Efficient post-polymerization modification of pendant aldehyde functional polymer via reductive etherification reaction

Abstract

Providing novel synthesis methods for functional polymers designed for specific applications is crucial in polymer chemistry research. While the most straightforward method for preparing functional polymers is the polymerization of specifically designed functional monomers, post-polymerization modification (PPM) of polymers is also an essential tool to obtain desired polymers. PPM is particularly useful when direct polymerization of functional monomers is not suitable due to the possibility of side reactions in the polymerization conditions that can lead to the loss of desired functionality. A good PPM technique should fulfill some requirements such as quantitative yields, easy to conduct under mild conditions, and easy to purify. The reactions classified under the term "click" chemistry are commonly used for the PPM of polymers. Aldehydes have always been a privilege in polymer science since the aldehyde carbonyl readily undergoes several reactions efficiently under mild conditions, ranging from non-aldol reactions to multicomponent reactions, mostly without any additive. Aldehyde-functional polymers can be synthesized via polymerization of monomers with aldehyde functionality. Polymers with pendant aldehyde groups are known as good platforms for PPM given the reactivity of the aldehyde group. Reductive etherification reaction (RER) is a method to synthesize ethers from ketone or aldehyde groups in the presence of an organosilane reductant, generally along with a Lewis or Bronsted-Lowry acid catalyst. Both symmetrical and unsymmetrical ethers can be obtained via the RER. While self-reduction of carbonyl compounds yields to symmetrical ethers, alcohols are used as nucleophiles to prepare unsymmetrical ethers. The RER is known to have high efficiency and good functional group tolerance under optimum conditions. It was shown that chlorodimethylsilane (CDMS)-mediated RER is a robust method for both synthesis and PPM of polymers. In the current study, the versatility of the aldehyde group has been exploited using the RER. For this purpose, a polymer platform containing pendant aldehyde units was synthesized via free radical polymerization (FRP) and modified with a variety of alcohols using CDMS as the reducing agent. The resulting polymers were characterized by using 1H NMR, 13C NMR, GPC, and FT-IR.