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The mechanism of the recently reported photocontrolled cationic polymerization of vinyl ethers was investigated using a variety of catalysts and chain-transfer agents (CTAs) as well as diverse spectroscopic and electrochemical analytical techniques. Our study revealed a complex activation step characterized by one-electron oxidation of the CTA. This oxidation is followed by mesolytic cleavage of the resulting radical cation species, which leads to the generation of a reactive cation-this species initiates the polymerization of the vinyl ether monomer-and a dithiocarbamate radical that is likely in equilibrium with the corresponding thiuram disulfide dimer. Reversible addition-fragmentation type degenerative chain transfer contributes to the narrow dispersities and control over chain growth observed under these conditions. Finally, the deactivation step is contingent upon the oxidation of the reduced photocatalyst by the dithiocarbamate radical concomitant with the production of a dithiocarbamate anion that caps the polymer chain end. The fine-tuning of the electronic properties and redox potentials of the photocatalyst in both the excited and the ground states is necessary to obtain a photocontrolled system rather than simply a photoinitiated system. The elucidation of the elementary steps of this process will aid the design of new catalytic systems and their real-world applications.

ABSTRACT Herein, we report the transformation of β-monomethyl itaconate, an inexpensive and biorenewable alternative to petroleum feedstocks, to the high-value monomer α-methylene-γ,γ-dimethyl-γ-butyrolactone (Me2MBL) through a selective addition strategy. This strategy is also applied to the synthesis of α-methylene-γ-butyrolactone (MBL, tulipalin A), a monomer that can be polymerized to give materials with desirable properties (high decomposition temperature, glass transition temperature, and refractive index). Subsequent polymerization of both Me2MBL and MBL through reversible addition-fragmentation chain-transfer polymerization generates well-defined poly(Me2MBL) and poly(MBL) (PMBL). Physical characterization of poly(Me2MBL) shows good physical properties comparable with known PMBL materials. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2730-2737 [ABSTRACT FROM AUTHOR]

The ability to combine two polymerization mechanisms in a one-pot setup and switch the monomer selectivity via an external stimulus provides an excellent opportunity to control polymer sequence and structure. We report a strategy that enables monomer incorporation to be determined via the selection of the wavelength of light through selective activation of either cationic or radical processes. This method enables the synthesis of varying polymeric structures under identical solution conditions but with simple modulation of the external stimulus. Additionally, changes in the ratios of the two photocatalysts afford complementary chemical control over these reactions to design elaborated polymeric structures. Our strategy takes advantage of the unique regulation that can be accessed through light. [ABSTRACT FROM AUTHOR]

Photoinitiated cationic polymerizations are widely used in industrial processes; however, gaining photocontrol over chain growth would expand the utility of these methods and facilitate the design of novel complex architectures. We report herein a cationic polymerization regulated by visible light. This polymerization proceeds under mild conditions: a combination of a metal-free photocatalyst, a chain-transfer agent, and light irradiation enables the synthesis of various poly(vinyl ether)s with good control over molecular weight and dispersity as well as excellent chain-end fidelity. Significantly, photoreversible cation formation in this system enables efficient control over polymer chain growth with light. [ABSTRACT FROM AUTHOR]