Mechanism Of Cationic Polymerization Research Articles

Optimization strategy for epoxy cross-linked molecular glass photoresist in EUV lithography

The development of new resist materials is vital for fabrication techniques for next-generation microelectronics. A class of photosensitizer compositions with reactivity differences has been developed that can be used in epoxy cross-linked photoresist formulations for advanced microlithography techniques like extreme ultraviolet lithography (EUVL). With “PDN first, PAG second” combination strategy containing slow photolysis initiators (photoacid generator, PAG) and fast photolysis terminators (photodegradable nucleophile, PDN), photoresists produce photolithographic patterns with dense structure that are insoluble in the developer by epoxy cationic polymerization. This combination enhances chemical contrast between the exposed and non-exposed areas while eliminating the stochastic impact to get a lithographic structure with high mechanical strength. Lithographic formulations have been developed and tested in line-and-space patterning experiments using EUVL, and 18 nm half-pitch (HP) at a dose of 25.2 mJ·cm−2 with a line edge roughness (LER) of 2.8 nm was achieved by the combination strategy. This strategy offers the possibility of achieving higher resolution for photoresists based on a cationic polymerization mechanism.

A theoretical study of the mechanism of cationic polymerization of isobutylene catalysed by EtAlCl2/t-BuCl with bis(2-chloroethyl)ether in hexanes.

The mechanism of cationic polymerization of isobutylene catalyzed by t-BuCl/ethylaluminum dichloride (EADC) combined with bis(2-chloroethyl)ether (CEE) in n-hexane solvent has been investigated using ab initio molecular dynamics (AIMD) and metadynamics (MTD) simulations. The results indicated that the polyisobutylene (PIB) initiation stage involves a clear two-step mechanism. Calculation of the free energy landscapes of the other two ether reactions reveals that the energy barriers of diisopropyl ether (i-Pr2O) and 2-chloroethyl ethyl ether (CEEE) are much higher than those of CEE, which is consistent with the experimental results. During the chain propagation phase, the required free energy barrier gradually decreases and tends to reach equilibrium as the chain length increases. Finally, the oxonium mechanism during the chain initiation stage was investigated by calculating the 1H NMR spectra and MTD simulation. Our calculations can confirm that the existence of tert-butyloxonium ions during the reaction is possible. Their contribution to the whole reaction is further discussed.

Design, synthesis and curing mechanism of two novel photothermal dual-curing adhesives for propellants and explosives

Photothermal dual-curing adhesive is not only required to realize the basic curing function, but also has the characteristics of rapid setting and strong curing, which possesses a vital role in the molding speed, stability and structure integrity for 3D-printed propellants and explosives. Herein, the acrylate hydroxyl terminated polybutadiene, as novel photothermal dual-curing binders, were designed and synthesized utilizing cationic ring opening polymerization and active monomer mechanism as the strategy of photothermal dual-curing reaction. The mechanical properties and thermal stability of the photothermal dual-curing elastomers were systematically investigated. The results suggested that the target MAHTPB(Acrylate hydroxy‑terminated polybutadiene)-based adhesives could be cured rapidly within 5 s under UV light irradiation and completely cured in 1.5 h under heating conditions. Specifically, the elastomer film formed by MAHTPB-based photothermal dual-curing has a tensile strength of 4.63 MPa and an elongation of 386%, which exhibits stronger mechanical properties than the elastomer film formed by single photo- or thermal-curing. As a result, the synthesized photothermally cured adhesives have performed 3D printing experiments and achieved relatively satisfactory printing effects. Our study aims to solve the problems of short photocuring time, slow curing rate and incomplete curing for traditional photocuring, which lays a solid foundation to achieve rapid prototyping and precise performance control in 3D printing of propellants and explosives.

Experimental and theoretical insights into cationic polymerization of para-N,N-dimethylaminostyrene

The cationic polymerization electron-rich para-N,N-dimethylaminostyrene (DMAS) for high-molecular-weight polymer is few and highly challenging because of the ease reaction of N,N-dimethylamino group with proton or carbocation. In this contribution, three kinds of initiating systems including Lewis’s acid (BF3•OEt2), Brønsted acid (CF3SO3H, TfOH), and the carbocation system (IBVE-HCl/SnCl4, IBVE: isobutyl vinyl ether) were used in DMAS polymerization·BF3•OEt2 showed the highest efficiency for DMAS polymerization to afford high-molecular-weight poly(para-N,N-dimethylaminostyrene) (PDMAS). Copolymerizations of DMAS and 4-methoxystyrene (MOS) were unsuccessful no matter what the monomer feeding mode was, which only produced PDMAS or the blends of two homopolymers. Polymer chain-end analysis and NMR analysis of the intermediate showed that DMAS polymerizations obeyed cationic chain polymerization mechanism. Comprehensive theoretical DFT studies were performed to gain insight into the polymerization mechanism of DMAS. The chain transfer to the dimethylamino group of DMAS monomer was clearly found to be unique and curial to unexpected DMAS polymerization behavior.

Kinetic and Chemical Effects of Clays and Other Fillers in the Preparation of Epoxy–Vinyl Ether Composites Using Radical-Induced Cationic Frontal Polymerization

Addition of fillers to formulations can generate composites with improved mechanical properties and lower the overall cost through a reduction of chemicals needed. In this study, fillers were added to resin systems consisting of epoxies and vinyl ethers that frontally polymerized through a radical-induced cationic frontal polymerization (RICFP) mechanism. Different clays, along with inert fumed silica, were added to increase the viscosity and reduce the convection, results of which did not follow many trends present in free-radical frontal polymerization. The clays were found to reduce the front velocity of RICFP systems overall compared to systems with only fumed silica. It is hypothesized that chemical effects and water content produce this reduction when clays are added to the cationic system. Mechanical and thermal properties of composites were studied, along with filler dispersion in the cured material. Drying the clays in an oven increased the front velocity. Comparing thermally insulating wood flour to thermally conducting carbon fibers, we observed that the carbon fibers resulted in an increase in front velocity, while the wood flour reduced the front velocity. Finally, it was shown that acid-treated montmorillonite K10 polymerizes RICFP systems containing vinyl ether even in the absence of an initiator, resulting in a short pot life.

The interaction of triglycidyl phosphate with europium nitrate and properties of obtained metal-containing polymer

The interaction of phosphorus-containing epoxy trifunctional monomer – triglycidyl phosphate (TGPhT), with europium (III) nitrate hexahydrate is studied. A dissolution of europium salt added into TGPhT is occurred due to the interaction of the cation with phosphoryl groups and oxygen atoms of the epoxy ring, that is accompanied by the opening reaction and led to the formation of a polymer. The interaction of triepoxide with salt is investigated by FTIR-spectroscopy and differential scanning calorimetry (DSC). The thermal stability of the samples is determined by combined method of thermogravimetry and differential scanning calorimetry (TG/DSC), coupled with a quadrupole mass spectrometry to identify the gaseous products evolved during the thermal analysis of the samples. The kinetic parameters of the curing reaction are computed by using Thermokinetics software. The interaction of TGPhT with europium nitrate is suggested to occur through opening of epoxy rings in the presence of europium ions via the mechanism of cationic polymerization. The cured epoxy polymer exhibits luminescent properties.

Unimolecular Benzodioxole-based Photoinitiators for Free Radical and Cationic Photopolymerization Under LED Light Irradiation

Compared to amines as coinitiators applied in photopolymerization, benzodioxole derivatives exhibit similar reactivity but less yellowing and lower toxicity. In this paper, a series of unimolecular type II photoinitiators, containing coumarins as chromophores and benzodioxoles as coinitiators, were synthesized. The substituents with different electron donating/withdrawing abilities were designed for systematical investigation of structure-property relationship. Under LED irradiation, the novel photoinitiators can induce not only free radical polymerization of acrylate monomers, but also cationic polymerization of epoxy monomers via radical promoted cationic polymerization mechanism.

Suspension and emulsion aqueous cationic homopolymerization and copolymerization of cyclohexyl vinyl ether by B(C6F5)3 initiating system

Aqueous cationic suspension polymerization and emulsion polymerization of cyclohexyl vinyl ether (CHVE) were successfully achieved by CumOH/B(C6F5)3/Et2O initiating system. The effects of the main initiator concentration, reaction temperature, and surfactant types on the conversion and polymerization rate were investigated. This work broke through the aqueous cationic polymerization of vinyl ether monomer at −15 °C and significantly improved the molecular weight of the polymer. The copolymerization behavior of CHVE with IBVE, n-BVE aqueous suspension polymerization, and emulsion polymerization was investigated. The mechanism of aqueous cationic polymerization of cyclohexyl vinyl ether was proposed.

Front velocity dependence on vinyl ether and initiator concentration in radical‐induced cationic frontal polymerization of epoxies

AbstractFormulations containing vinyl ethers and epoxy were successfully polymerized through a radical‐induced cationic frontal polymerization mechanism, using an iodonium salt superacid generator with a peroxide thermal radical initiator and fumed silica as a filler. It was found that an increase of vinyl ether content resulted in higher front velocities for divinyl ethers in formulations with trimethylolpropane triglycidyl ether. However, increased hydroxymonovinyl ether either decreased the front velocity or suppressed frontal polymerization. The kinetic effects of the superacid generator and thermal radical initiator with varying vinyl ether content were also studied. It was observed that increasing concentrations of initiators increased the front velocity, with the system exhibiting higher sensitivity to the superacid generator concentration.

Characterization and mechanism study of aqueous cationic polymerization of p-methylstyrene.

Aqueous cationic polymerization has attracted considerable interest as a novel polymerization technique, because it conforms to the “green chemistry” trend and challenges the concept of traditional cationic polymerization. In this paper, a CumOH/B(C6F5)3/Et2O system was used to initiate the aqueous polymerization of p-methylstyrene through suspension and emulsion methods. Several types of surfactants were used, including the cationic surfactant CTAB, non-ionic surfactant NP-40, and anionic surfactant SDBS, and the influences of initiator concentration and temperature on polymerization were investigated. Consistent with previous literature, initiator activity was positively correlated with temperature unlike in traditional cationic polymerization. Gaussian 09W simulation software was used to calculate and optimize changes in the bond lengths and angles of B(C6F5)3 after ether was added to the system. The addition of ether increased the polarity of B(C6F5)3, rendering it soluble in water. 1H-NMR was used in identifying the main chain and terminal structures of the polymer, and the mechanism of p-methylstyrene aqueous phase cationic polymerization was proposed.

Review on UV-Induced Cationic Frontal Polymerization of Epoxy Monomers.

Ultraviolet (UV)-induced cationic frontal polymerization has emerged as a novel technique that allows rapid curing of various epoxy monomers upon UV irradiation within a few seconds. In the presence of a diaryliodonium salt photoinitiator together with a thermal radical initiator, the cationic ring opening polymerization of an epoxide monomer is auto-accelerated in the form of a self-propagating front upon UV irradiation. This hot propagating front generates the required enthalpy to sustain curing reaction throughout the resin formulation without further need for UV irradiation. This unique reaction pathway makes the cationic frontal polymerization a promising route towards the efficient curing of epoxy-based thermosetting resins and related composite structures. This review represents a comprehensive overview of the mechanism and progress of UV-induced cationic frontal polymerization of epoxy monomers that have been reported so far in literature. At the same time, this review covers important aspects on the frontal polymerization of various epoxide monomers involving the chemistry of the initiators, the effect of appropriate sensitizers, diluents and fillers.

Phthalic anhydride promoted ring‐opening polymerization of cyclohexene oxide catalyzed by dinuclear chromium complex supported by piperazine‐bridged [ONSO] ligand

AbstractNew bimetallic chromium complexes bearing a piperazine‐bridged tetradentate‐dianionic iminethiobis(phenolate) (ONSO) ligand and an ancillary chloride group (complex 1) have been developed. Of interest, it was found that the complex 1 catalyzed copolymerization of cyclohexene oxide with phthalic anhydride (PA) gives a product with more than 97% ether linkage content, i.e. selective synthesis of poly(cyclohexene oxide), which is in sharp contrast to the mononuclear [ONSO]CrCl analogue where a resulting polymer with more than 86% ester units is achieved under identical conditions. The influences of PA loading, reaction time and temperature on the polymerization were investigated. According to the kinetics data, the apparent activation energy of the ring‐opening polymerization of cyclohexene oxide is 12.5 kJ mol−1. A cationic polymerization mechanism is proposed according to the polymer structure and the interaction between metal complex 1 and PA. © 2019 Society of Chemical Industry

About the Mechanism of Cationic Polymerization of P-Ethylstyrene in the Presence of a Complex Catalyst Boron Fluoride – Water

About the Mechanism of Cationic Polymerization of P-Ethylstyrene in the Presence of a Complex Catalyst Boron Fluoride – Water

Controlled polymerization of 3,4-dihydro-2H-1,3-benzoxazine and its properties tailored by Lewis acids

Polymerization reaction of a typical thermosetting benzoxazine monomer, BA-a, is tailored intentionally by particular Lewis acids including aluminium trichloride (AlCl3), phosphorus pentachloride (PCl5) and zinc chloride (ZnCl2), and polybenzoxazines with different crosslinking structures are obtained. Their rheological behaviors, polymerization mechanisms, chemical crosslinking structures and thermal properties are systematically studied. The results suggest that AlCl3 and PCl5 are much more efficient than ZnCl2 to affect the polymerization reaction of BA-a. PCl5 and AlCl3 can promote the generation of more carbocations, thus the polymerization of benzoxazine follows cationic chain polymerization mechanism. However, in the presence of less effective ZnCl2 or in the case of neat benzoxazine, the polymerization follows step polymerization mechanism. It is learned that the Lewis acids can promote crosslinking reaction of dangling arylamine benzene rings and form arylamine Mannich linkages that vary with the catalytic efficiency of the Lewis acids. As a result, the increase of impact strength by 36.4%, the increase of flexural strength by 243.4%, the increase of flexural modulus by 42% and the increase of char yield by 18.6% (absolute value) can be achieved by using different Lewis acids.

Characteristics and Mechanism of Vinyl Ether Cationic Polymerization in Aqueous Media Initiated by Alcohol/B(C₆F₅)₃/Et₂O.

Aqueous cationic polymerizations of vinyl ethers (isobutyl vinyl ether (IBVE), 2-chloroethyl vinyl ether (CEVE), and n-butyl vinyl ether (n-BVE)) were performed for the first time by a CumOH/B(C6F5)3/Et2O initiating system in an air atmosphere. The polymerization proceeded in a reproducible manner through the careful design of experimental conditions (adding initiator, co-solvents, and surfactant or decreasing the reaction temperature), and the polymerization characteristics were systematically tested and compared in the suspension and emulsion. The significant difference with traditional cationic polymerization is that the polymerization rate in aqueous media using B(C6F5)3/Et2O as a co-initiator decreases when the temperature is lowered. The polymerization sites are located on the monomer/water surface. Density functional theory (DFT) was applied to investigate the competition between H2O and alcohol combined with B(C6F5)3 for providing a theoretical basis. The effectiveness of the proposed mechanism for the aqueous cationic polymerization of vinyl ethers using CumOH/B(C6F5)3/Et2O was confirmed.

Unique self-catalyzed cationic ring-opening polymerization of a high performance deoxybenzoin-based 1,3-benzoxazine monomer

An asymmetric bis(1,3-benzoxazine) monomer based on deoxybenzoin has been synthesized through Mannich condensation. The chemical structure of this deoxybenzoin-based monomer has been confirmed using 1H NMR, 13C NMR, FT-IR and elemental analysis. The assignments for the oxazine protons and carbon atoms in the asymmetric structure have also been confirmed using two-dimensional (2D) NMR techniques, including 1H-1H nuclear Overhauser effect spectroscopy (NOESY) and 1H-13C heteronuclear multiple quantum coherence spectroscopy (HMQC). In addition, the effect of incorporation of deoxybenzoin on the mode of polymerization of benzoxazine has been investigated using differential scanning calorimetry (DSC), in situ FT-IR and 1H NMR spectroscopy. This deoxybenzoin containing bis(benzoxazine) exhibits a low polymerization temperature resulting from a unique self-catalyzed cationic polymerization mechanism. Furthermore, the thermal stability of the resulting polybenzoxazine has been studied using thermogravimetric analysis (TGA). This deoxybenzoin-based polybenzoxazine exhibits high thermal stability and low flammability, with a Td5 temperature of 403 °C, a high char yield value (68%) and low total heat release (THR of 11.4 kJ/g).

UV/thermal dual curing of tung oil-based polymers induced by cationic photoinitiator

With the increasing shortage of petroleum-based resources, the exploitation and application of the polymers derived from the renewable resources has becomes increasingly important for the industrial development. In this work, in order to promote the direct application of tung oil in the coating field, the tung oil-based polymers with the excellent mechanical properties by using cationic photoinitiator as the “green” initiator were prepared. The cationic polymerization mechanism and the optimal polymerization conditions of methyl eleostearate (ME) induced by triarylsulfonium salt (TAS) are characterized via the nuclear magnetic resonance spectroscopy. The effects of different monomers on the properties of tung oil-based polymers and the post curing behaviors of the polymers are studied by dynamic mechanical test and microtensile test. The results display that the heating treatment after UV irradiation is necessary and favorable for the cationic polymerization of ME induced by TAS. And the optimal reaction condition is 500 W of irradiation energy, 5 wt% of initiator concentration, 60 min of irradiation time, 100 °C of heating temperature and 3 h of heating time. Moreover, tung oil-based polymers with good hydrophobicity can be obtained under the optimal reaction condition. In addition, adding 20 wt% divinylbenzene and 10 wt% styrene to the tung oil can effectively increase the mechanical properties and glass transition temperatures (Tg) of tung oil-based polymers.

Disubstituted Aminoanthraquinone-Based Multicolor Photoinitiators: Photoinitiation Mechanism and Ability of Cationic Polymerization under Blue, Green, Yellow, and Red LEDs

The investigation and clarification of the photoinitiation mechanism of novel systems are of importance for the design and development of compounds with high photoinitiation efficiency of photopolymerization. Some disubstituted aminoanthraquinone derivatives have been reported to exhibit interesting photochemical/photophysical properties and have the potential to act as high performance multicolor photoinitiators under the irradiation of various wavelengths of visible light from light-emitting diodes (LEDs). Herein, three disubstituted aminoanthraquinone derivatives, i.e., 1-amino-4-hydroxyanthraquinone, 1,4-diaminoanthraquinone, and 1,5-diaminoanthraquinone, with iodonium salt and N-vinylcarbazole as additives, have been investigated. Their photoinitiation mechanism was studied using fluorescence spectroscopy, laser flash photolysis, steady state photolysis, computational quantum chemistry, and electron spin resonance spin trapping techniques. Then, their photoinitiation ability for the cationic photopol...

On Demand Switching of Polymerization Mechanism and Monomer Selectivity with Orthogonal Stimuli.

The development of next-generation materials is coupled with the ability to predictably and precisely synthesize polymers with well-defined structures and architectures. In this regard, the discovery of synthetic strategies that allow on demand control over monomer connectivity during polymerization would provide access to complex structures in a modular fashion and remains a grand challenge in polymer chemistry. In this Article, we report a method where monomer selectivity is controlled during the polymerization by the application of two orthogonal stimuli. Specifically, we developed a cationic polymerization where polymer chain growth is controlled by a chemical stimulus and paired it with a compatible photocontrolled radical polymerization. By alternating the application of the chemical and photochemical stimuli the incorporation of vinyl ethers and acrylates could be dictated by switching between cationic and radical polymerization mechanisms, respectively. This enables the synthesis of multiblock copolymers where each block length is governed by the amount of time a stimulus is applied, and the quantity of blocks is determined by the number of times the two stimuli are toggled. This new method allows on demand control over polymer structure with external influences and highlights the potential for using stimuli-controlled polymerizations to access novel materials.

Structural effects of highly π-conjugated mesogenic Schiff-base moiety on the cationic polymerization of benzoxazine and formation of ordered morphologies

A Schiff-base moiety was introduced into the chemical structure of benzoxazine through the Mannich reaction. With alternative imine groups (CN) and benzene rings in the chain segment, these highly π-conjugated systems favored the formation of strong intermolecular hydrogen bonds to the hydroxyl groups generated during polymerization, leading to a thermally initiated cationic polymerization mechanism. Compared with the bisphenol-A-based benzoxazine, the benzoxazine with the Schiff-base moiety needs higher energy to facilitate the realization of polymerization and to increase polymerization degree. In addition to the influences on the polymerization, the highly π-conjugated Schiff-base acting as a mesogenic moiety is found to form liquid crystal (LC) phases, like the nematic phase and smectic phase. Interestingly, some LC-rich domains can be stabilized by the polybenzoxazine network, which will contribute to form nitrogen-rich ordered porous carbon at the carbonization stage. For N2 and CO2 adsorption–desorption process, the carbon exhibits an enhanced CO2 adsorption performance, suggesting their capture and separation capacity for CO2.