Amino-yne reaction: An exquisite method for polymer-polymer conjugation and post-polymerization modification

Abstract

The amino-yne reaction, which performs between an electron-deficient alkyne and an amine, has been shown to proceed with high efficiency under mild conditions and has recently gained much interest in many fields of polymer and material science. However, this reaction has not been tested as a polymer–polymer conjugation method and has also not been employed for post-polymerization modification (PPM) of amine-functional polymers. In this study, we aimed to extend the feasibility of amino-yne reactions using the aforementioned strategies. For this purpose, for the first time, amine end-functional polymers, namely polystyrene (PS-NH2) and poly(N-isopropylacrylamide) (PNIPAM-NH2), which were prepared experimentally or obtained commercially, were reacted with activated alkyne end-functional poly(ethylene glycol) (mPEG-alkyne) via amino-yne reaction to achieve the corresponding block copolymers, PNIPAM-b-PEG and PS-b-PEG. Both reactions proceeded at room temperature without the use of any additives or catalysts. Polymer-polymer conjugation reactions were found to be highly effective, as confirmed by GPC and 1H NMR analyses. The amino-yne reaction was then utilized for the modifications of two readily available amine-functional polymers: polyethylene imine (PEI) and aminoethylaminopropylmethylsiloxane-dimethylsiloxane copolymer (poly(AEAPMS-co-DMS)). These polymers were reacted with various mono- and difunctional propiolate esters at room temperature for just two minutes. Experimental results show that both polymers could be modified with quantitative or near-quantitative efficiency, particularly with difunctional propiolates. We believe that this work has once again demonstrated the power of the amino-yne reaction, and this chemistry will definitely continue to attract interest among synthetic polymer chemists due to its rapid character, readily available starting materials, and mild conditions.