Effect of the Substituent Position on the Anionic Copolymerization of Styrene Derivatives: Experimental Results and Density Functional Theory Calculations

Abstract

In a combined synthetic, kinetic and theoretical study, the living anionic copolymerization of styrene and its ring-methylated derivatives ortho-, meta-, and para-methylstyrene (MS) was examined by real-time 1 H NMR spectroscopy in the nonpolar solvents toluene-d 8 and cyclohexane-d 12 as well as by density functional theory calculations. Based on the NMR kinetics data, reactivity ratios for each comonomer pair were determined by the Kelen−Tudos method and numerical integration of the copolymerization equation (Contour software). The reaction pathway was modeled and followed by density functional theory (DFT) calculations to validate and predict the experimentally derived reactivity ratios. Unexpectedly, two of the three styrene derivatives showed completely different reactivities in copolymerization, governed by the position of the methyl group. While para-MS is considerably less reactive than styrene, resulting in gradient copolymers (r S = 2.62; r pMS = 0.37), ortho-MS showed the opposite behavior and is more reactive than styrene (r S = 0.44; r oMS = 2.47), leading to a reversal of the copolymers' gradient. The substitution in the meta-position had nearly no influence on monomer reactivity, and copolymers with close to random comonomer distribution were formed (r S = 0.81; r mMS = 1.21). In all cases, the theoretical calculations showed good to excellent agreement with the experimental data. Monomer reactivities correlate with the chemical shifts of the β-carbon signals in 13 C NMR spectra that are predictive for the gradient structure. The results demonstrate the possibility of tailoring and validating the polymer structures of functional polystyrene copolymers by the choice of the substitution pattern of styrene derivatives, using both experimental and theoretical approaches.

Tapered copolymers of styrene and 4‐vinylbenzocyclobutene via carbanionic polymerization for crosslinkable polymer films

“…While the methylene group in meta position shows no significant influence with respect to charge distribution, the methylene group in para‐position gives a positive inductive effect to the monomer. Similar results were obtained in the copolymerization of 4‐methylstyrene with styrene ( r s = 2.62 and r 4‐MS = 0.37) . Thus, 4VBCM is less reactive than styrene.…”

“…Real‐time 1 H NMR copolymerization kinetics enables the determination of reactivity ratios and thus the analysis of the comonomer distribution in the polymer chain . In recent works of our group the copolymerization of styrene‐derivatives with styrene and isoprene were investigated via real‐time NMR measurements 16a‐f,17 . A detailed understanding of the polymer microstructure is essential for applications.…”

Tetrahydrofuran: More than a “Randomizer” in the Living Anionic Copolymerization of Styrene and Isoprene: Kinetics, Microstructures, Morphologies, and Mechanical Properties

“…Increase of the polymerization temperature can lead to a certain flattening of the gradient, which, however, may not be large enough . In contrast, changes in the gradient caused by variation of the monomers are larger (e.g., by using alkyl styrene derivatives and/or other 1,3-dienes), ,,,− albeit also affect other parameters considerably (e.g., χ AB , entanglement molecular weights, and thermal stabilities). , …”

Anionic Copolymerization of 4-Trimethylsilylstyrene: From Kinetics to Gradient and Block Copolymers

“…Since the development of living anionic polymerization, the method has occupied an eminent status for the synthesis of well-defined polymers with controlled molecular weights and dispersity. , Despite significant advances in the field of reversible deactivation radical polymerization techniques in the recent past, − living anionic polymerization is still the preferred technique for the commercial synthesis of a variety of high-value functional polymers and thermoplastic elastomers (TPEs). ,, Styrene and its derivatives − are amenable to living anionic polymerization leading to a wide range of macromolecular architectures such as star, graft, hyperbranched, multiblock, and so forth . Functionalized styrene monomers are of particular interest as polymers therefrom can be further employed for post-polymerization modification or serve as precursors for the synthesis of graft copolymers. − Notably, the nature and position of the substituent at the styrene monomer can drastically modify the reactivity of the substituted styrene monomer in anionic polymerization. − …”