The effect of the amount of in situ formed copolymers on the final morphology of reactive polymer blends with an in situ compatibilizer

The effect of the amount of in situ formed graft copolymers on the blend mo rphology was investigated for immiscible polymer blends of poly(butylene te rephthalate) (PBT) and polystyrene (PS) having various amounts of poly(styr ene-ran-glycidyl methacrylate) (PS-GMA) as an in situ compatibilizer. Two d ifferent blending methods were used to prepare the blends: a melt blending (MB) and a solution blending followed by an oscillatory shearing at a molte n state (SOM). The molecular weight of in situ PS-g-PBT copolymers formed f rom the reaction between PS-GMA and PET in the blend was determined by usin g high-temperature gel permeation chromatography (GPC). The concentration o f in situ formed graft copolymers of PS-g-PBT in the blends [C-copolymer (b lend)] prepared by either MB or SOM was determined by solvent extraction fo llowed by Fourier transform infrared spectroscopy (FTIR) analysis. On the b asis of the GPC and FTIR results, we concluded that the PS-g-PBT in the ble nds has 1.3-2 PET chains grafted onto a PS-GMA chain. From FTIR analysis an d the morphology of the blends investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), we found that the interf acial areal density (Sigma) of in situ formed PS-g-PBT is similar to 0.1 ch ains/nm(2) for the blends prepared by SOM regardless of the amounts of PS-G MA added initially in the blend. However, although C-copolymer (blend) in t he blend prepared by MB was similar to that prepared by SOM, the dispersed domain size of the former was larger than that of the latter, especially fo r blends with a large amount of PS-GMA (20 wt %). This suggests that at lea st some parts of in situ graft copolymers in the blend prepared by MB are l ocated in the matrix phase as micelles with sizes of 20-50 mu m.