Crystallization-Driven Self-Assembly of Polyferrocenyldimethylsilane Block Copolymers with the Corona Modified with Pendant Amino Groups

Abstract

Polyferrocenyldimethylsilane- block -polyisoprene (PFS- b -PI) with a PI block much longer than the PFS block typically forms one-dimensional (1D) rod-like micelles in a selective solvent like decane. Here, we test the idea that introducing polar amino groups into the PI block (ca. 10 mol % via a thiol–ene reaction) would reduce the corona dimensions in decane and promote the formation of 2D assemblies. For example, PFS 65 - b -PI 390 -NH 2 formed ribbon-like micelles when added as a unimer to rod-like PFS 44 - b -PMVS 250 (PMVS = polymethylvinylsiloxane) micelles as seeds in decane. Elongated platelets with fiber-like protrusions from the ends were formed when PFS 65 - b -PI 390 -NH 2 was combined with a second block copolymer (BCP) and added to the rod-like seed micelles. In the co-self-assembly of PFS 65 - b -PI 390 -NH 2 and PFS 25 - b -PI 1000 or PFS 50 - b -PI 1000, we varied the mass ratio from 3:7 to 1:1 and 7:3, leading to platelet@fiber structures with increased length and width. A similar phenomenon was seen in mixed micelles of PFS 65 - b -PI 390 -NH 2 with PFS 35 - b -PI 273 or PFS 38 - b -PI 850 . As the PFS 65 - b -PI 390 -NH 2 content in the BCP blends was increased from 30% by mass to 70%, the widths of the micelles nearly doubled. We explain this effect in terms of the influence of the amino groups on the corona chain dimensions: BCP mixtures with a larger fraction of corona chains bearing amino groups led to contracted corona dimensions, promoting epitaxial growth of unimers on the lateral edges of the micelles. If the second BCP had a long corona-forming block, then increasing amounts of this block led to longer micelles that were somewhat narrower in width. Here, the long corona chains suppress epitaxial growth along the lateral edge of the micelles. The introduction of polar amino groups into the PI block of PFS- b -PI BCPs led to new types of uniform structures by CDSA. Many of the 2D assemblies that we prepared had secondary crystals on their basal surfaces. We showed that adding PFS 65 - b -PI 390 -NH 2 unimer at high supersaturation to these micelles as seeds led to 3D assemblies associated with spherulite formation. In addition, direct self-assembly of each of the three PFS- b -PI-NH 2 BCPs also formed spherulites and their precursors.

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