Synthesis of diblock copolymer nano-assemblies: Comparison between PISA and micellization

Chirality-controlled polymerization-induced self-assembly

Recent studies have shown that biodegradable nanoparticles can be efficiently prepared with polymerization of N-carboxyanhydrides-induced self-assembly (NCA-PISA). However, thus far, the effect of chiral monomer ratio on such NCA-PISA formulations and the resulting nanoparticles has not yet been fully explored. Herein, we show, for the first time, that the morphology, secondary structure, and biodegradation rate of PISA nanoparticles can be controlled by altering the chiral ratio of the core-forming monomers. This chirality-controlled PISA (CC-PISA) method allowed the preparation of nanoparticles that are more adjustable and applicable for future biomedical applications. Additionally, the complex secondary peptide structure (ratio of α-helix to β-sheet) and π-π stacking affect the polymer self-assembly process. More specifically, a PEG45 macro-initiator was chain-extended with l- and d-phenylalanine (l- and d-Phe-NCA) in various molar ratios in dry THF at 15 wt%. This ring-opening polymerization (ROP) allowed the preparation of homo- and hetero-chiral Phe-peptide block copolymers that self-assembled in situ into nanoparticles. For homo-chiral formulations, polymers self-assembled into vesicles once a sufficiently high phenylalanine degree of polymerization (DP) was obtained. Hetero-chiral formulations formed larger nanoparticles with various morphologies and, much to our surprise, using an equal enantiomer ratio inhibited PISA and led to a polymer solution instead. Finally, it was shown that the enzymatic biodegradation rate of such PISA particles is greatly affected by the polymer chirality. This PISA approach could be of great value to fabricate nanoparticles that exploit chirality in disease treatment.

Microwave Irradiation-Assisted Reversible Addition-Fragmentation Chain Transfer Polymerization-Induced Self-Assembly of pH-Responsive Diblock Copolymer Nanoparticles

Herein, we present a versatile platform for the synthesis of pH-responsive poly([N-(2-hydroxypropyl)]methacrylamide)-b-poly[2-(diisopropylamino)ethyl methacrylate] diblock copolymer (PHPMA-b-PDPA) nanoparticles (NPs) obtained via microwave-assisted reversible addition-fragmentation chain transfer polymerization-induced self-assembly (MWI-PISA). The N-(2-hydroxypropyl) methacrylamide (HPMA) monomer was first polymerized to obtain a macrochain transfer agent with polymerization degrees (DPs) of 23 and 51. Subsequently, using mCTA and 2-(diisopropylamino)ethyl methacrylate (DPA) as monomers, we successfully conducted MWI-PISA emulsion polymerization in aqueous solution with a solid content of 10 wt %. The NPs were obtained with high monomer conversion and polymerization rates. The resulting diblock copolymer NPs were analyzed by dynamic light scattering (DLS) and cryogenic-transmission electron microscopy (cryo-TEM). cryo-TEM studies reveal the presence of only NPs with spherical morphology such as micelles and polymer vesicles known as polymersomes. Under the selected conditions, we were able to fine-tune the morphology from micelles to polymersomes, which may attract considerable attention in the drug-delivery field. The capability for drug encapsulation using the obtained in situ pH-responsive NPs, the polymersomes based on PHPMA₂₃-b-PDPA₁₀₀, and the micelles based on PHPMA₅₁-b-PDPA₁₀₀ was demonstrated using the hydrophobic agent and fluorescent dye as Nile red (NR). In addition, the NP disassembly in slightly acidic environments enables fast NR release.

The Effect of Topology on Block Copolymer Nanoparticles: Linear versus Star Block Copolymers in Toluene

Linear and star block copolymer (BCP) nanoparticles of (polystyrene-block-poly(4-vinylpyridine))_n (PS-b-P4VP)_n with arm numbers of 1, 2, 3, and 4 were prepared by two methods of polymerization-induced self-assembly (PISA) and general self-assembly of block copolymers in the low-polar organic solvent, toluene. The effect of the arm number on the size and/or morphology of the (PS-b-P4VP)_n nanoassemblies synthesized by the two methods in toluene and on the polymerization kinetics was investigated in detail. Our results show that in toluene, a low-polar solvent, the topology not only affected the morphology of the BCP nanoparticles prepared by PISA, but also influenced the BCP nanoparticles synthesized through general self-assembly.

RAFT Copolymerization of Vinyl Acetate and Acrylic Acid in the Selective Solvent

Reversible addition-fragmentation chain transfer polymerization was successfully applied to the synthesis of the gradient copolymer of acrylic acid and vinyl acetate in the selective solvent. The gradient degree of the copolymer was varied by the monomer feed. The monomer conversion was found to affect the ability of the copolymer to self-assemble in aqueous solutions in narrowly dispersed micelles with an average hydrodynamic radius of about 250 nm. Furthermore, the synthesized copolymers also tended to self-assemble throughout copolymerization in the selective solvent.

Exploration of the modification-induced self-assembly (MISA) technique and the preparation of nano-objects with a functional poly(acrylic acid) core

The hydrolysis-based post-polymerization modification method was introduced into the self-assembly process and a modification-induced self-assembly (MISA) technique was presented.

RAFT dispersion polymerisation of lauryl methacrylate in ethanol–water binary mixtures: synthesis of diblock copolymer vesicles with deformable membranes

Diblock copolymer vesicles with deformable membranes are prepared via RAFT dispersion polymerisation of lauryl methacrylate in an 80 : 20 w/w ethanol–water mixture; visible light irradiation allows facile RAFT chain-end removal from these nano-objects.