A Facile Synthetic Route to Amphiphilic Poly(Meta-Phenylene Ethynylene) and Poly(Meta-Phenylene Ethynylene)-Block-Polyisocyanide Using a Single Catalyst.

Xunhui Xu,Na Liu,Chonglong Li,Lei Xu

doi:10.3390/polym10090936

Xunhui Xu, Na Liu + Show 2 more

Open Access

https://doi.org/10.3390/polym10090936

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Journal: Polymers	Publication Date: Aug 23, 2018
Citations: 3	License type: CC BY 4.0

Affiliation: Hefei University of Technology, North Minzu University

Abstract

An optically active, amphiphilic meta-phenylene ethynylene (m-PE) bearing a chiral amide pendant was designed and synthesized. Living polymerization of m-PE using alkyne-Pd(II) as the initiator afforded well-defined poly(meta-phenylene ethynylene) (m-PPE). These m-PPEs were found to have a stable helical conformation in THF, 1,4-dioxane, and CH3CN and showed split Cotton effects over the range of 245–400 nm. The positive first Cotton effect was observed at a wavelength of approximately 308 nm, and the negative second Cotton effect was observed at a wavelength of approximately 289 nm. The m-PPEs exhibited helical conformational changes in different mixed solvents and showed effective solvent-dependent helix inversion in CHCl3/THF solutions. The sign of the Cotton effect of m-PPE was inverted at 25 °C by varying the mixing ratio of THF and CHCl3. Finally, amphiphilic poly(meta-phenylene ethynylene)-block-polyisocyanide containing hydrophilic PPE and hydrophobic PPI segments were facilely prepared using Pd(II)-terminated m-PPE as the macroinitiator. This block copolymer can self-assemble into well-defined spherical nanostructures in a selective THF/CH3OH solution. This efficient polymerization will open up enormous opportunities for the preparation of functional amphiphilic block copolymers in a wide variety of fields.

Highlights

Helical polymers, such as chiral packing materials for separating enantiomers in chromatography [1,2], asymmetric catalysis [3,4,5,6], and chiral selectors [7,8] have attracted considerable research attention during the past few decades in the fields of polymer chemistry and materials science
It is known that the synthesis of poly(meta-phenylene ethynylene)-block-polyisocyanide has been achieved in previous works using Pd(II)-terminated m-PPE as the macroinitiator
The optically active monomer 1 was synthesized according to literatures reported by Ramakrishnan and Yashima, as outlined in Scheme S1

Summary

Introduction

Helical polymers, such as chiral packing materials for separating enantiomers in chromatography [1,2], asymmetric catalysis [3,4,5,6], and chiral selectors [7,8] have attracted considerable research attention during the past few decades in the fields of polymer chemistry and materials science. Many optically active helical polymers have been synthesized by direct polymerization of monomers with the required functional groups Moore and his collaborators found that m-PPEs was able to fold into a compact helical conformation in polar solvents, such as acetonitrile [9,10,11], and were capable of binding small molecules, such as (−)-α-pinene [12]. Since polyisocyanide can form into a rigid helical conformation, it has been connected to PPE to provide better block copolymers. It is known that the synthesis of poly(meta-phenylene ethynylene)-block-polyisocyanide has been achieved in previous works using Pd(II)-terminated m-PPE as the macroinitiator. These block copolymers can self-assemble into well-defined spherical nanostructures in selective solvents. The development of novel well-defined block copolymers with stable helical conformation is of great interest

Chemicals and Reagents

Instrumentation and Characterization

Synthesis and Polymerization of Optically Active m-Phenylene Ethynylenes

CD and UV spectra of poly-1

One-Pot Synthesis of a PPE-b-PPI Block Copolymer and Chiroptical Properties

Results for the One-Pot

Emission

Conclusions