Mechanochemical Functionalization of Oxidized Carbon Black with PLA

The functionalization of carbon black (CB) represents a promising strategy to enhance its compatibility with polymers while addressing sustainability concerns. In this study, a solvent-free mechanochemical approach (ball milling) is proposed for the functionalization of oxidized carbon black (oCB) with post-consumed polylactic acid (PLA), overcoming the environmental drawbacks of conventional methods that mostly rely on toxic solvents and catalysts. The functionalized carbon black (f-CB) was characterized by Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), and thermogravimetric analysis (TGA) to confirm the successful modification. At the same time, the influence of f-CB as a nanofiller of residual PLA waste was evaluated using differential scanning calorimetry (DSC) and gel permeation chromatography (GPC), demonstrating its stabilization effect during melt extrusion by preserving the molecular weight of the starting polymer. On the other hand, the dynamic mechanical analysis (DMA) revealed that the addition of f-CB did not negatively affect the mechanical properties of the resulting composite. In conclusion, mechanochemistry was used as a sustainable and unique strategy for the upcycling of waste PLA into a PLA-based composite stabilized by CB functionalized with the waste PLA itself.

Polyesters and Polyester Nano- and Microcarriers for Drug Delivery

Many therapies require the transport of therapeutic compounds or substances encapsulated in carriers that reduce or, if possible, eliminate their direct contact with healthy tissue and components of the immune system, which may react to them as something foreign and dangerous to the patient's body. To date, inorganic nanoparticles, solid lipids, micelles and micellar aggregates, liposomes, polymeric micelles, and other polymer assemblies were tested as drug carriers. Specifically, using polymers creates a variety of options to prepare nanocarriers tailored to the chosen needs. Among polymers, aliphatic polyesters are a particularly important group. The review discusses controlled synthesis of poly(β-butyrolactone)s, polylactides, polyglycolide, poly(ε-caprolactone), and copolymers containing polymacrolactone units with double bonds suitable for preparation of functionalized nanoparticles. Discussed are syntheses of aliphatic polymers with controlled molar masses ranging from a few thousand to 106 and, in the case of polyesters with chiral centers in the chains, with controlled microstructure. The review presents also a collection of methods useful for the preparation of the drug-loaded nanocarriers: classical, developed and mastered more recently (e.g., nanoprecipitation), and forgotten but still with great potential (by the direct synthesis of the drug-loaded nanoparticles in the process comprising monomer and drug). The article describes also in-vitro and model in-vivo studies for the brain-targeted drugs based on polyester-containing nanocarriers and presents a brief update on the clinical studies and the polyester nanocarrier formulation approved for application in the clinics in South Korea for the treatment of breast, lung, and ovarian cancers.

Liquid-assisted grinding enables a direct mechanochemical functionalization of polystyrene waste

The plastic waste crisis has grave consequences for our environment, as most single-use commodity polymers remain in landfills and oceans long after their commercial lifetimes. Utilizing modern synthetic techniques to chemically modify the structure of these post-consumer plastics (e.g., upcycling) can impart new properties and added value for commercial applications. To expand beyond the abilities of current solution-state chemical processes, we demonstrate post-polymerization modification of polystyrene via solid-state mechanochemistry enabled by liquid-assisted grinding (LAG). Importantly, this emblematic trifluoromethylation study modifies discarded plastic, including dyed materials, using minimal exogenous solvent and plasticizers for improved sustainability. Ultimately, this work serves as a proof-of-concept for the direct mechanochemical post-polymerization modification of commodity polymers, and we expect future remediation of plastic waste via similar mechanochemical reactions.

Shake, shear, and grind! - the evolution of mechanoredox polymerization methodology

In the last half decade, mechanoredox catalysis has enabled an entirely new genre of polymerization methodology. In this paradigm, mechanical force, such as ultrasonic cavitation bubble collapse or ball mill grinding, polarizes piezoelectric nanoparticles; the resultant piezopotential drives the redox processes necessary for free- and controlled-radical polymerizations. Since being introduced, evolution of these methods facilitates exploration of mechanistic underpinnings behind key electron-transfer events. Mechanical force has not only been identified as a "greener" alternative to more traditional reaction stimuli (e.g., heat, light) for the synthesis of commodity polymers, but also a potential technology to enable the production of novel thermoplastic and thermoset materials that are either challenging, or even impossible, to access using conventional solution-state approaches. In this Feature Article, significant contributions to such methods are highlighted within. Advances and ongoing challenges in both ultrasound and ball milling driven reactions for radical polymerization and crosslinking are identified and discussed.

Anionic ring-opening polymerization of functional epoxide monomers in the solid state

Despite recent advancements in mechanochemical polymerization, understanding the unique mechanochemical reactivity during the ball milling polymerization process still requires extensive investigations. Herein, solid-state anionic ring-opening polymerization is used to synthesize polyethers from various functional epoxide monomers. The critical parameters of the monomers are investigated to elucidate the unique reactivity of ball milling polymerization. The controllable syntheses of the desired polyethers are characterized via NMR, GPC, and MALDI-ToF analyses. Interestingly, bulky monomers exhibit faster conversions in the solid-state in clear contrast to that observed for solution polymerization. Particularly, a close linear correlation is observed between the conversion of the ball milling polymerization and melting point of the functional epoxide monomers, indicating melting point as a critical predictor of mechanochemical polymerization reactivity. This study provides insights into the efficient design and understanding of mechanochemical polymerization.

TM-Free and TM-Catalyzed Mechanosynthesis of Functional Polymers

Mechanochemically induced methods are commonly used for the depolymerization of polymers, including plastic and agricultural wastes. So far, these methods have rarely been used for polymer synthesis. Compared to conventional polymerization in solutions, mechanochemical polymerization offers numerous advantages such as less or no solvent consumption, the accessibility of novel structures, the inclusion of co-polymers and post-modified polymers, and, most importantly, the avoidance of problems posed by low monomer/oligomer solubility and fast precipitation during polymerization. Consequently, the development of new functional polymers and materials, including those based on mechanochemically synthesized polymers, has drawn much interest, particularly from the perspective of green chemistry. In this review, we tried to highlight the most representative examples of transition-metal (TM)-free and TM-catalyzed mechanosynthesis of some functional polymers, such as semiconductive polymers, porous polymeric materials, sensory materials, materials for photovoltaics, etc.

Mechanically Driven Atom Transfer Radical Polymerization by Piezoelectricity

Targeting sustainable and eco-friendly polymer synthesis, we demonstrate here a synergistically catalyzed atom transfer radical polymerization (ATRP) induced and controlled by interplay between ball milling (BM) and piezoelectric nanoparticles (piezoNPs). BM-induced electron transfer can be achieved through piezoNPs deformation under impact force, serving as an external stimulus to mediate polymerization. The ppm level of copper loading is sufficient in fabrication of a polymer with well-defined molecular weight and low polydispersity. High-molecular-weight polymers ranging from 33 to 74 kDa were prepared successfully through DMSO-assisted grinding. Besides, its good performance on availability of water as liquid-assisted grinding additive, the recyclability of piezoNPs, and the formation of cross-linker-free composite resin make our ATRP approach a green and practical option alongside the existent heat-, electro-, and photo-induced methods.

Mechanochemical solid-state vinyl polymerization with anionic initiator

Mechanochemistry has been extended to various polymer syntheses to achieve efficiency, greenness, and new products. However, many fundamental polymerization reactions have not been explored, although anionic polymerization of vinyl compounds has been pursued under mechanochemical conditions. Two solid monomers, 4-biphenyl methacrylate and 4-vinyl biphenyl, representing methacrylate and styrenic classes, respectively, were reacted with secondary butyl lithium under high-speed ball-milling. The alkyl-anion-promoted polymerization process was established by excluding radical initiation and producing the expected polymers with good efficiency. However, the generally expected features of anionic polymerization, such as molecular weight control and narrow dispersity, were not observed. Analysis of the milling parameters, reaction monitoring, and microstructural analysis revealed that the mechanism of the mechanochemical process differs from that of conventional anionic polymerizations. The mechanical force fractured the newly formed polymer chains via anionic initiation and generated macroradicals, which participated in the polymerization process. The anionic process governs the initiation step and the radical process becomes dominant during the propagation step.

Diaryliodonium salts facilitate metal-free mechanoredox free radical polymerizations

Mechanically-induced redox processes offer a promising alternative to more conventional thermal and photochemical synthetic methods. For macromolecule synthesis, current methods utilize sensitive transition metal additives and suffer from background reactivity. Alternative methodology will offer exquisite control over these stimuli-induced mechanoredox reactions to couple force with redox-driven chemical transformations. Herein, we present the iodonium-initiated free-radical polymerization of (meth)acrylate monomers under ultrasonic irradiation and ball-milling conditions. We explore the kinetic and structural consequences of these complementary mechanical inputs to access high molecular weight polymers. This methodology will undoubtedly find broad utility across stimuli-controlled polymerization reactions and adaptive material design.

The mechanochemical synthesis of polymers

Mechanochemistry - the utilization of mechanical forces to induce chemical reactions - is a rarely considered tool for polymer synthesis. It offers numerous advantages such as reduced solvent consumption, accessibility of novel structures, and the avoidance of problems posed by low monomer solubility and fast precipitation. Consequently, the development of new high-performance materials based on mechanochemically synthesised polymers has drawn much interest, particularly from the perspective of green chemistry. This review covers the constructive mechanochemical synthesis of polymers, starting from early examples and progressing to the current state of the art while emphasising linear and porous polymers as well as post-polymerisation modifications.

Mechanochemical ring-opening metathesis polymerization: development, scope, and mechano-exclusive polymer synthesis

Ruthenium-alkylidene initiated ring-opening metathesis polymerization has been realized under solid-state conditions by employing a mechanochemical ball milling method. This method promotes greenness and broadens the scope to include mechano-exclusive products. The carbene- and pyridine-based Grubbs 3^rd-generation complex outperformed other catalysts and maintained similar mechanistic features of solution-phase reactions. High-speed ball milling provides sufficient mixing and energy to the solid reaction mixture, which is composed of an initiator and monomers, to minimize or eliminate the use of solvents. Therefore, the solubility and miscibility of monomers and Ru-initiators are not limiting factors in solid-state ball milling. A wide variety of solid monomers, including ionomers, fluorous monomers, and macromonomers, were successfully polymerized under ball milling conditions. Importantly, direct copolymerization of immiscible (ionic/hydrophobic) monomers exemplifies the synthesis of mechano-exclusive polymers that are difficult to make using traditional solution procedures. Finally, the addition of a small amount of a liquid additive (i.e., liquid-assisted grinding) minimized chain-degradation, enabling high-molecular-weight polymer synthesis.

Mechanochemical ball-milling ring-opening metathesis polymerization minimized solvent use and produced previously inaccessible polymers in solution.

Simple and Rapid Mechanochemical Synthesis of Lactide and 3S-(Isobutyl)morpholine-2,5-dione-Based Random Copolymers Using DBU and Thiourea

There is a growing interest surrounding morpholine-2,5-dione-based materials due to their impressive biocompatibility as well as their capacity to break down by hydrolytic and enzymatic pathways. In this study, the ring-opening (co)polymerization of leucine-derived 3S-(isobutyl)morpholine-2,5-dione (MD) and lactide (LA) was performed via ball-milling using a catalytic system composed of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 3-[3,5-bis(trifluoromethyl)phenyl]-1-cyclohexylthiourea (TU). Once the homopolymerizations of MD and LA optimized and numerous parameters were studied, the mechanochemical ring-opening copolymerization of these monomers was explored. The feasibility of ring-opening copolymerizations in mechanochemical systems was demonstrated and a range of P(MD-co-LA) copolymers were produced with varying proportions of MD (23%, 48%, and 69%). Furthermore, the beneficial cocatalytic effects of TU with regards to ROP control were found to be operative within mechanochemical systems. Further parallels were observed between solution- and mechanochemical-based ROPs.

Sustainability Assessment of Mechanochemistry by Using the Twelve Principles of Green Chemistry

In recent years, mechanochemistry has been growing into a widely accepted alternative for chemical synthesis. In addition to their efficiency and practicality, mechanochemical reactions are also recognized for their sustainability. The association between mechanochemistry and Green Chemistry often originates from the solvent-free nature of most mechanochemical protocols, which can reduce waste production. However, mechanochemistry satisfies more than one of the Principles of Green Chemistry. In this Review we will present a series of examples that will clearly illustrate how mechanochemistry can significantly contribute to the fulfillment of Green Chemistry in a more holistic manner.

Toughened PLA-b-PCL-b-PLA triblock copolymer based biomaterials: effect of self-assembled nanostructure and stereocomplexation on the mechanical properties

The current research unfolds the effect of block lengths, microdomain morphology and stereocomplexation on the mechanical properties of PLA-b-PCL-b-PLA triblock copolymers where PCL is involved to improve the poor extensibility of PLA.

Atom Transfer Radical Polymerization in the Solid-State

Poly(2-vinylnaphthalene) was synthesized in the solid-state by ball milling a mixture of the corresponding monomer, a Cu-based catalyst, and an activated haloalkane as the polymerization initiator. Various reaction conditions, including milling time, milling frequency and added reductant to accelerate the polymerization were optimized. Monomer conversion and the evolution of polymer molecular weight were monitored over time using 1 H NMR spectroscopy and size exclusion chromatography, respectively, and linear correlations were observed. While the polymer molecular weight was effectively tuned by changing the initial monomer-to-initiator ratio, the experimentally measured values were found to be lower than their theoretical values. The difference was attributed to premature mechanical decomposition and modeled to accurately account for the decrement. Random copolymers of two monomers with orthogonal solubilities, sodium styrene sulfonate and 2-vinylnaphthalene, were also synthesized in the solid-state. Inspection of the data revealed that the solid-state polymerization reaction was controlled, followed a mechanism similar to that described for solution-state atom transfer radical polymerizations, and may be used to prepare polymers that are inaccessible via solution-state methods.

Bio-Based Packaging: Materials, Modifications, Industrial Applications and Sustainability

Environmental impacts and consumer concerns have necessitated the study of bio-based materials as alternatives to petrochemicals for packaging applications. The purpose of this review is to summarize synthetic and non-synthetic materials feasible for packaging and textile applications, routes of upscaling, (industrial) applications, evaluation of sustainability, and end-of-life options. The outlined bio-based materials include polylactic acid, polyethylene furanoate, polybutylene succinate, and non-synthetically produced polymers such as polyhydrodyalkanoate, cellulose, starch, proteins, lipids, and waxes. Further emphasis is placed on modification techniques (coating and surface modification), biocomposites, multilayers, and additives used to adjust properties especially for barriers to gas and moisture and to tune their biodegradability. Overall, this review provides a holistic view of bio-based packaging material including processing, and an evaluation of the sustainability of and options for recycling. Thus, this review contributes to increasing the knowledge of available sustainable bio-based packaging material and enhancing the transfer of scientific results into applications.

Turning natural δ-lactones to thermodynamically stable polymers with triggered recyclability

Extending the use of natural δ-lactones in circular materials via a synthetic strategy yielding thermodynamically stable polyesters with triggered recyclability.

Mechanochemical synthesis of poly(trimethylene carbonate)s: an example of rate acceleration

Mechanochemical polymerization is a rapidly growing area and a number of polymeric materials can now be obtained through green mechanochemical synthesis. In addition to the general merits of mechanochemistry, such as being solvent-free and resulting in high conversions, we herein explore rate acceleration under ball-milling conditions while the conventional solution-state synthesis suffer from low reactivity. The solvent-free mechanochemical polymerization of trimethylene carbonate using the organocatalysts 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) are examined herein. The polymerizations under ball-milling conditions exhibited significant rate enhancements compared to polymerizations in solution. A number of milling parameters were evaluated for the ball-milling polymerization. Temperature increases due to ball collisions and exothermic energy output did not affect the polymerization rate significantly and the initial mixing speed was important for chain-length control. Liquid-assisted grinding was applied for the synthesis of high molecular weight polymers, but it failed to protect the polymer chain from mechanical degradation.