Nitroxide-mediated Radical Polymerization Research Articles

Thermoplastic elastomer obtained by photopolymerization‐induced concomitant macrophase and microphase separations

AbstractWe report on concomitant photoinitiated polymerization‐induced macrophase and microphase separation strategies to produce hierarchically structured recyclable poly(n‐butyl acrylate) based elastomeric materials. The investigated crosslinker‐free formulations are composed of n‐butyl acrylate monomer and a UV photo‐initiator mixed with poly(methyl methacrylate)‐b‐poly(n‐butyl acrylate)‐poly(methyl methacrylate) ABA triblock copolymers. Two different pre‐synthesized copolymers are used to control the macrophase separation. One synthesized by nitroxide‐mediated radical polymerization (NMRP), and a second by anionic polymerization (AP). Essentially, NMRP route leads to copolymer with unsaturated chain ends, activated during UV photopolymerization. On the other hand, the copolymer synthesized by AP are chemically inert. That dissimilarity is also highlighted by time‐resolved FTIR and SAXS, performed to monitor respectively monomer conversion and nanostructure evolution during photopolymerization. The experimental data demonstrate that the reactivity of the triblock copolymer impacts drastically the polymerization kinetics and the self‐assembly processes. Finally, the rheological analysis shows that the produced materials present a solid‐like behavior at low frequencies despite a large PnBA content (i.e., 85 wt%). This property is associated to the phase segregation and to the sample hierarchical morphology.

Accelerated nitroxide-mediated polymerization of styrene and butyl acrylate initiated by BlocBuilder MA using flow reactors

Flow reactors enable the nitroxide-mediated radical polymerization (NMP) of styrene (St) and butyl acrylate (BA) initiated by BlocBuilder MA (BB MA) with additives in a highly controlled manner, and BA–St di-block copolymers were also synthesized.

Synthesis of styrene-norbornene diblock copolymers via ring-opening metathesis polymerization and nitroxide-mediated radical polymerization

Diblock copolymers containing polynorbornene (PNB) and polystyrene (PS) were synthesized by ring-opening metathesis polymerization (ROMP) and nitroxide-mediated radical polymerization (NMRP) approach. PNB containing nitroxide free radical was prepared by ROMP in presence of Grubbs 2nd generation catalyst and served as a macro-initiator for NMRP of styrene to achieve the targeting diblock copolymers. The effects of the chain transfer agent (CTA) concentration, catalyst amount, reaction time and reaction temperature on the synthesis of macro-initiator as well as the effects of mole ratio of monomer to macro-initiator and reaction time on the synthesis of diblock copolymers were studied. As a result, the diblock copolymers with Mn ranging from 5 kDa to 10 kDa and PDI ranging from 1.5 to 1.8 were obtained successfully. The desired diblock copolymers have broad applications in polymer electrolytes, nanoporous membranes and many other fields.

Nitroxide mediated radical polymerization for the preparation of poly(vinyl chloride) grafted poly(acrylate) copolymers

Alkoxyamines grafted on PVC initiated the NMP of butylacrylate or PEGA to yield PVC-g-poly(acrylate) presenting Tg from 63.5 to −10.5 °C.

Synthesis of thiophene-containing acyclic alkoxyamine for nitroxide-mediated radical polymerization of acrylates and styrene

In this study, specific acyclic nitroxide and corresponding alkoxyamine compounds containing thiophenyl group and intramolecular hydrogen bonding were designed (i.e., 2-(oxyl(2-methyl-1-(thiophen-2-yl)propyl)amino)-2-methylpropan-1-ol (HOT2NO•) and 2-methyl-2-((2-methyl-1-(thiophen-2-yl)propyl)(1-phenylethoxy)amino)propan-1-ol (HOT2NOPhEt)). The type of acyclic structures could render nitroxide-mediated polymerizations (NMPs) of acrylates at mild reaction temperatures that can effectively suppress side reactions of (macro)radicals. To enhance the reactivity of the initiator, one of our design to introduce a thiophenyl group is to increase hindrance/polarity feature. Another introduction of intramolecular hydrogen bonding (IHB) is to decrease the bond dissociation energy (BDE) of the “NO–C″ linkage of the initiator. Accordingly, both azo- and alkoxyamine-initiated NMPs were examined. The azo-initiated NMPs (i.e., using HOT2NO•/AIBN) of n-butyl acrylate (BA) and methyl acrylate (MA) showed uncontrolled radical polymerization fashions, presumably due to insufficient reactivation/deactivation from HOT2NO• during polymerization. The alkoxyamine-initiated NMPs of BA with proper amounts of deactivator (i.e., BA/HOT2NOPhEt/HOT2NO•) revealed controlled/living radical polymerization fashions at 120 and 100 °C and afforded Ph-PBA-ON macroinitiator (Mn,max = ca. 38 k and PDI <1.43). Through the DFT estimations of different relevant alkoxyamines, significant suppression of the BDEs was acquired (ca. minus 10–20 kJ/mol), implying the importance of IHB. Eventually, successful chain extension of Ph-PBA-ON with styrene (St) was demonstrated and afforded well-defined PBA-b-PSt diblock copolymer (Mn = ca. 12 k and PDI = 1.10).

The Effect of Viscosity on the Coupling and Hydrogen-Abstraction Reaction between Transient and Persistent Radicals?

Abstract The effect of viscosity on the radical termination reaction between a transient radical and a persistent radical undergoing a coupling reaction (Coup) or hydrogen abstraction (Abst) was examined. In a non-viscous solvent, such as benzene (bulk viscosity ηbulk &amp;lt; 1 mPa s), all the transient radicals studied exclusively coupled with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) with &amp;gt;99% Coup/Abst selectivity, but Coup/Abst decreased as the viscosity increased (89/11 in PEG400 at 25 °C [ηbulk = 84 mPa s]). While bulk viscosity is a good parameter to predict the Coup/Abst selectivity in each solvent, microviscosity is the more general parameter. Poly(methyl methacrylate) (PMMA)-end radicals had a more significant viscosity effect than polystyrene (PSt)-end radicals, and the Coup/Abst ratio of the former dropped to 50/50 in highly viscous media (ηbulk = 3980 mPa s), while the latter maintained high Coup/Abst selectivity (84/16). These results, together with the low thermal stability of dormant PMMA-TEMPO species compared with that of PSt-TEMPO species, are attributed to the limitation of the nitroxide-mediated radical polymerization of MMA. While both organotellurium and bromine compounds were used as precursors of radicals, the former was superior to the latter for the clean generation of radical species.

The Role of Nitroxide Degradation on the Efficiency of the Controller in Nitroxide-Mediated Radical Polymerization (NMP) of Styrene

The effect of nitroxide degradation on polymerization rate and molar mass development in the nitroxide-mediated radical polymerization (NMP) of styrene is studied using electron spin resonance (ESR...

Correction to Supramolecular Four-Armed Star A2B2 Copolymer (Miktoarm Star) via Host–Guest Complexation and Nitroxide-Mediated Radical Polymerization

Correction to Supramolecular Four-Armed Star A₂B₂ Copolymer (Miktoarm Star) via Host–Guest Complexation and Nitroxide-Mediated Radical Polymerization

Cyan Ni1-x Al2+2x/3□ x/3O4 Single-Phase Pigment Synthesis and Modification for Electrophoretic Ink Formulation.

Cyan Ni1–xAl2+2x/3O4 single-phase pigments with various Ni/Al atomic ratios (from 1:2 down to 1:4) have been prepared by a sol–gel route (Pechini) followed by postannealing treatments. Nickel aluminates crystallize in the well-known spinel structure (Fd3m space group), where metals are located at two different Wyckoff positions: 16d (octahedron) and 8a (tetrahedron). Based on X-ray diffraction (XRD) Rietveld refinements, Ni2+ cations are shown to be partially located in both tetrahedral and octahedral sites and, in addition, cationic vacancies occupy the Oh environment. In the pure-phase series, Ni/Al = 0.35, 0.40, 0.45, as the Al content increases, the Ni2+ rate in the Td site decreases for Ni/Al = 0.45, thus altering the cyan color; within this series, the most saturated cyan coloration is reached for the highest Al concentration. Inorganic pigment drawbacks are their high density and hydrophilic surface, which induce sedimentation and aggregation in nonpolar media used in electrophoretic inks. Hybrid core–shell particle pigments have been synthesized from cyan pigments using nitroxide-mediated radical polymerization (NMRP) with methyl methacrylate monomer in Isopar G, leading to a dispersion of electrically charged hybrids in apolar media. Surface functionalization of the pigments by n-octyltrimethoxysilane (OTS) and n-dodecyltrimethoxysilane (DTS) modifiers has been compared. The inorganic pigments are successfully encapsulated by organic shells to allow a strong decrease in their density. Cyan inks, adequate for their use in e-book readers or other electrophoretic displays, taking further advantage of the high contrast ratio and reflectivity of inorganic pigments in regard to organic dyes, have been stabilized.

Supramolecular Four-Armed Star A2B2 Copolymer (Miktoarm Star) via Host–Guest Complexation and Nitroxide-Mediated Radical Polymerization

A supramolecular four-armed star copolymer was prepared from the pseudorotaxane complex of a crown-centered polystyrene and a bis(2,2,6,6-tetramethylpiperidinyl-1-oxy) viologen compound and n-butyl methacrylate (BMA) by nitroxide-mediated polymerization of the latter. Solvent fractionation with dioxane/THF/MeOH removed a small amount of a high molecular weight poly(BMA) homopolymer. The molecular weight increase from its monomodal size exclusion chromatographic trace gives direct evidence of the four-armed star copolymer formation; there is no residual starting polystyrene. NMR spectroscopy shows the two components of the copolymer and confirms the presence of the central [2]rotaxane unit. Differential scanning calorimetry displays two glass-transition temperatures, which correspond closely to those of polystyrene and poly(BMA).

Synthesis of a well-defined polyelectrolyte by controlled/“living” nitroxide-mediated radical polymerization. Kinetic study

The synthesis and characterization of potassium 4-styrenesulfonyl (trifluoromethylsulfonyl) imide (STFSIK) monomer as well as its controlled/living nitroxide-mediated radical polymerization (NMRP), using N-tert-Butyl-N-(2-methyl-1-phenylpropyl)-O-(1-phenylethyl) hydroxylamine as initiator in 50% w/v solutions of DMF at 125 °C, are reported. The kinetic studies of STFSIK indicated controlled/“living” polymerization process free of coupling and transfer reactions. 1H NMR and SEC were employed to determine the rate of monomer consumption and molecular weight distribution, Ð, of the synthesized samples. The polymerization reaction established high monomer conversion in just an hour with high end-group fidelity and the ability to continue polymerization with no visible terminations. Finally, the synthesis of the corresponding PSTFSILi homopolymer was achieved through a metathesis reaction between PSTFSIK and LiClO4, and the subsequent purification was successful against dialysis in water.

Cellulose Acetate-Graft-Poly (Methyl Methacrylate): A andldquo;Graft fromandrdquo; Approach of Nitroxide Mediated Radical Polymerization

Poly (methyl methacrylate) was grafted onto cellulose acetate backbone using a “graft from” of Nitroxide Mediated Radical Polymerization (NMRP). The formation of cellulose acetate-co-poly (methyl methacrylate) using N-tert-butyl- N- (1-diethylphosphono-2,2-dimethylpropyl) (SG1)-nitroxide based macroalkoxyamine system was confirmed by FTIR and NMR analyses. The copolymer exhibited living characteristics as shown by NMR. DSC investigations showed a copolymer with a rich poly (methyl methacrylate) phase around 120°C and a rich cellulose acetate phase at around 175°C.

Rapid synthesis of fluorescent single-chain nanoparticles via photoinduced step-growth polymerization of pendant carbazole units

An easy and rapid strategy is developed to synthesize light responsive single-chain nanoparticles via photoinduced radical coupling of carbazole moieties in the side chain of polymer. Firstly, nitroxide-mediated radical polymerization is carried out for the synthesis of chloride functional styrenic copolymer. Pendant chloride groups of the polystyrene copolymer are converted to carbazole units by one-step modification. Constructed functional polymer undergoes photochemically intramolecular crosslinking using carbazole step-growth polymerization. Size of the nanoparticles can be manipulated by changing the degree of polymerization which is dependent to the dose of UV exposure. Achieved single-chain nanoparticles exhibit higher glass transition temperatures and lower hydrodynamic radii compared to their linear analogue. Polymeric nanoparticles are successfully employed for the cyclohexane oxide polymerization as cationic photoinitiators in the presence of an iodonium salt.

Synthesis of CO2-based polycarbonate-g-polystyrene copolymers via NMRP.

The construction of a graft copolymer is an effective method to modify the properties of CO2-based aliphatic polycarbonate (CO2-APC) for meeting specific needs. Herein, we describe a facile route for the synthesis of CO2-based APC-graft-polystyrene copolymers using a "grafting from" strategy. Firstly, the copolymerization of CO2 and epichlorohydrin (ECH) was performed for the synthesis of the APC of poly(CO2/ECH). Then, a functionalized-APC can be prepared by the substitution reaction of poly(CO2/ECH) and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) that can serve as a precursor for the graft compolymer of P(CO2/ECH)-g-polystyrene via nitroxide-mediated radical polymerization (NMRP). The intermediates at each step and final graft copolymers were characterized using 1H NMR, GPC, DSC and TG analyses.

Investigation on the atom transfer nitroxide radical polymerization (ATNRP) mechanism and its versatile applications for bimodal polymers

The atom transfer nitroxide radical polymerization (ATNRP) was developed based on the synergistically happened nitroxide radical coupling (NRC) reaction, atom transfer radical polymerization (ATRP) and nitroxide mediated radical polymerization (NMRP) procedures. The ATNRP of styrene (St) and tert-butyl acrylate (tBA) monomers were systematically studied at different temperature with various molar ratio of [HO-TEMPO]0/[EBiB]0. In the case of St, both ATRP and NMRP can be combined into an ATNRP technique, while the polymerization rate was lowered with the increase of [HO-TEMPO]0/[EBiB]0. With the increase of temperature, the polymerization showed an increased polymerization rate. Alternatively, in the case of tBA, with the addition of HO-TMEPO agent, partial PtBA was terminated by the side reactions of H-abstraction or disproportionation. The remained PtBA was still functionalized with bromide group, and the ATRP can be still continued for a bimodal PtBA. Finally, the resulted PS or PtBA can be further cross-chain-extended by tBA or St, and the bimodal diblock copolymers can be generated. The compositions of the obtained bimodal homopolymer or diblock copolymer can be well controlled by the amount of [HO-TEMPO]0/[EBiB]0.

A versatile approach for the preparation of end‐functional polymers and block copolymers by stable radical exchange reactions

ABSTRACTA versatile strategy for the preparation of end‐functional polymers and block copolymers by radical exchange reactions is described. For this purpose, first polystyrene with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl end group (PS‐TEMPO) is prepared by nitroxide‐mediated radical polymerization (NMRP). In the subsequent step, these polymers are heated to 130 °C in the presence of independently prepared TEMPO derivatives bearing hydroxyl, azide and carboxylic acid functionalities, and polymers such as poly(ethylene glycol) (TEMPO‐PEG) and poly(ε‐caprolactone) (TEMPO‐PCL). Due to the simultaneous radical generation and reversible termination of the polymer radical, TEMPO moiety on polystyrene is replaced to form the corresponding end‐functional polymers and block copolymers. The intermediates and final polymers are characterized by 1H NMR, UV, IR, and GPC measurements. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2387–2395

Complex macromolecular structures from stable radical containing block copolymers

ABSTRACTA novel synthetic strategy for the synthesis of graft copolymers is reported. Block copolymers containing segments with stable nitroxyl radicals side groups were first prepared by anionic polymerization, which were then used as a precursor for the subsequent nitroxide‐mediated radical polymerization (NMRP) of styrene. This way, block–graft copolymers with polystyrene side chains grafted from one of the blocks were successfully synthesized in a controlled manner. In addition, block–graft copolymers with grafted polystyrene chains and a poly(tert‐butyl methacrylate) block were subjected to hydrolysis to yield the corresponding amphiphilic polymers. The structures and the molecular weight characteristics of the polymers were characterized by spectral and chromatographic analyses. The surface morphology of thus obtained polymers was also investigated by microscopic techniques. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 62–69

Construction of Paramagnetic Manganese-Chelated Polymeric Nanoparticles Using Pyrene-End-Modified Double-Hydrophilic Block Copolymers for Enhanced Magnetic Resonance Relaxivity: A Comparative Study with Cisplatin Pharmacophore.

Cationic metal-mediated self-assembly of double-hydrophilic block copolymers (DHBCs) has been of great interest for the preparation of hybrid nanoparticles for versatile applications. Among many functional transition-metal ions, manganese (MnII) is a highly attractive element due to its paramagnetic property with a high coordination number. However, MnII does not lead to the efficient self-assembly of DHBCs because of the relatively high aqueous solubility of coordinated MnII. This article reports a facile method for direct conjugation of MnII ions inside sterically stabilized polymer assemblies, composed of pyrene-end-modified DHBCs. Nitroxide-mediated radical polymerization was used to prepare the poly(ethylene glycol)- b-poly(acrylate) DHBC precursor, followed by the end-modification with pyrene maleimide via the radical-exchange reaction. Employing the self-associated DHBC as the nanoscale template, the simple addition of MnII enables a large number of polyvalent MnII ions to be immobilized at the chelating blocks of DHBCs, which can be readily monitored by the excimeric fluorescence emission change of the terminal pyrene fluorophore. The resulting MnII-loaded polymeric nanoparticles (MnII-PNPs) possess nanogel-like scaffolds, which allow for efficient water permeation at the MnII-incorporated interior for enhanced magnetic resonance contrasting effect. Additionally, by comparing the coordination properties of MnII and cisplatin, we endeavor to understand the internal structures and the relevant physicochemical features of metal-chelated nanoparticles.

β-Myrcene/isobornyl methacrylate SG1 nitroxide-mediated controlled radical polymerization: synthesis and characterization of gradient, diblock and triblock copolymers.

β-Myrcene (My), a natural 1,3-diene, and isobornyl methacrylate (IBOMA), from partially bio-based raw materials sources, were copolymerized by nitroxide-mediated polymerization (NMP) in bulk using the SG1-based BlocBuilder™ alkoxyamine functionalized with an N-succinimidyl ester group, NHS-BlocBuilder, at T = 100 °C with initial IBOMA molar feed compositions fIBOMA,0 = 0.10–0.90. Copolymer reactivity ratios were rMy = 1.90–2.16 and rIBOMA = 0.02–0.07 using Fineman–Ross, Kelen–Tudos and non-linear least-squares fitting to the Mayo–Lewis terminal model and indicated the possibility of gradient My/IBOMA copolymers. A linear increase in molecular weight versus conversion and a low dispersity (Đ ≤ 1.41) were exhibited by My/IBOMA copolymerization with fIBOMA,0 ≤ 0.80. My-rich and IBOMA-rich copolymers were shown to have a high degree of chain-end fidelity by performing subsequent chain-extensions with IBOMA and/or My, and by 31P NMR analysis. The preparation by NMP of My/IBOMA thermoplastic elastomers (TPEs), mostly bio-sourced, was then attempted. IBOMA-My-IBOMA triblock copolymers containing a minor fraction of My or styrene (S) units in the outer hard segments (Mn = 51–95 kg mol−1, Đ = 1.91–2.23 and FIBOMA = 0.28–0.36) were synthesized using SG1-terminated poly(ethylene-stat-butylene) dialkoxyamine. The micro-phase separation was suggested by the detection of two distinct Tgs at about −60 °C and +180 °C and confirmed by atomic force microscopy (AFM). A plastic stress–strain behavior (stress at break σB = 3.90 ± 0.22 MPa, elongation at break εB = 490 ± 31%) associated to an upper service temperature of about 140 °C were also highlighted for these triblock polymers.

Insights into the Network Structure of Cross-Linked Polymers Synthesized via Miniemulsion Nitroxide-Mediated Radical Polymerization

The effect of reversible-deactivation radical polymerization on the structure of the network formed by copolymerization of mono- and divinyl monomers is studied. The nitroxide-mediated radical copolymerization (NMP) of butyl methacrylate and ethylene glycol dimethacrylate, initiated with the alkoxyamine 3-(((2-cyanopropan-2-yl)oxy)cyclohexylamino)-2,2-dimethyl-3-phenylpropanenitrile (Dispolreg 007) in an aqueous miniemulsion was used as a case study. Combination of asymmetric-flow field-flow fractionation and small-angle X-ray scattering clearly showed that NMP led to a more homogeneous network structure formed by regions of relatively open networks connected with short polymer chain segments, whereas that of the polymer formed by free radical polymerization consists of densely cross-linked regions linked by long polymer chain portions.