Nitroxide-mediated Controlled Radical Polymerization Research Articles

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.

Synthesis of β-Myrcene-Based Polymers and Styrene Block and Statistical Copolymers by SG1 Nitroxide-Mediated Controlled Radical Polymerization

Nitroxide-mediated polymerization (NMP) of β-myrcene (My) at 120 °C in bulk using unimolecular SG1-based succinimidyl ester-functionalized BlocBuilder (BB) alkoxyamine resulted in low dispersity (Đ = 1.1–1.4) poly(myrcene)s P(My)s with high SG1 chain-end fidelity. The polymerizations also showed the number-average molecular weights (Mn) increased almost linearly with conversion. SG1-terminated P(My) macroinitiators were cleanly chain-extended with styrene (S) and the S-rich P(My-b-S) diblock copolymers exhibited two distinct glass transition temperatures (Tgs), indicative of microphase separation. P(My-b-S) diblocks showed brittle stress–strain behavior, plausibly due to relatively low Mn. My/S mixtures with initial S molar feed compositions fS,0 = 0.10–0.94 were also statistically copolymerized (Mn = 8.2–19.8 kg mol–1, Đ ≤ 1.37, and monomodal distributions). Copolymer reactivity ratios were rS = 0.25 ± 0.04/0.34 ± 0.19 and rMy = 1.88 ± 0.12/2.19 ± 0.07 using Fineman–Ross and Kelen–Tudos methods. The stat...

Radical polymerization of styrene in presence of poly(2,2,6,6-tetramethylpiperidine-N-oxyl-4-yl methacrylate) - formation of polymer brushes

The radical polymerization of styrene in presence of poly(2,2,6,6-tetramethylpiperidine-N-oxyl-4-yl methacrylate) (PTMA) is described. PTMA is a well-known polymer for organic radical batteries. Tetramethylpiperidine-N-oxyl (TEMPO) is the common reagent for nitroxide-mediated controlled radical polymerization (NMP). PTMA, as macromolecular counterpart of TEMPO, was found to lead to a partly controlled polymerization process. During the polymerization, large amounts of the graft copolymer PTMA-g-PS are formed via the grafting-to approach. No indication for insoluble gel formation at high conversion rates is observed. The isolated graft copolymers were characterized by dynamic light scattering and revealed hydrodynamic radii in the range of 30–50 nm. The polymerization in presence of PTMA offers a convenient way to the multigram-scale synthesis of bottle-brush polymers.

Poly(styrene-alt-maleic anhydride)-block-poly(methacrylate-ran-styrene) block copolymers with tunable mechanical properties by nitroxide mediated controlled radical polymerization

Poly(styrene-alt-maleic anhydride)-block-poly(methacrylate-ran-styrene) block copolymers were synthesized from low dispersity (Mw/Mn=1.24) and perfectly alternating poly(styrene-alt-maleic anhydride) macroinitiators, by nitroxide mediated controlled radical polymerization (NMP), using various methacrylate-rich mixtures: methyl methacrylate/styrene (MMA/S), ethyl methacrylate/styrene (EMMA/S), n-butyl methacrylate/styrene (BMA/S) and benzyl methacrylate/styrene (BzMA/S). Some irreversible termination was present during the chain extension from the macroinitiator, resulting in some bimodality in the molecular weight distribution of the final block copolymer (≈2% to ≈25% dead chains) which is common for methacrylate/styrene copolymerizations by NMP. The resulting final block copolymers were determined to be methacrylate-rich (molar ratio XMA/S ≈3.3 to 5.5) by 1H NMR and the resulting glass transition temperature (Tg) of the chain-extended segments were found to be similar to the coresponding pure poly(methacrylate)s. NMP allows the controlled placement of functional maleic anhydride containing segments within a block copolymer with tunable mechanical properties by simple substitution of methacrylate monomer used in synthesis.

Ring expansion-controlled radical polymerization: Synthesis of cyclic polymers and ring component quantification based on SEC–MALS analysis

We report a ring expansion vinyl polymerization producing cyclic polymers using a tetra(oxyethylene) (TOE)-tethered cyclic initiator for the nitroxide-mediated controlled radical polymerization (NMP). Styrene (St) was polymerized with the cyclic NMP initiator 1 in the bulk to produce polymer 2. Structural analyses of 2 were performed by a size exclusion chromatograph equipped with a multiangle laser light scattering (SEC–MALS) detector, focusing on the relationships between the z-averaged root-mean-square radii of gyration (〈S2〉z1/2) versus the molecular weights. The results proved that 2 would consist of ring components as a result of the ring expansion polymerizations and radical ring crossover reactions together with ring-opened linear components, in which the amount of ring components increased with the increasing molecular weights. The data also enabled the quantification that approximately 13–40wt% of the final polymer 2 could be identified as the ring species in the Mw range of 1×105–5×105gmol−1.

Thermosensitive copolymer synthesized by controlled living radical polymerization: Phase behavior of diblock copolymers of poly(N‐isopropyl acrylamide) families

ABSTRACTIn this study, we prepared a series of thermosensitive polymers with low polydispersity index (PDI) values by nitroxide‐mediated controlled radical polymerization (NMRP) with 2,2,6,6‐tetramethyl‐1‐piperdinyloxy nitroxide (TEMPO) as a stable nitroxide‐free radical. Poly(N‐isopropyl acrylamide) (PNIPAAm)‐block‐poly(N‐tert‐butyl acrylamide) (PNTBA) was successfully synthesized, first, through polymerization with N‐isopropyl acrylamide to obtain the reactive polymer PNIPAAm‐TEMPO and, second, through polymerization by the addition of N‐tert‐butyl acrylamide (NTBA). The added molar fraction of NTBA during the second polymerization was adjusted accordingly to obtain the final polymerization product, a thermosensitive polymer (PNIPAAm‐block‐PNTBA), which had a targeted lower critical solution temperature (LCST). The result shows that the synthesis method used in this study effectively controlled the formation of the polymer to obtain a low PDI. The thermosensitive block copolymer, PNIPAAm‐b‐PNTBA (molar ratio = 9:1), with LCSTs in the range 27.7–39.8°C, was obtained through controlled living radical polymerization with PNIPAAm–TEMPO. Specifically, the 5 wt % aqueous solution of PNIPAAm‐b‐PNTBA (molar ratio = 9:1) had an LCST of 37.4°C; this was close to body temperature, 37°C. The 5 wt % aqueous solution of PNIPAAm‐b‐PNTBA (molar ratio = 9:1) showed potential for use in biomedical applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43224.

Influence of Bound Ion on the Morphology and Conductivity of Anion-Conducting Block Copolymers

Anion-conducting membranes are important for several applications including fuel cells and artificial photosynthesis. In this study such membranes were made by quaternizing polystyrene-block-polychloromethylstyrene (PS-b-PCMS) copolymers. PS-b-PCMS copolymers with molecular weights ranging from 4 to 60 kg/mol were synthesized by nitroxide-mediated controlled radical polymerization. Separate aliquots of the PS-b-PCMS samples were quaternized to transform the PCMS block. This resulted in block copolymers with ionizable blocks containing either trimethylammonium chloride or n-butylimidazolium chloride. We refer to ion-containing block copolymers synthesized from the same precursor as matched pairs: SAM (containing trimethylammonium chloride) and SIM (containing n-butylimidazolium chloride). The volume fraction of the ion-containing block, ϕ, ranges from 0.26 to 0.50 for the case of SAM and from 0.35 to 0.60 for the case of SIM. Self-assembly in these copolymers resulted in the formation of lamellar phases regardless of ϕ, chemical formula of the bound ion, and chain length. Chloride ion conductivity and water uptake measurements on one of the matched pairs led to similar results. Preliminary experiments wherein the chloride ions in this matched pair were replaced by hydroxide ions were performed, and the changes in conductivity due to this are reported.

Preparation and Characterization of Poly (vinylbenzyl chloride)-<i>b</i>-poly (lactide) Copolymers via Nitroxide-Mediated Controlled Radical and Ring-Opening Polymerization

Hydroxyl-terminated poly(vinylbenzyl chloride) (PVBCOH) were synthesized using nitroxide-mediated controlled radical polymerization. Then, PVBCOH was used as a macro-initiator for ring-opening polymerization of lactide (LA) in the presence of stannous octanoate (Sn(Oct)2) as a catalyst. The structures, molecular weights and polydispersity index (PDI) of PVBCOH and PVBC-b-PLA were characterized by 1H-NMR, and GPC, respectively. The results indicated that PDI of PVBCOH and PVBC-b-PLA was 1.63 and 1.27, respectively. Moreover, the molecular weight and PDI of PVBCOH and PVBC-b-PLA could be well tuned by changing monomer-to-initiator ratio.

Fluorescent, Thermoresponsive Oligo(ethylene glycol) Methacrylate/9-(4-Vinylbenzyl)-9H-carbazole Copolymers Designed with Multiple LCSTs via Nitroxide Mediated Controlled Radical Polymerization

9-(4-Vinylbenzyl)-9H-carbazole (VBK) was used as the “controlling” comonomer for nitroxide mediated polymerization with 10 mol % SG1 free nitroxide relative to BlocBuilder initiator at 80 °C of oligo(ethylene glycol) methyl ether methacrylate (8–9 ethylene glycol (EG) units) (OEGMA8–9), 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and for an OEGMA8–9/MEO2MA-mixed feed. The synthesis of MEO2MA/VBK and OEGMA8–9/VBK copolymers and MEO2MA/OEGMA8–9/VBK terpolymers exhibited linear increases in number-average molecular weight (M̅n) versus conversion X, up until X = 0.6, with final copolymers characterized by relatively narrow, monomodal molecular weight distributions (M̅w/M̅n < 1.4, in most cases). A series of MEO2MA/OEGMA8–9/VBK terpolymers were synthesized and by varying the OEGMA8–9:MEO2MA feed ratios, the terpolymers exhibited tunable lower critical solution temperatures in water (28 °C < LCSTs < 81 °C). MEO2MA/OEGMA8–9/VBK terpolymers were deemed sufficiently pseudo-“living” to reinitiate a second batch of MEO2MA/OEGMA8–9/VBK, with few apparent dead chains, as indicated by the monomodal shift in the GPC chromatograms. The resulting MEO2MA/OEGMA8–9/VBK block copolymers were designed so that each block exhibited a distinct LCST, which was confirmed by UV–vis and dynamic light scattering. In addition to controlling the terpolymerization, the VBK units imparted thermo-responsive fluorescence into the final copolymers.

Structure and rheology of di- and triblock copolymers of polystyrene and poly(n-butyl acrylate)

Block copolymers based on acrylate matrices are expected to be good candidates for pressure sensitive adhesives formulations because (i) all-acrylic block copolymers are known to be stable over a wide temperature range and are more resistant to UV radiation than polydiene copolymers and (ii) the soft block exhibits an elasticity that is lower than that of polydiene and closer to the Dalhquist criterion (tacky properties). This last property is due to a higher molar mass between entanglements. The block segregation is the key parameter for these kinds of systems because it induces a solid-like behavior useful for adhesion applications. In this work, we have explored this point by synthesizing styrene/n-butyl acrylate (nBA) and methyl methacrylate/nBA block copolymers by nitroxide-mediated controlled radical polymerization. Atomic force microscopy and small-angle neutron scattering analysis have demonstrated the strong connection between the physico-chemical properties (molar mass, nature of the blocks, χ, dispersity, etc.), the microstructure, and the rheological properties of these block copolymers. Furthermore, the rheological behavior expected for good pressure sensitive adhesives performances is obtained under specific conditions. Finally, we will discuss the adherence performances of model formulations derived from these block copolymers.

Cyclic alkoxyamine‐initiator tethered by azide/alkyne‐“click”‐chemistry enabling ring‐expansion vinyl polymerization providing macrocyclic polymers

AbstractA cyclic initiator for the nitroxide‐mediated controlled radical polymerization (NMP) is a powerful tool for the preparation of macrocyclic polymers via a ring‐expansion vinyl polymerization mechanism. For this purpose, we prepared a Hawker‐type NMP‐initiator that includes an azide and a terminal alkyne as an acyclic precursor, which is subsequently tethered via an intramolecular azide/alkyne‐“click”‐reaction, producing the final cyclic NMP‐initiator. The polymerization reactions of styrene with cyclic initiator were demonstrated and the resultant polymers were characterized by the gel permeation chromatography (GPC) and the matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS). These results prove that the ring‐expansion polymerization of styrene occurred together with the radical ring‐crossover reactions originating from the exchange of the inherent nitroxides generating macrocyclic polystyrenes with higher expanded rings. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3402–3416, 2010

4‐Acetoxystyrene nitroxide‐mediated controlled radical polymerization: Comparison with styrene

AbstractThe nitroxide‐mediated controlled radical polymerization (NM‐CRP) of 4‐acetoxystyrene with an alkoxyamine was analyzed by a combined experimental and modeling approach. At low nitroxide concentrations, thermal initiation was significant, and control of the polydispersity was poor, as was observed previously for styrene. A continuum model based on the method of moments was used to regress the parameters for the reversible nitroxide uncoupling/coupling reactions (activation energy of uncoupling), thermal initiation (activation energy of initiation), and termination (frequency factor of recombination). The model was able to capture the molecular weight averages and the polydispersity index as a function of time and the nitroxide concentration qualitatively and quantitatively. Using this mechanistic framework, we developed kinetic Monte Carlo models that allowed the molecular weight distributions to be predicted explicitly in good agreement with experimental data. A comparison of the NM‐CRP of 4‐acetoxystyrene and styrene is provided to illustrate the effect of the acetoxy substituent. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Living Radical Polymerization of Styrene Derivatives Containing Trialkylmetal Groups

Fourteenth group oganometallic styrene derivatives were synthesised by nitroxide-mediated controlled radical polymerization using di-tert butyl nitroxide (A-T) as initiator. This is the first time that nitroxide-controlled radical polymerization has been successfully adapted for the synthesis of new polystyrenes bearing organometallic species with controlled molecular weights and narrow polydispersities. Monomer reactivity ratios were determined in controlled nitroxide-mediated radical copolymerization between styrene and substituted styrene. All experiments permitted the synthesis of new organometallic polymers that will be used for the development of a polymer capsule for Inertial Confinement Fusion Experiments.

Kinetics of Segment Formation in Nitroxide-Mediated Controlled Radical Polymerization: Comparison with Classic Theory

The kinetic details of segment formation in living radical polymerization (LRP) were investigated by studying styrene (S)/methyl methacrylate (MMA) copolymerization via nitroxide-mediated controlle...

Poly(tert-butyl methacrylate/styrene) Macroinitiators as Precursors for Organo- and Water-Soluble Functional Copolymers Using Nitroxide-Mediated Controlled Radical Polymerization

Styrene/tert-butyl methacrylate (S/TBMA) mixtures, with initial TBMA molar feed compositions fTBMA,0 = 0.1−0.92, were copolymerized by nitroxide-mediated polymerization (NMP) in bulk at 90 °C using 10 mol % {tert-butyl[1-(diethoxyphosphoryl)-2,2-dimethylpropyl]amino} nitroxide (SG1) relative to 2-({tert-butyl[1-(diethoxyphosphoryl)-2,2-dimethylpropyl]amino}oxy)-2-methylpropionic acid unimolecular initiator (BlocBuilder) to form SG1-terminated macroinitiators. kpK values (kp = propagation rate constant, K = equilibrium constant) for S/TBMA increased significantly as fTBMA,0 increased, with kpK = (7.4 ± 0.03) × 10−7 to (5.4 ± 0.9) × 10−5 s−1. Copolymer reactivity ratios were rTBMA= 0.13−0.27 and rS = 0.43−0.59 using Fineman−Ross, Kelen−Tudos, and nonlinear least-squares fitting to the Mayo−Lewis terminal model. All S/TBMA copolymers (number-average molecular weight Mn = 4.5−15.6 kg mol−1) exhibited low polydispersities (Mw/Mn ≤ 1.30), and Mn exhibited linear behavior with conversion up to 25−40% and mon...

Factors Affecting the Formation of the Monomer Sequence along Styrene/Methyl Methacrylate Gradient Copolymer Chains

The impact of the synthesis conditions on the formation of the monomer sequences of styrene (S) and methyl methacrylate (MMA) gradient copolymers synthesized by forced gradient copolymerization with nitroxide-mediated controlled radical polymerization (NM-CRP) was investigated using kinetic Monte Carlo (KMC) simulations. The factors affecting the formation of the individual segments, arrangement of these segments along the chain, and the uniformity of monomer sequences were investigated. It was shown that instantaneous segment lengths increase exponentially as a function of monomer composition. The concentration of nitroxyl radicals also plays a key role in the formation of segment lengths. In addition, the arrangement of the segments mainly depends on the feed profile of the second monomer. A constant feed profile, which is widely used in current syntheses of gradient copolymers, is shown to not be suitable to make a structural gradient along the chain. It was also demonstrated that the uniformity of seq...

Explicit Sequence of Styrene/Methyl Methacrylate Gradient Copolymers Synthesized by Forced Gradient Copolymerization with Nitroxide-Mediated Controlled Radical Polymerization

In spite of many efforts made to study gradient copolymers, the monomer-by-monomer sequence along the chain is still obscure. A general computational framework based on kinetic Monte Carlo simulations was developed to predict the explicit sequence of copolymers. We demonstrate our approach using styrene (S)/methyl methacrylate (MMA) gradient copolymers synthesized by a semibatch process with nitroxide-mediated controlled radical polymerization (NM-CRP). It was found that the variation in the average segment length as a function of chain length does not resemble that of the instantaneous composition. Our findings indicate that copolymers with compositional gradients may have monomer-by-monomer sequences resembling those of statistical copolymers. It was also found that the explicit sequence can significantly deviate from that of the instantaneous composition as a function of chain length when combination is the favored termination mode. These details of explicit sequence revealed by KMC simulations are obscured by only considering fractional composition measures to characterize the gradient shape.

Polystyrene-block-poly(ethylene oxide)-block-polystyrene: A New Synthesis Method Using Nitroxide-Mediated Polymerization from Poly(ethylene oxide) Macroinitiators and Characterization of the Architecture Formed

The strategy developed in this report consisted of synthesizing polystyrene (PS) blocks by nitroxide-mediated controlled radical polymerization from poly(ethylene oxide) (PEO) macroinitiators. Difunctional macroinitiators were first prepared in a two-step procedure by reacting PEO (Mn ranging from 1450 to 35000 g/mol) with MONAMS, an alkoxyamine based on N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl)nitroxide, called SG1. A series of polystyrene-block-poly(ethylene oxide)-block-polystyrene (PS-b-PEO-b-PS) triblock copolymers was then synthesized with various chain dimensions and PEO block mass fractions from 0.13 to 0.65. Precise insight into the prepared triblock copolymer structure in terms of molecular weight, block length, and polydispersity index was obtained using complementary characterization techniques such as 1H NMR spectroscopy and size exclusion chromatography (SEC). These data were completed by two-dimensional chromatography, a combination of liquid chromatography at the critical cond...

Supramolecular Triblock Copolymers Containing Complementary Nucleobase Molecular Recognition

A novel difunctional alkoxyamine initiator, DEPN2, was synthesized and utilized as an efficient initiator in nitroxide-mediated controlled radical polymerization of triblock copolymers. Complementary hydrogen-bonding triblock copolymers containing adenine (A) and thymine (T) nucleobase-functionalized outer blocks were synthesized. These thermoplastic elastomeric block copolymers contained short nucleobase-functionalized outer blocks (Mn ∼ 1K−4K) and n-butyl acrylate rubber blocks of variable length (Mn ∼ 14K−70K). Hydrogen-bonding interactions were observed for blends of the complementary nucleobase-functionalized block copolymers in terms of increased specific viscosity as well as higher scaling exponents for specific viscosity as a function of solution concentration. In the solid state, the blends exhibited evidence of a complementary A−T hard phase, which formed upon annealing, and dynamic mechanical analysis (DMA) revealed higher softening temperatures. Morphological development of the block copolymer...

Synthesis and Characterizations of Block Copolymer of Poly(n-butyl acrylate) and Gradient Poly(methyl methacrylate-co-N,N-dimethyl acrylamide) Made via Nitroxide-Mediated Controlled Radical Polymerization

Methyl methacrylate (MMA)/N,N-dimethyl acrylamide (DMA) gradient copolymers with various chemical composition were synthesized by nitroxide-mediated controlled radical polymerization (NMP). Molecular weight (MW) characterization via gel permeation chromatography demonstrated that these materials were made in a “controlled” manner. The reactivity ratios values r1(MMA) = 2.36 and r2(DMA) = 0.33 were experimentally determined using the linear least-squares numerical method, results in good agreement with the literature. Characterization of the glass transition temperature, Tg, by differential scanning calorimetry (DSC) of gradient copolymers exhibited one Tg, with a value intermediate to the Tg of pure poly(methyl methacrylate) (PMMA) and poly(N,N-dimethyl acrylamide) (PDMA). In contrast, di- and triblock copolymers made of poly(n-butyl acrylate) (PBA) as central block and PMMA/PDMA gradient copolymer as external block yielded two Tg, one corresponding to the Tg of PBA and the other intermediate to the Tg of PMMA and PDMA, indicating microphase separation which was confirmed by dynamic mechanical analysis and TEM observations of films of di- and triblock copolymers showing lamellae structure.