutions and gels of aPS (Mw = 1.8 x 106) into a convenient range for viscoelastic experiments, with only a modest impact on the gelation temperature Tgel. This facilitated the first systematic study of the viscoelastic properties through studies of the creep, recovery and sinusoidal deformation through the gel point of a system comprising aPS in the presence of CS 2. Measurements were made as functions of temperature (-5 to 26°C), polymer concentration (0.06--0.18 w/w), and the composition of mixed solvent. As reported elsewhere for solutions of aPS in a mixed solvent containing toluene and CS2 (Macromolecules 28:6539--50, 1995), the gel temperature did not depend too much on the composition of the mixed solvent. The results showed that aggregated states exist in the pregel solution (even though the solvents used are thermodynamically good solvents for aPS), that the formation of the gel is a retarded process, that cans take several hours to develop under some conditions, and that all gels formed exhibited some nonrecoverable deformation after a long time deformation in creep, corresponding to a viscosity in the range 108 Pa.s. The viscoelastic results are discussed in terms of the formation of a randomly branched structure, with the crosslink loci likely involving syndiotactic runs in the atactic polymer, with the persistence length of these runs enhanced by intercalation of CS2 between near adjacent phenylene rings, and with additional CS2 involved in the space between adjacent chains in the crosslink loci. This model is based on observations reported for the gelation of syndiotactic PS in thermodynamically good solvents.; The second project utilized the same rheological protocols with a segmented block-copolymer, poly(methyl acrylate)-b-poly(hexamethylene adipate) (PMA-b-PE) prepared from a crystallizable telechelic Cl(CO)-PE-(CO)Cl with acid chlorides at both ends, and an amorphous telechelic PMA, HO-PMA-T-R, having a -OH on one end and a TEMPO (T) moiety at the other end, where R is either -NH 2 or -OH. (Abstract shortened by UMI.)... |
