Methacrylate and Styrene Block Copolymer Synthesis by Cu‐Mediated Chain Extension of Acrylate Macroinitiator in a Semibatch Reactor

Abstract

A process for the well‐controlled growth of acrylates by Cu‐mediated polymerization has been developed, with macroinitiator synthesized continuously in a copper tubular reactor and subsequently chain‐extended in a semibatch reactor without additional copper. Extending this process to methacrylates and styrene, however, has proven difficult due to a significant reduction in reaction rate. This barrier has been overcome by chain‐extending the low molecular weight (Mn of 760 g mol–1) poly(methyl acrylate) macroinitiator with methacrylates and styrene using PMDETA (N,N,N′,N″,N″‐pentamethyldiethylenetriamine) as ligand. Methyl methacrylate conversions of >80% at 70 °C and diethylene glycol methyl ether methacrylate conversions of >90% at room temperature are achieved in 4 h, with the same room temperature conditions successfully applied for controlled chain extensions with butyl methacrylate. Although styrene conversions are slightly lower (60–70%) over 4 h at 85 °C, the rates achieved are substantially higher than achieved in other studies. Hydrophobic–hydrophilic triblock structures are produced through sequential monomer feeds to the semibatch reactor, keeping total reaction time to less than 5 h. The ability to incorporate methacrylates and/or styrene into structured block polymers greatly extends the range of products that can be efficiently synthesized with low copper levels by this process.

Scalable Routes to Acrylate and Methacrylate Block Copolymers via Copper-Mediated Reversible Deactivation Radical Polymerization

“…High conversion of the DEGMEMA block ( x p = 92%) was achieved with a reasonable control ( Đ = 1.26), with MA conversion reaching 88% after the total reaction time of 4 h. The MMD in Figure d shows a clear shift in the molar mass from the first block (150 min) to the second block (240 min), with the absence of the bimodality observed in both the benchmark experiment and BCP-SB-3. While some broadening occurred upon the addition of the second block, the measured dispersity of Đ = 1.45 is both consistent with that estimated for the P­(MA- b -DEGMEMA) population of BCP-SB-3 ( Đ = 1.37, see Figure S13) and is an improvement over the final dispersity of Đ = 1.62 obtained previously . Although there is incomplete initiation of the first block (81% based on PSt), there is no evidence of a second population of low-molar mass chains originating from the residual initiator.…”

“…M n grows linearly with overall monomer conversion, as expected for a well-controlled RDRP system. A representative MMD for the PMA macroinitiator produced in the tubular reactor, shown to exhibit excellent reproducibility, , is shown by the gray dotted line in Figure b.…”

“…An additional issue associated with the macroinitiator production is the inflexibility in initiator selection, as the current process is only able to successfully produce polyacrylate macroinitiators. Cooze investigated the incorporation of methacrylates in the copper tube reactor to produce a poly­(butyl methacrylate) macroinitiator, but the process proved challenging due to low initiation efficiency; thus, it was abandoned in favor of producing methacrylates by chain extension of the PMA macroinitiator . However, acrylate chain ends are poorer initiators for more active monomers (i.e., higher K ATRP ) like methacrylates, , and thus an alternative method to producing a more active chain-extendible species would be beneficial.…”

“…The advantages were demonstrated by Cooze et al, a study that first demonstrated chain extension of the PMA 10 macroinitiator with methyl methacrylate (MMA), butyl methacrylate (BMA), and di­(ethylene glycol) methyl ether methacrylate (DEGMEMA). While the methacrylate conversions ( x p > 80%) achieved after a 3 h feeding and 1 h holding period demonstrated a significant improvement in rate compared to previous literature, the copolymer MMDs were broadened ( Đ ≈ 1.6–1.8) compared to the acrylate only system, and polymerizations exhibited lowered initiation efficiencies . Various acrylate-methacrylate block copolymers were synthesized in the semibatch system under the same 4 h feed time; however, lowered conversion and initiation efficiencies led to some deviations from the target well-defined structure …”

“…34 Various acrylate-methacrylate block copolymers were synthesized in the semibatch system under the same 4 h feed time; however, lowered conversion and initiation efficiencies led to some deviations from the target well-defined structure. 34 Thus, it is the goal of this work to further the development of the two-step Cu-mediated process, shown schematically in Figure 1, for efficient production of well-controlled acrylate/ acrylate and methacrylate/acrylate block copolymers. The semibatch operating conditions and feeding policies have been improved to increase polymerization rates while retaining chain-end functionality to high conversions.…”