Salicylaldehyde-functionalized block copolymer nano-objects: one-pot synthesis via polymerization-induced self-assembly and their simultaneous cross-linking and fluorescence modification

Abstract

Salicylaldehyde-functional diblock copolymer nano-objects were synthesized by polymerization induced self-assembly (PISA) via RAFT dispersion polymerization of a newly designed core-forming monomer, 3-formyl-4-hydroxybenzyl methacrylate (FHMA), using poly(2-hydroxypropyl methacrylate) (PHPMA) macromolecular chain transfer agent as a steric stabilizer in methanol at 65 o C. A range of PHPMA-b-PFHMA block copolymer morphologies including sphere, worm and vesicle could be accessed by adjusting the degree of polymerization of core forming block PFHMA. Since the salicylaldehyde groups of core-forming PFHMA blocks could react with hydrazine in a 2:1 stoichiometry to form salicylaldazines with aggregation-induced emission, one-step post-modification of the PISA nano-objects using hydrazine enabled their inherent nanostructures to be stabilized via covalent cross-linking and simultaneously conferred luminescent features on the resulting stabilized nanoparticles. Solid nano-objects, obtained easily via precipitation into diethyl ether, could be re-dispersed well in methanol and THF. The nano-objects could also be re-dispersed in water to form colloidal dispersions at a low concentration (≤ 1% w/w). Thanks to the stability imparted by the cross-linking, the morphologies of the preformed PISA nano-objects remained intact even after re-dispersing these cross-linked nano-objects in THF (a good solvent for both blocks). The stabilized nano-objects displayed strong orange fluorescence in water, organic solvents or solid states. This work opens the possibility for simultaneous functionlization and stabilization of PISA-generated block copolymer nano-objects. Materials 2-Hydroxypropyl methacrylate (HPMA; J&K, 97%) was passed through a column of basic alumina to remove inhibitor and then stored at -20 °C prior to use. 2, 2′-Azobis(isobutyronitrile) (AIBN; Sinopharm Chemical Reagent, 99%) was purified by recrystallization from ethanol. 4-Cyano-4-(propylthiocarbonothioylthio)pentanoic acid (CPPA) 53 and 5-(chloromethyl)-2-hydroxybenzaldehyde 54 were synthesized according to literature procedures. Other reagents were all analytical grade and used as received. Synthesis of 3-formyl-4-hydroxybenzyl methacrylate (FHMA)A mixture of methacrylic acid (25.8 g, 0.3 mol), sodium hydroxide (12.0 g, 0.3 accelerating voltage of 120 kV. For preparation of TEM samples, a drop of diluted dispersion (0.15 % w/w) solution was deposited onto a carbon-coated copper grid and dried under ambient conditions. All samples were not stained. Results and discussion Synthesis of monomer 3-formyl-4-hydroxybenzyl methacrylate (FHMA)A novel salicylaldehyde functionalized methacrylate monomer FHMA was designed and synthesized readily by the reaction of methacrylic acid with 5-(chloromethyl)-2-hydroxybenzaldehyde (Scheme 1). The structure of FHMA was confirmed on the base of the elemental analysis, MS, and 1 H NMR spectroscopy. The 1 H NMR spectrum (Fig. 1) exhibits the characteristic signals corresponding to methacrylic vinyl (a,b), aldehyde (i) and hydroxyl (h) mo...

In Situ Crosslinking of Nanoparticles in Polymerization‐Induced Self‐Assembly via ARGET ATRP of Glycidyl Methacrylate

“…Therefore, the storage and application of the obtained nanoparticles are greatly limited. Consequently, stabilization is desirable to enhance the performance of the nanoparticles, such as mechanical stability and surfactant‐resistance; but stabilization, or crosslinking, of the nanoparticles formed in a PISA system remains a challenge …”

Reactive Polymorphic Nanoparticles: Preparation via Polymerization‐Induced Self‐Assembly and Postsynthesis Thiol–para‐Fluoro Core Modification

“…For PISA conducted in alcoholic dispersion, styrene, benzyl methacrylate, and phenylalkyl methacrylate homologues have been the most commonly employed core‐forming monomers . Chemical cross‐linking of the core‐forming blocks has been reported using diamines on ketone‐functional monomers and 3‐aminopropyltriethoxysilane to react with PISA cores containing epoxides and hydroxyl groups …”

Photoinitiated Polymerization‐Induced Self‐Assembly of Glycidyl Methacrylate for the Synthesis of Epoxy‐Functionalized Block Copolymer Nano‐Objects

“…Functionalization or cross‐linking is desirable to enhance the performance of block copolymer nano‐objects (e.g., mechanical stability, surfactant‐resistant) . The mPEG 45 –PGMA n diblock copolymer nano‐objects prepared in the present case contain a high density of epoxy functionality in the core.…”

“…Uniform vesicles were achieved by tuning reaction parameters. Huang et al reported the PISA of 3‐formyl‐4‐hydroxybenzyl methacrylate for the preparation of salicylaldehyde‐functional diblock copolymer nano‐objects. The obtained polymer nano‐objects were further cross‐linked or modified with fluorescent dyes using hydrazine.…”