Prediction of ionic copolymerization reactivity ratios

Copolymerization is a powerful tool for tuning the properties of synthetic polymers. In chain-growth polymerization, copolymer microstructure is controlled by the relative reactivity of comonomers, quantified by copolymer reactivity ratios. Yet, the complex macromolecular reactivity captured by reactivity ratios precludes the prediction of the resultant microstructures by intuition, and the established theory to understand reactivity ratios (i.e., Q-e scheme) has not been updated substantially since the development of quantum mechanics. Here, we combine modern computation, data science, and experimental validation to gain a detailed structure–reactivity understanding of the electronic, energetic, and steric parameters that govern comonomer reactivity. Using >450 reactivity ratios identified from primary literature sources, a combination of parametrization from density functional theory and data science methods identified discrete structure–reactivity relationships in free radical copolymerization. We demonstrate that the electronics of the radical species and the sterics of the monomers, neither of which were captured in the previous Q-e scheme, are pivotal to understanding the copolymerization reactivity. Experimentally measured reactivity ratios of a previously unstudied monomer combination validated the models, demonstrating the potential predictive power of this work to understand the comonomer sequence a priori. This work provides a framework to understand polymer microstructure from first-principles by relating specific and interpretable attributes of monomer structure to comonomer reactivity.

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Problems in the current experimental determination of radical reactivity ratios (i.e., 's values') in free-radical copolymerization and the resulting limited physical meaning of these reactivity ratios are highlighted in the present work. It is exemplified that the radical reactivity ratios obtained via fitting of average propagation rate coefficients are very sensitive to small uncertainties in monomer reactivity ratios and homopropagation rate coefficients. Furthermore, the failure to select an appropriate modelling method, and to design experiments so as to satisfy its assumptions, may lead to incorrect parameter estimates. These problems result in large uncertainties in the measured values of the radical reactivity ratios, which in turn lead to large uncertainties in calculated ratios of propagating radical concentrations. This suggests that experimental determinations of the relative radical concentrations may lead to complimentary means for obtaining information on radical reactivity ratios, and possible ways of obtaining this information through catalytic chain transfer experiments are discussed.

Emulsion copolymerizations of methyl acrylate (MA) with methyl methacrylate (MMA) and with acrylonitrile (AN) were carried out employing sodium lauryl sulphate (SLS) as a surfactant, potassium persulphate (KPS) as an initiator, and water as a dispersion medium at 70°C. The copolymers were characterized by FTIR, NMR, and TG/DTA techniques. Another series of emulsion copolymerization experiments were carried out employing HYOXYD X400 as a co-surfactant, along with SLS, and keeping all the other experimental conditions the same. The reactivity ratios of these monomer pairs were evaluated by employing the graphical procedures by Fineman–Ross (F–R) and Kelen–Tüdös (K–T). The K–T method yielded the reactivity ratios 0.95±0.05 (r MA) and 2.05±0.05 (r MMA), for the monomer pair MA/MMA, and 1.84 ± 0.05 (r MA) and 0.98 ± 0.05 (r AN) for the monomer pair MA/AN. When HYOXYD X400 was employed as a co-surfactant in the emulsion copolymerization experiments, the reactivity ratios were 0.75 ± 0.05 (r MA) and 2.17 ± 0.05 (r MMA) for the monomer pair MA/MMA, and 1.23 ± 0.05 (r MA) and 0.89 ± 0.05 (r AN) for the monomer pair MA/AN. These reactivity ratios obtained for the monomer pairs MA/MMA and MA/AN deviate from the values obtained by bulk and solution copolymerization methods reported in the literature.

Copolymers of furfuryl acrylate (A) with 2-hydroxyethyl methacrylate (H) were prepared by free radical copolymerization in DMF solution at 50°C, using 2,2'-azobisisobutyronitrile (AIBN) as initiator. The reactivity ratios of both monomers were calculated according to the general copolymerization equation using the Fineman-Röss and Kelen-Tüdos 1inearization methods, as well as the Tidwell-Mortimer non linear least-squares treatment and the Monte Carlo random method. The reactivity ratios obtained were rA = 0.93 and rH = 1.42. Similar results were obtained by both, the Monte Carlo and the non-linear least squares methods. The microstructure of copolymer chains based on the first order Markov statistics is described.

Chapter 1 - Gel-Type (Homogeneous) Polystyrene Networks

The phase separation of random copolymers during free radical copolymerization to high conversion was studied. In order to prepare in situ high impact thermoplastics during the copolymerization process, the attention was focussed on systems in which the more reactive comonomers form thermoplastics, whereas the less reactive components form elastomeric homopolymers. The studied systems (A, B) were (AN, EA), (AN, VA), (CHMA, MA) and (S, BA) (AN: acrylonitrile, EA: ethyl acrylate, VA: vinyl acetate, CHMA: cyclohexyl methacrylate, MA: methyl acrylate, S: styrene, BA: butyl acrylate). These copolymers display varying compositional heterogeneity depending on the different radical reactivity ratios and the feed composition used. Curves of instantaneous copolymer composition versus fractional conversion and the distribution functions of chemical composition were calculated for the various systems. In addition, miscibility diagrams of corresponding low conversion copolymers AxB1−x and AyB1−y, derived from the same monomer pair (A, B) but differing in composition, were recorded at high temperatures. Phase separation was detected by light microscopy and differential scanning calorimetry (DSC) using cast films. The onset of phase separation depending on the actual stage of copolymerization was recorded. The composition of the copolymers at the onset of phase separation was compared with the miscibility of low conversion copolymer blends. A satisfactory prediction of the start of phase separation during copolymerization is presented.

Copolymerization of styrene and 2‐hydroxyethyl methacrylate (2‐HEMA) was carried out in a microemulsion medium. The composition of the copolymers was estimated using proton 1H‐NMR. The reactivity ratios of styrene and 2‐HEMA in ternary microemulsions were observed and were considerable different from those reported for solution and bulk polymerization. In monomer pairs with a considerable difference in polarity, partitioning of a monomer between the aqueous phase and the microemulsion droplets develops a concentration gradient, which can be calculated from the distribution coefficient of the monomer between the two phases. This approach has led to more reliable reactivity ratios for the monomers. The study of styrene–2‐HEMA copolymerization in a sodium dodecylsulfate‐based microemulsion resulted in rS = 3.79 and rH = 0.17 as apparent reactivity ratios and rS = 0.57 and rH = 23.24 as true reactivity ratios for styrene and 2‐HEMA, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1832–1837, 2002; DOI 10.1002/app.10401

The copolymerization of the isobutylene (IB)-indene (In) monomer pair has been investigated by using the 2-chloro-2,4,4-trimethylpentane/TiCl4 initiating system and methyl chloride-methylcyclohexane (40/60 v/v) solvent mixture −80°C. According to the Kelen-Tüdös method, the reactivity ratios are r IB = 1.56 ± 0.72 and r In = 3.48 ± 0.89. The formation of copolymers was confirmed by 1H-NMR spectroscopy, selective solvent extraction, and glass transition temperature (T g) measurements. Copolymerization experiments in the presence of N,N-dimethylacetamide indicate that this electron donor does not affect the reactivity ratios.

Reactivity of a polymerizable amine activator in the free radical copolymerization with methyl methacrylate and surface properties of copolymers

Preparation, polymerization and copolymerization of some unsaturated dibutyltin carboxylates

The copolymerization of styrene (M1) with N-phenylmaleimide (M2) in chloroform with 2,2′-azobis(isobutyronitrile) as an initiator was investigated. The kinetic parameters, such as reactivity ratios, overall activity energy, and the effect of molar fraction of monomers on the initial copolymerization rate, were determined. The bimolecular termination of the copolymerization was proved. The treatment method proposed by Yoshimura and colleagues was used to estimate quantitatively the contribution of the charge-transfer complex (CTC) and the free monomers in the copolymerization process. The propagation reactivity ratios of CTC and free monomers were calculated by a new method. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1535–1542, 1997

The copolymerization of styrene (M1) with N-phenylmaleimide (M2) in chloroform with 2,2′-azobis(isobutyronitrile) as an initiator was investigated. The kinetic parameters, such as reactivity ratios, overall activity energy, and the effect of molar fraction of monomers on the initial copolymerization rate, were determined. The bimolecular termination of the copolymerization was proved. The treatment method proposed by Yoshimura and colleagues was used to estimate quantitatively the contribution of the charge-transfer complex (CTC) and the free monomers in the copolymerization process. The propagation reactivity ratios of CTC and free monomers were calculated by a new method. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1535–1542, 1997

Some aspects of copolymerization of dienes under the influence of π-allyl complexes of nickel

Copolymers of poly( n-alkyl acrylates): synthesis, characterization, and monomer reactivity ratios