Poly(Oxazoline)s with Tapered Minidendritic Side Groups as Models for the Design of Synthetic Macromolecules with Tertiary Structure. A Demonstration of the Limitations of Living Polymerization in the Design of 3-D Structures Based on Single Polymer Chains

Abstract

The synthesis and living cationic ring-opening polymerization of 2-[3,4-bis(n-alkan-1-yloxy)phenyl]-2-oxazolines with alkan being tetradecan and pentadecan, i.e., (3,4)nG1-Oxz with n = 14 and 15, is described. The structural analysis of the resulting polymers with well-defined molecular weights and narrow molecular weight distribution was carried out by a combination of techniques, including differential scanning calorimetry (DSC), thermal optical polarized microscopy (TOPM), and X-ray diffraction (XRD). At low molecular weights both polymers self-assemble into spherical supramolecules that self-organize into a Pm3n 3-D lattice while at high molecular weights they form cylindrical macromolecules that self-organize into a p6mm 2-D hexagonal columnar lattice. Both polymers exhibit a 3-D shape change as a function of their degree of polymerization as was reported for the first time in a previous publication from our laboratory (Percec, V.; Ahn, C.-H; Ungar, G.; Yeardley, D. J. P.; Möller, M.; Sheiko, S. S. Nature (London) 1998, 391, 161). Since these polymers can be obtained via a living polymerization, a detailed mechanistic investigation of the influence of the degree of polymerization and molecular weight distribution on the formation of a 3-D spherical macromolecule from a single polymer chain, i.e., a tertiary structure, was possible. The experimental results have demonstrated that the synthesis of nonbiological macromolecules exhibiting tertiary structure is possible in at most a few percent of all macromolecules via living polymerization. This is the case even when macromolecules with very narrow molecular weight distributions and well-defined molecular weights are used. Therefore, the design of synthetic macromolecules with tertiary structure requires not only chains with well-defined molecular weight but also, in particular, macromolecules with no distribution of their chain length.

Characterization of different poly(2‐oxazoline) block copolymers by MALDI‐TOF MS/MS and ESI‐Q‐TOF MS/MS

“…The cationic ring opening polymerization (CROP) of 2‐oxazolines was first reported in the 1960s5–8 and the living polymerization mechanism was also confirmed by MS 9. Because of the versatility of 2‐oxazoline monomers, the synthesis of a library of well‐defined copolymers with special properties, like self‐organizing features as well as thermoresponsive behavior10–13 is possible, as a consequence, they represent ideal candidates for the concept of functional multicompartment micelles 1, 14–16…”

Small‐Molecule Modulation of Soft‐Matter Frank–Kasper Phases: A Method for Adding Function to Form

“…[10b-f, 11a,f] On the other hand, this polymer blending strategy now requires solving the potentially even greater challenge of having to optimize synergistic interactions between multiple polymer components that are each still subject to the whims of synthetic variance in M n and values. [18] Accordingly, we decided to explore the use of a monomolecular weight small molecule as a FK phase diagram modulator that could be reliably sourced in pure form and in commercially scalable volumes as required. Here, the bioactive lipophilic antioxidant 2 (see Figure 1) appeared to be a good choice given the rich scientific literature available regarding its impact on the stability and phase behavior of lipid bilayers and self-assembling amphiphiles, including those developed for drug delivery systems.…”

Poly(2‐oxazoline): eine Polymerklasse mit vielfältigen Anwendungsmöglichkeiten

“…[93,94] Außerdem berichteten Percec et al über systematische Veränderungen der Molekülstruktur von Poly[2-{3,4-bis(n-alkoxy)phenyl}-2-oxazolinen] in Bezug auf den Polymerisationsgrad sowie die Länge der Alkoxyketten. [95,96] Die Polymere mit einer Alkoxykettenlänge von Octan bis Tridecan bildeten kolumnare hexagonale Gitter, deren Abmessungen von der Alkoxykettenlänge wie auch vom Polymerisationsgrad abhängen. [95] Im Unterschied dazu zeigten die Polymere mit Tetradecan-und Pentadecan-Alkoxyketten einen Übergang von einer dreidimensionalen kubischen Phase bei einem niedrigen Polymerisationsgrad zu einer zweidimensionalen hexagonalen kolumnaren Phase bei einem höheren Polymerisationsgrad (Abbildung 6).…”

“…[95] Im Unterschied dazu zeigten die Polymere mit Tetradecan-und Pentadecan-Alkoxyketten einen Übergang von einer dreidimensionalen kubischen Phase bei einem niedrigen Polymerisationsgrad zu einer zweidimensionalen hexagonalen kolumnaren Phase bei einem höheren Polymerisationsgrad (Abbildung 6). [96] Interessanterweise wurde für Polymere mit mittleren Kettenlän-gen ein thermischer Übergang zwischen den beiden Phasen beobachtet.…”