Key aspects to yield low dispersity of PEO-b-PCL diblock copolymers and their mesoscale self-assembly

Abstract

Poly(ethylene oxide)-block-polycaprolactone (PEO-b-PCL) is one of the widely used biocompatible amphiphilic block copolymers which is able to self-assemble into a variety of 3D structures, including polymersomes. Controlled self-assembly into a 3D structure with a certain size and morphology might require uniform PEO-b-PCL (Đ M < 1.1), which has not been possible to synthesize so far. In this work, we optimized the well-known synthesis of PEOb-PCL, catalyzed by SnOct 2 , leading to a low molecular-weight dispersity (< 1.1), and discussed the aging effects of SnOct 2 on the overall kinetics of the synthesis. To understand the effect of the dispersity of PEO-b-PCL on its self-assembly, we compared self-assembled structures formed by uniform PEO-b-PCL (Đ M < 1.1) with the ones formed by non-uniform analogues (Đ M > 1.1). Furthermore, we demonstrated the benefits of uniform PEO-b-PCL when a high degree of end-group activation is required through ω-tosylation.

A roadmap for poly(ethylene oxide)‐block‐poly‐ε‐caprolactone self‐assembly in water: Prediction, synthesis, and characterization

“…It appears that given the multiplicity of factors affecting block copolymers self‐assembly (blocks solubility, chain length, chain rigidity, and eventually specific interactions like hydrogen bonding), the construction of predictive self‐assembly phase diagrams of such compounds needs to be performed on a case‐by‐case basis for each specific copolymer. Furthermore, for PEO‐PCL, it is also clear that the preparation procedure has a drastic effect on the final morphology and size of the self‐assembled aggregates of these copolymers, as discussed by Konishcheva et al in a recent aricle . It will be shown that the outcome of our SCF computations can provide useful insights to understand these results, in particular to understand weather a structure is at thermodynamic equilibrium or not.…”

“…Hence, in the experimental design, it is extremely important to select a preparation procedure which ensures the formation of assemblies close to the thermodynamic equilibrium. For PEO‐PCL copolymers, it has been shown experimentally (see Supporting Information Fig. S8 for a visual comparison) that the final morphology can be dependent on the preparation procedure, leading to the coexistence of mesoscale and nanoscale aggregates of various morphologies.…”

“…The preparation process plays an important role, especially for objects with complex geometry as cylinders or hollow spheres. Two different kinds of approaches are usually followed to prepare self‐assembled structures: bottom‐up , when the polymer is molecularly dissolved in a good solvent and forced to assemble by a solvent switch, and top‐down , where a precursor phase is induced to rearrange in solution …”

“…To prepare complex architectures with a bottom‐up approach (e.g., solvent switch), the chains need time to organize into a stable conformation. If the solvent switch is too fast, the lyophobic chains tend to collapse forming spherical objects, as this is a faster way to reduce their interfacial area.…”

Synthesis of Linear ABC Triblock Copolymers and Their Self‐Assembly in Solution

“…The resulting PEO ‐b ‐PDMS‐ b ‐PMOXA self‐assembled into polymersomes with asymmetric membrane that induced a directed insertion of transmembrane proteins. A similar principle was also used for the synthesis of poly(ethylene oxide)‐ block ‐polycaprolactone‐ block ‐(poly‐2‐methyl‐2‐oxazoline) (PEO‐ b ‐PCL‐ b ‐PMOXA) . PEO‐ b ‐PCL was synthesized via Sn(Oct) 2 ‐catalyzed ROP of ε ‐CL using PEO as a macroinitiator.…”