Chain entanglement and molecular dynamics of solution-cast PMMA/SMA blend films affected by hydrogen bonding between casting solvents and polymer chains

Abstract

The effects of intermolecular interaction between casting solvents and polymer chains on molecular entanglement and dynamics in solution-cast poly(methyl methacrylate)/poly(styrene-co-maleic anhydride) (PMMA/SMA) films were investigated by dynamic rheological measurement and broadband dielectric spectroscopy. A series of polymer blend films were cast from the mixed solvents composed of m-xylene and acetic acid with different mass ratio of acetic acid (R_ac) at a solution concentration of 5 wt%, and in solutions the quantity of hydrogen bonding between PMMA and acetic acid was adjusted by R_ac. FTIR results confirmed the existence of hydrogen bonding between carbonyl in PMMA and hydroxyl in acetic acid. Although the topological entanglement density of the resultant films decreased with increasing R_ac, the α-relaxation peak shifted towards lower frequency and a higher glass transition temperature (T_g) appeared due to the increased cohesional entanglement in PMMA/SMA blend films induced by hydrogen bonding between PMMA and acetic acid. Furthermore, the dc conductivity decreased due to the more homogeneous structure in PMMA/SMA blend films cast from mixed solvents with higher R_ac. Neither the width distribution of α-relaxation nor the dynamics of β-relaxation in these films was influenced by hydrogen bonding between PMMA and acetic acid due to the unchanged heterogeneity of the segmental dynamics and local environment of the segments. These results revealed that the hydrogen bonding between polymers/solvent during casting film can greatly influence the chain entanglement and molecular dynamics of the resultant polymer blends due to the memory effect of polymer chain.