Polyolefins Vitrimers: Design Principles and Applications

Abstract

Less than 10% of plastics are recycled worldwide, among which polyolefins, which form two-thirds of all produced polymers, are the most discarded ones. This stems from the nonpolar nature of polyolefins, which limits their degradation and recycling. As such, any approach that may promote the recycling of polyolefins can significantly shift the statistics of polymer recycling toward a more sustainable future. To account for that, the vitrimer concept proposes a unique solution that not only increases the polarity of polyolefins, and as such promotes their degradation, but also expands the utility of polyolefin elastomers and compensates for the significant loss of mechanical properties upon sequential mechanical recycling in thermoplastic polyolefins. Vitrimers are polymer networks formed by reversible covalent cross-links that undergo percolation-conserving exchange reactions at high temperatures. Therefore, while they form a solid network at the service conditions, they can be reprocessed and recycled above a temperature threshold. Thanks to this, they have applications at the interface of thermoplastics and thermosets ranging from recyclable, self-healing, and adhesive materials to creep-resistant and shape-memory networks. This Review aims to classify cross-linking chemistries employed for the production of polyolefin-derived vitrimers and highlight subsequent changes in material properties and applications to promote further development of novel polyolefin vitrimers.

Phase separation in supramolecular and covalent adaptable networks

“…Recently, however, the possibility of tuning CANs through physical means has been proposed, 161–163 making use of phase separation and aggregation, which will be discussed in the next paragraphs. By inducing phase separation in CANs, the aim is mostly to enhance mechanical and physical properties ( e.g.…”

“…[154][155][156] In addition, network characteristics have also been considered, such as the crosslinking density, 157,158 or building in (a small degree of) permanent non-dynamic crosslinks. 159,160 Recently, however, the possibility of tuning CANs through physical means has been proposed, [161][162][163] making use of phase separation and aggregation, which will be discussed in the next paragraphs. By inducing phase separation in CANs, the aim is mostly to enhance mechanical and physical properties (e.g., to increase the T g or reduce creep), add new functionalities, and/ or change the overall morphology of the material through dividing the material in different domains.…”

Connectivity Defects in Metallo-Supramolecular Polymer Networks at Different Self-Sorting Regimes

“…Despite the diversity of transient bonds, which spans from reversible covalent to noncovalent interactions, including but not limited to hydrogen bonds, host–guest interaction, and metal–ligand coordination, only a few of them can react in a heterocomplementary fashion, which is necessary to avoid the formation of primary loops. This includes the majority of reversible covalent bonds, whose stability can be adjusted using external catalysts or stimuli. , A prime example is the hydrazone bond formed between aldehyde and hydrazine groups, whose dissociation rate can be tuned over two orders of magnitude using aniline as the catalyst . In the same way, the dissociation of boronic ester bonds formed between boronic acid and diols strongly depends on and can be tuned by pH and temperature. − Alternately, leveraging the combination of hydrophobic and electrostatic interactions, polymer precursors functionalized with heterocomplementary macrocycles and various guests are reported to form transient hydrogels with a stability that is tunable in more than five orders of magnitude. , Similarly, heterocomplementary hydrogen bonding groups are used to suppress the macroscopic phase separation between immiscible polymer precursors, but their utility in hydrogel formation is normally limited due to the competition with water. , In contrast, Sakai and co-workers have recently formed transient hydrogels using tetraPEG precursors grafted with DNA sequences, which form heterocomplementary duplexes mediated through hydrogen bonds .…”

Synthesis of Renewable, Recyclable, Degradable Thermosets Endowed with Highly Branched Polymeric Structures and Reinforced with Carbon Fibers

“…Bio-based thermosets that consist of biogenic carbons can be a solution because their use can reduce fossil fuel consumption and the carbon footprint . In particular, with the help of dynamic covalent chemistry, they are reprocessable and chemically recyclable; thus, they constitute bio-based covalent adaptable networks. , A variety of biomasses have been exploited for this purpose: vegetable oils − (including vanillin, − eugenol, , and cardanol , ), natural acids, − flavonoids, , and biopolymers, for example, polysaccharides, natural resins, and lignins. − Most of them contain β-hydroxy ester bonds that are commonly derived from epoxide, promoting transesterification due to the presence of free hydroxyl groups adjacent to the esters . Moreover, dynamic covalent bonds such as imine, disulfide, hindered urea, , acetal, boronic ester, and carbamate have been applied to build renewable dynamic networks.…”

“…24−30 Most of them contain β-hydroxy ester bonds that are commonly derived from epoxide, promoting transesterification due to the presence of free hydroxyl groups adjacent to the esters. 31 Moreover, dynamic covalent bonds such as imine, 32 disulfide, 16 hindered urea, 6,10 acetal, 27 boronic ester, 11 and carbamate 33 have been applied to build renewable dynamic networks.…”