Deactivation reactions in the modeled 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐mediated free‐radical polymerization of styrene: A comparative study with the 2,2,6,6‐tetramethyl‐1‐piperidinyloxy/acrylonitrile system

The competitiveness of the combination and disproportionation reactions between a 1‐phenylpropyl radical, standing for a growing polystyryl macroradical, and a 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) radical in the nitroxide‐mediated free‐radical polymerization of styrene was quantitatively evaluated by the study of the transition geometry and the potential energy profiles for the competing reactions with the use of quantum‐mechanical calculations at the density functional theory (DFT) UB3‐LYP/6‐311+G(3df, 2p)//(unrestricted) Austin Model 1 level of theory. The search for transition geometries resulted in six and two transition structures for the radical combination and disproportionation reactions, respectively. The former transition structures, mainly differing in the out‐of‐plane angle of the N? O bond in the transition structure TEMPO molecule, were correlated with the activation energy, which was determined to be in the range of 8.4–19.4 kcal mol^?1 from a single‐point calculation at the DFT UB3‐LYP/6‐311+G(3df, 2p)//unrestricted Austin Model 1 level. The calculated activation energy for the disproportionation reaction was less favorable by a value of more than 30 kcal mol^?1 in comparison with that for the combination reaction. The approximate barrier difference for the TEMPO addition and disproportionation reaction was slightly smaller for the styrene polymerization system than for the acrylonitrile polymerization system, thus indicating that a β‐proton abstraction through a TEMPO radical from the polymer backbone could diminish control over the radical polymerization of styrene with the nitroxide even more than in the latter system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 232–241, 2007     

Self‐Assembly of Conjugated Metallopolymers with Tunable Length and Controlled Regiochemistry

Self‐assembled materials can be designed to express useful optoelectronic properties; however, achieving structural control is a necessary precondition for the optimization of desired properties. Here we report a simple, metal‐templated polymerization process that generates helical metallopolymer strands over 75 repeat units long (28 kDa) from a single bifunctional monomer and Cu^I. The resulting polymer consists of a double helix of two identical conjugated organic strands enclosing a central column of metal ions. The length of this metallopolymer can be controlled by adding monofunctional subcomponents to end‐cap the conjugated ligands. The use of ditopic and bulky monotopic subcomponents, respectively, allows a head‐to‐head or head‐to‐tail double helix to be generated. Spectroscopic measurements of different polymer lengths demonstrate how control over polymer length leads to control over the electronic and luminescent properties of the resulting material, thereby enabling tunable white‐light emission.     

End‐group fidelity of copper(0)‐meditated radical polymerization at high monomer conversion: an ESI‐MS investigation

Copper(0)‐mediated radical polymerization (single electron transfer‐living radical polymerization) is an efficient polymerization technique that allows control over the polymerization of acrylates, vinyl chloride and other monomers, yielding bromide terminated polymer. In this contribution, we investigate the evolution of the end‐group fidelity at very high conversion both in the presence and in the absence of initially added copper (II) bromide (CuBr₂). High resolution electrospray‐ionization mass spectroscopy (ESI‐MS) allows determination of the precise chemical structure of the dead polymers formed during the polymerization to very high monomer conversion, including post polymerization conditions. Two different regimes can be identified via ESI‐MS analysis. During the polymerization, dead polymer results mainly from termination via disproportionation, whereas at very high conversion (or in the absence of monomer, that is, post‐polymerization), dead polymers are predominantly generated by chain transfer reactions (presumably to ligand). The addition of CuBr₂ significantly reduces the extent of termination by both chain transfer and disproportionation, at very high monomer conversion and under post‐polymerization conditions, offering a convenient approach to maintaining high end‐group fidelity in Cu(0)‐mediated radical polymerization. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Termination Mechanism of the Radical Polymerization of Acrylates

The termination mechanism of the radical polymerization of acrylates, namely the selectivity of disproportionation (Disp) and combination (Comb) between polymer end radicals, is unambiguously determined by the reaction of polyacrylate end radicals generated from corresponding “living” organotellurium ω‐end polymer. While textbooks describe the occurrence of Comb, the reaction at 25 °C exclusively gives the Disp products. Ab initio molecular dynamics suggests that the products form by two pathways: The direct disproportionation reaction and a novel stepwise process that involves the initial formation of the C–O coupling product followed by intramolecular rearrangement. The termination at high temperature and low radical concentration increases the contribution of back‐biting reaction giving mid‐chain radicals, and complex reaction pathways of the mid‐chain radicals are clarified for the first time.

     

Electrochemical and chemical polymerization of acrylamide

The electrochemical and chemical polymerization of acrylamide (AA) has been studied. The electrolysis of the monomer in N,N-dimethylformamide (DMF) containing (C₄H₉)₄NClO₄ as the supporting electrolyte leads to polymer formation in both anode and cathode compartments. The cathodic polymer dissolves in the reaction mixture and the anodic polymer precipitates during the course of polymerization. A plausible mechanism for the anodic and cathodic initiation reaction has been given. The chemical polymerization of acrylamide that has been initiated by HClO₄ is analogous to its anodic polymerization. The polymer yield increases with an increase in concentration of the monomer and HClO₄. Raising the reaction temperature also enhances the polymerization rate. The overall apparent activation energy of the polymerization was determined to be ca. 19 kcal/mole. The copolymerization of acrylamide was carried out with methyl methacrylate (MMA) in a solution of HClO₄ in DMF. The reactivity ratios are r₁ (AA) = 0.25 and r₂ = 2.50. The polymerization with HClO₄ appears to be by a free radical mechanism. When the polymerization of acrylamide is carried out with HClO₄ in H₂O, a crosslinked water-insoluble gel formation takes place.     

Thermal polymerization of acrylamide in the solid state

The role of imperfections in thermal polymerization of acrylamide in the solid state was studied. The polymer yield and the degree of polymerization are highly dependent on the particle size and on the pressure to which the monomer is subjected prior to polymerization reaction. There is an enhancement in the rate of polymerization in air unlike in the case of radiation-induced polymerization. Thermal polymerization of acrylamide in pelletized form results in the formation of water-soluble linear polymer and water-insoluble cross-linked product with the evolution of ammonia. The activation energy (E) values obtained in the present investigation reveal that basically there are two processes taking place, one with E = 34–36 kcal/mole, corresponding to the initiation process, and the other with E = 19 ± 3 kcal/more for the propagation process.     

Synthesis and characterization of ordered polyurethanes from nonsymmetric diisocyanate and ethylene glycol

An ordered polyurethane with a head‐to‐head (H‐H) or tail‐to‐tail (T‐T) content over 95% was prepared by polyaddition reaction of a nonsymmetric monomer, p‐isocyanatobenzyl isocyanate (1) with a symmetric monomer, ethylene glycol (2). The model reactions were studied in detail to demonstrate the feasibility of polymer formation. The polymerization was conducted in THF in the presence of triethylamine (TEA) at 0 °C by slow addition of a half amount of 2 to 1, followed by removing THF and then adding the rest of 2 in DMF at once at 30 °C in the presence of dibutyltin dilaurate (DBTL). The microstructure of the polymer obtained was investigated by ¹³C NMR spectroscopy, and it was found that the polymer had the expected structural regularity. The constitutional regularity of polymers influenced their thermal properties. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2106–2114, 2000     

A new sequence isomer of AB‐polybenzimidazole for high‐temperature PEM fuel cells

A new sequence isomer of AB‐polybenzimidazole (AB‐PBI) was developed as a candidate for high‐temperature polymer electrolyte membrane fuel cells. A diacid monomer, 2,2′‐bisbenzimidazole‐5,5′‐dicarboxylic acid, was synthesized and polymerized with 3,3′,4,4′‐tetraaminobiphenyl to prepare a polymer that was composed of repeating 2,5‐benzimidazole units. In contrast to previously prepared AB‐PBI, which contains only head‐to‐tail benzimidazole sequences, the new polymer also contains head‐to‐head and tail‐to‐tail benzimidazole sequences. The polymer was prepared in polyphosphoric acid (PPA) and cast into membranes using the sol–gel PPA process. Membranes formed from the new AB‐PBI were found to be mechanically stronger, possessed higher acid doping levels, and showed improved fuel cell performance, when compared to the previously known AB‐PBI. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Effect of sodium dodecyl benzene sulfonate to the displacement performance of hyperbranched polymer

Experimental studies were conducted to realize displacement performance effect of anionic surfactant sodium dodecyl benzene sulfonate (SDBS) on hyperbranched poly(AM/AA/AMPS/GA), which was successfully synthesized via free radical polymerization using modified dendritic functional monomer (GA), acrylamide (AM), acrylate (AA), and 2-acrylamido-2-methyl propane sulfonic acid (AMPS). Compared with individual polymer, SP (surfactant polymer) binary systems showed lower apparent viscosity, interfacial tension, and hydrodynamic radius as the result of the electrostatic repulsion between the tail end of hydrophilic polymer branched chain and the head of the surfactant. It was found from abundant static adsorption and dynamic retention tests that the values of static adsorption and dynamics retention of SDBS which is mixed with hyperbranched polymer decrease due to the competitive interaction. However, unlike this phenomenon, SDBS would heighten the dynamic retention value of poly(AM/AA/AMPS/GA), resulting in addition of residual resistance factor. Oil displacement experiment indicated that SP solutions have greater capability of enhance oil recovery than individual polymer under same conditions.     

Investigation of catalyst‐transfer condensation polymerization for the synthesis of n‐type π‐conjugated polymer,poly(2‐dioxaalkylpyridine‐3,6‐diyl)

Kumada‐Tamao coupling polymerization of 6‐bromo‐3‐chloromagnesio‐2‐(3‐(2‐methoxyethoxy)propyl)pyridine 1 with a Ni catalyst and Suzuki‐Miyaura coupling polymerization of boronic ester monomer 2 , which has the same substituted pyridine structure, with ^tBu₃PPd(o‐tolyl)Br were investigated for the synthesis of a well‐defined n‐type π‐conjugated polymer. We first carried out a model reaction of 2,5‐dibromopyridine with 0.5 equivalent of phenylmagnesium chloride in the presence of Ni(dppp)Cl₂ and then observed exclusive formation of 2,5‐diphenylpyridine, indicating that successive coupling reaction took place via intramolecular transfer of Ni(0) catalyst on the pyridine ring. Then, we examined the Kumada‐Tamao polymerization of 1 and found that it proceeded homogeneously to afford soluble, regioregular head‐to‐tail poly(pyridine‐2,5‐diyl), poly(3‐(2‐(2‐(methoxyethoxy)propyl)pyridine) (PMEPPy). However, the molecular weight distribution of the polymers obtained with several Ni and Pd catalysts was very broad, and the matrix‐assisted laser desorption ionization time‐of‐flight mass spectra showed that the polymer had Br/Br and Br/H end groups, implying that the catalyst‐transfer polymerization is accompanied with disproportionation. Suzuki‐Miyaura polymerization of 2 with ^tBu₃PPd(o‐tolyl)Br also afforded PMEPPy with a broad molecular weight distribution, and the tolyl/tolyl‐ended polymer was a major product, again indicating the occurrence of disproportionation. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis,Characterization and Photocrosslinking Properties of Poly(1‐(4‐Methacrylamidophenyl)‐1‐(4‐nitrophenyl)prop‐1‐en‐3‐one)

The phenylmethacrylamide monomer, 1‐(4‐methacrylamidophenyl)‐1‐(4‐nitrophenyl)prop‐1‐en‐3‐one (MPNP) containing a photosensitive group was synthesized by reacting 4‐nitrocinnamoylaniline with methacryloyl chloride in the presence of triethylamine at 0–5°C. The functional monomer, MPNP was polymerized in ethyl methyl ketone (EMK) under nitrogen atmosphere at 70°C using benzoyl peroxide (BPO) as the initiator. The synthesized polymer was characterized by UV, IR, ¹H‐NMR and ¹³C‐NMR spectroscopy. The molecular weight data of the polymer as obtained from gel permeation chromatography suggests a higher tendency for chain termination by radical recombination than disproportionation. The thermal studies of the polymer were obtained from thermogravimetric analysis. The glass transition temperature of the polymer was determined by differential scanning calorimetry. The solubility of the polymer was tested in various organic solvents at room temperature. The photosensitivity of the polymer was investigated in various solvents in the presence and absence of triplet photosensitizers. The effect of the different solvents nature and concentration on the rate of photocrosslinking of the polymer were also examined for using the polymer as negative photoresist materials.     

Atom transfer radical polymerization of ionic liquid 2‐(1‐butylimidazolium‐3‐yl)ethyl methacrylate tetrafluoroborate

Polymeric forms of ionic liquids may have many potential applications because of their high thermal stability and ionic nature. They are generally synthesized by conventional free‐radical polymerization. Here we report a living/controlled free‐radical polymerization of an ionic liquid monomer, 2‐(1‐butylimidazolium‐3‐yl)ethyl methacrylate tetrafluoroborate (BIMT), via atom transfer radical polymerization. Copper bromide/bromide based initiator systems polymerized BIMT very quickly with little control because of fast activation but slow deactivation. With copper chloride as the catalyst and trichloroacetate, CCl₄, or ethyl α‐chlorophenylacetate as the initiator, BIMT was polymerized at 60 °C in acetonitrile with first‐order kinetics with respect to the monomer concentration. The molecular weight was linearly dependent on the conversion. The monomer concentration strongly affected the polymerization: a low monomer concentration caused the polymerization to be incomplete, probably because of catalyst disproportionation in polar solvents. The addition of a small amount of pyridine suppressed such disproportionation, but a further increase in the amount of pyridine greatly slowed the polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5794–5801, 2004     

The Synthesis of Hydrophobically Modified Water‐Soluble Polyzwitterionic Copolymers and Responsiveness to Surfactants in Aqueous Solution

Abstract

A novel zwitterionic surfactant monomer containing a carboxybetaine moiety and a 10 carbon aliphatic tail was synthesized and copolymerized with acrylamide to yield a water‐soluble, hydrophobically modified zwitterionic polymer [Poly(acrylamide‐co‐(3‐(N,N‐dimethyl‐N‐3′‐(N′‐acryloyl)aza‐tridecyl) ammonio butanoate))]. The response of aqueous polymer solutions to the addition of various classes of surfactant was investigated and compared to that of an analogous novel polymer containing the sulfobetaine zwitterion [Poly(acrylamide‐co‐(N,N‐dimethyl‐N‐3′‐(N′‐acryloyl) aza‐tridecyl) ammonio propane sulfonate))]. It was found that the addition of sodium dodecyl sulfate (SDS) produced a pronounced maximum in viscosity, while dodecyltrimethylammoniumbromide (DTAB), N‐dodecyl‐N,N‐dimethylammonio‐1‐propanesulfonate (SB3‐12), and Triton X‐100 either had no effect, or produced a decrease in viscosity. The effect of pH on polymer–SDS interaction was also studied. Lowering pH increased the SDS–polymer interaction and significantly shifted viscosity enhancement to a higher SDS concentration.     

A calculation of thermal degradation initiated by random scission,unsteady radical concentration

Changes in molecular weight distribution and in sample volume were calculated for thermal degradation of a polymer. The thermal degradation scheme consists of random scission initiation, depropagation and disproportionation termination reactions. An unsteady radical concentration was considered. There are two parameters, normalized zip length z/x₀ and radical number per initial chain length z′x₀, describing the thermal degradation scheme with an unsteady radical concentration. The effects of the initial number-average molecular weight and order of the disproportionation termination reaction on changes in molecular weight, the sample volume and polydispersity are not significant as long as these two parameters have the same value for each polymer sample. Molecular weights of a degrading sample calculated from the steady state radical concentration tend to be over-estimated and sample volumes tend to be underestimated compared to those calculated with an unsteady radical concentration. The validity of approximations used in the calculation assuming a steady state radical concentration is examined by comparing with results calculated with an unsteady radical concentration for various values of the two parameters. An unrealistically large build-up of monomer radicals is found for both calculations based on the steady state and the unsteady radical concentrations. Two special treatments of monomer radicals can dissipate the build-up of monomer radicals: (1) their immediate vaporization, or (2) an enhanced rate of the termination reaction for the monomer radicals. As a guide, the model based on an unsteady radical concentration is preferred, if the value of z′x₀ exceeds 0.1.     

Synthesis,Characterization, and Photocrosslinking Properties of Poly(4‐Methacrylamidophenyl‐2′,3′‐benzostyryl Ketone)

Abstract

A new methacrylamide monomer, 4‐methacrylamidophenyl‐2′,3′‐benzostyryl ketone (MPBSK) having a free‐radical polymerizable group and a photocrosslinkable functional group, was synthesized by reacting 4‐(2′,3′‐benzocinnamoyl)aniline with methacryloyl chloride in the presence of triethyl amine. The monomer, MPBSK was polymerized in methyl ethyl ketone (MEK) at 70°C using benzoyl peroxide (BPO) as the initiator. The polymer was characterized by UV, IR, ¹H‐NMR, and ¹³C‐NMR spectroscopy. The polymer was found to be soluble in several polar aprotic solvents and in chlorinated solvents but insoluble in aliphatic and aromatic hydrocarbons and in alcohols. The molecular weight data of the polymer as obtained from gel permeation chromatography suggests a higher tendency for chain termination by disproportionation than dimerization. The glass transition temperature of the polymer was determined by differential scanning calorimetry. Thermogravimetric analysis of the polymer carried out in air reveals that it possesses good thermal stability required of a negative photoresist. The photocrosslinking property of the polymer was investigated by irradiating the polymer solution with UV light in the presence and absence of triplet photosensitizers. The effect of the solvent on the rate of photocrosslinking of the polymer was also studied.     

Embedding multiple site‐specific functionalities into polymer chains via nitrone‐mediated radical coupling reactions

A facile method to generate polymer materials with embedded functional groups at known and precise positions along the polymer backbone is described. In the presented approach, well‐defined bifunctional poly(isobornyl acrylate)s preformed via atom transfer radical polymerization (ATRP) containing α,ω‐bromo end groups are reactivated and subsequently coupled in a stepwise manner via the nitrone‐mediated radical coupling (NMRC) technique. The generated polymers contain on average four nitrone moieties at evenly spaced locations. The number of embedded functionalities, and thus, the size of the polymer is limited by disproportionation reactions occurring during the nitroxide termination sequence. Using the nitrone as a functional carrier, secondary functionalities can be incorporated into the polymer with ease. To exemplify such an approach, an alkyne‐functionalized nitrone is used to construct a multisegment structure via NMRC reactions followed by postmodification of the obtained polymers with 3‐mercaptopropionic acid via UV‐induced thiol‐yne reactions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Comprehensive Analysis of DNA Strand Breaks at the Guanosine Site Induced by Low‐Energy Electron Attachment

To elucidate the role of guanosine in DNA strand breaks caused by low‐energy electrons (LEEs), theoretical investigations of the LEE attachment‐induced C? O σ‐bonds and N‐glycosidic bond breaking of 2′‐deoxyguanosine‐3′,5′‐diphosphate (3′,5′‐dGMP) were performed using the B3LYP/DZP++ approach. The results reveal possible reaction pathways in the gas phase and in aqueous solutions. In the gas phase LEEs could attach to the phosphate group adjacent to the guanosine to form a radical anion. However, the small vertical detachment energy (VDE) of the radical anion of guanosine 3′,5′‐diphosphate in the gas phase excludes either C? O bond cleavage or N‐glycosidic bond breaking. In the presence of the polarizable surroundings, the solvent effects dramatically increase the electron affinities of the 3′,5′‐dGDP and the VDE of 3′,5′‐dGDP^?. Furthermore, the solvent–solute interactions greatly reduce the activation barriers of the C? O bond cleavage to 1.06–3.56 kcal mol^?1. These low‐energy barriers ensure that either C_5′? O_5′ or C_3′? O_3′ bond rupture takes place at the guanosine site in DNA single strands. On the other hand, the comparatively high energy barrier of the N‐glycosidic bond rupture implies that this reaction pathway is inferior to C? O bond cleavage. Qualitative agreement was found between the theoretical sequence of the bond breaking reaction pathways in the PCM model and the ratio for the corresponding bond breaks observed in the experiment of LEE‐induced damage in oligonucleotide tetramer CGTA. This concord suggests that the influence of the surroundings in the thin solid film on the LEE‐induced DNA damage resembles that of the solvent.     

Gelation in the Copolymerization of Diallyldimethylammonium Chloride with Acrylamide

Diallyldimethylammonium chloride (DADMAC) was free-radical copolymerized with acrylamide (AA) in water at a total monomer concentration of 4 mol/L and 40°C with different monomer feed compositions. Gelation occurred only for 20/80 DADMAC/AA monomer feed although crosslinking was observed for all monomer feed compositions. The gel point was at 51% conversion, and the swelling ratios of the resulting gels were quite high, from 1400 to 700. Addition of 2‐propanol as a chain‐transfer reagent reduced crosslinking and prevented gelation. These results are mechanistically discussed in connection with the cyclopolymerizability of DADMAC, and significant allylic hydrogen abstraction by the growing polymer radical characteristic of allyl polymerization is proposed.     

Recent developments in cellulose grafting chemistry utilizing Barton ester intermediates and nitroxide mediation

Esters or carbonates of N‐hydroxypyridine‐2‐thione (Barton esters) were appended to either carboxymethyl or hydroxypropyl cellulose. Irradiation of the cellulose bound Barton esters in monomer initiated free radical graft copolymerization with minimal concomitant homopolymerization. Grafting of styrene to carboxymethyl cellulose was accompanied by backbone cleavage. The hydroxypropyl spacer group minimized backbone degradation; styrene, acylamide and N‐isopropyl acrylamide could be grafted to hydroxypropyl cellulose in tetrahydrofuran solution. Treatment of Barton carbonate modified hydroxypropyl cellulose with styrene in the presence of TEMPO afforded corresponding TEMPO adducts, which can be used to promote the controlled radical graft polymerization of styrene. Grafts were analyzed independently after hydrolysis of the cellulose backbone.     

A novel approach to the characterization of end groups in styrene–methyl methacrylate copolymers by pyrolysis–gas chromatography

The end groups of styrene–methyl methacrylate (St‐MMA) copolymers polymerized radically with 2,2′‐azobisisobutyronitrile (AIBN) as an initiator, which are difficult to characterize even by NMR, were investigated by pyrolysis–gas chromatography. On the resulting pyrograms, characteristic products that formed from the end‐group moiety due to AIBN, such as 2‐cyanopropane, 2‐cyanopropen, and various compounds consisting of an isobutyronitrile group and a monomer unit, were observed together with those from the main chain, such as St and MMA monomers and various dimeric and trimeric products. The relative abundance between the recombination and disproportionation termination reactions in the copolymerization process was estimated from the relative intensities between the characteristic peaks of the end group and those of the main chain. Thus, the estimated abundance for the termination reactions suggested that the polymerization process for this particular copolymer system terminated preferentially by recombination rather than by disproportionation. Furthermore, the relative abundance between the monomer units adjacent to the chain‐end AIBN residues was estimated on the basis of the peak intensities of the products consisting of an isobutyronitrile group and either monomer unit, which reflected the penultimate neighboring structure of the end group in the polymer chain. Thus, the observed results suggested that the isobutyronitrile radical formed by the dissociation of AIBN in the initiation reaction was predominantly adjoined by St monomer rather than by MMA monomer. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1880–1888, 2000