Living Alternating Ring-Opening Metathesis Copolymerization of 2,3-Dihydrofuran to Provide Completely Degradable Polymers

2,3-Dihydrofuran (DHF) has recently been gaining significant attention as a comonomer in metathesis polymerization, thanks to its ability to provide the resultant polymer backbones with stimuli-responsive degradability. In this report, we present living alternating copolymerization of DHF with less reactive endo-tricyclo[4.2.2.02,5 ]deca-3,9-dienes (TDs) and endo-oxonorbornenes (oxoNBs). By carefully controlling the reactivity of both the Ru initiators and the monomers, we have achieved outstanding A, B-alternation (up to 98 %) under near stoichiometric DHF loading conditions. Notably, we have also found that the use of a more sterically hindered Ru initiator helps to attain polymer backbones with higher DHF incorporation and superior A, B-alternation. While preserving the living characteristics of DHF copolymerization, as evidenced by controlled molecular weights (up to 73.9 kDa), narrow dispersities (down to 1.05), and block copolymer formation, our DHF copolymers could be broken down to a single repeat unit level under acidic conditions. 1 H NMR analysis of the model copolymer revealed that after 24 hours of degradation, up to 80 % of the initial polymer was transformed into a single small molecule product, and after purification, up to 66 % of the degradation product was retrieved. This study provides a versatile approach to improve the alternation and degradability of DHF copolymers.

Synthesis of Degradable Polyolefins Bearing Disulfide Units via Metathesis Copolymerization

Disulfide bonds are dynamic covalent bonds, which are easy to cleave and reform upon chemical stimulus. Various methods including the oxidative coupling of thiols and polymerization of disulfide-containing monomers have been developed for the synthesis of poly(disulfide)s. However, installing small amounts of disulfide units in the main chain of polyolefins has received much less attention. Herein, we report a novel strategy for incorporating cleavable disulfide units into the backbone of polyolefins using commercially available diallyl disulfide (DADS) as a comonomer via metathesis copolymerization. The copolymerization of diallyl disulfide with cyclooctene occurred using the second-generation Grubbs catalyst under mild conditions, allowing for the synthesis of copolymers with adjustable disulfide content ranging from 0.7 to 8.5 mol%, and the molecular weight of the obtained copolymers ranged from 5.8 kg·mol^-1 to 42.8 kg·mol^-1. The resulting polyolefins with disulfide insertion retained excellent thermal processability and exhibited degradability. Treatment of the copolymer (8.5 mol% disulfide content) with tri-n-butylphosphine resulted in a significant reduction in molecular weight from 5.8 kg·mol^-1 to 1.6 kg·mol^-1. Successful copolymerization with diallyl disulfide provides a convenient and effective method for obtaining degradable polyolefins.

Chemically Recyclable Dithioacetal Polymers via Reversible Entropy-Driven Ring-Opening Polymerization

In a sustainable circular economy, polymers capable of chemical recycling to monomers are highly desirable. We report an efficient monomer-polymer recycling of polydithioacetal (PDTA). Pristine PDTAs were readily synthesized from 3,4,5-trimethoxybenzaldehyde and alkyl dithiols. They then exhibited depolymerizability via ring-closing depolymerization into macrocycles, followed by entropy-driven ring-opening polymerization (ED-ROP) to reform the virgin polymers. High conversions were obtained for both the forward and reverse reactions. Once crosslinked, the network exhibited thermal reprocessability enabled by acid-catalyzed dithioacetal exchange. The network retained the recyclability into macrocyclic monomers in solvent which can repolymerize to regenerate the crosslinked network. These results demonstrated PDTA as a new molecular platform for the design of recyclable polymers and the advantages of ED-ROP for which polymerization is favored at higher temperatures.

Orthogonally deconstructable and depolymerizable polysilylethers via entropy-driven ring-opening metathesis polymerization

The synthesis of novel polysilylethers via entropy-driven ring-opening metathesis polymerization (ED-ROMP) of cyclic bifunctional silyl ether-based monomers is reported. These polymers display good thermal stability and ultra-low T_g (-88 °C). Moreover, they are rapidly deconstructable via the cleavage of the silicon-oxygen linkages with acid or fluoride triggers, and they were partially depolymerizable by the addition of exogenous metathesis catalyst. Analysis of the deconstructed polymer products provided insight into the polymer microstructure, showing that the ED-ROMP process was regiorandom. Altogether, this work offers a new class of deconstructable polymers with a range of potential applications.

Recent advances in the ring-opening polymerization of sulfur-containing monomers

Inspired by the broad range of applications for sulfur-containing polymers, this article presents an overview regarding various ROP technologies (ROP/rROP/ROMP) which cement the importance of sulfur-containing monomers in modern polymer chemistry.

Poly(disulfide)s: From Synthesis to Drug Delivery

Bioresponsive polymers have been widely used in drug delivery because of their degradability. For example, poly(disulfide)s with repeating disulfide bonds in the main chain have attracted considerable research attention. The characteristics of the disulfide bonds, including their dynamic and reversible properties and their responsiveness to stimuli such as reductants, light, heat, and mechanical force, make them ideal platforms for on-demand drug delivery. This review introduces the synthesis methods and applications of poly(disulfide)s. Furthermore, the synthesis methods of poly(disulfide)s are classified on the basis of the monomers used: oxidative step-growth polymerization with dithiols, ring-opening polymerization with cyclic disulfides, and polymerization with linear disulfides. In addition, recent advances in poly(disulfide)s for the delivery of small-molecule or biomacromolecular drugs are discussed. Quantum-dot-loaded poly(disulfide) delivery systems for imaging are also included. This review provides an overview of the various design strategies employed in the construction of poly(disulfide) platforms to inspire new applications in the field of drug delivery.

A Guideline for the Synthesis of Amino-Acid-Functionalized Monomers and Their Polymerizations

Amino acids have emerged as a sustainable source for the design of functional polymers. Besides their wide availability, especially their high degree of biocompatibility makes them appealing for a broad range of applications in the biomedical research field. In addition to these favorable characteristics, the versatility of reactive functional groups in amino acids (i.e., carboxylic acids, amines, thiols, and hydroxyl groups) makes them suitable starting materials for various polymerization approaches, which include step- and chain-growth reactions. This review aims to provide an overview of strategies to incorporate amino acids into polymers. To this end, it focuses on the preparation of polymerizable monomers from amino acids, which yield main chain or side chain-functionalized polymers. Furthermore, postpolymerization modification approaches for polymer side chain functionalization are discussed. Amino acids are presented as a versatile platform for the development of polymers with tailored properties.

Degradable polymers via olefin metathesis polymerization

The development of degradable polymers has commanded significant attention over the past half century. Approaches have predominantly relied on ring-opening polymerization of cyclic esters (e.g., lactones, lactides) and N-carboxyanhydrides, as well as radical ring-opening polymerizations of cyclic ketene acetals. In recent years, there has been a significant effort applied to expand the family of degradable polymers accessible via olefin metathesis polymerization. Given the excellent functional group tolerance of olefin metathesis polymerization reactions generally, a broad range of conceivable degradable moieties can be incorporated into appropriate monomers and thus into polymer backbones. This approach has proven particularly versatile in synthesizing a broad spectrum of degradable polymers including poly(ester), poly(amino acid), poly(acetal), poly(carbonate), poly(phosphoester), poly(phosphoramidate), poly(enol ether), poly(azobenzene), poly(disulfide), poly(sulfonate ester), poly(silyl ether), and poly(oxazinone) among others. In this review, we will highlight the main olefin metathesis polymerization strategies that have been used to access degradable polymers, including (i) acyclic diene metathesis polymerization, (ii) entropy-driven and (iii) enthalpy-driven ring-opening metathesis polymerization, as well as (iv) cascade enyne metathesis polymerization. In addition, the livingness or control of polymerization reactions via different strategies are highlighted and compared. Potential applications, challenges and future perspectives of this new library of degradable polyolefins are discussed. It is clear from recent and accelerating developments in this field that olefin metathesis polymerization represents a powerful synthetic tool towards degradable polymers with novel structures and properties inaccessible by other polymerization approaches.

Aminolysis induced functionalization of (RAFT) polymer-dithioester with thiols and disulfides

Efficient exchange of the polymer-dithioester end group by aminolysis/functionalization with thiol or disulfide under ambient atmospheric conditions.