Addition-fragmentation Chain Transfer Research Articles

Monomer elution and shrinkage stress analysis of addition-fragmentation chain-transfer-modified resin composites in relation to the curing protocol

ObjectiveThe purpose was to compare the effects of rapid (3 s) and conventional (20 s) polymerization protocols (PP) of mono- and multichip LED curing units (LCU) on shrinkage stress (SS) and monomer elution (ME) in bulk-fill resin-based composites (RBC) with and without addition-fragmentation chain-transfer (AFCT) monomer. MethodsCylindrical (5x4mm) specimens were prepared from two RBCs containing different AFCT monomers (Filtek OneBulk-FOB; Tetric PowerFill-TPF) and one without (Tetric EvoCeram Bulk-TEC). After soaking for 3, 10, and 14 days (75 % ethanol), ME was quantified using standard monomers by High-Performance Liquid Chromatography. SS was measured from the start of polymerization to 5 min using a Materials Testing Machine. The radiant exitance of LCUs was measured using a spectrophotometer. ANOVA and Tukey's post-hoc test, multivariate analysis and partial eta-squared statistics were used to analyze the data (p < 0.05). ResultsAFCT-modification significantly decreased ME (p < 0.001). ME was reduced by half by day 10 and by one tenth by the end of the 14-day compared to the 3-day sampling. ME itself was dependent, whereas the percentage of monomers released was independent of the PP used (p > 0.05). FOB showed the lowest SS (p < 0.001), while there was no significant difference between TPF and TEC (p = 0.124). Both ME and SS were significantly influenced by material type and PP. SignificanceThe incorporation of the AFCT monomer reduced ME, but this was inversely related to a decrease in exposure time. SS values reduced by rapid PP in parallel with increasing ME values. The utilization of the AFCT molecule in conjunction with an appropriate resin-, initiator-system is of significant consequence for the kinetics of polymerization and the incorporation of monomers into the network.

Vat photopolymerization using catalytic chain transfer polymerization (CCTP) derived reactive oligomers to influence mechanical properties

ω-Vinyl terminated reactive oligomers of 2-ethylhexyl methacrylate and poly(ethylene glycol)methacrylate (PEGMA) were synthesized via CCTP and subsequent addition–fragmentation chain transfer (AFCT) polymerization.

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.

Nitrogen-Doped Graphene Quantum Dots as Electrochemiluminescence-Emitting Species for Sensitive Detection of KRAS G12C Mutation via PET-RAFT.

The levels of KRAS G12C point mutation is recognized to be closely related to the earlier diagnosis of non-small cell lung cancer (NSCLC). Here, based on nitrogen-doped graphene quantum dots (NGQDs) and photo-induced electron/energy transfer reversible addition-fragment chain transfer (PET-RAFT) signal amplification strategy, we fabricated a novel electrochemiluminescence (ECL) biosensor for the detection of KRAS G12C mutation for the first time. NGQDs as ECL-emitting species with cathodic ECL were prepared by a simple calcination method. Firstly, KRAS G12C mutation DNA, i. e., target DNA (tDNA), was captured by specific identification with hairpin DNA (hDNA). Then, PET-RAFT was initiated by blue light, and large numbers of monomers were successfully polymerized to form controllable polymer chains. Lastly, massive NGQDs was introduced via amidation reaction with N-(3-aminopropyl)methacrylamide hydrochloride (APMA), which significantly amplified the ECL signal intensity. Under optimal conditions, this biosensor achieved a good linear relationship between ECL intensity and logarithm of the levels of KRAS G12C mutation in the range from 10 fM to 10 nM. Moreover, this strategy exhibited high selectivity and excellent applicability for KRAS G12C mutation detection in the serum samples. Therefore, this biosensor has great potential in clinical diagnosis and practical application.

Preparation and controllable heavy oil viscosity reduction performance of pH-responsive star block copolymers

In this study, a series of S-PHEDM star block copolymers of hydrophilic N-hydroxyethyl acrylamide (HEAm) and pH-responsive N,N-dimethylaminoethyl methacrylate (DMAEMA) were synthesized by reversible addition-fragment chain transfer (RAFT) copolymerization for the controllable viscosity reduction of heavy oil. The structures and average molecular weights of the star polymers were characterized by FT-IR spectra, 1H NMR spectra and GPC measurements. The aggregation behavior and oil/water interfacial properties of S-PHEDM were studied using DLS, TEM and IFT measurements in aqueous solutions with various pH values. The properties of heavy oil emulsions formed by S-PHEDM were monitored under different pH conditions using Turbiscan Lab measurements and optical microscopy at ambient temperature, and cyclic regulation of emulsion stability was successfully achieved through regular adjustments of pH values in oil/water mixing systems. Then, S-PHEDM was applied to the field of heavy oil viscosity reduction. Therein, S-PHEDM-2 achieved a degree of viscosity reduction of 99.88% at a dosage of 1000 mg·L−1 for heavy oil (ηapp, 50 °C = 85820 mPa·s) under alkaline conditions. The dehydration rate of the formed emulsion was 25.58% after standing for 1 h. When the heavy oil mixing system was adjusted to acidic, the heavy oil emulsion demulsified rapidly and achieved a dehydration rate of 90.7% within 1 h. The flexible transformation between viscosity reduction and oil–water separation for the heavy oil/water mixing system by adjusting the pH values provided a new idea to enhance efficiency and reduce costs during heavy oil recovery.

Multi-signal amplification electrochemiluminescence biosensor based on GO-CDTPA-AuNPs composites and PET-RAFT for ultrasensitive detection of KRAS G12C mutation

The detection of the Kirsten Rat Sarcoma (KRAS) G12C point mutation plays an important role in the early diagnosis and individualized treatment of non-small cell lung cancer (NSCLC). Herein, a novel electrochemiluminescence (ECL) biosensor for the detection of KRAS G12C mutation via GO-CDTPA-AuNPs composites and photo-induced electron/energy transfer reversible addition-fragment chain transfer (PET-RAFT) multi-signal amplification strategy was fabricated for the first time. In this work, gold nanoparticles (AuNPs) were loaded onto the graphene oxide (GO) surface to form a luminol electrochemiluminescence enhanced composite by simple amide reaction and electrostatic adsorption. Specifically, in the presence of KRAS G12C mutation DNA, i.e. target DNA (tDNA), self-assembled hairpin DNA (hDNA) on the biosensor electrode surface was activated after hybridization with the tDNA to expose a 3′-terminal amino group, that could be further linked to GO-CDTPA-AuNPs composites. To increase luminol-based ECL, GO-CDTPA-AuNPs composites contained a lot of photo-induced electron/energy transfer reversible addition-fragment chain transfer (PET-RAFT) agent loaded onto GO surface. PET-RAFT polymerization of N-acryloxysuccinimide (NAS) monomer was initiated to form polymer chains containing multiple binding sites for luminol. Due to the amplification of luminol attachment sites, very high quantities of luminol could be introduced onto the biosensor electrode surface, resulting in significantly amplified ECL signal intensity. Under optimal biosensor fabrication conditions, a good linear relationship between ECL signal intensity and the logarithm of tDNA concentration was observed over the range of 1 fM to 10 nM with a 0.12 fM limit of detection. Moreover, this strategy exhibited high selectivity and excellent applicability for KRAS G12C mutation detection in the clinical human serum samples. Thus, the fabricated biosensor has great potential for application in the clinical diagnosis.

The effect of high-irradiance rapid polymerization on degree of conversion, monomer elution, polymerization shrinkage and porosity of bulk-fill resin composites.

The purpose was to compare the degree of conversion (DC), monomer elution (ME), polymerization shrinkage (PS) and porosity of two addition-fragmentation chain transfer (AFCT) modified resin-based composites (RBC) light-cured with rapid- (RP), turbo- (TP) or conventional polymerization (CP) settings. Cylindrical samples (6-mm wide, 4-mm thick) were prepared from Tetric PowerFill (TPF) and Filtek One Bulk (FOB). Four groups were established according to the polymerization settings: 3s-RP, 5s-TP, 10s-CP and 20s-CP. Samples in 1mm thickness with 20s-CP settings served as controls. The DC at the top and bottom surfaces was measured with micro-Raman spectroscopy. ME was detected with high-performance liquid chromatography. PS and porosity were analyzed by micro-computed tomography. ANOVA and Tukey's post-hoc test, multivariate analysis and partial eta-squared statistics were used to analyze the data (p<0.05). FOB showed higher DC values (61.5-77.5 %) at the top compared to TPF (43.5-67.8 %). At the bottom TPF samples achieved higher DCs (39.9-58.5 %) than FOB (18.21-66.18 %). Extending the curing time increased DC (except the top of FOB) and decreased ME. BisGMA release was the highest among the detected monomers from both RBCs. The amount was three-fold more from TPF. The factor Material and Exposure significantly influenced DC and ME. PS (1.8-2.5 %) did not differ among the groups and RBCs except for the lowest value of TPF cured with the 3s_RP setting (p=0.03). FOB showed 4.5-fold lower porosity (p<0.001). Significantly higher pore volume was detected after polymerization in 3s_RP (p<0.001). High-irradiance rapid 3-s curing of AFCT modified RBCs resulted in inferior results for some important material properties. A longer exposure time is recommended in a clinical situation.

Enzyme and pH dual responsive linear-dendritic block copolymer micelles based on a phenylalanyl-lysine motif and peripherally ketal-functionalized dendron as potential drug carriers.

Stimuli-responsive linear-dendritic block copolymers (LDBCs) have attracted significant research attention as novel drug carriers. We report here three generations of new enzyme and pH dual responsive linear-dendritic block copolymers (LDBCs) with a phenylalanyl-lysine (Phe-Lys) dipeptide linking hydrophilic linear poly(N-vinylpyrrolidone) (PNVP) and a hydrophobic peripherally ketal-functionalized dendron derived from 2,2'-bis(hydroxymethyl)propionic acid (bis-MPA). The LDBCs are synthesized via a combination of interchange of xanthates/reversible addition-fragmentation chain transfer (MADIX/RAFT) polymerization of N-vinylpyrrolidone (NVP) and "chain-first" strategy. Their structures are confirmed by 1H NMR spectra. The gel permeation chromatograph (GPC) analysis revealed that the LDBCs have a narrow molecular weight distribution (PDI ≤ 1.25). The amphiphilic LDBCs can self-assemble into spherical nanomicelles in aqueous solution. The presence of enzyme or/and the change of pH cause disassembly of micelles to release encapsulated cargos. The release rates of the guest molecules are faster in buffer solution at pH 5.0 than those upon the addition of the activating enzyme and can be fine-tuned by changing the generation of bis-MPA dendrons. The combination of enzyme and pH dual stimuli results in significantly accelerated and more complete release of the loaded hydrophobic guests. The cell viability assay confirmed the favorable biocompatibility until the LDBC micelle concentration reached 800 μg mL-1. These results indicate that the LDBCs can be considered as a good candidate for targeting drug delivery.

Diblock and Random Antifouling Bioactive Polymer Brushes on Gold Surfaces by Visible‐Light‐Induced Polymerization (SI‐PET‐RAFT) in Water

AbstractSurface‐initiated photoinduced electron‐transfer‐reversible addition–fragmentation chain transfer (SI‐PET‐RAFT) is, for the first time, used for the creation of antifouling polymer brushes on gold surfaces based on three monomers: oligo(ethylene glycol) methyl ether methacrylate (MeOEGMA), N‐(2‐hydroxypropyl) methacrylamide (HPMA), and carboxybetaine methacrylamide (CBMA). These coatings are subsequently characterized by X‐ray photoelectron spectroscopy (XPS) and ellipsometry. The living nature of this polymerization allows for the creation of random and diblock copolymer brushes, which are based on HPMA (superb antifouling) and CBMA (good antifouling and functionalizable via activated ester chemistry). The polymer brushes demonstrate good antifouling properties against undiluted human serum, as monitored by quartz crystal microbalance with dissipation (QCM‐D) and surface plasmon resonance (SPR) spectroscopy in real time. The amount of immobilization of bioactive moieties, here an antibody immobilized using N‐succinimidyl ester–1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide hydrochloride (NHS–EDC) coupling, in the diblock and random copolymer brushes is monitored by SPR, and is analyzed with respect to the brush structure, and is shown to be superior in the diblock copolymer brush. This approach represents a scalable, robust, mild, oxygen‐tolerant, and heavy‐metal‐free route toward the production of antifouling and functional copolymer brushes (on gold surfaces) that open up applications in biosensing and tissue engineering.

Recent advances to decrease shrinkage stress and enhance mechanical properties in free radical polymerization: a review

AbstractFree radical polymerizations have been widely used for a variety of applications, including coating, packaging, adhesives, inks and dental materials. However, shrinkage stress in network systems due to volumetric shrinkage during polymerization often results in poor mechanical performance of final materials, often limiting end use. Delaying gelation during polymerization while incorporating functional structure or functionalized groups into the polymer networks may lead to significantly reduced shrinkage stress and, consequently, enhanced thermomechanical properties. In this review, we summarize several practical methods, including thiol–ene radical polymerization, addition–fragmentation chain transfer, controlled radical polymerization, covalent adaptable networks, ring‐opening polymerization and cyclopolymerization, that have shown promise in reducing volumetric shrinkage and associated stress in network‐forming systems. The resulting enhanced (thermo)mechanical material properties of these modified polymers are also introduced. These methods have proven to be powerful tools for fabricating polymers with novel functionality and properties and thereby show potential to expand application of free radical thermoset materials. © 2021 Society of Industrial Chemistry.

Synthesis of allyl sulfones bearing urethane groups as efficient addition-fragmentation chain transfer agents for the development of low-shrinkage composites

Polymerization shrinkage represents one of the major drawbacks of dental composites. The incorporation of chain transfer agents into dental formulations is an efficient technology that enables a strong reduction of the shrinkage stress. In this contribution, the synthesis of four new addition-fragmentation chain transfer (AFCT) agents bearing urethane groups is described. These compounds were easily synthesized in three steps. Real-time (RT)-NIR photorheology measurements were performed to evaluate rheological behavior (i.e. time of gelation) and chemical conversion (i.e. double bond conversion at the gel point, final double bond conversion) of dimethacrylate resins containing the synthesized transfer agents. Composites based on these AFCT agents provide good mechanical properties as well as low shrinkage force. The presence of the urethane group results in a significant improvement of the mechanical properties. The addition of urethane AFCT agents to dental composites is an efficient technology that enables the formulation of low shrinkage materials having high flexural strength and modulus.

Scalable manufactured bio-based polymer nanocomposite with instantaneous near-infrared light-actuated targeted shape memory and remote-controlled accurate self-healing

Remote control and targeted activation are the elevated goals for shape-memory and self-healing polymers when responses to stimuli. Among so many stimuli, converting light into microstructure change or mechanical motions is now of particular interest. Herein, we report the ingenious design, synthesis and operation to advanced materials that capable of fast near-infrared (NIR) light-actuated targeted shape memory and remote accurately self-healing. Starting from biomass resources, a well-defined polymer nanocomposite, CNTs-graft-poly(tetrahydrofurfury methacryla-co-lauryl acrylate-co-1-vinylimidazole) copolymer ((CNTs-g-P(TMA-co-LA-co-VI)), was fabricated by addition-fragmentation chain transfer (RAFT) polymerization. After subsequent metal-ligand crosslinking with Zn2+ ion, CNTs-g-P(TMA-co-LA-co-VI)/Zn2+ with CNTs content of 1.1 wt % have a maximum stress of 1.68 MPa and an elongation at break of 450%. Most importantly, the photothermal conversion of CNTs can effectively trigger the association and dissociation process of the dynamic metallosupramolecular crosslinked bond between VI and Zn2+, leading to excellent instantaneous multiple shape memory and accurate self-healing performance under NIR light or heat. This approach can be generalized toward de novo design of self-healing and shape memory nanocomposites with tunable mechanical properties.

Polymerization shrinkage and shrinkage stress development in ultra-rapid photo-polymerized bulk fill resin composites

ObjectiveTo determine the polymerization shrinkage (%) and shrinkage stress (MPa) characteristics of ultra-rapid photo-polymerized bulk fill resin composites. MethodsTwo ultra-rapid photo-polymerized bulk fill (URPBF) materials: PFill and PFlow were studied, along with their comparators ECeram and EFlow. PFill contains an addition fragmentation chain transfer (AFCT) agent. The URPBR materials were irradiated using two different 3 s high irradiance protocols (3000 and 3200 mW/cm2 based on Bluephase PowerCure and VALO LCUs, respectively) and one 10 s standard protocol (1200 mW/cm2 based on a Bluephase PowerCure LCU). Bonded disk and Bioman II instruments were used to measure Polymerization shrinkage % and shrinkage stress MPa, respectively, for 60 min at 23 ± 1 °C (n = 5). Maximum shrinkage-rate and maximum shrinkage stress-rate were also calculated for 15 s via numerical differentiation. The data were analyzed via multiple One-way ANOVA and Tukey post-hoc tests (α = 0.05). ResultsPFill groups, regardless of their irradiance protocol, showed significantly lower PS than the comparator, ECeram (p < 0.05). However, PFlow irradiated via different protocols, was comparable to EFlow and ECeram (p > 0.05). PFill consistently produced stress results which were significantly lower than ECeram (p < 0.05) and were comparable for both high irradiance protocols (p > 0.05). PFlow only exhibited significantly higher shrinkage stress when polymerized with the 3 sVALO protocol (p < 0.05).The maximum shrinkage strain-rate (%/s) was significantly lower in PFill-10s and PFill-3s groups (using PowerCure LCU) compared to ECeram. However, no differences were seen between PFlow and EFlow (p > 0.05). The maximum shrinkage stress-rate of PFill and PFlow was comparable between different irradiation protocols, as well as to their comparator ECeram (p > 0.05). SignificanceHigh irradiation protocols over ultra-short periods led to slightly lower shrinkage strain but slightly higher stress, possibly due to reduced network mobility. The AFCT agent incorporated in PFill composite seemed to reduce shrinkage stress development, even with high irradiance protocols.

Heterotelechelic poly(propylene oxide) as migration-inhibited toughening agent in hot lithography based additive manufacturing

Linking an addition–fragmentation-chain-transfer (AFCT) functionality and methacrylate moiety via poly(propylene oxide)-oligomer within one molecule creates a non-migrating AFCT-reagent aiding network-homogeneity.

Different Strategies for the Preparation of Galactose-Functionalized Thermo-Responsive Nanogels with Potential as Smart Drug Delivery Systems.

Different synthetic strategies were tested for the incorporation of galactose molecules on thermoresponsive nanogels owing to their affinity for receptors expressed in cancer cells. Three families of galactose-functionalized poly(N-vinylcaprolactam) nanogels were prepared with the aim to control the introduction of galactose-moieties into the core, the core-shell interface and the shell. First and second of the above mentioned, were prepared via surfactant free emulsion polymerization (SFEP) by a free-radical mechanism and the third one, via SFEP/reversible addition-fragmentation chain transfer (RAFT) polymerization. Synthetic recipes for the SFEP/free radical method included besides N-vinylcaprolactam (NVCL), a shell forming poly(ethylene glycol) methyl ether methacrylate (PEGMA), while the galactose (GAL) moiety was introduced via 6-O-acryloyl-1,2,:3,4-bis-O-(1-methyl-ethylidene)-α-D-galactopiranose (6-ABG, protected GAL-monomer): nanogels I, or 2-lactobionamidoethyl methacrylate (LAMA, GAL-monomer): nanogels II. For the SFEP/RAFT methodology poly(2-lactobionamidoethyl methacrylate) as GAL macro-chain transfer agent (PLAMA macro-CTA) was first prepared and on a following stage, the macro-CTA was copolymerized with PEGMA and NVCL, nanogels III. The crosslinker ethylene glycol dimethacrylate (EGDMA) was added in both methodologies for the polymer network construction. Nanogel’s sizes obtained resulted between 90 and 370 nm. With higher content of PLAMA macro-CTA or GAL monomer in nanogels, a higher the phase-transition temperature (TVPT) was observed with values ranging from 28 to 46 °C. The ρ-parameter, calculated by the ratio of gyration and hydrodynamic radii from static (SLS) and dynamic (DLS) light scattering measurements, and transmission electron microscopy (TEM) micrographs suggest that core-shell nanogels of flexible chains were obtained; in either spherical (nanogels II and III) or hyperbranched (nanogels I) form.

Reconfigurable and Spatially Programmable Chameleon Skin‐Like Material Utilizing Light Responsive Covalent Adaptable Cholesteric Liquid Crystal Elastomers

AbstractA mechanochromic, programmable, cholesteric liquid crystalline elastomer (CLCE) is fabricated, and after straining, resulting in a blue shift through the visible spectrum, is returned to its initial shape and color upon heating through its isotropic phase transition. Light initiated, radical‐mediated, addition fragmentation chain transfer (AFT), facilitate permanent programming or erasure of thermoreversible shape and color by relaxing stress imparted on the strained network through reversible bond exchange. Thermoreversible strain is coupled with reversible color change and can be made permanent at any desired strain by light exposure and corresponding AFT activation, temporarily restoring nearly initial shape and color upon heating. The optical characteristics and photonic structure, inherently linked to the network, are measured as a function of strain, to confirm the reflection notch narrowing indicating that prepolymerization alignment via shearing is poor thereby causing a broad spectrum of reflected light that narrows when the material is stretched. Beyond programming a new shape and color, the reflection notch is erased and separately, photopatterned to achieve dynamic color schemes that are toggled with heating and cooling, similar to that of a chameleon's camouflaging technique that has the ability to manipulate multiple colors in a single material, also with use for strain mapping.

The Effect of Thiol Structure on Allyl Sulfide Photodegradable Hydrogels and their Application as a Degradable Scaffold for Organoid Passaging.

Intestinal organoids are useful in vitro models for basic and translational studies aimed at understanding and treating disease. However, their routine culture relies on animal-derived matrices that limit translation to clinical applications. In fact, there are few fully defined, synthetic hydrogel systems that allow for the expansion of intestinal organoids. Here, an allyl sulfide photodegradable hydrogel is presented, achieving rapid degradation through radical addition-fragmentation chain transfer (AFCT) reactions, to support routine passaging of intestinal organoids. Shear rheology to first characterize the effect of thiol and allyl sulfide crosslink structures on degradation kinetics is used. Irradiation with 365 nm light (5 mW cm-2 ) in the presence of a soluble thiol (glutathione at 15 × 10-3 m), and a photoinitiator (lithium phenyl-2,4,6-trimethylbenzoylphosphinate at 1 × 10-3 m), leads to complete hydrogel degradation in less than 15 s. Allyl sulfide hydrogels are used to support the formation of epithelial colonies from single intestinal stem cells, and rapid photodegradation is used to achieve repetitive passaging of stem cell colonies without loss in morphology or organoid formation potential. This platform could support long-term culture of intestinal organoids, potentially replacing the need for animal-derived matrices, while also allowing systematic variations to the hydrogel properties tailored for the organoid of interest.

Study on MMA and BA Emulsion Copolymerization Using 2,4-Diphenyl-4-methyl-1-pentene as the Irreversible Addition-Fragmentation Chain Transfer Agent.

As a chain transfer agent, 2,4-diphenyl-4-methyl-1-pentene (αMSD) was first introduced in the emulsion binary copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA) based on an irreversible addition–fragmentation chain transfer (AFCT) mechanism. The effects of αMSD on molecular weight and its distribution, the degree of polymerization, polymerization rate, monomer conversion, particle size, and tensile properties of the formed latexes were systematically investigated. Its potential chain transfer mechanism was also explored according to the 1H NMR analysis. The results showed that the increase in the content of αMSD could lead to a decline in molecular weight, its distribution, and the degree of polymerization. The mass percentage of MMA in the synthesized polymers was also improved as the amounts of αMSD increased. The chain transfer coefficients of αMSD for MMA and BA were 0.62 and 0.47, respectively. The regulation mechanism of αMSD in the emulsion polymerization of acrylates was found to be consistent with Yasummasa’s theory. Additionally, monomer conversion decreased greatly to 47.3% when the concentration of αMSD was higher than 1 wt% due to the extremely low polymerization rate. Moreover, the polymerization rate was also decreased probably due to the desorption and lower reactivity of the regenerative radicals from αMSD. Finally, the tensile properties of the resulting polyacrylate films were significantly affected due to the presence of αMSD.

A 20th anniversary perspective on the life of RAFT (RAFT coming of age)

AbstractRAFT (reversible addition–fragmentation chain transfer) polymerization, making use of thiocarbonylthio transfer agents, was announced to the world just over 21 years ago. RAFT arose out of a desire to achieve perfection in polymers (or at least to define and limit the imperfections) and to invent living radical polymerization. However, living radical polymerization cannot be and never was. This perspective looks at RAFT after 21 years of development. Is RAFT a mature technology? We briefly summarize areas of current interest focusing on what is happening at CSIRO and point to where RAFT is going in areas such as RAFT free from exogenous initiators (photoRAFT, PET‐RAFT, eRAFT), new RAFT agents, RAFT for sequence‐defined polymers and RAFT single unit monomer insertion, RAFT emulsion polymerization and RAFT polymerization‐induced self‐assembly (PISA), RAFT‐crosslinking polymerization and the industrial applications of RAFT. © 2019 Society of Chemical Industry

Facile synthesis of graft copolymers containing rigid poly(dialkyl fumarate) branches by macromonomer method

ABSTRACTGraft copolymers show microphase separated structure as seen in block copolymers and have lower intrinsic viscosity than block copolymers because of a branching structure. Therefore, considering molding processability, especially for polymers containing rigid segments, graft copolymers are useful architectures. In this work, graft copolymers containing rigid poly(diisopropyl fumarate) (PDiPF) branches were synthesized by full free‐radical polymerization process. First, synthesis of PDiPF macromonomers by addition‐fragmentation chain transfer (AFCT) was investigated. 2,2‐Dimethyl‐4‐methylene‐pentanedioic acid dimethyl ester was found to be an efficient AFCT agent for diisopropyl fumarate (DiPF) polymerization because of the suppression of undesired primary radical termination, which significantly took place when common AFCT agent, methyl 2‐(bromomethyl)acrylate, was used. Copolymerization of PDiPF macromonomer with ethyl acrylate accomplished the generation of the graft copolymer having flexible poly(ethyl acrylate) backbone and rigid PDiPF branches. The graft copolymer showed a microphase separated structure, high transparency, and characteristic thermal properties to PDiPF and poly(ethyl acrylate). © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2474–2480