Sustainable, Stereoregular, and Optically Active Polyamides via Cationic Polymerization of ε-Lactams Derived from the Terpene β-Pinene

Beyond nylon 6: polyamides via ring opening polymerization of designer lactam monomers for biomedical applications

Ring opening polymerization (ROP) of lactams is a highly efficient and versatile method to synthesize polyamides. Within the last ten years, significant advances in polymerization methodology and monomer diversity are ushering in a new era of polyamide chemistry. We begin with a discussion of polymerization techniques including the most widely used anionic ring opening polymerization (AROP), and less prevalent cationic ROP and enzyme-catalyzed ROP. Next, we describe new monomers being explored for ROP with increased functionality and stereochemistry. We emphasize the relationships between composition, structure, and properties, and how chemists can control composition and structure to dictate a desired property or performance. Finally, we discuss biomedical applications of the synthesized polyamides, specifically as biomaterials and pharmaceuticals, with examples to include as antimicrobial agents, cell adhesion substrates, and drug delivery scaffolds.

Bioenabled Platform to Access Polyamides with Built-In Target Properties

The diversification of platform chemicals is key to today's petroleum industry. Likewise, the flourishing of tomorrow's biorefineries will rely on molecules with next-generation properties from biomass. Herein, we explore this opportunity with a novel approach to monomers with custom property enhancements. Cyclic diacids with alkyl and aromatic decorations were synthesized from muconic acid by Diels-Alder cycloaddition, and copolymerized with hexamethylenediamine and adipic acid to yield polyamides with built-in hydrophobicity and flame retardancy. Testing shows a 70% reduction in water uptake and doubling of char production while largely retaining other key properties of the parent Nylon-6,6. The present approach can be generalized to access a wide range of performance-advantaged polyamides.

The pinene scaffold: its occurrence, chemistry, synthetic utility, and pharmacological importance

This review provides insight into the utility of pinene in the synthetic building block and as reagent in asymmetric synthesis.

Polyester synthesis based on 3-carene as renewable feedstock

Utilizing renewable feedstocks for the synthesis of biobased and preferrable biodegradable polyesters as substitute for fossile-based polymers remains one of the major challenges towards a sustainable polymer economy. One such...

Preparation and Chiral Applications of Optically Active Polyamides

Chirality is omnipresent in nature and plays vital roles in living organism, and has become a hot research topic across multidisciplinary fields including chemistry, biology, physics, and material science. Meanwhile, polyamides constitute an important class of polymers and have received significant attention owing to their outstanding properties and wide-ranging applications in many areas. Judiciously introducing chirality into polyamides will undoubtedly obtain attractive chiral polymers, namely, optically active polyamides. This review describes the preparation methods of chiral polyamides, including solution polycondensation, interfacial polycondensation, ring-open polymerization, and others; the newly emerging categories of chiral polyamides, i.e., helical polyamides, chiral polyamide-imides, are also presented. The applications of optically active polyamides in chiral research fields including asymmetric catalysis, membrane separation, and enantioselective crystallization are also summarized. In addition, current challenges in chiral polyamides are further presented and future perspectives in the field are proposed.

Ring-Opening Metathesis Polymerization of δ-Pinene: Well-Defined Polyolefins from Pine Sap

Well-controlled ring-opening metathesis polymerization (ROMP) of δ-pinene is reported. The monomer is produced through a facile, metal-free, three-step synthesis from highly abundant and sustainable α-pinene. Using Grubbs third-generation catalyst, δ-pinene undergoes ROMP to high conversion (>95%) with molar mass up to 70 kg mol^-1 and narrow dispersity (<1.2). A highly regioregular propagation mechanism was concluded by NMR spectroscopic analysis that revealed a head-to-tail (HT, >95%) microstructure and high trans content (>98%). Successful ROMP is corroborated with density functional theory calculations on δ-pinene's ring strain energy (∼35 kJ mol^-1). Poly(δ-pinene) has a high glass transition temperature (∼104 °C) and a unique chiral microstructure bearing gem-dimethylcyclobutane rings. Controlled ROMP also allowed the synthesis of block copolymers containing segments of poly(δ-pinene) and polynorbornene which are discussed. Finally, bulk polymerization of δ-pinene is possible, indicating a greener approach to these materials, albeit with some loss of control.

β-Pinene-Derived Polyesteramides and Their Blends: Advances in Their Upscaling, Processing, and Characterization

Terpene-based polyesteramides (PEAs) are sustainable and have a variety of favorable properties, making them suitable for a wide range of applications and for contribution to a much more sustainable polymer industry. This work focuses on the synthesis of the lactam from β-pinene and its copolymerization with ε-caprolactone. An important step in synthesizing β-pinene lactam is the oxidation of β-pinene to nopinone. To make the established oxidative cleavage more sustainable and efficient, the required amounts of Al₂ O₃ and KMnO₄ are significantly reduced by using H₂ SO₄ as a catalyst. For the Beckmann rearrangement various catalysts and co-reagents are screened. Among these, the reaction with tosyl chloride is found the most favorable. Subsequently, the chain lengths of the β-pinene-based PEAs are remarkably increased from 6000 g mol^-1 to more than 25 100 g mol^-1 by fine-tuning reaction time, temperature, and decreasing catalyst and initiator concentrations. Also, different catalysts for polymerization are tested. The resulting material shows melting temperatures of ≈55 °C and decomposition temperatures of 354 °C or higher. Processing via melt pressing or casting turned out to be quite difficult due to the polymer's brittleness. Furthermore, regarding biomedical applications, blends of PEA with polyethylene glycol were successfully prepared, yielding a more hydrophilic material.

Polyamides containing a biorenewable aromatic monomer based on coumalate esters: from synthesis to evaluation of the thermal and mechanical properties

A new biobased alternative for terephthalic acid (TPA) in (semi-)aromatic polyamides is proposed, namely 4-carboxybenzene propionic acid (4CBPA).

Poly(ε-lysine) and its derivatives via ring-opening polymerization of biorenewable cyclic lysine

Minireview focused on poly(ε-lysine) and its derivatives via ring-opening polymerization of biorenewable cyclic lysine.

Biobased chiral semi-crystalline or amorphous high-performance polyamides and their scalable stereoselective synthesis

The use of renewable feedstock is one of the twelve key principles of sustainable chemistry. Unfortunately, bio-based compounds often suffer from high production cost and low performance. To fully tap the potential of natural compounds it is important to utilize their functionalities that could make them superior compared to fossil-based resources. Here we show the conversion of (+)-3-carene, a by-product of the cellulose industry into ε-lactams from which polyamides. The lactams are selectively prepared in two diastereomeric configurations, leading to semi-crystalline or amorphous, transparent polymers that can compete with the thermal properties of commercial high-performance polyamides. Copolyamides with caprolactam and laurolactam exhibit an increased glass transition and amorphicity compared to the homopolyamides, potentially broadening the scope of standard polyamides. A four-step one-vessel monomer synthesis, applying chemo-enzymatic catalysis for the initial oxidation step, is established. The great potential of the polyamides is outlined.

From terpenes to sustainable and functional polymers

The use of renewable terpene-based monomers for the preparation of sustainable functional polymers is highlighted.

New Bio-Polyamides from Terpenes: α-Pinene and (+)-3-Carene as Valuable Resources for Lactam Production

The synthesis and polymerization of two β-lactams and two ε-lactams derived from the terpenes α-pinene and (+)-3-carene are reported. The new biopolymers can be considered as polyamide 2 (PA2) and polyamide 6 (PA6)-types with aliphatic stereoregular side chains, which lead to remarkable new properties. The macromolecules are investigated by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and infrared (IR). The (+)-3-carene-derived PA6-type is of particular interest, since it reaches a molecular weight of over 30 kDa, which is the highest value for lactam-based polyamides derived from terpenes reported to date. Additionally, a glass transition temperature (T_g ) of 120 °C is observed, surpassing the glass transition temperature of PA6 by 60 °C. The absence of a melting point (T_m ) indicates high amorphicity, another novelty for terpene-based polyamides, which might give transparent bio-polyamides access to new fields of application.

Radical polymerization of ‘dehydroaspirin’ with the formation of a hemiacetal ester skeleton: a hint for recyclable vinyl polymers

A recyclable vinyl polymer was developed via radical polymerization of ‘dehydroaspirin’ derived from acetylsalicylic acid.

Biochemical Characterization of β-Amino Acid Incorporation in Fluvirucin B2 Biosynthesis

Naturally occurring lactams, such as the polyketide-derived macrolactams, provide a diverse class of natural products that could enhance existing chemically produced lactams. Although β-amino acid loading in the fluvirucin B₂ polyketide pathway was proposed by a previously identified putative biosynthetic gene cluster, biochemical characterization of the complete loading enzymes has not been described. Here we elucidate the complete biosynthetic pathway of the β-amino acid loading pathway in fluvirucin B₂ biosynthesis. We demonstrate the promiscuity of the loading pathway to utilize a range of amino acids and further illustrate the ability to introduce non-native acyl transferases to selectively transfer β-amino acids onto a polyketide synthase (PKS) loading platform. The results presented here provide a detailed biochemical description of β-amino acid selection and will further aid in future efforts to develop engineered lactam-producing PKS platforms.

Sustainable terpene-based polyamides via anionic polymerization of a pinene-derived lactam

A sustainable lactam, which is derived from the renewable terpene β-pinene, is converted to polyamides with prosperous thermal properties via a convenient anionic ring-opening polymerization (ROP).