Degradable Silyl Ether Polymers Synthesized by Sequence-Controlled Cationic Terpolymerization of 1,3-Dioxa-2-silacycloalkanes with Vinyl Ethers and Aldehydes

Abstract

Polymers with silyl ether moieties have been gaining considerable interest due to both the properties derived from silicon–oxygen linkages and the acid-, base-, and fluoride ion-triggered degradability. In this study, 1,3-dioxa-2-silacycloalkanes were demonstrated to function as promising monomers for the synthesis of silyl ether polymers when combined with vinyl ethers and aldehydes in cationic terpolymerization with B­(C6F5)3 as a catalyst. Importantly, all three monomers were indispensable for efficient terpolymerization via frequent crossover reactions. For example, a degradable terpolymer with an M n of 29 × 103 was obtained from a six-membered 1,3-dioxa-2-silacycloalkane, 2-chloroethyl vinyl ether, and pivalaldehyde, which was superior to both the silyl monomer homopolymerization yielding a product with an M n of 3.3 × 103 and the inefficient copolymerizations in the absence of the silyl monomer, vinyl ether, or aldehyde. Moreover, the terpolymers likely had ABC-type, pseudo-periodic sequences as a result of frequent and selective crossover reactions. The resulting terpolymers have acetal and silyl ether moieties in the main chain, thus exhibiting acid-, base-, or fluoride ion-triggered degradability. Indeed, the terpolymer with an M n of 29 × 103 was smoothly degraded into a product with an M n of 0.3 × 103 under acidic conditions. The key to the terpolymerization reaction was the reaction of an aldehyde with the silyl monomer-derived oxonium ion to generate a carbocation that can react with a vinyl ether because a vinyl ether does not react with the silyl monomer-derived oxonium ion.

Entropy-Driven Depolymerization of Poly(dimethylsiloxane)

“…This is likely due to the Thorpe−Ingold effect, which favors cyclization by compressing the O−C−C bond angle and by minimizing the conformational degrees of freedom�an entropic benefit. 45 Based on this computational data, we expected pinacol, hexylene glycol, 2,5-dimethyl-2,5-hexanediol, and dipropylene glycol to yield the most stable rings for each possible ring size, as they have the most positive (or greatest) enthalpy of ring-opening.…”

“…Hada et al . recently reported terpolymerizations of 1,3-dioxasilacycloalkanes with vinyl ethers and aldehydes using Lewis acid catalysts at low temperatures . We first applied their method to 1 H NMR pure M2HG using ethyl vinyl ether and pivaldehyde comonomers in the presence of gallium­(III) chloride as catalyst (Table , entry 5) and obtained a colorless, low-molecular-weight terpolymer that also contains PDMS repeat units according to 1 H NMR (see Figure S62).…”

RAFT step-growth polymerization via the Z-group approach and deconstruction by RAFT interchange

“…The C-C single bonds in vinyl polymers offer excellent stability for the intended applications, yet these polyethylene-like polymers are notoriously difficult to degrade, posing grand challenges in recycling these polymers and when degradation is desirable (e.g., drug delivery). [1][2][3] Various strategies have been developed to overcome this challenge, including copolymerization with degradable monomers, [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] introduction of degradable groups by combining with step-growth polymerization, [19][20][21][22][23][24] depolymerization to monomers under special conditions, [25][26][27][28][29][30][31] and degradation to oligomers catalyzed by special reactions. [32][33][34][35] Among them, introducing labile carbon-heteroatom bonds (e.g., ester) into vinyl polymers via copolymerization of a second monomer containing such labile bonds is one of the most efficient methods.…”

“…, drug delivery). 1–3 Various strategies have been developed to overcome this challenge, including copolymerization with degradable monomers, 4–18 introduction of degradable groups by combining with step-growth polymerization, 19–24 depolymerization to monomers under special conditions, 25–31 and degradation to oligomers catalyzed by special reactions. 32–35 Among them, introducing labile carbon-heteroatom bonds ( e.g.…”

Synthesis and Degradation of Vinyl Polymers with Evenly Distributed Thioacetal Bonds in Main Chains: Cationic DT Copolymerization of Vinyl Ethers and Cyclic Thioacetals

“…Among them, copolymerization of heteroatom‐containing cyclic monomers with common vinyl monomers, by which labile carbon‐heteroatom bonds can be introduced via ring opening of the cyclic structures, is one of the most efficient methods [23–26] . Various cyclic compounds, which are copolymerizable via ring‐opening reactions, have been developed to date and include cyclic ketene acetals, [27–40] thionolactones, [41–47] and cyclic allylic sulfur compounds [48–52] for radical polymerization as well as oxiranes, [53, 54] cyclic acetals, [55, 56] hemiacetal esters, [57] and 1,3‐dioxa‐2‐silacycloalkanes [58] for cationic polymerization.…”