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

• Published in: Biomacromolecules Vol. 2; no. 3; pp. 729 - 740
• Main Authors: Percec, Virgil, Holerca, Marian N, Uchida, Satoshi, Yeardley, Duncan J. P, Ungar, Goran
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 01.09.2001; Amer Chemical Soc
• Subjects: Biochemistry & Molecular Biology; Calorimetry, Differential Scanning; Chemistry; Chemistry, Organic; Drug Design; Life Sciences & Biomedicine; Macromolecular Substances; Magnetic Resonance Spectroscopy; Models, Molecular; Molecular Structure; Molecular Weight; Oxazoles - chemical synthesis; Oxazoles - chemistry; Physical Sciences; Polymer Science; Polymers - chemical synthesis; Polymers - chemistry; Science & Technology; Thermodynamics; X-Ray Diffraction; MONODENDRONS; BUILDING-BLOCKS; OLIGO(ETHYLENE OXIDE); POLYMETHACRYLATE; JACKETED LINEAR-POLYMERS; TUBULAR-SUPRAMOLECULAR ARCHITECTURES; LIQUID-CRYSTALLINE PHASE; SHAPED MONOESTERS; DENDRIMERS; CROWN-ETHERS
• DOI: 10.1021/bm015559l
• ISSN: 1525-7797

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) n G1-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 Pm3̄n 3-D lattice while at high molecular weights they form cylindrical macromolecules that self-organize into a p6 mm 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.