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Two libraries of well-defined, degradable vinyl copolymers of opposite solubility, based either on methyl methacrylate (MMA) or on oligo(ethylene glycol) methyl ether methacrylate (OEGMA), and containing various amount of 2-methylene-4-phenyl-1,3-dioxolane (MPDL), were synthesized by nitroxide-mediated radical ring-opening polymerization. A comprehensive degradation study (long-term hydrolytic degradation, degradation of thick and thin films, water uptake, enzymatic degradation) was then performed, and results were compared with those from traditional aliphatic polyesters (PLGA, PLA, and PCL). It appeared that P(MMA-co-MPDL) copolymers slowly degraded in PBS with degradation kinetics slower than that of PCL whereas P(OEGMA-co-MPDL) copolymers led to significant degradation, in between that of PLA and PCL, depending on the amount of MPDL, but without leading to a dramatic drop of pH as for PLGA and PLA. Whereas P(MMA-co-MPDL) copolymers might be well-suited for biomaterials intended for long-term use (e.g., devices and implants), faster degrading P(OEGMA-co-MPDL) copolymers might be envisioned for short- or midterm applications such as nanoscale drug-delivery systems, meeting a need for hydrophilic degradable materials with tunable degradation kinetics. [ABSTRACT FROM AUTHOR]

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-TÜ dÖ s methods. The statistical P(My-stat-S) copolymers displayed a range of Tgs (-77 to +30 °C) depending on My molar fraction. My-rich and S-rich P(My-stat-S)s were then successfully chain-extended with both S and My.r [ABSTRACT FROM AUTHOR]

An innovative model-based design strategy to synthesize well-defined sequence-controlled polymers is presented, enabling selection of both the most appropriate mediating agent and reaction conditions. In combination with experimental analysis, advanced kinetic Monte Carlo simulations are conducted, allowing a visualization of the connectivity of all monomer units of ca. 105 individual copolymer chains. The product quality can therefore be uniquely and unambiguously predicted for the first time at the molecular level, explicitly accounting for chain-to-chain deviations. The strategy is illustrated for BlocBuilder MA-initiated nitroxide-mediated polymerization, with styrene and N-benzylmaleimide as comomomers, and is generally applicable for all reversible deactivation radical polymerization (RDRP) techniques. Further design of the nitroxide-mediating capabilities and the reaction conditions allows the realization of a targeted (multi)functionalization pattern, including an increase of the contribution of trifunctionalized chains above 75%. The reported results are interpreted in terms of the individual activation-growth-deactivation cycles and provide an unprecedented mechanistic understanding of RDRP in general. [ABSTRACT FROM AUTHOR]

The synthesis of poly(vinyl chloride) (PVC) by nitroxide-mediated polymerization (NMP) using the SG1-based BlocBuilder alkoxyamine at low temperature (30 and 42 °C) is reported. The reaction system was studied regarding the nature of the solvent, the monomer-to-solvent ratio, the polymerization temperature, and the target molecular weight. First-order kinetics and linear evolutions of the molecular weight with vinyl chloride (VC) conversion were obtained in dichloromethane (DCM) and dimethyl sulfoxide (DMSO) together with decreasing dispersities (Đ) down to 1.59-1.47. The resulting PVC was fully characterized by ¹H nuclear magnetic resonance spectroscopy (¹H NMR), 31P NMR, and size exclusion chromatography (SEC). The ¹H NMR and 31P NMR revealed the existence of very small content of structural defects and the presence of chain-end functional groups (~91% SG1 chain-end functionality). Chain extension experiments were performed with VC, methyl methacrylate (MMA), and a mixture of monomers (90% of MMA and 10% of styrene (S)) and confirmed the "livingness" of the PVC-SG1 macroinitiators, giving access to different PVC-based block copolymers. High level ab initio molecular orbital calculations suggested that the C-O bond in the PVC-SG1 alkoxyamine is too strong to mediate the NMP of VC by simple "classic" activation-deactivation equilibrium and is possibly being mediated by a SG1-mediated dehydrochlorination mechanism. The results presented in this study established a new route to afford a wide range of new complex macrostructures based on PVC segments. [ABSTRACT FROM AUTHOR]

A seriesof styrenic triarylamines bearing electron-withdrawingor electron-donating substituents were synthesized and readily polymerizedby nitroxide-mediated polymerization (NMP). The utility of the homopolymersas macroinitiators for the preparation of defined block copolymersis demonstrated. All redox-active polymers were characterized in detailby NMR, MS, and SEC measurements; in addition, their electrochemicalproperties were studied. The homopolymers undergo reversible oxidation,whereby the redox potential is modulated by the substitution pattern.In the case of the copolymers, the sequential oxidation of the individualblocks is observed and corroborated by (spectro)electrochemical measurements.The ratio of transferred charges per redox-active block agreed withthe stoichiometric composition, as readily quantified by the semi-integralanalysis of the electrochemical data. In addition, redox-titrationexperiments revealed effective electron transfer between the redox-activepolymers following the order of their redox potentials. These resultsdemonstrate the potential to achieve directional charge transfer inhierarchically defined block copolymers. [ABSTRACT FROM AUTHOR]

We report the first nitroxide-mediatedsynthesis of multipod-likesilica/polymer latexes by polymerization-induced self-assembly (PISA)of amphiphilic block copolymers in aqueous emulsion. A water-solublebrush-type PEO-based macroalkoxyamine initiator composed of poly(ethyleneoxide) methacrylate and a small amount of styrene (P[(PEOMA950)12-co-S1]-SG1, Mn= 11 700 g mol–1and Mw/Mn= 1.11) wassynthesized and physically adsorbed on the surface of silica particlesthrough hydrogen-bonding interactions. The adsorbed macroalkoxyamineinitiator was subsequently employed to initiate the emulsion polymerizationof n-butyl methacrylate with a small amount of styreneunder mild conditions (85 °C). Kinetic analysis indicates thatthe polymerizations exhibit the same behavior (i.e., the same reactionrates and the same level of control) as those reported in our previouswork in the absence of silica under otherwise similar experimentalconditions [QiaoMacromolecules2013, 46, 4285−4295]. This observation is fully consistent witha PISA process taking place at the silica surface. The resulting self-assembledblock copolymers formed polymer nodules randomly distributed aroundthe central silica spheres. Varying the macroinitiator concentrationor the silica particle size enabled the successful formation of hybridparticles with dumbbell-, daisy-, or raspberry-like morphologies usingthis new surface-PISA process. [ABSTRACT FROM AUTHOR]

Random copolymers of isoprene and4-vinylbenzyl chloride (VBCl)with varying compositions were synthesized via nitroxide-mediatedpolymerization. Subsequent quaternization afforded solvent processableand cross-linkable ionomers with a wide range of ion exchange capacities(IECs). Solution cast membranes were thermally cross-linked to formanion exchange membranes. Cross-linking was achieved by taking advantageof the unsaturations on the polyisoprene backbone, without added cross-linkers.A strong correlation was found between water uptake and ion conductivityof the membranes: conductivities of the membranes with IECs beyonda critical value were found to be constant related to their high waterabsorption. Environmentally controlled small-angle X-ray scatteringexperiments revealed a correlation between the average distance betweenionic clusters and the ion conductivity, indicating that a well-connectednetwork of ion clusters is necessary for efficient ion conductionand high ion conductivity. [ABSTRACT FROM AUTHOR]

Nitroxide-mediated polymerization(NMP) of 2-(diethylamino)ethylmethacrylate (DEAEMA) with a small amount of acrylonitrile (AN) asa comonomer was performed for the first time in water at 90 °Cand atmospheric pressure using n-hydroxysuccinimidylBlocBuilder (NHS-BB) alkoxyamine without addition of excess nitroxide.The same reaction was carried out using the bicomponent initiatingsystem composed of 2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride(VA-044) as initiator and N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl)nitroxide (SG1) as nitroxide. Both polymerization reactions were well-controlledand exhibited excellent livingness as evidenced by low molar dispersityand evolution of the molar mass distribution. The hydrolytic stabilityof DEAEMA at the polymerization conditions and the effects of severalparameters including initiating system, temperature, ratio of nitroxideto initiator, initiator and monomer concentrations, and comonomertype were investigated. Chain extension of the synthesized macroinitiatorwith methyl methacrylate (MMA) and styrene (S) in a one-pot processled to the in situformation of poly(DEAEMA-co-S)-b-poly(MMA-co-S)diblock copolymers based on the polymerization-induced self-assembly(PISA) process. [ABSTRACT FROM AUTHOR]

The thermal degradable poly(alkoxyamine)was synthesized througha novel nitroxide radical coupling step growth polymerization (NRC-SGP)mechanism. The monomers of 1,4-phenylene bis(2-bromo-2-methylpropanoate)(monomer 1) and 1,4-phenylene bis(2-bromopropanoate)(monomer 1′) with two bromide groups and 1,6-di(4-(2,2,6,6-tetramethylpiperidine-1-oxyl))-hexa-2,4-diyne(monomer 2) with two nitroxide radicals were first designedand synthesized. Then the NRC-SGP mechanism was investigated in detailby optimizing the factors such as polymerization time, temperature,solvents, catalysts, ligand, monomer concentration, and structuresconnected to halogen groups. The results showed that the terminationby disproportionation was the major side reaction in the NRC-SGP mechanism,and the lower temperature (25 °C) would favor an important contribution.The proper combination of all factors could lead to an ideal NRC-SGPprocedure. Finally, the thermal stability of formed poly(alkoxyamine)was monitored by TG, DSC and SEC instruments, and the results showedthat the poly(alkoxyamine) would suffer a severe thermal degradationat the elevated temperature above 140 °C. [ABSTRACT FROM AUTHOR]

Amphiphilic block copolymers basedon azido-functional polystyrene(PVBA) and hydrophilic poly(ethylene oxide) (PEO) have been synthesizedby nitroxide mediated polymerization and used to prepare aqueous sphericalmicelles. These micelles consisting of a PEO corona and a PVBA corewere stabilized by cores cross-linking under UV irradiation withoutaddition of photoreagent. The efficiency of the core cross-linkingwas estimated in term of the conversion of azide groups to dibenzyldiazenejunctions with liberation of gaseous nitrogen molecules. The micellarstructures were studied by dynamic light scattering (DLS) and atomicforce microscopy (AFM). Differential scanning calorimetry (DSC) wasused to characterize the thermal behavior of freeze-dried micelles.Attachment of PEO block to a rigid core modified considerably thethermal behavior of PEO. We observed a decrease of about 15 °Cfor the crystallization temperature and 50% for the degree of crystallinityof cross-linked micelles submitted to 45 min UV irradiation comparedto pristine copolymer. [ABSTRACT FROM AUTHOR]

End-brominated poly(methyl methacrylate)(PMMABr) was preparedby atom transfer radical polymerization (ATRP) and employed in a seriesof atom transfer radical coupling (ATRC) and radical trap-assistedATRC (RTA–ATRC) reactions. When coupling reactions were performedin the absence of a nitroso radical traptraditional ATRC conditionverylittle coupling of the PMMA chains was observed, consistent with disproportionationas the major termination pathway for two PMMA chain-end radicals inour reactions. When 2-methyl-2-nitrosopropane (MNP) was used as theradical trap, coupling of the PMMA chains in this attempted RTA–ATRCreaction was again unsuccessful, owing to capping of the PMMA chainswith a bulky nitroxide and preventing further coupling. Analogousreactions performed using nitrosobenzene (NBz) as the radical trapshowed significant dimerization, as observed by gel permeation chromatography(GPC) by a shift in the apparent molecular weight compared to thePMMABr precursors. The extent of coupling was found to depend on theconcentrion of NBz compared to the PMMABr chain ends, as well as thetemperature and time of the coupling reaction. To a lesser extent,the concentrations of copper(I) bromide (CuBr), nitrogen ligand (N,N,N′,N′,N″-pentamethyldiethylenetriamine= PMDETA), and elemental copper (Cu) were also found to play a rolein the success of the RTA–ATRC reaction. The highest levelsof dimerization were observed when the coupling reaction was carriedout at 80 °C for 0.5h, with ratio of 1:4:2.5:8:1 equiv of NBz:CuBr:Cu:PMDETA:PMMABr. [ABSTRACT FROM AUTHOR]

Sequence-controlled semicrystallinecopolymers were prepared bynitroxide-mediated copolymerization of a large excess of octadecylstyrenewith small amounts of functional N-substituted maleimides (i.e., N-(n-propyl)maleimide, N-benzylmaleimide, pentafluorophenyl4-maleimidobenzoate, 4-(N-maleimido)azobenzene, N-(1-pyrenyl)maleimide, and N-(2-(amino-BOC)ethylene)maleimide).These copolymers were prepared in bulk at 110 °C using the commercialalkoxyamine BlocBuilder MA as initiator and control agent. Time-controlledadditions protocols were used to place the N-substituted maleimidesat precise chain location along the poly(octadecylstyrene) backbones.Size exclusion chromatography and 1H NMR studies indicatedthat well-defined copolymers with controlled monomer sequences, composition,chain length, and molecular weight distribution were formed in allcases. Although possessing an atactic backbone, these polymers exhibita semicrystalline behavior. The electron diffraction method indicatedthat the octadecyl side chains form lamellar phases. Moreover, differentialscanning calorimetry studies evidenced a melting temperature in therange 40–45 °C and a crystallization temperature around30–35 °C. It was observed that melting is influenced bythe composition and sequence distribution of the copolymers. Thus,small microstructural variations allow a precise control over order–disordertransitions. [ABSTRACT FROM AUTHOR]

Well-defined water-soluble brush-typehomopolymers and copolymersentirely composed of poly(ethylene)oxide methacrylate (PEOMA) unitswith PEO side groups of various chain lengths (Mn= 300 and 950 g mol–1) were synthesizedby nitroxide-mediated polymerization (NMP) using a low molar massunimolecular alkoxyamine initiator (so-called BlocBuilder) and N-tert-butyl-N-(1-diethylphosphono-2,2-dimethyl propyl) nitroxide (SG1) in the presence ofa small amount of styrene. The resulting SG1-capped macroalkoxyaminespossessed the predicted molar masses based on the monomer/initiatormolar ratio and narrow molar mass distributions. They were then employedto initiate the emulsion polymerization of n-butylmethacrylate with a low amount of styrene under mild conditions (85°C) leading to amphiphilic block copolymers that in situself-assembled into sterically stabilized particles. Kinetics studyconfirmed the living character of the polymerization, while SEC analysisindicated the presence of a small fraction of dead chains formed byirreversible homotermination reactions. Spherical latex particleswith diameters comprised between 60 and 300 nm were obtained at pH4.2 when decreasing the macroinitiator concentration from 7.2 to 1.2mM in agreement with the in situformation of blockcopolymers. As expected, only the macroinitiators with long PEO sidegroups, and whose cloud points were above the reaction temperature,led to stable latex suspensions. A drastic change in particle morphologywith the formation of vesicles and anisotropic objects was observedwhen increasing the suspension pH from 4.2 to 6.7. As the macroalkoxyamineinitiator contained only one terminal methacrylic acid unit, sucha strong effect of pH on particles morphology was not expected. Theobserved results were interpreted in terms of a salting out effectinduced by the concomitant increase of ionic strength upon neutralizationof the alkoxyamine initiator. Hence, particle morphologies could betuned from spherical to elongated micelles and vesicles by the additionof increasing amounts of sodium chloride at a fixed pH of 4.2, whichconfirmed the above hypothesis. [ABSTRACT FROM AUTHOR]

Macromonomers are synthesized fromthermal reactivation of threedifferent precursors, Poly(n-butyl acrylate) P(nBuA), Poly(tert-butyl acrylate) P(tBuA), and Poly(2-ethylhexyl acrylate) P(EHA), synthesizedvia nitroxide mediated polymerization (NMP). Reactivation of the polymerchains is carried out at 140 °C, whereby the polyacrylate macroradicalsundergo chain transfer reactions forming midchain radicals, MCR, followedby β-scission reactions leading to unsaturated macromonomers.Soft-ionization mass spectrometry of product samples reveals thatin all cases predominantly macromonomers that carry a hydrogen endgroup on the other chain end are formed, which is also accompaniedby small reductions in molecular weight (−200 g·mol–1) and slight increases in polydispersity (+0.2). Furthermore,we demonstrate that macromonomers under these reaction conditionsare not only formed through simple backbiting/β-scission viasix-membered ring transition structures but also that complex addition–fragmentationequilibria must play a considerable role. As observed before for macromonomersmade from activation of atom transfer radical polymerization (ATRP)-madeprecursors, a size-selective reaction pathway is observed that favorsthe generation of macromonomers with only odd numbers of monomer unitson the backbone, supporting an MCR migration mechanism, which allowsMCRs to move along the backbone. [ABSTRACT FROM AUTHOR]

A novel synthetic route toward poly(4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl) (PTMA) is described. The polymerization of alkoxyamine-basedmonomers by atom transfer radical polymerization (ATRP) was investigated,as the polyalkoxyamine serves as the precursor for PTMA. The polydispersityindices (PDIs) and the kinetic data of the polymerization indicatea controlled reaction. The oxidative C–O bond cleavages ofthe polyalkoxyamine lead to PTMA. This transformation occurs withexcellent yields, and it is possible to transfer the narrow PDIs ofthe prepolymer to PTMA. The material is characterized in detail usingcyclic voltammetry in solution and magnetic susceptibility measurementsas well as multinuclear solid state NMR and EPR spectroscopies. Theconversion of the precursor polymer to the polynitroxide can be convenientlymonitored by 1H and 19F magic-angle spinning(MAS) as well as 13C{1H} cross-polarization(CP)-MAS NMR. In addition, the intermolecular interaction of the nitroxideside chain units in the polymer at high conversion can be detectedand monitored by the observation of pronounced low-frequency shifts. [ABSTRACT FROM AUTHOR]

Poly(l-glutamic acid) (PLGA)derivatives PTPALG and PTPOLG,which contain 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radicalslinked to PLGA via amide and ester bonds, respectively, were synthesizedby the dehydration-condensation reaction. The main chains of bothPTPALG and PTPOLG were found to adopt the right-handed α-helicalconformation, and accordingly, the terminal side-chain nitroxide radicalsadopted the spiral configuration synchronized with the helical conformationof the main chain. Polarized microscopy observations reveal that PTPALGexhibited the lyotropic liquid crystalline (LC) phase at greater than7.5 wt % concentration in chlorinated solvents, whereas PTPOLG keptthe anisotropic liquid phase at up to 10 wt % concentration. Fromthe analysis of superconducting quantum interference device (SQUID)magnetometer and electron spin resonance (ESR) data, the magneticproperties of PTPALG and PTPOLG appeared to result from interchainspin–spin interactions between nitroxide•radicals rather than intrachain interactions. Interestingly, observationof the double quantum |Δms| = 2line in a half-field region (g= 4.015) in the caseof PTPALG revealed the doublet (S= 1/2) to triplet (S= 1) state conversion ataround 6 K, exhibiting to be shifted the critical temperature in thesample evaporated the solvents from the LC phase. In contrast, PTPOLGretained its paramagnetic properties in the temperature range 4–200K. [ABSTRACT FROM AUTHOR]

Attachment of poly(ethylene glycol) (PEG) to polymericnanostructuresis a general strategy for sterically shielding and imparting watersolubility to hydrophobic payloads. In this report, we describe directgraft-through polymerization of branched, multifunctional macromonomersthat possess a PEG domain and a hydrophobic nitroxide domain. Electronparamagnetic resonance (EPR) spectroscopy was used to characterizemicroenvironments within these novel nanostructures. Comparisons weremade to nitroxide-labeled, traditional bottle-brush random and blockcopolymers. Our results demonstrate that bivalent bottle-brush polymershave greater microstructural homogeneity compared to random copolymersof similar composition. Furthermore, we found that compared to a traditionalbrush polymer, the branched-brush, “pseudo-alternating”microstructure provided more rotational freedom to core-bound nitroxides,and greater steric shielding from external reagents. The results willimpact further development of multivalent bottle-brush materials asnanoscaffolds for biological applications. [ABSTRACT FROM AUTHOR]

The confined space effect, which was found by the authors,in nitroxide-mediated radical polymerization (NMP) in a microemulsionsystem (microemulsion NMP) of n-butyl acrylate (BA)was investigated, where the diameter of micelles (monomer droplets)was 5–10 nm and that of poly(BA) (PBA) particles at the completionof the polymerization was ∼60 nm. To clarify the importanceof diameter of monomer droplets (dm) inthe initial stage of the microemulsion NMP, NMP in a miniemulsionsystem (miniemulsion NMP) (dm: ∼60nm) was carried out as a comparative experiment. The miniemulsionNMP proceeded without molecular weight distribution (MWD) control;on the other hand, in the microemulsion NMP the MWD shifted to highermolecular weight with increasing conversion. The livingnesses of PBAsobtained in the initial stages of the miniemulsion and microemulsionNMPs, which were determined by chain extension test, were 0.01% and64%, respectively. From these results, it is concluded that the confinedspace effect in the initial stage of the microemulsion NMP effectivelyoperated and resulted in PBA with predetermined molecular weight andgood control of MWD even if the diameter of polymerizing particlesincreased with conversion. [ABSTRACT FROM AUTHOR]

We present a study of the initiation step in copper(0)-mediatedatom transfer radical polymerization (also known as SET-LRP or SARAATRP), in which a nitroxide free radical, N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)] nitroxide (SG1),is used to trap radicals derived from ethyl 2-bromoisobutyrate (EBiB),copper metal and pentamethyl diethylene triamine (PMDETA) ligand.A kinetic model was developed relating the rate of conversion of EBiBto the rate constants of activation by copper metal (ka0) and comproportionation of Cu0and CuII(kcomp). This allowed the determinationof these parameters in several solvents, including dimethyl sulfoxide(DMSO), dimethylformamide (DMF), ethanol (EtOH), and acetonitrile(MeCN), in which significant levels of comproportionation were observed,leading to autoacceleration of the reaction. A similar treatment ofcopper-mediated polymerization kinetics predicts 1/2 order dependenceon initiator concentration and copper surface area, in accordancewith previously published experimental data. [ABSTRACT FROM AUTHOR]

The impact of formation of midchain radicalsandmore specificallythe follow up reactions of β-scission and macromonomer additionto propagating macroradicals stemming from this processonthe nitroxide-mediated polymerization of acrylates have been studiedvia kinetic modeling with the software package Predici on the exampleof butyl acrylate polymerization at 120 °C. Only small influencesof the midchain radical formation on the livingness of the processis observed, however, large effects must be envisaged by the (reverse)scission reaction at high monomer-to-polymer conversions. A significantloss of livingness, depending on the temperature, monomer and initiatorconcentration must be expected at elevated stages of polymerizations.For a polymerization at 120 °C and a target chain length of 100,less than 75% livingness of the polymer product can be expected at80% conversion. From this point of polymerization on, significantbroadening of the overall polymer product is predicted in accordanceto literature data and eventually the chain-length–conversionrelation is lost at the end of reaction. [ABSTRACT FROM AUTHOR]

We use a combination of click chemistry and nitroxide-mediatedradical polymerization (NMRP) for the incorporation of high molecularweight poly(3-hexylthiophenes) (P3HTs) segments into amphiphilic blockcopolymers. First, a high molecular weight alkyne-terminated P3HTwas synthesized using Kumada catalyst transfer polymerization followedby in-situ end-capping with alkyne and by quenching with methanol.We found out that hydrochloric acid, the best quenching agent fornonfunctionalized P3HTs, leads to addition reactions with the alkynegroup and therefore is not suitable for alkyne-terminated P3HT. Withthe use of copper-catalyzed azide–alkyne click reaction, P3HT-alkoxyamineis formed as a macroinitiator for NMRP. This was used to polymerize4-vinylpyridine to get amphiphilic rod–coil P3HT-b-P4VP block copolymers with 55 and 77 wt % of poly(4-vinylpyridine)(P4VP). We investigate how the optical and thermal properties as wellas the phase separation behavior depend on the block ratios. TheseP3HT-b-P4VP copolymers are interesting for hybridorganic photovoltaics as well as for studying the colloidal structuresof semiconductor amphiphilic systems. The high molecular weight rodinfluences the rod–rod interaction as described by the Maier–Saupeparameter μ and therefore has consequences in the microphaseseparation. [ABSTRACT FROM AUTHOR]

9-(4-Vinylbenzyl)-9H-carbazole (VBK)was used as the “controlling” comonomer for nitroxidemediated polymerization with 10 mol % SG1 free nitroxide relativeto BlocBuilder initiator at 80 °C of oligo(ethylene glycol) methylether methacrylate (8–9 ethylene glycol (EG) units) (OEGMA8–9), 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and for an OEGMA8–9/MEO2MA-mixedfeed. The synthesis of MEO2MA/VBK and OEGMA8–9/VBK copolymers and MEO2MA/OEGMA8–9/VBKterpolymers exhibited linear increases in number-average molecularweight (M̅n) versus conversion X, up until X= 0.6, with final copolymerscharacterized 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 varyingthe OEGMA8–9:MEO2MA feed ratios, theterpolymers exhibited tunable lower critical solution temperaturesin water (28 °C < LCSTs< 81 °C).MEO2MA/OEGMA8–9/VBK terpolymers weredeemed sufficiently pseudo-“living” to reinitiate asecond batch of MEO2MA/OEGMA8–9/VBK,with few apparent dead chains, as indicated by the monomodal shiftin the GPC chromatograms. The resulting MEO2MA/OEGMA8–9/VBK block copolymers were designed so that eachblock exhibited a distinct LCST, which was confirmed by UV–visand dynamic light scattering. In addition to controlling the terpolymerization,the VBK units imparted thermo-responsive fluorescence into the finalcopolymers. [ABSTRACT FROM AUTHOR]

Nitroxide-mediated polymerization of isoprene was carried out at 115 °C using a small library of SG1-based alkoxyamine initiators. Well-defined polymers were obtained, with no need to add free SG1. Efficient postfunctionalization reactions in α- (reaction of ethylene diamine with a succinimidyl-ester-functional initiator) and ω-positions (replacement of SG1 by benzyl trithiocarbonate) were demonstrated. Polymerizations mediated by alkoxyamines with tertiary initiating groups were observed to follow first order kinetics with respect to monomer, with number-average molecular weights (Mn) approximately 77% of theoretical Mn(Mn,theo). Use of alkoxyamines with primary and secondary initiating groups gave 2/3 order kinetics with respect to monomer and slightly lower molecular weights (Mn,exp∼ 0.61 × Mn,theo). At higher conversions, the polydispersity of all polyisoprenes approached 1.1. At low conversions, however, significant differences in polydispersity were observed, indicating differences in the rate of consumption of the initiators. Significantly, the alkoxyamines with propionic acid and isobutyric acid initiating groups were consumed substantially more slowly than their ester analogues or even cyanomethyl-SG1. This may be a result of intramolecular hydrogen bonding between the acid and phosphonate groups of the initiators. [ABSTRACT FROM AUTHOR]

Controlled/living radical polymerization is an efficient technique for the synthesis of well-defined polymeric architectures, including copolymers, block copolymers, stars, graft, and variations thereof. In this article, we report for the first time the synthesis of a decablock copolymer via a simple and efficient iterative Cu(0)-mediated radical polymerization technique. In this approach, purification is not required between the iterative chain extension steps, as each block formation is taken to full conversion. The final decablock copolymer can be obtained with a yield in mass of ∼90%. Using traditional controlled/living radical polymerization techniques, including reversible addition–fragmentation chain transfer (RAFT) polymerization, nitroxide-mediated polymerization (NMP), or atom transfer radical polymerization (ATRP), synthesis of decablock copolymer in such high yield is very difficult (and may be impossible) and requires numerous purification steps. The synthesis of the final complex copolymers required the concomitant synthesis of 16 architecturally discrete block copolymers. [ABSTRACT FROM AUTHOR]

This paper presents results on the independence of the rate of polymerization of n-butyl acrylate (n-BA) toward initial concentration of the alkoxyamine initiator. The alkoxyamine, 2-methyl-2-[N-tert-butyl-N-(1-diethoxyphosphoryl-2,2-dimethylpropyl)aminooxy]propionic acid (MAMA-DEPN), was used to initiate and mediate the polymerization of n-BA in the temperature range 90–120 °C. In situ1H NMR spectroscopy was used to follow the consumption of the monomer and monitor other related reactions. Intra- and intermolecular chain transfer processes are well-known phenomena in the polymerization of n-BA that result in the transformation of secondary propagating radicals (SPRs) into tertiary midchain radicals (MCRs). At high polymerization temperature (T≥ 110 °C), the MCRs undergo β-fragmentation. The concentrations of the products of the β-fragmentation process (in the form of chains bearing 1,1-disubstituted alkene end group) were measured as a function of polymerization time. The independence of rate of polymerization of n-BA initiated by MAMA-DEPN can be explained in terms of thermal autoinitiation in the case where free [DEPN]0is no larger than 1 mol % relative to [MAMA-DEPN]0. [ABSTRACT FROM AUTHOR]

The combination of in situ1H NMR and in situ31P NMR was used to study the nitroxide mediated copolymerization of styrene and n-butyl acrylate. The alkoxyamine MAMA-DEPN was employed to initiate and mediate the copolymerization. The nature of the ultimate/terminal monomer units of dormant polymer chains were identifiedand quantified by in situ31P NMR. Simulations of the styrene and n-butyl acrylate copolymerization mediated by DEPN were investigated using the Predici software package. The rate coefficients of reversible deactivation of chains with n-butyl acrylate as the terminal unit were estimated via parameter estimation studies using Predici. Good correlations were obtained between experimental data and simulated data. [ABSTRACT FROM AUTHOR]

Nitroxide-mediated radical polymerization (NMP) in microemulsion (microemulsion NMP) of n-butyl acrylate (BA) has been carried out at 100°C using N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide (SG1), 2,2′-azoisobutyronitrile (AIBN), and the cationic emulsifier tetradecyltrimethylammonium bromide (TTAB). At [SG1]0/[AIBN]0of 1.68 (molar ratio), the polymerization exhibited classical trend marks of a controlled/living system with the molecular weight distribution (MWD) shifting to higher molecular weights with increasing conversion and a linear increase in number-average molecular weight (Mn) vs conversion. Bulk NMP carried out under the same conditions (without water and TTAB) proceeded at an extremely high rate without control/livingness. From these results, it is concluded that the confined space effect (compartmentalization) operates in the microemulsion NMP; in other words, it is a useful tool to prepare nanosized monomer-solubilized micelles for regulation and improvement of NMP. [ABSTRACT FROM AUTHOR]

The SG1-mediated copolymerization of methacrylic acid and a small percentage of sodium 4-styrenesulfonate was performed in water solution at 76 °C, using BlocBuilder as an alkoxyamine initiator under acidic conditions. Unexpectedly, these conditions, which could be considered as rather unfavorable due to the instability of SG1 in acidic water, led to very good results in term of polymerization kinetics and control over polymer chain growth. It appeared that low temperature and short reaction time were the key parameters to maintain a good living character to the chains as evaluated by in situ 31P NMR. The aqueous system was then used directly as the polymerization medium for the emulsion copolymerization of methyl methacrylate and styrene performed at 90 °C. This one-pot procedure led to the synthesis of amphiphilic block copolymers that self-assembled into stable core–shell nanoparticles. [ABSTRACT FROM AUTHOR]

Controlling the rates of orthogonal “click” reactions in one-pot provides a method for designing highly branched macromolecular architectures. In this work, we constructed third generation (G3) dendrimers consisting of a wide range of chemically different polymer building blocks in one pot at 25 °C. This approach reduced the number of purification and chemical protection steps. Using the model polystyrene (PSTY) building block system, third generation dendrimers could be formed divergently, convergently or in parallel through modulating the Cu(I) activity for the copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) and nitroxide radical coupling (NRC) reactions. The parallel approach was the fastest, generating a G3 dendrimer in under 30 min, and the next fastest was the divergent pathway, followed by the very slow (24 h) convergent pathway. The resulting G3 dendrimer could be cleaved at the alkoxyamine sites back to linear polymers by heating the reaction mixture at 120 °C in the presence of an excess hydroxyl nitroxide. The synthetic utility of this method was further extended to coupling linear telechelic polymer building blocks, consisting of PSTY, PtBA, PEG, and PNIPAM, to form a range of dendrimers in high yields. Preparative SEC was used to fractionate excess starting reactants and intermediate polymer species from the product dendrimer. [ABSTRACT FROM AUTHOR]

This work describes, for the first time, the nitroxide-mediated polymerization (NMP) of styrene initiated from an SG1-based alkoxyamine grafted on both the inner and outer surfaces of ordered mesoporous silica (OMS) particles. The OMS particles with various morphologies were synthesized by sol−gel chemistry in the presence of a surfactant template. The initiator derived from the BlocBuilder alkoxyamine was covalently grafted via a dimethylethoxysilane functional group. The polymerizations were conducted in the presence of a free alkoxyamine with chemical structure similar to that of the grafted one. The monomer conversion was monitored by 1H NMR analysis and the concentration of released nitroxide could be calculated, providing an estimation of the fraction of dead chains. The weight fraction of grafted polymer and the molar mass distributions of the free and grafted chains were determined. From this information, an effect of the OMS particle structure on the outcome of the polymerization could be evaluated. [ABSTRACT FROM AUTHOR]

The application of a sterically hindered alkoxyamine initiator for the nitroxide-mediated copolymerization (NMP) of methyl methacrylate (MMA) and styrene is presented. Working under the assumption that addition of a styrene monomer as the last embedded monomer of each dormant nitroxide-terminated copolymer will bypass the β-H-transfer (disproportionation, hydroxylamine elimination) that leads to termination of the living polymerization as observed for MMA polymerization, we successfully developed a method for the sequence analysis of oligomers by applying ESI mass spectrometry by using an orbitrap. With this method we were able to analyze chain end composition. To learn about the mass spectrometry fragmentation behavior of these nitroxide-terminated copolymers, we first analyzed different homo-oligomers and then went on with examples of co-oligomers. Oligomers consisting of styrene, n-butyl acrylate, and N-isobutylacrylamide (NIPAM), copolymers prepared from MMA and styrene, and alternating co-oligomers prepared from maleic acid anhydride and styrene were investigated. With the premise that oligomers containing 5−10 monomers are representative models for high molecular weight polymers, we could prove the validity of the assumptions made above. [ABSTRACT FROM AUTHOR]

We report the first nitroxide-mediated microemulsion polymerization of methyl methacrylate-co-styrene as well as the synthesis of (MMA-co-St)-block-(n-BMA-co-St) polymers using a one-pot, two-stage differential monomer addition technique. These microemulsion polymerizations were conducted with commercially available materials and do not require a preliminary synthesis step. The latexes are optically translucent with monomodal particle size distributions, mean particle diameters ranging from 20 to 30 nm, low surfactant-to-monomer ratios (0.13−0.28 w/w), and solids contents up to 40 wt %. The polymerizations exhibited fast reaction rates, resulting in well-controlled reactions yielding high molecular weight polymer (>100 000 g mol−1). The styrene content and duration of the first stage were particularly important for obtaining narrow molecular weight distributions, with 30 mol % styrene in the first stage (∼8−10 mol % styrene overall in the polymer), resulting in the best controlled polymerizations. The overall styrene content in the latexes can be as low as 8 mol % while maintaining excellent control. The MMA-co-St microemulsion latexes can readily be chain extended with n-BMA-co-St while preserving monomodal particle size distributions. [ABSTRACT FROM AUTHOR]

Well-defined poly(N,N-diethylacrylamide)s were synthesized for the first time by nitroxide-mediated polymerization. The polymerizations were first performed in toluene solution, using BlocBuilder, a tertiary alkoxyamine based on the nitroxide SG1 (N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)] nitroxide), as an initiator without initial free nitroxide. High monomer conversions were reached, up to completion and the number-average molar masses increased linearly with conversion. However the polydispersity indices (PDI) remained quite high, despite a constant diminution with increasing conversion until a value of 1.9 at high conversion. This could be corrected by the addition of free SG1 at the onset of the reaction, leading to PDI of 1.2 at 93% conversion in the best case. Various alkoxyamine concentrations were used to target different molar masses. The presence of SG1 functionality at the ω-end of the polymer chains was evidenced by size-exclusion chromatography coupled to electospray ionization mass spectrometry (SEC/ESI−MS) and the living character of the latter was proved by efficient chain extension with styrene or N,N-dimethylacrylamide. [ABSTRACT FROM AUTHOR]

An ionic liquid, 1-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide ([C1C4Im]NTf2) was used as the polymerization medium for the SG1-mediated free-radical solution copolymerization of methyl methacrylate with a low percentage of styrene, initiated by the BlocBuilder alkoxyamine at 90 °C. Control over the polymer molar mass and molar mass distribution was good, slightly better than that obtained in bulk or classical organic solvent solutions for the same system. Compared to the results of nitroxide-mediated polymerizations in ionic liquids previously reported in the literature, the quality of control was significantly better. It seems that the ionic liquid did not influence the activation−deactivation mechanism but played a role on the polymerization kinetics only. Indeed, the overall polymerization rate was found to be larger and the final conversion higher, in good agreement with the increase of kpand the decrease of kt, which are key features of free-radical polymerization in ionic liquids. [ABSTRACT FROM AUTHOR]

Heterophasic propylene-ethylene copolymers (HPECs), also known as impact-modified polypropylene copolymers (IPC), are an important class of materials because of their attractive mechanical properties and low cost. Their chemical composition and phase heterogeneity have important effects on the physical and mechanical properties of these systems. Commercially used HPECs usually contain stabilizers such as hindered amines, which can be lost by diffusion (blooming). We present the measurement of the diffusion coefficient of nitroxide radicals by electron spin resonance imaging (ESRI); the radicals were obtained by oxidation of the commercial Tinuvin 770 hindered amine stabilizer (HAS) with m-chloroperoxybenzoic acid and consist of a mixture of mono- and biradicals. The diffusion rates were measured in two polymers, HPEC1 and HPEC2, which differed in the ethylene (E) to propylene (P) ratio, 25:75 and 10:90 wt %, respectively. One dimensional (1D) ESRI allowed the visualization of the radical distribution (“profiles”) within the sample as a function of storing time at 393 K. Simulation of this distribution led to the determination of the macroscopic diffusion coefficients, D, of the paramagnetic tracer in HPEC1 and HPEC2. The results indicate that the main factor determining the diffusion rates in these polymers is the amount of the crystalline phase, mostly composed of isotactic polypropylene (iPP). The Dvalue was the same within experimental error in both systems, 1.42 × 10−8cm2s−1. Comparison with literature data of the temperature variation of Dfor the same diffusant in polyethylene (PE) and polypropylene (PP) suggest that in both HPEC1 and HPEC2 the diffusion takes place in the amorphous phase restrained by the proximity of the crystalline domains. The results also indicate that ≈20% of the diffusant is lost by evaporation (“blooming”). Results of spectral-spatial 2D ESRI show that the ESR spectra of the nitroxides do not change significantly along the sample length during diffusion, suggesting that the loss of stabilizer is due to diffusion and not to chemical reactions. [ABSTRACT FROM AUTHOR]

A novel approach to prepare cyclic polymers via a combination of atom transfer radical polymerization (ATRP) and atom transfer radical cross-coupling (ATRC) is presented. A functional ATRP initiator possessing an alkoxyamine group was synthesized and used to prepare well-defined linear telechelic α-nitroxy,ω-bromo homo- and block copolymers via ATRP and subsequent thermal deprotection of the α-terminal nitroxide function. Cyclization reactions were achieved by intramolecular ATRC under high dilution. Ring expansion of a cyclic polystyrene alkoxyamine prepared by ATRC was conducted via nitroxide-mediated polymerization (NMP) of styrene and yielded a mixture of linear and cyclic polycondensates. This result is discussed in detail and explained by the persistent radical effect (PRE), thermal initiation, and the occurrence of radical crossover reactions during chain extension via NMP. [ABSTRACT FROM AUTHOR]

The N-phenylalkoxyamine N-(1-methyl-(1-(4-nitrophenoxy)carbonyl)ethoxy)-N-(1-methyl-(1-(4-nitrophenoxy)carbonyl)ethyl)benzenamine (1) was prepared by the addition of 4-nitrophenyl 2-methylpropionat-2-yl radicals across the double bond of nitrosobenzene and evaluated as an initiator for nitroxide-mediated polymerization (NMP). N-Phenylalkoxyamines have not been extensively studied in NMP, though they have shown promise in controlling methyl methacrylate (MMA) polymerization to moderate conversions. It is thought that delocalization of the nitroxide radical through the N-phenyl substituent may minimize cross-disproportionation of the nitroxide with the chain end that has made NMP of MMA difficult. Here, we show that alkoxyamine 1is capable of controlling the NMP of MMA to 50% conversion while maintaining narrow molecular weight distributions (Mw/Mn= 1.12−1.30). Additionally, chain extension from the resulting PMMA macroinitiators with MMA or styrene allows the formation of diblock copolymers. The corresponding N-tert-butylalkoxyamine, 2,2-dimethyl-3-(1-methyl-(1-(4-nitrophenoxy)carbonyl)ethoxy)-4-methyl-(4-(4-nitrophenoxy)carbonyl)ethyl-3-azapentane (2), was synthesized by the addition of 4-nitrophenyl 2-methylpropionat-2-yl radicals across the double bond of 2-methyl-2-nitrosopropane. Polymerization of MMA with alkoxyamine 2was uncontrolled, which suggests the paramount importance of the N-phenyl group for MMA polymerizations. [ABSTRACT FROM AUTHOR]

Controlled radical polymerizations (CRP) were pioneered in the late 1970s. Since then, tremendous investigations have been developed, especially from mid-1990s which generated much enthusiasm on CRP. However, the extraordinary scientific development of CRP contrasts with the limited number of commercially available products derived from these technologies. But, for fluoropolymers, the situation is different since iodine transfer polymerization of fluoroalkenes led to commercially available thermoplastic elastomers as soon as 1984. A browse or CRP of fluorinated monomers is presented and is classified into three families: (i) the CRP of fluorine-containing styrenic monomers mainly occur from nitroxide-mediated polymerization (NMP) or by atom radical transfer polymerization (ATRP); (ii) that of fluorinated (meth)acrylic monomers from NMP, ATRP, and in the presence of iniferters; and finally (iii) fluoroalkenes (which is a real challenge since these monomers are gaseous) can be (co)polymerized by iodine transfer polymerization or by processes that required either borinates or xanthates (MADIX). A peculiar interest lies in the CR copolymerization of fluoroalkenes with other comonomers (such as vinylidene fluoride, chlorotrifluoroethylene, 3,3,3-trifluoropropene, hexafluoropropylene, perfluoromethyl vinyl ether, or α-trifluoromethacrylic acid) in the presence of either xanthates, borinates, or iodo compounds. These technologies enable one to generate copolymers that exhibit well-defined architectures, such as telechelic, block, and graft copolymers. Merits and limitations of CRP of F-monomers are also reported. Finally, this Perspective is illustrated by several properties and applications of these fluorinated copolymers (such as surfactants, thermoplastic elastomers, fuel cell and ultrafiltration membranes, dielectrical polymers, optical storage devices, or polycondensates, the fluorinated segments of which bring softness and thermal stability). Hence, CRP can be regarded as a revolutionary method to produce precisely controlled, next-generation specialty fluorinated (co)polymers. [ABSTRACT FROM AUTHOR]

To maximize the theoretical redox capacity of polymers containing cyclic nitroxides as redox-active pendant groups for high-density charge storage application, a compact five-membered ring with the smallest equivalent weight among the robust cyclic nitroxides was directly bound to a poly(ethylene oxide) chain. 2,2,5,5-Tetramethyl-3-oxiranyl-3-pyrrolin-1-oxyl was synthesized and polymerized via anionic coordinated ring-opening polymerization utilizing diethyl zinc/H2O as an initiator. The unpaired electron in the monomer survived during the polymerization, giving rise to a high density redox polymer with a weight-specific theoretical capacity of 147 mA h/g. Cyclic voltammetry of the polymer layer confined at the surface of an electrode revealed a large redox capacity comparable to the theoretical capacity, which was ascribed to the efficient swelling and yet insoluble properties of the polyether in electrolyte solutions by virtue of the high molecular weight of >105and adhesive properties allowing immobilization of the layer on the electrode surface. The redox capacity also indicated that the ionophoric polyether matrix accommodated electrolyte anions through the polymer/electrolyte interface to neutralize positive charges produced by the oxidation of the neutral radicals at the polymer/electrode interface. The diffusion coefficient for the redox gradient-driven charge hopping process corresponded to a large second-order rate constant in the order of 107M−1s−1, which suggested an efficient electron self-exchange reaction throughout the polymer layer due to the large redox site population and hence to the small intersite distance. Test cells fabricated with a polymer/carbon fiber composite layer on an aluminum current collector as the cathode and a Li anode sandwiching an electrolyte layer were capable of charging and discharging as a secondary battery with an output voltage near 3.7 V and were durable for more than 103charging−discharging cycles without substantial degradation. [ABSTRACT FROM AUTHOR]

Nitroxide-mediated emulsion polymerization of n-butyl methacrylate (BMA) can produce highly living and well-controlled polymer chains when polymerized in the presence of 10 mol % styrene (St) using a one-pot, differential monomer addition technique. When n-BMA-co-St is polymerized in the presence of a surfactant above the critical micelle concentration, bimodal particle size distributions are obtained, likely as a result of combined micellar and aggregative nucleation mechanisms. This phenomenon is not observed for the more hydrophilic monomer system of methyl methacrylate and styrene. In the absence of surfactant, however, it is possible to prepare stable, monomodal latexes. Using N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide (SG1), we report the first nitroxide-mediated polymerization of n-butyl methacrylate with a small amount of styrene in a facile surfactant-free emulsion polymerization system. The surfactant-free system requires no separate macroinitiator synthesis step and produces highly living polymers with monomodal particle size distributions. The initiator efficiency can be increased by the addition of methyl acrylate or by the addition of surfactant at concentrations below the critical micelle concentration in the absence of methyl acrylate. [ABSTRACT FROM AUTHOR]

The synthesis of well-defined polymers with pendant perylene bisimide (PBI) groups by a combination of nitroxide-mediated radical polymerization (NMRP) of trimethylsilyl propargyl acrylate followed by copper-catalyzed azide−alkyne cycloaddition (CuAAC, “click” chemistry) is described. The kinetics of NMRP of trimethylsilyl propargyl acrylate polymerization was monitored by 1H NMR and size exclusion chromatography (SEC). Almost quantitative conversion in the “click” reaction with an azide functionalized PBI derivative was proven by FTIR and 1H NMR analysis. Thus, semiconductor polymers carrying PBI pendant groups with Mnup to 15800 g·mol−1and polydispersity indices as good as 1.16 were obtained by this route. These polymers were compared with poly(perylene bisimide acrylate)s, PPerAcr(CH2)11, and PPerAcr(CH2)6, which were synthesized by direct NMRP of PBI acrylates. These samples do not carry any triazol unit and they differ in their spacer length connecting the PBI unit to the main chain. All polymers were comparatively studied by SEC, thermogravimetry, differential scanning calorimetry, polarization microscopy, UV/vis spectroscopy, and photoluminescence measurements. The crystalline structure of the polymers was analyzed by X-ray diffraction. Inductively coupled plasma mass spectrometry analysis confirmed that copper content in the “click” polymer could be reduced down to 126 ppm (w/w). [ABSTRACT FROM AUTHOR]

We report in this article the synthesis of a series of mixed poly(tert-butyl acrylate) (PtBA)/polystyrene(PS) brushes with PtBA number-average molecular weight(Mn) being fixed at 24.5 kDa and PS Mnranging from 14.8 to 30.4 kDa on 160 nm silicaparticles and the study of their microphase separation behaviors usingdifferential scanning calorimetry (DSC) and transmission electronmicroscopy (TEM). The samples were synthesized by a two-step “graftingfrom” process from asymmetric difunctional initiator (Y-initiator)-functionalizedsilica particles using two different “living”/controlledradical polymerization techniques. PtBA brushes weregrown first from Y-initiator-functionalized particles by surface-initiatedatom transfer radical polymerization of tert-butylacrylate at 75 °C in the presence of a free initiator, followedby nitroxide-mediated radical polymerization (NMRP) of styrene at120 °C. The “living” nature of NMRP allowed thesynthesis of mixed PtBA/PS brushes with differentPS molecular weights (14.8, 18.7, 24.9, and 30.4 kDa) in a one-potpolymerization. DSC studies showed that all thermally annealed mixedbrush samples exhibited two glass transitions with the middle pointslocated at ∼47 and ∼90 °C, suggesting that thetwo tethered polymers microphase separated in the brush layer. ForTEM studies, the samples were dispersed in CHCl3, a goodsolvent for both PtBA and PS, drop-cast onto carbonfilms, thermally annealed in vacuum at 120 °C for 3 h, and thenstained with RuO4vapor. All samples showed clear microphaseseparation, consistent with the DSC results. With increasing PS Mnfrom 14.8, to 18.7, and 24.9 kDa, the morphologyof mixed brushes evolved from isolated, nearly spherical PS microdomainsburied inside the PtBA matrix, to short PS cylindricalmicrodomains in the PtBA matrix, and to nearly bicontinuousnanostructures. Further increasing the molecular weight of PS to 30.4kDa resulted in the formation of isolated PtBA microdomainswhich were covered by PS chains. [ABSTRACT FROM AUTHOR]

We report here a straightforward route to polymer−peptide conjugates via the convenient synthesis of SG1-functionalized peptides able to initiate nitroxide-mediated polymerization (NMP). The NMP initiator SG1-functionalized peptide (SG1-GGGWIKVAV) was prepared by solid-phase peptide synthesis (SPPS) using an automated synthesizer, with a last step consisting of reaction between the carboxylic acid function of the MAMA-SG1 (BlocBuilder) alkoxyamine with the peptide terminal amine in the presence of benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate (PyBOP) as coupling agent. The resulting SG1-functionalized resin-attached peptide was used to perform the controlled NMP of styrene, leading after trifluoroacetic acid cleavage to the corresponding polystyrene−peptide conjugate. The latter was thoroughly characterized by UV spectrometry, gel permeation chromatography (GPC), 1H NMR, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). [ABSTRACT FROM AUTHOR]

We have investigated a novel approach to well-defined peptide-decorated cross-linked nanoparticles. The particles were obtained from well-defined poly(γ-benzyl-l-glutamate-b-styrene) block copolymers with active nitroxide end-groups by reaction with divinylbenzene (DVB). The block length ratio and the amount of cross-linker (DVB) were systematically varied. Molecular weights of the cross-linked particles up to 548 000 g/mol with polydispersities around 1.5 were confirmed by size-exclusion chromatography. A clear dependence of the molecular weight from the block length ratio and the amount of cross-linker was observed. This was confirmed by dynamic light scattering results revealing the formation of nanoparticles up to 21 nm in size. The core−shell structure was evident from the TEM micrographs. Further deprotection of the peptide shell yielded water-soluble pH-responsive nanoparticles with a poly(l-glutamic acid) shell and a polystyrene core. Cryo-TEM micrographs confirmed the presence of individual core−shell particles in the aqueous solution. [ABSTRACT FROM AUTHOR]

The critical degree of polymerization (Jcrit) at which polymer chains become insoluble in the continuous medium and particle formation commences has been estimated under a variety of experimental conditions for the nitroxide-mediated precipitation polymerizations of styrene (St) at 110 °C and tert-butyl acrylate (t-BA) at 118 °C in supercritical carbon dioxide (scCO2) mediated by N-tert-butyl-N-[1-diethylphosphono(2,2-dimethylpropyl)]oxy (SG1). The value of Jcritincreases with increasing target molecular weight, initial monomer loading, and pressure. Under the conditions investigated, Jcritfor t-BA is higher than that for St, which is consistent with greater solubility of poly(acrylates) in neat scCO2. A simple graphical approach has been developed and successfully employed, whereby Jcritcan be predicted as a function of both target molecular weight and initial monomer loading on the basis of a data set of Jcritversus initial monomer loading. [ABSTRACT FROM AUTHOR]

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. kpKvalues (kp= propagation rate constant, K= equilibrium constant) for S/TBMA increased significantly as fTBMA,0increased, with kpK= (7.4 ± 0.03) × 10−7to (5.4 ± 0.9) × 10−5s−1. Copolymer reactivity ratios were rTBMA= 0.13−0.27 and rS= 0.43−0.59 using Fineman−Ross, Kelen−Tüdos, and nonlinear least-squares fitting to the Mayo−Lewis terminal model. All S/TBMA copolymers (number-average molecular weight M̅n= 4.5−15.6 kg mol−1) exhibited low polydispersities (M̅w/M̅n≤ 1.30), and M̅nexhibited linear behavior with conversion up to 25−40% and monomodal molecular weight distributions. TBMA-rich copolymer (M̅n= 14.2 kg mol−1and M̅w/M̅n= 1.30) was shown to have a high degree of “livingness” based upon 31P NMR measurements for the SG1 end group (≈75%), and successful reinitiations of fresh batches of styrene, tert-butylstyrene, N-isopropylacrylamide, and a ternary mixture of glycidyl methacrylate/methyl methacrylate/styrene (all products were monomodal with M̅n= 17.8−81.0 kg mol−1and M̅w/M̅n= 1.33−1.59). [ABSTRACT FROM AUTHOR]

The solvent uptake properties of sulfonated poly(styrene−isobutylene−styrene) (sSIBS) triblock copolymers exchanged with Mg2, Al3, Ba2, and Cs誉 are investigated using the electron spin resonance (ESR) spin probe method with the nitroxide probes 2,2,6,6-tetramethyl-4-piperidone N-oxide (TEMPONE) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPOL). sSIBS membranes were equilibrated with varying amounts of methanol, dimethyl methyl phosphonate (DMMP), both as pure solvents and as solvent−water mixtures. As a standard for comparison, Li誉 exchanged Nafion 117 membranes were also characterized using the same spin probes and solvent combinations. Solvent uptake trends were measured for each of the membrane-solvent combinations. Some membranes, particularly those exchanged with Cs, preferentially uptake water in the presence of organic solvent. sSIBS membranes containing pure methanol or DMMP exhibit two phases which were assigned to the sulfonated styrene block of the polymer, and to the hydrophobic isobutylene block. Whereas methanol enhances the phase separation, DMMP penetrates the less mobile hydrophobic phase at a concentration that depends upon the identity of the exchange ion, which increases in the order Cs> Ba2∼ Al3> Mg2. Thus, cations appear to disrupt the lamellar structure of the polymer, making the nonpolar phase more susceptible to permeation by the solvent. This disruption correlates with the free volume contribution to the rotational diffusion of the probe in both phases, suggesting that the cations affect the solvation of the different phases of sSIBS mainly through their influence on the ordering of the solvent. No clear correlation of this effect with either ionic radius or charge could be identified. [ABSTRACT FROM AUTHOR]

Styrene/maleic anhydride (S/MA) copolymerizations at initial molar MA feed concentrations fMA,0= 0.10−0.55 were done at 80−110 °C in 50 wt % 1,4-dioxane using 5 mol % {tert-butyl-[1-(diethoxyphosphoryl)-2,2-dimethylpropyl]amino}oxidanyl (SG1) relative to -2-({tert-butyl-[1-(diethoxyphosphoryl)-2,2-(dimethylpropyl)amino}oxy)-2-methylpropionic acid (BlocBuilder). As fMA,0increased, the apparent rate constants increased dramatically. Copolymerizations performed with nearly equimolar feeds fMA,0= 0.45−0.55 at 110 °C had apparent rate constants ∼20 times that of styrene at the same temperature. S/MA copolymerizations performed at 110 °C with practically equimolar feeds resulted in nearly alternating S/MA/S structures while those performed with fMA,0= 0.1−0.4 possessed little to no S/MA/S alternating structures as indicated by 13C NMR spectroscopy. However, NMP of S/MA done at 90 °C with a styrene-rich feed composition (fMA,0= 0.2) resulted in a poly(S-alt-MA)-block-poly(S) diblock in a single step. 13C NMR revealed two significant populations of triads corresponding to S/MA/S alternating sequences and to S/S/S homopoly(styrene) sequences. BlocBuilder enabled the polymerization of these one-step block copolymers with a strictly alternating S/MA first block by NMP, thus permitting NMP to join reversible addition−fragmentation transfer polymerization as another controlled radical polymerization method to attain alternating S/MA microstructures. [ABSTRACT FROM AUTHOR]

Self-assembly (SA) of amphiphilic block copolymers (poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide)) was investigated in dispersions of multi-walled carbon nanotubes (MWNT) as a function of temperature using spin probe electron paramagnetic resonance (EPR) spectroscopy. Nitroxide-labeled Pluronic with a short poly(ethylene oxide) block, L62-NO, and a small molecular probe, 4-hydroxy-TEMPO-benzoate, 4HTB, were used for probing the local dynamic and polarity of the polymer chains in the presence of the nanostructures. It was found that MWNT modify the temperature, and the dynamic behavior of polymer SA and comparison between the MWNT and single-walled nanotube (SWNT) showed that the structure and dynamical behavior of the nanostructure−polymer hybrids formed depend on the size matching between the diameter of the native micelles and the additives. While SWNT induced the formation of hybrid polymer−SWNT micelles, MWNT (with a diameter of 20−40 nm) induced the assembly of polymer aggregates at the surface of the MWNT. [ABSTRACT FROM AUTHOR]