Consequences of low-χ design in block copolymer self-assembly

Abstract

We performed the first systematic study of the phase behavior of ABC bottlebrush triblock terpolymers. Along the way, we discovered a new lamellar morphol. with unusual consequences for polymer properties and scaling behavior. We synthesized a series of ABC triblock terpolymers having grafted polylactide (L), polystyrene (S), and poly(ethylene oxide) (O) side chains. Partial mixing of L and O end blocks due to low-χ design produces a new morphol. (LAM_p) with mesoscopic ACBC connectivity, counter to all known examples for ABC triblock terpolymer self-assembly. For ABC triblock terpolymers, the std. model demands periodic domains with ABCB repeat units (i.e., LAM_3). In our system as designed, however, we can decouple the domain connectivity from the synthesized block connectivity. Other consequences of partial mixing in LAM_p include a dramatic decrease in domain spacing with increasing mol. wt. under certain conditions. LAM_p has been characterized by small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). SCF theory (SCFT) for brush polymers supports the exptl. model and affirms the importance of χ. Recently, we have extended these insights into low-χ design from ABC triblock terpolymers to polymer blends. To the best of our knowledge, these phenomena are unprecedented in block copolymer self-assembly. This discovery introduces a new tool for controlling polymer structure and properties in future materials design.