Radical Polymerization Mechanism Research Articles

Regioselective On-Surface Synthesis of [3]Triangulene Graphene Nanoribbons.

The integration of low-energy states into bottom-up engineered graphene nanoribbons (GNRs) is a robust strategy for realizing materials with tailored electronic band structure for nanoelectronics. Low-energy zero-modes (ZMs) can be introduced into nanographenes (NGs) by creating an imbalance between the two sublattices of graphene. This phenomenon is exemplified by the family of [n]triangulenes (n ∈ ). Here, we demonstrate the synthesis of [3]triangulene-GNRs, a regioregular one-dimensional (1D) chain of [3]triangulenes linked by five-membered rings. Hybridization between ZMs on adjacent [3]triangulenes leads to the emergence of a narrow band gap, Eg,exp ∼ 0.7 eV, and topological end states that are experimentally verified using scanning tunneling spectroscopy. Tight-binding and first-principles density functional theory calculations within the local density approximation corroborate our experimental observations. Our synthetic design takes advantage of a selective on-surface head-to-tail coupling of monomer building blocks enabling the regioselective synthesis of [3]triangulene-GNRs. Detailed ab initio theory provides insights into the mechanism of on-surface radical polymerization, revealing the pivotal role of Au-C bond formation/breakage in driving selectivity.

The renaissance and evolving design of radical polymerization

Abstract During the 49th World Polymer Congress held 17–21 July 2022 in Winnipeg, Canada, Graeme Moad presented the Stepto Lecture Award [1], describing the mechanism and terminological evolution of reversible deactivation radical polymerization (RDRP) [2, 3, 4], including more recent intricate designs through the use of light and electrical propulsion.

DFT Studies of Dimethylaminophenyl-Substituted Phthalocyanine and Its Silver Complexes.

The dimethylaminophenyl-substituted silver phthalocyanine [dmaphPcAg] can be used as a UV-vis photoinitiator for in situ preparation of a silver/polymer nanocomposite. To verify early steps of the supposed mechanism of radical polymerization, we performed quantum chemical calculations of m[dmaphPcAg]q complexes with charges q = +1 to -2 in the two lowest spin states m, of a free ligand and its dehydrogenated/deprotonated products m[dmaphPcHn]q, n = 2 to 0, q = 0, -1 or -2, in the lowest spin states m. The calculated electronic structures and electron transitions of all the optimized structures in CHCl3 solutions are compared with experimental EPR and UV-vis spectra, respectively. The unstable 3[dmaphPcAg]+ species deduced only from previous EPR spin trap experiments was identified. In addition to 2[dmaphPcAg]0, our results suggest the coexistence of both reaction intermediates 1[dmaphPcAg]- and 3[dmaphPcAg]- in reaction solutions. Silver nanoparticle formation is a weak point of the supposed reaction mechanism from the energetic, stereochemistry, and electronic structure points of view.

Kinetically Limited Bulk Polymerization of Polymer Thin Films by Initiated Chemical Vapor Deposition.

An experimental study and kinetic model analysis of the initiated chemical vapor deposition (iCVD) of polymer thin films have been performed at saturated monomer vapor conditions. Previous iCVD kinetic studies have focused on subsaturated monomer conditions where polymer deposition kinetics is known to be limited by monomer adsorption. However, iCVD kinetics at saturated conditions have so far not been systematically investigated, and it remains unclear whether the adsorption-limited phenomenon would still apply at saturation, given the abundance of monomer for reaction. To probe this question, a series of depositions of poly(vinylpyrrolidone) (PVP) thin films as a model system were performed by iCVD at substrate temperatures from 10 to 25 °C at both fully saturated (100%) and subsaturated (50%) conditions. While the deposition rates at subsaturated conditions exhibit the expected adsorption-limited behavior, the deposition rates at saturated conditions unexpectedly show two distinct deposition regimes with reaction time: an initial adsorption-limited regime followed by a kinetically limited steady-state regime. In the steady-state regime, the deposition kinetics is found to be thermally activated by raising substrate temperature with an overall activation energy of +86 kJ/mol, which agrees reasonably well with the experimentally determined value of +89 kJ/mol in the literature for bulk PVP polymerization and a mechanistically derived value of +91 kJ/mol based on the bulk free radical polymerization mechanism of PVP. These findings open new operating windows for iCVD polymerization and thin-film growth in which fast polymer deposition can be achieved without substrate cooling that can greatly simplify the iCVD scale-up to roll-to-roll processing and enable iCVD polymerization of highly volatile monomers relevant for diverse applications in biomedicine, smart wearables, and renewable energy.

The role of 2‐iminopyrrolyl copper(I) complexes in the Reversible‐Deactivation Radical Polymerization of methyl methacrylate

The role of 2‐iminopyrrolyl copper(I) complexes in the Reversible‐Deactivation Radical Polymerization (RDRP) of methyl methacrylate (MMA) is described. Mononuclear 2‐iminopyrrolyl copper(I) complexes [Cu{κ2N,N′‐NC4H3‐2‐C(H)=NR′}Ln] 1–7 (R′ = C6H5, Ln = (PPh3)2 (1); R′ = 2,6‐Me2C6H3, Ln = (PPh3)2 (2); R′ = 2,6‐iPr2C6H3, Ln = (PPh3)2 (3); R′ = 4‐NMe2C6H4, Ln = (PPh3)2 (4); R′ = CH3, Ln = (PPh3)2 (5); R′ = CH3, Ln = (PMe3)2 (6); R′ = CH3, Ln = PiPr3 (7)) were synthesized by the reaction of the in situ prepared sodium salts of precursors HL1–5 with [Cu(NCMe)4]BF4 with the respective phosphines. In their absence, the binuclear complex [Cu{κN,κN'‐NC4H3‐2‐C(H)=NCH3}]2 8 was formed instead, which, when treated with one equivalent of PR3 yielded the binuclear complexes [Cu2{κN,κN'‐NC4H3‐2‐C(H)=NCH3}2PR3] 9 (R = Ph) and 10 (R = Me).All complexes, except 8, were active in the RDRP of MMA using the initiator tert‐butyl‐α‐bromoisobutyrate (tBiB‐Br), achieving apparent propagation kinetic constants (kp') in the range of 0.5–7.5 × 10−5 s−1, at 90 °C and with a [MMA]0:[complex]0:[tBiB‐Br]0 ratio of 500:1:1. All reactions yielded poly (methyl methacrylate)s with molecular weights ( ) and dispersities higher than expected for Controlled Radical Polymerization processes. Complex 7 achieved the best results, with values being only 1.2‐fold higher than theoretically expected. Experimental and density functional theory (DFT) studies suggest that this system operates via Atom Transfer Radical Polymerization/Organometallic Mediated Radical Polymerization (ATRP/OMRP) mechanisms interplay.

Синтез и свойства привитых сополимеров ксантана и глюкоманнана с акриловыми мономерами

Graft copolymers of polysaccharides with acrylic monomers combine biodegradability, biocompatibility, the environmental friendliness of natural polymers and the increased thermal stability, chemical and mechanical resistance of synthetic polymers. This paper describes our search and analysis of the literature in English for 2002–2022 devoted to the graft polymerization of acrylamide, acrylic acid and 2-acrylamido- 2-methylpropanesulfonic acid onto xanthan and glucomannan macromolecular chains. It has been found that the synthesis of grafted copolymer chains proceeds by a radical polymerization mechanism using thermal homolytic decomposition of the initiator or microwave irradiation, or radiation initiation and frontal polymerization in some cases. Depending on the method of the reaction, the synthesis time of a graft copolymer varies from several minutes to several hours. The influence of the synthesis conditions and parameters on the monomer conversion, structure and properties of the resulting polymer has been considered. It has been found that decreasing the polysaccharide/monomer ratio and increasing the initiator concentration raise the efficiency and degree of grafting. Several methods for characterization of graft copolymers are discussed, including: IR spectroscopy to analyze the chemical structure of a sample, scanning electron microscopy to characterize structure, supramolecular ordering and porosity, differential thermal analysis to evaluate thermal effects and thermal stability. The effect of the synthesis conditions and the pH of the sorption medium on the water absorption and sorption capacity of this class of graft copolymers are discussed. The broad potential of graft copolymers for repeated cycles of absorption and release of liquid medium without loss of functional properties has been found. This opens prospects for the use of graft copolymers of xanthan and glucomannan with acrylic monomers as materials for water purification from metal ions and cationic dyes, targeted delivery and prolonged action of drugs and wound coatings for wound treatment.

Where is the induction from? Effect of disproportionation and comproportionation in Cu(0)-mediated reversible deactivation radical polymerization

There is a controversial debate about the mechanism of reversible deactivation radical polymerization (RDRP) in the presence of Cu(0). Two mechanism models have been proposed - supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) and single-electron transfer living radical polymerization (SET-LRP), however, they are contradictory to each other, and neither of them are able to fully explain experimental phenomenon in the Cu(0)-mediated RDRP process, especially a period of slow addition i.e., induction period occurs under certain reaction conditions. In this work, the induction phenomenon and its underlying mechanism was explored and clarified by using different catalyst systems (CuI, Cu(0), Cu(0)&CuII) and different initiator systems i.e., EBriB (ethyl α-bromoisobutyrate), EBrP (ethyl 2-bromopropionate), MBrP (methyl 2-bromopropionate) and MClP (methyl 2-chloropropionate). New insights on the roles of different copper species and their mutual conversion kinetics were provided. It is proved that the appearance/absence of the induction period is due to the difference in the relative concentrations of CuI and CuII accumulated at the early stage of the reaction. Moreover, the disproportionation and comproportionation co-exist in the Cu(0)-mediated RDRP system and play an essential role in establishing the equilibrium among different copper species (Cu0, CuI and CuII) at the early reaction stage.

Influence of Oblique Angle Deposition on Porous Polymer Film Formation.

In this study, we applied oblique angle deposition to a modified initiated chemical vapor deposition (iCVD) process to synthesize porous poly(methacrylic acid) (PMAA) films. During the modified iCVD process, frozen monomer molecules are first captured on a cooled substrate, then polymerization occurs via a free radical polymerization mechanism, and finally, the excess monomer is sublimated, resulting in a porous polymer film. We found that delivering the monomer through an extension at an oblique angle resulted in porous films with three morphological regions. Region 1 is located nearest to the monomer extension outlet and consists of porous polymer pillars; region 2 consists of densified pillars, which occur due to the recapturing and polymerization of the sublimated monomer; and region 3 is located furthest from the monomer extension outlet and consists of dendritic structures, which occur due to low monomer concentration. We investigated the role of substrate temperature and monomer deposition time on the growth process. We found that changing the extension angle influenced the location of the regions and the film coverage across the substrate. Our results provide useful guidelines for tuning the structures within porous polymer films by varying the angle of monomer delivery.

The Rational Design of Reducing Organophotoredox Catalysts Unlocks Proton-Coupled Electron-Transfer and Atom Transfer Radical Polymerization Mechanisms

Photocatalysis has become a prominent tool in the arsenal of organic chemists to develop and (re)imagine transformations. However, only a handful of versatile organic photocatalysts (PCs) are available, hampering the discovery of new reactivities. Here, we report the design and complete physicochemical characterization of 9-aryl dihydroacridines (9ADA) and 12-aryl dihydrobenzoacridines (12ADBA) as strong reducing organic PCs. Punctual structural variations modulate their molecular orbital distributions and unlock locally or charge-transfer (CT) excited states. The PCs presenting a locally excited state showed better performances in photoredox defunctionalization processes (yields up to 92%), whereas the PCs featuring a CT excited state produced promising results in atom transfer radical polymerization under visible light (up to 1.21 Đ, and 98% I*). Unlike all the PC classes reported so far, 9ADA and 12ADBA feature a free NH group that enables a catalytic multisite proton-coupled electron transfer (MS-PCET) mechanism. This manifold allows the reduction of redox-inert substrates including aryl, alkyl halides, azides, phosphate and ammonium salts (Ered up to -2.83 vs SCE) under single-photon excitation. We anticipate that these new PCs will open new mechanistic manifolds in the field of photocatalysis by allowing access to previously inaccessible radical intermediates under one-photon excitation.

Study of the radical polymerization mechanism and its application in the preparation of high-performance PMMA by reactive extrusion.

In this study, the mechanism of radical polymerization was further explored by pre-dissolving different polymers and studying the kinetics of the bulk polymerization of methyl methacrylate (MMA) under shear-free conditions. Based on the analysis of the conversion and absolute molecular weight, it was found that, contrary to the shearing effect, the inert polymer with viscosity was the key factor to preventing the mutual termination of radical active species and reducing the termination rate constant k t. Therefore, pre-dissolving the polymer could increase the polymerization rate and molecular weight of the system simultaneously, making the polymerization system enter the automatic acceleration zone faster and greatly reducing the generation of small molecular weight polymers, leading to a narrower molecular weight distribution. When the system entered the auto-acceleration zone, k t decreased rapidly and greatly and entered the second steady-state polymerization stage. Then, with the increase in the polymerization conversion, the molecular weight gradually increased, while the polymerization rate gradually decreased. In shear-free bulk polymerization systems, k t can be minimized and radical lifetimes maximized, but the polymerization system is at best a long-lived polymerization rather than a living polymerization. On this basis, by using MMA to pre-dissolve ultrahigh molecular weight PMMA and core-shell particles (CSR), the mechanical properties and heat resistance of the PMMA with pre-dissolved polymer obtained by reactive extrusion polymerization were better than for pure PMMA obtained under the same conditions. Compared with pure PMMA, the flexural strength and impact strength of PMMA with pre-dissolved CSR were up to 166.2% and 230.5%. With the same quality of CSR, the same two mechanical properties of the samples obtained by the blending method were just improved by 29.0% and 20.4%. This was closely related to the distribution of CSR in the pre-dissolved PMMA-CSR matrix with a distribution of spherical single particles 200-300 nm in diameter, which enabled PMMA-CSR to exhibit a high degree of transparency. This one-step process for realizing PMMA polymerization and high performance shows extremely high industrial application prospects.

The alkoxy radical polymerization of N-vinylpyrrolidone in organic solvents: theoretical insight into the mechanism and kinetics.

Poly(N-vinylpyrrolidone) (PVP) is a polymer with many applications in cosmetic, pharmaceutical, and biomedical formulations due to its minimal toxicity. PVP can be synthesized through radical polymerization in organic solvents; this well-known industrial process is thoroughly characterized experimentally, however, quantum chemical modeling of the process is scarce: the mechanism and kinetics have not been thoroughly investigated yet. In this work, the mechanism and kinetics of the alkoxy radical polymerization of N-vinylpyrrolidone in organic solvents, namely isopropanol (IP) and toluene (TL), were successfully modeled by computational chemistry. The initiator radicals di-tert-butyl peroxide (TBO˙) and dicumyl peroxide (CMO˙) as well as the solvents isopropanol and toluene, were shown to be capable of assisting in the initiation reactions. The rate constant was influenced by the combination of initiators and solvent and the values of the rate constant of propagation were approximately 101-103 M-1 s-1. The radical polymerization of NVP with dicumyl peroxide as an initiator was comparable to that of di-tert-butyl peroxide in all of the examined organic solvents, whereas the solvents had less of an effect.

Coupling of carboxymethyl starch with 2-carboxyethyl acrylate: A new sorbent for the wastewater remediation of methylene blue

Textile and printing industries play a vital role in the economy of any country. But the effluents of these industries, which contain toxic Methylene Blue (MB) dye when mixed with fresh water, make it unfit for human health and aquatic life. For the removal of MB, different adsorbents were used, but they were expensive, non-biodegradable or less effective. In this research, novel carboxymethyl starch grafted poly 2-carboxyethyl acrylate (CM-St-g-P2CEtA) was synthesized by reacting carboxymethyl starch with 2-carboxyethyl acrylate. The reaction followed a free radical polymerization mechanism. The structure and properties of CM-St-g-P2CEtA were investigated by advanced analytical techniques. The CM-St-g-P2CEtA was employed for the remediation of Methylene Blue (MB) dye from wastewater. The removal percentage (%R) of MB was checked under different parameters, like different pH levels, different initial concentrations of dye, different adsorbent doses, and different contact times. The results obtained during the experiment were subjected to different adsorption and kinetic models. In the kinetic investigation, the experimental results were best represented by the pseudo-second-order kinetic model due to its high R2 value of 0.999. Similarly, with a regression coefficient (R2) value of 0.947, the Langmuir adsorption isotherm was best represented by the experimental results. The Langmuir adsorption model showed that MB dye was adsorbed on the surface of CM-St-g-P2CEtA in a monolayer pattern. The pseudo 2nd order kinetic model suggested that the adsorption process favored chemisorption mechanism. The CM-St-g-P2CEtA showed maximum percentage removal efficiency (%R) of 99.3% for MB dye.

Visible light-induced radical polymerization of vinyl acetate mediated by organo-nickel N2O2 Schiff-base complexes

Four nickel(II) complexes with symmetrically substituted N2O2 tetradentate Schiff-base ligands, prepared from the 2:1 condensation of 3-tert-butyl-salicylaldehyde, and ethylenediamine (1), o-phenylenediamine (2), 1,2-cis,trans-cyclohexyldiamine (3), or 1,3-diaminepropane (4), were synthesized. These NiII Schiff-base complexes (1–4) were used as control agents for the polymerization of vinyl acetate (VAc) photoinitiated by diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) according to a photoinduced organometallic-mediated radical polymerization (photo-OMRP) mechanism. All complexes presented good control ability, although the polymerization mediated by 3 showed the best control over molecular weight (Mn matching Mn,th) and dispersity (Ð < 1.50). The livingness of the polymers has been confirmed by LED on and LED off experiments, the polymerization stopped immediately, and no monomer conversion was observed during the light-off period, indicating a negligible concentration of the active radical in the dark. Further, to demonstrate the living nature of this system, block copolymers of poly(vinyl acetate)-b-poly(methyl acrylate) were synthesized using the sequential visible-light-induced process. Kinetic results and computational investigations supported the activation/deactivation equilibrium exerted by complexes 1–4, which occurred on only one face of the complexes via reversible deactivation (RD) mechanism.

Graphene's effect on the mechanism of radical polymerization with in situ graphene composites

Polymerizing a monomer in the presence of graphene/graphite is a common approach to making composites. However, the role played by the graphitic carbon in the polymerization is often poorly understood or neglected. Specifically, the polymer formed at the interface between the graphite and filler is expected to be most affected by the presence of the filler and can have an outsized effect on the composite properties. Herein we study the impact of pristine graphene on the polymerization of styrene during the synthesis of styrene/graphene nanocomposites. Although there is reason to expect that pristine graphene will interact with radicals, the difficulty of suspending graphene in solution has meant that experimental investigations have been limited to graphene nanoplatelets produced from microcrystalline graphite. However, microcrystalline graphite is fundamentally different than flake graphite, possessing more defects and sheets of limited lateral dimension. We overcome this challenge and study graphene obtained from natural flake graphite using interfacial exfoliation and graphene trapping. We find that graphene plays an active role in radical polymerization, acting as a chain transfer agent. At high graphite/graphene loading, it reversibly couples growing chains, lowering the value of the dispersity (Ð) relative to controls without graphene by nearly an order of magnitude.

Потенційна небезпека УФ-фарб в процесі друкування пакувань для харчової і фармацевтичної продукції

The article is devoted to the problem of the potential danger of UV-inks with radical mechanism of photoinitiated polymerization during printing and operation of packages for food and pharmaceutical products. Pointing to the high level of environmental friendliness of the technology the use of UV-inks, which do not contain volatile organic solvents, their problem is noted application due to the possible migration of components from the ink layer and accordingly the risk of product contamination during packaging. An analysis of the processes occurring during the reaction was carried out radical polymerization, the reasons for the migration of printing ink components and by-products as a result of undergoing photoinitiated polymerization in aerobic conditions Accordingly, small amounts of unreacted components remain embedded in a three-dimensional polymer mesh and constitute the bulk of those components which can freely diffuse from the ink layer. The factors as the reason were analyzed refusal to use some types of oligomers, monomers and photoinitiators for the creation photopolymerizable ink compositions. Unreacted component residues, diffusing and mixing, depending on the chemical structure, can have a toxic or carcinogenic effect on living organisms. The analysis made it possible to classify ways of minimizing migration components of UV-inks when printing packages, namely, ways to minimize migration. The properties of UV-inks components can be divided into two types: chemical and physical. At the chemical method is a careful selection of UV-inks components and introduction synergists, and in the case of physical - compliance with technological regimes, reduction the concentration of oxygen both in the atmosphere and in the liquid composition by creating an inert gas environment and the creation of effective barriers by lamination.

Effects of Monomer Composition of Urethane Methacrylate Based Resins on the C=C Degree of Conversion, Residual Monomer Content and Mechanical Properties.

(1) Background: This study investigated the influence of Bis-GMA, TEGDMA, UDMA, and two different polyethylene glycol (PEG)-containing, UDMO-based co-monomers on the Young’s modulus and flexural strength, degree of methacrylate C=C double bond conversion and residual monomer elution of experimental dental resins. (2) Methods: Urethane methacrylate-based monomer was synthesised via a radical chain growth polymerization mechanism using PEG in order to improve the mechanical properties. Dental resins were formulated using Bis-GMA, UDMA, or UDMO as base monomers combined with TEGDMA as a dilution monomer and DMAEM + CQ as the photo-initiator system. Degree of conversion (DC), mechanical properties, and residual monomer content of light-activated methacrylate resin formulations were evaluated and statistically analysed by ANOVA and a Tukey’s test. (3) Results: PEG-containing UDMO resins had lower Young’s modulus and elastic strength than UDMA-derived resin for all irradiation times. The highest DC (67,418%) was observed for the PEG-containing UDMO-based resin formulation when light cured for 40 s. For all samples, DC increased with the photo-polymerization time. The amount of residual monomer decreased after increasing the light-curing period from 20 to 40 s, resin with UDMO content 0.01 mol of PEG having the smallest amount of free eluted monomer. (4) Conclusions: A strong structure–property relationship exists in photo-cured dimethacrylate-based dental resins. The time and quantity of the photochemical initiation system can influence the physical–mechanical properties of the resins but also the monomers in their composition.

Photoinduced organometallic mediating radical polymerization of acrylates mediated by CoII complexes of non-symmetrical tetradentate Schiff-base ligands

Three new cobalt(II) complexes with non-symmetrically-substituted N2O2 tetradentate Schiff-base ligands, prepared from the 1:1:1 condensation of 3-etoxy-salicylaldehyde, salicylaldehyde and ethylenediamine (H2Etsal − 1), o-phenylenediamine (H2Phsal − 2) or 1,2-cis,trans-cyclohexyldiamine (H2Cysal − 3), were synthesized. The complexes 1–3 were characterized by UV–Vis, FTIR, and MALDI-TOF spectroscopy, elemental analysis, molar conductance, cyclic voltammetry, and computational methods. The CoII-Schiff-base complexes (1–3) were used as controlling agents for the polymerization of n-butyl acrylate (BA) photoinitiated by diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), according to an organometallic-mediated radical polymerization (OMRP) mechanism. Although, all complexes have presented good control ability, the polymerization mediated by complex 1 showed the best control over molecular weight (Mn matching with Mn,th) and dispersity (Ð < 1.50). Kinetic results and computational investigations support the activation/deactivation equilibrium, exerted by complexes 1–3, occurring by one face of the complexes via reversible termination (RT) mechanism.minim.

Orthogonal synthesis and modification of polymer materials

AbstractIn this review, we detail the progress throughout the years toward developing truly orthogonal polymerization mechanisms and modification procedures en route to complex macromolecular structures built from synthetic polymer materials. The orthogonal modifications of polymer side‐chains and end‐groups via sequential click reactions is described providing post‐polymerization routes to functional materials and unique polymer topologies. Further, historical and modern orthogonal polymerization methodologies are thoroughly reviewed showing the evolution of the field through the decades long study of selective polymerization mechanisms that provide unique copolymer structures that are typically difficult to achieve. These include the combinations of reversible deactivation radical polymerization mechanisms with a variety of polymerization mechanisms including ring opening polymerizations, ring opening metathesis polymerizations, and cationic polymerizations, to name a few.

Conventional and controlled radical polymerization redox-initiated by Cerium(IV) and Acrylamide as an intrinsically reducing inimer: a facile strategy to branched polyacrylamide

Since cerium(IV) ammonium nitrate (CAN) could oxidize amidyl N–H moieties into nitrogen-centered radicals under proper conditions to initiate radical polymerization, CAN-acrylamide (AAm) redox-initiated radical homo/co-polymerization in a conventional or controlled manner was exploited with AAm as an intrinsically reducing inimer. CAN oxidized AAm to initiate conventional radical homopolymerization at 50–60 °C, and viscosity-average molecular weight (MW) of polyacrylamide (PAAm) steadily increased with conversion because of the oxidation of amidyl N–H moieties of in-chain -AAm- units, but MW was in a range from 104 to 105. CAN-AAm redox-initiated radical co-polymerization of N,N-dimethylacrylamide (DMAAm) proceeded readily under optimized conditions and formed PAAm-co-PDMAAm with MW in a range from 105 to 106, and increasing simultaneously with conversion. CAN-AAm redox-initiated controlled radical homopolymerization was performed with FeCl3 complexes as the deactivator, and the polymerization proceeded in a mechanism of reverse atom transfer radical polymerization (ATRP) and MW of PAAm increased in proportion to conversion. The PAAm chains contained a C–Cl terminal, which was confirmed by block co-polymerization with DMAAm via standard ATRP with PAAm as the macro-initiator.

Kinetics and mechanisms of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane with cyanuric acid

Mechanisms and kinetics of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane (BMI) with cyanuric acid (CA) were investigated. Competitive free radical polymerization and aza-Michael addition reaction mechanisms involved in the BMI/CA reaction system were characterized by using DSC, 1H-NMR, electron spin resonance (ESR) and gel permeation chromatography (GPC). Free radical polymerization mechanism predominated in the BMI/CA reaction system. Both model-free and model-fitting methods were used to determine the isoconversional activation energy (Eα) and pre-exponential factor (Aα). The values of Eα and Aα for aza-Michael addition reaction evaluated at α = 0.1 were 86 kJ mol−1 and 2.42 × 1010 min−1, respectively, and the reaction model was f(α) = 1.73(1 - α)α0.11. By contrast, Eα gradually decreased with increasing α (decreased from 88 to 48 kJ mol−1) in the α range 0.15−0.9, which was attributed to the inherent multi-step kinetics in free radical polymerization.