Conformations of Alternating Partially Fluorinated Copolymers in Dilute Ethanol Solutions

Equimolar copolymers of N-vinyl pyrrolidone with 1,1,1-3,3,3-hexafluoroisopropyl-α-fluoroacrylate were obtained by reversible addition-fragmentation chain transfer radical (RAFT) polymerization and by conventional radical polymerization (RAD). The copolymer conformation and compositional heterogeneity were analyzed by dynamic and static light scattering. RAFT copolymers of 41,000 ≤ M _w  ≤ 68,000 g/mol were shown to adopt cylindrical all-trans conformation. RAD copolymer of higher molecular mass (M_w = 390,000 g/mol) exhibited less extended conformation, thus indicating that the statistical Kuhn segment is less than RAD copolymer length.     

Determination of the Molar-Mass Averages of Random Poly(aspartate-co-lactide) Copolymers by Tuning the Ionic Strength of the Solvent

Water-soluble sodium poly(aspartate-co-lactide) (PALNa) copolymers with a molar ratio of aspartate-to-lactide units equal to 1:0.6, 1:1.0 and 1:1.5 were studied using NMR spectroscopy to determine the composition as well as SEC-MALS and static light-scattering measurements to determine the molar-mass characteristics of the copolymers. In the copolymer aqueous solutions, high-molar-mass species were detected, most probably due to the incomplete dissolution of the samples. The molar-mass averages determined in water with added simple electrolyte, i.e., NaCl, were much lower than the values determined in pure water. The concentration of the salt, which allows dissolution on a molecular level, and the separation predominantly according to a size-exclusion mechanism depend on the chemical composition of the PALNa copolymers. The optimal mobile phase for the PALNa-1/0.6 and the PALNa-1/1.0 copolymers was 0.1 M NaCl at pH 9, and for the PALNa-1/1.5 copolymer with a higher content of lactide units it was 0.05 M NaCl at pH 9. The molar-mass averages of the PALNa-1/1.0 copolymer, determined by SEC-MALS and static light-scattering measurements, were comparable.

     

Energetics of the binding of Cu(II) ions by thermosensitive copolymers of N-vinylcaprolactam and N-vinylimidazole in different conformational states of macromolecules

Random and protein-like copolymers based on N-vinylcaprolactam and N-vinylimidazole are synthesized by free radical polymerization in an aqueous solution. The above copolymers show a different thermal behavior in aqueous media at pH 7.2. At 45°C, the solution of a random copolymer experiences phase separation, whereas a protein-like copolymer undergoes a transition from the unfolded conformation to the compact conformation without any phase separation. The method of isothermal titration calorimetry is used to study the binding of Cu(II) ions by protein-like and random copolymers of N-vinylcaprolactam and N-vinylimidazole at 25 and 45°C, which correspond to different conformational states of macromolecules. The standard enthalpy and constant of binding are estimated. For both copolymers, the enthalpies of binding are negative and similar. When temperature is increased from 25 to 45°C, the constant of binding of copper ions by a protein-like copolymer increases by more than three orders of magnitude, whereas the corresponding constant of a random copolymer remains almost unchanged. Therefore, the transition of protein-like copolymer from the coiled conformation to the compact conformation noticeably facilitates the formation of an imidazole quasi-receptor, which is characterized by a certain spatial configuration and by a high affinity for the functional ligand. This effect is provided by an entropy gain no less than 50 J/(mol K).     

Thermal degradation kinetics of thermoresponsive poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) copolymers prepared via RAFT polymerization

Reversible addition-fragmentation chain transfer polymerization at 70 °C in N,N-dimethylformamide was used to prepare poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) copolymers in various compositions to afford well-defined polymers with pre-determined molecular weight, narrow molecular weight distribution, and precise chain end structure. The copolymer compositions were determined by ¹H NMR spectroscopy. The reactivity ratios of N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide (DMA) were calculated as r _NIPAM = 0.838 and r _DMA = 1.105, respectively, by the extended Kelen–Tüdös method at high conversions. The lower critical solution temperature of PNIPAM can be altered by changing the DMA content in the copolymer chain. Differential scanning calorimetry and thermogravimetric analysis at different heating rates were carried out on these copolymers to understand the nature of thermal degradation and to determine its kinetics. Different kinetic models were applied to estimate various parameters like the activation energy, the order, and the frequency factor. These studies are important to understand the solid state polymer degradation of N-alkyl substituted polymers, which show great potential in the preparation of miscible polymer blends due to their ability to interact through hydrogen bonding.     

Stabilization of kaolin suspension in the presence of copolymers of sodium 2-acrylamido-2-methylpropanesulfonate with N-vinylpyrrolidone

The kinetics of sedimentation of kaolin suspension in the presence of copolymers of sodium 2-acrylamido-2-methylpropanesulfonate with N-vinylpyrrolidone was studied as influenced by the concentrations, molecular weight, and chemical composition of the copolymer and by the concentration of salts added (NaCl, CaCl₂).     

A spectroelectrochemical study of conducting pyrrole-N-methylpyrrole copolymers in nonaqueous solution

Conducting poly(pyrrole-N-methylpyrrole) (P(Py-NMPy)) was electrochemically synthesized on a gold electrode in a lithium perchlorate-containing acetonitrile electrolyte solution and compared with polypyrrole (PPy) and poly(N-methylpyrrole) (PNMPy) prepared under the same conditions. The obtained polymers were characterized with cyclic voltammetry, in situ resistance measurements, in situ UV–vis spectroscopy, FTIR spectroscopy, and scanning electron microscopy. The onset potentials for pyrrole and N-methylpyrrole monomer oxidation differ by about 0.1 V. Nucleation processes initiated by the radical cations are followed by growth of nuclei into continuous films. The oxidation and reduction peaks for the P(Py-NMPy) copolymer synthesized at 1:1 M concentration ratio of the comonomers are between those of PPy and PNMPy. A decreased [Py]/[NMPy] comonomer concentration ratio yields in the copolymers shifts of peak potentials to more positive values. The in situ resistance of copolymers measured from ?0.20 to 0.90 V vs. Ag/AgCl decreased with increasing [Py]/[NMPy] concentration ratio. In situ UV–vis and ex situ FTIR spectra of copolymers show spectroscopic behavior intermediate between those of the homopolymers. Scanning electron microscopy micrographs of the samples show fundamental differences between the morphology of the homo- and copolymers.     

Sizes and conformations of hydrophilic and hydrophobic polyelectrolytes in solutions of various ionic strengths

The hydrodynamic characteristics of macromolecules of a random copolymer of N-methyl-N-vinylacetamide and N-methyl-N-vinylamine hydrochloride containing 43.6% charged units in the molecular-mass range of 27 × 10³ to 355 × 10³ are studied. For solutions in 0.2 M NaCl, sedimentation and translational-diffusion coefficients are determined. For salt-free solutions and for solutions in 0.2 and 5.0 M NaCl, the intrinsic viscosities of the fractions are found. The lengths of the statistical segments of the chains are estimated in terms of the Gray-Bloomfield-Hearst theory. The behavior of the polycation, whose uncharged counterpart is a hydrophilic polymer, is compared to the behavior of poly(sodium 4-styrenesulfonate), whose uncharged counterpart is a hydrophobic polymer. The comparison is based on normalized scaling relations. It is shown that the level of compaction of macromolecules of strong polyelectrolytes at a high ionic strength is determined by the degree of hydrophobicity of their polymer chains. Polyelectrolytes based on hydrophilic polymers cannot be compacted into a preglobular state; their chains preserve a swollen coil conformation up to maximally high values of ionic strength.     

Synthesis and self-assembly behaviors of well-defined poly(lauryl methacrylate)-block-poly[N-(2-methacryloylxyethyl)pyrrolidone] copolymers

A series of structurally controllable poly(lauryl methacrylate)-b-poly[N-(2-methacryloylxyethyl)pyrrolidone], PLMA-b-PNMP, diblock copolymers were synthesized by reversible addition–fragmentation chain transfer polymerization. The self-assembly behaviors of PLMA-b-PNMP in a selective solvent, tetrahydrofuran (THF), were studied by employing static light scattering, dynamic light scattering, and transmission electron microscopy in detail. The relationships between the aggregation parameters, such as critical micelle concentration and the aggregation number (N _agg), and the molecular structure were established. It was found that spherical micelles can be formed once the solvophobic block length of poly[N-(2-methacryloylxyethyl)pyrrolidone] is larger than 215. Moreover, extremely small and monodisperse gold nanoparticles (<2 nm) were synthesized by employing PLMA-b-PNMP diblock copolymers in THF.     

Hydrodynamic, molecular, and conformational characteristics of macromolecules of a random copolymer of N-Methyl-N-vinylacetamide and N-Methyl-N-vinylamine Hydrochloride

The development and optimization of processes involving polymeric molecules require determination and monitoring of key molecular characteristics of the polymer. Samples of poly-N-methyl-N-vinylacetamide were synthesized and fractionated. Partial hydrolysis of the homopolymer fractions was performed, and fractions of a random copolymer of N-methyl-N-vinylacetamide and N-methyl-N-vinylamine hydrochloride were obtained. The molecular weights and conformational parameters of the homo- and copolymers in 0.2 M aqueous NaCl were determined by methods of molecular hydrodynamics.     

Bioconversion of Glycerine Pitch into a Novel Yellow-Pigmented P(3HB-co-4HB) Copolymer: Synergistic Effect of Ammonium Acetate and Polymer Characteristics

Glycerine pitch waste generated from oleochemical industry was exploited as a carbon source for poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) copolymer production by a novel, yellow-pigmented bacterium Cupriavidus sp. USMAHM13 to improve the economics of microbial polyhydroxyalkanoate production and to establish a feasible waste management approach. Medium optimization using response surface methodology through shake-flask fermentation had led to the accumulation of P(3HB-co-51%4HB) copolymer using a combination of glycerine pitch (10 g/l), 1,4-butanediol (8.14 g/l), and ammonium acetate (2.39 g/l). P(3HB-co-4HB) copolymers with 4HB monomer compositions ranged from 3 to 40 mol% were obtained through batch fermentation in a bioreactor using different concentrations of ammonium acetate. The copolymers exhibited a wide range of material properties depending on the monomer composition and type of carbon sources. P(3HB-co-40%4HB) was a typical random copolymer, whereas other P(3HB-co-4HB) produced were blend copolymers. Carotenoid pigment which was produced simultaneously with the polymer production was found to have negligible effect on the mechanical and thermal properties of the P(3HB-co-4HB) copolymer films.     

Dilute solutions of polyelectrolytes—IV. Unperturbed dimensions of N,N-diethylacrylamide-N,N-dimethyldiallylammonium chloride copolymers

The behaviour of copolymers of N,N-diethylacrylamide with N,N-dimethyldiallylammonium chloride in aqueous NaCl solution has been studied by light-scattering. The parameters characterizing the short- and long-range interactions have been calculated. The influence of copolymer composition on the gyration radius and unperturbed dimensions shows that the macromolecules have maximum flexibility for a composition near equimolar. This behaviour was attributed to decrease of both the electrostatic repulsions and the steric hindrance of the structural units, as a result of pronounced alternation.     

Perfluoromethacrylate-styrene statistical copolymers synthesized in CO2-expanded monomers

Statistical copolymers of perfluoroalkyl ethyl methacrylate (Zonyl-TM) and styrene (S) were synthesized in CO₂-expanded monomer medium at a low initial pressure of 25 MPa. Different Zonyl-TM/S feed ratios were used during copolymerizations, and it was determined that the increase in the Zonyl-TM content and decrease of the CO₂ amount in the comonomer feed resulted in a decrease of the molecular weights of copolymers due to earlier precipitation of copolymers giving shorter chains. The cloudy CO₂-expanded liquid monomer phase was found to be the main loci of copolymerization. In addition, the increase in the Zonyl-TM feed ratio resulted in an increase in the critical degree of the polymerization time (J _crit) as the time when the copolymer chains start to precipitate. The higher the Zonyl-TM content used in the feed, the higher the J _crit time and the lower the weight-average molecular weight (M _w) of the copolymer obtained. Thermal analysis results of the copolymer indicated that the copolymers are stable up to 387–403 °C.     

Molecular properties of the copolymers of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diallyl-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylammonium chloride and maleic acid

The hydrodynamic and conformational properties of molecules of poly(N,N-diallyl-N,N-dimethylammonium chloride) and N,N-diallyl-N,N-dimethylammonium chloride-maleic acid copolymers of different compositions in solutions with various ionic-strength and pH values, as well as of the polyelectrolyte complex based on the copolymer with dodecyl sulfate anions in chloroform, are studied. For poly(N,N-diallyl-N,N-dimethylammonium chloride) molecules in a 1 M NaCl solution, the Kuhn segment length and the hydrodynamic diameter of the chain are estimated as A = 3.9 nm and d = 0.48 nm, respectively. In acidic solutions with pH 3.5, the copolymers demonstrate behavior typical for polyelectrolytes. In an alkaline solution with pH 13, when 1 M NaCl is added to the solution of the copolymer containing 29 mol % maleic acid units, there is an antipolyelectrolyte effect that manifests itself as an increase in the intrinsic viscosity of the copolymer and in the hydrodynamic radius of its molecules. It is found that an increase in the fraction of maleic acid units in the copolymer from 12 to 42 mol % brings about a reduction in the equilibrium rigidity of its macromolecules from 4.1 to 2.2 nm. The equilibrium rigidity of polyelectrolyte-complex molecules is higher than that of initial copolymer molecules owing to steric interactions arising between the aliphatic chains of dodecyl sulfate anions. In an electric field, the molecules of the complex are oriented owing to the induced dipole moment resulting from the displacement of dodecyl sulfate anions along the chain contour.     

Synthesis,characterization and self-assembly of amphiphilic block copolymer poly(4-vinyl benzene chloride)-b-poly(N-vinylpyrrolidone) in aqueous solution

The synthesis, characterization and self-assembly of a novel amphiphilic block copolymer containing a poly(N-vinylpyrrolidone) as a segment of hydrophilic and poly(4-vinyl benzene chloride) (PVBC) arms are reported. The copolymer was characterized by FT-IR spectroscopy ¹H NMR. The composition and the molecular weights of the block copolymers were established using gel permeation chromatography and ¹H NMR. The water-soluble fraction of poly(N-vinyl-2-pyrrolidone) (PVP)/PVBC block copolymers formed micelles which were investigated at 25 °C in water at 5 mg/ml concentration using a tensiometer. The morphology of micelles in aqueous solution was determined by the AFM, SANS, and SAXS methods.     

Thermosensitive copolymers having soluble and insoluble monomer units,poly(N‐vinylacetamide‐co‐methyl acrylate)s: Effect of additives on their lower critical solution temperatures

New thermosensitive polymers were synthesized by copolymerization between N‐vinylacetamide (NVA) and methyl acrylate whose homopolymers are soluble and insoluble in water, respectively. The lower critical solution temperature (LCST) of the obtained copolymers ranged between 59 and 83 °C, and the LCST increased with an increasing NVA content in the copolymers. The effectiveness of various salts addition on lowering the LCST of the copolymer solutions followed Hoffmeister series. NaCl and Na₂SO₄ addition linearly lowered the LCST with an increasing salts concentration, and slopes of the lines were almost constant regardless of the copolymer composition. The effectiveness of alcohols with various alkyl chain lengths on lowering the LCST did not follow the viscosity B coefficient values of the alcohols, which was probably the result of preferential adsorption of the alcohols to the copolymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2651–2658, 2004     

Phase separation of micellar solutions at extreme dilution: A study of polystyrene-b-poly(sodium acrylate) micelles in aqueous NaCl solutions

Micellar solutions of polystyrene-b-poly(sodium acrylate) copolymers in aqueous NaCl were studied by static light scattering (SLS). It was found that micellar solutions of the copolymer, at concentrations of NaCl at, or above, 2.0 mol dm⁻³, became turbid on dilution at constant salt concentration and at constant temperature. Turbidity arose from highly dilute solutions (typically at a concentration three orders of magnitude lower than the overlap concentration of the micelle, C*), but at concentrations above the expected critical micellization concentrations (c.m.c.s). The observed turbidity was attributed to the phase separation of the micellar phase. A systematic investigation of the phase separation phenomenon was performed. The effects of various parameters on the solution behavior of the micellar solutions were studied, including the effect of the concentration of NaCl, the effect of temperature, and the effect of the length of the hydrophilic, corona-forming poly(sodium acrylate) block. Phase separation was attributed to the presence of a very large excess of NaCl in the dilute micellar solutions. It was proposed that phase separation arose because of the reduced hydration of the polyion, the decreased electrostatic repulsion between the micelles, and the increase in the amount of ion binding, which occur in highly dilute salt solutions. © 1996 John Wiley & Sons, Inc.     

Tuning the diglycolamides for modifier-free minor actinide partitioning

The unsymmetrical diglycolamides (DGAs) such as N,N-dihexyl-N′,N′-dioctyl-3-oxapentane-1,5-diamide (DHDODGA), N,N-didecyl-N′,N′-dioctyl-3-oxapentane-1,5-diamide (D²DODGA), N,N-didodecyl-N′,N′-dioctyl-3-oxapentane-1,5-diamide (D³DODGA), were synthesized, and characterized by IR, NMR, and mass spectroscopic techniques. The extraction behaviour of Am(III), Eu(III), and Sr(II) by the solutions of these unsymmetrical DGAs in n-dodecane was studied as a function of concentration of nitric acid and DGA. The distribution ratio of Am(III) and Eu(III) increased with increase in the concentration of nitric acid; whereas, the distribution ratio of Sr(II) reached a maximum at 4 M nitric acid followed by decrease at higher acidities. The extraction of Am(III) and Eu(III) in 0.1 M DGA/n-dodecane decreased in the order DHDODGA > D²DODGA > D³DODGA. However, the order changed upon lowering the concentration of DGA. The third-phase formation behaviour of nitric acid and neodymium(III) in 0.1 M DGA/n-dodecane was studied as a function of concentration of nitric acid. The limiting organic concentration of nitric acid and neodymium increased with increase in the chain length of alkyl group attached to amidic nitrogen. Near stoichiometric amount of neodymium(III) was loaded in 0.1 M D³DODGA/n-dodecane without the formation of third-phase from 3 to 4 M nitric acid medium. The study revealed that the unsymmetrical diglycolamides D²DODGA and D³DODGA are superior candidates for partitioning the minor actinides from high-level liquid waste.     

Thermally responsive graft copolymer of soy protein isolate and N-isopropylacrylamide: synthesis and self-assembly behavior in aqueous solution

In recent years, soy protein isolate (SPI) has attracted great attention due to its biodegradability, biocompatibility, and wide availability. It has been used in food and pharmaceutical industry such as edible films and drug delivery systems. In this study, we report the synthesis and self-assembly behavior in aqueous solution of thermally responsive graft copolymer (SPI-g-poly(N-isopropylacrylamide) (PNIPA)) of soy protein isolate and N-isopropylacrylamide in aqueous solution. SPI-g-PNIPA was synthesized in the 8 mol/l urea cushioning solution, by using ammonium persulfate as the initiator and mercaptoacetic acid as the protein unfolding agent. Laser light scattering, transmission electron microscopy, and fluorescence spectroscopy have been used to study the self-assembly behavior of SPI-g-PNIPA in aqueous solution. Above the critical micelle concentration (cmc), SPI-g-PNIPA aggregates could assemble into different structures including the simple spherical structure, spherical core–shell structure, and random coil structure, depending on the graft copolymer concentration. The graft copolymer concentration, temperature, pH value, and ionic strength were found to influence the aggregate size and morphology of SPI-g-PNIPA in aqueous solution. With increasing ionic strength, the aggregate size increases. However, pH value, SPI-g-PNIPA concentration, and temperature have complicated influences on the aggregate size. The lower critical solution temperature of the SPI-g-PNIPA at pH 8.5 is 36 °C. The method of intrinsic fluorescence spectroscopy was used for the first time to determine the cmc value of SPI-g-PNIPA in aqueous solution.     

Conformational studies of copoly (N 5-ω-hydroxyalkyl-L-glutamine-L-glutamic acid)s

Copoly (α-amino acid)s consisting ofL-glutamic acid residue andN ⁵-ω hydroxyalkyl-L-glutamine residue, i.e., 2-hydroxyethyl, 3-hydroxypropyl, and di-2-hydroxyethyl derivatives were prepared by the reactions of copoly (L-glutamic acid) containing succinimide ester with corresponding amino alcohols. The conformation of these copolymers was examined by the CD and infrared measurements. These three copolymers containing about 20–30% hydroxyalkyl groups undergo a methanol-induced and a pH-induced conformational transitions. The copolymer containing about 50% 3-hydroxypropyl group assumes the α-helical conformation in the pH region from 2.5 to 11.6, and in a methanol-water mixture (9∶1). On the other hand, the copolymer containing about 60% di-2-hydroxyethyl groups does not allow any helical conformation even at lower pH and also even in a trifluoroethanol-water mixture (9∶1), suggesting that the branched hydroxyalkyl group is unfavorable for the formation of α-helix. Furthermore, the poly(N ⁵-di-2-hydroxyethyl-L-glutamine) is shown to have a rather disordered structure in the solid state.     

Thermal stability of poly(acryloyl chloride) homopolymer and copolymers of acryloyl chloride with methyl methacrylate

The thermal stabilities of poly(acryloyl chloride) homopolymer and copolymers of acryloyl chloride with methyl methacrylate covering the entire composition range were studied by thermogravimetric analysis. At each extreme of the composition range incorporation of comonomer units results in a copolymer which is less stable than the PMMA homopolymer. The activation energies of the decomposition of the copolymers were calculated using the Arrhenius equation and found to decrease from 32.2 to 12.5 kJ mol^?1 as acryloyl chloride concentration of the copolymer increases, indicating that the copolymers of higher acryloyl chloride concentration should easier decompose than other copolymers. The reactivity ratios of the copolymer were calculated and found to ber ₁(AC)=0.2±0.02 andr ₂(MMA)=0.9±0.1.