Jianwen Yang

Fast and facile one-step synthesis of monodisperse thermo-responsive core–shell microspheres and applications

Highly monodisperse PMMA microspheres covered with a thermo-responsive shell were synthesized in a single step by means of photoinitiated RAFT dispersion polymerization at room temperature. Thermo-responsive macro-RAFT agents (P(mPEGA-co-MEA)-TTCs) with different lower critical solution temperatures (LCST) were used as stabilizers in the process. Particle yields of over 95% were achieved within 45 min of UV irradiation, showing a fast process. The microspheres obtained were well-dispersed in water at a temperature below the LCST, and precipitated from the aqueous dispersion at a temperature above the LCST, exhibiting reversible thermo-responsive properties. The particle size can be precisely controlled by adding a monomer to the reaction in batches, and the microspheres maintained their high uniformities during the reaction. The thermo-responsive PMMA microspheres can be effectively conjugated to proteins via the carboxyl groups on the macro-RAFT chains. A thermo-responsive PMMA/ZIF-8 core–shell structure was also synthesized by using P(mPEGA-co-MEA)-b-PAA stabilized PMMA microspheres as the template, and exhibited good adsorption properties for methylene blue.

N-Phthaloyltranexamic acid ammonium salt derivatives as photocaged superbase for redox free radical photopolymerization

N-Phthaloyltranexamic acid ammonium salt derivatives integrating with peroxides can invoke redox photopolymerization and propagating polymerization. A series of N-phthaloyltranexamic acid ammonium salt derivatives based on benzophenone, thioxanthen, and naphtha chromophores as novel photocaged bases were synthesized and characterized. In combination with a benzoyl peroxide initiator, these structures were able to initiate the amine-mediated redox photopolymerization of acrylates. In particular, the covalent binding of N-phthalimidoamino acid and type II chromophores (thioxanthone, benzophenone) improved remarkably the photoreactivity of photocaged bases (thioxanthen-DBU and benzophenone-DBU) compared to the parent compound. Furthermore, naphthal-DBU matches well the emission spectra of the mercury lamp with a dominant emission wavelength at 365 nm. More importantly, phthal-DBU & BPO as a new photocaged redox combination can invoke controlled redox polymerization within an irradiation time of 3 min. Finally, due to the persistent interaction of the produced longeval amine with peroxides, remarkable post conversion after irradiation, which is significant for preparation of photo-screened materials, was thus initially achieved in the redox photopolymerization.

Phototriggered base proliferation: a powerful 365 nm LED photoclick tool for nucleophile-initiated thiol-Michael addition reaction

Photocaged amines (PCAs) can allow a spatiotemporal control of the highly versatile and widely implemented nucleophile-catalyzed thiol-Michael addition reaction. However, a major challenge with most PCAs is that their relatively low quantum yields easily lead to low photosensitivity, especially under the radiation of light-emitting diodes (LEDs). In this paper, the phototriggered base proliferation (PBP) reaction as a powerful 365 nm LED photoclick tool is presented for the nucleophile-initiated thiol-Michael addition reaction. Compared to the PCA system, the advantages of this approach lie in its enhanced photosensitivity, increased reaction rate and elevated conversion. Finally, due to the persistent interactions of the produced longeval amine, remarkable post conversion was thus initially achieved after irradiation.

Benzoylformamides as versatile photocaged bases for redox free radical photopolymerization

Benzoylformamides (BFAs) are proposed as photocaged bases for redox free radical photopolymerization (FRP). Initially the dissolving capacity of BFAs was evaluated. Besides our previously reported photo-latent anion polymerization, BFAs, as versatile photocaged bases, can not only initiate the FRP of acrylates unassisted, but also perform redox FRP in combination with a benzoyl peroxide initiator. We detail a model photopolymerization in the presence of BFA-dBA (N,N-dibenzyl-2-oxo-2-phenylacetamide) as the photocaged base. In combination with a benzoyl peroxide initiator, BFAs are able to initiate the amine-mediated redox photopolymerization of acrylates, and enhance the photopolymerization rate. Finally, we investigated the mechanism of the radical formation to initiate the redox FRP, as exemplified by BFA-dBA.