The role of diisocyanate and soft segment on the intersegmental interactions in urethane and urea based segmented copolymers: A DFT study

Structures and intersegmental interactions in segmented thermoplastic copolymers were studied by density functional theory (DFT) method at B3LYP and M06-2X/6-31g(d,p) levels. Hard segments were chosen to be highly polar urethane and urea groups with various diisocyanate groups. Soft segments were represented by flexible polymers with a wide range of polarity such as poly(ε-caprolactone) (PCL), poly(1,6-hexyl 1,2-ethyl carbonate) (PHEC), polytetramethylene oxide (PTMO), polydimethylsiloxane (PDMS), polyisobutylene (PIB) and polybutadiene (PBu). It was observed that the structural properties such as symmetry and planarity of the diisocyanate groups of the hard segments as well as the miscibility between the hard and soft segments played an important role on the packing of the hard segments and thus, on the phase behavior of copolymers. According to the experimental studies in the literature, these systems have always displayed phase separated morphologies. The calculated interaction energies here revealed that the phase separation is inevitable since the self interactions of the urea/urethane blocks were stronger than their interactions with the soft blocks due to the H-bonding. The control of the size and the shape of the micro phase domains in these materials is very important especially for their biotechnological applications and it can be achieved by varying the type and weight percentage of the soft segments as well as symmetry and planarity of the diisocyanate groups as shown in this work.