Iniferter Polymerization Research Articles

Visible-light-mediated, additive-free, and open-to-air controlled radical polymerization of acrylates and acrylamides.

Oxygen tolerance in ontrolled radical polymerizations has been an active field of study in recent years. Herein, we report a photocontrolled, additive-free iniferter polymerization that operates in completely open vials utilizing the "polymerizing through oxygen" mechanism. Trithiocarbonates are directly activated with high intensity 450 nm light to produce narrowly dispersed (M w/M n = 1.1-1.6) polyacrylates and polyacrylamides in only 1 hour of irradiation. Living behavior is demonstrated through chain extension, block copolymer synthesis, and control over molecular weight through varying the monomer:iniferter ratio. A slight increase in induction period is observed for the open vial polymerization compared to the air-free reaction, but polymers with similar M n and M w/M n values are produced after 30-60 minutes of irradiation. This system will provide a convenient platform for living additive manufacturing because of its fast reaction time, air tolerance, wide monomer scope, and lack of any additives beyond the monomer, iniferter, and DMSO solvent.

Versatile Approach to Building Dynamic Covalent Polymer Networks by Stimulating the Dormant Groups.

Despite many efforts, there is no versatile way to realize reversible cross-linking for most polymers. Inspired by the abstraction of hydrogen and the iniferter polymerization of benzophenone (BP), we report a versatile approach for building dynamic covalent networks for polymers containing C-H bonds. Under ultraviolet irradiation, BP can effectively abstract the hydrogen from polymers to form dormant diarylsemipinacol (DASP) groups on the polymer chains. Then, the dormant DASP-based linkages can be homolytically cleaved upon heating, after which they generate carbon-centered aliphatic radicals and DASP-based radicals. Therefore, the cross-linked polymer network can rearrange its topology through the dissociation and association of DASP-based linkages, which endow polymer networks with remodeling and self-healing abilities. Given that most commercially available polymers contain aliphatic C-H bonds, this provides a general method for forming thermal reversible cross-linked networks.

Association behaviors of poly(N-vinylpyrrolidone)-grafted fullerenes in aqueous solution

Poly(N-vinylpyrrolidone) (PVP)-grafted fullerenes (PVP-C60 and PVP-C70) were synthesized by iniferter polymerization in order to fabricate water-soluble fullerene containing micelles. PVP-C60 formed micelles with hydrodynamic diameters ranging from 15 to 33 nm. The solubilization of fullerene molecules into the core of the PVP-C60 micelles was also found to control the size of the micelles. By increasing the amount of added fullerene, we gradually increased the micelle size before drastically increasing it to that of 200 nm in hydrodynamic diameter. The drastic change occurred at a critical value of the added C60/PVP monomer ratio, almost independently of the molecular weight of PVP.

Light Leads to Ultra-Long Polymer Chains in Water

The synthesis of controlled ultra-high-molecular-weight polymers has been challenging in living radical polymerization. In this issue of Chem , Sumerlin and coworkers report that mild UV light irradiation activates thiocarbonylthio compounds in water to form those over 1 × 10 6 Da.

RAFT iniferter polymerization in miniemulsion using visible light

Methodology for the successful implementation of RAFT (4-cyano-4[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid (CDTPA)) iniferter polymerization of butyl methacrylate in miniemulsion using visible light (green light; λmax = 530 nm) has been developed.

Visible light-induced iniferter polymerization of methacrylates enhanced by continuous flow

Visible-light induced photoiniferter polymerization in continuous flow reactors is very efficient in yielding low dispersity methacrylate block copolymers.

An emerging approach for the targeting analysis of dimethoate in olive oil: The role of molecularly imprinted polymers based on photo-iniferter induced “living” radical polymerization

This study concerns the first attempt to prepare molecularly imprinted polymers for the selective recognition of dimethoate using an iniferter polymerization technique (Inif-MIP). The synthesized polymers were fully characterized. SEM micrographs show a large accessibility to the binding sites with a significant improvement in MIP morphology. Inif-MIPs displayed high adsorption capacity (Q=5.3mgg−1). The selectivity of this imprinting system was also assessed by means of cross-selectivity assays and the results obtained show that Inif-MIP displays a high selectivity for dimethoate, whereas some structural analogues (omethoate, malathion and methidathion) are poorly retained (6.3–28.7%) or not retained at all (fenthion). Inif-MISPE methodology was implemented by packing Inif-MIPs particles into a Solid Phase Extraction (SPE) cartridge and the loading, washing and eluting steps were optimized. The suitability of this sample preparation technique was demonstrated, as concentrations of dimethoate close to the tolerated maximum residue limits in the olive oil samples could be satisfactorily analyzed with good precision and accuracy. Some remarkable characteristics, like the sorbent reusability (at least 20 cycles without the lost of selectivity), low solvent consumption, reduced sample handling and, moreover higher recovery rates reaching 88% could be ascribed to the Inif-MISPE methodology.

Synthesis of H-shaped complex macromolecular structures by combination of atom transfer radical polymerization, photoinduced radical coupling, ring-opening polymerization, and iniferter processes

Three controlled/living polymerization processes, namely atom transfer radical polymerization (ATRP), ring opening polymerization (ROP) and iniferter polymerization, and photoinduced radical coupling reaction were combined for the preparation of ABCBD-type H-shaped complex copolymer. First, a-benzophenone functional polystyrene (BP-PS) and poly( methyl methacrylate) (BP-PMMA) were prepared independently by ATRP. The resulting polymers were irradiated to form ketyl radicals by hydrogen abstraction of the excited benzophenone moieties present at each chain end. Coupling of these radicals resulted in the formation of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) with benzpinacole structure at the junction point possessing both hydroxyl and iniferter functionalities. ROP of e-caprolactone (CL) by using PS-b-PMMA as bifunctional initiator, in the presence of stannous octoate yielded the corresponding tetrablock copolymer, PCL-PSPMMA- PCL. Finally, the polymerization of tert-butyl acrylate (tBA) via iniferter process gave the targeted H-shaped block copolymer

Synthesis of Surface Imprinted Polymer Microspheres with Ultrathin Polymer Shells via Surface-Initiated Iniferter Polymerization

A simple and effective approach was proposed to synthesize uniform surface imprinted polymer microspheres via surface-initiated iniferter polymerization. The chloromethyl groups were firstly introduced onto the surface of the polystyrene microspheres by a one-step dispersion polymerization. After that the photosensitive iniferter groups were modified by the reaction of the polystyrene microspheres surface-bound chloromethyl groups with N, N-diethyldithiocarbamate sodium. The grafting step was then carried out in a stirred solution of polystyrene microspheres containing surface-initiated iniferter in the presence of template molecules (glutathione, GSH), functional and cross-linking monomers. The synthesized surface imprinted polymer (GSH-MIP) microspheres were characterized using SEM and FT-IR. The GSH-MIP microspheres were spherical in shape, and showed homogeneous polymer layer and high encapsulation efficiency. The rebinding properties of GSH for GSH-MIP was evaluated by carrying out batch rebinding tests, the obtained GSH-MIP shows faster mass transfer and higher binding amounts rate toward template than non-imprinted polymer (NIP).

Synthesis and simultaneous self‐assembly of multiblock fluorinated polyurethane in iniferter polymerization

AbstractA multiblock fluorinated polyurethane was synthesized using tetraphenylethane‐based polyurethane as macroiniferter to free‐radically polymerize 1H,1H,3H‐trihydro perfluoro‐2,4‐dimethylpentyl methacrylate (FDPMA). Simultaneous self‐assembly occurred in FDPMA polymerization process and various nanostructures, like multicore particles, formed depending on FDPMA concentration. Fluorophobic effect and the cooperation of the fluorinated blocks with polyurethane blocks are demonstrated to be the main contribution. That soluble FDPMA in DMF becomes insoluble after polymerization triggers the self‐assembly process and leads to the nanostructure formation, and the polyurethane blocks that are soluble in DMF and immiscible with the fluorinated blocks stabilize the discrete nanostructures. Further, the nanostructures in solutions can evolve into various morphologies, such as disk and fiber, when dried to solid state. All these results not only reveal the feasibility and robustness of the multiblock copolymer on the modulation of self‐assembly structure but also represent a facile and efficient approach for novel nanostructure construction. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013

大分子引发剂的主链柔性对PDLC电光性能的影响

Polymer dispersed liquid crystal(PDLC) films were prepared with living graft macro-initiator(MI) with different main-chain flexibility,synthesized by reversible addition-fragmentation chain transfer(RAFT) and iniferter polymerization with four kinds of monomers with different glass transition temperature.The effect of main-chain flexibility of MIs on morphologies,transmittance,switching voltage and hysteresis of PDLC films based on graft polymer had been investigated.It was observed that the OFF-state transmittance(TOFF) and the size of LC droplet decreased at first and then increased with the increase in main-chain flexibility of MIs,and both showed the lowest value when MI was RAFT-P(BMA-co-CMSI).However,Vth and Vsat showed an opposite trend.It was found that the Vth value first increased from 8.0 V to 17.7 V and then decreased to 7.3 V,while the Vsat value first increased from 25.6 V to 32.9 V and then decreased to 20.2 V.In addition,the hyste-resis showed complex changes,due to a variety of factors.Therefore,the change of main-chain flexibility of MIs successfully improved the electro-optical properties of PDLC films based on graft polymer.

One‐pot synthesis of surface‐functionalized molecularly imprinted polymer microspheres by iniferter‐induced “living” radical precipitation polymerization

AbstractThis article describes for the first time the development of a new polymerization technique by introducing iniferter‐induced “living” radical polymerization mechanism into precipitation polymerization and its application in the molecular imprinting field. The resulting iniferter‐induced “living” radical precipitation polymerization (ILRPP) has proven to be an effective approach for generating not only narrow disperse poly(ethylene glycol dimethacrylate) microspheres but also molecularly imprinted polymer (MIP) microspheres with obvious molecular imprinting effects towards the template (a herbicide 2,4‐dichlorophenoxyacetic acid (2,4‐D)), rather fast template rebinding kinetics, and appreciable selectivity over structurally related compounds. The binding association constant Ka and apparent maximum number Nmax for the high‐affinity sites of the 2,4‐D imprinted polymer were determined by Scatchard analysis and found to be 1.18 × 104 M−1 and 4.37 μmol/g, respectively. In addition, the general applicability of ILRPP in molecular imprinting was also confirmed by the successful preparation of MIP microspheres with another template (2‐chloromandelic acid). In particular, the living nature of ILRPP makes it highly useful for the facile one‐pot synthesis of functional polymer/MIP microspheres with surface‐bound iniferter groups, which allows their direct controlled surface modification via surface‐initiated iniferter polymerization and is thus of great potential in preparing advanced polymer/MIP materials. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3217–3228, 2010

Synthesis of graft copolymers based on polyphenylene xylylene and fullerene grafted polystyrene

AbstractGraft copolymers containing poly(phenylene xylyene) (PPX) backbone and polystyrene fullerene (PSFu) grafting chains (PPX‐g‐PSFu) were prepared by using a purposed synthetic route comprising a combination of reaction mechanisms namely the modified Wessling route, an iniferter polymerization, and an atom transfer radical addition (ATRA). The monomer was first prepared by reacting dichloroxylene with tetrahydrothiophene. After that the monomer was polymerized in a sodium hydroxide solution to provide a polymer precursor. Subsequently, the polymer precursor was modified by reacting it with a dithiocarbamate (DTC) compound. The macroiniferter was obtained and then copolymerized with styrene and chloromethylstyrene via an iniferter polymerization. Finally, the graft copolymer was reacted with fullerene through an ATRA technique to attach the C60 groups onto the graft copolymer molecule. The products obtained from each of the steps were characterized by using various techniques including Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, gel permeation chromatography, differential scanning calorimetry, UV–visible spectroscopy, and thermal gravimetric analysis. The aforementioned results suggest that the graft copolymers were prepared. The grafting yield and grafting efficiency were found to increase with the monomers concentration and the amount of DTC used. Some homopolymer contaminants also occurred but those could be minimized and subsequently removed by extraction with selective solvents. These graft copolymer products might be used for the development of a bulk heterojunction polymer solar cell. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

The kinetics of dithiocarbamate-mediated polyurethane-block-poly(methyl methacrylate) polymers

One important advantage offered by polymeric iniferters is the possibility that polycondensation polymers could be further reacted with vinyl monomers to produce novel block copolymers with interesting properties. The objective of this work was the kinetic investigation of polyurethane-block-poly(methyl methacrylate) (PU-b-PMMA) using dithiocarbamate (DC)-based polyurethane macroiniferter (PUMI) at different concentrations. It is shown that the copolymerization reactions followed the first order dependency. A linear increase of molecular weight with monomer conversion demonstrated that the copolymerization followed the mechanism of controlled radical polymerization. The rate of polymerization (Rp) at specific reaction time increased as the PUMI concentration increased from 0.34 × 10−3 mol/L to 2.74 × 10−3 mol/L, pass through a maxima, and decreased as PUMI concentration was increased beyond 2.74 × 10−3 mol/L. The thermogravimetric analysis showed that both PUMI and PU-b-PMMA degraded in three distinctive stages but the PU-b-PMMA is thermally more stable than the PUMI especially at lower temperatures. Thus, a combination of polycondensation and free radical photopolymerization methods, as demonstrated in this study, could be used to synthesize polyurethane-based block copolymers with tailored chain lengths of different blocks suitable for biomedical applications.

Effect of molecular weight of macro‐iniferter on electro‐optical properties of polymer dispersed liquid crystal films prepared by iniferter polymerization

AbstractPolymer dispersed liquid crystal (PDLC) films were prepared by a devised method, in which photo‐polymerization induced phase separation in a mixtures of a macro‐iniferter, methyl acrylater, and liquid crystal. The morphology of the obtained PDLC films was examined on a polarized optical microscopy, and the effect of molecular weight of MIs on the electro‐optical properties was deliberately investigated. Decreasing the molecular weight of MIs in the films led to formation of larger liquid crystal droplets and a lower Vth values. Vsat increased and the memory effect decreased because of the increased interface anchoring strength induced by the higher molecular weight of polymer matrices. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1530–1534, 2009

The effect of the resultant microphase-separated structures of polymer matrices on the electro-optical properties of polymer dispersed liquid crystal films by Iniferter polymerization

Iniferter polymerization was employed to prepare polymer dispersed liquid crystal (PDLC) films and an additional photoinitiator was introduced to induce the phase separation of polymer matrices themselves on the process of preparing the PDLC. The effect of the polymerization kinetics and the resultant microphase-separated structures of polymer matrices on the electro-optical properties of PDLC films were studied. It was found that the bigger length scale of phase separation of polymer matrices induced strong light-scattering resulting in low ON-state transmittance. And faster polymerization kinetic induced higher threshold and saturation voltages.

Synergistic Interaction Between ATRP and RAFT: Taking the Best of Each World

This review covers recent developments on the combination of atom transfer radical polymerization (ATRP) and reversible addition–fragmentation chain transfer (RAFT) polymerization to produce well controlled (co)polymers. This review discusses the relative reactivity of the R group in ATRP and RAFT, provides a comparison of dithiocarbamate (DC), trithiocarbonate (TTC), dithioester (DTE), and xanthate versus bromine or chlorine, and an optimization of catalyst/ligand selection. The level of control in iniferter polymerization with DC was greatly improved by the addition of a copper complex. New TTC inifers with bromopropionate and bromoisobutyrate groups have been prepared to conduct, concurrently or sequentially, ATRP from Br-end groups, ATRP from the TTC moiety, and RAFT polymerization from the TTC moiety, depending on the combination of monomer and catalyst employed in the reaction. The use of concurrent ATRP/RAFT (or copper-catalyzed RAFT polymerization or ATRP with dithioester leaving groups), resulted in improved control over the synthesis of homo- and block (co)polymers and allowed preparation of well-defined high-molecular-weight polymers exceeding 1 million. Block copolymers that could not be prepared previously have been synthesized by sequential ATRP and RAFT polymerization using a bromoxanthate inifer. A simple, versatile, and one-step method involving atom-transfer radical addition–fragmentation (ATRAF) for the preparation of various chain transfer agents (including DC, DTE, and xanthate) in high purity is discussed and a one-pot, two-step polymerization starting with a RAFT agent synthesized by ATRAF, followed by polymerization, is demonstrated.

Modification of electro-optical properties of polymer dispersed liquid crystal films by iniferter polymerization

In this letter, iniferter polymerization was employed to prepare polymer dispersed liquid crystal (PDLC) films. Polystyrene (PS) was prepared as a macro-iniferter (MI). With the addition of MI in PDLC films, poly(methyl acrylate)-b-polystyrene was prepared in situ and used as polymer matrix in photopolymerization induced phase separation (PIPS). A reduction in driving voltages and an improvement in the ON state transmittance were observed for the sample prepared with a small amount of MI; while a poor electro-optical performance was obtained for that without any MI. Moreover, molecular weight and refractive index of the polymer matrix could be easily adjusted by the concentration of MI, and the matrix seems to be a prospective material for the PDLC devices.

Novel iniferter-based synthetic approach to hetero-telechelic precursors and multiblock copolymers composed of vinyl polymer blocks and condensation linkages

A novel synthetic approach, leading to the formation of hetero-telechelic precursors and multiblock copolymers composed of vinyl polymer [polystyrene or poly( N, N-dimethylacryl amide)] blocks and condensation linkages (ester or amide) or its polycondensate blocks, was developed using iniferters containing two different types of functional group (hydroxyl, carboxyl or amine) in their molecules via two different routes, each of which consisted of two-step reactions: photoiniferter living radical polymerization and subsequent polycondensation or vice versa. Both reactions proceeded at room temperature. The formation of multiblock copolymers was confirmed by 1H NMR and IR spectroscopic measurements and molecular weight measurements. Irrespective of the type of iniferter, the livingness of the iniferter polymerization step was verified by a linear relationship between the conversion and molecular weight under appropriate reaction conditions, indicating that the vinyl polymers’ block lengths were well controlled. The decrease in molecular weight of copolymers subjected to mild alkaline hydrolysis indicated that these multiblock copolymers might be degraded in a living body. This study is preliminary, but synthetic strategy proposed here may enable various choices of macromolecular architecture. Once the optimized reaction condition is achieved, functional macromolecular architectures with sequentially ordered complexity including well-controlled block lengths and multiple condensation linkages are feasible.

Flexibilized Styrene-N-Substituted Maleimide Copolymers with Enhanced Entanglement Density

High molecular weight poly(styrene-co-N-substituted-maleimide)-block-poly(tetrahydrofuran) multiblock copolymers with an excellent thermal stability were synthesized using the polymeric iniferter technique. Evidence for the existence of these multiblock copolymers was obtained by submitting them to gradient polymer elution chromatography and by snipping the chemical bonds between the SMI blocks and the PTHF blocks, after which the molecular weight distribution of the remaining SMI blocks was determined. Only one glass transition temperature was observed in a modulated temperature DSC scan of the segmented copolymers, typical for a homogeneous material. The Tg of these flexibilized, single-phase multiblock copolymers is still high enough to qualify them as engineering plastics. The entanglement density, which is closely related to the toughness of materials, of a styrene-N-phenylmaleimide copolymer flexibilized by 12 wt % PTHF was raised by a factor 1.6 as compared to the unflexibilized styrene-N-phenylmal...