We investigate the morphology and phase behavior of syndiotactic polypropylene- block -poly(ethylene- co -propylene) (sPP-EPR) and syndiotactic polypropylene- block -polyethylene (sPP-PE) block copolymers. Order−disorder transition temperatures of selected sPP-EPR block copolymers, determined by dynamic mechanical spectroscopy (DMS) and confirmed by transmission electron microscopy (TEM), were analyzed using mean field theory to obtain χ( T ), the Flory−Huggins interaction parameter for the sPP/PE pair, as χ sPP - PE = 6.2/ T − 0.0053 normalized to a four-carbon repeat unit. Various ordered morphologies were observed by TEM, including cylindrical, lamellar, and hexagonally perforated layer morphologies, the latter being most often observed despite the fact that it is expected to be metastable. The sPP crystallization and melting temperatures, T c and T m, determined by differential scanning calorimetry (DSC), show surprisingly little correlation with either block copolymer morphology or the state of block copolymer melt phase (ordered or disordered) but rather increase with decreasing total molecular weight of the block copolymer. Both blocks of the sPP-PE crystallize, but the PE T c and T m of an ordered lamellar sPP-PE are significantly higher than those of an ordered sPP-PE consisting of sPP cylinders in a PE matrix.
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Ruokolainen et al. (2005) studied this question.
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