Alternating Radical Ring-Opening Polymerization of Cyclic Ketene Acetals: Access to Tunable and Functional Polyester Copolymers

Degradable Alternating Copolymers by Radical Copolymerization of 2-Methylen-1,3-dioxepane and Crotonate Esters

Producing backbone degradable copolymers via free-radical copolymerization is a promising, yet challenging method to develop more sustainable materials for many applications. In this work, we present the copolymerization of 2-methylen-1,3-dioxepane (MDO) with crotonic acid derivative esters. MDO can copolymerize by radical ring-opening polymerization incorporating degradable ester moieties in the polymer backbone, although this can often be difficult due to the very unfavorable reactivity ratios. Crotonic acid derivatives, on the other hand, can be easily produced completely from biomass but are typically very difficult to (co)polymerize due to low propagation rates and very unfavorable reactivity ratios. Herein, we present the surprisingly easy copolymerization between MDO and butyl crotonate (BCr), which shows the ability to form alternating copolymers. The alternating nature of the copolymer was characterized by MALDI-TOF and supported by the reactivity ratios calculated experimentally (rMDO = 0.105 and rBCr = 0.017). The alternating nature of the copolymers favored the degradability that could be achieved under basic conditions (in 2 h, all chains have molar masses smaller than 2 kg/mol). Last, the work was expanded to other crotonate monomers to expand the portfolio and show the potential of this copolymer family.

Quantitative, Regiospecific, and Stereoselective Radical Ring-Opening Polymerization of Monosaccharide Cyclic Ketene Acetals

Cyclic ketene acetals (CKAs) are among the most well-studied monomers for radical ring-opening polymerization (rROP). However, ring-retaining side reactions and low reactivities in homopolymerization and copolymerization remain significant challenges for the existing CKAs. Here, we report that a class of monosaccharide CKAs can be facilely prepared from a short and scalable synthetic route and can undergo quantitative, regiospecific, and stereoselective rROP. NMR analyses and degradation experiments revealed a reaction mechanism involving a propagating radical at the C2 position of pyranose with different monosaccharides exhibiting distinct stereoselectivity in the radical addition of the monomer. Furthermore, the addition of maleimide was found to improve the incorporation efficiency of monosaccharide CKA in the copolymerization with vinyl monomers and produced unique degradable terpolymers with carbohydrate motifs in the polymer backbone.

Installing a Single Monomer within Acrylic Polymers Using Photoredox Catalysis

Incorporating exactly one monomer at a defined position during a chain polymerization is exceptionally challenging due to the statistical nature of monomer addition. Herein, photoinduced electron/energy transfer (PET) enables the incorporation of exactly one vinyl ether into polyacrylates synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Near-quantitative addition (>96%) of a single vinyl ether is achieved while retaining >99% of the thiocarbonylthio chain ends. Kinetic studies reveal that performing the reactions at 2 °C limits unwanted chain breaking events. Finally, the syntheses of diblock copolymers are reported where molecular weights and dispersities are well-controlled on either side of the vinyl ether. Overall, this report introduces an approach to access acrylic copolymers containing exactly one chemical handle at a defined position, enabling novel macromolecular architectures to probe structure-function properties, introduce sites for de/reconstruction, store information, etc.

Amphiphilic Block Copolymers PEG-b-PMTCs: Synthesis, Self-Assembly, Degradation Properties and Biocompatibility

As a hydrophilic cyclic ketene acetal (CKA), 2-methylene-1,3,6-trioxocane (MTC) has recently attracted a lot of attention owing to its ability to promote a quicker (bio)degradation as compared to other heavily studied CKAs. Here, we prepared amphiphilic block copolymers based on poly-MTC with varying chain lengths by radical ring opening polymerization. Self-assemblies of these amphiphiles were performed in PBS buffer to generate nanoparticles with sizes from 40 to 105 nm, which were verified by dynamic light scattering, electron microscopy, and static light scattering (Zimm plots). Subsequently, fluorescence spectroscopy was applied to study the enzymatic degradation of Nile red-loaded nanoparticles. By performing a point-by-point comparison of fluorescence intensity decline patterns between nanoparticles, we demonstrated that lipase from Pseudomonas cepacia was very efficient in degrading the nanoparticles. Hydrolysis degradations under basic conditions were also carried out, and a complete degradation was achieved after 4 h. Additionally, cytotoxicity assays were carried out on HEK293 cells, and the results affirmed cell viabilities over 90% when incubated with up to 1 mg/mL nanoparticles for 24 h. These biodegradable and biocompatible nanoparticles hence hold great potential for future applications such as drug release.

Umpolung Isomerization in Radical Copolymerization of Benzyl Vinyl Ether with Pentafluorophenylacrylate Leading to Degradable AAB Periodic Copolymers

This study revealed that benzyl vinyl ether (BnVE) shows a peculiar isomerization propagation in its radical copolymerization with an electron-deficient acrylate carrying a pentafluorophenyl group (PFA). The co-monomer pair inherently exhibits the cross-over propagation feature due to the large difference in the electron density. However, the radical species of PFA was found to undergo a backward isomerization to the penultimate BnVE pendant giving a benzyl radical species prior to propagation with BnVE. The isomerization brings a drastic change in the character of the growing radical species from electrophilic to nucleophilic, and thus the isomerized benzyl radial species propagates with PFA. Consequently, the two monomers were consumed in the order AAB (A: PFA; B: BnVE) and the unique periodic consumption was confirmed by the pseudo-reactivity ratios calculated by the penultimate model: r11 =0.174 and r21 =6600 for PFA (M1 ) with BnVE (M2 ). The pentafluorophenyl ester groups of the resulting copolymers are transformed into ester and amide groups by post-polymerization alcoholysis and aminolysis modifications. The unique isomerization in the AAB sequence allowed the periodic introduction of a benzyl ether structure in the backbone leading to efficient degradation under acid conditions.

Sustainable formulation polymers for home, beauty and personal care: challenges and opportunities

As society moves towards a net-zero future, the need to adopt more sustainable polymers is well understood, and as well as plastics, less visible formulation polymers should also be included within this shift. As researchers, industries and consumers move towards more sustainable products there is a clear need to define what sustainability means in fast moving consumer goods and how it can be considered at the design stage. In this perspective key challenges in achieving sustainable formulation polymers are highlighted, and opportunities to overcome them are presented.

Radical Ring Opening Polymerization of Cyclic Ketene Acetals Derived From d-Glucal

A cyclic ketene acetal (CKA) derived from d-glucal was synthesized, and its polymerization using free radicals has been investigated. NMR analysis of the resulting polymers revealed the formation of polyacetal-polyester copolymers, with up to 78% of ester linkages formed by radical ring-opening polymerization (rROP). Conversely, the polymerization of the monomer-saturated analogue only produced acetal linkages, demonstrating that the alkene functionality within the d-glucal pyranose ring is essential to promote ring-opening and ester formation, likely via the stabilization of an allyl radical. The thermal properties of the polymers were linked to the ratio of the ester and acetal linkages. Copolymerization with methyl methacrylate (MMA) afforded statistically PMMA-rich copolymers (66-98%) with linkages prone to hydrolytic degradation and decreased glass-transition temperatures. The retention of the pseudoglucal alkene function offers opportunities to functionalize further these bioderived (co)polymers.

Current Standing on Radical Ring-Opening Polymerizations of Cyclic Ketene Acetals as Homopolymers and Copolymers with one another

Radical Ring-opening polymerization (RROP) of cyclic ketene acetals (CKAs) emerges to be a valuable polymerization technique. In attracting more attention, RROP has seen a new spike in publications, which the authors will put into perspective. This review will hence address the progress made on the number of available CKAs and the synthetic strategies to get them. In grouping, the available monomers into distinct categories, the enormous variety of available CKAs will be highlighted. Polymerizations of CKAs without vinylenes have the potential to yield fully biodegradable polymers, which is why this kind of polymerization is the focus of this review. Detailing the current understanding of the mechanism, the various side reactions will be noted and also their effect on the overall properties of the final polymers. Current attempts to control the ring-retaining and branching reactions will be discussed as well. In addition to the polymerization itself, the available materials will be discussed as well as homopolymers, copolymers of CKAs, and block-copolymers with pure CKA-blocks have significantly widened the range of possible applications of materials from RROP. Altogether this review highlights the progress in the entire field of RROP just of CKAs to give a holistic overview of the field.

Increasing the Hydrophilicity of Cyclic Ketene Acetals Improves the Hydrolytic Degradation of Vinyl Copolymers and the Interaction of Glycopolymer Nanoparticles with Lectins

Radical ring-opening polymerization (rROP) of cyclic ketene acetals (CKAs) with traditional vinyl monomers allows the synthesis of degradable vinyl copolymers. However, since the most commonly used CKAs are hydrophobic, most degradable vinyl copolymers reported so far degrade very slowly by hydrolysis under physiological conditions (phosphate-buffered saline, pH 7.4, 37 °C), which can be detrimental for biomedical applications. Herein, to design advanced vinyl copolymers by rROP with high CKA content and enhanced degradation profiles, we reported the copolymerization of 2-methylene-1,3,6-trioxocane (MTC) as a CKA with vinyl ether (VE) or maleimide (MI) derivatives. By performing a point-by-point comparison between the MTC/VE and MTC/MI copolymerization systems, and their counterparts based on 2-methylene-1,3-dioxepane (MDO) and 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), we showed negligible impact on the macromolecular characteristics and similar reactivity ratios, suggesting successful substitution of MDO and BMDO by MTC. Interestingly, owing to the hydrophilicity of MTC, the obtained copolymers exhibited a faster hydrolytic degradation under both accelerated and physiological conditions. We then prepared MTC-based glycopolymers, which were formulated into surfactant-free nanoparticles, exhibiting excellent colloidal stability up to 4 months and complete degradation under enzymatic conditions. Importantly, MTC-based glyconanoparticles also showed a similar cytocompatibility toward two healthy cell lines and a much stronger lectin affinity than MDO-based glyconanoparticles.

Synthesis and Degradation of Vinyl Polymers with Evenly Distributed Thioacetal Bonds in Main Chains: Cationic DT Copolymerization of Vinyl Ethers and Cyclic Thioacetals

We report a novel method to synthesize degradable poly(vinyl ether)s with cleavable thioacetal bonds periodically arranged in the main chains using controlled cationic copolymerization of vinyl ethers with a 7-membered cyclic thioacetal (7-CTA) via degenerative chain transfer (DT) to the internal thioacetal bonds. The thioacetal bonds, which are introduced into the main chain by cationic ring-opening copolymerization of 7-CTA with vinyl ethers, serve as in-chain dormant species to allow homogeneous propagation of vinyl ethers for all internal segments to afford copolymers with controlled overall and segmental molecular weights. The obtained polymers can be degraded into low- and controlled-molecular-weight polymers with narrow molecular weight distributions via hydrolysis. Various vinyl ethers with hydrophobic, hydrophilic, and functional pendants are available. Finally, one-pot synthesis of multiblock copolymers and their degradation into diblock copolymers are also achieved.

Addition-Fragmentation Ring-Opening Polymerization of Bio-Based Thiocarbonyl l-Lactide for Dual Degradable Vinyl Copolymers

This study is designed to synthesize novel degradable polymers by radical addition-fragmentation ring-opening copolymerization of bio-based thiocarbonyl compounds with various vinyl monomers. Thiocarbonyl l-lactide is capable of radical copolymerization with acrylates and styrene via radical addition to the carbon-sulfur double bonds followed by ring-opening as well as controlled copolymerization in conjunction with the reversible addition-fragmentation chain transfer (RAFT) process. The obtained polymers possess ring-opened thioester and ring-retained thioacetal functionalities in the backbone, both of which could be cleaved under appropriate conditions with different chemical stimuli.

Backbone Degradation of Polymethacrylates via Metal-Free Ambient-Temperature Photoinduced Single-Electron Transfer

Polymeric materials comprised of all-carbon backbones are ubiquitous to modern society due to their low cost, impressive robustness, and unparalleled physical properties. It is well-known that these materials often persist long beyond their intended usage lifetime, resulting in environmental accumulation of plastic waste. A substantial barrier to the breakdown of these polymers is the relative chemical inertness of carbon-carbon bonds within their backbone. Herein, we describe a photocatalytic strategy for cleaving carbon-based polymer backbones. Inclusion of a low mole percent of a redox-active comonomer allows for a dramatic reduction in polymer molecular weight upon exposure to light. The N-(acyloxy)phthalimide comonomer, upon reception of an electron from a single-electron transfer (SET) donor, undergoes decarboxylation to yield a backbone-centered radical. Depending on the nature of this backbone radical, as well as the substitution on neighboring monomer repeat units, a β-scission pathway is thermodynamically favored, resulting in backbone cleavage. In this way, polymers with an all-carbon backbone may be degraded at ambient temperature under metal-free conditions.

Degradable Hydrogel Adhesives with Enhanced Tissue Adhesion, Superior Self-Healing, Cytocompatibility, and Antibacterial Property

Degradable hydrogel adhesives with multifunctional advantages are promising to be candidates as hemostatic agents, surgical sutures, and wound dressings. In this study, hydrogel adhesives are constructed by catechol-conjugated gelatin from natural resource, iron ions (Fe³⁺ ), and a synthetic polymer. Specifically, the latter is prepared by the radical ring-opening copolymerization of a cyclic ketene acetal monomer 5,6-benzo-2-methylene-1,3-dioxepane and N-(2-ethyl p-toluenesulfonate) maleimide. By the incorporation of ester bonds in the backbone and the combination with quaternary ammonium salt pendants in the polymer, it exhibits excellent degradability and antibacterial property. Remarkably, doping the synthetic polymer into the 3,4-dihydroxyphenylacetic acid-modified gelatin network forms a semi-interpenetrating polymer network which can effectively improve the rigidity, tissue adhesion, and antibacterial property of fabricated hydrogel adhesives. Moreover, non-covalent bonds from coordination interaction between catechol and Fe³⁺ contribute to the fast self-healing of the developed hydrogel adhesives. These hydrogel adhesives with the multiple merits including the degradability, enhanced tissue adhesion, superior self-healing, good cytocompatibility, and antibacterial property show the great potential to be used as tissue adhesives in biomedical fields.

Mechanistic investigation of cyclic ketene acetal radical ring-opening homo- and co-polymerization and preparation of PEO graft copolymers with tunable composition

Radical ring-opening polymerization of cyclic ketene acetals (CKAs) led to homogeneous ester insertion during semi-batch reactions with N-vinyl pyrrolidone (NVP). Investigation of CKA radical transfer allowed for CKA–NVP graft copolymer preparation.

Hybrid copolymerization of acrylate and thiirane monomers mediated by trithiocarbonate

The composition and structure of polymers have great influence on their performances.

Degradable Vinyl Random Copolymers via Photocontrolled Radical Ring-Opening Cascade Copolymerization

Degradable vinyl polymers by radical ring-opening polymerization are promising solutions to the challenges caused by non-degradable vinyl plastics. However, achieving even distributions of labile functional groups in the backbone of degradable vinyl polymers remains challenging. Herein, we report a photocatalytic approach to degradable vinyl random copolymers via radical ring-opening cascade copolymerization (rROCCP). The rROCCP of macrocyclic allylic sulfones and acrylates or acrylamides mediated by visible light at ambient temperature achieved near-unity comonomer reactivity ratios over the entire range of the feed compositions. Experimental and computational evidence revealed an unusual reversible inhibition of chain propagation by in situ generated sulfur dioxide (SO2), which was successfully overcome by reducing the solubility of SO2. This study provides a powerful approach to degradable vinyl random copolymers with comparable material properties to non-degradable vinyl polymers.

Backbone-Degradable Polymers via Radical Copolymerizations of Pentafluorophenyl Methacrylate with Cyclic Ketene Acetal: Pendant Modification and Efficient Degradation by Alternating-Rich Sequence

This work deals with syntheses of backbone-degradable polymers via the radical copolymerization of pentafluorophenyl methacrylate (PFMA) with 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), which undergoes ring-opening propagation to afford an ester-bonded backbone. The combination of the electron-deficient methacrylate with the electron-rich cyclic monomer allowed high crossover copolymerization, and the electronic effect was clarified by the comparison with the copolymerization of methyl methacrylate (MMA) and BMDO. The PFMA units of the resultant copolymer underwent quantitative alcoholysis or aminolysis transformation into methacrylate or methacrylamide units along with the pendant functionalization. The alternating-rich sequence was achieved by feeding an excess ratio of BMDO, which was supported by MALDI-TOF-MS of the copolymer obtained by the RAFT copolymerization. The methanolysis-transformed copolymer carrying MMA units was decomposed under basic condition, and the degradation efficiency was superior to that of the copolymer obtained via radical copolymerization of MMA with BMDO because of the alternating-rich sequence.

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.

Clip Chemistry: Diverse (Bio)(macro)molecular and Material Function through Breaking Covalent Bonds

In the two decades since the introduction of the "click chemistry" concept, the toolbox of "click reactions" has continually expanded, enabling chemists, materials scientists, and biologists to rapidly and selectively build complexity for their applications of interest. Similarly, selective and efficient covalent bond breaking reactions have provided and will continue to provide transformative advances. Here, we review key examples and applications of efficient, selective covalent bond cleavage reactions, which we refer to herein as "clip reactions." The strategic application of clip reactions offers opportunities to tailor the compositions and structures of complex (bio)(macro)molecular systems with exquisite control. Working in concert, click chemistry and clip chemistry offer scientists and engineers powerful methods to address next-generation challenges across the chemical sciences.

A cascade strategy towards the direct synthesis of green polyesters with versatile functional groups

The cascade coupling of ROP and CP enables the facile synthesis of high functional group content biodegradable polyesters.

ε-Thionocaprolactone: an accessible monomer for preparation of degradable poly(vinyl esters) by radical ring-opening polymerization

Readily accessible ε-thionocaprolactone can be copolymerized with vinyl esters under radical polymerization conditions to produce copolymers containing degradable thioester and thioacetal linkages.

Progress in the Preparation of Functional and (Bio)Degradable Polymers via Living Polymerizations

This review presents the latest developments in (bio)degradable approaches and functional aliphatic polyesters and polycarbonates prepared by typical ring-opening polymerization (ROP) of lactones and trimethylene carbonates. It also considers several recent innovative synthetic methods including radical ring-opening polymerization (RROP), atom transfer radical polyaddition (ATRPA), and simultaneous chain- and step-growth radical polymerization (SCSRP) that produce aliphatic polyesters. With regard to (bio)degradable approaches, we have summarized several representative cleavable linkages that make it possible to obtain cleavable polymers. In the section on functional aliphatic polyesters, we explore the syntheses of specific functional lactones, which can be performed by ring-opening copolymerization of typical lactone/lactide monomers. Last but not the least, in the recent innovative methods section, three interesting synthetic methodologies, RROP, ATRPA, and SCSRP are discussed in detail with regard to their reaction mechanisms and polymer functionalities.

100th Anniversary of Macromolecular Science Viewpoint: Degradable Polymers from Radical Ring-Opening Polymerization: Latest Advances, New Directions, and Ongoing Challenges

Radical ring-opening polymerization (rROP) allows facile incorporation of labile groups (e.g., ester) into the main chain of vinyl polymers to obtain (bio)degradable materials. rROP has focused a lot of attention especially since the advent of reversible deactivation radical polymerization (RDRP) techniques and is still incredibly moving forward, as attested by the numerous achievements in terms of monomer synthesis, macromolecular engineering, and potential biomedical applications of the resulting degradable polymers. In the present Viewpoint, we will cover the latest progress made in rROP in the last ∼5 years, such as its recent directions, its remaining limitations, and the ongoing challenges. More specifically, this will be achieved through the three different classes of monomers that recently caught most of the attention: cyclic ketene acetals (CKA), thionolactones, and macrocyclic monomers.

Degradable Polyphosphoramidate via Ring-Opening Metathesis Polymerization

We report the synthesis of a degradable polyphosphoramidate via ring-opening metathesis polymerization (ROMP) with the Grubbs initiator (IMesH2)(C5H5N)2(Cl)2Ru═CHPh. Controlled ROMP of a low ring strain diazaphosphepine-based cyclic olefin was achieved at low temperatures to afford well-defined polymers that readily undergo degradation in acidic conditions via the cleavage of the acid-labile phosphoramidate linkages. The diazaphosphepine monomer was compatible in random and block copolymerizations with phenyl and oligo(ethylene glycol) bearing norbornenes. This approach introduced partial or complete degradability into the polymer backbones. With this chemistry, we accessed amphiphilic poly(diazaphosphepine-norbornene) copolymers that could be used to prepare micellar nanoparticles.

Next-Generation Polymeric Nanomedicines for Oncology: Perspectives and Future Directions

Precision polymers as advanced nanomedicines represent an appealing approach for the treatment of otherwise untreatable malignancies. By taking advantage of unique nanomaterial properties and implementing judicious design strategies, polymeric nanomedicines are able to be produced that overcome many barriers to effective treatment. Current key research focus areas anticipated to produce the greatest impact in polymer applications in nanomedicine for oncology include new strategies to achieve "active" targeting, polymeric pro-drug activation, and combinatorial polymer drug delivery approaches in combination with enhanced understanding of complex bio-nano interactions. These approaches, both in isolation or combination, form the next generation of precision nanomedicines with significant anticipated future health outcomes. Of necessity, these approaches will combine an intimate understanding of biological interactions with advanced materials design. This perspectives piece aims to highlight emerging opportunities that promise to be game changers in the nanomedicine oncology field. Discussed herein are current and next generation polymeric nanomedicines with a focus towards structures that are, or could, undergo clinical translation as well as highlight key advances in the field.

Degradable PE-Based Copolymer with Controlled Ester Structure Incorporation by Cobalt-Mediated Radical Copolymerization under Mild Condition

Polyethylene (PE) is one of the most widely used materials in the world, but it is virtually undegradable and quickly accumulates in nature, which may contaminate the environment. We utilized the cobalt-mediated radical copolymerization (CMRP) of ethylene and cyclic ketene acetals (CKAs) to effectively incorporate ester groups into PE backbone as cleavable structures to make PE-based copolymer degradable under mild conditions. The content of ethylene and ester units in the produced copolymer could be finely regulated by CKA concentration or ethylene pressure. Also, the copolymerization of ethylene and CKA with other functional vinyl monomers can produce functional and degradable PE-based copolymer. All the formed PE-based copolymers could degrade in the presence of trimethylamine (Et3N).

DFT-calculation-assisted prediction of the copolymerization between cyclic ketene acetals and traditional vinyl monomers

The ring-opening polymerization of cyclic ketene acetals (CKAs) and vinyl monomers is an elegant method to produce degradable copolymers. Owing to DFT calculations, we are now able to better understand the reactivity of CKAs & common vinyl monomers.

Reversible-deactivation radical polymerization of cyclic ketene acetals

This review discusses the history of reversible-deactivation radical ring-opening polymerization of cyclic ketene acetals, focusing on the preparation of degradable complex polymeric architectures.

Chemoselective, Postpolymerization Modification of Bioactive, Degradable Polymers

Degradable polymers promote sustainability, mitigate environmental impact, and facilitate biological applications. Tailoring degradable polymers is challenging because installing functional group-rich side chains is difficult when the backbone itself is susceptible to degradation. A convenient means of side chain installation is through postpolymerization modification (PPM). In functionalizing polyoxazinones, a class of degradable polymers generated by the ring-opening metathesis polymerization (ROMP), we predictably found PPM challenging. Even the versatile azide-alkyne cycloaddition click reaction was ineffective. To solve this problem, we screened PPM reactions whose efficiencies could be assessed using photochemistry (excimer formation). The mildest, pH-neutral process was functionalization of a ketone-containing polymer to yield either oxime (acid labile)- or alkyoxylamine (stable)-substituted polymers. Using this approach, we equipped polymers with fluorophores, reporter groups, and bioactive epitopes. These modifications imbued the polymers with distinctive spectral properties and biological activities. Thus, polyoxazinones are now tunable through a modular method to diversify these macromolecules' function.

Dynamic surface antifouling: mechanism and systems

Marine biofouling is a global problem today. High efficiency and eco-friendly antifouling systems are in pressing need. In recent years, we have proposed the concept of dynamic surface antifouling (DSA). That is, a continuously changing surface can effectively prevent marine fouling organisms from landing and adhesion. Based on this strategy, we developed coatings with dynamic surfaces by using degradable polymers including polyester-polyurethane, modified polyester and poly(ester-co-acrylate). They exhibit tunable renewability, and excellent antifouling and mechanical performance. Moreover, the polymers can serve as carrier and controlled release systems of antifoulants so that they have long service life. This paper reviews the progress and trends in marine anti-biofouling, and presents the mechanism and systems of DSA.

Novel monomers in radical ring-opening polymerisation for biodegradable and pH responsive nanoparticles

We report the first amine-bearing cyclic ketene acetals (CKAs) for radical ring-opening polymerisation (RROP). The resulting polyesters and their corresponding nanoparticles were biodegradable and showed the desired pH sensitive behaviour.

Degradable vinyl copolymers through thiocarbonyl addition-ring-opening (TARO) polymerization

The radical copolymerization of the thionolactone dibenzo[c,e]oxepane-5-thione with acrylates, acrylonitrile, and N,N-dimethylacrylamide afforded copolymers containing a controllable amount of backbone thioesters which could be selectively cleaved. The process is compatible with RAFT polymerization and promising for the development of advanced degradable polymers.

Synthesis of Multifunctional Homopolymers through Using Thiazolidine Chemistry and Post-Polymerization Modification

Multifunctional homopolymers, defined here as polymers that contain multiple reactive functional groups per repeat unit, are versatile scaffolds for preparing complex macromolecules via post-polymerization modification. However, there are limited methods for preparing multifunctional homopolymers that contain more than one nucleophilic site per repeat unit. Herein, a strategy to synthesize a multifunctional homopolymer using thiazolidine chemistry is demonstrated. Controlled radical polymerization of a thiazolidine-containing acrylamido monomer allows for the synthesis of a polymer with pendent latent nucleophiles. Ring-opening of the thiazolidine affords a homopolymer with two side-chain reactive sites, an amine and a thiol. One-pot functionalization via disulfide formation and acyl substitution is performed to introduce two distinct groups in each repeat unit.

Synthesis of multifunctional homopolymers via sequential post-polymerization reactions

This mini-review highlights recent developments in the synthesis of multifunctional homopolymers, i.e., homopolymers with multiple pendent functionalities.