Quantitative comparison of the copolymerisation kinetics in catalyst-transfer copolymerisation to synthesise polythiophenes

Polythiophenes are one of the most widely studied conjugated polymers. With the discovery of the chain mechanism of Kumada catalyst-transfer polymerisation (KCTP), various polythiophene copolymer structures, such as random, block, and gradient copolymers, have been synthesized via batch or semi-batch (sequential addition) methods. However, the lack of quantitative kinetic data for thiophene monomers brings challenges to experimental design and structure prediction when synthesizing the copolymers. In this study, the reactivity ratios and the polymerisation rate constants of 3-hexylthiophene with 4 thiophene comonomers in KCTP are measured by adapting the Mayo-Lewis equation and the first-order kinetic behaviour of chain polymerisation. The obtained kinetic information highlights the impact of the monomer structure on the reactivity in the copolymerisations. The kinetic data are used to predict the copolymer structure of equimolar batch copolymerisations of the 4 thiophene derivatives with 3-hexylthiophene, with the experimental data agreeing well with the predictions. 3-Dodecylthiophene and 3-(6-bromo)hexylthiophene, which have higher structural similarity to 3-hexylthiophene, show nearly equivalent reactivity to 3-hexylthiophene and give random copolymers in the batch copolymerisation. 3-(2-Ethylhexyl)thiophene with a branched side chain is less reactive compared to 3-hexylthiophene and failed to homopolymerize at room temperature, but produced gradient copolymers with 3-hexylthiophene. Finally, the bulkiest 3-(4-octylphenyl)thiophene, despite its ability to homopolymerize, failed to maintain chain polymerisation in the copolymerisation with 3-hexylthiophene, possibly due to the large steric hindrance caused by the phenyl ring directly attached to the thiophene center. This study highlights the importance of monomer structures in copolymerisations and the need for accurate kinetic data.

Theoretical Insights into Midchain Radicals and Branching Characteristics in Solution Copolymerization of Ethylene and Vinyl Acetate

The kinetics of intermolecular chain transfer to polymer (CTP) and chain transfer to monomer (CTM), as well as backbiting in solution copolymerization of ethylene and vinyl acetate (VAc), are calculated by density functional theory. An intrinsic rate coefficient for each reaction type, whose Arrhenius parameters are expressed as functions of unreacted monomer composition, is extracted from calculated elementary reactions, and hence it applies to a wide range of fragment compositions of EVA. Backbiting controls the generation of midchain radicals (MCRs) on the backbone, and its rate maximizes at a medium fraction of VAc in the unreacted monomers. CTP plays an insignificant role in MCR generation even at high conversion rates due to its low pre-exponential factor. The concentration of MCRs is quantified and is close to that of ECRs at high conversions and high fractions of VAc in monomers. Additionally, branching characteristics are explored; concentrations of short-chain branching (SCB) and long-chain branching (LCB) are about 0.7-2.5 and 0.1-0.4%, respectively, and drop with VAc fraction rapidly. The role of the migration of MCRs is highlighted, which transforms about 10% of SCB points into LCB points. Disagreeing with insights from laboratory experiments, it is the migration, rather than CTP, which increases the LCB concentration at high conversions.

Verification for Temperature Dependence of Tacticity in Polystyrene Radical Polymerization with the Combination of Reaction Pathway Analysis and Red Moon Methodology

Radical polymerization is an economic and practical polymerization method over ionic and coordination polymerizations and is widely used for polymer production. Although many efforts have been made to improve the convenience and controllability of radical polymerization, it is still a challenge to directly observe the microbehaviors of propagation, which may provide inspiration for the development of polymerization processes. In this study, we focused on the tacticity of polystyrene produced by bulk radical polymerization since there is a debate over the temperature dependence. The propagation process is simulated via Red Moon methodology, which is a cost-effective method for handling complex chemical reaction systems. By the multiple pathway analysis for the propagation reaction model composed of the dimer radical and the monomer using density functional theory, we obtained the relative energies in multiple transition states, whose energy differences are partly explained by the π-π stacking interactions. Via performing Red Moon simulations from 30 to 190 °C, we confirmed that meso contents moderately increase as the temperature increases, which is explained by the influence of temperature on the probability density of the reaction conformations of each pathway. The successful prediction and explanation for tacticity demonstrate the potential of Red Moon methodology in unveiling the microbehaviors of propagation.

A unified kinetic Monte Carlo approach to evaluate (a)symmetric block and gradient copolymers with linear and branched chains illustrated for poly(2-oxazoline)s

The synthesis of well-defined gradient, block-gradient and di-block copolymers with both asymmetric and symmetric compositions considering hydrophilic and hydrophobic monomer units is relevant for application fields, such as drug/gene delivery...

Coupled matrix kinetic Monte Carlo simulations applied for advanced understanding of polymer grafting kinetics

An innovative coupled matrix-based Monte Carlo (CMMC) concept has been applied to successfully assess the detailed description of the molecular build-up of linear and non-linear chains in the free-radical induced grafting of linear precursors chains.

Progress in Reaction Mechanisms and Reactor Technologies for Thermochemical Recycling of Poly(methyl methacrylate)

Chemical or feedstock recycling of poly(methyl methacrylate) (PMMA) by thermal degradation is an important societal challenge to enable polymer circularity. The annual PMMA world production capacity is over 2.4 × 10⁶ tons, but currently only 3.0 × 10⁴ tons are collected and recycled in Europe each year. Despite the rather simple chemical structure of MMA, a debate still exists on the possible PMMA degradation mechanisms and only basic batch and continuous reactor technologies have been developed, without significant knowledge of the decomposition chemistry or the multiphase nature of the reaction mixture. It is demonstrated in this review that it is essential to link PMMA thermochemical recycling with the PMMA synthesis as certain structural defects from the synthesis step are affecting the nature and relevance of the subsequent degradation reaction mechanisms. Here, random fission plays a key role, specifically for PMMA made by anionic polymerization. It is further highlighted that kinetic modeling tools are useful to further unravel the dominant PMMA degradation mechanisms. A novel distinction is made between global conversion or average chain length models, on the one hand, and elementary reaction step-based models on the other hand. It is put forward that only by the dedicated development of the latter models, the temporal evolution of degradation product spectra under specific chemical recycling conditions will become possible, making reactor design no longer an art but a science.

Visualization and design of the functional group distribution during statistical copolymerization

Even though functional copolymers with a low percentage of functional comonomer units (up to 20 mol%) are widely used, for instance for the development of polymer therapeutics and hydrogels, insights in the functional group distribution over the actual chains are lacking and the average composition is conventionally used to describe the functionalization degree. Here we report the visualization of the monomer distribution over the different polymer chains by a synergetic combination of experimental and theoretical analysis aiming at the construction of functionality-chain length distributions (FUNC-CLDs). A successful design of the chemical structure of the comonomer pair, the initial functional comonomer amount (13 mol%), and the temperature (100 °C) is performed to tune the FUNC-CLD of copoly(2-oxazoline)s toward high functionalization degree for both low (100) and high (400) target degrees of polymerization. The proposed research strategy is generic and extendable to a broad range of copolymerization chemistries, including reversible deactivation radical polymerization.

Understanding copolymerisation kinetics for the design of functional copolymers via free radical polymerisation

We report the free radical copolymerisation kinetics and co-monomer sequence distribution for a series of functional copolymers based on MMA.

Coupled stochastic simulation of the chain length and particle size distribution in miniemulsion radical copolymerization of styrene and N-vinylcaprolactam

Kinetic Monte Carlo modeling is applied for the coupled simulation of the chain length and particle size distribution in isothermal batch miniemulsion copolymerization of styrene and N-vinylcaprolactam.