Controlling Morphology of Polymer Particles Synthesized from Condensed Monomer Droplets

Non-spherical polymer nanoparticles with tunable morphologyarean emerging class of functional materials with enormous potentialin drug delivery, sensing, and soft robotics. However, their developmentis currently limited by the laborious synthesis with limited controlover particle morphology. To bridge that gap, we demonstrate the capabilityof a facile synthesis technique, namely, condensed droplet polymerization(CDP), to obtain non-spherical particles with disparate morphologiesin a vapor deposition apparatus. The morphological control is enabledby a unique in situ digital microscopy, which reveals the evolutionof particle morphology development in real time as the unreacted monomerwas removed from the partially polymerized droplets through evaporation.To guide particle morphology design, the effect of fundamental properties,such as the monomer propagation constant (k (p)) and polymer glass transition temperature (T (g)), on the resulting particle morphology was investigated usingbenzyl methacrylate (BzMA, low k (p) andlow T (g)) and acrylic acid (AA, high k (p) and high T (g)) asexamples. Partially polymerized BzMA droplets shrank isotropicallyduring monomer evaporation, giving rise to compact polymer domes,whereas partial polymerization led to a polymerized layer encompassingunreactedAA monomer, which became wrinkled polymer shells or granular particlesupon monomer removal. Such insight provides a framework for understandingthe fundamental mechanisms of particle morphology formation. The process-propertycorrelations serve to advance the control over polymer morphologyin CDP with useful applications ranging from drug delivery to softrobotics.