Hyperbranched polyphosphoesters with reactive end groups synthesized via acyclic diene metathesis polymerization and their transformation to crosslinked nanoparticles

Advanced Biomaterials Derived from Functional Polyphosphoesters: Synthesis, Properties, and Biomedical Applications

Polyphosphoesters (PPEs) represent an innovative class of biodegradable polymers, with the phosphate ester serving as the core repeating unit of their polymeric backbone. Recently, biomaterials derived from functionalized PPEs have garnered significant interest in biomedical applications because of their commendable biocompatibility, biodegradability, and the capacity for functional modification. This review commences with a brief overview of synthesis methodologies and the distinctive properties of PPEs, including thermoresponsiveness, degradability, stealth effect, and biocompatibility. Subsequently, the review delves into the latest applications of PPEs-based nanocarriers for drug or gene delivery and PPEs-based polymeric prodrugs and scaffolds in the biomedical field, presenting several illustrative examples for each application. By encapsulating the advancements of recent years, this review aims to offer an enhanced understanding and serve as a reference for the synthesis and biomedical applications of functional PPEs.

Precision Aliphatic Polyesters via Cross-Metathesis Polymerization

Cross-metathesis (CM), a carbon-carbon bond transformation that features exceptional selectivity, reactivity and tolerance to functionalities, has been extensively investigated in organic chemistry. On the other hand, the use of CM in polymer synthesis is also growing in both scope and breadth, thus offering a wealth of opportunities for introducing a vast range of functionalities into polymer backbone so as to manipulate properties and expand applications. In this review, we propose the concept of "cross-metathesis polymerization" (CMP) referring to polymer synthesis via repetitive CM reaction and summarize emerging strategies for the precision synthesis of aliphatic polyesters via CMP based on the high CM tendency between acrylates and α- olefins. Due to the carbon-carbon bond-forming step-growth polymerization nature, CMP brings a new concept to polyester synthesis. This remarkable polymerization method possesses unique advantages such as mild condition, full conversion, fast kinetics, almost quantitative yield and extraordinary tolerance to functionalities. In particular, CMP provides the ability to regulate macromolecular architectures including linear, block, cyclic, star, graft, dendron, hyperbranched and dendrimer topologies. Ultimately, advanced polymeric materials with outstanding performances can be facially constructed based on these sophisticated macromolecular architectures.

Photoresponsive Polymeric Reversible Nanoparticles via Self-Assembly of Reactive ABA Triblock Copolymers and Their Transformation to Permanent Nanostructures

Azobenzene-functionalized ABA triblock copolymers with controlled molecular weights are prepared first via a sequential ring-opening metathesis polymerization and acyclic diene metathesis polymerization in one-pot, which are readily converted, by a facile esterification, to the modified ABA triblock copolymers. Then, these reactive triblock copolymers can spontaneously self-assemble in a selective solvent to form reproducible and reversible polymeric core-shell nanoparticles. Finally, the stable and permanent shell-crosslinked nanoparticles are obtained by an intramolecular crosslinking reaction in dilute solution under UV light irradiation. These as-prepared polymeric nanoparticles and their precursor incorporating azobenzene chromophores exhibit distinct photoresponsive performance and morphological variation.

Novel Photoresponsive Linear, Graft, and Comb-Like Copolymers with Azobenzene Chromophores in the Main-Chain and/or Side-Chain: Facile One-Pot Synthesis and Photoresponse Properties

Novel photoresponsive linear, graft, and comb-like copolymers with azobenzene chromophores in the main-chain and/or side-chain are prepared via a sequential ring-opening metathesis polymerization (ROMP) and head-to-tail acyclic diene metathesis (ADMET) polymerization in a one-pot procedure using Grubbs ruthenium-based catalysts. The diluted solutions of these as-prepared copolymers containing azobenzene chromophores exhibit photochemical trans-cis isomerization under the irradiation of UV light, followed by their cis-trans back-isomerization in visible light. The rates of photoisomerization are found to be slower than those of back-isomerization, and the rate for the comb-like copolymer is found to be from 3 to 7 times slower than that obtained for the linear or graft copolymer. This is ascribed to the differences in structure of the copolymers and the specific location of azobenzene chromophores in the copolymer, which favor a side-chain graft structure.

Ladder- and bridge-like polynorbornenes with phosphate linkers: facile one-pot synthesis and excellent properties

A novel telechelic double-stranded polymer with two terminal alkenyl groups was prepared through ROMP of the corresponding monomer bearing a phosphate linker, and was then used as a macromonomer in ADMET polymerization to yield a bridge-like polymer.

Hyperbranched unsaturated polyphosphates as a protective matrix for long-term photon upconversion in air

The energy stored in the triplet states of organic molecules, capable of energy transfer via an emissive process (phosphorescence) or a nonemissive process (triplet-triplet transfer), is actively dissipated in the presence of molecular oxygen. The reason is that photoexcited singlet oxygen is highly reactive, so the photoactive molecules in the system are quickly oxidized. Oxidation leads to further loss of efficiency and various undesirable side effects. In this work we have developed a structurally diverse library of hyperbranched unsaturated poly(phosphoester)s that allow efficient scavenging of singlet oxygen, but do not react with molecular oxygen in the ground state, i.e., triplet state. The triplet-triplet annihilation photon upconversion was chosen as a highly oxygen-sensitive process as proof for a long-term protection against singlet oxygen quenching, with comparable efficiencies of the photon upconversion under ambient conditions as in an oxygen-free environment in several unsaturated polyphosphates. The experimental results are further correlated to NMR spectroscopy and theoretical calculations evidencing the importance of the phosphate center. These results open a technological window toward efficient solar cells but also for sustainable solar upconversion devices, harvesting a broad-band sunlight excitation spectrum.

Star-shaped polyphosphoesters with reactive end groups synthesized via acyclic diene metathesis polymerization and their transformation to nanostructures

Four-arm star shaped polyphosphoesters are synthesized via acyclic diene metathesis (ADMET) polymerization.

Convenient divergent synthesis of linear-dendron block polyphosphoesters via acyclic diene metathesis polymerization

ADMET polymerization was successfully applied for the synthesis of linear-dendritic polyphosphoester structures by using macromolecular chain stoppers.