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. 2022 Apr 24;14(9):1733.
doi: 10.3390/polym14091733.

A Degradable Difunctional Initiator for ATRP That Responds to Hydrogen Peroxide

Lawrence Hill  1 , Hunter Sims  1   2 , Ngoc Nguyen  1 , Christopher Collins  1 , Jeffery Palmer  1 , Fiona Wasson  1   3
Affiliations

A Degradable Difunctional Initiator for ATRP That Responds to Hydrogen Peroxide

Lawrence Hill et al. Polymers (Basel). .

Abstract

Mid-chain degradable polymers can be prepared by atom transfer radical polymerization from difunctional initiators that include triggers for the desired stimuli. While many difunctional initiators can respond to reducing conditions, procedures to prepare difunctional initiators that respond to oxidizing conditions are significantly less available in the literature. Here, a difunctional initiator incorporating an oxidizable boronic ester trigger was synthesized over four steps using simple and scalable procedures. Methyl methacrylate was polymerized by atom transfer radical polymerization using this initiator, and the polymerization kinetics were consistent with a controlled polymerization. The polymer synthesized using the difunctional initiator was found to decrease in molecular weight by 58% in the presence of hydrogen peroxide, while a control experiment using poly(methyl methacrylate) without a degradable linkage showed a much smaller decrease in molecular weight of only 9%. These observed molecular weight decreases were consistent with cleavage of the difunctional initiator via a quinone methide shift and hydrolysis of the methyl ester pendent groups in both polymers, and both polymers increased in polydispersity after oxidative degradation.

Keywords: ATRP; boronic ester; degradable polymer; difunctional initiator.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Synthesis of the degradable difunctional initiator (DFI) over four steps.
Figure 2
Figure 2
1H-NMR spectrum of the difunctional initiator (DFI) compound 4 in CDCl3.
Figure 3
Figure 3
13C-NMR spectrum of the difunctional initiator (DFI) compound 4 in CDCl3.
Figure 4
Figure 4
Monitoring the evolution of molecular weight and polydispersity in the ATRP of methyl methacrylate using the difunctional initiator (DFI): (a) Polymerization of methyl methacrylate using the DFI, T = 55 °C, [MMA]0/[DFI]0/[CuCl]0/[PMDETA]0 = 400/1/2.24/2; (b) SEC traces obtained from samples taken at 15, 50, 95, 120, 160, and 200 min for a representative synthesis of pMMA-DFI-pMMA (versus pMMA standards in THF); (c) Evolution of molecular weight (solid black squares) and polydispersity (hollow red circles) versus monomer conversion in the ATRP of MMA during a representative polymerization; (d) First-order kinetic plot for the ATRP of MMA using the DFI.
Figure 5
Figure 5
Molecular weights and polydispersity indexes for poly(methyl methacrylate) synthesized by ATRP using two different initiators before and after oxidative degradation experiments: (a) pMMA-DFI-pMMA; (b) ebib-pMMA. Plots of relative molecular weight distributions were obtained versus poly(methyl methacrylate) standards in tetrahydrofuran.
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