Engineering internal nanostructure in 3D‐printed materials via polymer molecular weight distribution

Abstract The distribution of molecular weights in polymers, known as the molecular weight distribution (MWD), plays a significant role in dictating the behavior of polymer self‐assembly and influencing the characteristics of the resulting materials. This study investigates how MWD of macromolecular chain‐transfer agents (macroCTAs) impact internal nanostructures in materials prepared by polymerization‐induced microphase separation (PIMS) 3D printing. In the aim of elucidating this relationship, the study initially harnessed the precision offered by narrow‐MWD macroCTAs, which provide precise control over phase separation, as assessed by atomic force microscopy (AFM) and small‐angle X‐ray scattering (SAXS) measurements. Through systematic variation of macroCTA molecular weights, the dimensions of the distinct domains were precisely tuned from 10 to 90 nanometers and a decrease of materials stiffness was observed with increased domain size. In contrast, the utilization of a broader MWD, achieved by blending two distinct macroCTAs, resulted in increased domain size dispersity and reduced interface sharpness, without significantly affecting the mechanical properties of the 3D‐printed materials. Overall, this approach expands the strategies for manipulating the nanoscale architecture of 3D‐printed PIMS materials, opening new possibilities for printing advanced engineering materials with tailorable properties.