1,154 research outputs found
Bifunctional ATRP initiators for the synthesis of α,ω-dichloropolystyrene: new functionalities and thermal stability study
No full textAtom Transfer Radical Polymerization (ATRP) allows to obtain living polymers with a well-defined molecular weight distribution, as well as control over topology, composition, and functionality, enabling to develop advanced materials for specific applications. Functional groups can be introduced into the polymer by post-functionalization of the halogenated chain-end moieties, or on the alkyl residue of the initiator, or by direct introduction of punctually functionalized (co)monomers – greatly enhancing the targetable applications. In addition, the desired functional group can also be carried by the ATRP initiator, provided that the functionality is impervious to radical reactions. For example, some authors explored the use of initiators containing hydrolysis- or heat-sensitive functionalities such that the final polymer exhibits self-healing properties. Thermoplastics, like polystyrene, require thermal and thermomechanical stability under extrusion conditions (150-220°C) in order to be reprocessed. Therefore, it is important that the initiator employed is also thermally stable, otherwise there would be a reduction in chain length and consequently a loss of telechelecity. Unfortunately, the aliphatic halide esters typically employed as initiators have shown poor thermal stability. Thus, in this study we demonstrate the enhanced thermal stability of α,ω-dichloropolystyrene synthetized via ARGET ATRP using a novel bifunctional benzamide-containing initiator instead of the formerly reported aliphatic esters. Emphasis was placed on investigating the reason why the structure and functionality of the initiator improved thermal stability
Amide-Imide Terpolymer Dynamic Network
No full textSince the 1950s, 6300 million tons of plastics have been produced of which only 9% have been recycled once. Thermosets account for 22% of the total plastic production. Since they cannot be recycled, or reprocessed, they are incinerated or are accumulated in landfills. Thermosets possess enhanced thermo-mechanical stability and better chemical, wear, and creep resistance properties than thermoplastics. Therefore, these network materials are employed in many advanced lightweight applications, such as aerospace, automotive, wind turbine, and thermal insulation.
Dynamic covalent networks can combine the peculiar properties of thermosets and the re-processability of thermoplastics due to the presence of exchangeable chemical bonds activated by simple external stimuli, such as light or heat.
The ever-increasing number of dynamic exchange mechanisms, coupled with the wide variety of monomers exploited to obtain polymer chains, enables the tailored synthesis of advanced materials with desired mechanical properties for specific applications.
In this study, we present a new dynamic network formed through the dissociative amide-imide exchange mechanism on a terpolymer containing also a biobased co-monomer
Incorporating Biobased Monomers into a Terpolymer Dynamic Network
No full textGlobal thermosets production in 2021 was about 49.2 million tons accounting for 12.6% of global plastic production, while the European one was about 6.9 million tons accounting for 12.1% of total plastic production.
Thermosets are cross-linked materials with enhanced thermo-mechanical stability and better chemical, wear, and creep resistance properties than thermoplastics. Therefore, these network materials are employed in many advanced lightweight applications, such as aerospace, automotive, wind turbine, and thermal insulation. Unfortunately, they also have a drawback: they cannot be reshaped, reprocessed, or recycled.
Dynamic covalent networks overcome this issue due to the presence of exchangeable chemical bonds activated by simple external stimuli, such as light or heat, making them fully reprocessable.
The ever-increasing number of dynamic exchange mechanisms, coupled with the wide variety of monomers exploited to obtain polymer chains, enables the tailored synthesis of advanced materials with desired mechanical properties for specific applications.
In this study, we present a new dynamic network formed through the dissociative amide-imide exchange mechanism on a terpolymer containing also a biobased monomer
Synthesis and Characterization of Bifunctional ATRP Initiators with Tailored Functionalities: Study of the Thermal Stability
No full textFree radical polymerization is the most diffused process in industry to produce polymers. Nevertheless, the main drawback of this synthetic method is the lack of control over the molecular weight of the resultant polymers, due to unavoidable chain transfer and termination processes.
Atom Transfer Radical Polymerization (ATRP) represents one of the most versatile techniques to achieve polymers with low polydispersity and well-defined architecture. We have recently demonstrated that this technique can be implemented on a greener industrial scale and optimized through a homogeneous catalytic system. Moreover, ATRP allows for the introduction of chain functionalities that can be exploited to obtain materials suitable for specific applications. One approach involves the use of functional initiators capable of impart the desired properties to the polymer. For example, some authors explored the use of initiators containing hydrolysis- or heat-sensitive functionalities such that the final polymer exhibits self-healing properties.
Since initiators are integrated into the polymer chain, their thermostability is crucial to avoid thermal degradation of the polymer during processing stages. Unfortunately, aliphatic halide esters, the typically employed ATRP initiators, have shown poor thermal stability.
In this study, we present the synthesis of a series of new properly functionalised initiators together with a deep study of how their chemical structure influences the thermal stability of the generated polymers
PARTIALLY BIOBASED POLY(STYRENE-B-VANILLIN METHACRYLATE) BY ATRP: HOW THE COPOLYMER COMPOSITION INFLUENCES THE VITRIMER
No full textNovel Bifunctional Amide-Based Initiator for the Atom Transfer Radical Polymerization of Styrene with Ascorbic Acid Acetonide as Reducing Agent
No full textThis study focuses on the synthesis and characterization of a new bifunctional benzamide initiator, CMB2HexDA, for the production of thermostable α,ω-dichloropolystyrene via ARGET ATRP. The motivation behind this research is the need to obtain functionalized polystyrene that can withstand the high temperatures used in industrial extrusion processes, as well as the previous development of a method to obtain α,ω-dialkenepolystyrene by solventless thermal dehydrohalogenation. The commonly used initiators in ATRP undergo thermal fragmentation, leading to chain length reduction and loss of telechelicity.
The synthesized initiator was purified and characterized, and the resulting α,ω-dichloropolystyrenes were analyzed through GPC and NMR. The telechelic polystyrene produced with the new initiator exhibited enhanced thermal stability compared to aliphatic-halide ester initiators. Although the specific diamine used does not confer specific functionality, the developed synthetic pathway allows for the introduction of other functionalities into thermostable polystyrenes. Furthermore, the benzamidic function could be exploited to achieve controlled chemical degradation of polystyrene, resulting in more readly degradable oligomeric fragments
A Trifunctional ATRP Initiator Bearing Adaptable Bonds
No full textAtom Transfer Radical Polymerization (ATRP) allows for the production of polymers with precise control over molecular weight, dispersity, topology, composition, and functionality. Functional groups can be introduced into the polymer through post-functionalization of chain ends, or on the alkyl residue of the initiator, or by introducing functionalized (co)monomers, greatly greatly enhancing the targetable applications. In addition, the desired functional group can also be carried by the ATRP initiator. Some researchers have explored initiators with hydrolysis- or heat-sensitive functionalities to impart self-healing properties to the final polymer. However, the commonly used aliphatic halide ester initiators have shown poor thermal stability. To address this issue, we recently developed a novel bifunctional benzamide-containing initiator employed in ARGET ATRP of styrene, demonstrating enhanced thermal stability.
Covalent Adaptable Networks (CANs) have emerged as a solution for improving the recyclability of thermoset materials. CANs can reorganize connectivity between chains upon thermal treatment, enabling reprocessing. Our goal is to modify the structure of the benzamide-containing initiator to develop a trifunctional initiator bearing adaptable bonds
Synthesis of biobased monomers and polymers
No full textThe project aim is to develop sustainable reaction pathways for the synthesis of bio-based monomers and, consequently, the development of polymers of biological origin. Vegetable originated substrates deriving from the agri-food sector are of particular interest. Additional benefit comes from the upgrading of waste materials, characterized by low cost and wide availability, into high added value products. Four lines of research are presented, two focused on the production of biobased olefin monomers suitable for chain-growth polymerization processes, while the other two are devoted to the generation of monomers useful for step-growth polymerizations.
Synthetic endeavors were directed towards the production of vinyl monomers (olefins) for atom transfer radical polymerization (ATRP) processes. The ATRP technique relies on the establishment of a reversible activation/deactivation equilibrium between dormant species and growing chains mediated by a complex of a transition metal, which is usually copper. 4-vinyl guaiacol was successfully synthesised from vanillin with satisfactory yields through a green Knoevenagel-Doebner condensation. Efforts towards establishing a one-pot synthesis are being made with the objectives of minimizing cost and environmental impact. A telescopic synthesis of 4-vinyl guaiacol acetate was developed, affording the hydroxyl-protected monomer in a single step.
Another olefin monomer is obtained from cinnamaldehyde through a condensation reaction with allylamine. Its controlled polymerization is under study.
On the step-growth polymerization side, the production of amines from renewable phenols is under study. The method involves a three-step approach, involving a Blanc-Quelet reaction and subsequent amination. Amination of furfural to furfuryl amine was also studied, together with a coupling process with carbonyl compounds. Potential application of these monomers are as building blocks for non-isocyanate polyurethanes, epoxy resins, or polyamides.
Another upgrading of furfural deals with its transformation towards an unsaturated diacid monomer, through an oxidative ring opening procedure
Basicity Can Choregraph Regeneration in Homogeneous ARGET ATRP of Styrene
No full textThere are two drawbacks in the use of H2AA when polymerizing a hydrophobic monomer such as styrene. First, the low solubility of the reducing agent in non-aqueous solvents. Second, the reduction kinetic rate constant of the catalyst by H2AA is around two-orders of magnitude lower than that of ascorbate (HAA–). In non-dissociating solvents this means that the polymerization is much slower since it is strictly related to the amount of reduced catalyst. To overcome this, we employed for the first time a
more lipophilic ascorbic acid derivative (5,6-isopropylidene ascorbic acid) in place of H2AA, complemented by nitrogen bases
of varying basicity: trimethylpyridine (TMP), diisopropylethylamine (DIPEA), and 1,8-diazabicyclo(5.4.0)undec-7-ene
(DBU). The resulting system is an efficient and effective, homogeneous ARGET ATRP of styrene. Furthermore, it highlighted
how basicity influences the concentration of radicals, and thus control over the final product
Giulia Veronica Varisco
No full textThe headword explains the biography and the contribution of the author Giulia Varisco to the children's literatur
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