In the present work, synthesis and characteristics of the interpenetrating polymer networks(IPN's) based on styrenic triblock copolymer has been studied. For the preparation of IPN, styrenic copolymers, polystyrene-polybutadiene-polystyrene(SBS) and polystyrene-poly(ethylene buthylene)-polystyrene(SEBS), were dissolved into the mixture of methyl methacrylate(MMA) and n-butyl acrylate(n-BA), or styrene monomer respectively. 3 mol\% of ethylene glycol dimethacrylate(EGDMA) or 1.5 mol% divinyl benzene(DVB)was used as a crosslinking agent and 1 wt% 2,2'-azobisisobutyronitrile(AIBN) was used as a initiator. Reaction temperature was kept at 60℃. Common solvent was used to know the influence of the presence of cosolvent during reaction, and toluene was selected as a cosolvent via swelling test. Corresponding semi-IPN, synthesized without crosslinking agent, of the same polymer composition was also evaluated for comparison. To characterize the IPN's, phase separation behavior, dynamic mechanical and tensile properties were examined as well as the investigation of morphology by TEM.
The conversion of P(MMA-co-nBA) during the synthesis of IPN decreased by the presence of cosolvent in reaction medium and by increasing SBS concentration. Cloud conversion at the onset of phase separation was found to be higher in IPN than in semi-IPN and increased by the cosolvent. The phase separation mechanism during reaction was thought to be the spinodal decomposition through the light scattering measurement and morphology investigation using TEM. For the SBS/P(MMA-co-nBA) IPN, SBS appeared to be more continuous because of the low concentration of polyacrylate when the phase separation begins. Domain size increased by the presence of cosolvent and by decreasing of SBS content. From the dynamic mechanical behavior, two Tg peaks moved toward each other depending on the SBS concentration, which implied the improved intermixing. For the SEBS/P(MMA-co-nBA) IPN, spinodal structure was observed. The domain size was found to be larger than that of corresponding SBS/P(MMA-co-nBA), and this can be attributed to the fact that little grafting between components formed during the reaction of SEBS/P(MMA-co-nBA) IPN. Similar results were also obtained for SBS/PS IPN's.
