Lipid-driven Crystallization of Block Copolymers in Lipid-Polymer Alloys

Tailoring crystallinity of blocks in crystalline-crystalline diblock copolymers (BCPs) is a route to gain control over the material’s optical and mechanical properties. One methodology that has successfully tuned BCPs crystallinity is to include additives to the assembly.[1] In this work, we investigate the crystallization behavior of BCPs as tuned by the addition of a biological lipidic component. We adopted 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) as an additive to induce crystallization-driven self-assembly of poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO). Herein, we scrutinize the effects of the lipids on crystallization of each block in PCL-b-PEO at multiple length scales by IR spectroscopy, differential scanning calorimetry, wide-angle X-ray scattering, small-angle X-ray scattering, and polarization optical microscopy. We discovered that DPPC and BCPs assemble in a uniform alloy with a lamellar structure at the mesoscale. Within this structure, the lipid can enhance crystallinity of PCL while suppressing that of PEO. The crystalline domains appear tubular at the nanoscale and the alloy displays large platelet morphologies at the microscale compared to pure neat polymeric systems. [1] ACS Nano 2015, 9, 4, 3627-3640