Isoprene polymerization via reversible addition fragmentation chain transfer polymerization

Until recently, the primary living radical polymerization method available for preparing polyisoprene was nitroxide‐mediated radical polymerization, with reversible addition‐fragmentation chain transfer polymerization being applied only in a few cases within the last couple of years. We report here the preparation of polyisoprene by RAFT in the presence of the trithiocarbonate transfer agent S‐1‐dodecyl‐S′‐(r,r′‐dimethyl‐r′′‐acetic acid)trithiocarbonate and t‐butyl peroxide as the radical initiator. The kinetics of this polymerization at an optimized temperature of 125 °C and radical initiator concentration of 0.2 equiv relative to transfer agent have been studied in triplicate and demonstrate the living nature of the polymerization. These conditions resulted in polymers with narrow polydispersity indices, on the order of 1.2, with monomer conversions up to 30%. Retention of chain‐end functionality was demonstrated by polymerizing styrene as a second block from a polyisoprene macrotransfer agent, resulting in a block copolymer presenting a unimodal gel permeation chromatogram, and narrow molecular weight distribution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4100–4108, 2007     

可逆加成-断裂链转移自由基聚合研究进展

综述了活性/可控自由基聚合中的可逆加成-断裂链转移(RAFT)自由基聚合研究进展;总结了RAFT试剂、RAFT聚合反应条件、RAFT聚合物及其结构形貌的最新研究进展;指出RAFT自由基聚合反应已被作为重要方法之一用于合成具有特定分子结构的聚合物.     

Reversible addition‐fragmentation chain transfer polymerization of diisopropyl fumarate using various dithiobenzoates as chain transfer agents

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     

Study on Unexpected Cycloaddition Reactions of Imines with THF

Thesynthesisofnitrogen-containingheterocylesthroughcycloadditionreactionofimineshasstimulatedmuchpreparativeandmechanisticwork'".Whenweattemptedtosynthesizeapolycycliccompound3byadditionreactionofimineland5-norbornene-2,3-dicarboxylicacid2,however,unexpectedtricycliccompounds4and6wereobtainedinsteadofthedesignedproduct3(Schemcl).Heretetrahydrofuran(THF)servedasthesourceofdihydrofiJranwhichunderwentcycloadditionwithlgiving4and6.Ananalogousreactionwasnotedpreviouslyinthislaboratory'(Scheme2).…     

Controllable fabrication of nanocrystal-polymer hybrids via the catalytic chain transfer polymerization process

A facile catalytic chain transfer polymerization (CCTP) technique has been developed to synthesize covalently linked CdS nanocrystal-polymer hybrids with good optical properties. The in situ polymerization of methyl methacrylate (MMA) on the surface of modified CdS nanocrystals (NCs) with diameter of 5 nm via CCTP process yielded CdS-polymethylmethacrylate (PMMA) hybrid nanocomposites; while the incorporation of hydroxyl-coated CdS NCs into poly(methacryloxypropyltrimethoxysilane) (PMPS)-co-PMMA matrices prepared by CCTP afforded CdS-PMPS-co-PMMA hybrid nanocomposites, which were further cross-linked by free radical polymerization to form CdS NC-polymer network. The spectroscopic studies indicate that as-prepared CdS NC-polymer hybrids show good photoluminescence (PL) and the NC-polymer network exhibits highly enhanced PL property with respect to that before cross-linking. Also described are the probable mechanism for the catalytic chain transfer polymerization on the surface of modified nanocrystal and the measurement of chain transfer constants.     

Substituent effects in the catalytic chain transfer polymerization of 2-hydroxyethyl methacrylate

The catalytic chain transfer behavior of 2-hydroxyethyl methacrylate (HEMA) was studied in bulk at 40 and 60 °C. The chain transfer constant of cobaloxime boron fluoride (COBF) was found to be 6×10² at 40 and 60 °C, which corresponds to chain transfer rate coefficients of about 1.2×10⁶ and 2.0×10⁶ l mol⁻¹ s⁻¹, respectively. These values are about 10-15 times lower than those found previously for methyl methacrylate (MMA) and this decrease can be conceivably ascribed to the combination of a monomer viscosity effect, which lowers the rate coefficient by a factor of 6-8, and the complexation of the hydroxyl group with the catalyst, which causes an additional lowering by a factor of about two. The latter effect was studied by UV/Vis spectroscopy and additional kinetic studies of the COBF-mediated polymerization of MMA in the presence of ethanol. Similar UV/Vis spectra as in the case of HEMA and a reduction in chain transfer constant by a factor of two were observed.     

Reversible addition–fragmentation chain transfer polymerization of methyl methacrylate in emulsion

Theoretical simulations showed that for controlled/living radical polymerization in an emulsion system, some of the earliest born particles could be superswollen to a size close to 1 μm. We hypothesized that the superswelling of these particles would lead to colloidal instability. Under the guidance of the simulation results, reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization of methyl methacrylate (MMA) was carried out. Experimental results showed that increasing the initiation rate, surfactant level, and targeted molecular weight could improve the colloidal stability of the RAFT polymerization of MMA in an emulsion. The experimental results were in full accord with the theoretical predictions. The poor control of the molecular weight and polydispersity index was found to have a close relationship with the colloidal instability. For the first time, we demonstrated that RAFT polymerization could successfully be implemented with little coagulum, good control of the molecular weight, and a low polydispersity index with the same process used for traditional emulsion polymerization but with higher surfactant levels and initiation rates. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44:2837–2847, 2006     

Exploiting catalytic chain transfer polymerization for the synthesis of carboxylated latexes via sulfur‐free RAFT

We present a systematic study of incorporating carboxyl groups into latex particles to enhance colloidal stability and the physical properties of the latex. Statistical copolymers of methacrylic acid and methyl methacrylate) were synthesized via catalytic chain transfer polymerization (CCTP) in emulsion. The vinyl‐terminated oligomers were in turn successfully utilized as chain transfer agents for the formation of diblock and pseudo triblock copolymers via sulfur‐free reversible addition–fragmentation chain transfer polymerization (SF‐RAFT). These copolymers were characterized using ¹H NMR, size exclusion chromatography (SEC), dynamic light scattering (DLS), dynamic mechanical analysis (DMA), contact angle measurements and matrix‐assisted laser desorption/ionization time of flight mass spectroscopy (MALDI‐TOF‐MS) techniques. © 2019 The Authors. Journal of Polymer Science Part A: Polymer Chemistry published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, E1–E9     

The future of reversible addition fragmentation chain transfer polymerization

We examine the reversible addition fragmentation chain transfer (RAFT) process with regard to its potential and limits in future industrial applications (including those conducted on a larger scale) as well as materials science. The outlook for the RAFT process is bright: Its unrivaled inherent process simplicity coupled with a wide tolerance to monomer classes and functionalities makes it a prime candidate for the use in large reactors. At the same time, it allows for ready access to complex macromolecular architectures of variable shape and size. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5715–5723, 2008     

Reversible addition–fragmentation chain transfer polymerization of methyl methacrylate in suspension

The reversible addition–fragmentation chain transfer polymerization of methyl methacrylate mediated by 2‐cyanoprop‐2‐yl dithiobenzoate (CPDB) in bulk (60 and 70 °C) and suspension (70 °C) was studied, and in both polymerization systems, a good control of the molecular weight and polydispersity was observed. Stable suspension polymerizations were carried out over a range of CPDB concentrations, and with increasing CPDB concentration, the particle size and polydispersity index of the produced polymer decreased. The former was ascribed to the lower viscosities of the monomer and polymer droplets at low conversions, which caused easier breakup with the applied shear stresses. Lower polydispersity indices at higher CPDB concentrations were probably caused by a diminished gel effect, which was observed at lower CPDB concentrations at high conversions, causing a broadening of the molecular weight distribution. The livingness of the polymers formed in suspension was proven by successful chain extensions with methyl methacrylate, styrene, and 2‐hydroxyethyl methacrylate. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2001–2012, 2005     

Triallylstannyllithium-allyllithium as an initiator for the anionic reversible chain transfer polymerization of 1,3-butadiene

The anionic polymerization of 1,3-butadiene using a novel metalloidal anion initiator, triallylstannyllithium (TALi)-allyllithium (ALi), was studied. The TALi-ALi initiated anionic polymerization of 1,3-butadiene gave the star polymer along with the linear polybutadiene (PBD). The star polymer consisted of three PBD branches and a central tin atom. What is striking is a fact that the number-average molecular weights (M_n) and molecular weight distribution of three PBD branches and linear PBD were almost identical. A reversible chain transfer polymerization mechanism, which includes the equilibrium between tri(macroallyl)-stannyllithium and macroallylic anion, is proposed. © 1996 John Wiley & Sons, Inc.     

Synthesis of polystyrene-styrene/butadiene diblock copolymers via reversible addition-fragmentation chain transfer miniemulsion polymerization

<正>Polystyrene-styrene/butadiene diblock copolymers were synthesized via reversible addition-fragmentation chain transfer (RAFT) miniemulsion polymerization.During the polymerization process,the molecular weight distribution was narrow and the numerical molecular weight of the copolymers increased with increasing conversion of monomers,which was close to the theoretical.FT-IR and ~1H NMR results indicated that the microstructure of the polymer was mainly 1,4-trans-butadiene with small amount of 1,2-units,and composition in the copolymers was obtained.     

Evaluation of the clenbuterol imprinted monolithic column prepared by reversible addition-fragmentation chain transfer polymerization

To make more homogenous organic monolithic structure,reversible addition-fragmentation chain transfer(RAFT) process was employed in the synthesis of the clenbuterol imprinted polymer.In the synthesis,the influence of synthetic conditions on the polymer structure and separation efficiency was studied.The result demonstrated that the imprinted columns prepared with RAFT process have higher column efficiency and selectivity than the columns prepared with conventional polymerization in the present study,whic...     

The reversible addition-fragmentation chain transfer （RAFT） miniemulsion polymerization of vinyl acetate mediated by xanthate

The reversible addition-fragmentation chain transfer(RAFT) miniemulsion polymerization of vinyl acetate(VAc) mediated by methyl(methoxycarbonothioyl) sulfanyl acetate(MMSA) was carried out.The results showed that polymerizations initiated by AIBN and KPS proceeded in a controlled way.The RAFT miniemulsion polymerization of VAc initiated by KPS showed the shorter inhibition period,higher propagation rate coefficient and final conversion than those in experiment initiated by AIBN.When the monomer conversio...     

Effect of catalyst partitioning in Co(II) mediated catalytic chain transfer miniemulsion polymerization of methyl methacrylate

The effect of catalyst partitioning over the organic and water phases in the catalytic chain transfer mediated miniemulsion polymerization was investigated and a mathematical model developed to describe the instantaneous degree of polymerization of the formed polymer. Experimental and predicted instantaneous degrees of polymerization prove to be in excellent agreement. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5839–5849, 2008     

Controllable synthesis of nanosilica surface-grafted PMMA macromonomers via catalytic chain transfer polymerization

Catalytic chain transfer polymerization (CCTP) has emerged as an efficacious method to produce low-molecular weight polymers. In this paper, we reported the first controllable synthesis of nanosilica surface-grafted poly(methyl methacrylate) (PMMA) (SI-PMMA) macromonomers by using bis(aqua)bis((difluoroboryl)-dimethylglyoximato)cobalt(II) (CoBF) as a chain transfer catalyst via CCTP. In a typical run, we firstly prepared functionalized nanosilica by using 3-(trimethoxysilyl)propylmethacrylate (MPS) as the coupling agent, allowing naosilica containing unsaturated double bonds in end groups. Subsequently, SI-PMMA macromonomers were prepared by PMMA surface-grafted onto the functionalized nanosilica via CCTP. The as-prepared products were characterized by Fourier transforms infrared (FT-IR) spectrum, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transforms Raman (FT-Raman) spectrum and gel permeation chromatography (GPC). We also investigated the dependence of macromonomers on CoBF concentrations.