Miscibility of Polymer Blends Comprising Poly (Ethylene Oxide) - Epoxidized Natural Rubber

Miscibilty of thermoplastic-elastomer blends comprising poly(ethylene oxide) (PEO) and epoxidized natural rubber with 25 mol% epoxide level (ENR-25) were studied by differential scanning calorimetry (DSC) and polarized optical microscope (POM), respectively. Two glass transition temperatures (Tg), corresponding to those of neat PEO and ENR-25 are observed over the entire composition range. It reflects the immiscibility of the two constituents in the molten state. Hoffman-Weeks method was employed to determine the equilibrium melting temperatures (Tm o ) for the PEO/ENR-25 blends. No systematic variations of Tm o and equivalently the apparent melting temperature (Tm) with ascending ENR-25 content for the blends are detected. However, quantities Tm increase with ascending isothermal crystallization temperature (Tc). There is no melting transition of PEO in PEO/ENR-25 blends when the ENR-25 content in the blend > 50 wt%. Reciprocal half time (t1/2 -1 ) is applied to characterize the isothermal crystallization kinetics of the phase-separated blends. The rate of crystallization and equivalently the spherulite growth rate (G) of PEO decreases with increasing Tc but exhibit no systematic variations with ascending ENR-25 content. No crystallization is observed for the blends when the PEO content is ≤ 50 and  40 wt% when analyzed using DSC and POM, respectively. The birefringence Maltese cross structure of PEO appears deformed with irregular border and coarse texture when the amount of ENR-25 in the blend  40 wt%.