Monomer Sequence Distribution Research Articles

Influence of multiple stimuli on the lower critical solution temperature of new cationic poly(N‐acryloyl‐N′‐ethylpiperazine‐co‐N‐isopropylacrylamide) solutions

ABSTRACTNew multi‐stimuli responsive cationic copolymers based on N‐acryloyl‐N′‐ethyl piperazine (AcrNEP) and N‐isopropylacrylamide (NIPAM) were prepared by thermal free‐radical solution polymerization in dioxane at 75 °C. The chemical composition of the copolymers was determined by 1H NMR spectroscopy and was found that the copolymers were slightly rich in NIPAM content than that of AcrNEP. The reactivity of the two monomers for the copolymerization reaction was evaluated by the extended Kelen‐Tüdös method. The distribution of monomer sequence in the copolymer chain was estimated using the terminal copolymerization model. The maximum tendency to alternation (∼ 70%) was at 60 mol % of AcrNEP in the monomer feed. The copolymers were readily soluble in water at room temperature at all compositions and exhibited well‐defined lower critical solution temperature (LCST) phenomenon. The influence of various stimuli such as pH, temperature, simple inorganic salts, and surfactants on the LCST of the copolymers was studied in detail. Simple inorganic salts such as sodium chloride, sodium bromide, and sodium sulfate showed a salting‐out effect while sodium iodide showed a salting‐in effect. The salting‐out coefficient of the salts were calculated using the Sestchenow method, and the salting trend followed the order SO42− > Cl− > Br− > I−. The divalent salt was more effective in lowering the LCST than the monovalent salts. The cationic surfactant hexadecyl trimethylammonium bromide at concentrations above the critical micelle concentration caused a gradual increase in the LCST of the copolymer solutions. The intrinsic viscosity and light scattering behavior of the copolymers in water and in sodium chloride solutions were studied in detail. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1175–1183

Microstructure Analysis and Model Discrimination of Enzyme-Catalyzed Copolyesters.

The comonomer sequence distributions were analyzed for a series of poly(ε-caprolactone-co-δ-valerolactone) (PCV) copolymers using 13C nuclear magnetic resonance (NMR) spectroscopy. The four dyad sequences each showed well-resolved peaks in the NMR spectra that allowed easy quantification of the dyad and triad fractions. Although compositional analysis could not discriminate between terminal and penultimate model copolymerization kinetics, the monomer sequence distributions clearly indicated that the lipase-catalyzed copolymerization proceeds via terminal model kinetics. This NMR analytical tool enables rapid characterization of lipase-catalyzed copolymers.

Effects of compositional polydispersity on gradient copolymer melts

The phase behavior of gradient copolymers is studied theoretically using random phase approximation (RPA) and self-consistent field theory (SCFT), focusing on the effects of monomer sequence distribution, or compositional polydispersity, of the polymer chains. The stability of the disordered phase is examined using RPA analysis, whereas the ordered phases of the system are studied using SCFT calculations. It is discovered that the critical domain spacing increases and the disorder-order transition temperature moves to higher values with the increase of the compositional polydispersity. SCFT results reveal that, depending on the value of the degree of segregation, structural change due to the different chain-to-chain monomer sequence distribution is controlled by two different mechanisms.

Radical copolymerization in homogenous medium and emulsion system monomers acrylonitrile/styrene

This study examines the radical copolymerization in homogeneous and emulsion of the monomer system acrylonitrile/styrene. These copolymers are of great interest to the plastics industry, because they combine the good mechanical properties and implementation provided by the styrene units in the very high solvent resistance and extreme gas impermeability provided by the acrylonitrile units. The properties of a copolymer are directly related to its composition and distribution of monomer units in its macromolecular chains. Based on the reports of the couple reactivity's of monomers (AN/S) found in the literature, the objective of the work is to provide theoretical simulation (by analytical and numerical integration of the equation of copolymerization): The kinetics of the reaction copolymerization of AN/S in a homogeneous medium and emulsion (drift composition, azeotropic) and the microstructure (distribution of monomer sequences) and the glass transition property of the macromolecular chains instant formed throughout the copolymerization reaction.

Possibilities for reducing tractor engine friction losses at cold start using an ultrasonic irradiation technique

Redox copolymerization of N-vinyl-2-pyrrolidone (NVP) with methyl methacrylate (MMA) was carried out using titanium(III)-- dimethylglyoxime [Ti(III)-DMG] redox initiator in aqueous sulfuric acid-alcohol media. The resulting copolymer was characterized by FTIR, 1H-NMR, and 13C-NMR spectroscopic methods and elemental analysis. Thermal properties of the copolymer were determined by differential scanning calorimetric technique and thermogravimetric analysis. The reactivity ratios of the monomers were computed by Fineman-Ross, Kelen-Tudos, and extended Kelen-Tudos methods at lower conversion. The reactivity ratios obtained r1 (MMA) 1.69 and r2 (NVP) 0.03 showed richer content of MMA than NVP in the copolymer having extreme ideal behavior. The distribution of monomer sequence along the copolymer chain was calculated using a statistical method based on reactivity ratios. Ti(III)-DMG redox initiator showed increased addition of NVP to MMA during copolymerization.

New Cationic Linear Copolymers and Hydrogels of N-Vinyl Caprolactam and N-Acryloyl-N′-ethyl Piperazine: Synthesis, Reactivity, Influence of External Stimuli on the LCST and Swelling Properties

New cationic linear copolymers of N-vinyl caprolactam (VCL) and N-acryloyl-N′-ethyl piperazine (AcrNEP) were synthesized by thermal free-radical solution polymerization in dioxane at 75 °C. The chemical composition of the copolymers was determined by 1H NMR spectroscopy. The copolymers were water-soluble at all composition and exhibited lower critical solution temperature (LCST) behavior. The LCST was greatly influenced by the AcrNEP content, changes in pH, temperature, salt and surfactant concentration of the external medium. The copolymers were rich in AcrNEP content due to its higher reactivity over VCL. The reactivity of AcrNEP and VCL were determined by the extended Kelen–Tudos method to be r1AcrNEP = 0.41 and r2VCL = 0.13. The distribution of monomer sequence in the polymer chain was estimated using the terminal copolymerization model and the maximum tendency to alternation (∼70%) was at 45 mol % of AcrNEP in the feed. The effect of polymer concentration in the range 0.02 to 20 wt % on the LCST beha...

Determining the Polydispersity in Chemical Composition and Monomer Sequence Distribution in Random Copolymers Prepared by Postpolymerization Modification of Homopolymers.

We report on establishing the polydispersity in chemical composition (PCC) and polydispersity in monomer sequence distribution (PMSD) in random copolymers of poly(styrene-co-4-bromostyrene) (PBrxS), where x = (0.385 ± 0.035) is the mole fraction of the 4-bromostyrene units (4-BrS), prepared by electrophilic substitution of bromine in the para-position of the phenyl ring of the parent polystyrene. Upon fixing the total number of repeating units, we tune the distribution of styrene and 4-BrS segments in PBrxS by carrying out the bromination reaction on polystyrene homopolymers in different solvents. While PBrxS with relatively random comonomer distribution is prepared in 1-chlorodecane, random-blocky sequences of 4-BrS in PBrxS are achieved by carrying out the bromination reaction in 1-chlorododecane. The PCC in both copolymers is established by fractionating both polymers using interaction chromatography (IC) and determining the chemical composition of the individual fractions by neutron activation analysis (NAA). The NAA data along with IC experiments reveal that the random-blocky sample possesses a narrowed PCC relative to a specimen with a more random comonomer sequence distribution. The full width at half-maximum (fwhm) in the chemical composition profile from IC is used to quantify PCC; the random mother sample possessed a 25% fwhm, while the random blocky mother sample has a fwhm equal to 8.7%. The change in the adsorption enthalpy per brominated segment due to adsorption is determined to be ≈1.5 times greater for the random-blocky than the relatively random sample, proving that more pronounced cooperative adsorption occurs in the case of the random-blocky sample relative to the random copolymer sample. Computer simulation employing the discontinuous molecular dynamic scheme further reveals that the distribution of comonomer sequences, that is, PMSD, in the random-blocky copolymer is narrower than that in the copolymer with a random distribution of both monomers.

Statistical determination of chemical composition and monomer sequence distribution of poly(methyl methacrylate-co-tert-butyl methacrylate)s by multivariate analysis of 13C NMR spectra

To evaluate chemical compositions and heterogeneity of comonomer sequences in methyl methacrylate (MMA)-tert-butyl methacrylate (TBMA) copolymers, multivariate analysis was applied to the 13C nuclear magnetic resonance (NMR) spectra of the carbonyl, backbone quaternary and α-methyl carbons of the copolymers. A better linear relationship was found between the first principal component score and the chemical composition in copolymers than was found between the results from spectra of the carbonyl and backbone quaternary carbons. The chemical compositions of 16 copolymers were successfully predicted by partial least squares regression (PLSR). The second principal component was found to reflect the fraction of MMA-TBMA hetero dyad sequence. Dyad sequence distributions of copolymers that were obtained at higher conversions were successfully determined by PLSR with those of copolymers obtained at low conversions as a training set. Multivariate analysis using properly prepared samples provided us with quantitative information of chemical compositions and comonomer sequence distributions, without assignment of the 13C NMR resonance peaks. Multivariate analysis was applied to the 13C nuclear magnetic resonance spectra of homopolymers, homopolymer blends and copolymers of methyl methacrylate (MMA) and tert-butyl methacrylate (TBMA). The first (PC1) and second (PC2) principal components reflected chemical composition of the copolymers and fraction of the MMA-TBMA dyad sequence (fMT), respectively. Dyad and triad sequence distributions of copolymers that were obtained at higher conversions were successfully determined by partial least squares regression with those of copolymers obtained at low conversions as a training set.

Synthesis and Characterization of Copolymers of Methyl Methacrylate and 2-Ethoxyethyl Methacrylate

The free-radical initiated copolymerizations of methyl methacrylate (MMA) with 2-ethoxyethyl methacrylate (2-EOEMA) were carried out using 2,2-azo-bisisobutyronitrile (AIBN) as the initiator in 1,4-dioxane solutions. The co- polymer products were characterized by IR, 1 H-NMR, and 13 C-NMR spectroscopic techniques. The reactivity ratios of the monomers were computed by the Fineman-Rose (F-R) and Kelen-Tudos (K-T) methods at lower conversion, using the IR data. The results are in good agreement with each other and the mean reactivity ratios for MMA/EOEMA copolymers are r1=0.8436, r2= 0.7751, and r1r2 = 0.6614. The reactivity ratios indicate the formation of random copolymers, which have been supported by the azeotropic composition evaluations. The distribution of monomer sequence along the copolymer chain has been calculated using a statistical method based on the reactivity ratios. The probability of finding the mean sequence lengths of 2-EOEMA and MMA units has also been evaluated.

Copolymerization of N-Vinyl pyrrolidone with methyl methacrylate by Ti(III)-DMG redox initiator

Redox copolymerization of N-vinyl-2-pyrrolidone (NVP) with methyl methacrylate (MMA) was carried out using titanium(III)-- dimethylglyoxime [Ti(III)-DMG] redox initiator in aqueous sulfuric acid-alcohol media. The resulting copolymer was characterized by FTIR, ^1H-NMR, and ^{13}C-NMR spectroscopic methods and elemental analysis. Thermal properties of the copolymer were determined by differential scanning calorimetric technique and thermogravimetric analysis. The reactivity ratios of the monomers were computed by Fineman-Ross, Kelen-Tudos, and extended Kelen-Tudos methods at lower conversion. The reactivity ratios obtained r_1 (MMA) 1.69 and r_2 (NVP) 0.03 showed richer content of MMA than NVP in the copolymer having extreme ideal behavior. The distribution of monomer sequence along the copolymer chain was calculated using a statistical method based on reactivity ratios. Ti(III)-DMG redox initiator showed increased addition of NVP to MMA during copolymerization.

Characterization and Analysis of Ethylene-Propylene Copolymers

The compositions of a series of ethylene-propylene copolymers were quantitatively determined by13C-NMR at 300K in the solvent o-dichlorobenzene. The monomer composition and sequence distribution were analyzed. The glass transition temperatureTg, half temperature of decomposition and crystallinity were found to be closely related to the sequence structures of methylene. The Tg, half temperature of composition, and crystallinity appeared an abrupt change when the methylene length arrived 7~8 because of the movement of the ethylene segments. Also, theTgof copolymers were simulated according to the monomer compositions. The simulatedTgtended to decrease with the increasing methylene, which was opposite to that of experimented. That was due to the increased crystallization along with the growth of methylene length. While the polymer was amorphous constructed in the simulation, theTgtended to decrease with the increasing soft segment methylene.

Effects of hydrophilic unit and its distribution on interfacial binding between single-walled carbon nanotubes, vinyl pyrrolidone and vinyl acetate copolymers

In this work, a molecular dynamic (MD) simulation method was employed to study the interfacial binding between the single-walled carbon nanotubes (SWCNTs) and some polymers and copolymers. The polymers studied include poly(vinyl pyrrolidone) as hydrophilic and poly(vinyl acetate) as hydrophobic polymers and also copolymers consisting of a series of vinyl pyrrolidone and vinyl acetate copolymers with different homogeneities in the backbone. The copolymers investigated have different structures and include alternative, diblock and triblock copolymers. This study has computed the intermolecular interaction energies between SWCNTs and polymers/copolymers in order to assess the effects of compositional heterogeneity on the interfacial binding between SWCNTs and polymers/copolymers. Also, the morphology of polymers/copolymers adsorbed to the surface of nanotubes has been studied. The obtained results showed that the intermolecular interactions in the simulated systems are strongly influenced by the monomer sequence distribution of hydrophilic and hydrophobic monomers in copolymers. The different values of intermolecular interaction energy for copolymers with identical numbers of hydrophilic and hydrophobic monomers but with different distributions suggest that an efficient load transfer through the interface between nanotube and copolymers is highly dependent on compositional heterogeneity of copolymers. Furthermore, we obtained the plots of the radial distribution function and the radius of gyration in order to study the effects of compositional heterogeneity on behavior of the studied nanocomposites. The results of the radial distribution function and the radius of gyration are in agreement with the findings of interfacial binding between SWCNTs and polymers/copolymers.

Cloud point suppression in dilute solutions of model gradient copolymers with prespecified composition profiles

Gradient copolymers of 2-hydroxyethyl methacrylate (HEMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) having prescribed linear, parabolic, and hyperbolic composition profiles were synthesized with the guidance of a numerical model that determines the instantaneous comonomer feed rate. These materials exhibit low polydispersity indices (<1.1); the evolution of the overall DMAEMA content and the absolute molecular weight of the copolymers are all in good agreement with the quantities predicted by our model. Compared to random copolymers of HEMA and DMAEMA, the cloud points of dilute buffered aqueous solutions of gradient copolymers decrease with increasing gradient strength; where the gradient strength is defined as the largest difference in the instantaneous composition along the copolymer. The temperature range over which the solutions transition from transparent to turbid also broadens significantly with increasing gradient strength. Both observations suggest the onset of transition to be dictated by the least soluble ends of the polymer chains. These correlations point to the importance of monomer sequence distribution in determining the macroscopic physical properties of copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

Antimitogenic Polymer Drugs Based on AMPS: Monomer Distribution−Bioactivity Relationship of Water-Soluble Macromolecules

A number of polysulfonated molecules have demonstrated their interaction with fibroblast growth factor (FGF), hampering their binding to its receptors (low affinity heparan sulfate proteoglycans (HSPG) and high affinity tyrosine kinase FGF receptors) and inhibiting the intracellular signaling and mitogenic response in cultured endothelial cells. The aim of this work was the synthesis and characterization of new copolymers based on 2-acrylamido-2-methylpropane sulfonic acid (AMPS) with antiproliferative activity for antitumoral applications. N-Vinylpyrrolidone (VP) or butyl acrylate (BA) was copolymerized with the sulfonated monomer to obtain macromolecules with different hydrophilic/hydrophobic balance and distribution of the sulfonated groups within the macromolecules. In vitro cell culture proliferative assays showed that monomer distribution affected the inhibition of the proliferative action of FGF. Reactivity ratios of the systems were determined following the free radical copolymerization by in situ (1)H NMR, and the correlation of the monomer sequence distribution with the bioactivity is discussed.

Copolymerization ofN-vinyl pyrrolidone with functionalized vinyl monomers: Synthesis, characterization and reactivity relationships

Copolymers of N-vinylpyrrolidone (NVP) comonomer with styrene (St), hydroxypropyl methacrylate (HPMA) and carboxyphenyl maleimide (CPMI) were synthesized by free radical polymerization using 2,2'-azobi- sisobutyronitrile (AIBN) initiator in 1,4-dioxane solvent. The copolymers formed were characterized by FTIR, H NMR and C NMR techniques and their thermal properties were studied by DSC and TGA. Copolymer composi- tion was determined by H NMR and/or by elemental analysis and monomer reactivity ratios (MRR) were estimated by the linear methods of Kelen-Tudos (K-T) and extended Kelen-Tudos (EK-T) and the non-linear approach. Copoly- mers of St and HPMA with NVP formed blocks of one of the monomer units, whereas alternating copolymers were obtained in CPMI-NVP, depending upon the side chain substitution. The MRR values are discussed in terms of monomer structural properties such as electronegativity and electron delocalization. The sequence distribution of monomers in the copolymers was studied by statistical method based on the average reactivity ratios obtained by EK-T method.

Influence of feeding strategies of mixed microbial cultures on the chemical composition and microstructure of copolyesters P(3HB‐co‐3HV) analyzed by NMR and statistical analysis

NMR spectroscopy was applied for quantitative and qualitative characterization of the chemical composition and microstructure of a series of poly(3-hydroxybutyrate-co-3-hydoxyvalerate) copolymers, P(3HB-co-3HV), synthesized by mixed microbial cultures at several different feeding strategies. The monomer sequence distribution of the bacterially synthesized P(3HB-co-3HV) was defined by analysis of their high-resolution 1D (13)C NMR and 2D (1)H/(13)C HSQC and (1)H/(13)C HMBC NMR spectra. The results were verified by employment of statistical methods and suggest a block copolymer microstructure of the P(3HB-co-3HV) copolymers studied. Definitive distinction between block copolymers or a mixture of random copolymers could not be achieved. NMR spectral analysis indicates that the chemical composition and microstructure of the copolymers can be tuned by choosing a correct feeding strategy.

N-vinylpyrrolidone and 4-vinyl Benzylchloride Copolymers: Synthesis, Characterization and Reactivity Ratios

The copolymers prepared in this study by free radical copolymerization of N-vinylpyrrolidone (M 2) with 4-vinylbenzylchloride (M 1) using 2,2′-azobisisobutyronotrile (AIBN) initiator in 1,4-dioxane solvent at 70°C were characterized by FTIR, 1H-NMR and 13C-NMR techniques. Polymer solubility was tested in both polar and nonpolar solvents. The thermal properties were studied by thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC). Copolymer compositions were established by H1-NMR spectra, while reactivity ratios of the monomers were computed using the linearization methods viz., Fineman-Ross (FR) (r 1 = 1.67 and r 2 = 0.67), Kelen-Tudos (KT) (r 1 = 1.77 and r 2 = 0.65) and extended Kelen-Tudos (EK-T) (r 1 = 1.72 and r 2 = 0.63) methods at lower conversion. Furthermore, reactivity ratios in nonlinear error-in-variables method (RREVM) also compute the reactivity ratios (r 1 = 1.76 and r 2 = 0.66); these are found to be in good agreement with each other. The distribution of monomer sequence along the copolymer chain was calculated using a statistical method based on the calculated reactivity ratios.

Microstructure of copolymers of polyhydroxyalkanoates produced by glycogen accumulating organisms with acetate as the sole carbon source

The so-called glycogen accumulating organisms (GAOs), found in mixed culture anaerobic–aerobic wastewater treatment processes, are used to produce polyhydroxyalkanoates (PHAs) copolymers from a single, simple carbon source—acetate. These polymers consist of 3-hydroxybutyrate (HB), 3-hydroxyvalerate (HV), 3-hydroxy-2-methylvalerate (HmV) and 3-hydroxy-2-methylbutyrate (HmB) with a non-HB fraction of up to 37%. A detailed characterisation using 1H and 13C nuclear magnetic resonance (NMR) spectroscopy demonstrates that these products are true copolymers if produced under anaerobic conditions. The HmV and HmB monomers are identified and their incorporation in the polymer verified via two-dimensional (2D) NMR spectroscopy. The monomer sequence distribution analysis using a known polymer characterisation model suggests that these polyesters are mixtures of random copolymers and thus likely possess desirable properties for practical use. This assessment is supported by the polymers’ physical characteristics. It was further revealed from the study that the inclusion of aerobic periods into the process could improve the overall polymer yields but resulted in production of HB monomers only, likely in the form of separate homopolymer blocks. The study for the first time investigated the microstructure of GAO-produced biopolymers and shows that GAOs have a potential for producing high-quality polymers from a simple carbon source.

Facile Method of Controlling Monomer Sequence Distributions in Random Copolymers

Inthis report, we present a simple methodology facilitating theformation of A-B random copolymers with tunable sequencedistributions. We demonstrate that varying the degree ofblockiness in the sequence distribution of A and B monomershas a profound impact on the partition of random copolymersat interfaces.Random copolymers (RCPs) are long chain moleculesmade of covalently bound monomers comprising at least twodifferent chemical moieties (say, A and B). In addition to theoverall molecular weight, RCPs are characterized by theircomposition and monomer sequence distribution. The abilityof A-B RCPs to act as “homopolymers with tunable composi-tion”, ranging between A and B homopolymers, has recentlyattracted considerable attention in controlling polymer misci-bility

N‐Vinylpyrrolidone and Ethoxyethyl Methacrylate Copolymer: Synthesis, Characterization and Reactivity Ratios

Free radical copolymerization of N‐vinyl‐2‐pyrrolidone with 2‐ethoxyethyl methacrylates was carried out with 2,2′‐azobisisobutyronotrile as an initiator in 1,4‐dioxane. The resulting copolymer was characterized by FTIR, H1‐NMR and C13‐NMR spectroscopic techniques thermal properties of copolymer were determined by DSC and TGA. The reactivity ratios of the monomers were computed by the Fineman‐Rose (F‐R), Kelen‐Tudos (K‐T) and extended Kelen‐Tudos (EK‐T) method at lower conversion, using the data obtained from both FTIR and elemental analysis studies; the results are in good agreement with each other. The average reactivity ratio, Alfrey‐Price Q and e values were found to be r 1=0.769, r 2=0.266 and Q 1=0.0859, e 1=0.4508, respectively for NVP/EOEMA copolymer. The distribution of monomer sequence along the copolymer chain was calculated using a statistical method based on obtained reactivity ratio. The number average molecular weight and polydispersity were determined by GPC.