Propagation Rate Coefficients of Acrylate−Methacrylate Free-Radical Bulk Copolymerizations

Direct restoration of photocurable cross-linkers for repeated light-based 3D printing of covalent adaptable networks

Light-based processing of thermosets has gained increasing attention because of its broad application field including its use in digital light processing (DLP) 3D printing. This technique offers efficient design and fabrication of complex structures but typically results in non-recyclable thermoset-based products. To address this issue, we describe here a photocurable, dynamic β-amino ester (BAE) based cross-linker that is not only suitable for DLP printing but can also be chemically degraded via transesterification upon the addition of 2-hydroxyethyl methacrylate (HEMA) as a decross-linker. This conceptually new protocol allows for efficient depolymerization with the direct restoration of curable monomers in a single step without the addition of external catalysts or solvents. By implementing this protocol, we have established a chemical recycling loop for multiple cycles of photo-cross-linking and restoration of cross-linkers, facilitating repeatable DLP 3D printing without generating any waste. The recycled materials exhibit full recovery of thermal properties and Young's modulus while maintaining 75% of their tensile strength for at least three cycles. Simultaneously, the presence of BAE moieties enables the (re)processability of these materials through compression molding.

Preparation and Characterization of Acrylic and Methacrylic Phospholipid-Mimetic Polymer Hydrogels and Their Applications in Optical Tissue Clearing

The 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers are mimetic to phospholipids, being widely used as biocompatible polymers. In our previous study, MPC polymer hydrogels proved more effective for optical tissue clearing compared to acrylamide (AAm) polymer hydrogels. In the present study, 2-acryloyloxyethyl phosphorylcholine (APC) was synthesized and employed to create hydrogels for a comparative analysis with methacrylic MPC-based hydrogels. APC, an acrylic monomer, was copolymerized with AAm in a similar reactivity. In contrast, MPC, as a methacrylic monomer, demonstrated higher copolymerization reactivity than AAm, leading to a spontaneously delayed two-step polymerization behavior. This suggests that the polymer sequences and network structures became heterogeneous when both methacrylic and acrylic monomers, as well as crosslinkers, were present in the copolymerization system. The molecular weight of the APC polymers was considerably smaller than that of the MPC polymers due to the formation of mid-chain radicals and subsequent β-scission during polymerization. The swelling ratios in water and strain sweep profiles of hydrogels prepared using acrylic and methacrylic compounds differed from those of hydrogels prepared using only acrylic compounds. This implies that copolymerization reactivity influences the polymer network structures and crosslinking density in addition to the copolymer composition. APC-based hydrogels are effective for the optical clearing of tumor tissues and are applicable to both passive and electrophoretic methods.

Photochemically Activated 3D Printing Inks: Current Status, Challenges, and Opportunities

3D printing with light is enabled by the photochemistry underpinning it. Without fine control over the ability to photochemically gate covalent bond formation by the light at a certain wavelength and intensity, advanced photoresists with functions spanning from on-demand degradability, adaptability, rapid printing speeds, and tailored functionality are impossible to design. Herein, recent advances in photoresist design for light-driven 3D printing applications are critically assessed, and an outlook of the outstanding challenges and opportunities is provided. This is achieved by classing the discussed photoresists in chemistries that function photoinitiator-free and those that require a photoinitiator to proceed. Such a taxonomy is based on the efficiency with which photons are able to generate covalent bonds, with each concept featuring distinct advantages and drawbacks.

Mechanistic aspect for the atom transfer radical polymerization of itaconimide monomers with methyl methacrylate: a computational study

Atom transfer radical polymerization (ATRP) is a versatile & famous technique for the synthesis of well defined molecular architectures. In ATRP, there is a dynamic equilibrium exists between active & dormant species. Therefore, ATRP progress through a sequence of activation & deactivation cycles, ending upon complete monomer consumption & termination reactions are minimized. This paper presents a systematic computational study on kinetics & thermodynamics associates in the ATRP of itaconimide monomers & methyl methacrylate (MMA). For this, the copolymerization system is modeled as a unimer, dimer & trimer of various itaconimides & MMA monomer. The density functional theory with B3LYP functional & 6–31 + G(d)/LanL2DZ basis sets is used in the prediction of geometries & energetics associated with the dissociation of terminal R–X bond present in the unimer, dimer & trimer. The relative equilibrium constant (K ATRP) for the ATRP activation/deactivation steps is calculated from the free energy values associated with dissociation of R–X bond. The relative K ATRP values of dimer & trimer of selected monomers is compared with their respective unimer. From the transition state geometries of the dimeric propagating radical, activation energy is calculated. The gas phase rate coefficients for propagation (k p) (of itaconimides & MMA copolymerization) are calculated using the standard transition state theory. The effect of system parameters such as solvent, temperature & substituent on K ATRP & k p values of dimer is investigated systematically. The change in the initiating system & temperature has significant effect on k p values as compared to solvent & various substituent. The K ATRP values of dimer & trimer dormant species are higher as compared to their respective monomeric species. The neighboring monomer & penultimate monomer plays vital role in kinetics & thermodynamics associated with copolymerization. The obtained initial results show that the mechanism of copolymerization of itaconimide monomers & MMA follows penultimate model.

Alternating Terpolymers through Cyclopolymerization and Subsequent Orthogonal Functionalization

A method for the synthesis of functionalized alternating copolymers by reversible deactivation radical polymerization was developed. Copolymerization by reversible addition-fragmentation chain transfer of hexenyl vinyl ether with a novel fluorinated divinyl monomer yields alternating cyclopolymers that can be chemoselectively modified by three distinct orthogonal functionalization reactions. Along the thiol-ene click reaction and amidation, a third functionalization was achieved via NHC-catalyzed transesterification or acylation resulting in a small library of ABC-type alternating terpolymers.

Combining Chromatographic, Rheological, and Mechanical Analysis to Study the Manufacturing Potential of Acrylic Blends into Polyacrylic Casts

Polyacrylics have been considered for a broad range of material applications, including coatings, dental applications, and adhesives. In this experimental study, the casting potential of a group of (co)monomers belonging to the acrylic family has been explored to enable a more sustainable use of these polymer materials in the medical and veterinary science field. The individual contributions of each comonomer have been analyzed, the reaction conversion has been studied via gas chromatography (GC), the rheological behavior has been characterized via stress-controlled measurements, and the final mechanical properties have been obtained from tensile, flexure, and impact tests. The GC results allow assessing the pot life and thus the working window of the casting process. For the rheological measurements, which start from low-viscous mixtures, a novel protocol has been introduced to obtain accurate absolute data. The rheological data reflect the time dependencies of the GC data but facilitate a more direct link with the macroscopic material data. Specifically, the steep increase in the viscosity with increasing reaction time for the methyl methacrylate (MMA)/ethylene glycol dimethyl methacrylate (EGDMA) case (2% crosslinker) allows maximizing several mechanical properties: the tensile/flexure modulus, the tensile/flexure stress at break, and the impact strength. This opens the pathway to more dedicated chemistry design for corrosion casting and polyacrylic material design in general.

Computational prediction of the molecular configuration of three-dimensional network polymers

The three-dimensional arrangement of natural and synthetic network materials determines their application range. Control over the real-time incorporation of each building block and functional group is desired to regulate the macroscopic properties of the material from the molecular level onwards. Here we report an approach combining kinetic Monte Carlo and molecular dynamics simulations that chemically and physically predicts the interactions between building blocks in time and in space for the entire formation process of three-dimensional networks. This framework takes into account variations in inter- and intramolecular chemical reactivity, diffusivity, segmental compositions, branch/network point locations and defects. From the kinetic and three-dimensional structural information gathered, we construct structure-property relationships based on molecular descriptors such as pore size or dangling chain distribution and differentiate ideal from non-ideal structural elements. We validate such relationships by synthesizing organosilica, epoxy-amine and Diels-Alder networks with tailored properties and functions, further demonstrating the broad applicability of the platform.

Green Hydrophilic Capsules from Cellulose Nanocrystal-Stabilized Pickering Emulsion Polymerization: Morphology Control and Spongelike Behavior

Pickering inverse emulsions of hydroxyl oligoethylene glycol methacrylate were stabilized in isopropyl myristate, a biofriendly oil, using surface-modified cellulose nanocrystals (CNCs) as stabilizing particles. The emulsions were further polymerized by free or controlled radical polymerization (ATRP), taking advantage of the bromoisobutyrate functions grafted on the CNC surface. Suspension polymerization of the emulsion led to full bead or empty capsule morphologies, depending on the initiation locus. The thickness of the CNC shell surrounding the polymerized emulsions could be tuned by modulating the aggregation state of the CNCs after their surface modification. An increase from 6 to 40 CNC layers helped improve the compression moduli of the beads from a dozen to hundreds of kPa.

From n-butyl acrylate Arrhenius parameters for backbiting and tertiary propagation to β-scission via stepwise pulsed laser polymerization

A stepwise method to estimate the Arrhenius parameters for backbiting, tertiary propagation, and β-scission in acrylate radical polymerization.

Poly(vinylidene fluoride) Containing Phosphonic Acid as Anticorrosion Coating for Steel

Vinylidene fluoride (VDF)-based copolymers bearing pendant phosphonic acid function for potential application as anticorrosion coatings were synthesized via free radical copolymerization of VDF with a new phosphorus containing 2-trifluoromethacrylate monomer, (dimethoxyphosphoryl)methyl 2-(trifluoromethyl)acrylate (MAF-DMP). MAF-DMP was prepared from 2-trifluoromethacrylic acid in 60% overall yield. Radical copolymerizations of VDF with MAF-DMP initiated by tert-amyl peroxy-2-ethylhexanoate at varying ([VDF]₀/[MAF-DMP]₀) feed ratios led to several poly(VDF-co-MAF-DMP) copolymers having different molar percentages of VDF (79-96%) and number-average molecular weights (M_n's) up to ca. 10 000 g mol^-1 in fair yields (47-53%). Determination of the composition and microstructure of all the synthesized copolymers was done by ¹H and ¹⁹F NMR spectroscopies. The monomer reactivity ratios of this new VDF/MAF-DMP pair were also determined (r_VDF = 0.76 ± 0.34 and r_MAF-DMP = 0 at 74 °C). The resulting poly(VDF-co-MAF-DMP) copolymers exhibited high melting temperature (162-171 °C, with respect to the VDF content), and the degree of crystallinity reached up to 51%. Finally, the pendant dimethyl phosphonate ester groups of the synthesized poly(VDF-co-MAF-DMP) copolymer were quantitatively hydrolyzed, giving rise to novel phosphonic acid-functionalized PVDF (PVDF-PA). In comparison to hydrophobic poly(VDF-co-MAF-DMP) copolymers (the water contact angle, WCA, was 98°), the hydrophilic character of the PVDF-PA was found to be surprisingly rather pronounced, exhibiting low WCA (15°). Finally, steel plates coated with PVDF-PA displayed satisfactory anticorrosion properties under simulated seawater environment.

Poly(fluoroacrylate)s with tunable surface hydrophobicity via radical copolymerization of 2,2,2-trifluoroethyl α-fluoroacrylate and 2-(trifluoromethyl)acrylic acid

Fluorinated polyacrylates with tunable surface hydrophobicity are prepared via radical copolymerization of an α-fluoroacrylate and 2-(trifluoromethyl)acrylic acid.

Effect of Very High Charge Density and Monomer Constitution on the Synthesis and Properties of Cationic Polyelectrolytes

The free-radical homopolymerization of 1,3-bis(N,N,N-trimethylammonium)-2-propylmethacrylate dichloride (di-M) and 1,3-bis(N,N,N-trimethylammonium)-2-propylacrylate dichloride (di-A) in aqueous solution yields cationic polyelectrolytes (PEL) with theoretical/structural charge spacing of only ≈0.12 nm. The high charge density causes condensation of ≈82% of the chloride counterions. The high level of counterion condensation reduces the ionic strength in the polymerizing batch when the monomer molecules connect to PEL chains. This has the consequence that the hydrodynamic and excluded volume of the PEL molecules will change. Studies of the free radical polymerization revealed non-ideal polymerization kinetics already at low conversion and additionally autoacceleration above a certain monomer concentration and conversion. Similar autoacceleration was not observed for monomers yielding PEL with charge spacing of 0.25 or 0.5 nm. Coulomb interactions, monomer association, steric effects, and specific features of the monomer constitution have been evaluated concerning their contributions to the concentration dependence and conversion dependence of kinetic parameters. The different backbone constitutions of di-M and di-A not only influence the polymerization kinetics but also equip poly(di-M) with higher hydrolytic stability. The experimental results confirm the impact of electrochemical parameters and the necessity to reconsider their inclusion in kinetic models.

The influence of hydrogen bonding on radical chain-growth parameters for butyl methacrylate/2-hydroxyethyl acrylate solution copolymerization

Pulsed laser polymerizations coupled with size exclusion chromatography (PLP-SEC) and NMR analyses were performed to determine radical kinetic parameters for BMA/HEA, with a focus on the effect of solvent choice and H-bonding on both copolymer composition and copolymer-averaged propagation rate coefficients.

Alternating copolymerization by nitroxide-mediated polymerization and subsequent orthogonal functionalization

A novel method for the preparation of functionalized alternating copolymers is presented. Nitroxide-mediated polymerization of hexafluoroisopropyl acrylate with 7-octenyl vinyl ether provides the corresponding alternating polymer, which can be chemically modified using two orthogonal polymer-analogous reactions. A thiol-ene click reaction followed by amidation provides dual-functionalized alternating copolymers. The potential of this method is illustrated by the preparation of a small library (15 examples) of functionalized alternating copolymers.

Pulsed-laser and quantum mechanics study of n-butyl cyanoacrylate and methyl methacrylate free-radical copolymerization

Improved control over polymer microstructure is achieved by radical copolymerization of n-butyl cyanoacrylate with methacrylates.

Thermomechanical Synergisms from Ionic Liquid Doping of Poly(methyl methacrylate)

A synergism between methyl methacrylate and an amphiphilic ionic liquid acrylate 1-(11-acryloyloxyundecyl)-3-methyl imidazolium bromide (IL) not only increases the apparent thermal stability (kinetic retardation of thermal decomposition) of poly(MMA-co-IL) copolymers by 50 °C at relatively low doping levels of 0.5 mol %, but also increases the storage (∼10%) and loss (15-25%) moduli over 0-75 °C (increasing the elasticity). Moderate to high doping levels provide plasticization without the risk of leaching or plasticizer contamination.

Porating anion-responsive copolymeric gels

A polymerizable ionic liquid surfactant, 1-(11-acryloyloxyundecyl)-3-methylimidiazolium bromide (ILBr), was copolymerized with methyl methacrylate (MMA) in aqueous microemulsions at 30% (ILBr w/w) and various water to MMA ratios. The ternary phase diagram of the ILBr/MMA/water system was constructed at 25 and 60 °C. Homopolymers and copolymers of ILBr and MMA were produced by thermally initiated chain radical microemulsion polymerization at various compositions in bicontinuous and reverse microemulsion subdomains. Microemulsion polymerization reaction products varied from being gel-like to solid, and these materials were analyzed by thermal and scanning electron microscopy methods. Microemulsion polymerized materials were insoluble in all solvents tested, consistent with light cross-linking. Ion exchange between Br(-) and PF6(-) in these copolymeric materials resulted in the formation of open-cell porous structures in some of these materials, as was confirmed by scanning electron microscopy (SEM). Several compositions illustrate the capture of prepolymerization nanoscale structure by thermally initiated polymerization, expanding the domain of compositions exhibiting this feat and yet to be demonstrated in any other system. Regular cylindrical pores in interpenetrating ILBr-co-MMA and PMMA networks are produced by anion exchange in the absence of templates. A percolating cluster/bicontinuous transition is "captured" by SEM after using anion exchange to visualize the mixed cluster/pore morphology. Some design principles for achieving this capture and for obtaining stimuli responsive solvogels are articulated, and the importance of producing solvogels in capturing the nanoscale is highlighted.

Investigation of free-radical copolymerization propagation kinetics of vinyl acetate and methyl methacrylate

The free-radical copolymerization propagation kinetics of vinyl acetate (VAc) and methyl methacrylate (MMA) at 50 degrees C were investigated through an experimental study combined with a computational analysis based on quantum chemistry. Copolymer composition data, obtained using pulsed laser polymerization followed by size exclusion chromatography (PLP-SEC) and proton nuclear magnetic resonance (NMR), were well represented by the terminal model using monomer reactivity ratios obtained with the computational approach (r(VAc) = 0.001 and r(MMA) = 27.9). Concerning the composition-averaged copolymerization propagation rate coefficient k(p,cop), the differences between the terminal model and the implicit penultimate unit effect (IPUE) model (s(MMA) = 0.544 and s(VAc) = 0.173) are small for VAc/MMA, with the terminal model sufficient to describe the experimental k(p,cop) data measured by PLP-SEC. Monomer and radical charge distributions determined computationally are used to explain the reactivity exhibited by the VAc/MMA system.