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Scheme 1 Synthesis of a linear polymer and SCPNs. CPDB = 2cyanopropan-2-yl benzothioate. AIBN = Azobisisobutyronitrile.
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Addition of intramolecular cross-links to linear polymers significantly improves their resistance to mechanochemical fragmentation and hence polymer solution physical properties are maintained under shear. However, while fragmentation is suppressed, mechanochemistry of chemical bonds still occur. In linear polymers, the rate of mechanochemistry has...
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Elastomers are highly valued soft materials finding many applications in the engineering and biomedical fields for their ability to stretch reversibly to large deformations. Yet their maximum extensibility is limited by the occurrence of fracture, which is currently still poorly understood. Because of a lack of experimental evidence, current physic...
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... [15] In contrast, random covalent folding (intramolecular collapse) of polymer chains can significantly reduce their hydrodynamic volume and lead to more compact conformations, effectively repressing polymer extension prior to covalent bond scission. [16][17][18][19][20] Block copolymers (BCPs) are an intriguing class of polymers in which different monomers are covalently bound in large clusters inside the same covalent macromolecule. Given that most polymer chains are thermodynamically incompatible, BCPs have the ability to self-assemble into a wide range of nanoscale structures and therefore have found wide applications in modern materials science. ...
Mechanochemistry can lead to the degradation of the properties of covalent macromolecules. In recent years, numerous functional materials have been developed based on block copolymers (BCPs), however, like homopolymers, their chains could undergo mechanochemical damage during processing, which could have crucial impact on their performance. To investigate the mechanochemical response of BCPs, multiple polymers comprising different ratios of butyl acrylate and methyl methacrylate were prepared with similar degree of polymerization and stressed in solution via ultrasonication. Interestingly, all BCPs, regardless of the amount of the methacrylate monomer, presented a mechanochemistry rate constant similar to that of the methacrylate homopolymer, while a random copolymer reacted like the acrylate homopolymer. Size‐exclusion chromatography showed that, in addition to the typical main peak shift towards higher retention times, a different daughter fragment was produced indicating a secondary selective scission site, situated around the covalent connection between the two blocks. Molecular dynamics modeling using acrylate and methacrylate oligomers were carried out and indicated that dynamic phase separation occurs even in a good solvent. Such non‐random conformations can explain the faster polymer mechanochemistry. Moreover, the dynamic model for end‐to‐end chain overstretching supports bond scission which is not necessarily chain‐centered.
... [16,17] Va rious design principles influence mechanochemical reactivity including the location of mechanophores, [18] regio-and stereochemistry, [19][20][21][22][23] linkers, [24][25][26] polymer composition, [27,28] and polymer topology. [29] In regard to topology,i ntramolecularly cross-linked, [30][31][32][33][34] cyclic, [35] dendritic, [36,37] star, [38][39][40][41][42][43] bottlebrush, [44][45][46] and dendronized polymers, [47] have been utilized to tune mechanochemical reaction kinetics and/or mechanophore activation efficiency. Them ajority of these topology studies have been conducted using ultrasonication (US) or, to alesser extent, ball-mill grinding (BMG). ...
We explored the mechanochemical degradation of bottlebrush and dendronized polymers in solution (with ultrasonication, US) and solid states (with ball‐mill grinding, BMG). Over 50 polymers were prepared with varying backbone length and arm architecture, composition, and size. With US, we found that bottlebrush and dendronized polymers exhibited consistent backbone scission behavior, which was related to their elongated conformations in solution. Considerably different behavior was observed with BMG, as arm architecture and composition had a significant impact on backbone scission rates. Arm scission was also observed for bottlebrush polymers in both solution and solid states, but only in the solid state for dendronized polymers. Motivated by these results, multi‐mechanophore polymers with bottlebrush and dendronized polymer architectures were prepared and their reactivity was compared. Although dendronized polymers showed slower arm‐scission, the selectivity for mechanophore activation was much higher. Overall, these results have important implications to the development of new mechanoresponsive materials.
... [7,8] In this framework, during the last two decades, we explored the use of 2-(acetoacetoxy) ethyl methacrylate (HAAEMA) as a ligand to prepare several MCMs for the obtainment of relevant MCPs. HAAEMA (Scheme 2) is a clear or light-yellow liquid which finds use as versatile functional acrylic monomer [9][10][11][12][13][14] for making copolymers to be used in various applications such as, by way of example, dental resins, [15,16] coatings for glass and metal surfaces, [17] wound sealants, [18] waterborne coatings, [19,20] thermal nanoimprint lithography, [21] and nanoparticles [22][23][24][25]. On the other hand, exploiting the fact that the reactivity of the β-ketoester functionality in HAAEMA towards transition metal salts or complexes is very close to that of acetylacetone, we were able to prepare several transition metal complexes containing the ligand AAEMA -(Scheme 2). ...
Among the synthetic strategies commonly used for supporting a metal complex onto an organic polymer in order to obtain an heterogenous catalyst, a valid choice is to synthesize a metal containing monomer (MCM), which can subsequently be subjected to polymerization with suitable comonomers and crosslinkers, achieving a supported transition metal catalyst as a metal-containing polymer (MCP). In this context, during the last two decades, we explored the use of 2-(acetoacetoxy)ethyl methacrylate (HAAEMA) as a ligand to prepare several MCMs for the relevant MCPs. In this review we summarize and discuss our developments in the studies of the catalytic activity of these “hybrid” catalysts. These catalysts have demonstrated high efficiency and/or excellent selectivity in several kinds of chemical reactions and very often they could be recovered and reused in multiple cycles maintaining their activity and selectivity without suffering from appreciable metal leaching.
Mechanochemistry can lead to the degradation of the properties of covalent macromolecules. In recent years, numerous functional materials have been developed based on block copolymers (BCPs), however, like homopolymers, their chains could undergo mechanochemical damage during processing, which could have crucial impact on their performance. To investigate the mechanochemical response of BCPs, multiple polymers comprising different ratios of butyl acrylate and methyl methacrylate were prepared with similar degree of polymerization and stressed in solution via ultrasonication. Interestingly, all BCPs, regardless of the amount of the methacrylate monomer, presented a mechanochemistry rate constant similar to that of the methacrylate homopolymer, while a random copolymer reacted like the acrylate homopolymer. Size‐exclusion chromatography showed that, in addition to the typical main peak shift towards higher retention times, a different daughter fragment was produced indicating a secondary selective scission site, situated around the covalent connection between the two blocks. Molecular dynamics modeling using acrylate and methacrylate oligomers were carried out and indicated that dynamic phase separation occurs even in a good solvent. Such non‐random conformations can explain the faster polymer mechanochemistry. Moreover, the dynamic model for end‐to‐end chain overstretching supports bond scission which is not necessarily chain‐centered.
A series of monodisperse cyclic and linear poly(d,l-lactide)s (c-PLA and l-PLA, respectively) were prepared with various degrees of polymerization (DP) using an iterative convergent synthesis approach. The absence of a molecular weight distribution provided us a chance to study their mechanochemical reactivity without obstructions arising from the size distribution. Additionally, we prepared l- and c-PLAs with identical DPs, which enabled us to attribute differences in scission rates to the cyclic polymer architecture alone. The polymers were subjected to ultrasonication (US) and ball-mill grinding (BMG), and their degradation kinetics were explored. Up to 9.0 times larger scission rates were observed for l-PLA (compared to c-PLA) with US, but the difference was less than 1.9 times with BMG. Fragmentation requires two backbone scission events for c-PLA, and we were able to observe linear intermediates (formed after a single scission) for the first time. We also developed a new method of studying the dynamic memory effect in US by characterizing and comparing the daughter fragment molecular weight distributions of l- and c-PLAs. These results provide new insights into the influence of the cyclic polymer architecture on mechanochemical reactions as well as differences in reactivity observed with US and BMG.
The development of nanosized aggregates that respond to mechanical stimuli is of great importance for applications related to ultrasound imaging or sensors, etc. In this work, we fabricate model assemblies...
Emerging nano-scale materials are under development for multiple uses in high-performance product applications such as advanced polymers. We apply prospective life cycle assessment (LCA) methods to evaluate alternative process scenarios for single chain polymer nanoparticles (SCNPs) synthesis through a photochemistry process, emphasizing the role of limiting solvent quantity and type used. SCNPs are promising high-performance materials with multiple potential applications in catalysts, lubricants, nanoreactors and more. However, as of today, SCNPs synthetic routes are still under development and usually require an excessive amount of solvent, imposing costly environmental impacts. In this study, we perform LCA to evaluate SCNPs production through a flow photochemical process compared to a classical batch process. We apply LCA to compare the performance of different scenarios for batch and flow processes, considering solvent recovery through vacuum distillation, atmospheric distillation, and solvent replacement. The results indicate that there are environmental benefits under the flow process over conventionally used batch processes where the solvent is recovered through atmospheric distillation, and toluene is the preferred solvent. In addition, we compare the LCA results to a common green chemistry metric known as the Environmental factor and conclude that a green metric calculation alone is insufficient. Hence, a comprehensive and systematic life cycle approach is needed to understand the environmental impacts of flow chemistry with potential scenarios prior to scaling up production.
Block copolymers (BCPs) are used in numerous applications in modern materials science. Yet, like homopolymers, BCPs can undergo covalent bond scission when mechanically stressed (mechanochemistry), which could lead to unexpected consequences in such applications. BCPs' heterogeneity may affect force transduction, perhaps changing force distribution and localization. To verify this, a gem‐dichlorocyclopropane (gDCC) embedded linear chain is prepared and extended with a poly(methyl methacrylate) block. When stressed in solution, the mechanochemical ring‐opening of gDCC is accelerated compared to homopolymers, even though the mechanophores are at the chain ends. Moreover, a higher mechanophore activation selectivity is obtained. These results indicate that mechanochemical response outside, and even far from the chain center is quite prominent in BCPs, and that forces along the polymer chain can efficiently activate multi‐mechanophores regions, even when far from the polymer midchain.
Block copolymers (BCPs) are used in numerous applications in modern materials science. Yet, like homopolymers, BCPs can undergo covalent bond scission when mechanically stressed (mechanochemistry), which could lead to unexpected consequences in such applications. BCPs’ heterogeneity may affect force transduction, perhaps changing force distribution and localization. To verify this, a gem‐dichlorocyclopropane (gDCC) embedded linear chain is prepared and extended with a poly(methyl methacrylate) block. When stressed in solution, the mechanochemical ring‐opening of gDCC is accelerated compared to homopolymers, even though the mechanophores are at the chain ends. Moreover, a higher mechanophore activation selectivity is obtained. These results indicate that mechanochemical response outside, and even far from the chain center is quite prominent in BCPs, and that forces along the polymer chain can efficiently activate multi‐mechanophores regions, even when far from the polymer midchain.
