A highly active cobalt complex ((salph)CoOAc; salph = N,N'-bis(3,5-di-tert-butylsalicylidine-1,2-benzenediamine)) was discovered for the isospecific polymerization of rac-propylene oxide.

A thermosensitive biodegradable homopolymer with a lower critical solution temperature (LCST) at body temperature was developed, with a poly(trimethylene carbonate) (PTMC) backbone and oligoethylene glycol (OEG). The novel monomer was designed by the direct connection of OEG into trimethylene carbonate (TMC), and no other functional groups exist in the polymer structure. Such a well-defined monomer unit contributed to its homogeneous characteristics. Three units of ethylene glycol in the TMC derivative resulted in a water-soluble nature at room temperature, and the solution became cloudy at higher temperatures. The LCST ranged from 31 to 35 °C and was influenced by the molecular weight and polymer concentration. Four units of ethylene glycol, however, increased the LCST temperature to 72 °C. It is noteworthy that the present characteristics, thermosensitivity at body temperature, biodegradablility, and a well-defined homopolymer structure, are promising for biomedical applications as an essential material.

The surface design and control of substrates with nanometer- or micrometer-sized polymer films are of considerable interest for both fundamental and applied studies in the biomedical field because of the required surface properties. The layer-by-layer (LbL) technique was discovered in 1991 by Decher and co-workers for the fabrication of polymer multilayers constructed mainly through electrostatic interaction. The scope and applicability of this LbL assembly has been extended by introducing molecularly regular conformations of polymers or proteins by employing, for the first time, weak interactions such as van der Waals interactions and biological recognition. Since these weak interactions are the sum of the attractive or repulsive forces between parts of the same molecule, they allow macromolecules to be easily arranged into the most stable conformation in a LbL film. By applying this characteristic feature, the template polymerization of stereoregular polymers, stereoregular control of surface biological properties, drastic morphological control of biodegradable nano materials, and the development of three-dimensional cellular multilayers as a tissue model were successfully achieved. It is expected that LbL assembly using weak interactions will promote further interest into fundamental and applied studies on the design of surface chemistry in the biomedical field.

Gas hydrates in the upstream oil and gas industry often cause problems during production, such as plugged pipelines causing down time and loss of revenue. Kinetic hydrate inhibitors (KHIs) have successfully been used in the field for about 2 decades. KHIs work to delay hydrate nucleation and/or crystal growth in the hydrate-stable operating region. KHIs, such as polymers containing N-vinyl amide units, for example, methacrylamide-based KHI polymers with isopropyl groups, have been commercialized and are now used in field operations. However, there are no reports of polymers with n-propyl groups that have been commercialized as a KHI. Using a structure-II-forming natural gas, we have now investigated the KHI performance of homopolymers with n-propyl and isopropyl groups based on the N-vinylformamide (NVF) monomer. A range of copolymers with NVF with higher cloud points were also synthesized and tested because the cloud points of these homopolymers were found to be lower than preferred for most field operations. The polymer series containing nPr-NVF monomer was found to perform better as KHIs than the iPr-NVF series as KHIs at 2500 ppm concentration in deionized water at all copolymer ratios with a similar molecular weight. Two of the best polymers from each of the nPr-NVF and iPr-NVF series were tested at varying concentrations from 1500 to 5000 ppm. A similar trend was found as with the tests of the complete series, in which the nPr-NVF polymer performed better than the iPr-NVF polymer. Poly(N-(n-propyl)-N-vinylformamide) homopolymer gave a similar KHI performance as a commercial sample of polyvinylcaprolactam (PVCap). ■ INTRODUCTIONNatural gas hydrates tend to form at elevated pressures and low temperatures, which are typical conditions in cold-climate upstream oil and gas fields and subsea multiphase pipelines. 1,2 Under these thermodynamic conditions, water molecules form cage-like structures and trap small gas molecules within these hydrate structures. Typical gas molecules are small hydrocarbons, such as methane, ethane, and propane, as well as carbon dioxide and hydrogen sulfide. 2−4 Low-dosage hydrate inhibitors (LDHIs), such as kinetic hydrate inhibitors (KHIs), are used in the oil and gas industry as a method for preventing the formation of gas hydrates; logistically, they can be more efficient and/or less expensive than other hydrate management methods. 2,5−8 KHIs delay the hydrate nucleation, which is the first stage of hydrate formation. 9 When the temperature and pressure conditions reach the hydrate-stable region, hydrate nuclei (clusters of water and gas) come together, grow, and disperse to reach the critical size for hydrate crystal growth. 2,10 Mechanisms for how the inhibition works on a molecular level are not fully understood, but some theories have been proposed. 11,12 It is generally believed that the KHI causes perturbation of the water and/or water/gas (hydrocarbon) interaction; therefore, the hydrate clusters will not reach the critical size, thus delaying the hydrate formation. 13,14 ...

Kinetic hydrate inhibitors (KHIs) have been used successfully for about the last 16 years to prevent gas hydrate formation mostly in gas and oilfield production lines. They work by delaying the nucleation and often also the growth of gas hydrate crystals for periods of time dependent mostly on the subcooling in the system. Poly(N-alkyl-N-vinylamide)s have been briefly investigated previously but no work has previously been published detailing a systematic study of structure versus performance. In this paper we report the KHI performance of a series of poly(N-alkyl-N-vinylacetamide)s polymers with alkyl side groups up to five carbon atoms. The study includes hydrate crystal growth tests on structure II tetrahydrofuran hydrate crystals as well as high pressure nucleation and crystal growth studies on a synthetic natural gas mixture giving structure II hydrates. The SII gas hydrate inhibition results correlate well with the THF hydrate crystal growth inhibition results since the polymers with the larger isopentyl or isobutyl groups performed best in both equipments but not significantly better than a commercial low molecular weight Nvinyl caprolactam-N-vinyl pyrrolidone 1:1 copolymer.