The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. This review aims to introduce the chemistry of low dosage inhibitors of clathrate hydrate formation 5 within the context of their role in the oil and gas industry. The review covers both kinetic hydrate inhibitors and anti-agglomerants from the point of view of structure-function relationships, focussing on recent refinements in mechanistic understanding and chemical design, and the consequently evolving and increasingly fine-tuned properties of these fascinating compounds. Clathrate hydrates 10Clathrate hydrates are crystalline, non-stoichiometric host-guest compounds comprising a hydrogen bonded water framework, into which small molecular guest species such as methane are included within cavities formed by the water cages. Because there are no strong directional interactions between guest and host the 15 guests are free to vibrate and rotate but possess limited translational motion. 1 Typically common clathrate hydrates comprise 85 mol% water and 15 mol% guest(s) when all of the cavities are occupied.2 These materials form when the components are subjected to ambient temperatures (generally less 20 than 300 K) and moderate pressures (>0.6 MPa); conditions frequently found in oil and gas pipelines. 3 The initial reporting of gas hydrates is accredited to Sir Humphrey Davy in 1811, who focussed upon the crystallisation 25 of a cold aqueous solution of chlorine (known as oxymuriatic gas at the time). 4 In 1934 a pivotal report by Hammerschmidt acted as a catalyst for stimulating research in this area, by confirming that clathrate hydrates are responsible for the plugging of gas and oil pipelines and thereby dramatically increasing industrial 30 investment and research on the topic. 5 Today clathrate hydrates pose a major problem to the oil and gas industry with pipeline blockage causing many safety concerns in addition to requiring the shutdown of the pipeline for a time 35 whilst the plug is removed. This shutdown period results in reduced field site performance and may cause significant financial loss. Avoidance of pipeline shutdown is a priority to many oil and gas companies, and as such considerable investment is being made into research into clathrate hydrate inhibition to 40 circumvent such potentially catastrophic effects. Problems associated with gas hydrate formation reached the headlines in 2010 due to their destructive effects during BP's efforts to contain the oil spillage after the Deepwater Horizon blowout, thereby illustrating the importance of research in this area. While...

A poly(glycerol monomethacrylate) (PGMA) macromolecular chain transfer agent has been utilized to polymerize benzyl methacrylate (BzMA) via reversible addition−fragmentation chain transfer (RAFT)-mediated aqueous emulsion polymerization. This formulation leads to the efficient formation of spherical diblock copolymer nanoparticles at up to 50% solids. The degree of polymerization (DP) of the core-forming PBzMA block has been systematically varied to control the mean particle diameter from 20 to 193 nm. Conversions of more than 99% were achieved for PGMA 51 −PBzMA 250 within 6 h at 70 °C using macro-CTA/initiator molar ratios ranging from 3.0 to 10.0. DMF GPC analyses confirmed that relatively low polydispersities (M w /M n < 1.30) and high blocking efficiencies could be achieved. These spherical nanoparticles are stable to both freeze−thaw cycles and the presence of added salt (up to 0.25 M MgSO 4 ). Three sets of PGMA 51 −PBzMA x spherical nanoparticles have been used to prepare stable Pickering emulsions at various copolymer concentrations in four model oils: sunflower oil, n-dodecane, nhexane, and isopropyl myristate. A reduction in mean droplet diameter was observed via laser diffraction on increasing the nanoparticle concentration. Finally, the cis diol functionality on the PGMA stabilizer chains has been exploited to demonstrate the selective adsorption of PGMA 51 −PBzMA 100 nanoparticles onto a micropatterned phenylboronic acid-functionalized planar surface. Formation of a cyclic boronate ester at pH 10 causes strong selective binding of the nanoparticles via the cis-diol groups in the PGMA stabilizer chains, as judged by AFM studies. Control experiments confirmed that minimal selective nanoparticle binding occurred at pH 4, or if the PGMA 51 stabilizer block was replaced with a poly(ethylene glycol) PEG 113 stabilizer block.

A kinetic scale for dialkylaminyl radicals was established by measuring unimolecular rate constants for a series of dialkylaminyl radical clocks that spans eight orders of magnitude and using clock reactions to measure the second order rate constants for reactions of several hydrogen atom donors. N-Hydroxypyridine-2-thione derivatives of carbamic acids (so-called PTOC carbamates) were used as radical precursors in direct, laser-flash kinetic measurements and in indirect, radical chain kinetic studies. The calibrated radical clocks are N-methyl-6,6-diphenyl-5-hexenaminyl, N-methyl-trans-5-phenyl-4-pentenaminyl, N-methyl-5,5-diphenyl-4-pentenaminyl, N-methyl-trans-2-phenylcyclobutanaminyl, and N-methyl-trans-2-phenylcyclopropanaminyl. Calibrated hydrogen atom donors are Bu 3 SnH, t-BuSH, PhSH, and PhSeH. Whereas the tin hydride reactions with dialkylaminyl radicals are slower than reactions with alkyl radicals, the polarity-matched reactions of the electron-rich dialkylaminyl radicals with the electronpoor hydrogen donors t-BuSH, PhSH, and PhSeH have rate constants nearly equal to those for reactions of alkyl radicals with the same donor.

An absolute kinetic scale for amidyl radical reactions was established by a combination of direct laser flash photolysis (LFP) and indirect competition kinetic studies. Six amidyl radicals were studied by LFP. Arrhenius parameters were determined for 6-exo cyclizations of the N-butyl-6,6-diphenyl-5-hexenamidyl radical (2) and the N-butyl-6-(trans-2-phenylcyclopropyl)-5-hexenamidyl radical (5) and for 1,5-hydrogen transfer in the N- (6,6-diphenyl-5-hexenyl)acetamidyl radical (3); rate constants for these reactions at 20 °C are 3.0 × 10 7 s -1 (2), 5.5 × 10 6 s -1 (3), and 1 × 10 7 s -1 (5). Kinetic limits were established by LFP for the fast cyclizations of the N-methyl-5,5-diphenyl-4-pentenamidyl radical (1) and the N-methyl-5-(trans-2-phenylcyclopropyl)-4-pentenamidyl radical (4) (k > 2 × 10 8 s -1 at ambient temperature) and for the slow fragmentation of the N-(2,2-diphenylethyl)acetamidyl radical (6) (k ) 2 × 10 4 s -1 at 48 °C). Rate constants for amidyl radical reactions with Bu 3 SnH and PhSH were determined by competition kinetics; respective rate constants are 1.3 × 10 9 M -1 s -1 at 20 °C and 9 × 10 7 M -1 s -1 at 23 °C. Cyclizations of simple amidyl radicals were determined from competition kinetic studies by employing Bu 3 SnH and N-(phenylthio)amide radical precursors using data from the literature and from studies in this work. Rate constants at 65 °C for 5-exo cyclizations of the N-butyl-4-pentenamidyl radical and the N-(4-pentenyl)butanamidyl radical and for 6-exo cyclization of the N-ethyl-5-hexenamidyl radical are 3 × 10 9 s -1 , 7 × 10 8 s -1 , and 1.0 × 10 7 s -1 , respectively. The kinetic values determined in this work can be employed in synthetic planning involving amidyl radicals, and the simple amidyl radical clocks can be used for measuring rate constants of bimolecular reactions. A compilation of the kinetics of nitrogen-centered radical cyclizations and bimolecular reactions of nitrogen radicals with Bu 3 SnH and PhSH is presented.

Block copolymer spheres, worms or vesicles can be prepared via RAFT dispersion polymerisation of N-(methacryloyloxy)ethyl pyrrolidone in n-dodecane using a poly(stearyl methacrylate) chain transfer agent.

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The kinetic conclusions of a recent report by Maxwell and Tsanaktsidis (J. Am. Chem. Soc. 1996, 118, 4276) were investigated. The kinetics of ring opening of the (N-butyl-2-pyrrolidinyl)methyl radical (2) to the N-butyl-4-pentenaminyl radical (1) and the reverse reaction, 5-exo cyclization of 1 to 2, were determined at 50 and 80 °C by competitive Bu 3 SnH trapping. Rate constants for 5-exo cyclization of a dialkylaminyl radical and for β-fragmentation of a β-(dialkylamino)ethyl radical were measured by direct laser flash photolysis (LFP) methods. In contrast to the conclusions of Maxwell and Tsanaktsidis, all of these radical reactions were facile with rate constants of at least 1 × 10 4 s -1 . The claim by Maxwell and Tsanaktsidis that bis(tributyltin oxide) catalyzes dialkylaminyl radical reactions was investigated by LFP kinetic studies of the 5-exo cyclization of the N-methyl-5,5-diphenyl-4-pentenaminyl radical (20) in the presence of the additive which demonstrated that (Bu 3 Sn) 2 O does not have a catalytic effect on the reaction. Computations of the energies of the N-methyl analogs of radicals 1 and 2 with a high level of theory (fourth-order Møller-Plesset perturbation theory) and by a hybrid density functional theory with a very large basis set indicate that the cyclization reaction is expected to be slightly exergonic at 298 K. This work demonstrates that the kinetic results reported by Maxwell and Tsanaktsidis were spurious. We speculate that impurities of dichalcogens in their radical precursor samples were reduced by Bu 3 SnH to highly reactive chalcogen hydrides (arylthiols and benzeneselenol) in their kinetic studies.

RAFT solution polymerization of N-(2-(methacryoyloxy)ethyl)pyrrolidone (NMEP) in ethanol at 70 °C was conducted to produce a series of PNMEP homopolymers with mean degrees of polymerization (DP) varying from 31 to 467. Turbidimetry was used to assess their inverse temperature solubility behavior in dilute aqueous solution, with an LCST of approximately 55 °C being observed in the high molecular weight limit. Then a poly(glycerol monomethacylate) (PGMA) macro-CTA with a mean DP of 63 was chain-extended with NMEP using a RAFT aqueous dispersion polymerization formulation at 70 °C. The target PNMEP DP was systematically varied from 100 up to 6000 to generate a series of PGMA63–PNMEPx diblock copolymers. High conversions (≥92%) could be achieved when targeting up to x = 5000. GPC analysis confirmed high blocking efficiencies and a linear evolution in Mn with increasing PNMEP DP. A gradual increase in Mw/Mn was also observed when targeting higher DPs. However, this problem could be minimized (Mw/Mn < 1.50) by utilizing a higher purity grade of NMEP (98% vs 96%). This suggests that the broader molecular weight distributions observed at higher DPs are simply the result of a dimethacrylate impurity causing light branching, rather than an intrinsic side reaction such as chain transfer to polymer. Kinetic studies confirmed that the RAFT aqueous dispersion polymerization of NMEP was approximately four times faster than the RAFT solution polymerization of NMEP in ethanol when targeting the same DP in each case. This is perhaps surprising because both 1H NMR and SAXS studies indicate that the core-forming PNMEP chains remain relatively solvated at 70 °C in the latter formulation. Moreover, dissolution of the initial PGMA63–PNMEPx particles occurs on cooling from 70 to 20 °C as the PNMEP block passes through its LCST. Hence this RAFT aqueous dispersion polymerization formulation offers an efficient route to a high molecular weight water-soluble polymer in a rather convenient low-viscosity form. Finally, the relatively expensive PGMA macro-CTA was replaced with a poly(methacrylic acid) (PMAA) macro-CTA. High conversions were also achieved for PMAA85–PNMEPx diblock copolymers prepared via RAFT aqueous dispersion polymerization for x ≤ 4000. Again, better control was achieved when using the 98% purity NMEP monomer in such syntheses.