Improved Gas Hydrate Kinetic Inhibition for 5-Methyl-3-vinyl-2-oxazolidinone Copolymers and Synergists.

Kinetic hydrate inhibitors (KHIs) are used to prevent deposits and plugging of oil and gas production flow lines by gas hydrates. The key ingredient in a KHI formulation is a water-soluble amphiphilic polymer. Recently, polymers of a new commercially available 5-ring vinylic monomer 5-methyl-3-vinyl-2-oxazolidinone (VMOX) were investigated as KHIs and shown to perform better than some commercial KHI polymers such as poly(N-vinyl pyrrolidone). This initial study using slow constant cooling (SCC) in rocking cells with a synthetic natural gas has now been expanded to further explore low molecular weight PVMOX homopolymers and VMOX copolymers as well as blends with nonpolymeric synergists. A PVMOX homopolymer with improved KHI performance was found using 3-mercaptoacetic acid as a chain transfer agent in the radical polymerization of VMOX. Among a range of copolymers, VMOX:n-butyl acrylate copolymers in particular gave good KHI performance, better than the PVMOX homopolymer. Among the potential synergists, trialkylamine oxides (alkyl = n-butyl or iso-pentyl) and tetra(n-pentyl)ammonium bromide to 2500 ppm were found to be antagonistic with PVMOX at the test concentrations while some alcohols and glycols were synergetic. The best synergist was 2,4,7,9-tetramethyl-5-decyne-4,7-diol (TMDD). For example, a mixture of 2500 ppm TMDD with 2500 ppm PVMOX (Mw 2400 g/mol) performed significantly better than 5000 ppm PVMOX. Addition of 1250 ppm TMDD to 2500 ppm VMOX:n-butyl acrylate 6:4 copolymer lowered the hydrate onset temperature in SCC tests by a further 3 °C compared to the copolymer alone giving hydrate onset at 4.2 °C.

Maleic and Methacrylic Homopolymers with Pendant Dibutylamine or Dibutylamine Oxide Groups as Kinetic Hydrate Inhibitors.

Kinetic hydrate inhibitors (KHIs) are applied in oil and gas fields to prevent gas hydrate formation, most often in cold subsea flow lines. The main component in industrial KHI formulations is a water-soluble polymer with many amphiphilic groups of which the hydrophilic part is most commonly the amide functional group. In the last decade, we have investigated polyamine oxides as alternatives to polyamides due to the strong hydrogen bonding of the amine oxide group. Here, we report the KHI performance of maleic and methacrylic homopolymers with dialkylamine and dialkylamine oxide pendant groups. Performance screening experiments were conducted under high pressure with a Structure II-forming natural gas mixture in steel rocking cells using the slow (1 °C/h) constant cooling test method. Polymers with dibutylamine groups gave much better KHI performance than polymers with dimethylamine or diethylamine groups. Polyamines formed from polymaleic anhydride reacted with 3-(dibutylamino)-1-propylamine (DBAPA) or 2-(dibutylamino)-ethanol (DBAE) gave good water solubility and good KHI performance, probably due to self-ionization between the dibutylamino and carboxylic acid groups. The lack of self-ionization for the methacryl homopolymers of DBAPA and DBAE explains why these polymers are not water-soluble. Oxidation of the maleic or methacryl polyamines to polyamine oxides gave water-soluble polymers with good compatibility with brines (0.5-7.0 wt % NaCl), but only the DBAPA-based polyamine oxides gave improved KHI performance compared to the polyamines. Poly(3-(dibutylamino oxide)-1-propyl methacrylamide) gave a similar performance to commercial N-vinyl pyrrolidone:N-vinyl caprolactam 1:1 copolymer and without a cloud point in deionized water up to +95 °C.

Oxyvinylenelactam Polymers-A New Class of Lactam-Based Kinetic Hydrate Inhibitor Polymers.

The deployment of kinetic hydrate inhibitors (KHIs) is a chemical method for the prevention of gas hydrate plugging in gas, condensate, and oil production flow lines. Polymers made using the monomer N-vinylcaprolactam (VCap) are one of the most common KHI classes. Alternative classes of polymers containing caprolactam groups are rare. Here, we present a study on oxyvinylenelactam polymers and copolymers with pendant piperidone or caprolactam groups. Low-molecular-weight homo- and copolymers were obtained. The nonrotating vinylene groups impart rigidity to the polymer backbone. Poly(oxyvinylenecaprolactam) (POVCap) was insoluble in water, but poly(oxyvinylenepiperidone) (POVPip) and OVPip:OVCap copolymers with 60+ mol % OVPip were soluble with low cloud points. KHI screening tests were carried out using the slow constant cooling method in steel rocking cells. POVPip was water soluble with no cloud point up to 95 °C but showed a poor KHI performance. In contrast, OVPip:OVCap copolymers with about 60-70 mol % OVPip were also water soluble and showed a reasonable KHI performance, better than that of poly(N-vinylpyrrolidone) but not as good as that of poly(N-vinylcaprolactam). Surprisingly, several additives known to be good synergists for VCap-based polymers showed negligible synergy or were antagonistic with the 62:38 OVPip:OVCap copolymer with regard to lowering the onset temperature of hydrate formation. However, a blend with hexabutylguanidinium chloride showed a strong effect to delay the onset of rapid hydrate formation.

Synthesis of Aliphatic Polyanhydrides with Controllable and Reproducible Molecular Weight.

Polyanhydrides have been synthesized for decades by melt-polycondensation of diacid monomers and 5 to >10 times mole excess acetic anhydride to diacid monomers to form polymers with a polydispersity ranging from 2.5 to 6 and low reproducibility. Hydrophobic segments in polyanhydrides are beneficial to hinder the characteristic hydrolytic cleavage of an anhydride bond that provides stable polyanhydrides at room temperature. The objective of this work is to synthesize aliphatic polyanhydrides with various hydrophobic segments, controllable and reproducible molecular weight, and low polydispersity that are essential for potential use as drug carriers. A series of polyanhydrides of suberic, azelaic, sebacic, and dodecanedioic acids with controlled molecular weight, reduced polydispersity, and standard deviation of molecular weights, have been synthesized. All synthesized polyanhydrides were thoroughly characterized by NMR, Fourier transform infrared spectroscopy, and gel permeation chromatography. Molecular weights of the synthesized polyanhydrides are highly controllable, depending on the degree of activation of the dicarboxylic acid monomers, i.e., the amount of acetic anhydride used during synthesis. Polyanhydrides have been synthesized in triplicate by melt-polycondensation, using various mole ratios of acetic anhydride to diacids. The standard deviation of the molecular weights of the polyanhydrides is minute when using 1 equivalent of acetic anhydride during the activation of dicarboxylic acids, whereas if excess acetic anhydride is used, the standard deviation is very high. The effect of safe and natural inorganic catalysts, Calcium oxide, Zinc oxide, and Calcium carbonate on polymerization is also studied. As-synthesized poly(sebacic acid) can offer convenience to use in controlled drug delivery applications. In vitro drug release study using Temozolamide (TMZ), a medication used to treat brain tumors such as glioblastoma and anaplastic astrocytoma, shows 14% TMZ release after the first hour and 70% release over one day from the poly(sebacic acid) wafers.

Poly(ester-anhydrides) Derived from Esters of Hydroxy Acid and Cyclic Anhydrides.

The alternating architecture and hydrophobic side chains hinder hydrolytic cleavage and anhydride interchange in poly(sebacic acid-ricinoleic acid) (P(SA-RA)), which provides stable polyanhydrides at room temperature. In this report, a series of polyanhydrides were designed to investigate the effect of ester bonds, hydrophobic side chains, phenyl moieties, and their distance from anhydride bonds on their stability and properties. Polyanhydrides with alternating architecture are constructed by the polymerization of ester-diacids prepared from ricinoleic or other hydroxy acids with anhydrides such as succinic, maleic, and phthalic anhydrides. The hydrophobic side chains are designed closer to anhydride bonds to investigate hindrance to hydrolytic cleavage and anhydride interchange. Polyanhydrides were obtained by the activation of ester-diacid using acetic anhydride followed by melt condensation. The reactions were monitored by NMR, Fourier transform infrared (FTIR), and gel permeation chromatography (GPC). The synthesized poly(ester-anhydride)s with a shorter chain length compared to P(SA-RA) were stable at room temperature. The hydrolytic degradation studies reveal that the phenyl moiety present in poly(ricinoleic acid phthalate) (PRAP) and poly(hydroxystearic acid phthalate) (PHSAP) reduces the hydrolysis of anhydride bonds. Poly(hydroxyoctanoic acid succinate) (PHOAS) demonstrates the highest molecular weight of all tested polymers. The results reveal that the presence of hydrophobic side chains, phenyl moieties, and their distance from anhydride bonds significantly improves the stability. These stable polyanhydrides can provide convenience to use in control drug-delivery applications. The in vitro drug release study using ibuprofen shows that polymers with aromatic units such as PRAP and PHSAP establish sustained release, which presents more than 50 and 40% of ibuprofen over a period of 28 days.

Nonpolymeric Citramide-Based Kinetic Hydrate Inhibitors: Good Performance with Just Six Alkylamide Groups.

The use of kinetic hydrate inhibitors (KHIs) is a well-known method for preventing gas hydrate formation in oil and gas production flow lines. The main ingredient in KHI formulations is one or more polymers with amphiphilic groups. Here, we report a series of citramide-based nonpolymeric KHIs. The KHI performance of these citramide derivatives has been studied using a synthetic natural gas mixture (forming structure II hydrate as the thermodynamically preferred phase) in slow constant cooling (ca. 1 °C/h starting from 20.5 °C) high-pressure (76 bar) rocking cell experiments. Isobutyl-substituted alkyl chains in the mono/bis(trialkyl citric acid) amide derivative gave better KHI performance than n-propyl-substituted citramide derivatives. Moreover, biscitramides with six alkylamide functional groups gave better performance than the equivalent monocitramides with three alkylamide groups. A solution of 2500 ppm of bis(tributyl citric acid) amide gave an average gas hydrate onset temperature (T o) of 8.4 °C compared to 8.9 °C for a low molecular weight N-vinyl pyrrolidone/N-vinyl caprolactam 1:1 copolymer. For the bis(tributyl citric acid) amide, addition of liquid hydrocarbon (n-decane) lowered further the average T o value to 6.2 °C, although this is at least partly due to lowering of the hydrate equilibrium temperature. This study demonstrates that good KHI performance can be obtained from molecules with as little as six amphiphilic alkylamide groups.

Non-Amide Polymers as Kinetic Hydrate Inhibitors-Maleic Acid/Alkyl Acrylate Copolymers and the Effect of pH on Performance.

Kinetic hydrate inhibitors (KHIs) have been used for over 25 years to prevent gas hydrate formation in oil and gas production flow lines. The main component in KHI formulations is a water-soluble polymer with many amphiphilic groups, usually made up of amide groups and adjacent hydrophobic groups with 3-6 carbon atoms. KHI polymers are one of the most expensive oilfield production chemicals. Therefore, methods to make cheaper but effective KHIs could improve the range of applications. Continuing earlier work from our group with maleic-based polymers, here, we explore maleic acid/alkyl acrylate copolymers as potential low-cost KHIs. Performance experiments were conducted under high pressure with a structure II-forming natural gas mixture in steel rocking cells using the slow (1 °C/h) constant cooling test method. Under typical pipeline conditions of pH (4-6), the performance of the maleic acid/alkyl acrylate copolymers (alkyl = iso-propyl, iso-butyl, n-butyl, tetrahydrofurfuryl, and cyclohexyl) was poor. However, good performance was observed at very high pH (13-14) due to the thermodynamic effect from added salts in the aqueous phase and the removal of CO2 from the gas phase. A methyl maleamide/n-butyl acrylate copolymer gave very poor performance, giving evidence that direct bonding of the hydrophilic amide and C4 hydrophobic groups is needed for good KHI performance. Reaction of the maleic anhydride (MA) units in MA/alkyl acrylate 1:1 copolymers with dibutylaminopropylamine or dibutylaminoethanol gave polymers with good KHI performance, with MA/tetrahydrofurfuryl methacrylate being the best. Oxidation of the pendant dibutylamino groups to amine oxide groups improved the performance further, better than poly(N-vinyl caprolactam).

Reversible Stimuli-Dependent Aggregation-Induced Emission from a "Nonfluorescent" Amphiphilic PVDF Graft Copolymer.

A poly(vinylidine fluoride) graft random copolymer of t-butyl aminoethyl methacrylate (tBAEMA) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA, Mn = 300) [PVDF-g-P(tBAEMA-ran-OEGMA), PVBO] is synthesized by atom transfer radical polymerization (ATRP), and PVBO is fractionated to get a highly water-soluble fraction (PVBO-1) showing a reversible on/off fluorescence behavior with gradual increase and decrease in pH, respectively, achieving a maximum quantum yield of 0.18 at pH = 12. PVBO-1 dissolved in water shows large multimicellar aggregates (MMcA), but at pH 12, crumbling of larger aggregates to much smaller micelles occurs, forming nonconjugated polymer dots (NCPDs), as supported by transmission electron microscopy and dynamic light scattering study. The reversible fluorescence on/off behavior also occurs with the decrease and increase of temperature. Theoretical study indicates that, at high pH, most of the amino groups become neutral and exhibit a strong tendency to form aggregates from crowding of a large number of carbonyl and amine groups, minimizing the HOMO-LUMO gap, showing an absorption peak at the visible region, and generating aggregation-induced emission.

Zwitterionic Poly(vinylidene fluoride) Graft Copolymer with Unexpected Fluorescence Property.

Recently, there has been a growth of research on the nonconjugated polymer exhibiting fluorescence property and it would be exciting if fluorescence property is developed in zwitterionic polymers because of their good water solubility. Poly(vinylidene fluoride) (PVDF) grafted with poly(dimethyl amino ethyl methacrylate) (PDMAEMA) is fractionated and a highly water-soluble fraction (PVDM-1) is quaternized with 1,3-propane sultone, producing a zwitterionic polymer, PVDF- g-PDMAEMA-sultone (PVDMS). PVDM-1 shows the fluorescence property with very low quantum yield (1%) in water, but on quaternization, fluorescence quantum yield increases to 8%. Transmission electron microscopy results indicate that the PVDM-1 cast from water has vesicular morphology, whereas PVDMS exhibits aggregated vesicular morphology. The 1H NMR spectra indicate the presence of 72 mol % DMAEMA in PVDM-1 wherein 66% of -NMe2 groups is quaternized upon postpolymerization modification. PVDM-1 exhibits absorption peaks at 210, 276, and 457 nm with a hump at 430 nm, whereas PVDMS exhibits two absorption peaks at 203 and 297 nm. PVDM-1 exhibits a broad emission peak at 534 nm, whereas PVDMS exhibits a sharp emission peak at 438 nm. An attempt has been made from density functional theory calculations to shed light on the origin of fluorescence in both PVDM-1 and in the zwitterionic PVDMS. The excitonic decay occurs from the lowest unoccupied molecular orbital (LUMO) of carbonyl group to the highest occupied molecular orbital (HOMO) of tertiary amine group for PVDM-1, whereas in PVDMS, the excitonic transition occurs from the LUMO situated over the quaternary ammonium group to the HOMO located on the electron-rich terminal sulfonate group.

Light-Induced Conformational Change of Uracil-Anchored Polythiophene-Regulating Thermo-Responsiveness.

Tuning the electronic structure of a π-conjugated polymer from the responsive side chains is generally done to get desired optoelectronic properties, and it would be very fruitful when light is used as an exciting tool that can also affect the backbone chain conformation. For this purpose, polythiophene- g-poly-[ N-(6-methyluracilyl)- N, N-dimethylamino chloride]ethyl methacrylate (PTDU) is synthesized. On exposure to diffuse sunlight, the uracil moieties of the grafted chains cause the absorption maximum of PTDU solution to show gradual blue shift of 87 nm and a gradual blue shift of 46 nm in the emission maximum, quenching its fluorescence with time. These effects occur specifically at the absorption range of polythiophene (PT) chromophore on direct exposure of light of different wavelengths, and the optimum wavelength is found to be 420 nm. Impedance study suggests a decrease in charge transfer resistance upon exposure because of conformational change of PTDU. Theoretical study indicates that on exposure to visible light, uracil moieties move toward the backbone to facilitate photoinduced electron transfer between the PT and the uracil, attributing to the variation in optoelectronic properties. Morphological and light-scattering studies exhibit a decrease in particle size because of coiling of the PT backbone and squeezing of the grafted chain on light exposure. The transparent orange-colored PTDU solution becomes hazy with a hike in emission intensity on addition of sodium halides and becomes reversibly transparent or hazy on heating or cooling. The screening of cationic centers of PTDU by varying halide anion concentration tunes the phase transition temperature. Thus, the light-induced variation in the backbone conformation is responsible for tuning the optoelectronic properties and regulates the thermos-responsiveness of the PTDU solution in the presence of halide ions.

Optoelectronic Properties of Self-Assembled Nanostructures of Polymer Functionalized Polythiophene and Graphene.

In this Feature Article, we discuss the variation of optoelectronic properties with the aggregation style of polythiophene (PT) graft copolymers and polymer-modified graphene systems. Grafting of flexible polymers on a PT chain exhibits several self-organized patterns under various conditions, causing different optical and electronic properties, arising from the different conformational states of the conjugated chain. Graphene, a zero band gap material, is functionalized with polymers both covalently and noncovalently to create a finite band gap importing new optoelectronic properties. The polymer-triggered self-assembled nanostructures of PT and graphene-based materials bring unique optical/electronic properties suitable for sensing toxic ions, nitroaromatics, and surfactants, for drug delivery, and also for fabricating molecular logic gates, electronic rectifiers, photocurrent devices, etc.

Influence of Hofmeister I- on Tuning Optoelectronic Properties of Ampholytic Polythiophene by Varying pH and Conjugating with RNA.

A significant tuning of optoelectronic properties of polythiophene (PT) chains due to Hofmeister iodide (I-) ion is demonstrated in ampholytic polythiophene [polythiophene-g-poly{(N,N,N-trimethylamino iodide)ethyl methacrylate-co-methacrylic acid}, APT] at different pHs. In acidic medium, the absorption and emission signals of PT chromophore exhibit appreciable blue shift in the presence of I- as counteranion only. The cooperative effect of undissociated -COOH and quaternary ammonium groups immobilize I- near the apolar PT chain causing threading of grafted chains and hence twisting of the backbone attributing to the blue shift. As medium pH is increased, dethreading of the PT backbone occurs due to ionization of -COOH group, releasing quencher iodide ions from the vicinity of the PT chains resulting in a red shift in absorption and a sharp hike in fluorescence intensity (390 times) for an increase of excitons lifetime. With an increase of pH, morphology changes from a multivesicular aggregate with vacuoles to smaller size vesicles and finally to nanofibrillar network structure. Dethreading is also found when APT interacts with RNA showing a significant hike of fluorescence (22 times) for displacing iodide ions forming a nanofibrillar network morphology. Threading and dethreading also affect the resistance, capacitance, and Warburg impedance values of APT. Molecular dynamics simulation of a model APT chain in a water box supports the threading at lower pH where the iodide ions pose nearer to the PT chain than that at higher pH causing dethreading. So the influence of Hofmeister I- ion is established for tuning the optoelectronic properties of a novel PT based polyampholyte by changing pH or by conjugating with RNA.

Surfactant-Triggered Fluorescence Turn "on/off" Behavior of a Polythiophene-graft-Polyampholyte.

Polythiophene-graft-polyampholyte (PTP) is synthesized using N,N-dimethylaminoethyl methacrylate and tert-butyl methacrylate monomers by grafting from polythiophene backbone, followed by hydrolysis. The resulting polymer exhibits aqueous solubility via formation of small-sized miceller aggregates with hydrophobic polythiophene at the center and radiating polyionic side chains (cationic or anionic depending on the pH of the medium) at the outer periphery. The critical micelle concentration of PTP in acidic solution (0.025 mg/mL, pH = 2.7) is determined from fluorescence spectroscopy. PTP exhibits reversible fluorescence on and off response in both acidic and basic medium with the sequential addition of differently charged ionic surfactants, repeatedly. The fluorescence intensity of PTP at pH 2.7 increases with the addition of an anionic surfactant, sodium dodecyl benzenesulfonate (SDBS), due to the self-aggregation forming compound micelles. The fluorescence intensity of these solutions again decreases on addition of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), because of assembling of SDBS with CTAB, thus deassembling the PTP-SDBS aggregates. At pH 9.2, these turn on and turn off responses are also shown by PTP with the sequential addition of cationic surfactant (CTAB) and anionic surfactant (SDBS), respectively. This result shows that PTP has potential for surfactant-induced reversible fluorescence turn on and off using ionic surfactant (SDBS and CTAB) through self-assembling and deassembling of the ionic aggregates. The reversible aggregation and disaggregation process of PTP with the surfactants at both acidic and basic pH is supported from dynamic light scattering and Fourier transform infrared spectroscopy. The morphology of the above systems studied by transmission and scanning electron microscopy also supports the above aggregation and disaggregation process.