Deog Man Baek

Rheological behaviour of block copolymers in the disordered state: effects of molecular weight and block length ratio

Abstract The effects of molecular weight and block length ratio on the rheological behaviour of polystyrene-block-polyisoprene-block-polystyrene (SIS) copolymers in the disordered state were investigated. For the study, SIS triblock copolymers were synthesized via anionic polymerization, and linear dynamic viscoelastic properties (i.e. dynamic storage and loss moduli, G′ and G″) of the SIS block copolymers were measured at various temperatures as functions of angular frequency (ω), using a cone-and-plate rheometer. The disordered state of the samples was determined by the threshold temperature at which the plot of log G′ versus log G″ becomes virtually independent of temperature as the temperature was increased. It has been found that when the block length ratio is kept the same, the melt elasticity of SIS block copolymers in the disordered state becomes independent of molecular weight, while the viscosity increases with molecular weight, and the block length ratio greatly influences both melt viscosity and elasticity.

Phase equilibria in mixtures of block copolymer and homopolymer

Abstract Phase diagrams were constructed experimentally for mixtures of a polystyrene-block-polyisoprene-block-polystyrene (SIS) copolymer and a homopolymer polystyrene. For the study, two SIS triblock copolymers having spherical and cylindrical microdomain structures, respectively, and a series of homopolymer polystyrenes were synthesized via anionic polymerization. In constructing phase diagrams, we combined the results of dynamic viscoelastic measurement (i.e. logarithmic plots of dynamic storage modulus versus dynamic loss modulus), which allowed us to determine the boundary between the mesophase and homogeneous phase, and turbidity measurement, which allowed us to determine cloud point curves for liquid-liquid (macrophase) separation. Experimental results are compared with predictions made by the theory of Hong and Noolandi. We have found that predicted results are at variance with experimental results.

Viscoelastic Behavior, Thermodynamic Compatibility, and Phase Equilibria in Block Copolymer-Based Pressure-Sensitive Adhesives

Abstract The viscoelastic behavior, thermodynamic compatibility, and phase equilibria in block copolymer-based pressure-sensitive adhesives were investigated. The block copolymers investigated were: (1) polystyrene-block-polybutadiene-block-polystyrene (SBS) copolymer (KRATON® D-1102, Shell Development Company) and (2) polystyrene-block-polyisoprene-block-polystyrene (SIS) copolymer (KRATON® D-1107, Shell Development Company). The tackifying resins investigated were: (1) WINGTACK® 86 (Goodyear Tire & Rubber Company) and (2) PICCOTAC® 95BHT (Hercules Inc.). Samples of various compositions were prepared by a solution-casting method with toluene as solvent. Measurements of dynamic storage modulus (G″), dynamic loss modulus (G″), and loss tangent (tan δ) were taken, using a Rheometrics Mechanical Spectrometer. It was found that: (1) both WINGTACK 86 and PICCOTAC 95BHT were equally effective in decreasing the plateau modulus (G O N ), and increasing the glass transition temperature (Tg ) of the polyisoprene mi...