Probing the Growth Kinetics for the Formation of Uniform 1D Block Copolymer Nanoparticles by Living Crystallization-Driven Self-Assembly

Abstract

Living crystallization-driven self-assembly (CDSA) is a seeded growth method for crystallizable block copolymers (BCPs) and related amphiphiles in solution and has recently emerged as a highly promising and versatile route to uniform core-shell nanoparticles (micelles) with control of dimensions and architecture. However, the factors that influence the rate of nanoparticle growth have not been systematically studied. Using transmission electron microscopy, small- and wide-angle X-ray scattering, and super-resolution fluorescence microscopy techniques, we have investigated the kinetics of the seeded growth of poly(ferrocenyldimethylsilane)- b-(polydimethylsiloxane) (PFS- b-PDMS), as a model living CDSA system for those employing, for example, crystallizable emissive and biocompatible polymers. By altering various self-assembly parameters including concentration, temperature, solvent, and BCP composition our results have established that the time taken to prepare fiber-like micelles via the living CDSA method can be reduced by decreasing temperature, by employing solvents that are poorer for the crystallizable PFS core-forming block, and by increasing the length of the PFS core-forming block. These results are of general importance for the future optimization of a wide variety of living CDSA systems. Our studies also demonstrate that the growth kinetics for living CDSA do not exhibit the first-order dependence of growth rate on unimer concentration anticipated by analogy with living covalent polymerizations of molecular monomers. This difference may be caused by the combined influence of chain conformational effects of the BCP on addition to the seed termini and chain length dispersity.

Solution self-assembly of ABC triblock terpolymers with a central crystallizable poly(ferrocenyldimethylsilane) core-forming segment

“…In this case, EtOAc was used as a selective solvent over a less polar solvent such as hexanes (which is typically used for PFDMS-b-PDMS self-assembly) as it is a good solvent for both the PMMA and PIP blocks. Self-assembly in EtOAc is typically slower than in less polar solvents such as hexanes as EtOAc is only moderately poor for the PFDMS core-forming block 67,68. PFDMS 52 -b-PDMS 414 seed micelles (block ratio 8.0 : 1.0, L n = 49 nm, L w /L n = 1.10) were prepared by sonication of a solution of long polydisperse micelles formed by self-nucleation in EtOAc for 2 h at 0 °C.…”

One‐dimensional growth kinetics for formation of cylindrical crystalline micelles of block copolymers

“…Boott et al recently reported a detailed study on the growth kinetics of a series of PFS‐ b ‐poly(dimethylsiloxane) (PFS‐ b ‐PDMS) BCPs . However, they found that, at all concentrations and over a series of different T c s, micelle growth did not fit Equation .…”

“…Usually, altering T c and tuning solvency have a similar effect on the growth kinetics. At a higher T c or in a solvent with better solubility toward the core‐forming block, the exchange between the unimer and crystalline micelles is accelerated and the equilibrium shifts to dissolution, thus the growth rate of cylindrical crystalline micelles is reduced . Moreover, T c may also affect the width of the cylindrical micelles .…”

“…At a higher T c or in a solvent with better solubility toward the core‐forming block, the exchange between the unimer and crystalline micelles is accelerated and the equilibrium shifts to dissolution, thus the growth rate of cylindrical crystalline micelles is reduced . Moreover, T c may also affect the width of the cylindrical micelles . Simulations revealed that, when the corona‐forming block had lower affinity to the solvent or the core‐forming block had higher affinity to the solvent, the growth rate of the fibril crystalline micelles could be effectively reduced .…”

“…Winnik and Manners studied the growth kinetics of two PFS‐ b ‐PDMS BCPs with different PFS lengths but similar PDMS lengths. It was found that, a shorter PFS block led to both reduced growth rate and shorter micelles, which were ascribed to the weak crystallizability of shorter PFS block and different aggregation numbers in unit length for two different BCPs . This means that the value of Q in Equation varies with the length of the core‐forming block.…”