High pressure radical polymerization of ethylene with nitrogen

The radical polymerization of ethylene has been performed in the presence of nitrogen. The structural characteristics of polymers prepared with 0–25 weight % of nitrogen at 1,200 atm were determined by usual solution methods (viscometry, GPC) and by infrared spectroscopy. The experimental results show that, when the demixing in two phases appears, long chain branching decreases and unsaturation increases.     

1,2-disubstituted ethylene in radical polymerization

Effect of Tsinkamin-02 additive on characteristics of electrolytically fabricated zinc electrode for backup power sources was studied. Its influence on how a zinc powder is formed, deposition process parameters (current efficiency by zinc, cathodic polarization), and utilization factor of the active substance of the negative electrode in a nickel-zinc power source discharged in a high-intensity mode was determined. The component concentrations of the electrolyte used to deposit the zinc powder were optimized. An explanation was suggested for the mechanism of Tsinkamin-02 action.     

High pressure ethylene polymerization with a post‐metallocene bis‐phenyl phenoxy catalyst

The use of post‐metallocene bis‐phenylphenoxy catalysts to polymerize ethylene under high ethylene pressures (>25,000 psi) results in some remarkable catalytic properties. The high ethylene pressure produces molar ethylene concentrations in the reactor as much as 40 times higher than in typical low pressure ethylene polymerizations. This high ethylene concentration results in high catalyst efficiency at high temperatures and low reactor residence time, between 180 °C and 240 °C the catalyst efficiency surprisingly increases with increasing temperature, allowing for use of these catalysts at temperatures much higher than can be utilized in the low pressure processes. It has further been demonstrated that under these conditions increasing hydrogen levels up to 0.5 mol% does not significantly affect the polymer molecular weight; however, polymer molecular weight control can be realized with varying reactor temperature. The polymer produced is shown to be high density polyethylene made from a single site catalyst and not free radical initiated low density polymer. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 861–866     

The mechanism of the high-pressure free radical polymerization of ethylene

The reaction path of the free radical polymerization of ethylene is usually considered identical to the polymerization mechanism of other vinyl monomers. Available experimental data on the polymerization of ethylene, however, hardly fitted the well-established path of free radical polymerization. Obviously the mechanism of ethylene polymerization is more complex and not well understood. One reason for this, in our opinion, is insufficient knowledge of the physicochemical state of ethylene under high pressure. A model that described the behavior of ethylene under compression has been proposed. According to the model, and increase in pressure causes the formation of various supermolecular forms of ethylene, each accompanied by transition of the second order. By proposing a stereochemical shape for each supermolecular form calculation of activation volumes for each of these transitions was made. Good agreement was obtained when calculated volumes of activation were compared with corresponding experimental values in the literature.     

Copolymerization of vinyl acetate with 1-octene and ethylene by cobalt-mediated radical polymerization

The cobalt-mediated radical polymerization of vinyl acetate was extended to copolymerization with 1-alkenes (ethylene or 1-octene). In agreement with the low amount of 1-alkene that could be incorporated into the copolymer, a gradient structure was predictable, but a rather low polydispersity was observed. A poly(vinyl acetate)-b-poly(octene) copolymer was also successfully synthesized, leading to a poly (vinyl alcohol)-b-poly(octene) amphiphilic copolymer upon the methanolysis of the poly (vinyl acetate) block. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2532–2542, 2007     

Nitroxide-mediated radical polymerization of acrylamide in water solution

This study shows that reasonably controlled nitroxide-mediated polymerization of acrylamide is achieved in pure water solution at 120 °C and high concentration (40 wt%), using a combination of a conventional hydrosoluble radical initiator (Vazo56) and a β-phosphonylated nitroxide, SG1. Moreover, some chain extensions can be performed from a polyacrylamide macroinitiator. Under these experimental conditions, we have demonstrated the conservation of the acrylamide structure without hydrolysis side reactions. The physico-chemical characterizations of polymers obtained from this method demonstrates that the controlled growing chain arises as a star-like shape from the hydrophobic core composed of SG1-functionalized polyacrylamide in the presence of a slight excess of SG1.     

PolyPEGA with predetermined molecular weights from enzyme-mediated radical polymerization in water

The preparation of acrylic polymers with predetermined molecular weights using metalloenzymes as catalysts, ascorbic acid as reducing agent and alkyl halides as initiators is reported. The mechanism of polymerization resembles an ARGET ATRP process.     

Effect of water on copper mediated living radical polymerization

The use of water as a solvent for copper mediated living radical polymerization has been further investigated. Optimal conditions for effective living radical polymerization using catalyst complexes based on CuBr and N-(n-alkyl)-2-pyridylmethanimine ligands were found, leading to well defined polymer structures. The effect of water on the rate of polymerization was studied, and it was found that competitive complexation of ligand and water occurs at copper in addition to an enhanced polymerization rate on increasing the polarity of the medium.     

Atom-transfer radical polymerization of poly(ethylene oxide) macromonomers in aqueous media

Soluble comb-shaped and swelling network polymers based on monomethacrylate (M = 2080) and bismethacrylate (M = 4000) poly(ethylene oxide) macromonomers, have been synthesized by the controlled atom-transfer radical polymerization in aqueous media. PEG 2000 methyl ether ethyl-2-bromoisobutyrate and 2-bromoisobutyrate, in combination with CuBr, CuBr₂, and 2,2′-bipyridyl, have been used as initiators. The length of the main chain of comb-shaped polymers, as estimated with multidetector chromatography, is in good agreement with the calculated values in the 15–20 range at M _w /M _n = 1.42–1.89. The polymerization of the methacrylate macromonomer proceeds at a high rate and with a nearly quantitative conversion. The replacement of 10–80 mol % CuBr with CuBr₂ appreciably decelerates polymerization and decreases polydispersity to 1.14–1.21, while the experimental and calculated values of chain lengths remain equal. This finding indicates a higher level of process control. The polymer networks thus prepared manifest Gaussian elastic behavior, as is evident from the relationship between the elastic modulus G and the swelling degree Q that is consistent with the classical prediction G ～ Q ^m , where m = ?1/3. Within the framework of the accepted model of networks of this type, this fact suggests the short length of polymethacrylate chains. In addition, the relationship between the time of attainment of the gelation point and the composition of the initiation system agrees with the atomtransfer controlled polymerization mechanism. The efficiencies of various radical polymerization methods for controlling the network structure are compared.     

Analysis of polymerization rates in radical polymerization with primary radical termination of some methacrylates

Polymerization rates in polymerizations with primary radical termination of ethyl methacrylate, β-phenylethyl methacrylate, β-methoxyethyl methacrylate, and phenyl methacrylate initiated by 2,2'-azobis-(2,4-dimethylvaleronitrile) at 60°C were analyzed by using a simple linear equation. The values obtained of k_ti/k_ik_p (where k_ti is the primary radical termination rate constant, k_i is the rate constant of addition on to monomer of primary radical, and k_p is the propagation rate constant) on these analyses are discussed on the theoretical base.     

Surface-initiated living radical polymerization from silica particles functionalized with poly(ethylene glycol)-carrying initiator

A novel yet versatile approach is described for surface-initiated living radical polymerization (SI-LRP) from silica particles (SiPs). Monodisperse SiPs were surface-modified with a newly designed surface-fixable initiator (BPEGE) having three components: a triethoxysilane moiety, a poly(ethylene glycol) (PEG) unit, and an initiation site for atom transfer radical polymerization (ATRP) in the form of a 2-bromoisobutyryl group. The surface-initiated ATRP of methyl methacrylate (MMA) mediated by a copper complex was carried out with the BPEGE-fixed SiPs. The polymerization proceeded in a living manner, producing SiPs coated with well-defined poly(MMA) of a target molecular weight with a graft density as high as 0.5 chains/nm². Thanks to the amphiphilic property of PEG, the system was successfully applied for SI-ATRP of PEG methacrylate and sodium p-styrenesulfonate in aqueous media in which the BPEGE-fixed SiPs were highly dispersed without causing any aggregations. The formation of colloidal crystals with the polymer brush-afforded SiPs demonstrated the high uniformity and perfect dispersibility of the hybrid particles.     

Effect of pressure on the radiation-induced polymerization of ethylene in tert-butyl alcohol

The effects of pressure of the radiation-induced polymerization of ethylene in tert-butyl alcohol were studied. The reaction was carried out by use of a reactor with a capacity of 100 ml under the following conditions; pressure, 60–400 kg/cm²; temperature, 24 ± 3°C; dose rate, 2.0 × 10⁴?1.6 × 10⁵ rad/hr; amount of medium (tert-butyl alcohol containing 5 vol-% water), 70 ml. The results of polymerization were analyzed by a kinetical treatment based on a reaction mechanism with both first- and second-order terminations for the concentration of propagating, radical. On the basis of the kinetical treatment the rate constants of each elementary reaction at several pressures were determined, and the activation volumes of elementary reactions were obtained and are discussed in connection with the reaction mechanism. Consequently, the rate constants of propagation, first-order termination, and second-order termination at pressure p and at 24°C were expressed by,      

New neutral and ionic poly(ethylene oxide) networks by radical polymerization

New opportunities resulting from a turn to radical polymerization in the synthesis of poly(ethylene oxide) (PEO) networks are discussed and exemplified. Several series of such networks have been prepared by radical homo‐ and copolymerization in aqueous media of “macromonomers”, i.e. partly methacrylated poly(ethylene glycol) (PEG) of varied molecular weight (MW ≅ 2000‐12000) and functionality (f_n ≅ 1.25‐1.8). This family of gels as a whole has the volume swelling degree Q in the range of 10 to 200 ml/ml. The hydrogels are characterized by means of Q, elastic modulus, swelling pressure, and with the use of some probes. The swelling behaviour of neutral hydrogels of this kind is briefly resumed. The multifunctional junctions formed in the propagation reaction of methacrylate end groups determine their main peculiarity. Anomalous elastic behaviour of the swollen networks prepared at high concentration of polymer has been observed and attributed to the network chains stretching of the same nature as in polymer stars or brushes. The junctions' functionality (F ≈ 20‐300) is evaluated from these data as well as from MW of the soluble models of network junctions. The PEO networks with charged units in junctions have been obtained by copolymerization of macromonomers with some ionic (meth)acrylic monomers. These gels display all the polyelectrolyte features, e.g. enhanced Q values in water (up to 50‐70) and, contrary to neutral PEO gels, the strong dependence on salt content. However, the osmotic contribution of mobile ions into swelling is shown to be low due to localization of charges in the junctions. The hydrogels that combine PEO and polymethacrylic acid chains capable of interpolymer complexation have been prepared and studied. They show much higher swelling in pure water (Q up to 200), strong deswelling by NaCl, and very sharp drop in swelling (ca. two order in Q) at pH ≈ 4.5‐5.5 due to complexation.     

Preparation of polyethylene block copolymers by a combination of postmetallocene catalysis of ethylene polymerization and atom transfer radical polymerization

The synthesis of block copolymers consisting of a polyethylene segment and either a poly(meth)acrylate or polystyrene segment was accomplished through the combination of postmetallocene-mediated ethylene polymerization and subsequent atom transfer radical polymerization. A vinyl-terminated polyethylene (number-average molecular weight = 1800, weight-average molecular weight/number-average molecular weight =1.70) was synthesized by the polymerization of ethylene with a phenoxyimine zirconium complex as a catalyst activated with methylalumoxane (MAO). This polyethylene was efficiently converted into an atom transfer radical polymerization macroinitiator by the addition of α-bromoisobutyric acid to the vinyl chain end, and the polyethylene macroinitiator was used for the atom transfer radical polymerization of n-butyl acrylate, methyl methacrylate, or styrene; this resulted in defined polyethylene-b-poly(n-butyl acrylate), polyethylene-b-poly(methyl methacrylate), and polyethylene-b-polystyrene block copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 496–504, 2004     

Chain transfer in ethylene polymerization. VI. The effect of pressure

The chain-transfer reaction, which controls the molecular weight level of the polymer, apparently has not been studied as a function of pressure for ethylene. Therefore, the chain-transfer constants for eleven transfer agents were determined at 1360 and 2380 atm at 130°C. The results were interpreted according to transition-state theory as the difference between the volumes of activation for the transfer and propagation steps. It was found that the effect of pressure on the transfer constant is small for most transfer agents, indicating that the volumes of activation for hydrogen abstraction and addition to the ethylene double bond are similar. Aralkanes, however, gave anomalous results.     

Reactions of diacetylene radical cation with ethylene

Ion-molecule reactions and energy-resolved mass spectrometry have been used to determine the structures of the products formed in the reaction of diacetylene radical cation with ethylene in a flowing afterglow-triple quadrupole instrument. The structure of the adduct ion, C(6)H(6)(.+), has been determined to be that of singly ionized benzene. The reaction thus presents a first example of the ability of diacetylene radical cation to undergo an aromatic ring forming reaction. The other products formed in the reaction are m/z 52, C(4)H(4)(.+), and m/z 39, C(3)H(3)(+). Isotopic labeling studies show that C(4)H(4)(.+) and C(3)H(3)(+) are formed with nearly statistical hydrogen incorporation, indicating a complex mechanism that scrambles all protons.     

Atom transfer radical polymerization of styrene in toluene/water mixtures

The atom transfer radical polymerization (ATRP) of styrene in water/toluene mixtures was studied. A linear dependence of the molecular weight on conversion was observed, but the initiation efficiency decreased when the catalyst concentration increased. The variation of the amount of water in the system affected the control of the ATRP, indicating that the presence of the aqueous phase influenced the concentration of copper halides in the organic phase. The partitioning of copper halides resulted in almost complete migration of Cu^II into the aqueous phase, which assisted with catalyst removal after polymerization. For example, the amount of residual copper in the organic phase determined by inductively coupled plasma was less than 1 ppm when the polymerization mixture was exposed to air for 30 min. The ATRP of styrene in water/toluene mixtures occurred with the preservation of Br at the polymer chain end, as confirmed by successful block copolymerization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3153–3160, 2002