Phase Behavior of poly styrene-block-poly (4-vinylpyridine) copolymers coordinated by metal chloride

The effect of cadmium chloride (CdCl2) on the phase behavior of polystyrene-block-poly(4-vinylpyridine) copolymer (S4VP) was investigated by using rheometry, small-angle X-ray scattering, and transmission electron microscopy. For this purpose, symmetric S4VPs with various molecular weights were prepared by anionic polymerization. We found that with the addition of CdCl2 the order-to-disorder transition of S4VP was significantly increased because of the intermolecular coordination connecting different P4VP block chains. We also studied the change of the domain spacing (D) upon addition of CdCl2 as well as gelation behavior. At a relatively low content of CdCl2 (gamma < 6, where gamma is the number of coordinated CdCl2 per chain), D remains unchanged. However, when the amount of CdCl2 increases further, D begins to decrease due to many coordinations of CdCl2 that strongly perturb block copolymer conformation, including many ring closures. Furthermore, it is found that the scaled gelation point increases with increasing molecular weights of S4VP.