Tailored (ABAC)n segmented copolymers, composed of hydrophilic polyethylene glycol (PEG) containing segments, less hydrophobic polypropylene glycol (PPG) segments and thermoreversible physically crosslinking bisurea segments.
The polymers were synthesized in melt by a polyaddition reaction from an amino-terminated PPG-PEG-PPG macromonomer , low molecular amino-terminated PPG and hexamethylene diisocyanate (HMDI). The molecular weight was regulated by the addition of monofunctional PPG-amine as terminating agent. Endcapping of residual amino endgroups was done with acetic anhydride. The melt synthesis provides the preparation of (ABAC)n copolymers in large quantities (up to several 100 g per batch). Because no by-products are formed in melt polyaddition reactions and no solvents are used, no purification is required.
Our products show a low reversible melting transition from the elastomeric state to the molten state around 100 °C. The low melt viscosity (100 Pa s at 100 °C) enables an easy processing by different extrusion-based additive manufacturing techniques, such as melt electrowriting and extrusion based 3D printing. We successfully prepared 3D printed constructs by both methods. These printed constructs swell in water and form hydrogels with sufficient mechanical stability and adjustable disintegration behavior which is of importance for applications in biofabrication.