Influence of Solvent Polarity on the Self-Assembly of the Crystalline–Coil Diblock Copolymer Polyferrocenylsilane-b-polyisoprene

Abstract

Many poly(ferrocenyldimethylsilane) (PFS) block copolymers form fiber-like micelles with a semicrystalline core in selective solvents. Solvent effects on micelle formation are not well understood. This paper compares micelle formation for a sample of PFS50–PI1000 (the subscripts refer to the number-average degrees of polymerization) in decane with that in tert-butyl acetate (tBA), a more polar solvent. When micelle formation is seeded, by adding block copolymer as a concentrated solution in tetrahydrofuran to solutions of micelle fragments, micelle growth was similar in both solvents. Micelles with a narrow length distribution were formed and the length increased in proportion to the amount of polymer added. In contrast, when micelles were prepared by heating a sample of the block copolymer in decane or tBA to 90 °C and allowing the solution to cool, pronounced differences were observed. In decane, micelles with a uniform width (10 nm) and a length on the order of 5 μm formed after 1 h, and grew to about 10 μm after 5 days. In tBA, aliquots taken from solution 1 h after cooling appeared to undergo microphase separation only upon solvent evaporation. Ribbon-like structures were observed after 1 and 5 days aging, but these evolved into fiber-like structures with a uniform 10 nm width and lengths greater than 30 μm after 25 days. These differences observed in the rate of micelle formation likely reflect differences in the nucleation stage of micelle formation. tBA is a better solvent for the PFS block than decane. As a consequence, it appears to take much longer for semicrystalline micelle nuclei to form in tBA. The seeded growth experiments demonstrate that once seed micelles are present, growth occurs similarly in both solvents.

A design strategy for the hierarchical fabrication of colloidal hybrid mesostructures

“…While CDSA has been reported for BCPs with poly (3-hexylthiophene) 22 , polylactide 23 , polycaprolactone 24 and polyethylene 25 as the crystallizable block, one has the greatest control over this kind of seeded growth for polyferrocenylsilane (PFS) BCPs. Under appropriately chosen self-assembly conditions, all of the added unimer of a PFS BCP grow off the ends of the crystallite seeds in the sample, and uniform elongated structures can be formed [26][27][28][29][30][31] . The 'living' nature of micelle elongation by CDSA thus becomes a tool to control the morphological homogeneity of the structure.…”

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

“…On the other hand, higher solvent affinity of the core‐forming block will suppress the equilibrium melting temperature of the core crystals, leading to a small supercooling for crystallization and accordingly a slow growth rate . This effect was experimentally confirmed by the slower growth rate of PFS 50 ‐ b ‐PI 1000 micelles in tert ‐butyl acetate than in decane . Besides, T c and solvent also affect the uniformity of the formed crystalline micelles.…”

Hierarchical Polymer–Carbon Nanotube Hybrid Mesostructures by Crystallization-Driven Self-Assembly

“…By TEM one finds that these micelles are long (5 to >30 μm), smooth, and very uniform in width. 52 Another way to obtain these micelles is by seeded growth. For example, if a PFS block copolymer (with a long corona-forming block) in THF is added to a hexane or decane solution containing micelle fragments, one also finds smooth cylindrical micelles uniform in width.…”