Penultimate Reactivity Ratios Research Articles

Kinetics on the copolymerization of acrylonitrile with itaconic acid or methyl acrylate in dimethylsulfoxide by NMR spectroscopy

The free radical solution polymerization of acrylonitrile (AN) with itaconic acid (IA) or methyl acrylate (MA) was carried out in dimethylsulfoxide (DMSO) using 2 2'-azobisisobutyronitrile (AIBN) as the initiator. Based on the monomer conversion versus time data, the copolymerization rate was retarded by IA but promoted by MA. The monomer sequence distribution was characterized by 13C NMR to explain the significant difference in the copolymerization kinetics of the ANIA and AN-MA copolymers. The results of the copolymer composition curves and 13C NMR spectral analysis illustrated that the penultimate model was suitable for describing the copolymerization behavior of AN-IA, and the terminal and penultimate models were adequate for AN-MA. The penultimate reactivity ratios, rMA, were ~2 times higher than rIA, indicating that the reactivity of AN-terminated radical having MA as the preceding group was higher than that with IA. Then, the corresponding content of triads sequence AN-AN-AN (AAA) in the AN-MA copolymers was higher than those in the AN-IA copolymers. The appearance of new resonance signals of the quaternary and methyl carbon indicated a higher content of IA in copolymers. The higher IA concentrations the lower viscosity-average molecular weight of the polymers. The decrease in the molecular weight was correlated to the formation of the oligomers.

Terminal and Penultimate Reactivity Ratios in Single-Site Ethene/Propene Copolymerizations: Comparison of Kakugo and Direct Peak Methods

The original, first-order Kakugo method is extended to find second-order reactivity ratios of homogeneous catalysts in ethene/propene copolymerizations based on triad fractions. Subsequently, the first- and second-order reactivity ratios of eight Si-bridged C 2 -symmetric ansa-zirconocenes or hafnocenes, as obtained by the Direct Peak method, are used to compare with the Kakugo methods. From the results it is clear that the second-order methods give better descriptions than the first-order methods. Only the results of the second-order Direct Peak method are statistically justified, reflecting reliabilities >99.5%. Though the Direct Peak method in all cases gives the most reliable reactivity ratios, the second-order Kakugo method turns out to be a practical tool to find estimates.

POLYACRYLONITRILE PRECURSORS FOR CARBON FIBER WITH IMIDOCARBOX YLIC ACID UNITS: COPOLYMERIZATION OF ACRYLONITRILE WITH MALEIMIDOBENZOIC ACID

ABSTRACT 4-Maleimidobenzoic acid (MBA) was explored as a comonomer in polyacrylonitrile (PAN) precursors for carbon fiber. The copolymerization of acrylonitrile (AN) with MBA was carried out in DMF. The reactivity of MBA was considerably less than that of AN, which was manifested as a negative reactivity ratio for the former. The r MBA- values from −0.24 to −0.33 and r AN values of 1.07 were obtained by Kelen-Tudos and extended Kelen-Tudos methods. The penultimate reactivity ratios were determined by both linear and non-linear methods. The values were r 1=0.0093, r 1′=0.0132, r 2=1.063 and r 2′=1.625. The relative MBA concentration in the copolymer decreased drastically on enhancing its content in the monomer mixture. The penultimate model could satisfactorily explain the feed-copolymer composition profile for the whole composition range. MBA caused a decrease in the apparent copolymerization rate and molecular weight in agreement with the observed trends in the reactivity ratios. A statistical prediction of monomer sequences based on reactivity ratios implied that MBA existed as a lone monomer unit between the long sequences of AN units. This sequence distribution is suited for the efficiency of MBA in cyclisation reaction, which stabilizes PAN during its pyrolysis. Optimum thermal stabilization effect and char yield were observed for copolymers with around 3 mol% MBA in the chain.

Solvent and kinetic penultimate unit effects in the copolymerization of acrylonitrile with itaconic acid

Copolymerization of acrylonitrile (AN) with itaconic acid (IA) in dimethylformamide (DMF) and DMF/water mixture was investigated at enhanced concentrations of the latter. Analysis of the copolymer composition revealed the existence of a marked penultimate unit effect with respect to radicals terminated in AN. The reactivity of IA was considerably less than that of AN, manifested as a negative reactivity ratio for the former. The r IA values ranging from −0.28 to −0.50 and r AN values ranging from 0.53 to 0.70, were obtained by Kelen–Tudo's (KT) and extended KT methods. The penultimate reactivity ratios were determined by both linear and non-linear methods. The values ranged from r 1=0.009 to 0.01, r 1 ′=0.0015 to 0.0043, r 2=0.54 to 0.69 and r 2 ′=0.9 to 1.03. The reactivity of AN radical towards IA decreased about twofold when the latter formed the penultimate group. The penultimate model explained an acceptable rational feed-copolymer composition profile for the whole composition range. Addition of water decreased the reactivity of IA slightly. IA caused a decrease in the apparent copolymerization rate in agreement with the observed trends in the reactivity ratios; presence of water caused a further decrease in the rate of polymerization. A statistical prediction of monomer sequences based on reactivity ratios implied that IA existed as a lone monomer unit between the long sequences of AN units.

Terminal and Penultimate Reactivity Ratios in the Styrene-Acrylonitrile Free-Radical Copolymerization System in Bulk

ABSTRACT The terminal and penultimate model reactivity ratios for the styrene-acrylonitrile monomer system in bulk have been investigated by the simplex and scanning method. It has been shown that Mayo-Lewis equation has an unique solution when determining the reactivity ratios according to the terminal model while for the penultimate model the non-uniqueness in determination of the reactivity ratios has been found. The numerical values of the penultimate r-parameters calculated with the simplex method depend on the initial guess for r-parameters. Several sets of penultimate reactivity ratios for the styrene-acrylonitrile system in bulk have been found to be equal from mathematical point of view. The reactivity ratios with comparable standard deviation have an equivalent graphical representation on the copolymerization diagragm. It has been also confirmed that the penultimate model is a more appropriate of the models considered to describe the variation of the copolymer composition with the monomer feed. Taking into account previous results for the styrene-methyl methacrylate system in bulk it is thereby assumed that the occurrence non-uniqueness in determination of the penultimate model reactivity ratios does not depend on the monomer system.

Styrene‐methyl methacrylate copolymer microstructure according to terminal and penultimate model for free‐radical copolymerization

AbstractMicrostructure of styrene‐methyl methacrylate copolymers was determined according to the “bootstrap model” description using the terminal and the penultimate model of copolymerization. The implication of non‐uniqueness in determining the penultimate model reactivity ratios from the copolymer microstructure is discussed. The styrene centred triad sequences in the copolymer obtained in the free‐radical copolymerization of styrene and methyl methacrylate in bulk at 40°C were calculated using various sets of terminal and penultimate model reactivity ratios with very similar standard deviations. Calculations showed that for both models, the terminal model and the penultimate model, different reactivity ratios with very similar standard deviations are equally well suited for the quantitative description of the triad sequence distribution in the copolymer. The terminal and penultimate models produce different styrene centred triad sequence distributions in the copolymer, the difference depending on the penultimate model reactivity ratios used for calculation and on the type of the styrene centred triad sequence. The best equivalence of the two kinetic models was found when the initial r‐parameters guess used for determining the penultimate reactivity ratios by the simplex method were r11 = r21 = r1 and r22 = r12 = r2. The results suggest that the penultimate effect on the styrene‐methyl methacrylate free‐radical copolymerization system is limited.

Microstructure determination of styrene/ethyl acrylate copolymers by NMR spectroscopy and its correlation with glass transition temperature

AbstractStyrene/ethyl acrylate (S/E) copolymers of different compositions were prepared by bulk polymerization using benzoyl peroxide as an initiator. Copolymer compositions were determined from NMR spectra and reactivity ratios r1 and r2 were calculated using a non‐linear least‐squares errors‐in‐variables method (EVM) which gives more reliable values of r1 and r2. The copolymerization parameters such as terminal, penultimate reactivity ratios, diad concentrations, conditional probabilities, number‐average sequence lengths and run numbers in the copolymers were calculated by evaluating 13C{1H} NMR spectra. The observed sequence concentrations of triads as determined from 13C{1H} NMR spectra were in good agreement with those calculated from the reactivity ratios. The coisotacticity parameter (σ) was calculated from NMR spectroscopy data using the oxymethylene resonance signal in 1H NMR spectra. The glass transition temperatures (Tg) of various copolymers were obtained from Barton's equation (using diad relation) and are in agreement with those determined by means of differential scanning calorimetry.

Compositional sequence determination of acrylonitrile-butyl acrylate copolymers by 13C n.m.r. spectroscopy

Acrylonitrile-butyl acrylate (A/B) copolymers of different monomer compositions were prepared by bulk polymerization using a free radical initiator. Copolymer compositions were determined by elemental analyses and comonomer reactivity ratios were determined using a non-linear least squares errors-in-variables model. Terminal and penultimate reactivity ratios were calculated using the observed monomer triad sequence distribution determined from 13C{H} n.m.r. spectra. The triad sequence distribution was used to calculate diad concentrations, conditional probability parameters, number-average sequence lengths and block character of the copolymers. The observed triad sequence concentrations determined from 13C{ 1H} n.m.r. spectra agreed well with those calculated from reactivity ratios.

Determination of microstructure and glass‐transition temperature of acrylonitrile‐methyl acrylate copolymers by 13C‐NMR spectroscopy

AbstractAcrylonitrile‐methyl acrylate (A/M) copolymers of different monomer compositions were prepared by bulk polymerization using free radical initiator (benzoyl peroxide). Copolymer compositions were determined by elemental analyses and comonomer reactivity ratios were determined by the nonlinear least squares errors‐in‐variables methods (EVM). Terminal and penultimate reactivity ratios have been calculated using the observed monomer triad sequence distribution determined from 13C{1H}‐NMR spectra. The triad sequence distribution was used to calculate diad concentrations, conditional probability parameters, number‐average sequence lengths, and run number in the copolymers. The observed triad sequence concentrations determined from 13C{1H}‐NMR spectrum agreed well with those calculated from reactivity ratios. Glass transition temperatures (Tg) of various copolymers determined from DSC gave good agreement with those obtained from NMR. © 1992 John Wiley & Sons, Inc.

Sequence determination of acrylonitrile-(ethyl acrylate) copolymers by 13C-NMR spectroscopy and correlation with glass transition temperature

Acrylonitrile-(ethyl acrylate) copolymers of various compositions were prepared by bulk polymerization using benzoyl peroxide as initiator. Copolymer compositions were determined by elemental analyses; monomer reactivity ratios were determined using a nonlinear least square errors in variables model which gave more reliable value of r 1 and r 2. Terminal and penultimate reactivity ratios have been calculated using the observed monomer triad sequence distribution determined from 13C{ 1H}-NMR spectra. The triad sequence distribution was used to calculate diad concentrations, conditional probability parameters and number—average sequence lengths in the copolymers. The observed triad sequence concentrations determined from 13C{ 1H}-NMR spectra agreed well with those calculated from reactivity ratios. Glass transition temperatures of various copolymers determined from DSC agreed well with those obtained from diad concentrations.

13C‐NMR studies of compositional and configurational sequence distribution in acrylonitrile–ethyl methacrylate copolymers

AbstractAcrylonitrile–ethyl methacrylate (A/E) copolymers of different monomer concentrations were prepared in bulk by free radical initiation. Copolymer composition was determined by nitrogen analysis and the comonomer reactivity ratios were determined by the method of Kelen‐Tüdos. 13C‐NMR spectra of several acrylonitrile/ethyl methacrylate copolymers are discussed in terms of their triad monomer sequence and cotacticity. Terminal and penultimate reactivity ratios have been calculated using the observed monomer triad sequence distribution determined from 13C‐NMR spectroscopy for individual samples. Triad sequence distribution was used to calculate dyad concentrations, probability parameters, number average sequence lengths, and the comonomer mole fractions in the copolymers. The configurational sequence distributions in terms of all the 10 A‐centered and 10 E‐centered triad cotactic sequences have been determined and found to be in excellent agreement with those obtained using various cotactic probability parameters.

Determination of compositional and configurational sequence distribution of acrylonitrile-methyl methacrylate copolymers by 13C n.m.r. spectroscopy

Acrylonitrile-methyl methacrylate (AM) copolymers of different monomer concentrations were prepared in bulk by free radical initiation. 13C n.m.r. spectra of several acrylonitrile-methyl methacrylate copolymers are discussed in terms of their triad monomer sequence and cotacticity. Terminal and penultimate reactivity ratios were calculated using the observed monomer triad sequence distribution obtained from 13C n.m.r. spectra. Triad sequence distributions were used to calculate diad concentrations, probability parameters, number average sequence lengths and the comonomer mole fractions in the copolymers. The experimental fractions of all the ten A centred and ten M centred triad cotactic sequences were found to be in excellent agreement with those calculated using the probabilities parameters.

Determination by 13C-NMR spectroscopy of the microstructure of copolymers of acrylic acid with vinyl acetate

Acrylic acid-vinyl acetate copolymers were prepared in bulk using benzoyl peroxide as initiator. Copolymer compositions were determined by volumetric titration; monomer reactivity ratios were determined by the method of Kelen-Tüdös. Terminal and penultimate reactivity ratios have been calculated using the observed monomer triad sequence distribution determined from 13C-NMR spectroscopy. Triad sequence distribution was used to calculate dyad concentrations, probability parameters, number-average sequence lengths and comonomer mol fractions in the copolymers. The observed triad sequence concentrations as determined from 13C-NMR agreed well with those calculated from reactivity ratios.

Methyl methacrylate-chloroprene copolymerization: an evaluation of copolymerization models

The composition and triad fraction data of Ebdon ( Polymer 1974, 15, 782) for the copolymerization of methyl methacrylate with chloroprene have been re-evaluated using non-linear least squares curve-fitting procedures and statistical testing of conclusions. Using the compositions and triad fractions separately, best estimates of reactivity ratios together with the joint confidence intervals for these parameters for terminal and penultimate models have been calculated. It has been shown that the terminal model cannot describe adequately the experimental compositions or triad fractions. While the allowance of a penultimate effect for methyl methacrylate chain end radicals provides a significant improvement over the fit of the terminal model to the copolymer compositions, there is only a small probability that both the triad fraction and the composition data can be described adequately by one set of penultimate reactivity ratios.

Search for a Steric Penultimate Effect: Copolymerization of 2,3,4-Trimethyl-3-pentyl Methacrylate with Styrene

Abstract The hindered monomer, 2,3,4-trimethyl-3-pentyl methacrylate (I), was synthesized for penultimate effect studies. Since it readily homopoiymerized (km111≠ 0) and readily copolymerized with styrene, copolymerizations of I with styrene were carried out at 60°C in benzene with AIBN as initiator. The conversion to copolymer and the copolymer composition were determined by using GLC techniques. Composition-conversion data was analyzed by performing a computerized nonlinear least-squares fitting to the integrated form of the penultimate model equation. The experimental design included the use of optimized M1°/M2° ratios. The penultimate reactivity ratios calculated from these data were r1′ = 0.23, r1′= 0.59, r2 = 0.59, r2′ = 1.34. Thus, when I is the penultimate unit, a terminal styryl radical prefers to add styrene, whereas when styrene is the penultimate unit, terminal styryl radicals prefer to add I. These results constitute the best evidence for a steric penultimate effect yet available in the liter...

220 MHz proton magnetic resonance analysis of some methyl methacrylate-chloroprene copolymers

220MHz proton magnetic resonance (p.m.r.) spectra of some free-radically prepared methyl methacrylate-chloroprene copolymers have been recorded. The intensities of the α-methyl signals are related to the relative proportions of various methyl methacrylate (MMA) centred triads. Triad fractions obtained from the α-methyl signals indicate that the Mayo-Lewis copolymerization scheme is not strictly applicable to this system, and are in good agreement with those calculated from the penultimate reactivity ratios r 11=0.107 ± 0.008, r 21 = 0.057 ± 0.004 and r 2 = 6.7 ± 0.5 where MMA = monomer 1. However, although a small penultimate group effect is indicated, some deviation from the Mayo-Lewis scheme may be due to the occurrence of anomalous head-head and tail-tail methyl methacrylate-chloroprene linkages.

Fortran IV programs for the penultimate copolymerization model

AbstractThree programs have been written for calculations involving use of the penultimate copolymerization model. The first computes the penultimate reactivity ratios from composition‐conversion data, without constraints, at any conversion. A nonlinear leastsquares technique using Marquardt's algorithm is employed. The second program computes the four optimum starting monomer feed ratios, M10/M20 which should be used by the experimenter from the penultimate reactivity ratios. These optimum feed ratios are obtained by choosing the conditions necessary to minimize the determinant of the variance‐covariance matrix. The input for the first program includes estimates of known values of the penultimate reactivity ratios. By using these two programs sequentially the experimenter has an optimized experimental approach toward evaluating penultimate reactivity ratios at any conversion. Finally, a program has been provided to calculate composition–conversion data, given penultimate reactivity ratios.