High-T_g and Degradable Isosorbide-Based Polybenzoxazine Vitrimer

Abstract

This work describes new fully bio-based vitrimers prepared from isosorbide, a renewable sugar-based chemical. Isosorbide was reacted with 4-hydroxypropionic acid, paraformaldehyde, mono-ethanolamine, and/or furfurylamine via consecutive solvent-free Fischer esterification and Mannich-like ring-closure reactions. The two-step synthesis led to the formation of a ditelechelic benzoxazine-terminated isosorbide monomer, containing ester bonds and aliphatic hydroxyl and/or furan groups. The atom economy factor yields 85%. The structural features of the resulting products were substantiated by spectroscopic techniques. The ringopening polymerization was monitored by rheological and differential scanning calorimetry (DSC) measurements. Very high T g values afforded by the isosorbide substructure were measured (from 143 to 193 °C), which increase with furan ring content. Internally catalyzed transesterification reactions conferred fast dynamic exchanges (τ* = 300 s at 180 °C). Self-healing and chemical and mechanical recycling were also demonstrated. Finally, the degradability of the sugar-based polybenzoxazine vitrimers was demonstrated as well. The materials were highly stable in pH-neutral water, even at 80 °C for 60 days, but owing to the isosorbide structure, pronounced degradation was observed under acidic or alkaline conditions. In summary, isosorbide is a suitable building block for the design of degradable and 100% recyclable high-T g polybenzoxazine vitrimers.

Formaldehyde-Free Synthesis of Fully Bio-Based Multifunctional Bisbenzoxazine Resins from Natural Renewable Starting Materials

“…Its polymeric product can form through thermal ring-opening polymerization (ROP) without the need to add any potentially harmful catalysts (Scheme S1). − Holly and Cope prepared the first monofunctional BZ, 3,4-dihydro-2 H -1,3-benzoxazine, through Mannich condensation . Although the chemical structures of PBZs are similar to those of traditional phenolic resins, PBZs are generally prepared by using simple and self-catalyzed polymerization processes and display good heat resistance, high degradation and glass transition ( T g ) temperatures, near-zero volumetric shrinkage during polymerization, excellent flame retardancy, good mechanical properties, low dielectric constants, water absorption properties, and variable surface free energies. ,− In addition, high flexibility in the molecular design of BZ resins allows a variety of physical and mechanical properties to be introduced into the resulting PBZ materials. − Moreover, the properties of PBZs lead to many potential applications in, for example, adsorbents, metal capture, energy storage, gas uptake, shape-memory and self-healing polymers, anticorrosion coatings, adhesives, and electronic materials. − The syntheses and characteristics of mono-, bi-, tri-, and tetrafunctional BZs have been investigated in detail by many research groups. ,,,,,,, In general, monofunctionalized BZs tend to form linear polymers of relatively lower molecular weight, while bifunctional BZs form cross-linked macromolecules featuring more stable networks …”

Exploiting the reversible covalent bonding of boronic acids for self-healing/recycling of main-chain polybenzoxazines

“…21 It is also possible to impart dynamic covalent bonding sites on PBzs or supramolecular interactions to produce selfhealable materials. [22][23][24] For example, self-healing by light triggered [2 + 2] cycloaddition was accomplished using coumarin functional benzoxazines. 25 Although deep light penetration into such materials is limited, these systems were shown to be capable of initiating the healing process on demand.…”

Reprocessable Polybenzoxazine Thermosets with High Tgs and Mechanical Strength Retentions Using Boronic Ester Bonds as Crosslinkages

“…Benzoxazine resin, as a new class of thermosetting polymer, has gained considerable attention in recent years on account of its brilliant heat resistance, excellent flame retardance, and high hydrophobicity [ 13 , 14 , 15 ]. Recently, various dynamic covalent bonds have been introduced into polybenzoxazine networks to achieve self-healabilty or reprocessability [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. However, there have been few reports on introducing boronic ester bonds into benzoxazine resins until now.…”