Effect of block composition on thermal properties and melt viscosity of poly[2-(dimethylamino)ethyl methacrylate], poly(ethylene oxide) and poly(propylene oxide) block co-polymers

Abstract

To modify the rheological properties of certain commercial polymers, a set of block copolymers were synthe- sized through oxyanionic polymerization of 2-(dimethylamino)ethyl methacrylate to the chain ends of commercial pre- polymers, namely poly(ethylene oxide) (PEO), poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO), and poly(propylene oxide) (PPO). The formed block copolymers were analysed with size exclu- sion chromatography and nuclear magnetic resonance spectroscopy in order to confirm block formation. Thermal charac- terization of the resulting polymers was done with differential scanning calorimetry. Thermal transition points were also confirmed with rotational rheometry, which was primarily used to measure melt strength properties of the resulting block co-polymers. It was observed that the synthesised poly(2-(dimethylamino)ethyl methacrylate)-block (PDM) affected slightly the thermal transition points of crystalline PEO-block but the influence was stronger on amorphous PPO-blocks. Frequency sweeps measured above the melting temperatures for the materials confirmed that the pre-polymers (PEO and PEO-PPO-PEO) behave as Newtonian fluids whereas polymers with a PDM block structure exhibit clear shear thinning behaviour. In addition, the PDM block increased the melt viscosity when compared with that one of the pre-polymer. As a final result, it became obvious that pre-polymers modified with PDM were in entangled form, in the melted state as well in the solidified form.