The effects of simple alkyl alcohols on the radical polymerization of N‐isopropylacrylamide in toluene at low temperatures were investigated. We succeeded in the induction of syndiotactic specificity and the acceleration of polymerization reactions at the same time by adding simple alkyl alcohols such as 3‐methyl‐3‐pentanol (3Me3PenOH) to N‐isopropylacrylamide polymerizations. The dyad syndiotacticity increased with a decrease in the temperature and an increase in the bulkiness of the added alcohol and reached up to 71% at −60 °C in the presence of 3Me3PenOH. With the assistance of NMR analysis, it was revealed that the alcohol compounds played dual roles in this polymerization system; an alcohol compound coordinating to the NH proton induced syndiotactic specificity, and that hydrogen‐bonded to the CO oxygen accelerated the polymerization reaction. The effect of syndiotacticity on the properties of poly(N‐isopropylacrylamide)s was also examined in some detail. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4450–4460, 2006

The copolymerization of divinylbenzene (DVB) and ethylstyrene (EtSt) was carried out at 70 and 80 °C in benzene with dimethyl 2,2‐azobisisobutyrate (MAIB) at high concentrations as initiator in the presence of methyl benzyloxyiminoacetate (MBOIA), a glyoxylic oxime ether, as a retarder. The copolymerization system of DVB (0.25 mol/L), EtSt (0.25 mol/L), MBOIA (0.5 mol/L), and MAIB (0.5 mol/L) gave benzene‐soluble copolymers despite a considerably high concentration of DVB as an excellent crosslinker. The yield and molecular weight of the resulting copolymers increased with time both at 70 and 80 °C and then leveled off because of initiator consumption. The homogeneous polymerization system involved electron spin resonance (ESR), observable nitrogen‐centered polymer radicals (MBOIA·) under the actual polymerization conditions. The MBOIA· concentration increased with time despite a homogeneous polymerization system, suggesting the formation of rigid hyperbranched polymers. A benzene solution of isolated copolymer also showed an ESR signal. The copolymer was soluble in acetone, toluene, chloroform, ethyl acetate, tetrahydrofuran, and N,N‐dimethylformamide but insoluble in n‐hexane, methanol, and dimethyl sulfoxide. MAIB fragments as high as 30–40 mol % were incorporated into the copolymers through initiation and primary radical termination, on the basis of which this polymerization was named the initiator‐fragment incorporation radical polymerization. MBOIA (13–16 mol%) was also incorporated into the copolymers through an opening of the CN bond. The intrinsic viscosity of the copolymers was very low (0.08 dL/g), and the reduced viscosity was almost independent of the polymer concentration, supporting a hyperbranched structure of them. Gel permeation chromatography and multi‐angle laser light scattering and transmission electron microscopy revealed that the copolymer was formed as a hyperbranched nanoparticle. The thermal behavior of the copolymer was examined by dynamic thermogravimetry and differential scanning calorimetry. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3038–3047, 2003

Poly(N-isopropylacrylamide)s (PNIPAMs) and poly(N-isopropylmethacrylamide)s have been investigated recently as kinetic hydrate inhibitors (KHIs). Now, poly(N-isopropylmethacrylamide) is commercialized. These are usually made by standard radical polymerization methods, which do not allow for control over the polymer tacticity. For this study, PNIPAMs were synthesized using new polymerization methods, giving a fairly high degree of tacticity control. We report here results on the performance of different tacticities of PNIPAMs with similar molecular weights in KHI tests with natural gas in stirred autoclaves and on tetrahydrofuran (THF) structure II hydrate crystal growth. From the results, we can conclude that the polymer tacticity does affect the KHI performance of PNIPAMs. PNIPAM with a higher syndiotactic percentage performed better than PNIPAM with a lower syndiotactic percentage. Both polymers demonstrated some kind of crystal surface adsorption by affecting the morphology of the THF hydrate crystals. ■ INTRODUCTIONNatural gas hydrates are crystalline solids, in which gas molecules (guest molecules) are trapped inside hydrogenbonded water cavities. Typical guest molecules include carbon dioxide and small hydrocarbons, such as methane, ethane, and propane. In the mid-1930s, it was discovered that thermodynamic conditions (elevated pressure and low temperature) favoring hydrate formation occur in pipelines and that natural gas hydrates were blocking gas transmission lines. 1 Natural gas hydrate plugging is one of the costly and challenging problems for the oil and gas industry, especially for deepwater fields. The prevention of gas hydrate formation can be accomplished in a few methods. Among them is the chemical treatment, which includes the usage of kinetic hydrate inhibitors (KHIs). They are generally water-soluble polymers. The mechanism is to delay the nucleation and crystal growth. The main classes of KHIs that have been in commercial use are polymers based on homo-polymers and co-polymers of vinyl caprolactam (VCap) as well as hyperbranched polyesteramides. 2 A group of KHIs based on the polymer of alkylacrylamide was developed. It was also pointed out that poly(N-monoalkyl(meth)acrylamide)s are also known to perform well as KHIs, especially when isopropyl serves as the alkyl group. 3 Therefore, we are interested in studying the KHI performance of this new KHI class.One of the important properties of polymers are their tacticity, which describes the relative stereochemistry of adjacent chiral centers within a macromolecule. 4 As shown in Figure 1, there are three types of tacticities, namely, isotactic with all pendant groups located on one side of the backbone, syndiotactic with alternating orientated pendant groups, and atactic with randomly orientated pendant groups. In a previous work, the KHI performance of poly(N,N-dialkylacrylamide)s was studied to determine the effect of polymer tacticity of this KHI class. 5 The results show that syndiotactic poly(N,Ndialkylacrylamide)s perform better than other...

The radical polymerizations of N‐alkylacrylamides, such as N‐methyl‐(NMAAm), N‐n‐propyl‐(NNPAAm), N‐benzyl‐(NBnAAm), and N‐(1‐phenylethyl)acrylamides (NPhEAAm), at low temperatures were investigated in the absence or presence of hexamethylphosphoramide (HMPA) and 3‐methyl‐3‐pentanol (3Me3PenOH), which induced the syndiotactic specificities in the radical polymerization of N‐isopropylacrylamide (NIPAAm). In the absence of the syndiotactic‐specificity inducers, the syndiotacticities of the obtained polymers gradually increased as the bulkiness of the N‐substituents increased. Both HMPA and 3Me3PenOH induced the syndiotactic specificities in the NNPAAm polymerizations as well as in the NIPAAm polymerizations. The addition of 3Me3PenOH into the polymerizations of NMAAm significantly induced the syndiotactic specificities, whereas the tacticities of the obtained polymers were hardly affected by adding HMPA. In the polymerizations of bulkier monomers, such as NBnAAm and NPhEAAm, HMPA worked as the syndiotactic specificity inducer at higher temperatures, whereas 3Me3PenOH hardly influenced the stereospecificity, regardless of the temperatures. The phase‐transition behaviors of the aqueous solutions of poly(NNPAAm)s were also investigated. It appeared that the poly (NNPAAm) with racemo dyad content of 70% exhibited unusual large hysteresis between the heating and cooling processes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4575–4583, 2008

Radical polymerization of N‐isopropylacrylamide (NIPAAm) in toluene at low temperatures, in the presence of fluorinated‐alcohols, produced heterotactic polymer comprising an alternating sequence of meso and racemo dyads. The heterotacticity reached 70% in triads when polymerization was carried out at −40 °C using nonafluoro‐tert‐butanol as the added alcohol. NMR analysis revealed that formation of a 1:1 complex of NIPAAm and fluorinated‐alcohol through CO···HO hydrogen bonding induces the heterotactic specificity. A mechanism for the heterotactic‐specific polymerization is proposed. Examination of the phase transition behavior of aqueous solutions of heterotactic poly(NIPAAm) revealed that the hysteresis of the phase transition between the heating and cooling cycles depended on the average length of meso dyads in poly(NIPAAm). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2539–2550, 2009

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The radical polymerization of N,N-dimethylacrylamide (DMAAm) has been investigated in the presence of several alkali metal salts, including lithium bis(trifluoromethanesulfonyl)imide (LiNTf 2 ). The addition of an alkali metal salt led to a significant increase in the yield and molecular weight of the resulting polymer.NMR analysis of mixtures of DMAAm and LiNTf 2 suggested that DMAAm was being activated by the coordination of Li + to its CvO group. Electron spin resonance analysis of the DMAAm polymerization in the presence of LiNTf 2 suggested that the propagating radical was being stabilized by Li + through a single-electron lithium bond, because a signal for the propagating radical of the acrylamide derivatives was observed for the first time in solution when LiNTf 2 was added. Based on these results, we have proposed a mechanism for this polymerization, where the propagation steps occur between a lithium ionstabilized propagating radical and a lithium ion-activated incoming monomer. Furthermore, polymers with a wide range of stereoregularities, such as isotactic, syndiotactic and heterotactic systems, were successfully prepared using this method by carefully selecting the appropriate combination of solvent and alkali metal salt. † Electronic supplementary information (ESI) available: Dependence of polymer yield on the added amount of LiNTf 2 in toluene, additional 1 H NMR spectra of the main-chain methylene groups of the poly(DMAAm)s prepared in this study and changes in the chemical shifts of DMAAm in the presence of MNTf 2 . See View Article Online a [Monomer] 0 = 1.0 mol L −1 , [MAIB] 0 = 1.0 × 10 −2 mol L −1 , [alkali metal salts] 0 = 1.0 mol L −1 . b Determined from 1 H NMR signals. c Determined by SEC (PMMA standards). d Alkali metal salt was not completely dissolved. e Polymer precipitated during polymerization reaction. Polymer Chemistry PaperThis journal is

The copolymerization of divinylbenzene (DVB) and N‐isopropylacrylamide (NIPAm) with dimethyl 2,2′‐azobisisobutyrate of a concentration as high as 0.50 mol/L proceeded homogeneously without any gelation at 80 °C in N,N‐dimethylformamide, where the concentrations of DVB and NIPAm were 0.15 and 0.50 mol/L. The copolymer yield increased with time and leveled off over 50 min. Although DVB was consumed more rapidly than NIPAm, both comonomers were completely consumed in 50 min. The homogeneous polymerization system at 80 °C involved electron spin resonance‐observable propagating polymer radicals, the total concentration of which increased with time. The resulting copolymer was soluble in tetrahydrofuran, chloroform, acetone, ethyl acetate, acetonitrile, N,N‐dimethylformamide, dimethyl sulfoxide, and methanol, but insoluble in benzene, n‐hexane, and water. The copolymer showed an upper critical solution temperature (50 °C on cooling) in a methanol–water [11:3 (v/v)] mixture. Dimethyl 2,2′‐azobisisobutyrate fragments as high as 37–45 mol % were incorporated as terminal groups in the copolymers through initiation and primary radical termination. The contents of DVB and NIPAm were 10–30 mol % and 30–50 mol %, respectively. The intrinsic viscosity of the copolymer was very low (0.09 dL/g) at 30 °C in tetrahydrofuran despite high weight‐average molecular weight (1.2 × l06 by multi‐angle laser light scattering). These results indicate that the copolymer was of hyperbranched structure. By transmission electron microscopy observation, the individual copolymer molecules were visualized as nanoparticle of 6–20 nm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1609–1617, 2004