Abstract:

Molecular self-assembly processes lead to arrangements in which units are spontaneously organized into ordered structures using mechanisms driven by free energy that include, Van der Waals, electrostatic, hydrogen  bonding, and hydrophobic interactions [1,2]. Self-assembled structures have potential as carriers of genes and in controlled drug release applications, because of advantages such as controllable architecture, biocompatibility, and biodegradability [3,4]. In this presentation, we will discuss different aspects on the self-assembly process by employing three copolymer systems of various natures.

            Pluronic (tradename) is a non-ionic water-soluble triblock copolymer (PEO-PPO-PEO), comprising of poly(ethylene oxide) and poly(propylene oxide) blocks, which is known to self-assemble in water into micelles. These micelles consist of a hydrophobic core of PPO and a shell of solvated PEO. In drug delivery, the problem with Pluronic as a long-time delivery vehicle is the inability of micelles or nanogels to provide sustained drug delivery over longer times than a few days. By attaching poly(caprolactone) (PCL) to both ends of Pluronic (F127), the copolymer (PCLm-Pluronic-PCLm, where m is 5 or 11) becomes more hydrophobic and this improves the stability of the self-assembled structures [5]. The results show that both micellization and inter-micellization are controlled by polymer concentration, temperature, and length of the PCL block.

            Thermoresponsive amphiphilic biodegradable block copolymers of the type poly(e-caprolactone-co-lactide)-poly(ethylene glycol)-poly(e-caprolactone-co-lactide) (PCLA-PEGm-PCLA) have great potential for various biomedical applications. Effects of PEG-spacer length (m=1000 and 1500), temperature, and polymer concentration on the self-assembling process to form supramolecular structures in aqueous solutions of the PCLA-PEGm-PCLA copolymer [6]. Effects of spacer length (PEG) and temperature on the creation and structure of micelles will be presented and discussed.

            Atom transfer radical polymerization (ATRP) is a powerful method for synthesis of low polydispersity block copolymers in aqueous media. There are two possible routes to synthesize block copolymers with the aid of ATRP, “one-pot” and “two-pot” approaches. In the “two-pot”, the first block is isolated, purified, and then utilized as a macroinitiator, whereas in “one-pot” the synthesis proceeds through sequential monomer addition without isolation and purification. The aim is to scrutinize the effect of polymerization method on the self-assembly and micellization in the polymerization of methoxyl-poly(ethylene glycol)-block-poly(2-acrylamido-2-methyl-1-propanesulfonic sodium)-block-poly(N-isopropyl acrylamide) (MPEG-b-PAMPS-b-PNIPAAM) triblock copolymer.

 

References

[1] Whitesides, G. M. and Grzybowski, B. Science, 295, 2418-2421 (2002).

[2] Mandal, D., Shirazi, A. N. and Parang, K. Org. Biomol. Chem., 12, 3544–3561 (2014).

[3] Yang, B., Lowe, J. P., Schweins, R. and Edler, K. J. Biomacromolecules, 16, 457-464 (2015).

[4] Bonacucina, G., Cespi, M., Mencarelli, G., Giorgioni, G. and Palmieri, G. F. Polymer, 2,

779−811 (2011).

[5] Gjerde, N., Zhu, K., Nyström, B. and K. D. Knudsen, K.D. Phys. Chem. Chem. Phys., 20,

2585—2596 (2018).

[6] Nielsen, J. E., Zhu, K., Sande, S. A., Kováčik, L., Cmarko, D., Knudsen, K. D. and  Nyström,

B. Phys. Chem. B, 121, 4885−4899 (2017).

​