Sequence Distribution Of Monomer Units Research Articles

INTERPOLYMER ASSOCIATION OF ACRYLAMIDE COPOLYMERS WITH POLY(ETHYLENEIMINE): STABILITY, THERMODYNAMIC PARAMETERS, AND THEIR CORRELATION WITH THE COPOLYMER MICROSTRUCTURE

Acrylamide/vinyl acetate and acrylamide/vinyl propionate copolymers were prepared by solution polymerization using benzoyl peroxide as the initiator. The copolymer composition was determined from the percent nitrogen in the copolymers. The stability constants and related thermodynamic parameters (e.g., ΔG°, ΔH°, and ΔS°,) of the interpolymer complexes with Poly(ethyleneimine) were determined by using Osada's method. These parameters have been correlated with the sequence distribution of monomer units in the copolymer chains which were obtained from 13C{1H} NMR spectroscopy. The sequence distribution of the comonomer units in the copolymer chains influence the association between the copolymers and the polyelectrolyte which is reflected on the stability of the interpolymer complexes.

Stability and thermodynamic parameters of interpolymer complexes of acrylamide/alkyl acrylate copolymers with poly(ethyleneimine): effects of microstructure and alkyl substituents of copolymers on interpolymer association

Acrylamide/ethyl acrylate (A/E) and acrylamide/butyl acrylate (A/B) copolymers of different compositions were prepared in solution by free radical polymerization. The copolymer compositions were determined from the nitrogen content in the copolymers. Interpolymer complexes of both A/E and A/B copolymers with polyethyleneimine (PEI) were prepared in DMF-water (80: 20 v/v). The stability constants and related thermodynamic parameters (e. g., ΔG 0 . ΔH 0 and ΔS 0 ) of the interpolymer complexes were determined using Osada's method. These parameters were correlated with the sequence distribution of monomer units in the copolymer chains which were obtained from 13 C{ 1 H} NMR spectroscopy. The size of the alkyl group and the microstructure of the copolymers influence the association between the copolymer and PEI, which is reflected in the stability of the interpolymer complexes.

Determination of Monomer Unit Sequence Distribution and Linkage Configuration of Copolymers of Styrene and Citraconic Anhydride, and Possibility of a Participation of Electron Donor-Acceptor Complex in the Copolymerization

The copolymerization system of styrene (ST) and citraconic (α-methymaleic) anhydride (CA) was found to form semi-alternating copolymers when polymerized with a total monomer concentration of 4 mol/L in CCl4 at 50°C, with alternating copolymers being formed only when the CA mole fraction in feed was greater than 0.9. More than 50% of the linkage configurations at the cyclic CA units in the copolymers were found to be in cis configuration. This, together with the following observations, is consistent with a participation of the electron donor-acceptor (EDA) complex formed between ST and CA: (a) the complex participation model fits best, although only marginally, to the experimental triad mole fraction of alternating sequences; (b) the alternating monomer unit sequences and the cis linkage configuration at the cyclic CA units are more efficiently formed in non polar CCl4 solutions than in polar methy ethyl ketone. The equilibrium constant for the EDA complexation of ST and CA in CCl4 at 23°C is determined to be 0.142 ± 0.015 L/mol.

Monomer unit sequence distribution and linkage configurations at citraconic anhydride units in the copolymers of citraconic anhydride and styrene prepared in carbon tetrachloride

The triad monomer unit sequence distribution and the cis and trans linkage configurations at the cyclic citraconic anhydride units are quantitatively determined for the copolymers of citraconic anhydride (α-methylmaleic anhydride) (CA) and styrene (ST) prepared with AIBN in CCU solutions at 50 °C. Semi-alternating copolymers are obtained for most feed compositions with rigidly alternating copolymers being formed when CA in feed is more than 90 %. Greater than 50 % of the linkages at CA units are found to be in cis configuration in semi-alternating copolymers. This may be explained if the donor-acceptor complex formed between CA and ST participates in the copolymerization.

Copolymer Sequence Distribution with Chiral Stereoregularity and Its Application to Poly(acrylonitrile-co-methacrylonitrile)

An attempt was made to elucidate the general mathematical expression of the polymer sequence distribution for copolymers with two stereoregular monomer units by considering their chirality (D or L form) distribution based on Markov statistics. The equations derived (DL equations) were compared with those based on conventional meso and racemo conformation (mr equations) [K. Kamide and K. Hisatani, Polym. J., 24, 1377 (1992)]. For this purpose the literature data of NMR on sequence distribution of three kinds of poly(acrylonitrile-co-methacrylonitrile) i.e., poly(AN-co-MAN), prepared by radical polymerization using redox catalysis and anionic method using dialkylmagnesium as initiator at high and low temperature, were analyzed. DL equations were found to explain well the monomer unit sequence distribution with cotacticity of two poly(AN-co-MAN), polymerized by radical method and by anionic methods at temperatures, rather than mr equations. The reaction probability of these copolymers estimated by [Bernoulli]−[1st Markov]cor statistics where monomer unit sequence and its cotacticity obey Bernoulli and 1st order Markov processes, respectively, has revealed that racemo addition of MAN monomer does not occur in the above anionic polymerization essentially. For all of three samples, the stereoregular sequences obey 1st order Markov statistics, but monomer unit ones obey 2nd order Markov statistics for low temperature anionic method and Bernoulli for the other two method.

The Triad Distribution and The cis/trans Configurations at the Cyclic Maleic Anhydride Units in Maleic Anhydridestyrene Copolymers Prepared in N,N-Dimethylformamide

Abstract The monomer unit sequence distribution and the cis/trans linkage configurations of maleic anhydride units in maleic anhydride (Ma)-styrene (St) copolymers prepared in N,N-dimethylformamide with N,N'-azobisisobutyronitrile at 50°C over a wide range of Ma monomer feed mole fractions were determined using DEPT 13C-NMR spectroscopy. It was found that when the Ma feed mole fraction is more than 0.4, the monomer unit sequence becomes almost alternating and the mole fraction of the cis linkages at the Ma units in the copolymer attain a nearly defined maximum value of 0.54 ± 0.06.

Miscibility, Thermal Properties, and Enzymatic Degradability of Binary Blends of Poly[(R)-3-hydroxybutyric acid] with Poly(ε-caprolactone-co-lactide)

The miscibility, morphology, and biodegradability of binary blends of poly[(R)-3-hydroxybutyric acid] (P[(R)-3HB]) (Mn = 300 000) with poly(ε-caprolactone-co-lactide) (P(CL-co-LA)) (Mn = 1500−40 000) have been studied by means of differential scanning calorimetry (DSC), optical microscopy, scanning electron microscopy (SEM), enzymatic hydrolysis, and biodegradation in river water. Copolymers of ε-caprolactone (CL) and (R,S)-lactide (LA) with a wide range of compositions were prepared by ring-opening copolymerization of ε-caprolactone with (R,S)-lactide in the presence of aluminum triisopropoxide as an initiator. The P(CL-co-LA) samples were found to have a random sequence distribution of monomer units by 13C NMR analysis. The P(CL-co-LA) films were hydrolyzed by a lipase from Rhizopus delemar, and the rates of enzymatic hydrolysis were higher than that of PCL homopolymer. DSC analysis revealed that the solid-state structure of P[(R)-3HB]/P(CL-co-LA) blends was strongly dependent on the copolymer composition of the P(CL-co-LA) component. The miscible blends of P[(R)-3HB] were prepared with amorphous P(CL-co-LA) ranging from 30 to 100 mol % LA. The spherulites of P[(R)-3HB] in the miscible P[(R)-3HB]/P(CL-co-LA) blends were volume-filled, and the spherulitic growth rate decreased with an increase in the content of the P(CL-co-LA) component. The enzymatic hydrolysis of P[(R)-3HB]/P(CL-co-LA) blend films was carried out at 37 °C and pH 7.4 in a potassium phosphate buffer with an extracellular PHB depolymerase from Alcaligenes faecalis. The rates of enzymatic hydrolysis on the films of P[(R)-3HB]/P(CL-co-LA) blends decreased with an increase in the P(CL-co-LA) content.

Determination Method of Sequence Distribution for Bi-component Copolymer System in Which One Monomer Unit Only Has Stereoregularity and Its Application for Poly(acrylonitrile-co-vinylidene chloride)

An attempt was made to extend the method for explaining monomer unit sequence distribution of a bi-component copolymer system proposed already by Kamide and Hisatani, in which both monomer units have possibility of yielding stereoregular homopolymers, to the system in which only one monomer is capable to give stereoregular homopolymer. The method includes a concept of correlation and non-correlation between sequence distributions of monomer unit and its cotacticity, and all of expressions of pentad sequences are described. Simultaneously, the sort of four kinds of n-length bi-component copolymer sequence has been enumerated up employing difference equation method, in which copolymer system only one monomer unit has stereoregularity. The method established in this paper was applied to poly(acrylonitrile-co-vinylidene chloride) sample as a model copolymer, of which 13C NMR peak assignment was already attained based on pentad sequence distribution [H. Yamazaki, K. Okajima, and K. Kamide, Polym. J., 20, 1143 (1988)].

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.

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.

Structures and compositions of copolymers

AbstractAlthough studies on reactions of model radicals with olefins are becoming of increasing importance, most understanding of copolymerization has come from studies on copolymer composition and monomer unit sequence distribution information. A number of models for copolymerization have resulted from such studies. For most copolymerization systems the terminal model provides an adequate representation, but more complicated models which allow for the effects of penultimate units on radical reactivity, for reversibility of propagation steps and for participation of monomer complexes in copolymerization processes must be considered in some cases. Modeling of such copolymerization systems is considerably simplified by computer‐oriented approaches such as matrix–multiplication, Monte Carlo simulation and CSMP or ACSL programming. Recent studies on solvent effects in copolymerizations involving polar monomers indicate that partitioning of monomers between solvent and growing polymer radicals is a very significant phenomenon.

Monomer Unit Sequence Distribution in Partly-Epoxidized trans-1,4-Polyisoprene

The monomer unit sequence distribution in partly epoxidized trans-1,4-polyisoprene was determined by the 13C NMR spectrometry available. Epoxidation of polymer was carried out by peracid prepared in situ from hydrogen peroxide and a small amount of formic acid, and the epoxy content in the modified polymer was determined by 1H NMR. The 13C NMR spectra of the partly epoxidized trans-1,4-polyisoprene exhibited new signals both in the olefinic and aliphatic carbon regions, in addition to the signals due to the original trans-1,4-polyisoprene. Each signal, except for the methyl carbon signals, was interpreted in terms of the dyad or triad of trans-1,4 and epoxidized units, taking into consideration the results from the signal assignments made by off-resonance decoupling techniques and lanthanide shift reagent experiments. The monomer unit sequence distribution in partly epoxidized trans-1,4-polyisoprene determined by 13C NMR agreed very closely with that calculated on the basis of the random distribution of trans-1,4 and epoxidized isoprene units. These results suggest that the site of the epoxy group formed is not affected by such groups previously formed in polyisoprene.

Microstructure of propene‐butene copolymers studied by flash‐pyrolysis‐G.L.chromatography

AbstractPropene‐butene copolymers of various composition were prepared using different kinds of catalysts and were characterized by gel permeation chromatography and X‐ray analysis. Using flash‐pyrolysis coupled with gas chromatography and mass spectrometry, trimers, produced through the 1–5 internal transfer and ß‐6–7 scission mechanism, could be separated and identified. They allowed a study of the sequence distribution of monomer units. Using the TiCl4Al(C2H5)3 catalyst, although a simple check of a first order Markovian distribution had been positive, a detailed study lead to the conclusion of a distribution of active sites with different reactivities versus the two monomers. The different selectivities of the different sites in the case of the TiCl3Al(C2H5)I catalyst are even more pronounced.

Determination of the composition and structure of polymers by pyrolysis gas chromatography

The applications of pyrolysis gas chromatography for quantitative analysis of copolymers and for the evaluation of their microstructure are described. Three types of widely accepted pyrolyzers were examined to determine their different applications and to select the most satisfactory ones for quantitative analysis. It was established that all types of pyrolyzers may be used for the determination of the composition of copolymers and that a Curie-point pyrolyzer is preferable for the evaluation of polymer microstructure. The pyrolysis gas chromatographic conditions of different copolymers and rubber mixtures are given in this paper. The linear relationship between the ratio of characteristic peak areas and the ratio of the concentration of monomer units in copolymers was used for the determination of copolymer composition using the pyrograms. The difference that was found between the ratio of peak areas for block and random copolymers was used for the evaluation of the sequence distribution of monomer units. The optimum pyrolysis temperature was determined for that purpose. An equation for calculating the contents of monomer units in blocks is suggested.

Dilute solution properties and molecular characterization of poly(butyl methacrylate‐co‐styrene)

AbstractDilute solution properties of fractionated poly(butyl methacrylate‐co‐styrene) PBMAS prepared by bulk polymerization, have been investigated by means of light scattering, viscometry, and osmometry. As the composition heterogeneity was narrow, the characterization of the copolymer was effected in a single solvent by light scattering. Infrared and nuclear magnetic resonance spectra were used to determine the composition and sequence distribution of monomer units of the copolymer. The molecular weight dependence of the limiting viscosity number and of the root‐mean‐square end‐to‐end distance have been established. The Mark‐Houwink relation showed that methylethyl ketone is a good solvent compared with cyclohexane. The validity of various extrapolation procedures that have been proposed to calculate the unperturbed dimensions have been examined. Root‐mean‐square end‐to‐end distances have been calculated from the Debye‐Bueche and Kirkwood‐Riseman methods and compared with the experimental values. The molecular weight dependence of the second virial coefficient agreed well with that calculated from the Orofino‐Flory equation. The value of the steric hindrance parameter σ for the copolymer has been found to be 2.27 compared to 2.05 for poly(butyl methacrylate) and 2.22 for polystyrene, which indicates that PBMAS is a stiffer chain in solution than those of the constituent homopolymers.

Solution properties of ethylene‐vinyl acetate copolymers

AbstractHigh‐pressure ethylene–vinyl acetate copolymers of four different chemical compositions(9%, 15%, 45%, and 70% VA) were characterized to determine molecular weight and distribution. The four samples were fractionated by solvent–nonsolvent precipitation methods. Light‐scattering, osmometry, and viscosity measurements were made on these fractionated copolymers to determine weight‐average molecular weight \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {M_w } $\end{document}, number‐average molecular weight \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {M_n } $\end{document}, molecular size in solution, and interaction constants. Dilute solution viscosity was measured on the fractions to determine intrinsic viscosity and Huggins' constant k′. Viscosity–molecular weight equations were established for the four copolymer compositions. The log intrinsic viscosity versus log molecular weight diagrams were analyzed and the average length of branches calculated. The composition of the polymer fractions, determined by C and H combustion analysis, was found not to vary significantly with molecular weight. The uniformly random character of the E/VA copolymers was thereby confirmed. The density of the fractions was determined by density‐gradient column method. Chain sequence distribution of monomer units for the four copolymers was calculated by using IBM 704 computations involving the actual monomer reactivity ratios. Long sequences of either ethylene or vinyl acetate are improbable, except at the extremes of copolymer composition.