A Statistical Theory Of Viscoelasticity And Its Application For Styrene-Diene Block Copolymers-Thermoplastic Elastomers Dissertation

The unusual physical properties and good processability of commercial thermoplastic elastomers SDS, synthesized by anionic polymerization, hae stimulated interest in new application and new products. Many literatures have reported the mechanical properties and the flow behavior of these two -phase block copolymers. Unfortunately, a systematical and reasonable treatment on their viscoelasticity and mechanical properties has not yet been developed because of their complexity of gradual structure breakdown with increasing temperatures and shear rates (or shear stresses). From a point of view of technological importance, a better understanding and knowledge of the mechanical properties of elastomers and the processing behaviors necessitates a development towards a valid rheological equation of state.Based on a detailed investigation on the structure, morphology and mechanical properties, a multiphase model structure which varies with the temperature and rate of deformation is proposed in this thesis for styrene -diene block copolymers at solid or melt states. Further more, a statistical theory of viscoelasticity is developed for SBS(SIS) elastomers and melts or concentrated solutions. The theory can not only describe the elastic behavior of swollen and unswollen elastomers, but characterize the rheological properties of SDS structured fluids. Also, it can be extensively used to treat the ultimate properties of multiphase copolymers.It is general accepted in the modern rheology that no restricted discrepancy exists between solid and fluid of polymers. A polymer can show all the features of a glassy, brittle solid or an elastic rubber or a viscuous liquid depending on the temperature and time scale of measurement. There are different structure units and motion units at different mechanical states. Each motion or flow unit has its own characteristic relaxation time. On the basis of this concept, we consider in our model that the local motion of SDS segment chain is an ordinary motion mode when at forced high-elastic state (lower than T. of PD segment) ; While at high-elastic state, the constituent chains by crosslink, entanglement and physical adsorption in three-dimensional network are considered as elementary structure and motion units for SDS elastomers at two-phase state; While at monomolecular melt state, the network segment by tail, the entangled constituent chain and the monomolecules are the flow and motion units. The continual breakage and reformation of entangled constituent chain on monomolecules due to shear motion and local Brownian diffusion drive the movement of mass center of monomolecules. As increasing the temperature and shear stress, the PS segment is continuously pulled out from PS domain, and then migrated into D...