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Probing Side Chain Dynamics of Branched Macromolecules by Pyrene Excimer Fluorescence

Shiva Farhangi Supervisor: Jean Duhamel 38 th IPR symposium University of Waterloo May, 2016. Probing Side Chain Dynamics of Branched Macromolecules by Pyrene Excimer Fluorescence. Introduction Importance of Chain Dynamics. Motivation:

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Probing Side Chain Dynamics of Branched Macromolecules by Pyrene Excimer Fluorescence

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  1. Shiva Farhangi Supervisor: Jean Duhamel 38th IPR symposium University of Waterloo May, 2016 Probing Side Chain Dynamics of Branched Macromolecules by PyreneExcimer Fluorescence

  2. IntroductionImportance of Chain Dynamics Motivation: • The dynamics of polymer chains in solution play an important role in different polymeric systems Examples: Viscosity modifiers Polymeric dispersants in oil and aqueous solutions will have different solution properties depending on backbone flexibility. Protein folding in biological systems • the backbone dynamics of polymer chains are influenced by the ability of the polymer backbone to move. • The goal is to characterize the internal dynamics of individual polymer chains in their native state in solution.

  3. Introduction End-to-End Quenching k1 + hn Q Q (QD) D D* 1/tD • Only the chain ends are being probed. • Monodispersed samples only can be probed. • Limited to short chains. kcy decrease and no quenching can be observed while the chromophore remains excited. Winnik, M. A. End-to-End Cyclization of Polymer Chains. Acc. Chem. Res. 1985, 18, 73-79.

  4. Introduction End-to-End Quenching with Pyrene End-Labeled Chains k1 + hn Py Py (PyPy)* Py Py* 1/tE 1/tM • Only the chain ends are being probed. • Monodispersed samples only can be probed. • Limited to short chains. kcy decrease and no quenching can be observed while the chromophore remains excited. Winnik, M. A. End-to-End Cyclization of Polymer Chains. Acc. Chem. Res. 1985, 18, 73-79.

  5. Introduction Quenching Experiments with Randomly Labeled Polymers Fluorescence Blob Model (FBM) * kblob kblob= rate constant for excimer formation within a blob Nblob= number of units per blob < kblob  Nblob >: average rate constant of excimer formation of polymer The Fluorescence Blob Model (FBM) has been applied to probe the polymer chain dynamics of many polymers such as polystyrene, poly(N,N-dimethylacrylamide), polyisoprene, poly(N-isopropylacrylamide), and several poly(alkyl methacrylate)s. The product < kblob  Nblob > is believe to represent a measure of the the magnitude of the chain dynamics of a polymer in solution in the same manner as Tg describes the chain dynamics of polymer sin the bulk. Duhamel, J. Polymer Chain Dynamics in Solution Probed with a Fluorescence Blob Model. Acc. Chem. Res. 2006, 39, 953-960.

  6. Introduction Quenching Experiments with Randomly Labeled Polymers Fluorescence Blob Model (FBM) * kblob kblob= rate constant for excimer formation within a blob Nblob= number of units per blob < kblob  Nblob >: average rate constant of excimer formation of polymer The effect of the length of the linker connecting the pyrene label to the main chain has never been investigated. Duhamel, J. Polymer Chain Dynamics in Solution Probed with a Fluorescence Blob Model. Acc. Chem. Res. 2006, 39, 953-960.

  7. Four Different Pyrene-Labeled Poly(alkyl methacrylate)s PyEG0-PBMA PyEG1-PBMA PyEG2-PBMA PyEG3-PBMA

  8. Characterization of Polymer • NMR : • Determine the degree of conversion. • GPC: • Check for unreacted pyrene monomer using UV-Vis absorption detector. • Determine molecular the absolute molecular weight. • Absorption spectroscopy: • Pyrene content was determined for all polymers samples.

  9. 1H NMR spectra of PyEG2OH 45% yield b H2O g DMSO a

  10. 1H NMR spectra of PyEG2MA Percentage Yield: 90% c,d,e H2O CHCl3 a b f h g h´

  11. GPC Characterization

  12. Steady-State Fluorescence Spectra * < k1 > * + hn PyEG0-PBMA k-1 1/tM 1/tE0 Py content, % 4.0 5.3 6.3 7.1 8.1 IM IE

  13. Ratio IE/IM of Pyrene-Labeled Poly(alkyl methacrylate)s

  14. Analysis of Time-Resolved Fluorescence Decays kblob= rate constant for excimer formation within a blob Nblob= number of units per blob * kblob Pydiff Pyfree < kblob  Nblob >: average rate constant of excimer formation of polymer Pyagg For more details please refer to: Farthing Shiva, Henning Weiss, and Jean Duhamel. "Effect of Side-Chain Length on the Polymer Chain Dynamics of Poly (alkyl methacrylate) s in Solution." Macromolecules 46.24 (2013): 9738-9747

  15. Analysis of Time-Resolved Fluorescence Decays in THF

  16. Determination of the Hydrodynamic Radius of a Blob d Rh Mark-Houwink-Sakurada equation (0.5 < a < 1.0)

  17. Relationship between the Rblob and d Rblob d d4 d2 d3 d1 From Hyper CHEM

  18. Conclusions Four pyrene labeled PBMA samples carrying dyes with a different number of atoms in the side chains were synthesized. The IE/IM ratios obtained from the steady-state fluorescence showed that the dyes with longer linkers formed excimer more efficiently. Fluorescence decays were analyzed with the FBM and the results obtained showed that the product kblob×Nblobis increasing with increasing length of the linker. We can observe that there is a linear correlation between the hydrodynamic radius of a blob and the number of the atoms in the side chain connecting the dye to the main chain.

  19. Acknowledgements • Prof. Duhamel • Profs. Gauthier, McManus and Wang • Duhamel and Gauthier Group • Funding provided by NSERC

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