Abstract: The effect of Cu(0) wire dimensions on the Cu(0) wire/Me6-TREN-catalyzed heterogeneous single-electron transfer living radical polymerization (SET-LRP) of methyl acrylate (MA) initiated with methyl 2-bromopropionate (MBP) in DMSO at 25 °C was analyzed by kinetic experiments. These kinetic results were compared with those of Cu(0) powder/Me6-TREN-catalyzed SET-LRP. Both wire and powder produce perfect SET-LRP with a first-order rate of polymerization in growing species up to 100% conversion. Nevertheless, Cu(0) wire experiments demonstrated SET-LRP with greater perfection, allowing for the accurate determination of the external rate order (vis-a-vis surface area) for heterogeneous Cu(0) catalyst and accurate prediction of kpapp from wire dimension. Cu(0) wire also exhibited a significantly greater control of molecular weight distribution than Cu(0) powder. The combined advantages of easier catalyst preparation, handling, predictability, tunability, simple recovery/recycling, and enhanced control of molecul...

Abstract: Disproportionation of Cu(I)X is the major step in Single-Electron Transfer Living Radical Polymerization (SET-LRP). The disproportionation of Cu(I)X mediated by Me-6-TREN in various solvents was studied through UV-vis spectroscopy and Dynamic Light Scattering (DLS). UV-vis experiments reveal that disproportionation is dependent on both solvent composition and concentration of Me-6-TREN, consistent with a revised equilibrium expression and corroborated by mathematical models. Electrochemistry data do not accurately predict the extent of disproportionation in the presence of Me6-TREN. Exemplified by DMSO, a favored solvent for SET-LRP, LTV-vis spectroscopy shows that under certain conditions disproportionation is four-orders of magnitude greater than the value reported from electrochemistry experiments. Through LTV-vis and DLS analysis, it was demonstrated that DMSO, DMF, DMAC, and NMP, stabilize colloidal Cu(0), while acetone, EtOH, EC, MeOH, PC, and H2O facilitate agglomeration of Cu(0) particles. Additionally, for colloidal Cu(0) stabilizing solvents, the amount of ligand and solvent composition decide the particle size distribution. Therefore, the kinetics of SET-LRP are cooperatively and synergistically determined by the complex interplay of solvent polarity, the extent of disproportionation in the solvent/ligand mixture, and the ability of that mixture to stabilize colloidal Cu(0) or control particle size distribution. The implications of these results for SET-LRP are discussed. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47:5606-5628, 2009

Abstract: The dimethylaluminum compounds {3-tBu-2-(O)C6H3CH═N−R}AlMe2 [R = C6H5 (1); 2,6-iPr2C6H3 (2); C6F5 (3)] were used as initiators in the ring-opening polymerization (ROP) of e-caprolactone, l-lactide, and d,l-lactide. Compound 3, in combination with 1 equiv of methanol, exhibited a living behavior in the ROP of the cyclic esters. Such a feature allowed the preparation of poly(d,l-lactide-block-e-caprolactone) and poly(l-lactide-block-e-caprolactone) copolymers. Random copolymers of e-caprolactone and l-lactide and of e-caprolactone and d,l-lactide were also synthesized by compound 3. NMR and DSC characterization confirmed a highly random structure of these copolymers, even in the absence of transesterification reactions. All the materials, characterized by GPC, showed high molecular weight and narrow molecular weight distributions.

Abstract: SET-LRP is mediated by a combination of solvent and ligand that promotes disproportionation of Cu(I)X into Cu(0) and Cu(II)X 2 . Therefore, the diversity of solvents suitable for SET-LRP is limited. SET-LRP of MA in a library of solvents with different equilibrium constants for disproportionation of Cu(I)X such as DMSO, DMF, DMAC, EC, PC, EtOH, MeOH, methoxyethanol, NMP, acetone and in their binary mixtures with H 2 O was examined. H 2 O exhibits the highest equilibrium constant for disproportionation of Cu(I)X. The apparent rate constant of the polymerization exhibits a linear increase with the addition of H 2 O. This is consistent with higher equilibrium constants for disproportionation generated by addition of H 2 O to organic solvents. Furthermore, with the exception of alcohols and carbonates, the rate constant of polymerization in binary mixtures could be correlated with the Dimroth-Reichardt solvent polarity parameter. This is consistent with the single-electron transfer mechanism proposed for SET-LRP that involves a polar transition state. These experiments demonstrate that the use of binary mixtures of solvents with H 2 O provides a new, simple and efficient method for the elaboration of a large diversity of reaction media that are suitable for SET-LRP even when one of the two solvents does not mediate disproportionation of Cu(I)X.

Abstract: We report the synthesis of poly(e-caprolactone) utilizing N-heterocyclic carbene (NHC) organocatalysts. Sterically unencumbered NHCs were found to be highly effective for the living ring-opening polymerization of e-caprolactone under mild conditions. The NHCs were able to produce poly(e-caprolactone)s with controlled molecular weights, low polydispersities, and well-defined end groups derived from the alcohol initiator. Star-shaped poly(e-caprolactone)s with three and four arms were prepared using NHC organocatalysts and characterized by 1H NMR and GPC.

Abstract: SET-LRP requires a combination of ligand and solvent that mediates the disproportionation of Cu(I)X into Cu(O) activator, and Cu(II) deactivator. The solvent also modulates the kinetics of the reaction. More polar solvents, including mixtures of water and organic solvents enhance the rate of polymerization in accord with the Dimroth-Reichardt parameter. Here, it is demonstrated that a similar effect is observed in binary mixtures of organic solvents, wherein the addition of a more polar solvent to a less polar solvent provides a linear increase in the apparent rate constant of propagation, k . However, this linear relationship does not hold for the entire range of volume fraction for binary mixtures when ethylene carbonate (EC) or MeOH are one of the two components. Results herein, suggest that the kinetics of SET-LRP in these solvent mixtures is cooperatively and synergistically determined by polarity, degree of disproportionation, and also by another parameter related to the ability of the solvent to stabilize colloidal Cu(0) and determine its particle size.

Abstract: A series of aluminum ethyls and isopropoxides based on a bis(pyrrolidene) Schiff base ligand framework has been prepared and characterized. NMR studies of the dissolved complexes indicate that they adopt a symmetric structure with a monomeric, five-coordinated aluminum center core. The aluminum ethyls used as catalysts in the presence of 2-propanol as initiator and the aluminum isopropoxides were applied for lactide polymerization in toluene to test their activities and stereoselectivities. All polymerizations are living, as evidenced by the narrow polydispersities and the good fit between calculated and found number-average molecular weights of the isolated polymers. All of these aluminum complexes polymerized (S,S)-lactide to highly isotactic PLA without epimerization of the monomer, furnished isotactic-biased polymer from rac-lactide, and gave atactic polymer from meso-lactide. The study of kinetics indicated that the activity of the bis(pyrrolidene) Schiff base aluminum initiator systems toward lactid...

Abstract: Cationic polymerization of isobutyl vinyl ether (IBVE) was examined using a variety of metal halides. In the presence of an appropriate added base, ester or ether, the living polymerization of IBVE proceeded for almost all Lewis acids (MCln; M: Fe, Ga, Sn, In, Zn, Al, Hf, Zr, Bi, Ti, Si, Ge, Sb) used in conjunction with an IBVE−HCl adduct in toluene at 0 °C. The difference in the polymerization activity of these Lewis acids was significant. As examples, polymerization with some acids, such as FeCl3, proceeded in the order of seconds, whereas it took more than a few weeks with others such as SiCl4 and GeCl4. The difference in activity is based on the strength of the interaction between the Lewis acid and the propagating end chloride anion and/or the basic carbonyl (or ether) oxygen atom of the added base, that is, the chlorophilic or oxophilic nature of each metal halide is a decisive factor. In addition, a suitable combination of a Lewis acid and an additive was indispensable for living polymerization. Wi...

Abstract: Fine polythiophene (PTh) microparticles were successfully synthesized by a novel interfacial polymerization at a dynamic interface between two immiscible solvents, i.e., n-hexane and acetonitrile or nitromethane containing thiophene and oxidant, respectively. The polymerization yield, size, and electrical conductivity of the microparticles are optimized by facilely regulating the medium species, oxidant species, oxidant/monomer ratio, monomer concentration, and polymerization temperature. The microparticles were thoroughly characterized by IR, UV−vis spectroscopy, wide-angle X-ray diffractometry, laser particle-size analyzer, and simultaneous TG-DSC technique. The yield rises with increasing oxidant/monomer ratio, monomer concentration, and polymerization temperature. However, low monomer concentration, low polymerization temperature, and modest oxidant/monomer ratio are all favorable for the formation of the PTh with good, large π-conjugation and high conductivity. With decreasing the thiophene concentra...

Abstract: N-Heterocyclic carbenes (NHCs), namely, 1,3-bis-(diisopropyl)imidazol-2-ylidene (1) and 1,3-bis(di-tert-butyl)imidazol-2-ylidene (2) were employed as neutral organocatalysts to bring about the grou...

Abstract: An investigation for the initiation of a chain-growth polymerization, Kumada catalyst-transfer polycondensation, for the synthesis of poly(3-hexylthiophene) is described. A novel method for the generation of an active catalyst/initiator complex was developed utilizing the inexpensive, air stable Ni(PPh3)2Cl2 precursor to generate the active Ni(PPh3)4 catalyst in situ. Poly(3-hexylthiophene) polymerization reactions were carried out using aryl halides with various substituents on the phenyl ring as external initiators, and it was found that the type of the functional group present on the initiator plays a crucial role in the polymerization. The new method provided a more efficient way to initiate polymerization yielding polymers with higher regioregularity, larger molecular weight, and lower polydispersity than the previously reported methods.

Abstract: Here we report the grafting of N,N-dimethylaminoethyl methacrylate (DMAEMA) directly from poly(vinylidene fluoride) (PVDF) backbone in solution phase by atom transfer radical polymerization (ATRP). The graft length is same for different times of polymerization but graft density increases with increasing polymerization time. Four graft copolymers are prepared and depending on the time of conversion they are designated as PD-6, PD-12, PD-18, and PD-24, the number indicates time (h) of polymerization. A maximum of 36% (w/w) conversion with respect to monomer is achieved in the PD-24 sample. Gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), and polymerization kinetics study conclude the ATRP nature of the polymerization. The graft copolymer shows induced solubility in water and the effective particle diameter in aqueous medium decreases from PD-6 to PD-24 samples. The enthalpy of fusion values are same in graft copolymers with more than 50% reduction and the melting points reduce by 5−6 °...

Abstract: Pulsed-laser polymerization (PLP) in conjunction with aqueous-phase size-exclusion-chromatography (SEC) was employed to determine the propagation rate coefficient, kp, of methacrylic acid (MAA) free-radical polymerization in aqueous solution. This was done over a wide range of degree of MAA ionization, at MAA concentrations between 5 and 40 wt %, and at temperatures from 6 to 80 °C. Depending on monomer concentration, the degree of ionization, α, may largely affect kp. At 5 wt % MAA, kp is lowered by about 1 order of magnitude in passing from nonionized to fully ionized MAA, whereas the associated decrease in kp at 40 wt % MAA is only by 20%. The changes of MAA kp with α are assigned to intermolecular interactions affecting the friction that is experienced by the relevant internal rotations of the transition state structure for propagation. Increasing hindrance of rotational motion is associated with a lowering of the pre-exponential factor, A(kp). The observed effects are primarily of entropic origin, bu...

Abstract: Four metal benzylalkoxides, [L(2)M(2)(mu-OBn)(2)] (M = Mg or Zn), based on NNO-tridentate ketiminate ligands are synthesized and characterized. X-ray crystal structural studies of [(L(1))(2)Mg(2)(mu-OBn)(2)] (1a) and [(L(1))(2)Zn(2)(mu-OBn)(2)] (1b) (L(1)-H = (Z)-4-((2-(dimethylamino)ethylamino)(phenyl)methylene)-3-methyl-1-phenyl-pyrazol-5-one) reveal that both complexes 1a and 1b are dinuclear species whereas the geometry around the metal center is penta-coordinated bridging through the benzylalkoxy oxygen atoms in the solid structure. The activities and stereoselectivities of these four complexes toward the ring-opening polymerization Of L-lactide and rac-lactide are investigated. Polymerization Of L-lactide initiated by these four metal benzyloxides proceeds rapidly with good molecular weight control and yields polymer with a very narrow molecular weight distribution. The kinetic studies for the polymerization of L-lactide with compound 1a show first order in both compound 1a and lactide concentrations with the polymerization rate constant, k, of 6.94 M/min. Besides, experimental results demonstrate that among these metal benzylalkoxides, complex 1a exhibits the highest stereoselectivity with a Pr up to 87% and complex 1b possesses the highest activity indicating that the terminal group of NNO-tridentate ketimine ligands exerts a significant influence on both the reactivity and stereoselectivity of these complexes. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2318-2329, 2009

Abstract: A novel tridentate anilido-aldimine ligand, [o-C6H4(NHAr)HCNCH2CH2NMe2] (Ar = 2,6-iPr2C6H3, L-H, 1), has been prepared by the condensation of N, N-dimethylethylenediamine with one molar equivalent of 2-fluoro-benzaldehyde in hexane, followed by the addition of the lithium salt of diisopropylaniline in THF. Magnesium (Mg) and zinc (Zn) complexes supported by the tridentate anilido-aldimine ligand have been synthesized and structurally characterized. Reaction of L-H (1) with an equivalent amount of MgnBu2 or ZnEt2 produces the monomeric complex [LMgnBu] (2) or [LZnEt] (3), respectively. Experimental results show that complexes 2 and 3 are efficient catalysts for ring-opening polymerization of e-caprolactone (CL) and L-lactide (LA) in the presence of benzyl alcohol and catalyze the polymerization of e-CL and L-LA in a controlled fashion yielding polymers with a narrow polydispersity index. In both polymerizations, the activity of Mg complex 2 is higher than that of Zn complex 3, which is probably due to the higher Lewis acidity and better oxophilic nature of Mg2+ metal. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4927–4936, 2009

Abstract: We developed concurrent tandem living radical polymerization as a novel methodology to efficiently, conveniently, and in one-pot produce gradient copolymers via in situ monomer transformation. The key is to employ a metal alkoxide [Al(Oi-Pr)3, Ti(Oi-Pr)4] and an alcohol solvent (ROH) in ruthenium-catalyzed polymerization of conventional ester-based methyl (meth)acrylate [M(M)A], where the monomer was directly transformed into R(M)A via in situ transesterification to gradually vary the monomer composition during the copolymerization. Typically, methyl methacrylate (MMA) was polymerized with a ruthenium catalyst in the presence of excess ethanol (EtOH) and Al(Oi-Pr)3 cocatalyst to give well-controlled gradient copolymers from MMA to EMA along the polymer chain, in which the original MMA was gradually converted into ethyl methacrylate (EMA) by the cocatalyst. This concurrent tandem polymerization, in conjunction with a wide variety of alcohols, efficiently and conveniently produced various gradient copolymer...

Abstract: High-vacuum polymerization of α-(amino acid)-N-carboxyanhydrides (NCAs) affords polymers with controlled molecular weights and narrow polydispersities; however, a comprehensive study of the end-group composition of the resulting polypeptides has not yet been performed. This reveals crucial information, as the end-groups are indicative of both the polymerization mechanism (i.e., initiation event) and the termination pathways. To this end, poly(O-benzyl-l-tyrosine) initiated by 1,6-diaminohexane was synthesized and subsequently characterized by MALDI-TOF MS, NALDI-TOF MS, and 13C NMR spectroscopy to ascertain the end-group structure. Polymers were prepared by both high-vacuum and glovebox techniques in DMF/THF. Preparation of poly(O-benzyl-l-tyrosine) by high-vacuum techniques yielded a polymer initiated exclusively by the normal amine mechanism, and termination by reaction with DMF was observed. In contrast, polymers prepared in the glovebox were initiated by the normal amine and activated monomer mechanis...

Abstract: The simulation of polymerization processes is of enormous industrial importance. A quantum chemical method based on density functional theory is developed and validated that provides almost chemical accuracy for radical polymerization propagation of industrially relevant monomers in aqueous solution. The necessary corrections are computed using the CC level of theory. Solvent effects are accounted for by the solvation model COSMO-RS. The method is capable of reproducing and rationalizing, for example, monomer concentration effects on the propagation rate for NVP. A comparison is performed with recent PLP experimental data. The method does not rely on error compensation effects or empiric corrections and is suitable for industrially relevant systems.

Abstract: We recently reported on the synthesis and characterization of CoCl2(PRPh2)2 (R = methyl, ethyl, n-propyl, isopropyl, and cyclohexyl). The catalyst systems obtained by combining the above complexes with methylaluminoxanes (MAO) were highly active in the polymerization of 1,3-dienes, giving 1,2 syndiotactic polymers from butadiene and terminally substituted butadienes (e.g., E-1,3-pentadiene and E-1,3-hexadiene) and 1,2 isotactic polymers from internally substituted 1,3-dienes such as E-3-methyl-1,3-pentadiene. We have now polymerized isoprene with the same cobalt catalysts, and unexpectedly the polymers obtained resulted to have an equibinary, alternating cis-1,4/3,4 structure, as indicated by the two-dimensional NMR data. A structure of this type is rather unusual in the field of diolefins stereospecific polymerization, and only few cases have been reported in the literature. An interpretation for the formation of such a polymer is proposed. The structure of cis-1,4-alt-3,4 polyisoprene, with alternating ...

Abstract: A typical reversible addition−fragmentation chain transfer (RAFT) agent, 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN), was used as a single electron transfer-living radical polymerization (SET−LRP) initiator for methyl methacrylate (MMA) polymerization at 25 °C. At 1:1 molar ratio of [CPDN]0/[Cu(0)]0, the apparent rate constants of propagation (kpapp) were 0.037, 0.049, and 0.072 h−1 for [MMA]0/[CPDN]0 of 225/0.2, 225/0.5, and 225/1, respectively. The number-average molecular weight of poly(methyl methacrylate) (PMMA) increased linearly with monomer conversion, and narrow molecular weight distributions (Mw/Mn < 1.50) were found at most cases. At high molar ratio of [CPDN]0 to [Cu(0)]0, such as 1:0.1 in this work, the polymerization was also controllable, whereas it a presented markedly depressed polymerization rate and an obvious induction period. 1H NMR spectroscope and matrix assisted laser desorption/ionization time-of-flight mass spectrometry confirmed that PMMA chain was end-capped by CPDN species wit...

Abstract: RAFT polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA, 1100 g mol−1) was first performed using cyanoisopropyl dithiobenzoate (CPDB). The control of PEGMA homopolymerization, carried out in THF ([PEGMA] = 40 wt %) at 65 °C (reflux) using 2,2′-Azobis(isobutyronitrile) (AIBN) as initiator, was shown by the linear increase of molar masses and the low polydispersity indices (PDI) observed with conversion and also by the determination of a high chain transfer constant (Ctr = 9.1) for CPDB in this system. Copolymerization of PEGMA with methacrylic acid (MAA) ([PEGMA]/[MAA] = 40/60) was then undertaken first in dioxane at 85 °C. High conversion (89%) was obtained in 3 h without any composition drift and with a good level of control (PDI < 1.40). When the polymerization was performed in water, a strong increase in polymerization rate was observed with almost quantitative conversion (98%) in 2 h without affecting the level of control of the final copolymers (PDI ∼ 1.30). These last results were tentatively explained by the formation of hydrophobic domains in which the polymerization occurred as in bulk. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3045–3055, 2009

Abstract: Superabsorbents used in agricultural and ecological projects with low-cost, slow-release fertilizers and environmentally friendly characteristics have been extensively studied. The use of a natural polymer as the matrix and then further polymerization with some func- tional material has become the preferred method. In this work, with natural guar gum (GG), partially neutralized acrylic acid, and sodium humate (SH) as the raw materi- als, ammonium persulfate as the initiator, and N,N 0 -meth- ylenebisacrylamide (MBA) as the crosslinker, GG-g- poly(sodium acrylate) (PNaA)/SH superabsorbents were synthesized through a solution polymerization reaction and were characterized with Fourier transform infrared spectroscopy, scanning electron microscopy, and thermog- ravimetric analysis. The effects of the SH content and MBA concentration on the water absorbency were investi- gated. The results showed that the introduction of SH into the GG-g-PNaA system could improve the water absorb- ency, swelling rate, pH-resistant property, and reswelling capability, and the superabsorbent containing 15 wt % SH had the highest water absorbency of 532 g/g of sample in distilled water and 62 g/g of sample in a 0.9 wt % NaCl solution. The slow release in water and water retention in sandy soil tests revealed that the superabsorbent could act as a fertilizer as well as an effective water-saving material for agricultural applications. V C 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 2102-2111, 2009