SYNOPSISMixed networks based on polystyrene (PS) and styrene-ethylene/butylene triblock copolymer (SEBS) binary blends were synthesized via a postpolymerization FriedelCrafts-type reaction employing styrene units and a bis-chloromethylated crosslinking agent. The swelling behavior of the produced gels was studied in relation to network density, SEBS/PS mass ratio, and solubility parameter of the swelling media, in a range of aliphatic, chlorinated, and aromatic solvents. Swelling characteristics of the mixed macronets were found to differ markedly from those of pure homopolymer gels. Selective swelling was observed in three different regions in respect t o the solvent solubility parameter, in contrast to pure PS networks where adsorption was favored in a single region of solvents. This phenomenon was found to depend primarily on the SEBS/PS constitution of gels, while the solvent holding capacity depended directly on the crosslinking density. 0 1995 John Wiley & Sons, Inc.
I NTRO DUCT10 NBlock copolymers and blends with the corresponding homopolymers are a category of materials with increasing scientific interest. Physical, rheological, and thermodynamic properties of styrene-ethylene / butylene and other ABA triblock copolymers have been noted to be the subject of several recent investigations.It has been experimentally proved' that the midblock's chemical structure and the incompatibility between the mid-and the end block have a strong effect on physical and rheological properties of styrene-ethylenelbutylene copolymer (SEBS ). Microphase separation transition ( MST) of diblock copolymers, diblock copolymer-homopolymer mixtures, and triblock copolymers has been both theoretically and experimentally ~i e w e d .~-~ As a result, styrenic block copolymers like SEBS have been shown to exist in a two-phase order, i.e., polystyrene (PS) domains dispersed in a rubbery phase, which is converted to a homogeneous one at elevated temperatures. Weiss et al.6*7 introduced chemical modifications on SEBS by partially sulfonating the PS end blocks.The prepared ionomers were found to exhibit a three-phase structure, owning to polar associations of the composed ionic groups, while viscoelastic and mechanical properties were also studied. Mixing of block copolymers with the corresponding homopolymers has been reporteda12 to lead to materials having improved and desired mechanical properties. In the present work, mixed networks composed of PS and SEBS were prepared through a Friedel-Crafts postpolymerization reaction.Grassie and Gilks13 and Davankov et al.'* reported crosslinking of PS with the use of a FriedelCrafts-type reaction which employed chloromethylated aromatic compounds as crosslinkers. 1,Li-Dichloromethyl-2,5-dimethylbenzene ( DCMDMB ) has been proved to be a desirable Friedel-Crafts crosslinking agent by the work of Peppas and Valkana~.'~ 1517
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