Viscoelastic behavior and order-disorder transition in mixtures of a block copolymer and a midblock-associating resin

The viscoelastic behavior and order-disorder transition in mixtures of a block copolymer and a midblock-associating resin were investigated. The block copolymers investigated were polystyrene-block-polysioprene-block-polystyrene (SIS) copolymers (Shell Development Company), specifically Kraton D-1107, with the block molecular weights 10,000S-120,000I-10,000S, and Kraton D-1111, with the block molecular weights 15,000S-100,000I-15,000S. The midblock-associating resin investigated was a resin polymerized from C₅ hydrocarbon, referred to as Piccotac 95BHT (Hercules Inc.), which is an aliphatic hydrocarbon containing considerable amounts of cyclic structures, with a weight-average molecular weight of 1,100 and a glass transition temperature T_g of 43°C. In the investigation, mixtures of the block copolymer and Piccotac 95BHT were prepared with toluene as solvent. Temperature scans of the samples were made to obtain information on dynamic storage modulus G′, dynamic loss modulus G″, and loss tangent tan δ, using a Rheometrics dynamic mechanical spectrometer. It was found that Piccotac 95BHT decreased the plateau modulus G⁰_N and increased the T_g of the polyisoprene midblock of the SIS block copolymer in the mixture. This experimental observation led to the conclusion that Piccotac 95BHT associates (or is compatible) with the rubbery polyisoprene midblock of the SIS block copolymer. The order-disorder transition behavior of mixtures of SIS block copolymer and Piccotac 95BHT was also investigated by a rheological technique proposed by Han and Kim (Ref. 21). The order-disorder transition temperature T_r (i.e., the temperature at which the ordered microdomain structure of the block copolymer completely disappears) of the SIS block copolymer decreased steadily with increasing amount of Piccotac 95BHT in the mixture. With the information determined on T_r, a phase diagram for the mixture was constructed, showing the boundary between the mesophase and homogeneous phase in the mixture. The phase diagram is in qualitative agreement with the theoretical predictions of Whitmore and Noolandi (Ref. 28).