Rigid-to-Flexible Transition in a Molecular Brush in a Good Solvent at a Semidilute Concentration

Abstract

The structures of a molecular brush in a good solvent are investigated using synchrotron small-angle X-ray scattering in a wide range of concentrations. The brush under study, PiPOx 239 -g-PnPrOx 14 , features a relatively long poly(2-isopropenyl-2-oxazoline) (PiPOx) backbone and short poly(2-n-propyl-2-oxazoline) (PnPrOx) side chains. As a solvent, ethanol is used. By model fitting, the overall size and the persistence length as well as the interaction length and interaction strength are determined. At this, the interplay between form and structure factor is taken into account. The conformation of the molecular brush is traced upon increasing the solution concentration, and a rigid-to-flexible transition is found near the overlap concentration. Finally, the results of computer simulations of the molecular brush solutions confirm the experimental results.

Glycopolymers Prepared by Alternating Ring-Opening Metathesis Polymerization Provide Access to Distinct, Multivalent Structures for the Probing of Biological Activity

“…1 H NMR (700 MHz, CDCl 3 ) δ 5.83 (q, 1H, J = 5.8 Hz), 5.26 (d, 1H, J = 3.5 Hz), 5.19 (dd, 1H, J = 10.5, 8.2 Hz), 5.03 (ddd, 1H, J = 10.5, 3.4, 1.5 Hz), 4.47 (d, 1H, J = 8.0 Hz), 3.93 (m, 1H), 3.83 (q, 1H, J = 6. ■ GENERAL PREPARATION OF POLY(2′) 50 To a septum-sealed vial containing nitrogen and a stir bar, an aliquot (280 μL) of 4 stock solution (0.013 M) in dichloromethane was added (0.0059 M, 1 equiv). of excess ethyl vinyl ether (0.2 mL).…”

“…Poly(3a′) 50 : Poly(2′) 50 or poly(3′) 50 (30 mg) was added to a reaction vial and dissolved in 0.5 mL of THF. One milliliter of a mixture of MeOH:H 2 O (2:1.5 v/v) containing K 2 CO 3 (in excess) was then added.…”

“…The Kuhn lengths of poly(1) 50 suggested that there were long, rigid segments within the polymer chains. Poly(1a) 50 and poly(1b) 50 each had a Kuhn length of 4.7 ± 0.2 and 9.0 ± 0.03 nm, respectively. Surprisingly, the Kuhn lengths of poly(1a) 100 and poly(1b) 100 dropped significantly to 2.9 ± 0.2 and 4.6 ± 0.2 nm, respectively.…”

Self-Assembly of Molecular Brushes with Responsive Alternating Copolymer Side Chains

“…Among the variety of polymer architectures, branched macromolecules are highly promising candidates for obtaining responsive systems with dominating either intra- or intermolecular associations . In particular, molecular brushes, which are characterized by a long polymer backbone with densely grafted side chains, can form both unimolecular micelles with a high capacity for guest molecules and hydrogels with excellent mechanical properties due to the diminished amount of topological defects. − The physical reason for such behavior is the increased (induced) persistence length of the brush because of the steric repulsion between side chains, which results in the suppression of intermolecular entanglements. Regarding the responsive copolymer brushes, there have been several recent examples of successful thermoresponsive gelation. , Namely, macromolecules with blocky ,, and random ,, sequences of responsive and non-responsive side chains along the backbone have been studied. , However, the complexity of the polymer structure often implies an elaborate polymer synthesis.…”

Preface to the Françoise M. Winnik Special Issue

“…This special issue celebrates her career with contributions from colleagues across the world. The included papers represent many topical areas, including microgels, elastomers, microbubbles, microemulsions, supramolecular assemblies, and thin films, with critical physical properties enabling applications as broad-ranging as carbon capture, medicine, and electronics. − Nonetheless, many of the papers are fundamental in nature, reflecting Professor Winnik’s enduring commitment to and interest in basic colloid and interfacial science.…”