Modification of Polyketone via Chlorodimethylsilane-Mediated Reductive Etherification Reaction: A Practical Way for Alkoxy-Functional Polymers

Abstract

This study describes a straightforward post-polymerization modification (PPM) methodology from polyketone via chlorodimethylsilane (CDMS)-mediated reductive etherification reaction (RER). The polyketone platform was prepared via acyclic diene metathesis (ADMET) polymerization and reacted with a variety of alcohols in the presence of CDMS to create a wide range of polymers possessing pendant functional-alkoxy structures under mild conditions. The effect of parameters such as solvents and the amount of reactants on RER were studied. We have also explored the effect of other silane compounds on RER, none of which provided as high efficiency as the CDMS-mediated one. It has been found that the primary alcohols yielded corresponding alkoxy structures in high efficiencies, high isolated yields, and a wide range of functional group tolerance. It was also found that the formation of polyalcohol was inevitable, to some extent, during the RERs in addition to the alkoxy-functional polymers. All the polymers obtained were characterized in detail by various spectroscopic measurements, and a mechanistic aspect was also presented to evaluate the product distributions. Since operationally simple chemical methods, with a high yield and functional group tolerance, that can be easily adapted to the macromolecular level are always desired in synthetic polymer chemistry, this study promises remarkable opportunities for synthesizing functional polymers and may pave a way for the development of a novel metal-free PPM method.

Chlorodimethylsilane-Mediated Reductive Etherification Reaction: A Robust Method for Polyether Synthesis

“…As highlighted in the introduction part, the formation of alcohol segment due to reduction of the carbonyl to alcohol was inevitable during the functionalization of polyketone via CDMS-mediated RERs . Given this information, we hypothesized that if such a reduction occurs, this may lead to a loss at the aldehyde end, which in turn may trigger the self-condensation polymerization of TPA.…”

“…First, the equivalent optimization study for TPA, BD, and CDMS was performed, and the results are summarized in Table . We previously reported that CH 3 NO 2 was an essential solvent for CDMS-mediated RER, and excess amounts of CDMS were required for high RER efficiency . Hence, in the first attempt equimolar amounts of TPA and BD were reacted in 1 mL of CH 3 NO 2 using 4 equiv of CDMS.…”

“…Importantly, when the reaction was performed at 0 °C, a polymer with very low molecular weight ( M w = 3.7 kDa) was obtained, indicating that the reactivity of CDMS is minimized at lower temperatures (run 9, Table ). Additionally, a relatively high molecular weight polymer ( M w = 36.0 kDa) was obtained when DCM, known as a suitable co-solvent in the RER, , was used together with CH 3 NO 2 (run 10, Table ). Meanwhile, unlike the studies mentioned above, the reaction medium was initially homogeneous then turned turbid after a few hours and remained the same until the end of polymerization.…”

“…It was found that the primary alcohols delivered the corresponding alkoxy pendant polymers in high RER efficiency (up to 90%), a similar high-efficiency trend was also observed in the case of secondary alcohols (up to 80%), and no reaction was observed when a tert -alcohol was used. It should be noted here that the formation of free hydroxyl functional polymers was inevitable during RERs due to the direct reduction of the ketone carbonyl to the secondary alcohol in the presence of excess amounts of CDMS in the reactions . We hypothesized that CDMS-mediated RER may also be a suitable and viable method for the preparation of linear polyethers, enabling the direct use of unprotected alcohols in polymerizations.…”

“…It should be noted here that the formation of free hydroxyl functional polymers was inevitable during RERs due to the direct reduction of the ketone carbonyl to the secondary alcohol in the presence of excess amounts of CDMS in the reactions. 41 We hypothesized that CDMSmediated RER may also be a suitable and viable method for the preparation of linear polyethers, enabling the direct use of unprotected alcohols in polymerizations. To further demonstrate the versatility of RER chemistry, in the current study, a wide range of diols were reacted with terephthalaldehyde (TPA) (and its isomers) in the presence of CDMS through a step-growth polymerization technique, yielding polyethers with different chemical backbones (Scheme 1).…”