Visible-light-mediated, additive-free, and open-to-air controlled radical polymerization of acrylates and acrylamides.

Jessica R Lamb,K Peter Qin,Jeremiah A Johnson

doi:10.1039/c9py00022d

Jessica R Lamb, K Peter Qin + Show 1 more

Open Access

https://doi.org/10.1039/c9py00022d

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Abstract

Oxygen tolerance in ontrolled radical polymerizations has been an active field of study in recent years. Herein, we report a photocontrolled, additive-free iniferter polymerization that operates in completely open vials utilizing the "polymerizing through oxygen" mechanism. Trithiocarbonates are directly activated with high intensity 450 nm light to produce narrowly dispersed (M w/M n = 1.1-1.6) polyacrylates and polyacrylamides in only 1 hour of irradiation. Living behavior is demonstrated through chain extension, block copolymer synthesis, and control over molecular weight through varying the monomer:iniferter ratio. A slight increase in induction period is observed for the open vial polymerization compared to the air-free reaction, but polymers with similar M n and M w/M n values are produced after 30-60 minutes of irradiation. This system will provide a convenient platform for living additive manufacturing because of its fast reaction time, air tolerance, wide monomer scope, and lack of any additives beyond the monomer, iniferter, and DMSO solvent.

Highlights

Controlled radical polymerization (CRP) techniques have transformed macromolecular synthesis by enabling access to polymers with controlled molecular weights, narrow molecular weight distributions, and well-defined architectures.[1,2,3] Photocontrolled CRP affords the additional benefits of spatiotemporal control by using light as a low cost external stimulus
Inspired by the open vial polymerization achieved by Boyer and coworkers using zinc tetraphenylporphyrin (ZnTPP),[19] we began to pursue open to air polymerizations using symmetrical TTC 1 (Fig. 2) with various photocatalysts in our custom-built photoreactor.[34]
The unstirred completely open vials are possible, including methyl acrylate polymerization in DMSO using ZnTPP19 (Fig. 1A) and acrylic acid polymerization in water using a combination of fluorescein and ascorbic acid.[21]

Summary

Introduction

Controlled radical polymerization (CRP) techniques have transformed macromolecular synthesis by enabling access to polymers with controlled molecular weights, narrow molecular weight distributions, and well-defined architectures.[1,2,3] Photocontrolled CRP ( photo-CRP) affords the additional benefits of spatiotemporal control by using light as a low cost external stimulus. Qiao and coworkers achieved oxygen tolerance without a photocatalyst by using tertiary amines as sacrificial reductants for both oxygen scrubbing and photoredox polymerization (Fig. 1B).[32] While this system demonstrated excellent control over molecular weight and was effective for the synthesis of block copolymers through chain extension, it was performed in a closed vial and required multiple hours to days of irradiation to yield high molecular weight polymers. The reaction was run on different scales (0.2–0.6 ml, Table S2, entries 18–22 and Fig. S9†) in a 1 dram vial which revealed that a reaction volume of at least 0.4–0.5 ml is needed for this setup to achieve well-controlled and high molecular weight polymers (vide infra).

Results

Conclusion