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Ionic liquids (ILs) served perfectly as solvents for the organotellurium-mediated living radical polymerization (TERP) of methyl methacrylate (MMA), methyl acrylate (MA), and styrene. The reaction rate of polymerizing MMA and MA was significantly increased as previously reported, and the controllability of the polydispersity index (PDI) was also improved by a great margin. The TERP of MMA can now give poly(methyl methacrylates) (PMMAs) with PDIs less than 1.1 and nearly full conversion in a half hour without the presence of (TeMe)2. The kinetic study revealed that the improved control could be ascribed to a faster degenerative chain transfer (DT) reaction which plays a key role in the control of PDI for TERP. Besides the polar effect of ILs, the existence of Lewis acid–base interaction between ILs and the Te atom was proven by UV–vis spectroscopy and 125Te NMR results. Such positive interaction lowered the activation energy of the DT process.

Research on controlling cationic polymerization through a degenerative chain-transfer (DCT) process has primarily focused on the family of vinyl ether monomers. To expand the monomer scope, a bette...

Mixtures of a weak protonic acid and a trace amount of superstrong protonic acid were used for the simple control of the cationic polymerization of vinyl ethers via a degenerative chain-transfer mechanism, in which the former acid works as a precursor of the chain transfer agent (CTA) or the dormant species and the latter works as a source of the cationic propagating species. The addition of mixtures of phosphoric acid dibutyl ester ((n-BuO)2PO2H) or 1-octanethiol (n-C8H17SH) and a trace amount of trifluoromethanesulfonic acid (TfOH) to a solution of isobutyl vinyl ether (IBVE) at −78 °C resulted in polymers with controlled molecular weights, which were basically determined by the feed ratio of IBVE to the weak protonic acid, and narrow molecular weight distributions (Mw/Mn ≈ 1.1). These results were almost the same as those obtained using their prepared adducts of IBVE as CTAs in the presence of a trace amount of TfOH under similar conditions. Methanesulfonic acid (CH3SO3H), whose adduct of IBVE has not been isolated due to instability, was similarly used in conjunction with trace TfOH to result in controlled molecular weights but slightly broader MWDs (Mw/Mn = 1.2–1.8). These results indicate that the sulfoxonium ion is also an effective intermediate in the cationic DT polymerization in addition to the phosphonium and sulfonium intermediates derived from (n-BuO)2PO2H and n-C8H17SH, respectively. The simple living cationic polymerization was thus achieved by using a combination of a weak protonic acid and a trace amount of TfOH, which are both easily available, low cost, free from metal, and easy to handle, without need for preparation of the initiator., ファイル公開：2020/09/01

The use of dormant species has opened a new era in precision polymerization and has changed the concept of living polymerization. The dormant species can be exchanged into the active species via reversible termination or via reversible chain transfer. Professor Mitsuo Sawamoto has greatly contributed to the establishment of the concepts of living cationic and radical polymerizations based on the reversible activation of dormant species. This highlight, dedicated to Professor Sawamoto on his retirement from Kyoto University, provides an overview of reversible or degenerative chain‐transfer (DT) processes, which are effective in controlling all chain‐growth polymerizations, including radical, cationic, anionic, coordination, ring‐opening metathesis, and ring‐opening polymerizations. In addition, structures with novel sequences accessible only by a combination of different propagating species with a common DT agent are reviewed., ファイル公開：2020-02-01

The dialkyldiazene or azo-compound initiators, which include azonitriles such as azobis(isobutyronitrile) (AIBN), are one of the most important classes of initiator being widely used in both conventional and reversible-deactivation radical polymerization (RDRP). This paper briefly reviews the mechanism of radical generation from dialkyldiazenes and provides a critical assessment and recommended values for the decomposition rate coefficients (kd) and efficiencies (f) of those that are commercially available. A critique of the methods that have been used for the determination of these kinetic parameters is also provided. In this review, a focus is placed on initiation of radical polymerization of the more reactive monomers such as methyl methacrylate (MMA) and styrene at low monomer conversions; where addition of the initiator-derived radicals to monomer is not rate determining (i.e., ki>kp) and, thus, the efficiencies for radical generation (fg) and for initiation of polymerization (fi) are similar. However, the dependence of the kinetic parameters on such factors as monomer type, monomer conversion, reaction medium, temperature, photo-irradiation, microwave irradiation and magnetic fields is also discussed. We additionally provide comment on the use of dialkyldiazenes in heterogeneous polymerization (emulsion or dispersion polymerization) and in RDRP. Dialkyldiazenes are the most used initiators in RAFT (reversible addition-fragmentation chain-transfer) polymerization and other RDRP based on degenerative chain transfer, which include iodine transfer polymerization (ITP) and tellurium-mediated polymerization (TERP). They also find significant use in various forms of stable-radical-mediated radical polymerization (SRMP), in particular nitroxide-mediated polymerization (NMP) and cobalt-mediated radical polymerization (CMRP), and have an integral role in certain atom-transfer radical polymerization (ATRP) processes, such as reverse and ICAR (initiators for continuous activator regeneration) ATRP and variations on these procedures. In each of these RDRP methods, knowledge of the parameters that characterize the kinetics and efficiency of dialkyldiazene decomposition and the mechanism of initiation is beneficial to understanding and for optimizing control over the process.

In this report we demonstrate methanol as an effective degenerative chain transfer agent to control the cationic polymerisation (initiated by triflic acid) of electron rich p-alkoxy-styrenes, such as p-methoxystyrene (p-MOS). Kinetic analysis revealed that an induction period occurs initially during which free cationic polymerisation occurs at low monomer conversion before proceeding through the pseudo first order rate, analogous to the RAFT mechanism. Ethanol and isopropanol also demonstrated excellent control (Đ > 1.30), however, with an apparent increase in experimental molecular weight. Furthermore, methanol controlled polymers were successfully chain extended upon sequential monomer addition, demonstrating the ‘livingness’ of the alcohol mediated cationic polymerisation.

Poly(vinyl chloride) (PVC) is one of the more consumed polymers worldwide due to its general versatility and low cost. It is currently used in various applications ranging from packaging to construction. Currently PVC is only being prepared on an industrial scale by free-radical polymerization (FRP). However, the several intrinsic limitations of FRP triggered interest in synthesizing this polymer by reversible deactivation radical polymerization (RDRP) methods. At the present time, single electron transfer living radical polymerization (SET-LRP), single electron transfer degenerative chain transfer living radical polymerization (SET-DTLRP), cobalt-mediated radical polymerization (CMRP), supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP), reversible addition-fragmentation chain transfer polymerization (RAFT) and nitroxide-mediated polymerization (NMP) are RDRP methods that have been reported for vinyl chloride (VC) (co)polymerization. Here, these RDRP methods are critically discussed from three major standpoints. These are degree of control over polymerization, limitations and potential applications on an industrial scale.

Since the first report of cationic reversible addition-fragmentation chain transfer (RAFT) polymerization in 2015, there have been great developments in many aspects of cationic RAFT and degenerative chain transfer (DT) polymerizations, including effective chain-transfer agents, applicable initiators or catalysts, controllable monomers, and controlled architectures of polymers. Cationic RAFT polymerizations exhibit not only many similarities to radical RAFT polymerizations in terms of thiocarbonylthio-based RAFT agents, RAFT mechanisms, and controlled polymer structures but also differences originating from the cationic polymerizations, such as novel RAFT or DT agents, initiation and propagation mechanisms, controllable monomers, and stereostructures of the resulting polymers. This review covers the progress made with cationic RAFT and DT polymerizations, focusing on the similarities and differences between cationic and radical RAFT polymerizations. In total, the characteristics and expanding potentials of cationic RAFT and DT polymerizations are discussed.

Random poly (vinyl chloride-co-butyl acrylate) and poly (vinyl chloride-co-2-ethylhexyl acrylate copolymers obtained by single electron transfer-degenerative chain transfer living radical polymerization (SET- DTLRP) are investigated as potential candidates for 3D Printing. The analysis of the rheological implications of 3D Printing process allows establishing the basic viscoelastic conditions that the samples should fulfil to be printable, avoiding the ‘trial and error’ procedure. The effect of temperature and acrylates concentration on the rheological properties and 3D printing feasibility is contemplated. Eventually, thermal degradation is also considered. It is demonstrated that the copolymers which contain butyl acrylate comonomer, instead of 2-ethylhexyl acrylate, give raise to the best results. Although the study is carried out with PVCacrylate copolymers and a 3D printing device that possesses set up characteristics, it shows a way to work out sound strategies with other polymers and 3D printing machines.

How to achieve the toughening of hydrogels has always been a problem that researchers are committed to solving. Recently, many strategies have been proposed to improve the toughness of hydrogels. However, most of them involve complicated processes, which severely restrict the practical application of hydrogels. Herein, we provide a straightforward method to toughen polyacrylamide (PAM) hydrogels via a degenerative chain transfer effect of allylamine (XBA). The produced hydrogels crosslinked by a traditional crosslinker N,N-methylenebisacrylamide (MBA) possess a relatively uniform network with the existence of entangled pendant chains. The homogeneous network distributes stress evenly, while the disentanglement of the entangled pendant chains dissipates energy and the chemical crosslinks maintain elasticity. As a result, the breaking strain and toughness of the hydrogels can reach 1370% and 1.41 MJ/m3, which are 1.9 and 1.6 folds higher than those of pure PAM hydrogels, respectively. More importantly, the toughening mechanism based on the degenerative chain transfer effect is generalizable to other allyl monomers and other hydrogel systems. Overall, this research offers a facile strategy for designing tough hydrogels and may pave the way for their practical application in industrialized production.

The first successfully controlled radical polymerization (CRP) of ethylene is reported using several organotellurium chain-transfer agents (CTAs) under mild conditions (70 °C, 200 bar of ethylene) within the concept of organotellurium-mediated radical polymerization (TERP). In contrast to preceding works on CRPs of ethylene applying reversible addition–fragmentation chain-transfer (RAFT), the TERP system provided a high livingness and chain-end functionalization of polyethylene chains. Molar-mass distributions with dispersities between 1.3 and 2.1 were obtained up to average molar masses of 5000 g mol−1. As in the RAFT system, the high reactivity of the growing polyethylenyl radical led to an inherent side reaction. For the presented TERP systems, however, this side reaction did not result in dead chains, while it could even be effectively suppressed by a good choice of the CTA.

Dialkyl fumarates as 1,2-disubstituted ethylenes exhibit unique features of radical polymerization kinetics due to their significant steric hindrance in propagation and termination processes and provide polymers with a rigid chain structure different from conventional vinyl polymers. In this study, we carried out reversible addition-fragmentation chain transfer polymerization of diisopropyl fumarate (DiPF) in bulk at 80 °C using various dithiobenzoates with different leaving R groups as chain transfer agents to reveal their performance for control of molecular weight, molecular weight distribution, and chain end functionality of the resulting poly(DiPF) (PDiPF). 2-(Ethoxycarbonyl)-2-propyl dithiobenzoate (DB1) and 2,4,4-trimethyl-2-pentyl dithiobenzoate (DB2) underwent fragmentation and reinitiation at a moderate rate and consequently led to the formation of PDiPF with well-controlled chain structures. It was confirmed that molecular weight of PDiPF produced by controlled polymerization with DB1 and DB2 agreed with theoretical one and molecular weight distribution was narrow. Dithiobenzoate and R fragments were introduced into the polymer chain ends with high functionality as 95% by the use of DB1. In contrast, polymerizations using 1-(ethoxycarbonyl)benzyl dithiobenzoate (DB3), 1-phenylethyl dithiobenzoate (DB4), and 2-phenyl-2-propyl dithiobenzoate (DB5) resulted in poor control of molecular weight, molecular weight distribution, and chain end structures of PDiPF. Fragmentation and reinitiation rates of the used benzoates as chain transfer agents significantly varied depending on the R structures in an opposite fashion; that is, introduction of bulky and conjugating substituents accelerated fragmentation, but it retarded initiation of DiPF polymerization. It was revealed that balance of fragmentation and reinitiation was important for controlled polymerization of DiPF. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3266–3275

Reversible deactivation radical polymerization (RDRP) of biomass-based acrylates, (S)- and (R)-2-isopropyl-5-methylene-1,3-dioxolan-4-ones (S-MiPDO and R-MiPDO), was successfully performed to produce a well-defined polymer with simultaneously controlled tacticity and molecular weight, and low dispersity (Đ

Transfer to polymer in the radical polymerization of acrylic monomers results in chain branching and has significant implications for both reaction kinetics and the microstructure of the resulting polymer. While intramolecular transfer to polymer is more prevalent than the intermolecular pathway, intermolecular transfer to polymer is of particular importance for understanding polymer microstructures. Despite this, the magnitude of the rate coefficient is uncertain, and therefore, predicting the effects of intermolecular transfer remains a challenge. Herein, we seek to provide an estimate of the rate of intermolecular transfer of butyl acrylate by conducting reversible addition–fragmentation chain transfer (RAFT) polymerizations in the presence of a low molecular weight dead polymer. In these experiments, intermolecular transfer to polymer yields a characteristic low molecular shoulder in the polymer detected by UV in the SEC. We obtain a value significantly higher than those previously estimated and discu...

A new type of chain transfer agent used in reversible addition fragmentation chain transfer (RAFT) polymerization named 9-anthracenylmethyl (4-cyano-4-(N-carbazylcarbodithioate) pentanoate) (ACCP) was synthesized with a total yield over 75% by the incorporation of both fluorescent donor and acceptor chromophores. Polymerization of heterotelechelic α,ω end-labeled dye-functionalized polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(n-butyl methacrylate) (PBMA) with adjustable molecular weights and narrow polydispersity could be conducted by a one-pot procedure through RAFT polymerization with this bischromophore chain transfer agent. The polymerizations demonstrated “living” controlled characteristics. By taking advantage of the characteristic fluorescence resonance energy transfer (FRET) response between the polymer chain terminals, the variation of chain dimensions in solution from the dilute region to the semidilute region can be monitored by changes in the ratio of the fluorescence intensities of the carbazolyl group to the anthryl group, which lends itself to potential applications in characterizing chain dimensions in solutions for thermodynamic or dynamic studies. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2413–2420

A novel method is presented to determine transfer coefficients in degenerative reversible addition fragmentation chain transfer (RAFT) polymerization from experimental dispersity data. Both the exchange reactivity with the small RAFT agent (CTA; Ctr,0) and the macro-RAFT agent (Ctr) can be measured at specific monomer conversions. The method is able to capture for the first time a possible intrinsic or apparent chain length dependency of Ctr(0) or thus the RAFT addition rate coefficient, an outstanding challenge in the mechanistic understanding of RAFT polymerization up to high monomer conversion. In its development stage, the method has been theoretically evaluated via the simulation of test cases in the absence and presence of artificial error. Experimental data at 353 K for azobis(isobutyronitrile) (AIBN) initiated RAFT polymerization of methyl methacrylate (MMA) with cyano-2-propyl dithiobenzoate (CPDB) as a small RAFT agent are successfully analyzed with the novel method. A highly accurate value of 20 is obtained for the exchange with CPDB. For the RAFT exchange with the macro-RAFT agent, an approximate but higher value of 76 is obtained and no chain length dependency is detected. The method is implemented in a spreadsheet, including a step by step explanation of the input parameters.

We propose a route to synthesizing ultra-high molecular weight (>106) polystyrene (PS) having a narrow molecular weight distribution by controlled/living radical polymerization. The process is an emulsifier-free, emulsion organotellurium-mediated living radical polymerization (emulsion TERP) using poly(methacrylic acid)-methyltellanyl as a macro-chain transfer agent with a degenerative chain transfer (DT) mechanism. Under the polymerization conditions in which PS particles were formed by a self-assembly nucleation of polymerizing macro-chain transfer agents, very stable PS particles were successfully obtained. The segregation effect in the emulsion polymerization system can suppress the radical termination reaction, resulting in an ultra-high number-average molecular weight (Mn) PS in almost 24 h under 1 atm. The final Mn value was controlled by changing the initial monomer loading (solid contents of styrene), and then PS having a Mn ∼1.2 × 106 with a low polydispersity index (∼1.3) was successfully obtained.

High molecular weight polyacrylonitrile (PAN) with low dispersity has been successfully synthesized utilizing reversible addition-fragmentation chain transfer (RAFT) polymerization. A comprehensive study was performed to understand the influence of reaction temperature, RAFT agent structure, and [M]0:[CTA]0[I]0 on the polymerization kinetics, molecular weight, and dispersity. Enhanced control is attributed to reduction of side reactions by conducting the polymerization at lower temperature, and optimizing the radical exchange between active and dormant states via appropriate selection of RAFT agent and initiator. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015

Cationic degenerative chain-transfer polymerization of vinyl ethers and p-alkoxystyrenes was investigated using a series of thioethers as a reversible chain-transfer agent via the equilibrium between a growing carbocationic species and the resulting sulfonium intermediate in the presence of a small amount of triflic acid (TfOH) as a cationogen. The stable thioether, which was easily prepared from isobutyl vinyl ether (IBVE) and n-butanethiol, efficiently controls the molecular weight of the resulting poly(IBVE) up to Mn ∼ 1 × 105 with narrow molecular weight distributions (MWDs) (Mw/Mn ∼ 1.2). Upon increasing the bulkiness of the alkyl substituents in the thiols (R–SH; R: n-Bu < s-Bu < t-Bu) or those in the monomers (CH2═CHOR′, R′: ethyl < isobutyl < cyclohexyl), the MWDs became broader due to the slower formation of the sulfonium intermediate for the degenerative chain-transfer reaction. For p-methoxystyrene, thioethers derived from bulkier alkylthiols or more electron-rich thiophenols are more effective...

The reversible addition-fragmentation chain transfer (RAFT) polymerization mechanism is a powerful technique for synthesizing functional block polymers for myriad applications. Most kinetic studies regarding the RAFT mechanism have focused on low molecular weight homopolymer and block polymer syntheses using a dithiobenzoate chain transfer agent (CTA). Here, the polymerization kinetics are evaluated for a high molecular weight A-B-C triblock polymer system, polyisoprene-b-polystyrene-b-poly(N,N-dimethylacrylamide) (PI-PS-PDMA), using a trithiocarbonate agent for application of these types of polymers. Importantly, it is demonstrated that the polymerization of polyisoprene is the step that generates the block with the largest dispersity for high molecular weight PI-PS-PDMA polymers. As such, the kinetics of isoprene polymerization must be altered systematically for desired nanostructures to be formed. In addition, it is established that the PS and PDMA block additions exhibit polymerization rate retardation, which is due to slow chain fragmentation of the CTA, as demonstrated by the magnitudes of the equilibrium constants for both the styrene and N,N-dimethylacrylamide reactions, and as calculated using ab initio modeling. This elucidation of the nature of the controlled RAFT mechanism provides a critical handle for the more precise design and control of other next-generation high molecular weight block polymer systems that are polymerized using the RAFT mechanism.

A new mathematical model of Reversible Addition-Fragmentation chain Transfer (RAFT) polymerization is proposed, describing a series of experimental data on styrene bulk polymerization in the presence of various RAFT agents. The polymerization slowdown observed with increasing concentration of the RAFT agent is attributable to the accumulation of intermediate products that participate in chain transfers to both low-molecular and polymer RAFT agents, whereas the length of the initiation period is determined entirely by the activity of the low-molecular RAFT agent.

The metal-free RAFT cationic polymerization (MRCP) of vinyl ethers (VEs) mediated by HCl·Et2O and 1-isobutoxyethyl ethanedithioate (IDTA) as a RAFT cationogen was demonstrated. The IDTA was efficiently catalyzed and the cationic polymerization was initiated by the HCl·Et2O, allowing good control over the molecular weight, polydispersity, and chain end structure of the resulting polyVEs. The propagation step is considered to involve a reversible addition–fragmentation chain transfer (RAFT) to the growing carbocationic species. Thus, the resulting polyVEs can exhibit high number-average end functionality at the RAFT terminal group, depending on the [IDTA]0/[HCl]0 ratio. The polymers obtained by this process could be used as macro-chain transfer agents for the RAFT radical polymerization of radically polymerizable monomers such as (meth)acrylates and styrenes to synthesize novel block copolymers. Significantly, this MRCP system allows a one-pot transformation from MRCP to RAFT radical polymerization as a res...

The potential of 1H NMR spectroscopy for determining the constants of chain transfer to a symmetric bifunctional agent of reversible chain transfer and for studying the changes in the current concentrations of the initial and final agents formed during the replacement of one leaving group with a polymer (oligomeric) radical of the agents of reversible chain transfer during the homopolymerization of N-vinyl succinimide, the homopolymerization of vinyl acetate, and the copolymerization of 4-vinylpyridine and tert-butyl acrylate in the presence S,S-dibenzyltrithiocarbonate is studied. The correct calculation of the constants of chain transfer is shown to be possible only during agreement of the studied system with the taken scheme of polymerization with reversible chain transfer, a minimum contribution of side reactions, and signal separation that is sufficient for the quantitative analysis of initial and polymer (monosubstituted) agents of reversible chain transfer in the 1H NMR spectra. The lower limit of the constants of transfer to the polymer agents of reversible chain transfer is estimated, and the great efficiency of these agents in comparison to that of the initial low-molecular-mass ones is directly confirmed. A complex of necessary investigations to study any new polymerization system where the controlled radical homoand copolymerization with reversible chain transfer in the presence of symmetric trithiocarbonates occurs is performed.

Metal-free, visible light-initiated, living cationic polymerization of 4-methoxystyrene using 2,4,6-tri(p-tolyl)pyrylium tetrafluoroborate and methanol is demonstrated. Molecular weight and dispersity are controlled by the concentration of methanol. Initial mechanistic analysis suggests that methanol likely serves to regulate propagation of the cation chain end via reversible chain transfer in a manner analogous to reversible addition-fragmentation chain transfer polymerization.

Acid-cleavable branched polymers composed of a methacrylate and two acrylates were prepared through reversible addition-fragmentation chain transfer (RAFT) polymerization. The molecular weight of primary chains and the degree of branching of the polymers were controlled by the feed ratio of monomer/chain transfer agent (CTA) and brancher/CTA, respectively. Glass transition temperatures of the polymers increased as the degree of branching grew due to an increase in molecular weight. When the branched polymers were hydrolyzed, molecular weight and polydispersity index value were similar to those of linear polymer prepared by RAFT polymerization with the same molar feed ratio of monomer/CTA.

The negative effect that a RAFT agent with a poor leaving group has on the evolution of molecular dispersity in a RAFT-mediated polymerization was shown to be mitigated by performing the polymerization in semi-batch mode. The result is attributed to an increase in the probability of transfer between the propagating radical and the leaving group during the polymerization. Also for RAFT-mediated polymerizations that use RAFT agents with efficient leaving groups, the evolution of molecular dispersity during a semi-batch polymerization improves compared to that for an analogous batch-mode reaction.

Reversible Addition–Fragmentation chain Transfer (RAFT) polymerization has emerged as one of the most versatile reversible deactivation radical polymerization techniques and is capable of polymerizing a wide range of monomers under various conditions. One of the most important factors governing the success of a RAFT polymerization is the fraction of living chains at the end of the reaction, which can be maximized by using a low amount of initiator. From the point of view of the process, it is tempting to perform the polymerization in solution, which allows a better mixing. However, in this work it is shown that this choice may be negative for the quality of the polymer. Detailed analysis using Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS) of poly(n-butyl acrylate) (pBA) obtained at high conversion in the RAFT solution polymerization revealed that in addition to the polymer chains, formed by the RAFT mechanism, there were two distinct populations resulting from chain transfer to solvent and transfer to polymer followed by β-scission. Complementary results from Size Exclusion Chromatography coupled with Multi Angle Light Scattering detector (SEC/MALS), quantum chemical calculations, and a mathematical model that predicts product distributions, were also used to further confirm the assigned structures. The results highlight the scope and limitation on the living fraction of chains due to chain transfer events using RAFT polymerization and reversible deactivation radical polymerizations in general, and furthermore, yielded information about the fate of midchain radicals formed by intramolecular transfer to polymer.

This work presents results on the prediction of the molecular weight distributions (MWD) of chain growth polymerization using conventional software and hardware tools. The investigation focuses on two kinds of polymerization processes: free radical batch and continuous polymerization processes with application to low density polyethylene synthesis (LDPE); and coordination polymerization via metallocenes with application to high density polyethylene synthesis (HDPE). For both processes, kinetic models, consisting of sets of differential equations describing the dynamic behavior of all the chemical species in the reaction media, are presented. From these sets is possible to obtain the molecular weight distribution of the polymer1,2,4Strategies for the simulation of the polymerization models were developed and results of these simulations are presented. On the free radical polymerization case, the next results are highlighted: i) It was confirmed that the chain transfer to polymer step produces strong asymmetries on the MWD as well as a high polydispersity index; ii) It’s possible to calculate the MWD in the CSTR process through a simulation strategy that permits the decoupling of the live and dead chains populations. On the metallocene polymerization case, it was demonstrated that the coordination standard model represents well the system experimentally studied and it can be employed to directly calculate the molecular weight distribution.These results confirm the idea that the complete MWD can be directly calculated with conventional hardware and software tools.

The mechanism of the recently reported photocontrolled cationic polymerization of vinyl ethers was investigated using a variety of catalysts and chain-transfer agents (CTAs) as well as diverse spectroscopic and electrochemical analytical techniques. Our study revealed a complex activation step characterized by one-electron oxidation of the CTA. This oxidation is followed by mesolytic cleavage of the resulting radical cation species, which leads to the generation of a reactive cation–this species initiates the polymerization of the vinyl ether monomer–and a dithiocarbamate radical that is likely in equilibrium with the corresponding thiuram disulfide dimer. Reversible addition–fragmentation type degenerative chain transfer contributes to the narrow dispersities and control over chain growth observed under these conditions. Finally, the deactivation step is contingent upon the oxidation of the reduced photocatalyst by the dithiocarbamate radical concomitant with the production of a dithiocarbamate anion that caps the polymer chain end. The fine-tuning of the electronic properties and redox potentials of the photocatalyst in both the excited and the ground states is necessary to obtain a photocontrolled system rather than simply a photoinitiated system. The elucidation of the elementary steps of this process will aid the design of new catalytic systems and their real-world applications.

Linear and nonlinear rheological properties of poly(vinyl chloride) (PVC)-poly(n-butyl acrylate)-PVC triblocks of different compositions, obtained by single electron transfer-degenerative chain transfer living radical polymerization, are investigated, focusing on the effect of crystallites. Dynamic mechanical thermal analysis results show the existence of two glass transition temperatures, denoting microphase segregation. However, rather than phase separation, it is the presence of two types of crystals that melt at Tm1 = 127 ± 0.8°C and Tm2 = 185 ± 2°C, respectively, the factor that determines the rheological response of the copolymers. To the difference with PVC homopolymers, extrusion flow measurements at very low temperatures (T = 100°C) are possible with the copolymers. A change in the viscosity-temperature dependence is observed below and above the lowest melting temperature. Notwithstanding the microphase separation and the presence of crystallites, experiments carried out in conditions similar to industrial processing reveal a remarkable viscosity reduction for our copolymers with respect to PVC obtained by single electron transfer-degenerative chain transfer living radical polymerization, conventional PVC, and PVC/[diethyl-(2-ethylhexyl) phthalate] compounds. Extrudates free of surface instabilities are obtained at low extrusion temperatures, such as 90–100°C. J. VINYL ADDIT. TECHNOL., 21:24–32, 2015. © 2014 Society of Plastics Engineers

The use of reversible addition–fragmentation chain transfer (RAFT) crosslinking (co)polymerization of multi-olefinic monomers to produce three-dimensional polymer networks is reviewed. We give specific attention to differences between RAFT and conventional processes, differences between RAFT and other forms of reversible deactivation radical polymerization (such as atom transfer radical and nitroxide-mediated polymerizations) and the dependence of the polymerization process and network properties on RAFT agent structure. This knowledge is important in network optimization for applications as dynamic covalent polymers (in self-healing polymers), as porous polymer monoliths or gels (used as chromatographic media, flow reactors, controlled release media, drug delivery vehicles and in molecular imprinting) and as coatings. © 2014 Society of Chemical Industry

The controlled synthesis of narrowly distributed low molecular weight polymers with functionalization possibilities is of great industrial interests. Although living polymerization allows for control over polymer architecture, the production of low molecular weight polymers with low polydispersities via living polymerization systems is challenged by the use of large amounts of catalysts and broadening in molecular weight distribution. This review addresses the synthesis of narrowly distributed, functional, low molecular weight polyethylene and polyethylene mimics. The review is structured for quick identification of relevant systems for the production of specific polymer architectures with specific cost, efficiency, and safety concerns.

Based on a kinetic model of “living” radical polymerization of butyl acrylate with reversible chain-transfer, the characteristics of altering the molecular weight properties of the polymer by varying the initial concentrations of the reactants and temperature are established.

It is now well established that controlling the grafted chain lengths and densities on nanoparticle surfaces determines the effective interactions between particles, and their assembly. Here, we present unusual kinetic results for achieving grafted chain lengths longer than the free chains using reversible addition-fragmentation chain transfer (RAFT) polymerization and discuss the limitations to obtaining polymer grafting density higher than ∼0.06 chains/nm2. We observe that surface initiated polymerization grows faster than the free chains in solution with high RAFT agent coverage (1.95 agents/nm2) on nanoparticles. The time-dependence of graft density suggests that activation of the anchored chain transfer agent (CTA) is limited by the diffusion of macro-radicals within growing grafts. Thus, radical transfer and exchange reactions become inefficient between grafts and free polymer, and convert the surface-initiated RAFT mechanism to a free radical polymerization. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1700–1705

Reversible addition-fragmentation chain-transfer (RAFT) polymerization was used to control the alternating copolymerization of styrene and 2,3,4,5,6-pentaflurostyrene. The RAFT polymerization yields a high degree of control over the molecular weight of the polymers and does not significantly influence the reactivity ratios of the monomers. The controlled free-radical polymerization could be initiated using AIBN at elevated temperatures or using a redox couple (benzoyl peroxide/N,N-dimethylaniline) at room temperature, while maintaining control over molecular weight and dispersity. The influence of temperature and solvent on the molecular weight distribution and reactivity ratios were investigated. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1555–1559

Reversible addition-fragmentation chain transfer (RAFT) polymerization allows the design of tailored polymers by inducing addition and fragmentation reactions via a powerful kinetic mechanism; the process, however, is not well understood. A parametric analysis was conducted in conjunction with experimental data to provide insights into the RAFT mechanism, accounting for the key kinetics events in RAFT polymerization of styrene. The effects of overall, forward and backward fragmentations of intermediate radicals were analysed with experimental data and sensitivity investigations. Our results show that the intermediate radicals undergo relatively fast fragmentation and that the radical cleavage is symmetrical. These factors, critical in design and control, were found to profoundly influence the process kinetics and the final polymer product attributes.

Dithiobenzoates are among the most popular agents for reversible addition-fragmentation chain transfer (RAFT) polymerization. This is attributed to the better control over molecular weight and end-group fidelity found in RAFT polymerization of methacrylates and methacrylamides. However, in polymerization of styrenes, acrylates, and acrylamides, their use has diminished, mainly in favour of trithiocarbonates, because of issues with retardation, as well as hydrolytic and thermal instability. This paper critically assesses developments in understanding the mechanism and kinetics of dithiobenzoate-mediated RAFT polymerization from 2006 to 2013, with specific reference to the choice of reagents, polymerization conditions, side reactions, and factors leading to retardation.

Although controlled/living radical polymerization processes have significantly facilitated the synthesis of well-defined low polydispersity polymers with specific functionalities, a detailed and systematic knowledge of the thermal stability of the products–highly important for most industrial processes–is not available. Linear polystyrene (PS) carrying a trithiocarbonate mid-chain functionality (thus emulating the structure of the Z-group approach via reversible addition–fragmentation chain transfer (RAFT) based macromolecular architectures) with various chain lengths (20 kDa ≤ Mn,SEC ≤ 150 kDa, 1.27 ≤ Đ = Mw/Mn ≤ 1.72) and chain-end functionality were synthesized via RAFT polymerization. The thermal stability behavior of the polymers was studied at temperatures ranging from 100 to 200 °C for up to 504 h (3 weeks). The thermally treated polymers were analyzed via size exclusion chromatography (SEC) to obtain the dependence of the polymer molecular weight distribution on time at a specific temperature unde...