Dibutyl phosphate catalyzed commercial relevant ring-opening polymerizations to bio-based polyesters

Sustainable Bio-Based UV-Cured Epoxy Vitrimer from Castor Oil

Vitrimers brought new properties in thermosets by allowing their reshaping, self-healing, reprocessing, and network rearrangement without changing structural integrity. In this study, epoxidized castor oil (ECO) was successfully used for the straightforward synthesis of a bio-based solvent-free vitrimer. The synthesis was based on a UV-curing process, which proceeded at low temperatures in the absence of any solvents, and within a short time. Real time Fourier-transformed infrared spectroscopy and photo-DSC were exploited to monitor the cationic photocurable process. The UV-cured polymer networks were able to efficiently undergo thermo-activated bond exchange reactions due to the presence of dibutyl phosphate as a transesterification catalyst. Mechanical properties, thermal resistance, glass transition temperature, and stress relaxation were investigated as a function of the amount of transesterification catalyst. Mechanical properties were determined by both DMTA and tensile tests. Glass transition temperature (T_g) was evaluated by DMTA. Thermal stability was assessed by thermogravimetric analysis, whilst vitrimeric properties were studied by stress relaxation experiments. Overall, the ECO-based vitrimer showed high thermal resistance (up to 200 °C) and good mechanical properties (elastic modulus of about 10 MPa) and can therefore be considered as a promising starting point for obtaining more sustainable vitrimers.

Cyclodextrin-Oligocaprolactone Derivatives—Synthesis and Advanced Structural Characterization by MALDI Mass Spectrometry

Cyclodextrins have previously been proven to be active in the catalysis of cyclic ester ring-opening reactions, hypothetically in a similar way to lipase-catalyzed reactions. However, the way they act remains unclear. Here, we focus on β-cyclodextrin’s involvement in the synthesis and characterization of β-cyclodextrin-oligocaprolactone (CDCL) products obtained via the organo-catalyzed ring-opening of ε-caprolactone. Previously, bulk or supercritical carbon dioxide polymerizations has led to inhomogeneous products. Our approach consists of solution polymerization (dimethyl sulfoxide and dimethylformamide) to obtain homogeneous CDCL derivatives with four monomer units on average. Oligomerization kinetics, performed by a matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) optimized method in tandem with 1H NMR, revealed that monomer conversion occurs in two stages: first, the monomer is rapidly attached to the secondary OH groups of β-cyclodextrin and, secondly, the monomer conversion is slower with attachment to the primary OH groups. MALDI MS was further employed for the measurement of the ring-opening kinetics to establish the influence of the solvents as well as the effect of organocatalysts (4-dimethylaminopyridine and (–)-sparteine). Additionally, the mass spectrometry structural evaluation was further enhanced by fragmentation studies which confirmed the attachment of oligoesters to the cyclodextrin and the cleavage of dimethylformamide amide bonds during the ring-opening process.

Activated Monomer Mechanism (AMM) in Cationic Ring-Opening Polymerization. The Origin of the AMM and Further Development in Polymerization of Cyclic Esters

The origin of the activated monomer mechanism (AMM) in cationic ring-opening polymerization (CROP) is described first. Then, conditions leading to the active chain end (ACE) mechanism and AMM are compared, as well as methods allowing to distinguish between these two mechanisms. These methods are based on the "ion trapping" of the active ionic species using highly basic phosphines or by comparing ACE and AMM kinetics of polymerization. The major factors deciding on the actual mechanism include: basicity of the monomers, ring strain, and the presence of the protic additives in the reaction system. These factors are tabulated for major cyclic ethers and cyclic esters. The historically evolved subsequent steps of AMM in the polymerization of cyclic esters are described: from the first experiments with trialkyloxonium salts, precursors of protonic acids, and added alcohols, via HCl as catalyst, and then CF₃S(═O)₂OH (polymerizing lactides) to the most popular derivatives of phosphoric acid, like diphenyl phosphate. Conditions allowing to synthesize poly(ε-caprolactone) (PCL), according to AMM-CROP, with molar mass up to 10⁵ g·mol^-1, are described as well as methods to polymerize CL with a protic initiator and acidic catalyst in one molecule. Then various methods enhancing the activity of the polymerizing systems are compared, based predominantly on hydrogen bonding, either to the polymer active end group (usually the hydroxyl group) or to the acid anion. Finally, kinetic equations for ACE and AMM are compared, and it is shown that the majority of the AMM-CROP systems, mostly studied for CL and lactides, proceed as living/controlled polymerizations. Since polymer end groups are hydroxyl groups, then, as it was shown in several papers, any initiator with one or many hydroxyl groups provides macromolecules with the corresponding architecture. The papers on synthetic methods are not discussed in detail.

Synthesis, Microstructure, and Properties of High-Molar-Mass Polyglycolide Copolymers with Isolated Methyl Defects

An efficient, fast, and reliable method for the synthesis of high-molar-mass polyglycolide (PGA) in bulk using bismuth (III) subsalicylate through ring-opening transesterification polymerization is described. The difference between the crystallization (T_c ≈ 180 °C)/degradation (T_d ≈ 245 °C) temperatures and the melting temperature (T_m ≈ 222 °C) significantly affects the ability to melt-process PGA homopolymer. To expand these windows, the effect of copolymer microstructure differences through incorporation of methyl groups in pairs using lactide or isolated using methyl glycolide (≤10% methyl) as comonomers on the thermal, mechanical, and barrier properties were studied. Structures of copolymers were characterized by nuclear magnetic resonance (¹H and ¹³C NMR) spectroscopies. Films of copolymers were obtained, and the microstructural and physical properties were analyzed. PGA homopolymers exhibited an approximately 30 °C difference between T_m and T_c, which increased to 68 °C by incorporating up to 10% methyl groups in the chain while maintaining overall thermal stability. Oxygen and water vapor permeation values of solvent-cast nonoriented films of PGA homopolymers were found to be 4.6 cc·mil·m^-2·d^-1·atm^-1 and 2.6 g·mil·m^-2·d^-1·atm^-1, respectively. Different methyl distributions in the copolymer sequence, provided through either lactide or methyl glycolide, affected the resulting gas barrier properties. At 10% methyl insertion, using lactide as a comonomer significantly increased both O₂ (32 cc·mil·m^-2·d^-1·atm^-1) and water vapor (12 g·mil·m^-2·d^-1·atm^-1) permeation. However, when methyl glycolide was utilized for methyl insertion at 10% Me content, excellent barrier properties for both O₂ (2.9 cc·mil·m^-2·d^-1·atm^-1) and water vapor (1.0 g·mil·m^-2·d^-1·atm^-1) were achieved.

Strategies for the synthesis of block copolymers with biodegradable polyester segments

Oxygenated block copolymers with biodegradable polyester segments can be prepared in one-pot through sequential or simultaneous addition of monomers. This review highlights the state of the art in this area.

Poly(trimethylene carbonate-co-valerolactone) copolymers are materials with tailorable properties: from soft to thermoplastic elastomers

Aliphatic poly(ester-carbonates) are receiving extensive research attention as tailorable materials suitable for multiple applications from tissue engineering and 3D scaffold printing to drug delivery. Thus, simple reliable procedures for producing easily tailorable poly(ester-carbonates) without metal residues are continuously sought after. In this work, we report on one-pot synthesis of random copolymers of TMC and δ-VL using metal-free biocompatible 1,5,7-triazabicyclo[4.4.0]dec-5-ene as a catalyst and benzyl alcohol and poly(ethylene oxide) as initiators. Random poly(ester-carbonates) with TMC : VL unit ratios ranging from 80 : 20 to 20 : 80 were synthesized via ring-opening polymerization while displaying excellent agreement of comonomers' ratios in the feed and copolymer chains. The copolymers' supramolecular structure, thermal and mechanical properties were thoroughly analyzed by various methods. The obtained results clearly indicated that the physicochemical properties can be controlled simply by varying the ratio of comonomers and the length of segments in the copolymer chain. Several copolymers exhibited behavior of thermoplastic elastomers with the most promising one exhibiting a 2200% increase in elongation at break compared to the poly(valerolactone) homopolymer while retaining tensile strength and Young's modulus suitable for biomedical applications. Overall, our work contributed to widening the portfolio of tailorable copolymers for specialized bioapplications and possibly paving a way for the use of more sustainable polymers in the biomedical field.