Photoinduced Electron/energy Transfer-reversible Addition-fragmentation Chain Transfer Research Articles

Pushing the Limit of Photo-Controlled Polymerization: Hyperchromic and Bathochromic Effects.

The photocatalyst (PC) zinc tetraphenylporphyrin (ZnTPP) is highly efficient for photoinduced electron/energy transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. However, ZnTPP suffers from poor absorbance of orange light by the so-called Q-band of the absorption spectrum (maximum absorption wavelength λmax = 600 nm, at which molar extinction coefficient εmax = 1.0×104 L/(mol·cm)), hindering photo-curing applications that entail long light penetration paths. Over the past decade, there has not been any competing candidate in terms of efficiency, despite a myriad of efforts in PC design. By theoretical evaluation, here we rationally introduce a peripheral benzo moiety on each of the pyrrole rings of ZnTPP, giving zinc tetraphenyl tetrabenzoporphyrin (ZnTPTBP). This modification not only enlarges the conjugation length of the system, but also alters the a1u occupied π molecular orbital energy level and breaks the accidental degeneracy between the a1u and a2u orbitals, which is responsible for the low absorption intensity of the Q-band. As a consequence, not only is there a pronounced hyperchromic and bathochromic effect (λmax = 655 nm and εmax = 5.2×104 L/(mol·cm)) of the Q-band, but the hyperchromic effect is achieved without increasing the intensity of the less useful, low wavelength absorption peaks of the PC. Remarkably, this strong 655 nm absorption takes advantage of deep-red (650-700 nm) light, a major component of solar light exhibiting good atmosphere penetration, exploited by the natural PC chlorophyll a as well. Compared with ZnTPP, ZnTPTBP displayed a 49% increase in PET-RAFT polymerization rate with good control, marking a significant leap in the area of photo-controlled polymerization.

Poly(amino acid)-based drug delivery nanoparticles eliminate Methicillin resistant Staphylococcus aureus via tunable release of antibiotic

Bacterial infections threaten public health, and novel therapeutic strategies critically demand to be explored. Herein, poly(amino acid) (PAA)-based drug delivery nanoparticles (NPs) were designed for eliminating Methicillin resistant Staphylococcus aureus (MRSA) via tunable release of antibiotic. Using N-acryloyl amino acids (valine, valine methyl ester, aspartic acid, serine) as monomers, four kinds of amphiphilic PAAs were synthesized via photoinduced electron/energy transfer–reversible addition fragmentation chain-transfer (PET-RAFT) polymerization and were further assembled into nano-sized delivery systems. Their assemble behavior was drove mainly by hydrophobic/hydrophilic interaction, which determined the particle size, efficacy of drug loading and release; but numerous hydrogen bonding (HB) interaction also played an important role in regulating morphologies of the NPs and enriching drug-binding capacity. By changing the HB- and hydrophobic-interaction of the PAAs, the particle sizes (240.7 nm-302.7 nm), the drug loading efficiency (9.57%-19.76%), and the Rifampicin (Rif) release rate (49.6%-69.7%) of the PAA-based NPs could be tunable. Specially, the antimicrobial properties of the Rif-loaded NPs are found to be related to the release of Rif, which was determined by its hydrophobic interaction with hydrophobic blocks and HB interaction with hydrophilic blocks. These studies provide a new outlook for the design of delivery systems for the therapy of bacterial infection.

Orthogonal synthesis and modification of hyperbranched polymers via different colors of light

AbstractA versatile and straightforward approach for the synthesis of functional hyperbranched polymers with tunable properties is represented utilizing a chromatic orthogonal protocol. The method involves the combination of photo‐induced electron/energy transfer‐reversible addition‐fragmentation chain transfer (PET‐RAFT) and self‐condensing vinyl polymerization (SCVP) under visible light irradiation leading to the formation of hyperbranched polymers with well‐defined properties possessing photo‐caged diene moieties. Upon UV light irradiation, the remaining photoenol functionality was efficiently activated for the post‐functionalization of the synthesized hyperbranched polymers with maleimide functional molecules via Diels‐Alder photo‐click chemistry. Both low molar mass and polymeric maleimide functional click components, namely N‐phenylmaleimide, poly(ethylene glycol)‐maleimide and polycaprolactone‐maleimide were quantitively attached onto the hyperbranched polymers under ambient conditions. The results obtained from our protocol indicate high efficiency and convenience, offering a straightforward strategy for the design and synthesis of functionalized hyperbranched polymers. The chromatic orthogonal nature of the protocol enables precise control over the modification process, adding versatility to the materials obtained. Overall, this research lays the groundwork for novel pathways in material design, opening new possibilities for advanced materials with tailored properties.

Integrating Hybrid Perovskite Nanocrystals into Metal-Organic Framework as Efficient S-Scheme Heterojunction Photocatalyst for Synergistically Boosting Controlled Radical Photopolymerization under 980 nm NIR Light.

S-scheme heterojunction photocatalyst MAPbI3@PCN-222 with light absorption extending to the NIR region is constructed by embedding organic-inorganic hybrid perovskite (MAPbI3) into porphyrinic Zr-MOF (PCN-222). Both in situ X-ray photoelectron spectroscopy, ultraviolet photoelectron spectral characterization, and photocatalytic polymerization experiment prove the formation of S-scheme heterojunction. MAPbI3@PCN-222 with a low dosage (90 ppm) displays an impressive photocatalytic ability for 980 nm light-mediated photoinduced electron/energy-transfer-reversible addition-fragmentation chain-transfer (PET-RAFT) polymerization in air. The well-defined controllable-molecular weight polymers including block copolymers and ultrahigh-molecular weight polymers can be achieved with narrow distributions (Mw/Mn < 1.20) via rapid photopolymerization. The industrial application potential of the photocatalyst also has been proved by scale-up synthesis of polymers with low polydispersity under NIR light-induced photopolymerization in a large-volume reaction system (200 mL) with high monomer conversion up to 99%. The penetration photopolymerization through the 5 mm polytetrafluoroethylene plate and excellent photocontrollable behavior illustrate the existence of long-term photogenerated electron transfer of heterojunction and abundant free radicals in photopolymerization. The photocatalyst still retains high catalytic activity after 10 cycles of photopolymerization in air. It is revealed for the first time that the special PET-RAFT polymerization pathway is initiated by the aldehyde-bearing α-aminoalkyl radical derived from the oxidization of triethanolamine (TEOA) by the heterojunction photocatalyst. This research offers a new insight into understanding the NIR-light-activated PET-RAFT polymerization mechanism in the presence of TEOA.

Shape-Controlled synthesis of conjugated microporous polymer nanotubes and their implementation in continuous flow polymerization

Flow reactors have materialized as a reliable and sustainable approach toward polymer production and processing to promote efficient and uniform irradiation pathways. However, the disadvantages of existing homogeneous photocatalysts including noxiousness, restricted photocatalytic activity and stability, and difficult separation and purification, still pose a great challenge to the advancement of this technique. Herein, conjugated microporous polymer nanotubes (hPorBDP NTs) were fabricated through Sonogashira-Hagihara cross-coupling polycondensation with silica nanorods as sacrificial templates, followed by etching of the inner cores. The hPorBDP NTs with a hollow nanostructure and a highly porous texture were demonstrated to facilitate the separation procedure and provide more accessible active sites for photocatalytic reactions. The hPorBDP NTs were employed as heterogeneous catalysts to activate photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization in batch and in continuous flow system. Screening of the initial monomer concentrations and pump flow rates, high monomer conversions (ɑ > 80%) and narrow dispersities (Đ < 1.15) were achieved in continuous flow system for upscaled production of polymers. Separation and reutilization of the catalyst-bound NTs were realized through facile centrifugation, which resulted in negligible leaching and maintenance of catalytic performance over multiple polymerization cycles. As such, the development of photosynthesis system using hPorBDP NTs as heterogeneous photocatalysts should broaden the application scope of these fascinating catalysts while benefiting synthetic upscaling by continuous flow polymerization.

Photons and photocatalysts as limiting reagents for PET-RAFT photopolymerization

The kinetics of photoinduced electron/energy transfer - reversible addition fragmentation chain transfer (PET-RAFT) polymerization were investigated using a model system of methyl acrylate (MA) in the presence of trithiocarbonate chain transfer agents and tris(2-phenylpyridine)iridium(III) (Ir(ppy)3) as the photocatalyst. A powerful polymerization through oxygen approach was developed. Efficient PET-RAFT occurred under blue, violet, and green light with catalyst loadings of 10 ppm. Minimal polymerization was observed under orange or red light. Kinetic scaling analysis was developed to evaluate the impact of light intensity, catalyst loading and geometry of both the light source and the reaction vessel. A universal scaling law was developed for Ir(ppy)3 and other energy transfer catalyzed PET-RAFT, allowing both polymerization through oxygen and deoxygenated systems from the literature to be described across a range of light intensities, reaction conditions and geometries. Finally, the scaling analysis indicates that PET-RAFT systems should be subject to less retardation than conventional RAFT systems, due to the chain transfer agent being involved in radical generation steps.

Aqueous One-pot and Oxygen-tolerant Synthesis of Glycopolymers Using Polymer-backbone-bearing Water-soluble Activated Esters

A simple environment-friendly system is attractive for synthesizing functional polymer materials, including glycopolymers. Herein, we successfully synthesized glycopolymers via an aqueous one-pot and open-air system combined with photoinduced electron/energy transfer-reversible addition-fragmentation chain-transfer (PET-RAFT) polymerization using a novel water-soluble monomer having an activated ester, followed by modification with amine-containing saccharide derivatives in water at room temperature.

Highly Efficient Near-Infrared Photoinduced Electron/Energy Transfer-Reversible Addition–Fragmentation Chain Transfer Polymerization via the Energy Transfer Upconversion Mechanism

Near-infrared (NIR) light-mediated polymerization has been of particular interest owing to the deep penetration into opaque materials, giving rise to great potential for biomedical applications and solar photochemistry. Photoinduced electron/energy transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization presented unprecedented spatiotemporal control over the controlled radical polymerization process. Herein, we greatly extended the NIR region up to 980 nm by introducing rationally designed upconversion nanocrystals with low toxicity and resistance to photobleaching into PET-RAFT polymerization. Well-defined polymers with predictable molecular weight and narrow dispersity were prepared within a few hours by 980 nm NIR light-regulated PET-RAFT polymerization via the energy transfer upconversion mechanism. The livingness feature of this photopolymerization was confirmed by polymerization kinetics, chain extension experiments, and multiple controlled “on–off” light switching cycles. Furthermore, the polymerizations could be successfully performed using different monomers, in the presence of several visible light-proof barriers (i.e., pork/chicken skin) and even under aerobic conditions, demonstrating the multifold advantages of our approach.

PET‐RAFT polymerization under flow chemistry and surface‐initiated reactions

AbstractRecently, photoinduced electron/energy transfer reversible addition–fragmentation chain transfer (PET‐RAFT) polymerization has been developed and gaining wide acceptance. PET‐RAFT polymerization uses visible light to initiate the reaction and is compatible with ambient conditions and green solvents. It also maintains the ability to produce well‐defined polymers and possesses high potential as an alternative to the conventional RAFT technique. This review aims to summarize the fundamentals of PET‐RAFT polymerization, highlight two of the most commonly studied applications of PET‐RAFT process (i.e. flow chemistry and surface‐initiated polymerization), and explore perspectives and new possibilities of the technique. © 2022 Society of Industrial Chemistry.

Tethering inorganic luminous upconverting nanoparticles with macromolecular chppendixains using silica functionalized with RAFT agent

Upconversion nanoparticles (UCNPs) are superior next-generation nanomaterials due to their exclusive features, such as tunable emission, high quantum yield, and excellent stability against photo-blinking/bleaching/degradation. One can compel these UCNPs to target selective applications by surface functionalization of these nanocrystals with functional groups or polymers to make them chemically active, possessing colloidal stability, better biocompatibility as well as tunable emission region. Herein, we report the preparation of rare earth (Er 3+ , 0.5% mmol) doped upconversion nanoparticles (UCNPs) and their surface functionalization using RAFT agent primed silica followed by polymer functionalization. The polymer functionalization was performed using photo-induced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization in the presence of Eosin Y (EY) which act as a photocatalyst when exposed to blue light at room temperature. The polymer functionalization of UCNPs was performed with different types of polymers, for example, poly( N -isopropyl acrylamide), poly(acrylic acid), poly(ethylene glycol)methacrylate, and poly(methyl methacrylate) via “grafting-from” approach. Numerous characterizations were performed which confirm the successful grafting of polymers via PET-RAFT polymerization. The enhancement of photoluminescent efficiency towards the red region/window was observed after the grafting of polymers. The emission in the red region is marked as suitable for biological applications. Thus, indicating the potential use of the as-synthesized core@shell@shell system for various biological platforms. Interestingly, the cytocompatibility studies render the polymer functionalized UCNPs’ potential to be used in a variety of biological applications.

Lactic Acid-Derived Copolymeric Surfactants with Monomer Distribution Profile-Dependent Solution and Thermoresponsive Properties

We report the synthesis and solution properties of novel biobased thermoresponsive amphiphilic copolymers prepared using N,N-dimethyl lactamide acrylate (DMLA) and ethyl lactate acrylate (ELA) as hydrophilic and hydrophobic monomers, respectively. Copolymers with similar overall molecular weight but different monomer distribution profiles, such as random, diblock, triblock, and random–blocks, were prepared using photoinduced electron/energy transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization activated by a Zn-based photoredox catalyst. The synthesized polymers show interesting self-assembly and thermoresponsive behavior in water, depending on the monomers distribution along the chain. Different critical solution temperatures, in the range of 13–70 °C, were observed by tuning the monomers molar ratio and distribution. The formation of aggregates of various types was proven by transmission electron microscopy (TEM). The prepared polymers also display different surface activity with the fully random copolymer being significantly more surface active than block systems. A study of emulsion stabilization was performed with oils of various polarity, showing promising results for applications of these novel polymers as biobased surfactants and water/oil (w/o) emulsion stabilizers.

Exploiting PET-RAFT polymerization mediated by cross-linked zinc porphyrins for the thermo-sensitive regulation of poly(N-isopropylacrylamide-b-acrylamide)

A series of thermo-sensitive block copolymers poly(N-isopropylacrylamide-b-acrylamide) (P(NIPAm-b-AM)) are prepared via photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization mediated by the cross-linked zinc porphyrins (ZnTHP-Me2Si) with superior photo-catalytic properties using one-pot method. The thermal transition temperatures of P(NIPAm-b-AM) samples are analyzed via lower critical solution temperature (LCST) measurements in water/P(NIPAm-b-AM) mixtures, which show that the thermo-sensitive of P(NIPAm-b-AM) could be tuned by regulating the molar ratio of AM/NIPAm. Very interestingly, when the mole fraction of AM increased from 0 to 0.4, the LCST and water contact angle of P(NIPAm-b-AM) aqueous solution increased linearly, which means the thermo-sensitive polymers with target LCST or hydrophilicity could be prepared by increasing or decreasing AM content. In addition, the hardness of P(NIPAm-b-AM) also enhanced as the AM content increased. According to the density functional theory (DFT) calculations and radial distribution function (RDF) analyses, ZnTHP-Me2Si has smaller energy gap, and the H-bonding interaction between P(NIPAm-b-AM) and water molecules could be enhanced with increasing AM content. The outcomes of this work open new approaches to develop thermo-sensitive polymers with biocompatibility for the wide applications in highly efficient and controlled drug delivery system.

RAFT Polymerization of Semifluorinated Monomers Mediated by a NIR Fluorinated Photocatalyst.

Near-infrared (NIR) light plays an increasingly important role in the field of photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization due to its unique properties. Yet, the NIR photocatalyst with good stability for PET-RAFT polymerization remains promising. Here, a strategy of NIR PET-RAFT polymerization of semifluorinated monomers using fluorophenyl bacteriochlorin as a photocatalyst with strong absorption at the NIR light region (710-780nm) is reported. In which, the F atoms are used to modify reduced tetraphenylporphyrin structure with enhanced photostability of photocatalyst. Under the irradiation of NIR light (λmax = 740nm), the PET-RAFT polymerization of semifluorinated methylacrylic monomers presents living/control characteristics and temporal modulation. By the PET-RAFT polymerization-induced self-assembly (PISA) strategy, stable fluorine-containing micelles are constructed in various solvents. In addition, the fluorinated hydrophobic surface is fabricated via a surface-initiated PET-RAFT (SI-PET-RAFT) polymerization using silicon wafer bearing RAFT agents with tunable surface hydrophobicity. This strategy not only enlightens the application of further modified compounds based on porphyrin structure in photopolymerization, but also shows promising potential for the construction of well-defined functional fluoropolymers.

Facile Preparation of a Glycopolymer Library by PET-RAFT Polymerization for Screening the Polymer Structures of GM1 Mimics.

Commercialized oligosaccharides such as GM1 are useful for biological applications but generally expensive. Thus, facile access to an effective alternative is desired. Glycopolymers displaying both carbohydrate and hydrophobic units are promising materials as alternatives to oligosaccharides. Prediction of the appropriate polymer structure as an oligosaccharide mimic is difficult, and screening of the many candidates (glycopolymer library) is required. However, repeating polymerization manipulation for each polymer sample to prepare the glycopolymer library is time-consuming. Herein, we report a facile preparation of the glycopolymer library of GM1 mimics by photoinduced electron/energy transfer-reversible addition–fragmentation chain-transfer (PET-RAFT) polymerization. Glycopolymers displaying galactose units were synthesized in various ratios of hydrophobic acrylamide derivatives. The synthesized glycopolymers were immobilized on a gold surface, and the interactions with cholera toxin B subunits (CTB) were analyzed using surface plasmon resonance imaging (SPRI). The screening by SPRI revealed the correlation between the log P values of the hydrophobic monomers and the interactions of the glycopolymers with CTB, and the appropriate polymer structure as a GM1 mimic was determined. The combination of the one-time preparation and the fast screening of the glycopolymer library provides a new strategy to access the synthetic materials for critical biomolecular recognition.

Versatile Bilayer Hydrogel for Wound Dressing through PET-RAFT Polymerization.

Multifunctional hydrogel-based wound dressings have been explored for decades due to their huge potential in multifaceted medical intervention to wound healing. However, it is usually not easy to fabricate a single hydrogel with all of the desirable functions at one time. Herein, a bilayer model with an outer layer for hydrogel wound dressing was proposed. The inner layer (Hm-PNn) was a hybrid hydrogel prepared by N-isopropylacrylamide and chitosan-N-2-hydroxypropyl trimethylammonium chloride (HACC), and the outer layer (PVAo-PAmp) was prepared by polyvinyl alcohols and acrylamide. The two hydrogel layers of the bilayer model were covalently connected with excellent interfacial strength by photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. The outer layer exposed to the ambient environment exhibited good stretchability and toughness, while the inner-layer hydrogel adhered to the skin exhibited excellent softness, antibacterial activity, thermoresponsivity, and biocompatibility. In particular, the inner layer of a hydrogel demonstrated excellent antibacterial capability toward both Staphylococcus aureus as Gram-positive bacteria and Escherichia coli as Gram-negative bacteria. Cell cytotoxicity showed that the cell viability of all Hm-PNn layer hydrogels exceeds 80%, confirming that the hydrogels bear excellent biocompatibility. In vivo experimental results indicated that the Hm-PNn/PVAo-PAmp bilayer hydrogel has a significant effect on the acceleration of wound healing, which was demonstrated in a full-thickness skin defect model showing improved collagen disposition and granulation tissue thickness. With these results, the established multifunctional bilayer hydrogel exhibits potential as an excellent wound dressing for wound healing applications, especially for open and infected traumas.

Photo-Enhanced Antimicrobial Activity of Polymers Containing an Embedded Photosensitiser.

This work presents the synthesis of a novel photosensitive acrylate monomer for use as both a self-catalyst in the photoinduced electron/energy transfer-reversible addition fragmentation chain transfer (PET-RAFT) polymerisation process and a photosensitiser (PS) for antibacterial applications. Hydrophilic, cationic, and antimicrobial formulations are explored to compare the antibacterial effects between charged and non-charged polymers. Covalent attachment of the catalyst to well-defined linear polymer chains has no effect on polymerisation control or singlet oxygen generation. The addition of the PS to polymers provides activity against S. aureus for all polymer formulations, resulting in up to a 99.99999 % killing efficacy in 30 min. Antimicrobial peptide mimetic polymers previously active against P. aeruginosa, but not S. aureus, gain significant bactericidal activity against S. aureus through the inclusion of PS groups, with 99.998 % killing efficiency after 30 min incubation with light. Thus, a broader spectrum of antimicrobial activity is achieved using two distinct mechanisms of bactericidal activity via the incorporation of a photosensitiser monomer into an antimicrobial polymer.

Photo‐Enhanced Antimicrobial Activity of Polymers Containing an Embedded Photosensitiser

AbstractThis work presents the synthesis of a novel photosensitive acrylate monomer for use as both a self‐catalyst in the photoinduced electron/energy transfer–reversible addition fragmentation chain transfer (PET‐RAFT) polymerisation process and a photosensitiser (PS) for antibacterial applications. Hydrophilic, cationic, and antimicrobial formulations are explored to compare the antibacterial effects between charged and non‐charged polymers. Covalent attachment of the catalyst to well‐defined linear polymer chains has no effect on polymerisation control or singlet oxygen generation. The addition of the PS to polymers provides activity against S. aureus for all polymer formulations, resulting in up to a 99.99999 % killing efficacy in 30 min. Antimicrobial peptide mimetic polymers previously active against P. aeruginosa, but not S. aureus, gain significant bactericidal activity against S. aureus through the inclusion of PS groups, with 99.998 % killing efficiency after 30 min incubation with light. Thus, a broader spectrum of antimicrobial activity is achieved using two distinct mechanisms of bactericidal activity via the incorporation of a photosensitiser monomer into an antimicrobial polymer.

Aqueous Protein-Polymer Bioconjugation via Photoinduced RAFT Polymerization Using High Loading Heterogeneous Catalyst.

Light-driven polymerization, such as photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization, enables biological benign conditions and versatile functional polymer structure design, which is readily used in protein-polymer bioconjugates. However, conventional metalloporphyrinic homogeneous catalysts for PET-RAFT polymerization suffer from limited aqueous solubility and tedious purification. Here we demonstrate the design of PET-RAFT photocatalyst from the reticular assembled Zr-porphyrinic metal-organic frameworks (MOFs), along with a biomacromolecule-based chain transfer agent, as efficient bioconjugation tools in water. Our methodology offers manufacturing advantages on bioconjugates under mild conditions such that MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) and cytotoxicity assays have shown the preservation of the protein integrity, bioactivity, and high cell viability after PET-RAFT polymerization. We find that the fast kinetics are benefiting from the ultrahigh loading of metalloporphyrins in MOF-525-Zn. This heterogeneous catalyst also allows us to maintain living characteristics to incorporate myriads of monomers into block copolymers. Other advantages like easy postreaction purification, reusability, and high oxygen tolerance even in an open system are demonstrated. This study provides a tool of highly efficient heterogeneous photocatalysts for polymer-protein bioconjugation in aqueous media and paves the road for biological applications.

Exploiting nanofibrous chitin microspheres as heterogeneous photocatalysts for high throughput PET-RAFT polymerization and bioconjugation

High throughput approaches have become increasingly prevalent in the interdisciplinary space of polymer chemistry and biomedical engineering for the screening of polymer structure and biological activity. However, the syntheses of bioconjugates at high monomer dilutions and in a high throughput format are still challenging as there are typically limited quantities of the biological substrates available and cumbersome procedures for catalyst removal. Chitin is one of the most abundant natural polymers derived from seafood waste. This has inspired us to modify chitin for fabricating catalyst support. In this contribution, nanofibrous chitin (NC) microspheres as the matrix were employed for surface conjugation of eosin Y-bound copolymers via activated ester-amine reaction to prepare NCPNIEY microspheres. These microspheres hold great prospects for enabling high throughput polymerizations that possess advantages of photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization such as low-energy input, ultralow catalyst dosages and spatiotemporal control over chain propagation. The robustness of the NCPNIEY microspheres mediated protocol was demonstrated in the well-structured polymer syntheses and protein-polymer bioconjugation alongside catalyst-recycling experiments in multi-well plates. Raising the temperature of the reaction mixture to 37 °C caused segregation of the NCPNIEY microspheres in a hydrophilic-to-hydrophobic transition, allowing for the rapid purification of the protein-polymer bioconjugates without compromising protein activity. This work provides a versatile approach and useful insights for bioconjugate manufacturing in a high throughput format owing to simplified purification and improved sustainability.

Influence of Molecular Weight Distribution on the Thermoresponsive Transition of Poly(N-isopropylacrylamide).

A series of poly(N-isopropylacrylamide) (PNIPAm) homopolymers with narrow molecular weight distributions (MWDs) is prepared via photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. The thermal transition temperature of these polymer samples is analyzed via turbidity measurements in water/N,N'-dimethylformamide mixtures, which show that the cloud point temperatures are inversely proportional to the weight average molecular weight (Mw ). Binary mixtures of the narrowly distributed PNIPAm samples are also prepared and the statistical parameters for the MWDs of these blends are determined. Very interestingly, for binary blends of the PNIPAm samples, the thermoresponsive transition is not only dependent on the Mw , which has been shown previously, but also on higher order statistical parameters of the MWDs. Specifically, at very high values of skewness and kurtosis, the polymer blends deviate from a single sharp thermoresponsive transition toward a broader thermal response, and eventually to a regime of two more distinct transitions. This work highlights the importance of in-depth characterization of polymer MWDs for thermoresponsive polymers.