Ionic Polymerization Research Articles

Dual Network Formation in Polyelectrolyte Hydrogel via Viscoelastic Phase Separation: Role of Ionic Strength and Polymerization Kinetics

In this Article, we report a systematic research on a hydrogel with dual networks of 104 times difference in mesh sizes. The structure was developed by polymerizing a cationic monomer N-[3-(N,N-dimethylamino)propyl] acrylamide methyl chloride quarternary (DMAPAA-Q) in the presence of a small amount of semirigid polyanion, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT). During the polymerization, polyion complexes were formed, which caused viscoelastic phase separation (VPS) due to the self-assembly of the semirigid polyion complexes, whereupon the dynamic coupling of phase separation and gelation is crucial for the structure formation. When PBDT was above its overlap concentration (CPBDT > C*), a critical concentration of cationic monomer, CQ ≈ 1.5 M, was observed, below which VPS occurred and turbid hydrogels with the dual network structure were formed, whereas above which, a transparent, anisotropic hydrogel was formed. It has been elucidated that the critical effect of CQ on the VPS process is through the ionic strength mechanism. That is, the abundant unreacted cationic monomer at high CQ behaves as a simple salt that screens the electrostatic interaction between the polycation and PBDT and therefore suppresses the occurrence of the phase separation. Furthermore, we investigated the effects of reaction kinetics on the VPS and the microstructure of gels by changing the concentrations of photoinitiator and chemical cross-linker. The dual network gels possess controllable turbidity degrees and mesh sizes corresponding to different quench depths of the phase separation. On the basis of these results, as well as in situ observation of the structure formation during the polymerization, we proposed a detailed mechanism for the formation of dual networks and the anisotropic hydrogels.

Polyhomologation. A Living C1 Polymerization

The physical properties of synthetic macromolecules are strongly coupled to their molecular weight (MW), topology, and polydispersity index (PDI). Factors that contribute to their utility include the control of functionality at the macromolecule termini and copolymer composition. Conventional polymerization reactions that produce carbon backbone polymers (ionic, free radical, and coordination) provide little opportunity for controlling these variables. Living polymerizations, sometimes referred to as controlled polymerizations, have provided the means for achieving these goals. Not surprisingly, these reactions have had a profound impact on polymer and materials science. Three basic reaction types are used for the synthesis of most carbon backbone polymers. The first examples of "living" polymerizations were developed for ionic polymerizations (cationic and anionic). These reactions, which can be technically challenging to perform, can yield excellent control of molecular weight with very low polydispersity. The second reaction type, free radical polymerization, is one of the most widely used polymerizations for the commercial production of high molecular weight carbon backbone polymers. Nitroxide mediated polymerization (NMP), reversible addition-fragmentation chain transfer polymerization (RAFT), and atom transfer radical polymerization (ATRP) have emerged as three of the more successful approaches for controlling these reactions. The third type, transition metal mediated coordination polymerization, is the most important method for large-scale commercial polyolefin production. Simple nonfunctional hydrocarbon polymers such as polyethylene (PE), polypropylene, poly-α-olefins, and their copolymers are synthesized by high pressure-high temperature free radical polymerization, Ziegler-Natta or metallocene catalysts. Although these catalysts of exceptional efficiency that produce polymers on a huge scale are in common use, control that approaches a "living polymerization" is rare. Although the controlled synthesis of linear "polyethylene" described in this Account is not competitive with existing commercial processes for bulk polymer production, they can provide quantities of specialized materials for the study of structure-property relationships. This information can guide the production of polymers for new commercial applications. We initiated a search for novel polymerization reactions that would produce simple hydrocarbon polymers with the potential for molecular weight and topological control. Our research focused on polymerization reactions that employ nonolefin monomers, more specifically the polymerization of ylides and diazoalkanes. In this reaction, the carbon backbone is built one carbon at a time (C1 polymerization). These studies draw upon earlier investigations of the Lewis acid catalyzed polymerization of diazoalkanes and build upon our discovery of the trialkylborane initiated living polymerization of dimethylsulfoxonium methylide 1.

ChemInform Abstract: Metallacarboranes as Labile Anions for Ionic Zirconocene Olefin Polymerization Catalysts.

Catalysts synthesized by reacting Cp{sub 2}ZrMe{sub 2} and [PhNMe{sub 2}H][(C{sub 2}B{sub 9}H{sub 11}){sub 2}M] are active for the polymerization and copolymerization of ethylene and {alpha}-olefins. The authors use NMR spectroscopy to investigate the coordination strength of these anions within the cobalt complexes. Catalytic effects of the complexes toward olefin polymerization were investigated. 25 refs., 4 figs., 2 tabs.

Fundamentals of Atom Transfer Radical Polymerization

Today’s market increasingly demands sophisticated materials for advanced technologies and high-value applications, such as nanocomposites, optoelectronic, or biomedical materials. Therefore, the demand for well-defined polymers with very specific molecular architecture and properties increases. Until recently, these kinds of polymers could only be prepared via living ionic polymerization, a process that requires very stringent experimental conditions. Recently, atom transfer radical polymerization (ATRP), a controlled/living radical polymerization (CRP) process, has emerged as a viable alternative. ATRP allows the synthesis of polymeric structures that are well-defined in terms of composition and molecular architecture. By virtue of its simplicity, versatility and scope to make polymers with site-specific functionality and novel architecture, ATRP has become the most extensively studied CRP technique.

Reaction Engineering and Industrial Aspects of Controlled/Living Radical Polymerization

Reaction Engineering and Industrial Aspects of Controlled/Living Radical Polymerization

Cationic Polymerization of Vinyl Monomers in Aqueous Media: From Monofunctional Oligomers to Long-Lived Polymer Chains

Polymer latexes are easily prepared on a multimillion ton scale in industry using free radical initiated emulsion and suspension polymerizations in water, a cheap, nonviscous, heat-controlling, and environmentally benign solvent. Until recently, researchers had done little investigation into ionic polymerization because even a small amount of water would easily deactivate the conventional catalysts used in these processes. In the last decade, however, cationic polymerization in aqueous media has emerged as a new and attractive method for controlling the polymerization reactions using mild experimental conditions. This Account reviews the current science of and future outlook for cationic polymerization of vinyl monomers in aqueous media. We particularly emphasize the design and evolution of catalytic systems and the precision synthesis of functional polymers. Early work to tailor the suspension and emulsion cationic polymerizations of reactive monomers such as p-methoxystyrene and vinyl ethers used long-chain strong acids, called INISURF for their dual roles as initiators and surfactants, and lanthanide triflates. These polymerization processes shared two main features: (i) all reactions (initiation, propagation, and termination) occurred at the particle interface; (ii) synthesized polymers have limits on their molecular weight, attributed to the "critical DP" effect, related to the entry of oligomers inside the particles as they become increasingly hydrophobic. The next generation of catalysts, named "Lewis acid-surfactant combined catalysts" (LASC), shifted the polymerization locus from the interface to the inside of the monomer droplets, allowing for the production of long polymer chains. Recently, catalytic systems based on boranes, (BF(3)OEt(2), B(C(6)F(5))(3), (C(6)F(4)-1,2-[B(C(6)F(5))(2)]), and (C(6)F(4)-1,2-[B(C(12)F(8))](2))), have shown great potential in controlling the cationic polymerization in "wet" solution, containing an excess of water relative to Lewis acid, or aqueous media of such industrially important monomers as styrene, cyclopentadiene, and even isobutylene.

Molecularly imprinted solid phase extraction coupled to high-performance liquid chromatography for determination of trace dichlorvos residues in vegetables

Abstract In this paper, we prepared a highly selective imprinted polymer by a room temperature ionic liquid-mediated bulk polymerization technique, using dichlorvos as the template, methacrylic acid as the functional monomers, and trimethylolpropane trimethacrylate as the cross-linker. This functionalized material was characterized by FT-IR, static and kinetic adsorption experiments, and the results showed that this imprinted sorbent exhibited good recognition and selective ability, and offered fast kinetics for the adsorption and desorption of dichlorvos. Using the prepared material as a solid phase extraction sorbent, a novel sample pre-treatment technique that can be coupled to high-performance liquid chromatography (HPLC) had been developed for determination of trace dichlorvos residues in foods. Under the selected experimental condition, the detection limit ( S / N = 3) of dichlorvos was 94.8 ng L −1 , and the peak area precision (RSD) for five replicate detections of 10 μg L −1 dichlorvos was 4.41%. The blank samples of cucumber and lettuce spiked with dichlorvos at 0.005 and 0.02 μg g −1 levels were determined with recoveries ranging from 82.1% to 94.0%.

Differential Regulation of Actin Polymerization and Structure by Yeast Formin Isoforms

The budding yeast formins, Bnr1 and Bni1, behave very differently with respect to their interactions with muscle actin. However, the mechanisms underlying these differences are unclear, and these formins do not interact with muscle actin in vivo. We use yeast wild type and mutant actins to further assess these differences between Bnr1 and Bni1. Low ionic strength G-buffer does not promote actin polymerization. However, Bnr1, but not Bni1, causes the polymerization of pyrene-labeled Mg-G-actin in G-buffer into single filaments based on fluorometric and EM observations. Polymerization by Bnr1 does not occur with Ca-G-actin. By cosedimentation, maximum filament formation occurs at a Bnr1:actin ratio of 1:2. The interaction of Bnr1 with pyrene-labeled S265C Mg-actin yields a pyrene excimer peak, from the cross-strand interaction of pyrene probes, which only occurs in the context of F-actin. In F-buffer, Bnr1 promotes much faster yeast actin polymerization than Bni1. It also bundles the F-actin in contrast to the low ionic strength situation where only single filaments form. Thus, the differences previously observed with muscle actin are not actin isoform-specific. The binding of both formins to F-actin saturate at an equimolar ratio, but only about 30% of each formin cosediments with F-actin. Finally, addition of Bnr1 but not Bni1 to pyrene-labeled wild type and S265C Mg-F actins enhanced the pyrene- and pyrene-excimer fluorescence, respectively, suggesting Bnr1 also alters F-actin structure. These differences may facilitate the ability of Bnr1 to form the actin cables needed for polarized delivery of nutrients and organelles to the growing yeast bud.

Development of a Biomimetic Enzyme-Linked Immunosorbent Assay Method for the Determination of Estrone in Environmental Water using Novel Molecularly Imprinted Films of Controlled Thickness as Artificial Antibodies

We developed a fast and new direct competitive biomimetic enzyme-linked immunosorbent assay (BELISA) method for the determination of estrone in environmental water based on a novel molecularly imprinted film of controlled thickness as an artificial antibody. The imprinted film was directly synthesized on the well surface of MaxiSorp polystyrene 96-well plate by a room temperature ionic liquid-mediated chemical oxidative polymerization in conjunction with molecular imprinting technology. This novel film was characterized, and results showed that it exhibited an antibody-like binding ability, rapid adsorption speed, high stability, and hydrophilicity, which was particularly advantageous and suitable for BELISA development. This BELISA method had a higher selectivity for estrone than for the structurally related compounds, and competitive binding studies demonstrated various degrees of cross-reactivity with five estrogenic compounds ranging from 30 to 47%. Eighty minutes of analysis time was reduced when compared to that of traditional ELISA, while the imprinted film was able to be reused for more than 50 times without loss of sensitivity. The IC(50) (calculated as the concentration giving 50% inhibition of color development) and the detection limit values under optimized experimental conditions were 200 +/- 40 microg L(-1) and 8.0 +/- 0.2 microg L(-1), respectively. This developed method was applied to the determination of estrone in spiked environmental water samples with excellent recoveries ranging from 80 to 95%, and the results correlated well with that obtained using the high performance liquid chromatography method.

Cyclic Trifunctional Peroxide On Living Free Radical Polymerization

Until the mid 90's, free radical polymerization (FRP) was characterized by producing polymers with high average molecular weights (1x10-1x10) since the beginning of polymerization, index of polidispersity (PDI) greater than 1.5 and wide molecular weight distribution (MWD). When necessary to produce polymers with more defined structure, it was usually used anionic polymerization, which is capable to produce polymers with narrow molecular weight distribution and PDI around 1.0 (1.1-1.2). The ionic polymerization, however, needs to be held in a high degree of purity and in the absence of inhibitors, what make the ionic polymerization expensive and not very practical from the industrial point of view. A promising alternative to ionic polymerization has been the living radical polymerization (LFRP), which is much more robust to the impurities and kind of solvent and it is able to produce polymers with polidispersity close to one. Nevertheless, the LFRP presents lower polymerization rates compared to standard and smaller polymer chains (lower molecular weights averages). In this work the effect of cyclic trifunctional initiator on the Living Free Radical Polymerization is analyzed. The Nitroxide Mediated Radical Polymerization (NMRP) is considered, using TEMPO as controller and styrene as monomer. It can be observed that the polidispersity can vary in a very broad range when this initiator is used, changing from PDI lower than 1.5 until PDI bigger than 4.0, depending on the operating conditions considered.

Gradient copolymers: Synthesis, structure, and properties

Conditions of formation of gradient copolymers characterized by a continuous change in composition along each chain and methods of their synthesis by living ionic and pseudoliving radical polymerizations are considered. Characteristics, structure, and physicochemical properties of gradient copolymers are discussed.

Thermosensitive gradient copolymers by living cationic polymerization: Semibatch precision synthesis and stepwise dehydration‐induced micellization and physical gelation

AbstractThermosensitive forced gradient copolymers with various sequence distributions were synthesized by living cationic polymerization in the presence of an added base. The synthesis was conducted using a semibatch reaction method, which is unfavorable for ionic polymerization, especially when a simple apparatus is employed. Polymerization of 2‐ethoxyethyl vinyl ether (EOVE) was initiated using a conventional syringe technique. Immediately after initiation, 2‐methoxyethyl vinyl ether (MOVE) was continuously added using a syringe pump at regulated feed rates, which allowed control of the sequence distribution. The resulting gradient copolymers of EOVE and MOVE underwent thermally induced association in water, forming micelles with a hydrophobic core derived from EOVE‐rich segments. Interestingly, the size of the micelles obtained from gradient copolymers decreased monotonously with increasing solution temperature, while the micelles of the corresponding block copolymers were unchanged in size. This self‐association behavior can be controlled by designing the gradient pattern of the instantaneous composition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6151–6164, 2008

Chloroaluminate ionic liquids as a medium of titanocene catalyst activated by alkyl aluminum compounds for ethylene polymerization

1-Ethyl-3-methylimidazolium tetrachloroaluminate ([EMIM]+[AlCl4]-) and 1-n-butyl-3- -methylimidazolium tetrachloroaluminate ([BMIM]+[AlCl4]-) ionic liquids were applied in biphasic ethylene polymerization as a medium of Cp2TiCl2 titanocene catalyst. The effects of alkylaluminum compound (MAO, AlEt3, AlEt2Cl, AlEtCl2), the activator/catalyst molar ratio, polymerization time, ethylene pressure, catalyst recycling and the volume of the ionic liquid/hexane medium on the polymerization yield were investigated. Physical properties of polyethylene (PE) obtained are presented. It was shown that AlEtCl2 is the best activator investigated so far. The [BMIM]+[AlCl4]- ionic liquid is a better medium for the titanocene catalyst than [EMIM]+[AlCl4]- one. The product obtained is characterized primarily by its high crystallity degree and shows the properties of a typical linear polyethylene. Thus, biphasic ionic liquid polymerization of ethylene can be a potential alternative to that with a metallocene catalyst immobilized on a solid carrier.

On the effect of the nature of a main-group metal in its organic derivative on the stage of formation of active sites of ionic coordination polymerization initiated by two-component Ziegler-Natta catalysts

On the effect of the nature of a main-group metal in its organic derivative on the stage of formation of active sites of ionic coordination polymerization initiated by two-component Ziegler-Natta catalysts

Polymers: chemistry and physics of modern materials

Introduction. Step-Growth Polymerization. Free Radical Addition Polymerization. Ionic Polymerization. Copolymerization. Polymer Stereochemistry. Polymerization Reactions Initiated by Metal Catalysts and Transfer Reactions. Polymer Characterization-Chain Dimensions and Structures. The Crystalline State. The Amorphous State. Mechanical Properties. The Elastomeric State. Structure-Property Relations. Polymer Liquid Crystals. Polymers for the Electronics Industry. Index.

Statistical copolymers of 2‐(trimethylsilyloxy)ethyl methacrylate and methyl methacrylate synthesized by ATRP

AbstractNo Abtract.

Polymerization ofo‐quinodimethanes. V. Ionic polymerization ofo‐quinodimethanes generated by thermal isomerization of corresponding benzocyclobutenes

AbstractThe ionic polymerization of substitutedo‐quinodimethanes via thermal isomerization of benzocyclobutenes is described. In the cationic polymerizations of 1‐methoxy‐o‐quinodimethane in the presence of various cationic initiators at 110 °C for 12 h, chain transfer reactions also considerably underwent besides the polymerization. Meanwhile, cationic polymerizations of 1‐trimethylsilyloxy‐o‐quinodimethane under the same conditions gave good yields of the corresponding polymer. Anionic polymerizations of 1‐cyano‐o‐quinodimethane in the presence of anionic initiators such asn‐BuLi ort‐BuOK were performed at various temperatures for 12 h. Good yields of hexane‐insoluble polymer, which was produced by anionic polymerization of correspondingo‐quinodimethane as an intermediate, were obtained above 120 °C. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 844–850, 2008

Preparation of PP-g-PA6 copolymers through reactive blending

Block or graft copolymers have gained much interests recently, not only because of their general application as compatibilizers in blends with thermodynamically immiscible polymer pairs [1], but also of many special and important characteristics of themselves, such as the formation of self assembly morphologies, which can be used for drug delivery, nanoreactor and molecular templating, etc. [2, 3]. In general, copolymers can be prepared by ionic polymerization [4], controlled radical polymerization [5] and some other special polymerization methods [6, 7]. However, for some specific polymer pairs, such as polypropylene (PP) and polyamide 6 (PA6), it is still a challenge to prepare premade PP-g-PA6 copolymer. Although, maleic anhydride can react with the end amino group of PA6 and in situ forming PP-g-PA6 graft copolymer at the phase interface when maleic anhydride modified PP (PP-g-MAH) is used as an interfacial compatibilizer in PP and PA6 blends [8, 9], the amount of such copolymer is too small to be extracted out because of the relatively low grafting degree of MAH on PP. Preparing such kind of copolymers is still unpractical so far. Recently, Leibler et al. [10] successfully increased the MAH content by preparing the poly (ethylene-ethylacrylate-MAH) copolymer (PE-1) before blending with PA6. They have extracted the PE-1-g-PA6 copolymer out from the blending system in their work. In this communication, we will report another novel exploration of preparing PP-g-PA6 copolymers through reactive blending. Isotactic-PP homopolymer was purchased from Montell (Profax 6331, melt index 10 dg/min at 230 C, density 902 kg/m). Dicumyl peroxide (DCP), e-caprolactam, adipic acid, 3-isopropenyl-a,a0-dimethylbenzene isocyanate (TMI), x-aminocaproic acid and m-cresol were obtained from Aldrich Co. Ltd. Formic acid, xylene and acetone were purchased from Riedel-de Haen. All the chemicals are reagent grade and used as received. PA6 ‘‘end-functionalized’’ by unsaturated double bonds (PA6-TMI) was synthesized by condensation polymerization under the protection of nitrogen gas. Condensation polymerization of e-caprolactam was initiated by x-aminocaproic acid at 260 C. The molecular weight was adjusted by stoichiometrically adding adipic acid into the polymerization system. At the end of polymerization, a certain amount of 3-isopropenyl-a,a-dimethylbenzeneisocyanate (TMI) was added into the polymeric melt. The isocyanate group in TMI will react with the end carboxyl (COOH) group of PA6 to form amide [11], which will result in the TMI attachment to the PA6 molecular chain ends (PA6-TMI). About 50 ml of m-cresol was added to terminate all the reaction and drop down the system temperature to room temperature. After precipitated in acetone, filtrated and dried in a vacuum oven at 85 C for 48 h, end functional PA6 powder were stored in a dry box for further blending with PP. The molecular weight of end functionalized PA6 was measured by relative viscosity method. Table 1 lists the PA6 samples with and without TMI end functionalization used in this experiment. PP/PA6 blend was prepared by reactive blending of PP and the PA6-TMI using DCP as initiator. Melt blending was performed in a Brabender internal mixer at 230 C for 5 min. The blend weight ratio employed was PP/PA6D. Shi R. K. Y. Li (&) Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong e-mail: aprkyl@cityu.edu.hk

Biphasic ethylene polymerisation using ionic liquid over a titanocene catalyst activated by an alkyl aluminium compound

1- n-Butyl-3-methylimidazolium tetrachloroaluminate ([BMIM] +[AlCl 4] −) was applied to biphasic ionic liquid/hexane ethylene polymerisation as a medium of the Cp 2TiCl 2 titanocene catalyst activated by alkylaluminium compounds (MAO, AlEt 2Cl, AlEt 3). The best results were obtained using AlEt 2Cl. The results show that catalyst recycling, higher ethylene pressure, and greater Al/Ti molar ratio along with a greater volume of the ionic liquid phase enhance catalyst activity. The polyethylene gathered from the hexane phase is characterised primarily by its high purity. Its physical properties remain polyethylene obtained over a heterogeneous metallocene catalyst. Thus, biphasic ionic liquid polymerisation using a metallocene catalyst is possible and offers interesting technological implications.

Copper-catalyzed oxidative coupling of 2,6-dimethylphenol: A radicalar or an ionic polymerization?

The copper-catalyzed oxidative coupling of 2,6-dimethylphenol to produce poly(1,4-phenylene ether) (PPE), a valuable industrial thermoplastic, has been discovered in the late 1950s. Nevertheless, after almost 50 years of intensive research investigations, its mechanism is not yet entirely elucidated. Some groups advocate the involvement of phenoxyl radicals, while others claim for a carbocationic pathway. This account is meant to briefly summarize the past five decades of mechanistic studies on this polymerization reaction, with an emphasis on experimental data corroborating a heterolytic (ionic) pathway for the polymer chain growth.