Reversible Chain Transfer Research Articles

Living radical polymerization of diisopropyl fumarate to obtain block copolymers containing rigid poly(substituted methylene) and flexible polyacrylate segments

ABSTRACTLiving radical polymerizations of diisopropyl fumarate (DiPF) are carried out to synthesize poly(diisopropyl fumarate) (PDiPF) as a rigid poly(substituted methylene) and its block copolymers combined with a flexible polyacrylate segment. Reversible addition‐fragmentation chain transfer (RAFT) polymerization is suitable to obtain a high‐molecular‐weight PDiPF with well‐controlled molecular weight, molecular weight distribution, and chain‐end structures, while organotellurium‐mediated living radical polymerization (TERP) and reversible chain transfer catalyzed polymerization (RTCP) give PDiPF with controlled chain structures under limited polymerization conditions. In contrast, controlled polymerization for the production of high‐molecular‐weight and well‐defined PDiPF is not achieved by atom transfer radical polymerization (ATRP) and nitroxide‐mediated radical polymerization (NMP). The block copolymers consisting of rigid poly(substituted methylene) and flexible polyacrylate segments are synthesized by the RAFT polymerization. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2136–2147

Wavelength selective polymer network formation of end-functional star polymers.

A wavelength selective technique for light-induced network formation based on two photo-active moieties, namely ortho-methylbenzaldehyde and tetrazole is introduced. The network forming species are photo-reactive star polymers generated via reversible activation fragmentation chain transfer (RAFT) polymerization, allowing the network to be based on almost any vinylic monomer. Direct laser writing (DLW) allows to form any complex three-dimensional structure based on the photo-reactive star polymers.

Dehydrocoupling of phosphine-boranes using the [RhCp*Me(PMe3)(CH2Cl2)][BArF4] precatalyst: stoichiometric and catalytic studies.

We report a detailed, combined experimental and computational study on the fundamental B-H and P-H bond activation steps involved in the dehydrocoupling/dehydropolymerization of primary and secondary phosphine-boranes, H3B·PPhR'H (R = Ph, H), using [RhCp*(PMe3)Me(ClCH2Cl)][BArF4], to either form polyphosphino-boranes [H2B·PPhH] n (Mn ∼ 15 000 g mol-1, PDI = 2.2) or the linear diboraphosphine H3B·PPh2BH2·PPh2H. A likely polymer-growth pathway of reversible chain transfer step-growth is suggested for H3B·PPhH2. Using secondary phosphine-boranes as model substrates a combined synthesis, structural (X-ray crystallography), labelling and computational approach reveals: initial bond activation pathways (B-H activation precedes P-H activation); key intermediates (phosphido-boranes, α-B-agostic base-stabilized boryls); and a catalytic route to the primary diboraphosphine (H3B·PPhHBH2·PPhH2). It is also shown that by changing the substituent at phosphorus (Ph or Cy versust Bu) different final products result (phosphido-borane or base stabilized phosphino-borane respectively). These studies provide detailed insight into the pathways that are operating during dehydropolymerization.

Regularities of the kinetics of miniemulsion polymerization of styrene in the presence of dithiobenzoates as reversible chain transfer agents

The results of comparative kinetic study of the miniemulsion controlled radical polymerization of styrene in the presence of reversible chain transfer agents (benzyl dithiobenzoate and polystyrene dithiobenzoate) and bulk polymerization of similar systems are presented. The influence of the reactant nature and dithiobenzoate concentration of the kinetics of the process is discussed.

Molecularly imprinted polymers by reversible chain transfer catalysed polymerization

Molecularly imprinted polymers (MIPs) are tailor-made biomimetic receptors obtained by polymerization in the presence of molecular templates. They contain binding sites for target molecules with affinities and specificities on a par with those of antibodies, hormone receptors or enzymes. Mainly synthesized via radical polymerization of vinyl monomers, MIPs have also recently taken advantage of the introduction of modern methods of controlled/living radical polymerization (CRPs). In this paper, we report for the first time the use for MIP synthesis of a recently developed CRP method based on an iodide-transfer polymerization with a reversible activation mechanism, referred to as Reversible chain-Transfer Catalysed Polymerization (RTCP). Using S-propranolol as model template, we show that this technique is a convenient method for the synthesis of MIPs, both in the format of bulk polymers and nanoparticles, yielding polymers with reactive chain ends for an easy surface functionalization.

Reversible addition-fragmentation chain transfer (RAFT) (Co)polymerization of isobornyl acrylate

Controlled/living radical homopolymerization of isobornyl acrylate and its copolymerization with styrene with reversible chain transfer via the addition-fragmentation mechanism in the presence of benzyl dithiobenzoate have been studied. It has been shown that the (co)polymerization proceeds through living chains, a result that is confirmed by a linear increase in the number-average molecular weight with conversion and by low polydispersity indexes. With the use of polymer RAFT agents block copolymers have been synthesized. Amphiphilic copolymers have been obtained through acid hydrolysis of isobornyl acrylate units in copolymers of various microstructures.

The potential of 1H NMR spectroscopy for studying the kinetics and mechanism of controlled radical polymerization with reversible chain transfer

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.

Visible Light Photoinitiated Metal-Free Living Cationic Polymerization of 4-Methoxystyrene.

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.

Kinetics and Modeling of Ring‐Opening Copolymerization of l‐Lactide and ε‐Caprolactone

The bulk ring‐opening copolymerization of l‐lactide with ε‐caprolactone was conducted at 140 °C. The reaction was catalyzed with stannous octoate and initiated using hydroxyethyl methylacrylate to produce acrylated biomass macromonomers. The effects of varying monomer compositions as well as polymer chain lengths on the copolymerizations were experimentally investigated. A mathematical model is developed considering reversible initiation, propagation, chain transfer, and transesterification reactions. The diffusion control associated with polymer chain length is considered in the model. The model successfully predicts monomers conversions, number‐average molecular weights, polydispersity index values, and cumulative copolymer compositions for ring‐opening copolymerizations of l‐lactide with ε‐caprolactone.

Dispersion Reversible Chain Transfer Catalyzed Polymerization (Dispersion RTCP) of Methyl Methacrylate in Supercritical Carbon Dioxide: Pushing the Limit of Selectivity of Chain Transfer Agent

We demonstrated a dispersion reversible chain transfer catalyzed polymerization (dispersion RTCP) of methyl methacrylate (MMA) with 1-phenylethyl iodide (PE-I) as chain transfer agent and GeI4 as catalyst in supercritical carbon dioxide (scCO2), where the PE-I was known as noneffective chain transfer agent for polymerization of MMA in RTCP. The dispersion RTCP in scCO2 proceeded with control/livingness. On the other hand, in bulk system (bulk RTCP) and in dispersion iodine transfer polymerization (dispersion ITP) in scCO2 under the same conditions except for GeI4, no livingness was maintained. From these results, it was assumed that the reason for the living character in the dispersion RTCP in scCO2 is based on an accelerated reversible chain transfer reaction in scCO2. Based on the insight, when the dispersion RTCP of MMA was carried out at higher scCO2 pressure, poly(MMA) (PMMA) having a narrower molecular weight distribution was obtained because of the higher degree of PMMA plasticization by scCO2. Mor...

Reversible chain transfer catalyzed polymerization (RTCP) in nitrogen-based solvents without additional catalysts

N,N-Dimethylformamide (DMF) andN-methyl-2-pyrrolidone (NMP) as typical nitrogen-based solvents were used as the catalyst for RTCP without additional catalyst, which could also be carried out in the presence of a limited amount of air.

Phosphinoyl and thiophosphinoylcarbodithioates: synthesis, molecular structure, and application as new efficient mediators for RAFT polymerization.

New phosphinoyl and thiophosphinoylcarbodithioates were synthesized in a one-pot reaction from the corresponding phosphinochalcogenides. Compounds of this new generation of thiocarbonylthio derivatives have been fully characterized by IR as well as (1)H, (31)P, and (13)C NMR spectroscopy and by mass spectrometry. Their solid-state structures reveal that they are isostructural but crystallize in different space groups. These new compounds are highly efficient reversible chain-transfer agents for the reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene (St) and n-butyl acrylate (nBA), with controlled number-average molecular weights (Mn) and narrow dispersity values (Ð<1.3). The controlled character of the polymerization was further exemplified by MALDI-TOF mass spectrometry and the synthesis of PSt-P(nBA) diblock copolymers.

Effect of polymer matrix and photoacid generator on the lithographic properties of chemically amplified photoresist

Resistive compositions based on ter-copolymers of isobornylacrylate with methylmethacrylate and (meth)acrylic acid, which are synthesized using the controlled radical polymerization with reversible chain transfer, as well as triphenylsulphoniumtriflate as a photo-sensitive catalyst are studied. The effect of the chain-transfer agent, as well as the composition and molecular weight of the copolymer on the sensitivity of the resists to UV radiation (222 nm), is determined. Using the ter-copolymer of tert-butoxycarbonyloxystyrene with methylmethacrylate and methacrylic acid, the dependence of the lithographic properties of the photoresist on the chemical composition of the photoacid generator is analyzed. The plasma-chemical stability of (co)polymer resists of methacrylic series in the plasma of Ar + SF6 is studied.

Synthesis of a novel branched–hyperbranched diblock polyolefin via chain walking and chain transfer polymerization from ethylene alone

A new strategy was explored to achieve hyperbranched–branched diblock polyolefin from ethylene alone via chain walking and chain transfer polymerization. In ethylene polymerization process, {2,6-iPr2–C6H3 N=C(CH3)–(CH3)C=N–iPr2 –C6H2}NiBr2/methylaluminoxane/ZnEt2 first produced hyperbranched polyethylene chains via rapid chain walk under 40 °C and then, prepared branched chains via moderate chain walk at 0 °C. ZnEt2, as chain transfer agent, was added into catalyst system to facilitate reversible chain transfer between nickel metal active centers and zinc metal inactive centers to synthesize hyperbranched–branched diblock polyolefin. The resultant polyethylenes were analyzed by gel permeation chromatography and 13C NMR spectra and the results indicated that hyperbranched–branched diblock polyolefin was successfully synthesized via chain walking and chain transfer polymerization.

Low-temperature reversible addition-fragmentation chain transfer (RAFT) polymerization of methyl methacrylate

Controlled/living radical polymerization of methyl methacrylate under the conditions of reversible addition-fragmentation chain transfer was performed. The reaction occurs at high rates, with the control over molecular-weight characteristics of poly(methyl methacrylate) preserved. The polymeric reversible chain-transfer agent exhibits high performance in polymerization of methyl methacrylate and in its block copolymerization with styrene.

Amphiphilic copolymer of poly(ethylene glycol)-block-polypyridine; synthesis, physicochemical characterization, and adsorption onto silica nanoparticle.

In this study, we newly synthesized amphiphilic block copolymers composed of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic pyridine segments (PEG-b-Py). Chain transfer agent terminated PEG was subsequently chain-extended with 3-(4-pyridyl)-propyl acrylate to obtain PEG-b-Py by reversible additional-fragmentation chain transfer (RAFT) polymerization. Particularly, the effect of varying PEG molecular weight (M(n)) of the block copolymers (M(n) = 2000 (2k), and 5000 (5k)) was investigated in terms of critical micelle concentration (cmc), pyrene solubilization, micelle size distribution, and association number per micelle. Based on the amphiphilic balance, PEG-b-Pys formed core-shell type polymer micelle. The cmc value of PEG2k-b-Py was lower than that of PEG5k-b-Py, suggesting the degree of phase separation was strongly depended on PEG M(n). Furthermore, the adsorption of PEG-b-Py copolymer onto silica nanoparticles as dispersant was studied to estimate the effect of PEG M(n) in the copolymers and their solubility in the medium on the adsorption. Adsorbed density of PEG2k-b-Py copolymer onto silica nanoparticle was higher than that of PEG5k-b-Py, which was significantly correlated with the degree of phase-separation based on the amphiphilic balance. The adsorbed amount of copolymer was further changed as a function of solvent polarity, phase separation predicting the presence of the acid-base interaction between Py and silanol group existed on silica nanoparticles. The resultant dispersion stability was highly correlated with the graft density of copolymer onto silica surface. As a result, PEG2k-b-Py coated silica nanoparticles in aqueous media (with high solvent polarity) showed high dispersion stability. These fundamental investigations for the surface modification of the nanoparticle provide the insight into the highly stable colloidal dispersion as well as the design of dispersant molecular structure.

Molecular weight properties of poly(butyl acrylate): Computational experiment based on a kinetic model of “living” radical polymerization with reversible addition-fragmentation chain transfer

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.

Reversible addition-fragmentation chain transfer copolymerization of methyl methacrylate and methyl acrylate

Pseudo-living radical copolymerization of methyl methacrylate and methyl acrylate under reversible addition-fragmentation chain transfer in a mass in the presence of reversible chain transfer agents of different nature was implemented. A comparison of physical and mechanical properties of narrowly dispersed copolymers was performed as well as copolymers obtained by uncontrolled radical polymerization.

Controlling the molecular weight and polydispersity index of polystyrene by varying the initial parameters of addition-fragmentation radical polymerization

Numerical experiments are used to examine how the molecular mass and polydispersity index of polystyrene synthesized by controlled addition-fragmentation radical polymerization depend on various control parameters of the process, such as the temperature and initial concentrations of monomer, initiator, and reversible chain transfer agent.

Modeling of Molecular Weight Distribution in Ring-Opening Polymerization of l,l-Lactide

The molecular weight distributions of poly(lactic acid) produced by ring-opening polymerization of l,l-lactide in bulk melt are measured and compared with the ones predicted using a kinetic model accounting for reversible catalyst activation, reversible propagation, reversible chain transfer to cocatalyst, and intermolecular transesterification. The same values of the model parameters as evaluated in previous works are used without any adjustment; i.e. the model is used in a fully predictive way. In order to calculate the complete molecular weight distribution, the model equations are solved through two different numerical methods, “direct integration” of the population balances at all values of chain length, and “fractionated moments”, where the chains are artificially classified into two different categories, depending upon the experienced reaction steps. The accuracy of the molecular weight distributions calculated in the latter case is evaluated by comparison with those computed by solving the model e...