Copolymer Composition Distribution Research Articles

Determination of the chemical composition distribution of copolymers of styrene and butadiene by gradient polymer elution chromatography

In order to determine the chemical composition distribution (CCD) of styrene-butadiene copolymers, gradient polymer elution chromatography has been performed. The separation is mainly based on differences in solubility among the copolymer molecules with different chemical composition. The solubility of a copolymer is dependent on the following parameters: temperature, type of solvent/non-solvent mixture, molecular mass of the polymer and the chemical composition of the polymer. The resolution of the gradient polymer elution chromatographic separation and the molecular mass dependency are influenced by the solvent/non-solvent combination. In order to obtian a reliable separation according to chemical composition, the differences in solubility must be sufficientyl high and the molecular mass dependence must be negligible. In order to separate styrene-butadiene copolymers, synthesized by emulsion polymerization, a tetrahydrofuran-acetonitrile gradient was used. After calibration of the chromatographic system with styren-butadiene copolymer standards, the CCD of styrene-butadiene copolymers could be calculated.

Chemical composition distribution of graft copolymer prepared by macromonomer technique: Determination by gradient HPLC

AbstractThe chemical composition distributions (CCDs) of poly(methyl methacrylate)‐graft‐polystyrene samples prepared from the polystyrene macromonomers having methacryloyl and p‐vinylbenzyl end‐groups were determined by high‐performance liquid chromatography (HPLC) based on reversed‐phase and normal‐phase adsorption modes. The CCDs determined by both modes were in good agreement with one another, indicating that the effect of the molecular weight distribution on the CCD is negligible. The results demonstrated the features of the CCDs in agreement with the theoretical predictions and the strong effect of the intrinsic reactivity of the end‐group on the copolymerization reactivity of the macromonomer.

A qualitative study to the influence of molar mass on retention in gradient polymer elution chromatography (GPEC)

AbstractGradient Polymer Elution Chromatography (GPEC) appears to be a powerful method for the determination of chemical composition distributions (CCD) of high molar mass copolymers. In order to perform these experiments, molar mass dependence of the retention time must be minimized. It is shown that variation in solvent and non‐solvent strength is a powerful method for adjusting the molar mass dependence. There appears to be a relation between molar mass dependence of retention behavior in GPEC on one hand and solubility under critical solvent conditions on the other hand. This phenomenon can be explained qualitatively from the important precipitation/redissolution mechanism in GPEC.

Compositional characterization of styrene copolymers by non‐exclusion liquid chromatography

AbstractRecent advances in high‐performance liquid chromatography enable us to separate synthetic copolymers according to composition. Several techniques for non‐exclusion liquid chromatography (NELC) for polymers and copolymers are reviewed, focusing on the technique developed in our laboratory. Size exclusion chromatography in combination with NELC makes possible the accurate determination of both molecular weight distribution and chemical composition distribution of copolymers at the same time.

Polymerization reactor modeling: A review of recent developments and future directions

Synthetic polymers are produced via a multitude of reaction mechanisms and processes, including addition (e.g. free-radical, ionic, group-transfer, Ziegler-Natta coordination) and step-growth polymerizations. A major objective of polymerization reaction engineering is to understand how the reaction mechanism, the physical transport processes (e.g. mass and heat transfer, mixing), reactor configuration and reactor operating conditions affect the macromolecular architecture (e.g. molar mass, molecular weight distribution, copolymer composition distribution, branching distribution, stereoregularity, etc.) as well as the morphological properties of the polymer product (e.g. particle size distribution, porosity, etc.). As the polymer industry becomes more competitive, polymer manufacturers face increasing pressures for production cost reductions and more stringent “polymer quality” requirements. To achieve these goals one needs to develop comprehensive mathematical models capable of predicting the molecular and morphological properties in terms of reactor configuration and operating conditions. These mathematical representations can be classified into microscale kinetic models, mesoscale physical, transport and thermodynamic models and dynamic reactor ones. The present paper provides an overview of the different polymerization processes and mathematical modeling approaches. It is also addresses the problems related with the computer-aided design, monitoring, optimization and control of polymerization reactors.

Studies on sequence distribution of aliphatic/aromatic copolyesters by high‐resolution 13C nuclear magnetic resonance spectroscopy for evaluation of biodegradability

AbstractCopolyesters with different stoichiometric compositions, obtained from 1,4‐butanediol, adipic acid, and terephthalic acid by molten‐state polycondensation, are studied by means of high resolution 13C NMR spectroscopy with respect to copolymer composition and block length distribution. The ratio of aliphatic and aromatic dicarboxylic acids in the polymer, which sensitively influences the biodegradability of the polymers, reflects the initial monomer composition during polycondensation. This indicates that under the conditions applied for polycondensation no loss for example of terephthalic acid due to sublimation occurs. It was found that the aliphatic and aromatic repeating units are randomly distributed within the polymer chain. The experimentally determined average sequence length distribution dependence on stoichiometric copolymer compositions are in accord with ideal polycondensation statistics. In combination with the results of the degradability of aromatic oligomers, predictions about the degradation characteristics of the aliphatic/aromatic copolymers can be made.

Surface Segregation Studies of Fluorine-Containing Diblock Copolymers

A diblock copolymer of deuterated styrene and isoprene (dPS−PI) with a small volume fraction of isoprene was chemically modified to incorporate pendant fluorinated side chains (“fingers”). The composition distribution of the diblock copolymers within a high molecular weight polystyrene (PS) homopolymer was determined by forward recoil spectrometry. Surface segregation and interfacial segregation of the modified block copolymers from a polystyrene matrix are observed in as-spun films. Equilibrium segregation was achieved on annealing at 160 °C for several days. The segregation isotherms at the air−polymer interface are shown to be quantitatively described by a self-consistent mean field theory (SCMF), and these permit us to estimate an effective Flory parameter which describes the attraction of the fluorinated segments to the surface and their repulsion from the bulk. The change in the surface tension as a result of the adsorption of the block copolymers at the air−homopolymer interface was evaluated from the predictions of SCMF theory and compared with the changes in the water contact angle observed. Advancing water contact angle data are consistent with the presence of a nonuniform layer of PS, CF2, and CF3 segments on the surface of the segregated samples.

The comppen model: A combined complex‐participation/penultimate effect model for free‐radical copolymerization

AbstractThe Comppen model for the mechanism of free‐radical copolymerization has been developed to account for both penultimate effects and the participation of 1:1 electron donor‐acceptor complexes during chain propagation. This was achieved by incorporating penultimate effects into the existing complex participation model of Cais, Farmer, Hill, and O'Donnell, using probability theory to derive new copolymer composition and sequence distribution equations that are solely functions of the reactivity ratios, the composition of the comonomer feed, and the equilibrium constant for 1:1 electron donor‐acceptor complex formation. The model was applied to experimental data from styrene/maleic anhydride copolymers prepared in methyl ethyl ketone at 50°C over a wide range of comonomer feed compositions, using nonlinear least‐squares curve fitting techniques to determine best estimates of the reactivity ratios. Copolymer compositions and sequence distributions for copolymers in this comonomer system were then predicted using the Comppen model and compared to those determined experimentally via 13C‐NMR spectroscopy. © 1994 John Wiley & Sons, Inc.

Biodegradation of copoly(n-hydroxypropyl- d,l-glutamine) in vitro

Random copolypeptides (PHPDLG) consisting of N-hydroxypropyl- d-glutamine (HPDG) and N-hydroxypropyl- l-glutamine (HPLG) covering the whole range of d,l-copolymer composition were prepared by carrying out aminolysis reactions with 3-amino-1-propanol (P) on starting random copolymers consisting of γ-benzyl- d-glutamate and γ-benzyl- l-glutamate (PBDLG). The effects of copolymer composition and sequential distributions on the rate of hydrolysis by papain in a pseudo-extracellular fluid (PECF) at pH 7.4 and 37.0°C were studied to simulate in vivo polymer degradation. Degradation data for these samples followed the Michaelis-Menten rate law, being of the first order to the enzyme concentration. It was shown that the rate of degradation by papain was controlled by the comonomer composition as well as sequential distributions of comonomers in the copolymer chains.

A novel mechanistic study of the radical copolymerization of styrene with citraconic anhydride via 13C n.m.r. spectroscopy

The composition and monomer unit sequence distributions of copolymers of styrene with citraconic (α-methylmaleic) anhydride (CA) prepared in methyl ethyl ketone at 50.0±0.1°C have been determined over a range of comonomer feed mole fractions using 13C n.m.r. spectroscopy. The monomer units in these copolymers were found to display an increasingly strong tendency to alternate as the mole fraction of CA in the feed increased. The terminal, penultimate, complex-participation and complex-dissociation models were each tested for applicability to the mechanism of copolymerization for this comonomer system by applying reactivity ratio related test functions to the experimental sequence distribution data, enabling a direct visual assessment of the applicability of each model to be made. On the basis of these test functions, the terminal, penultimate and complex-dissociation models were each found to provide inadequate descriptions of this copolymerization system.

A mechanistic study of the radical copolymerisation of p‐chlorostyrene with citraconic anhydride via 13C NMR spectroscopy

AbstractThe composition and monomer unit sequence distribution of copolymers of p‐chlorostyrene (p‐CST) with citraconic (α‐methylmaleic) anhydride (CA) prepared in methyl ethyl ketone (MEK) at 50,0 ± 0,1°C were determined over a range of comonomer feed mole fractions using 13C NMR spectroscopy. The monomeric units in these copolymers were found to display a mild tendency to alternate, which increased as the mole fraction of CA in the feed increased. The existence of a 1:1 charge‐transfer complex formed between p‐CST and CA in the feed was confirmed via UV spectroscopy and the equilibrium constant for complex formation determined to be 0,10 ± 0,04 L/mol in MEK at ambient temperature. The terminal, penultimate, complex‐participation and complex‐dissociation models were each tested for applicability to the mechanism of copolymerisation for this comonomer system. On the basis of copolymer composition data, the penultimate, complex‐participation and complex‐dissociation models were each found to provide an adequate description of the mechanism of copolymerisation in the comonomer system via non‐linear least squares methods. An analysis of the comonomer unit sequence distributions for these semi‐alternating copolymers and the application of reactivity ratio related test functions to this data allowed applicability of the four models under investigation to be separated more explicitly, with the complex‐dissociation model providing the best fit to the data.

チグラー・ナッタ触媒の立体特異性とオレフィン共重合体の構造

Since heterogeneous Ziegler-Natta catalysts usually contain multiple active species with different chemical properties, it is difficult to control the composition and monomer sequence distribution of copolymers by using them as catalyst.In the present paper, therefore, we have prepared both heterogeneous and homogeneous model catalysts which completely differ in stereospecificity and regiospecificity and applied them for olefin copolymerizations to investigate the effect of catalyst stereo- and regiospecificity on copolymers.A detailed analysis of copolymers produced with isospecific and aspecific heterogeneous catalysts has led to the conclusion that isospecific sites give blocky copolymers with less contents of higher olefins while aspecific ones give random copolymers abundant in higher olefin contents. Homogeneous Kaminsky-Sinn type catalysts are known to produce random copolymers. It was found, however, the microstructure of copolymers is slightly dependent upon the stereospecificity, i.e., bulkiness or symmetry of ligand attached to the active site. On the other hand, the Al2O3 supported CpTiCl3 catalyst was found to give atactic polypropene with frequent chemical inversion as well as random olefin copolymers, which are very different from those obtained with ordinary Ti-based heterogeneous catalysts.

Imperfect/incomplete micromixing effects on copolymerization in a premixed-feed stirred tank reactor

The effects of varying degrees of micromixing on overall conversion, average copolymer composition and copolymer composition distributions in a premixed feed-stirred tank reactor have been theoretically analyzed. The analysis is based on kinematical considerations from continuum mechanics and the Atiqullah-Nauman micromixing model. The calculated, macroscopic composition distributions widen with the increase in segregation number N seg . However, the overall conversion and average copolymer composition remain relatively unaffected. The study also shows how the micromixing parameter, that is, the striation thickness s 0, can be calculated from the measured- and model-predicted composition distributions, and N seg .

Microstructural analysis of methacrylonitrile‐styrene copolymers to obtain reactivity ratios

AbstractThe copolymerization of methacrylonitrile (M) and Styrene (S) at 60°C in bulk has been studied at low conversion by the use of 1H‐ and 13C‐NMR to examine the copolymer microstructure for copolymer composition and sequence distribution. The penultimate model was found to provide the best description of the polymerization with rMM = 0.220, rSM = 0.519, rSS = 0.241, rMS = 0.570. These results have been compared with those found for the corresponding acrylonitrile‐styrene copolymerization. © 1993 John Wiley & Sons, Inc.

A mechanistic study of the radical copolymerisation of p‐methoxystyrene with citraconic anhydride via 13C NMR spectroscopy

AbstractThe composition and monomer unit sequence distribution of copolymers of p‐methoxystyrene (p‐MST) with citraconic anhydride (CA) prepared in methyl ethyl ketone (MEK) at 50,0 ± 0,1°C were determined over a range of comonomer feed mole fractions using 13C NMR spectroscopy. The monomer units in these copolymers were found to display an increasingly strong tendency to alternate as the mole fraction of CA in the feed increases. The existence of a 1:1 charge‐transfer complex formed between p‐MST and CA in the feed was confirmed via UV spectroscopy and the equilibrium constant for complex formation was determined. The terminal, penultimate and complex‐participation models were tested for applicability to the mechanism of copolymerisation for this comonomer system. On the basis of copolymer composition data, the penultimate and complex‐participation models were found to provide each an adequate description of the mechanism of copolymerisation in the comonomer system via non‐linear least squares methods. The inadequacies of the terminal and penultimate models in describing the copolymers were exposed more explicitly through an analysis of their comonomer unit sequence distributions using reactivity ratio related test functions.

The applicability of copolymer composition and sequence distribution data to the mechanistic study of the alternating copolymerisation of maleic anhydride with substituted styrene derivatives

AbstractThe composition and sequence distribution of copolymers of maleic anhydride (MA) with p‐methoxystyrene (p‐MST) and p‐chlorostyrene (p‐CST) prepared in ethyl methyl ketone at 50 ± 0,1°C were analysed using 13C DEPT NMR techniques, in order to compare the applicability of composition and sequence distribution data to the study of the mechanism of copolymerisation using the terminal, penultimate and complex‐participation models. In the case of the strongly alternating copolymerisation of p‐MST with MA, the comparison of models on the basis of sequence distribution data was found to be better at separating each model in terms of its applicability, with the complex‐participation model providing the best fit to the data. In the case of the less strongly alternating copolymerisation of p‐CST with MA, neither method of comparison could clearly distinguish between the penultimate and complex‐participation models.

Interpreting the copolymerization of styrene with maleic anhydride and with methyl methacrylate in terms of the bootstrap model

The bootstrap model was proposed by Harwood to explain copolymer sequence distribution which is dependent only on copolymer composition in solvents which cause changes in the apparent reactivity ratios for a number of pairs of monomers. This work presents an explicit formulation of the equations describing copolymer composition and sequence distribution in terms of the bootstrap model for both the simple Mayo-Lewis model and the penultimate unit model. Inspection of these equations reveals the necessary and sufficient conditions for sequence distribution to be a function only of copolymer composition. The results of copolymerizations of styrene with methyl methacrylate and with maleic anhydride under various conditions are interpreted in terms of the bootstrap model.

Free‐radical multicomponent polymerization reactors and chemical composition distribution

AbstractFormulae to calculate the statistically caused instantaneous copolymer composition distribution as well as the chemical distribution of accumulated macromolecules, which is due to polymerization statistics and shifts in mean polymer composition during the reaction process, are derived on the basis of a universal model for free‐radical solution polymerization with any number of monomers proceeding in a batch, semi‐batch or continuous, ideally mixed vessel. The influence of the reactor type on chemical composition distributions is investigated for a copolymerization of different reactive components (methyl methacrylate/styrene/maleic anhydride), a system with nearly equal reactive monomers (methyl methacrylate/styrene), and the ternary polymerization of methyl methacrylate/styrene/maleic anhydride. Though products of constant mean composition are obtainable in a semi‐batch or steady‐state continuous reactors, considerable statistical dispersion cannot be removed in any case.

The oxidation of hydroquinone catalysed by poly(4-vinyl pyridine-co-N-vinyl pyrrolidone)-Cu(II) complexes: effect of the copolymer composition distribution on the catalytic activity

Abstract 4-Vinyl pyridine-N-vinyl pyrrolidone copolymers having various copolymer compositions and composition distribution were prepared. The latter was estimated by means of Spinner's equation. The copolymer prepared during the early stage of copolymerization was a random like copolymer, and the polymer polymerized completely was a blend like copolymer. Cu(II) complexes of the prepared copolymers had sufficient catalytic activity for the oxidation of hydroquinone, depending upon their composition distribution and the composition. The Cu(II) complex of the random like copolymer showed a higher catalytic activity than that of the blend like copolymer, even if the copolymers had a similar composition.

Sequence distribution and stereoregularity in methyl methacrylate-methyl acrylate copolymers at high conversions

Methyl methacrylate (MMA)-methyl acrylate (MA) copolymerizations have been analysed over a wide range of conversions with the purpose of predicting the changes in copolymer composition and comonomer sequence distribution as a function of conversion. High resolution 1H n.m.r. spectra (200 MHz) of MMA-MA copolymers, prepared at two overall comonomer concentrations by free radical copolymerization in benzene solution at 50°C at low conversion, have been analysed in terms of comonomer composition, sequence distribution and stereoregularity. Reactivity ratios for the terminal model, statistical parameters, P ij , and co-isotacticity parameters, σ 11 = 0.23 and σ = σ 12 = σ 21 = 0.50, estimated at low conversion were used to describe the changes in copolymer composition and triad fraction intensities with conversion. The experimental sequence distribution intensities were in agreement with the estimated values. From the good agreement found between experimental and calculated values, it can be concluded that the terminal model, through reactivity ratios and Bernoullian statistics, provides a very precise description of copolymerization over the whole range of conversion and composition and overall concentration of monomers.