No abstract

A new type of mediator for cobalt(II)-mediated radical polymerization is reported which is based on 1,3-bis(2-pyridylimino)isoindolate (bpi) as ancillary ligand. The modular synthesis of the bis(pyridylimino)isoindoles (bpiH) employed in this work is based on the condensation of 2-aminopyridines with phthalodinitriles. Reaction of the bpiH protio-ligands with a twofold excess of cobalt(II) acetate or cobalt(II) acetylacetonate in methanol gave [Co(bpi)(OAc)], which crystallize as coordination polymers, and a series of [Co(acac)(bpi)(MeOH)], which are mononuclear octahedral complexes. Upon heating the [Co(acac)(bpi)(MeOH)] compounds to 100 degrees C under high vacuum, the coordinated methanol was removed to give the five-coordinate complexes [Co(acac)(bpi)]. The polymerization of methyl acrylate at 60 degrees C was investigated by using one molar equivalent of the relatively short-lived radical source 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) as initiator (monomer/catalyst/V-70: 600:1:1). The low solubility of the acetato complexes inhibits their significant activity as mediators in this reaction, whereas the acetylacetonate complexes control the radical polymerization of methyl acrylate more effectively. The radical polymerizations of the hexacoordinate complexes did not show a linear increase in number-average molecular weight (M(n)) with conversion; however, the polydispersities were relatively low (PDI=1.12-1.40). By using the pentacoordinate complexes [Co(acac)(bpi)] as mediators, a linear increase in M(n) values with conversion, which were very close to the theoretical values for living systems, and very low polydispersities (PDI<1.13) were obtained. This was also achieved in the block copolymerization of methyl acrylate and n-butyl acrylate. The intermediates with the growing acrylate polymer radical ((.)PA) were identified by liquid injection field desorption/ionization mass spectrometry as following the general formula [Co(acac)(4-methoxy-bpi)-(MA)(n)-R] (MA: methyl acrylate; R: C(CH(3))(CH(2)C(CH(3))(2)OCH(3))CN), a notion also confirmed by NMR end-group analysis.

The oil recovery potential of acrylamide-based, associative thickening polymers has recently been evaluated in a coreflood study of our department. Associative polymers are anionic, water-soluble copolymers modified with varying degress of pendant hydrophobic groups. By intermolecular interactions of these hydrophobic moieties a fully reversible network of polymer coils can be formed.The oil recovery efficiency of a series of copolymers based on acrylamide, 2-acrylamidopropane sulfonic acid (ATBS) in combination with a hydrophobic comonomer has been determined in linear coreflood experiments at a temperature of 60°C. Synthetic sea water was used as brine and Bentheimer sandstone as core material. The evaluated polymers differed in molecular weight and associative groups' content.While anionic polyacrylamide (APAM) shows very similar resistance factors (RF) in coreflood experiments with and without oil, a significantly reduced RF in the presence of oil has been found for the associative polymers. The magnitude of this decrease in resistance factor was dependent on the specific type of associative polymer.The effect can be ascribed to the weakend intermolecular interaction of the hydrophobic groups in the associative polymers in the presence of oil. Even though the RF value is reduced in the presence of oil, it still remains higher than that of regular APAM.At low flow rates representing reservoir conditions a high resistance factor was observed and oil production was improved. This observation can be explained by an increase of the capillary number caused by the high RF of the polymer drive. A good correlation between oil production and capillary number was established.Permeability reduction effects explained the high mobility reduction observed with the associative polymers, as the bulk viscosity data did not correlate with the in-situ flow properties of the polymers in porous media.

A new thickener based on associative properties and its application in polymer flooding is discussed. The new thickener is an anionic, water-soluble copolymer containing pendant associative groups. These associative groups are based on a novel chemistry (patent application filed). The viscosity of the new copolymer shows superior behavior compared to existing technologies like partially hydrolyzed polyacrylamide (PHPA), especially at elevated temperature and in presence of salt respectively divalent ions. A viscosity of 33 mPas at 60°C could be obtained by adding 900 ppm of the new copolymer to synthetic sea water. In comparison, with a high molecular weight standard partially hydrolyzed polyacrylamide (PHPA) a value of only 3 mPas was reached. Moreover, the new polymer shows good resistance to shear during injection. Core flood experiments were run to prove that the new associative thickening polymer is applicable in the field. These data show injectivity into a 2 Darcy core. Moreover the apparent viscosity of the polymer flood in the core outperforms the values found with commonly used polymers by far. The residual resistance factor indicates low adsorption onto sandstone.

Hinten geschützt, vorne aktiv: Bis(2‐pyridylimino)isoindol(bpi)‐Pinzettenliganden, die ein Metallzentrum gegen einen Angriff von der Rückseite abschirmen (durch die grünen Gruppen, siehe Schema), können an der Peripherie durch chirale Gruppen (rot) funktionalisiert werden. Damit wurden effiziente Katalysatoren erhalten, die in der Fe‐katalysierten Hydrosilylierung von Arylketonen und der Co‐katalysierten Cyclopropanierung von Alkenen hervorragende Enantioselektivitäten erzielten.