Nitroxide-mediated Polymerization Of Styrene Research Articles

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.

Molecular Weight Distribution of Two Types of Living Chains Formed during Nitroxide-Mediated Polymerization of Styrene.

Different types of polymer chains generated during the nitroxide-mediated polymerization of styrene are separated for the first time, and their molecular weight distribution (MWD) is investigated. Living and dead chains are monitored during the reaction; specifically, two types of living chains derived from the initiation of the alkoxyamine (RT) and the self-initiation of styrene and dead chains present in the as-prepared polystyrene (PS). To distinguish between each polymer species, different numbers of hydroxyl groups are introduced onto the T and R groups of the alkoxyamine (one and two groups, respectively). Each living and dead chains is resolved according to the distinct number of hydroxyl groups on its chain-end using high-performance liquid chromatography. Molecular structures of the fractionated PS are characterized using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and 1 H nuclear magnetic resonance spectroscopy, and the results of which show two distinct initiation paths: one originating from RT and the other from the self-initiation of styrene. Molecular weight and MWD are measured using size-exclusion chromatography and reveal a narrow MWD for the living chains derived from RT. Contrastingly, a broad and skewed MWD is observed for the other living chains derived from the self-initiation of styrene and the dead chains.

Nitroxide-mediated polymerization of styrene and limonene in the framework of synthesis of potentially functional polymers using naturally occurring terpenes

In the framework of synthesis of potentially functional macromolecules based on commodity polymers with naturally occurring compounds, the nitroxide-mediated polymerization of styrene with limonene was investigated here. Various ratios of styrene and limonene were used, and the incorporation of limonene in the final polymer was monitored. Results from benzoyl peroxide/TEMPO-initiated polymerization showed small incorporation of limonene in the polystyrene chains, while it was also involved in forming oligomers (such as dimers or trimers). The presence of limonene resulted in a reduction in polymer average molecular weight through chain transfer reactions. From the kinetic analysis, limonene was found to inhibit styrene thermal auto-polymerization at high temperatures, acting as a radical scavenger. Using TEMPO-functionalized polystyrene macroinitiators to initiate the polymerization, no limonene oligomers in the final product were observed. Finally, when polystyrene macroinitiators and limonene were reacted in the absence of styrene monomer, limonene moieties were identified in the final polymer, resulting thus in polystyrene functionalization. This functionalization can be extended to the synthesis of novel materials based on naturally occurring terpenes, considering the variety of structures that can be obtained by applying NMP.

Coordination-Initiated Nitroxide-Mediated Polymerization (CI-NMP)

Preparation of materials by nitroxide-mediated polymerization (NMP) is well known nowadays. To increase the possible usefulness of NMP for the production of hybrid materials or polymer-decorated complexes, coordination-initiated NMP (CI-NMP) was developed and investigated here. CI-NMP was exemplified using the instantaneous and spontaneous reaction of alkoxyamines carrying a pyridyl moiety on the alkyl group and the Zn(hfac)2 (hfac: hexafluoroacetylacetonate) complex as a metal centre. NMP of styrene and n-butyl acrylate was carried out with either previously or in situ-prepared complexes. Both approaches afforded NMP of the same quality. The positive influence of metal centre coordination is highlighted by efficient NMP at 90°C.

Facile Synthesis of Multiblock Copolymers Containing Sequence-Controlled Peptides and Well-Defined Vinyl Polymers by Nitroxide-Mediated Polymerization.

Precisely incorporating a wide range of structural and functional multiblocks along a polymer backbone is a significant challenge in polymer chemistry and offers promising opportunities to design highly ordered materials, including controlled polymer folding. Herein, a facile and versatile strategy for preparing functional multiblock copolymers composed of sequential peptides and well-defined vinyl polymers with a narrow polydispersity is reported. Cyclic oligopeptides have been developed that contain an alkoxyamine bond in the framework. By using this type of cyclic initiator, peptide-containing multiblock copolymers are successfully synthesized by nitroxide-mediated polymerization of styrene. To demonstrate the versatility of this method, radical (co)polymerizations were carried out for different monomers (p-chlorostyrene, 4-vinylpyridine, and styrene/acrylonitrile) and by three different cyclic peptide initiators with specific amino acid sequences. The resultant multiblock copolymer is foldable through intramolecular interactions between peptide blocks. It is believed that this approach will significantly advance the field of controlled polymer synthesis for complex structures and single-chain folding.

2,2,6,6-Tetramethylpiperydinyl-1-oxyl (TEMPO) Functionalized Benzoxazines Prepared with a One-Pot Synthesis for Reactive/Crosslinkable Initiators of Nitroxide Mediated Polymerization.

In this work, the incorporation of a 2,2,6,6-tetramethylpiperydinyl-1-oxyl (TEMPO) group to a benzoxazine ring is performed using a one-pot synthesis for the preparation of TEMPO-functionalized benzoxazine compounds and polymers as reactive and crosslinkable initiators for nitroxide-mediated polymerization (NMP). The TEMPO-functionalization reaction of benzoxazine, traced with 1 H NMR, is conducted with sequential radical transfer and coupling reactions. Moreover, polystyrene-grafted polybenzoxazine copolymers are prepared with the TEMPO-benzoxazine initiator and NMP of styrene. The polymerization system exhibits the characteristics of controlled radical polymerization, including controlled molecular weights of products and ability for sequential polymerization. Moreover, based on the chemical reactivity and crosslinking ability of benzoxazine groups, the synthesis route developed in this work will widen the scope of the design and synthesis of functional and high-performance polymers.

NMP of styrene in batch and CSTR at elevated temperatures: Modeling experimental trends

Nitroxide-mediated polymerization (NMP) is conducted in batch and in a continuous stirred-tank reactor (CSTR) at temperatures up to 200°C using a thermally stable nitroxide. A kinetic model was developed using the Predici® software package to further understand the experimental trends under batch and continuous operation. Using the estimated activation/deactivation rate coefficients from the batch polymerization, the model predicts that a significant amount of alkoxyamine is exiting the CSTR under steady state conditions, consistent with a low molecular weight peak found experimentally. The predicted outlet concentration of alkoxyamine at steady state is decreased by increasing the temperature and residence time in the reactor. Batch chain extension of the polymer produced in the CSTR supports the potential for continuous production of block copolymers.

MAMA-SG1 initiated nitroxide mediated polymerization of styrene: From Arrhenius parameters to model-based design

Activation and deactivation Arrhenius parameters are estimated for nitroxide mediated polymerization (NMP) of styrene initiated by BlocBuilder MA, based on an extensive set of experimental data covering a broad range of polymerization temperatures (90–120°C) and initial molar ratios of monomer to NMP initiator (100–1000). Data regression analysis is limited to conversions below 0.65 to avoid the possible influence of diffusional limitations on the activation/deactivation process. The applied kinetic model accounts for thermal initiation, chain transfer reactions and diffusional limitations on termination. A distinction is made between (de)activation of NMP initiator and macrospecies. The activation energy for the activation of the NMP initiator is 43±3.5kJmol−1 lower than the one for the dormant macrospecies. At 120°C, the activation rate coefficients amount respectively to 1.18×10−1s−1 and 7.08×10−3s−1, indicative of a fast NMP initiation. Using the obtained parameter estimates, a visualization of ca. 750 polymer chains is performed via advanced kinetic Monte Carlo simulations, explicitly specifying, for the first time, according to the living nature, and chain initiation and dead polymer mechanism. At 120°C, chain transfer to dimer lowers the level of control over chain length and end-group functionality. Model-based optimization reveals the beneficial effect of the use of a stepwise temperature program, as confirmed experimentally via a lowering of the dispersity from a conversion of 0.3 on due to a suppression of thermal initiation and chain transfer to dimer.

Precise insertion of clickable monomer along polymer backbone by dynamic temperature controlled radical polymerization

Styrenic copolymers have been prepared that contain localized areas of high azide functionality by exploiting the unexpected copolymerization behavior of azidomethyl styrene with styrene. Kinetic studies have shown that during the nitroxide-mediated polymerization of styrene and azidomethyl styrene, small equivalents of azidomethyl styrene are consumed at a relatively higher rate. This property was further enhanced by lowering the reaction temperature, leading to a more precisely defined area of azide functionality. Furthermore, by actively controlling the reaction temperature azidomethyl styrene can be inserted into different points along the polymer backbone. This approach was used in combination with previous sequence control techniques, strong donor/acceptor comonomer pairs, to synthesize well-defined copolymers with controlled areas of functional monomers allowing for a wide scope of post-polymerization modification methods.

Controlled/living polymerization of methyl methacrylate using new sterically hindered imidazoline nitroxides prepared via intramolecular 1,3-dipolar cycloaddition reaction

A series of imidazoline nitroxides with bulky spirocyclic moieties at the positions 2 or 5 of imidazole ring were synthesized using intramolecular 1,3-dipolar cycloaddition in 2H-imidazole 1-oxides or 4H-imidazole 3-oxides with pent-4-enyl groups followed by isoxazolidine ring opening and oxidation. Capability of the nitroxides to control radical polymerization of methyl methacrylate (MMA) and styrene was investigated. For that purpose, alkoxyamines were synthesized from the aforementioned nitroxides and tert-butyl α-bromoisobutyrate. Homolysis rate constants of the alkoxyamines were measured and possible contributions of side reactions were quantified. Nitroxide-mediated polymerization of styrene and MMA was studied using the alkoxyamines as initiators. MMA polymerization was found to proceed in controlled regime up to 55% of monomer conversion and the polymer obtained was able to reinitiate the polymerization of styrene. Quota of “living” chains estimated to reach 90%. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 929–943

Nitroxide-Mediated Polymerization of Styrene, Butyl Acrylate, or Methyl Methacrylate by Microflow Reactor Technology

The nitroxide-mediated radical polymerization (NMP) of styrene and butyl acrylate in microflow tubular reactors was examined. In comparison with polymerizations conducted in a batch reactor under otherwise identical conditions, the microflow setup gave higher conversions and produced polymers with lower polydispersity indices. Block copolymers of the two monomers could be synthesized by connecting two microflow tubular reactors through a T-junction. The NMP of methyl methacrylate in a microflow tubular reactor was also investigated.

Kinetic Modeling as a Tool to Understand and Improve the Nitroxide Mediated Polymerization of Styrene

AbstractKinetic modeling is used to obtain insight in the complex interplay between reaction rates and obtained polymer properties in the SG1 and the TEMPO mediated bulk polymerization of styrene at 396 K. The increase of the viscosity during NMP is accounted for. At higher targeted chain lengths, chain transfer to dimer and transfer from nitroxide to dimer are shown to cause the experimentally observed reduced control over the average polymer properties and to result in a clear fronting of the polymer chain length distribution. The potential of kinetic modeling to design tailor‐made synthesis strategies is illustrated. Simulations indicate that careful control of the polymerization conditions allows to obtain an important improvement of the polymer properties. The approach is also applicable for NMP mediated by other alkoxyamines/nitroxides and allows to expand the application range of NMP for styrene polymerization in particular to synthesize complex polymer architectures by assembly of functionalized polymers. magnified image

Nitroxide-mediated polymerization of styrene in the presence of a novel trinitroxide

AbstractThe bulk polymerizations of styrene were performed in the presence of a novel trinitroxide, 2,4,6-tri(4’-oxy-2’,2’,6’,6’-tetramethyl-1’-piperidinyloxy)-1,3,5- triazine (TTPT). Typical features of controlled polymerization were observed, such as the first-order kinetics, the molecular weights (Mn) linearly increased with the conversion, and relatively narrow molecular weight distributions (Mw/Mn). The 1H NMR was used to characterize the obtained polystyrene. The most of obtained polymers at 110 °C were the polymer with two-arm linear structure, not the expected three-arm structure, which was confirmed by the analysis of degradation of obtained polymer by ascorbic acid. A proposed polymerization route of styrene mediated by TTPT was also discussed.

One‐Pot Synthesis of Lactide–Styrene Diblock Copolymers via Catalytic Immortal Ring‐Opening Polymerization of Lactide and Nitroxide‐Mediated Polymerization of Styrene

An efficient, practical, and industrially relevant procedure for the production of polymer materials, in which a part of the oil-derived polyolefins has been replaced by a renewable, biodegradable, and biocompatible poly(lactide) block, is presented. Binary catalytic systems combining innocuous metals (yttrium, zinc, magnesium, or calcium) and bifunctional alcohols (acting as transfer agents) were developed to promote the immortal ring-opening polymerization of lactide directly in styrene. Up to 20,000 equivalents of lactide were polymerized (metal catalyst loading of 50-100 ppm) in a controlled fashion in the presence of 10-100 equivalents of a double-headed transfer agent to give as many end-functionalized poly(lactide) macromolecules that can be used eventually as macroinitiators for the controlled nitroxide-mediated polymerization of styrene. The specific use of the sterically shielded complex [BDI-iPr]Zn-N(SiMe(3))(2) ([BDI-iPr]=bis(diketiminate) ligand) allowed the efficient, catalytic, and controlled production of poly(lactide)-block-poly(styrene) materials in a one-pot, solvent-free sequential procedure, with nearly 100% atom-efficiency.

Monitoring the Nitroxide-Mediated Polymerization of Styrene Using Gel Permeation Chromatography and Proton NMR

This laboratory exercise is designed to give students experience in controlled radical polymerization (CRP) techniques, with an emphasis on monitoring the conversion of monomer into polymer as the reaction proceeds. Specifically, nitroxide-mediated polymerization (NMP) is used to synthesize polystyrene, with reaction-mixture aliquots removed and analyzed via gel permeation chromatography (GPC) and 1H NMR at varying time intervals. Students obtain and analyze data from 1H NMR during the laboratory period, which allows them to calculate the percent monomer conversion at each time interval. Number-average molecular weight (Mn) and polydispersity index (PDI) values are determined by GPC analysis, which is performed by the instructor or teaching assistant and the data given to the students. From the experimental data, Mn values show a linear relationship to percent monomer conversion, consistent with controlled polymerization. Additionally, kinetic plots, which show ln([M]0/[M]t) as a function of reaction time...

Effect of an Acid Protecting Group on the “Livingness” of Poly(acrylic acid-ran-styrene) Random Copolymer Macroinitiators for Nitroxide-Mediated Polymerization of Styrene

Poly(acrylic acid-ran-styrene) (P(AA-r-S)) and poly(tert-butyl acrylate-ran-styrene) (P(tBuA-r-S)) random copolymers previously made with different molar ratios (0, 4.5, and 9 mol %) of additional free nitroxide mediator, N-tert-butyl-N-[1-(diethylphosphono)-2,2-dimethylpropyl]nitroxide (SG1), relative to 2-[[N-tert-butyl-N-[1-(diethylphosphono)-2,2-dimethylpropyl]amino]oxy]-2-methylpropionic acid (BlocBuilder) alkoxyamine unimolecular initiator were used as macroinitiators for styrene chain extension. The reinitiating experiments were performed in the bulk at 115 °C when using P(tBuA-r-S) macroinitiators or 30−50 wt % dioxane solution at 120 °C when using P(AA-r-S) macroinitiators. The P(tBuA-r-S)-containing macroinitiators (number-average molecular weight Mn = 13.4−25.8 kg·mol−1) with polydispersities Mw/Mn = 1.13−1.57 were capable of initiating chains extended with styrene as indicated by monomodal and narrow molecular weight distributions with Mn = 34.6−66.3 kg·mol−1 and Mw/Mn ranging from 1.24 ...

TEMPO-mediated radical polymerization of styrene in aqueous miniemulsion: Macroinitiator concentration effects

The control/livingness in nitroxide-mediated polymerization of styrene (S) in aqueous miniemulsion at 125°C employing a poly(S)-2,2,6,6-tetramethylpiperidinyl-1-oxy (PS-TEMPO) macroinitiator and the surfactant sodium dodecylbenzenesulfonate has been shown to depend strongly on the macroinitiator concentration for particles of approximate number-average diameter 65nm. The control/livingness was relatively poor at [PS-TEMPO]0≤0.02M due to the combined effect of enhanced spontaneous initiation and the interface effect (whereby deactivation is suppressed due to interfacial activity of TEMPO). Satisfactory control/livingness was obtained at higher [PS-TEMPO]0 as a result of the interface effect and enhanced spontaneous initiation exerting less pronounced influence per chain than at lower [PS-TEMPO]0. Polymerizations using the sulfonate surfactant DOWFAX 8390 gave similar results, indicating that the present macroinitiator concentration effects are not specific to SDBS-based systems. The results also demonstrate that TEMPO-mediated polymerization of S in miniemulsion can proceed at a higher rate than in bulk with good control/livingness.

Synthesis of amphiphilic and thermosensitive graft copolymers with fluorescence P(St‐co‐(p‐CMS))‐g‐PNIPAAM by combination of NMP and RAFT methods

AbstractA three‐step process, combining nitroxide‐mediated polymerization (NMP) and reversible addition‐fragmentation chain transfer (RAFT) polymerization techniques, for synthesizing well‐defined amphiphilic and thermosensitive graft copolymers with fluorescence poly(styrene‐co‐(p‐chloromethylstyrene))‐g‐poly(N‐isopropylacrylamide) (P(St‐co‐(p‐CMS))‐g‐PNIPAAM), was conducted. Firstly, the NMP of styrene (St) and p‐chloromethylstyrene (p‐CMS) were carried out using benzoyl peroxide (BPO) as the initiator to obtain the random copolymers of P(St‐co‐(p‐CMS)). Secondly, the random copolymers were converted into macro‐RAFT agents with fluorescent carbazole as Z‐group through a simple method. Then the macro‐RAFT agents were used in the RAFT polymerization of N‐isopropylacrylamide (NIPAAM) to prepare fluorescent amphiphilic graft copolymers P(St‐co‐(p‐CMS))‐g‐PNIPAAM with controlled molecular weights and well‐defined structures. The copolymers obtained were characterized by gel permeation chromatography (GPC), 1H nuclear magnetic resonance (NMR) spectroscopy, and FT‐IR spectroscopy. The size of self‐assembly micelles of the resulting graft copolymers in deionized water was studied by high performance particle sizer (HPPS), the results showed that the Z‐average size of the micelles increased with the increase of molecular weights of PNIPAAM in side chains. The aqueous solution of the micelles prepared from P(St‐co‐(p‐CMS))‐g‐PNIPAAM using a dialysis method showed a lower critical solution temperature (LCST) at ∼ 27.5 °C, which was below the value of NIPAAM homopolymer (32 °C). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5318–5328, 2007

Nitroxide-Mediated Polymerization of Styrene Initiated from the Surface of Laponite Clay Platelets

Polystyrene chains were grown from the surface of synthetic Laponite clay platelets by nitroxide-mediated polymerization (NMP) of styrene using N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)] (DEPN) as mediator. A novel water-soluble quaternary ammonium alkoxyamine was first synthesized and intercalated into the clay galleries by cation exchange. Polystyrene chains with controlled molecular weights and narrow polydispersities were then grown from the organoclay. The kinetics of styrene surface NMP polymerizations were investigated and compared with model polymerizations mediated by free alkoxyamine initiator molecules. Both reactions exhibited similar kinetics behaviors indicating that the clay platelets did not affect the livingness of polymerization. The PS-functionalized clay particles were colloidaly stable into toluene, a good solvent for polystyrene, and could be redispersed into tetrahydrofuran (THF) and a series of monomers after drying. Transmission electron microscopy (TEM) analysis of the films cast from the suspensions revealed a fully exfoliated structure of the clay tactoids within the polymer matrix.

Synthesis and Evaluation of Sterically Hindered 1,1-Diadamantyl Nitroxide as a Low-Temperature Mediator for the Stable Free Radical Polymerization Process

An efficient procedure for the oxidation of 1,1-diadamantylamine with m-chloroperbenzoic acid (m-CPBA) to the corresponding sterically hindered nitroxide in high yield (72%) is reported. The corresponding styrene-based alkoxyamine was synthesized by an atom transfer radical addition (ATRA) reaction. Because of the bulkiness of the adamantyl substituents, the cleavage of the C−ON bond of the alkoxyamine occurred readily at temperatures below 100 °C. However, in spite of the low bond dissociation temperature of the alkoxyamine, the (co)polymerizations of styrene and n-butyl acrylate proceeded poorly. The results in this paper support the argument that the most important determinant in a nitroxide-mediated polymerization of styrene and acrylate is the ability to control the excess concentration of nitroxide in solution either by an inherent instability of the nitroxide or by the use of additives that destroy the excess nitroxide. Thus, for the 1,1-diadamantyl nitroxide case, and maybe more generally, while a lower C−O bond dissociation energy of an alkoxyamine moiety at the end of the chain may allow lower polymerization temperatures and faster reactions rates, it does not enable polymerizations to proceed to high conversions if the excess nitroxide is not controlled in some manner.