Probing Side Chain Dynamics of Branched Macromolecules by Pyrene Excimer Fluorescence

Abstract

Four different pyrene-labeled polymers were prepared by radical copolymerization of n-butyl methacrylate (BMA) and 1-pyrenemethyl methacrylate (PyEG0MA), 1-pyrenemethoxyethyl methacrylate (PyEG1MA), 1-pyrenemethoxyethoxyethyl methacrylate (PyEG2MA), and 1-pyrenemethoxydiethoxyethyl methacrylate (PyEG3MA) to yield PyEG0-PBMA, PyEG1-PBMA, PyEG2-PBMA, and PyEG3-PBMA, respectively. The only structural difference between the polymers was the length of the oligo(ethylene glycol) spacer separating the pyrene label from the main chain. Steady-state and time-resolved fluorescence were applied to investigate how the length of the spacer affected the photophysical properties of the pyrene-labeled polymers. Excimer formation between an excited and a ground-state pyrene was enhanced by a longer spacer which increased the probability of encounter between two pyrene labels. This conclusion was supported through the analysis of the fluorescence decays of the polymers according to the Fluorescence Blob Model (FBM) which yielded the number (Nblob) of monomers constituting the volume in the polymer coil probed by an excited pyrene and the rate constant of excimer formation, kblob, inside a blob. Nblob increased more or less linearly with increasing spacer length reflecting a larger blob volume. kblob for PyEG0-PBMA was small due to steric hindrance while kblob took a larger but similar value within experimental error for all polymers labeled with pyrene derivatives having oligo(ethylene glycol) spacers. These experiments demonstrate that for a branched macromolecule, the volume probed by the tip of a side chain and its dynamics can be characterized quantitatively by monitoring pyrene excimer fluorescence. They are expected to provide important dynamic and structural information about the numerous highly branched macromolecules that are currently under intense scientific scrutiny.2

Synthesis and characterisation of fluorescent pyrene‐end‐capped polylactide fibres

“…The structures of the polymers generated in our study were characterised spectroscopically (IR, 1 H NMR and 13 C NMR) and using GPC. The structures of AH1, AH2 and AH3, and reactant quantities are listed in Table ; these polymers have M n values similar to those recently reported for polymers derived from the ROP of L‐LA with pyrenebutanol …”

“…IR ( max , cm −1 ): 3400 (OH) (br), 3047 (Ar CH), 2918 and 2871.2 (CH), 1588 and 1499 (Ar CC), 1114 and 1057 (CO). The 1 H NMR data for this compound were identical to those reported in the literature …”

“…The synthesis of 2-(2-(2-(pyren-1-ylmethoxy)ethoxy)ethoxy)ethan-1-ol has been reported by Farhangi and Duhamel. 27 However, in our hands, a modified Williamson ether synthesis, similar to that reported by Ward and co-workers, 28 proved highly effective and obviated the use of stoichiometric quantities of silver oxide. We found that the use of an excess (8 eq.)…”

“…The use of DBU allows a high degree of polymerisation, very narrow controlled molecular weight and low catalyst concentration of 1 mol%. This methodology is preferable to that employing stannous octanoate, one of the most commonly used catalysts currently employed for the promotion of these polymerisation reactions, and is experimentally easy to adopt . Most notably, the DBU‐catalysed process is free from the toxicity associated with the tin‐based systems which limits their potential utility, especially for biomedical use.…”

“…This methodology is preferable to that employing stannous octanoate, one of the most commonly used catalysts currently employed for the promotion of these polymerisation reactions, and is experimentally easy to adopt. 27,29,30 Most notably, the DBU-catalysed process is free from the toxicity associated with the tin-based systems which limits their potential utility, especially for biomedical use. The structures of the polymers generated in our study were characterised spectroscopically (IR, 1 H NMR and 13 C NMR) and using GPC.…”