Copolymers Of Different Compositions Research Articles

Vibration damping and electrical conductivity of styrene–butyl acrylate random copolymers filled with carbon black

AbstractEmulsion‐polymerized poly(styrene‐rand‐butyl acrylate) (St–BA) copolymers exhibit damping capabilities over a wide temperature range with changes in the monomer ratio. Blending copolymers of different compositions results in a multidamping peak, further widening the effective damping temperature range. Adding carbon black (CB) reduces the peak damping intensity but enhances damping at higher temperatures. The addition of dodecyl benzene sulfonic acid to an St–BA/CB aqueous dispersion improves the dispersion of CB in the polymer, reducing the percolation threshold and improving the conductivity while slightly affecting the mechanical behavior. The electrical properties of the St–BA/CB system are affected by the copolymer composition, influencing the polymer surface tension. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Phase Behavior in Self-Assembly of Inorganic/Poly(4-vinylpyridine)-b-poly(ε-caprolactone) Hybrid

A series of poly(4-vinylpyridine)-b-poly(e-caprolactone) (P4VP-PCL) diblock copolymers of different composition (namely, various nanostructured phases) were synthesized for hybridization with gold precursors. Interesting phase behavior of gold precursors/P4VP-PCL hybrids was found as evidenced by transmission electron microscopy and small-angle X-ray scattering (SAXS). Consistent with theoretical prediction, phase transformation in the hybrids with PCL-rich P4VP-PCL can be induced by the introduction of the gold precursors. In particular, the phase transformation can be achieved by introducing a very small amount of the gold precursors because of the significant increase in the effective excluded volume of hybridized P4VP microdomain as identified by SAXS experiments through the analysis of the 1D correlation function. This morphological evolution is referred to as the bridging mechanism, suggesting that the PCL block of the P4VP-PCL in the hybrids might play an important role in blocking the interconnect...

Photocatalytic and Thermal Degradation of Poly(methyl methacrylate), Poly(butyl acrylate), and Their Copolymers

The photocatalytic and thermal degradations of poly(methyl methacrylate), poly(butyl acrylate), and their copolymers of different compositions were studied. The photocatalytic degradation was investigated in o-dichlorobenzene in the presence of two different catalysts, namely, Degussa P-25 and combustion synthesized nanotitania (CSN-TiO2). The samples were analyzed by using gel permeation chromatography (GPC) to obtain the molecular weight distributions (MWDs) as a function of reaction time. Experimental data indicated that the photodegradation of these polymers occurs by both random and chain end scission. A continuous distribution kinetic model was used to determine the degradation rate coefficients by fitting the experimental data with the model. Both the random and specific rate coefficients of the copolymers decreased with increasing percentage of butyl acrylate (BA). Thermal degradation of the copolymers was investigated by thermogravimetry. The normalized weight loss profiles for the copolymers showed that the thermal stability of the copolymers increased with mole percentage of BA in the copolymer (PMMABA). The Ozawa method was used to determine the activation energies at different conversions. At low acrylate content in the copolymer, the activation energy depends on conversion, indicating multiple degradation mechanisms. At high acrylate content in the copolymer, the activation energy is independent of conversion, indicating degradation by a one-step mechanism.

Colloidal Drug Delivery Systems – Recent Advances With Polymeric Micelles

With the emergence of nanotechnology in drug delivery, colloidal systems and particularly polymeric micelles have attracted great attention. Polymeric micelles formed by the self-assembly of amphiphilic copolymers adopt a core-shell structure, which can be loaded with drugs and used as drug delivery systems for various medical applications. The most interesting aspects involve extended blood circulation times and stability upon dilution, which enable polymeric micelles to accumulate in tumor or inflammation sites due to the enhanced permeation and retention effect (EPR). In the first part of this paper polymeric micelles with different morphologies and different circulating-, active- and passive targeting, and stimuli responsive properties will be reviewed. Furthermore amphiphilic block copolymers of different compositions for pharmaceutical micelle formulations will be discussed. The hydrophilic block is often composed of the biocompatible polyethylene glycol (PEG), whereas diverse polymers are used for the hydrophobic block. The biodegradable and biocompatible polylactide (PLA) is one of the most tested core-forming blocks for micelles, in part because of approval by the FDA for numerous drug products for use in humans. However, PLA has limitations with respect to the incorporation of poorly water-soluble drugs. Considering this we will present in the second part of this paper briefly our strategy and contribution to overcome these limitations and recent results for the envisioned application of these micelles in the field of cancer treatment. In order to increase the hydrophobicity of PLA methyl groups are substituted by more hydrophobic hexyl groups. The hexyl-substituted polylactides in combination with PEG form the amphiphilic block copolymers PEG-hexPLA, which self-assemble in aqueous solution into stable spherical, homogenous micelles with a diameter of 20–45 nm. The increased hydrophobicity of the hexPLA micelle core leads to higher incorporation rates of hydrophobic drugs, like the poorly water soluble photosensitizer, meso-tetra(p-hydroxyphenyl)porphine (THPP). THPP water solubility is increased 200-fold using these micelles. Their application in photodynamic therapy (PDT), coupled with the increased accumulation of the photosensitizer in a tumor, followed by irradiation at a special wavelength, should lead to tumor death. The encouraging drug incorporation results reveal the potential of hexyl-substituted polylactide micelles as drug carriers for PDT applications.

Swelling properties of copolymer hydrogels in the presence of montmorillonite and alkylammonium montmorillonite

Copolymers of different compositions were produced by polymerization of various acrylic compounds [ N-isopropyl-acrylamide (NIPAAm), acrylamide (AAm) and acrylic acid (AAc)]. The swelling stability of the gels was enhanced by the addition of fillers [Na-montmorillonite (Na-m.) and montmorillonites hydrophobized with alkylammonium ions (C n-m.), n = 4, 12, 18]. Verified by X-ray diffraction (XRD) measurements that exfoliated and/or intercalated nanocomposites were formed. In the course of the experiments the monomer composition (0/100–100/0 mol% of the initial monomers) of the gels and, in the case of composites, the quality (Na-montmorillonite and hydrophobized montmorillonite) and quantity (1–25 wt.%) of fillers were varied. The extent of swelling was manipulated through the ratios of these parameters. In the course of swelling measurements the relationship between the composition of the gels and their swelling characteristics was established. In view of the intended use of the samples (skin extender), the difference between swelling measured in distilled water and under physiological conditions was also studied and the swelling kinetics of the gels was also analyzed. In the case of polymer and composite gels, values of desorption enthalpy (Δ H m) corresponding to the actual water contents were also determined by thermoanalytical measurements (DSC). Swelling values determined by gravimetry and enthalpies calculated from DSC measurements were found to be in good correlation. Even in the case of the relatively hydrophobic poly(NIPAAm)-based gels an enthalpy value of 98.41 kJ/mol was obtained, which is twice the value measured in pure water (41.74 kJ/mol). The extent of swelling was found to be controllable through the hydrophilicity of the initial monomers: in the case of NIPAAm-AAm and NIPAAm-AAc gels, the samples containing hydrophilic monomers swelled more extensively, whereas in the case of AAm-AAc gels the copolymer exhibited more pronounced swelling than did the gels synthesized from pure polymers. The swelling of gels was enhanced by the addition of fillers, but only at relatively low filler concentrations (1–5 wt.%). Hydrophilic Na and C 4-m. fillers increased the swelling of hydrophilic polymers and compolymers, whereas the addition of the hydrophobic C 12- and C 18-m. improved swelling of hydrophobic polymers. The effect of changes in pH was most pronounced in the case of poly(AAc) gels, which exhibited maximal swelling at pH = 9, swelling at this pH exceeds 250 g/g. The samples most sensitive to electrolyte content (physiological saline) were poly(AAm-co-AAc) gels, whereas the lowest reaction to electrolyte content was observed in the case of AAm-based gels.

Kinetics of ethylene polymerization reactions with chromium oxide catalysts

Principal kinetic data are presented for ethylene homopolymerization and ethylene/1-hexene copolymerization reactions with two types of chromium oxide catalyst. The reaction rate of the homopolymerization reaction is first order with respect to ethylene concentration (both for gas-phase and slurry reactions); its effective activation energy is 10.2 kcal/mol (42.8 kJ/mol). The r1 value for ethylene/1-hexene copolymerization reactions with the catalysts is ∼30, which places these catalysts in terms of efficiency of α-olefin copolymerization with ethylene between metallocene catalysts (r1 ∼ 20) and Ti-based Ziegler-Natta catalysts (r1 in the 80–120 range). GPC, DSC, and Crystaf data for ethylene/1-hexene copolymers of different compositions produced with the catalysts show that the reaction products have broad molecular weight and compositional distributions. A combination of kinetic data and structural data for the copolymers provided detailed information about the frequency of chain transfer reactions for several types of active centers present in the catalysts, their copolymerization efficiency, and stability. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5315–5329, 2008

Photocatalytic Degradation of Poly(Acrylamide-co-acrylic Acid)

Poly(acrylamide-co-acrylic acid) copolymers of different compositions were synthesized and characterized. The copolymers were statistical with a relatively high percentage of acrylamide units, as determined by (13)C NMR. Reactivity ratios calculated by the Finemann-Ross and Kelen-Tudos methods showed that the copolymers were random with a reactivity ratio of r AM = 3.76 and r AA = 0.28. The photolytic and photocatalytic degradation of the copolymers and the homopolymers was conducted in the presence of combustion-synthesized nano anatase titania. The degradation of the copolymer in the presence of combustion-synthesized titania was significantly higher than that observed in the presence of commercial titania, Degussa P-25. The degradation was modeled by using continuous distribution kinetics by following the time evolution of molecular weight distribution. The degradation follows a two step mechanism, wherein the rapid first step comprises the scission of weak acrylic acid units along the chain which is followed by the breakage of relatively strong acrylamide units. The rate constants for the weak and strong links follow a linear trend with the percentage of acrylic acid and acrylamide in the copolymer, respectively. This linear variation can be correlated with a similar trend observed for the activation energies obtained for the pyrolytic degradation of the polymers.

Phase equilibrium and diffusion in binary systems based on nonyl acrylate, acrylic acid, and their homo- and copolymers

The phase equilibrium and diffusion in systems based on nonyl acrylate, acrylic acid, and their homopolymers and copolymers of different compositions have been studied in the range of 20–100°C by the microinterference technique. For the systems with the limited solubility of components, the phase diagrams have been constructed. It has been established that, with a rise in the content of carboxyl groups in the copolymers, the diffusion coefficients and the thermodynamic compatibility of the monomers decrease. It is suggested that the nonlinear pattern of a variation in the diffusion coefficient with the content of acrylic acid in the copolymers is predominantly associated with a change in the type of hydrogen bonds and the formation of carboxyl dimers upon the transition to poly(acrylic acid). The concentration of carboxyl groups may serve as a parameter indicating variations in thermodynamic compatibility and diffusion constants of the monomers with the intensity and type of hydrogen bonds in the polymers under study. The presence of hydrogen bonds and their type are estimated on the basis of the IR spectra of the homo- and copolymers of interest.

Radiation-chemical synthesis of thermosensitive copolymers based on the vinylbutyl ether and their complexing and emulgating abilities

Novel water-soluble thermosensitive copolymers of vinyl butyl ether (VBE) with vinyl ether of ethyleneglycol (VEEG) and N-vinylpyrrolidone (NVP) and ternary copolymers based on VBE, 2-hydroxyethylacrylate (HEA) and acrylic acid (AA) were synthesized by γ-induced radiation copolymerization. The composition of copolymers and average molecular weight of copolymers were determined using NMR 13C-spectroscopy and gel-permeation chromatography. It was shown that aqueous solutions of VBE–VEEG, VBE–NVP, VBE–HEA–AA have lower critical solution temperature (LCST) depending on copolymer composition. The complexation of copolymers with polyacrylic acid (PAA) was studied by turbidimetry method. Critical pH value of complexation (pH crit.) was used as the criterion of complexing ability. The effect of composition and concentration of copolymers, as well as pH of medium on the formation of IPC was investigated. The effect of VBE–VEEG copolymers of different compositions on the stability of model hexane–water emulsions was studied. It was determined that the regulation of hydrophilic–hydrophobic balance of macrochains and copolymer concentration allows effectively influence on the stability of hexane–water emulsions.

Development and characterization of homopolymers and copolymers from the family of polyphenylene oxides

AbstractPoly(2,6‐dimethyl‐1,4‐phenylene oxide), PDMPO, poly(2,6‐diphenyl‐1,4‐phenylene oxide), PDPPO, as well as their copolymers of different compositions, having both random and block structures, have been synthesized and characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, and gel permeation chromatography. Solution‐cast films were prepared from all synthesized polymers using chloroform as a solvent. The thermal properties of the resulting films were characterized by differential thermal analysis and differential scanning calorimetry, whereas their morphology was investigated using X‐ray diffraction. Ultimately, the potential of the synthesized polymers for gas separation was studied by examining gas permeation properties of the respective thin films in single gas permeation tests involving N2, O2, CH4, and CO2. In general, the O2 and CO2 permeability coefficients decrease with the PDPPO content. However, the largest drop in the permeability coefficients occurs between PDMPO and a copolymer having the lowest PDPPO content, and the permeability coefficients PDPPO are comparable or even lower than the permeability coefficients of the copolymers having the largest PDDPO content. On the basis of combination of the permeability coefficients and their ratios for CO2/CH4 and O2/N2, random copolymers appear to be a better candidate for gas separation membranes than their block counterparts. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Crosslinking of reactive α‐olefins and maleic anhydride copolymers as oil sorbers

AbstractOctene (OC) and tetradecene (TD) monomers were copolymerized with maleic anhydride (MA) with a low conversion (<10% conversion) to determine their reactivity ratios. The monomers were copolymerized with different molar percentages of MA and OC or TD (90/10, 70/30, 50/50, and 10/90) with benzoyl peroxide as an initiator to produce MA/α‐olefin copolymers of different compositions. Fourier transform infrared was used to determine the copolymer compositions. The monomer reactivity ratios of the MA/OC and MA/TD copolymers were determined with the Fineman–Ross and Kelen–Tudos methods. Crosslinked MA/TD and MA/OC (50 : 50 mol/mol) copolymers were prepared by the condensation of the prepared linear copolymers with different glycols. The crosslinked copolymers were evaluated for oil absorbency applications. The effects of the glycol type, composition, crosslinker weight percentage, and type of oil on the swelling properties of the crosslinked polymers were studied with oil absorption tests. The swelling parameters, such as the maximum oil absorbency, characteristic oil absorbency, characteristic swelling time, and swelling rate constant, were evaluated for the synthesized sorbers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 871–881, 2007

Adsorbed and Spread Layers of Poly(ethylene oxide)−Poly(propylene oxide)−Poly(ethylene oxide) Block Copolymers at the Air−Water Interface Studied by Sum-Frequency Vibrational Spectroscopy and Tensiometry

The surface properties of three water-soluble and amphiphilic PEO−PPO−PEO triblock copolymers of different composition (Pluronic 6100, 6400, and 6800) are investigated by tensiometry and sum-frequency vibrational spectroscopy. We compared the concentration dependence of the structure of surface layers prepared by three different methods: (i) adsorption from aqueous solution, (ii) dropwise spreading from an organic solution onto a surface of constant area, and (iii) compression of the spread film in a Langmuir trough. The surface density and conformation of the polymers were deduced from the vibrational band intensities of the methyl groups of the central hydrophobic PPO block and from the surface tension isotherms. A transition range related to a conformational change was observed by tensiometry for the adsorbed and the compressed Langmuir films of Pluronics with short PEO blocks, whereas the Pluronic with longest PEO blocks displays a gradual change of surface pressure without the sign of a phase transition. This difference reveals the effect of the relative lengths of the hydrophilic and hydrophobic blocks on the structural changes in the surface layers of block copolymers. A clear indication of the influence of the hydrophilic blocks on the structure of the whole molecule at the interface was also observed in the sum-frequency experiments. Above a given concentration the Pluronic with longest PEO chains exhibited lower sum-frequency intensities and methyl symmetric/asymmetric amplitude ratios than the other Pluronic compounds for all of the layers formed by the various methods. The differences in the surface properties of the dropwise spread layers and of the compressed Langmuir layers exposed the importance of the kinetic aspects of polymer monolayer formation. In the case of the spread films the possible large degree of nonequilibrium chain entanglements might hinder the accomplishment of preferred orientation and conformation of the polymer chains.

Synthesis and characterization of amphiphilic star copolymers of 2-(dimethylamino)ethyl methacrylate and methyl methacrylate: Effects of architecture and composition

Six amphiphilic star copolymers comprising hydrophilic units of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and hydrophobic units of methyl methacrylate (MMA) were prepared by the sequential group transfer polymerization (GTP) of the two comonomers and ethylene glycol dimethacrylate (EGDMA) cross-linker. Four star-block copolymers of different compositions, one miktoarm star, and one statistical copolymer star were synthesized. The molecular weights (MWs) and MW distributions of all the star copolymers and their linear homopolymer and copolymer precursors were characterized by gel permeation chromatography (GPC), while the compositions of the stars were determined by proton nuclear magnetic resonance ( 1H NMR) spectroscopy. Tetrahydrofuran (THF) solutions of all the star copolymers were characterized by static light scattering to determine the absolute weight-average MW ( M ¯ w ) and the number of arms of the stars. The M ¯ w of the stars ranged between 359,000 and 565,000 g mol −1, while their number of arms ranged between 39 and 120. The star copolymers were soluble in acidic water at pH 4 giving transparent or slightly opaque solutions, with the exception of the very hydrophobic DMAEMA 10- b-MMA 30- star, which gave a very opaque solution. Only the random copolymer star was completely dispersed in neutral water, giving a very opaque solution. The effective p Ks of the copolymer stars were determined by hydrogen ion titration and were found to be in the range 6.5–7.6. The pHs of precipitation of the star copolymer solutions/dispersions were found to be between 8.8–10.1, except for the most hydrophobic DMAEMA 10-b-MMA 30- star, which gave a very opaque solution over the whole pH range.

Phase diagrams of ethylene-vinyl acetate copolymers

The miscibility of ethylene-vinyl acetate copolymers of different compositions was studied by X-ray microanalysis over a wide temperature range, and phase diagrams were obtained. The dependences of critical temperature and compositions of coexisting phases on the difference in compositions of blended copolymers were determined. The data obtained were analyzed in terms of the Flory-Huggins-Scott concept. It was shown that the predictive power of the Scott equation is rather low. A more general expression that takes into account the difference in the molecular mass of copolymers was proposed. The interaction parameters were calculated and their enthalpy and entropy terms were estimated. It was found that the deviations in the experimental critical temperatures from the values calculated with the proposed equation are due to the contribution of the entropic term to the interaction parameter.

Capillary electrophoresis using copolymers of different composition as physical coatings: A comparative study

In this work, a comparative study on the use of different polymers as physically adsorbed coatings for CE is presented. It is demonstrated that the use of ad hoc synthesized polymers as coatings allows tailoring the EOF in CE increasing the flexibility of this analytical technique. Namely, different polymers were synthesized at our laboratory using different percentages of ethylpyrrolidine methacrylate (EpyM) and N,N-dimethylacrylamide (DMA). Thus, by modifying the percentage of EpyM and DMA monomers it is possible to manipulate the positive charge of the copolymer, varying the global electrical charge on the capillary wall and with that the EOF. These coated capillaries are obtained by simply flushing a given EpyM-DMA aqueous solution into bare silica capillaries. It is shown that by using these coated capillaries at adequate pHs, faster or more resolved CE separations can be achieved depending on the requirements of each analysis. Moreover, it is demonstrated that these coated capillaries reduce the electrostatic adsorption of basic proteins onto the capillary wall. Furthermore, EpyM-DMA coatings allow the reproducible chiral separation of enantiomers through the partial filling technique (PFT). The EpyM-DMA coated capillaries are demonstrated to provide reproducible EOF values independently of the pH and polymer composition with%RSD values lower than 2% for the same day. It is also demonstrated that the coating procedure is reproducible between capillaries. The compatibility of this coating protocol with CE in microchips is discussed.

Structural investigations of (9-ethyl-carbazol-6-yl) methyl methacrylate/methyl acrylate copolymers using two-dimensional NMR spectroscopy

(9-Ethyl-carbazol-6-yl) methyl methacrylate/methyl acrylate (E/A) copolymers of different compositions were prepared by solution polymerization by varying the molar infeed ratio, using AIBN as initiator at 60°C. The reactivity ratios calculated by Kelen–Tudos (KT) method were found to be rE = 1.16 ± 0.02 and rA = 0.69 ± 0.01 whereas those calculated from RREVM method were found to be rE = 1.18 and rA = 0.68. The molecular weights (Mw) and polydispersity index (PDI, Mw/Mn) were determined using gel permeation chromatography (GPC). Glass transition temperatures (Tg) for different compositions of E/A copolymers were determined using differential scanning calorimetry (DSC). Copolymer molar outfeed ratio (FE) was calculated from 1H NMR spectra. The α-methyl, methine, backbone methylene, and quaternary carbon resonance signals of the copolymers were distinguished using 13C{1H}, DEPT-45, -90, and -135 NMR techniques. The α-methyl and β-methylene showed compositional and configurational sensitivity up to pentad and tetrad level, respectively, whereas methine showed only compositional sensitivity up to pentad level. Unambiguous assignments for 1H and 13C{1H} NMR spectra were done by correlating 1D (1H, 13C{1H}, DEPT) and 2D (HSQC, TOCSY) NMR data. The spectral assignments for carbonyl region were done by studying higher bond order couplings by heteronuclear multibond correlation (HMBC) spectra. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5595–5606, 2006

Improvement of Photoinduced Birefringence Properties of Optically Active Methacrylic Polymers through Copolymerization of Monomers Bearing Azoaromatic Moieties

Optically active photochromic copolymers of different composition, deriving from the conformationally rigid chiral monomer (S)-3-methacryloyloxy-1-(4‘-nitro-4-azobenzene)pyrrolidine [(S)-MAP-N] and the isosteric and isopolar methacrylic ester of the flexible achiral chromophore 4‘-[(2-hydroxyethyl)ethylamino]-4-nitrobenzene [DR1M], have been prepared and characterized in solution and in the solid state with the aim to investigate the effect on their thermal and chirooptical properties originated by the presence of isosteric and isopolar azoaromatic moieties in the side chain. The photoinduction of birefringence has been assessed on films of the investigated copolymers in order to evaluate their behavior as materials for optical data storage. The results are interpreted in terms of copolymer composition and different cooperative behavior and conformational stiffness of DR1M and (S)-MAP-N azoaromatic chromophoric counits.

Microstructure analysis of methyl acrylate/methyl methacrylate copolymers by two‐dimensional NMR spectroscopy

AbstractMethyl acrylate (A)/methyl methacrylate (B) copolymers of different compositions were synthesized in bulk at 50°C and the compositions were determined from 1H NMR spectra. Reactivity ratios were optimized using the least square methodology. Compositional and configurational assignments were done using two‐dimensional (2D) Heteronuclear Single Quantum Correlation (HSQC) and Total Correlation Spectroscopy (TOCSY) experiments. Methylene proton and carbon resonances were assigned for compositional and configurational sensitivity at tetrad level. Carbon resonances of methine group of methyl acrylate were assigned for compositional sensitivity up to triad level with the help of 2D HSQC spectra. α‐Methyl group of methyl methacrylate was assigned up to triad level of compositional and configurational placements for carbon and proton resonances by 2D HSQC spectroscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1437–1445, 2006

Energetics of Cooperative Transitions of N‐Vinylcaprolactam Polymers in Aqueous Solutions

AbstractSummary: Phase and conformational behavior of poly(N‐vinylcaprolactam) was studied as a function of polymer concentration, concentration of NaCl, and concentration of sodium dodecyl sulfate (SDS). Precise measurements of the partial heat capacity of the polymer were first carried out within the temperature range 10–125 °C. Thermodynamic parameters of the phase separation transition (transition temperature, enthalpy, and heat capacity increment) do not change with variations in polymer concentration. In the presence of salt the transition temperature decreases, the enthalpy increases, and the heat capacity increment does not vary significantly. Beginning with the SDS concentration of 0.005 M, the phase separation is suppressed and the heat capacity peak splits into two peaks. Upon further increase in surfactant concentration the amplitude of the low‐temperature peak increases while that of the high‐temperature peak vanishes. Phase separation transition in aqueous solutions of N‐vinylcaprolactam‐methacrylic acid copolymers of different compositions were studied at different polymer concentrations and pH (4–12). The transition parameters do not depend on polymer concentration and pH.“Macroglobule” formed spontaneously as a result of the phase separation of a poly(N‐vinylcaprolactam) solution.image“Macroglobule” formed spontaneously as a result of the phase separation of a poly(N‐vinylcaprolactam) solution.

Compositional and configurational sequence determination of methacrylonitrile–vinylidene chloride copolymers by nuclear magnetic resonance spectroscopy

AbstractMethacrylonitrile–vinylidene chloride (M/V) copolymers of different composition were prepared by bulk polymerization using benzoyl peroxide as an initiator under nitrogen atmosphere in a sealed tube. The copolymer composition was determined from quantitative 13C[1H] NMR spectra. The reactivity ratios for M/V copolymers obtained from a linear Kelen–Tudos method and nonlinear error‐in‐variables method are rM = 2.47 ± 0.14, rV = 0.40 ± 0.02, and rM = 2.43, rV = 0.39, respectively. The complete spectral assignment in term of compositional and conformational sequences of these copolymers were done with the help of distortionless enhancement by polarization transfer, two‐dimensional heteronuclear single‐quantum coherence spectroscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1865–1874, 2005