The Polymer and Colloids Group
At the turn of the 21st century we began a collaboration with Ian Manners to study the self-assembly of polyferrocenylsilane (PFS) block copolymers in selective solvents. What is special about block copolymers such as PFS-polyisoprene (PI) and PFS-polydimethylsiloxane (PDMS) is that they are crystalline-coil block copolymers. When dissolved in a selective solvent for the non-PFS block, the block copolymer forms fiber like micelles with a semicrystalline PFS core and a solvent swollen corona. In 2007, we reported that this self-assembly was driven by the crystallization of the PFS block, and that in turn endowed these polymers with special properties. We discovered that the initially formed micelles can be elongated in a living manner, by adding more PFS block copolymer unimers and that this process can be used to generate more complex structures such as block comicelles.
Wang, X.-S.; Guerin, G.; Wang, H. ; Wang, Y.; Manners, I.; Winnik, M. A. “Cylindrical Block Copolymer Micelles and Co-Micelles of Controlled Length and Architecture”, Science, 317, 644-647 (2007).
This paper and subsequent publications in Nature Materials and Nature Chemistry led to the creation of living crystallization-driven self-assembly (CDSA) as a recognized field of block copolymer self-assembly. The concept has been extended to many other examples of crystalline-coil block copolymers. Over the years, we remain active in this area and our work is highly cited. As of 2023, according to the Web of Science, Manners and Winnik have 189 joint publications, and these publications (>12,000 citations) have an H index of 63!
We use PFS block copolymers (BCPs) as prototypes to explore the factors influencing CDSA.. For example, we have examined the self-assembly behavior of binary mixtures of PFS BCPs and showed that the seeded-growth kinetics of block copolymer unimers dominates their crystallization driven co-assembly behavior. One can manipulate the kinetics to control the growth sequence of unimers and thus the comicelle morphology. Patchy comicelles are formed when the growth rates of unimers are similar, while dissimilar growth rates lead to block comicelles.
Self-Assembly Kinetics as a Route to Controlling the Morphology of Micelles
Xu, J.; Zhou, H.; Yu, Q.; Manners, I.; Winnik, M.A. Competitive Self-Assembly Kinetics as a Route to Controlling the Morphology of Core-Crystalline Cylindrical Micelles, J. Am. Chem. Soc, 2018, 140 (7), 2619-2638, DOI: 10.1021/jacs.7b12444
Addition of small amounts of a PFS homopolymer to a corresponding PFS BCP leads to formation of uniform rod-like micelles in a one-pot process just by heating the mixture to the point where almost all the BCP dissolves and allowing the solution to cool. This process can be scaled up to achieve micelle concentrations of up to 10 wt%. Song, S.; Liu, X.; Nikbin, E.; Howe, J. Y.; Yu, Q.; Manners, I.; Winnik, M. A. Uniform 1D Micelles and Patchy and Block Comicelles via Scalable, One-Step Crystallization-Driven Block Copolymer Self-Assembly, J. Am. Chem. Soc., 2021, 143 (16), 6266–6280. doi.org/10.1021/jacs.1c02395
In one rather unusual example, we synthesized a PFS BCP with an amphiphilic corona chain. This polymer was able to generate objects of different shapes in solvents of different polarities. For example, in a 1:1 hexane-octanol mixture, it formed uniform oval platelets for which the size could be controlled by seeded growth.
Song, S.; Yu, Q.; Zhou, H.; Hicks, G.; Zhu, H.; Rastogi, C. K.; Manners, I.; Winnik. M. A. Solvent effects leading to a variety of different 2D structures in the self-assembly of a crystalline-coil block copolymer with an amphiphilic corona-forming block. Chemical Science, 2020, 11, 4631-4643, DOI: 10.1039/d0sc01453b
While self-assembly to form 1D rod-like structures and 2D platelets is now well documented, much less is known about self-assembly to form 3D objects. We have recently become interested in polymer spherulites. Spherulites have been extensively studied in many fields, including organic optoelectronics, coatings, nanocomposites, perovskite solar cells, biochemistry, biomineral composite synthesis, medical, and supramolecular functional materials. Spherulites are commonly formed in crystallization of polymer melts. The mechanism of spherulite formation is often studied in polymer melts because the long chains slow down the crystallization process. However, before our work, spherulites were not known for BCPs in dilute solution.
We have now shown that spherulites and their precursors can be formed as uniform colloidally stable species by CDSA from a variety of PFS BCPs. One needs an appropriate platelet precursor with patches of secondary crystals on the basal face. These structures and subsequent growth are promoted by high degrees of supersaturation upon unimer addition or by an annealing process that promotes high supersaturation upon cooling. One example is shown here.
Jiang, J.; Nikbin, E.; Hicks, G.; Song, S.; Liu, Y.; Wong, E. C. N.; Manners, I.; Howe, J. Y.; Winnik, M. A. Polyferrocenylsilane block copolymer spherulites in dilute solution, J. Am. Chem. Soc., 2023, 145(2), 1247-1261. DOI:10.1021/jacs.2c11119
