Kinetic Modeling of Nitroxide-Mediated Polymerization: Conditions for Living and Controlled Polymerization

Beauty of Explicit Dispersity (Đ) Equations in Controlled Polymerizations

Dispersity (Đ) as a critical parameter indicates the level of uniformity of the polymer molar mass or chain length. In the past several decades, the development of explicit equations for calculating Đ experiences a continual revolution. This viewpoint tracks the historical evolution of the explicit equations from living to reversible-deactivation polymerization systems. Emphasis is laid on displaying the charm of explicit Đ equations in batch reversible-deactivation radical polymerization (RDRP), with highlights of the relevant elegant mathematical manipulations. Some representative emerging applications enabled by the existing explicit equations are shown, involving nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP), and reversible addition-fragmentation chain transfer (RAFT) polymerization systems. Stemming from the several outlined challenges and outlooks, sustained concerns about the explicit Đ equations are still highly deserved. It is expected that these equations will continue to play an important role not only in traditional polymerization kinetic simulation and design of experiments but also in modern intelligent manufacturing of precision polymers and classroom education.

Virtual Free-Radical Polymerization of Vinyl Monomers in View of Digital Twins

The first case of virtual polymerization based on the concept of digital twins (DTs) is presented. The free-radical polymerization of vinyl monomers is considered to be a chain reaction consisting of a set of elementary ones. Those three types, related to the polymerization initiation and propagation as well as to the termination of polymer chain growth, are discussed. Special sets of DTs, whose total number approaches 60, distinguish each reaction type. The calculations are carried out using a semi-empirical version of the unrestricted Hartree-Fock approximation. The main energy and spin-density parameters of the ground state of the DTs are determined. The barrier profiles of two pairs of DTs are calculated, based on which two Evans-Polanyi-Semenov relations, attributed to elementary reactions of type (1) and (2), are constructed. These provide a quite reliable evaluation of the activation energy for the initiation and propagation of the free-radical polymerization of vinyl monomers in all the cases. The decisive role of spins in the formation of the elementary reaction transition states is established.

Development and Experimental Validation of a Dispersity Model for In Silico RAFT Polymerization

The exploitation of computational techniques to predict the outcome of chemical reactions is becoming commonplace, enabling a reduction in the number of physical experiments required to optimize a reaction. Here, we adapt and combine models for polymerization kinetics and molar mass dispersity as a function of conversion for reversible addition fragmentation chain transfer (RAFT) solution polymerization, including the introduction of a novel expression accounting for termination. A flow reactor operating under isothermal conditions was used to experimentally validate the models for the RAFT polymerization of dimethyl acrylamide with an additional term to accommodate the effect of residence time distribution. Further validation is conducted in a batch reactor, where a previously recorded in situ temperature monitoring provides the ability to model the system under more representative batch conditions, accounting for slow heat transfer and the observed exotherm. The model also shows agreement with several literature examples of the RAFT polymerization of acrylamide and acrylate monomers in batch reactors. In principle, the model not only provides a tool for polymer chemists to estimate ideal conditions for a polymerization, but it can also automatically define the initial parameter space for exploration by computationally controlled reactor platforms provided a reliable estimation of rate constants is available. The model is compiled into an easily accessible application to enable simulation of RAFT polymerization of several monomers.

β-Myrcene/isobornyl methacrylate SG1 nitroxide-mediated controlled radical polymerization: synthesis and characterization of gradient, diblock and triblock copolymers

β-Myrcene (My), a natural 1,3-diene, and isobornyl methacrylate (IBOMA), from partially bio-based raw materials sources, were copolymerized by nitroxide-mediated polymerization (NMP) in bulk.

Why can Dispolreg 007 control the nitroxide mediated polymerization of methacrylates?

The alkoxyamine 3-(((2-cyanopropan-2-yl)oxy)(cyclohexyl)amino)-2,2-dimethyl-3-phenylpropanenitrile (Dispolreg 007) has recently emerged as a robust regulator for the controlled (co)polymerization of methacrylates and styrene by nitroxide mediated polymerization.

Deterministic Approaches for Simulation of Nitroxide-Mediated Radical Polymerization

Since its development in the last decades, controlled radical polymerization (CRP) has become a very promising option for the synthesis of polymers with controlled structure. The design and production of tailor-made materials can be significantly improved by developing models capable of predicting the polymer properties from the operating conditions. Nitroxide-mediated polymerization (NMP) was the first of the three main variants of CRP to be discovered. Although it has lost preference over the years against other CRP alternatives, NMP is still an attractive synthesis method because of its simple experimental implementation and environmental friendliness. This review focuses on deterministic methods employed in mathematical models of NMP. It presents an overview of the different techniques that have been reported for modelling NMP processes in homogeneous and heterogeneous media, covering from the prediction of average properties to the latest techniques for modelling univariate and multivariate distributions of polymer properties. Finally, an outlook of model-based design studies of NMP processes is given.

Trityl-based alkoxyamines as NMP controllers and spin-labels

Recently, new applications of trityl-nitroxide biradicals were proposed. In the present study, attachment of a trityl radical to alkoxyamines was performed for the first time. The rate constants kd of C-ON bond homolysis in these alkoxyamines were measured and found to be equal to those for alkoxyamines without trityl. The electron paramagnetic resonance (EPR) spectra of the products of alkoxyamine homolysis (trityl-TEMPO and trityl-SG1 biradicals) were recorded, and the corresponding exchange interactions were estimated. The decomposition of trityl-alkoxyamine showed more than an 80% yield of biradicals, meaning that the C-ON bond homolysis is the main reaction. The suitability of these labelled initiators/controllers for polymerisation was exemplified by means of successful nitroxide-mediated polymerisation (NMP) of styrene. Thus, this is the first report of a spin-labelled alkoxyamine suitable for NMP.

Nitroxide-Mediated Polymerization of Methacrylic Esters: Insights and Solutions to a Long-Standing Problem

Nitroxide-mediated polymerization (NMP) is one of the most powerful reversible deactivation radical polymerization techniques and has incredibly gained in maturity and robustness over the last decades. However, control of methacrylic esters is one of the different aspects of NMP that still requires improvement. This family of monomers always represented an important challenge for NMP, despite the many different nitroxide structures that have been designed over the course of time. This Review aims to present the most successful strategies directed toward the control of the NMP technique of methacrylic esters and especially methyl methacrylate. NMP-derived materials comprising uncontrolled methacrylate segments will also be discussed.

Novel polymer synthesis methodologies using combinations of thermally- and photochemically-induced nitroxide mediated polymerization

The combination of thermally- and photochemically-induced polymerization using light sensitive alkoxyamines was investigated.

Model-based design of the polymer microstructure: bridging the gap between polymer chemistry and engineering

A state-of-the-art review is presented on model-based design for next-generation polymer synthesis and modification.

Highlight on the Mathematical Modeling of Controlled Free Radical Polymerization

Over the last quarter century, controlled free radical polymerization (CFRP) has received great attention by the researchers of polymer science and engineering. In addition to the experimental studies, many publications in the literature dealt with the modeling of CFRP processes. A review of acknowledged and well-received researches on mathematical modeling in the area of CFRP is presented in this work. Three main categories of CFRP (namely, ATRP, RAFT, and NMP) are taken into consideration in the review. The different techniques used in modeling CFRP processes are also enumerated with more emphasis on Monte Carlo simulation and the method of moments. The review provides a better understanding of the processes and the recent efforts to model CFRP.

Synthesis of polystyrene-grafted cellulose acetate copolymers via nitroxide-mediated polymerization

Cellulose acetate-g-polystyrene grafted copolymers have been synthesized by NMP under homogeneous conditions by using the 1,2-intermolecular radical addition methodology.

Separation and Characterization of Synthetic Polyelectrolytes and Polysaccharides with Capillary Electrophoresis

The development of macromolecular engineering and the need for renewable and sustainable polymer sources make polymeric materials progressively more sophisticated but also increasingly complex to characterize. Size-exclusion chromatography (SEC or GPC) has a monopoly in the separation and characterization of polymers, but it faces a number of proven, though regularly ignored, limitations for the characterization of a number of complex samples such as polyelectrolytes and polysaccharides. Free solution capillary electrophoresis (CE), or capillary zone electrophoresis, allows usually more robust separations than SEC due to the absence of a stationary phase. It is, for example, not necessary to filter the samples for analysis with CE. CE is mostly limited to polymers that are charged or can be charged, but in the case of polyelectrolytes it has similarities with liquid chromatography in the critical conditions: it does not separate a charged homopolymer by molar mass. It can thus characterize the topology of a branched polymer, such as poly(acrylic acid), or the purity or composition of copolymers, either natural ones such as pectin, chitosan, and gellan gum or synthetic ones.

SG1 Nitroxide Analogues: a Comparative Study

Due to a specific balance between steric, polar, and stabilization effects, SG1 nitroxide and its corresponding alkoxyamine BlocBuilder MA are now well recognized as two of the most potent compounds in nitroxide-mediated polymerization (NMP). In this work, alternatives to SG1, based on various aldehydes, were targeted using structure–reactivity relationships already developed by our group. Compared with SG1, we show that the substitution of the tert-butyl group on the carbon α to the aminoxyl function by a 2-ethylhexyl group led to a new nitroxide (ETHEXNO), which exhibited an half-life time at 120°C similar to SG1 and a slightly slower kd for the alkoxyamine (2–3 times lower than the SG1). The styrene polymerization mediated by the ETHEXNO nitroxide has a similar behaviour to the one mediated by the SG1 in terms of livingness and control but the kinetics is affected (2–3 times lower). Concerning the n-butyl acrylate polymerization, an unexpected overheating occurred at 120°C, which led us to perform the polymerization in toluene at 100°C. The slow kinetics impedes the use of this nitroxide as a good alternative to SG1 and shows that the structure of the SG1 nitroxide is already delicately optimized and finding good alternatives is not straightforward.