Maleic acid-alt-styrene copolymer as compatibilizer for poly(ethylene oxide)-poly(styrene) blends

Maleic acid-alt-styrene (MAaS) copolymer with number-average molecular weight M̄_n = 2500 was used as a compatibilizer in blends of poly(ethylene oxide) (PEO) and poly(styrene) (PS). PEO with weight-average molecular weight M̄_w = 10⁵ (PEO₁₀₀) and two PS samples with M̄_w = 9×10⁴ and 4×10⁵, respectively (PS₉₀ and PS₄₀₀, respectively) were used. A depression of the melting temperature T_m of PEO in blends containing MAaS relative to pure PEO and PEO/PS blends was observed. The melting enthalpy ΔH_m for the PEO/PS blends containing MAaS was lower than those of pure PEO and PEO/PS blends without compatibilizer. The crystallization kinetics of PEO and the blends were studied by differential scanning calorimetry (DSC) at different crystallization temperatures T_c. Flory-Huggins interaction parameters χ₁₂ for the blends were estimated. Their values are in good agreement with those obtained for similar systems and suggest that the free energy of mixing ΔG_mix should be negative. Polarized optical microscopy shows differences in the macroscopic homogeneity of the blends containing compatibilizer that could be attributed to a compatibilization process.