A comparative study of oxygen diffusion in PET and PEF using molecular modelling:Computational Insights into the Mechanism for Gas Transport in Bulk Polymer Systems

Bio-derived polyethylene furanoate (PEF) has recently gained attention as a sustainable alternative to polyethylene terephthalate (PET), amidst environmental concerns over fossil fuel depletion. Herein, we outline a computational approach to investigate the tenfold difference in barrier properties between the two materials, using a statistically robust methodology to predict diffusion coefficients from molecular dynamics simulation. Oxygen diffusion was predicted to a high level of accuracy, at 3.24 × 10–8 and 2.88 × 10–9 cm2 s–1 for PET and PEF, respectively (Dexperimental = 1.16 × 10–8 and 1.04 × 10–9 cm2 s–1). Simulations quantifiably demonstrated the contributions of ring-flipping chain dynamics on oxygen diffusion, and novel Monte Carlo techniques revealed atomistic insights into the mechanism by which this occurs. Areas of accessible volume within the polymer matrix were seen to converge to facilitate lateral oxygen displacement. Infrequent convergences in PEF, due to subdued polymer chain dynamics and higher system density, accounted for the slower oxygen diffusion relative to PET

Xylose-Based Polyethers and Polyesters Via ADMET Polymerization toward Polyethylene-Like Materials:ACS Applied Polymer Materials

One of the challenges of developing bioderived polymers is to obtain materials with competitive properties. This study investigates the structure-properties relationships of polyesters and polyethers that can be derived from d-xylose through metathesis polymerization, in order to produce bioderived plastic materials that are sourced from sustainable feedstocks and whose properties can compete with those of polyolefins such as polyethylene. Bicyclic diol 1,2-O-isopropylidene-α-d-xylofuranose was coupled with ω-unsaturated fatty acids and alcohols of different chain lengths (C11, C5, C3), and the resulting α,ω-unsaturated esters and ethers polymerized via an acyclic diene metathesis (ADMET) polymerization using a commercial Grubbs second-generation catalyst, obtaining polymers with Mn up to 63.0 kg mol–1. Glass transition temperatures (Tg) decreased linearly with increasing chain length and were lower for polyethers (−32 to 14 °C) compared to polyesters (−14 to 45 °C). ADMET polymers could be modified postpolymerization by reacting their internal carbon–carbon double bonds. Thiol–ene reaction with methyl thioglycolate lowered the Tg while allowing insertion of additional functional groups. Alkene hydrogenation turned the polyester and polyether with C20 hydrocarbon linkers into semicrystalline polymers with Tm ≈ 50 °C. The latter, when cast into films, displayed remarkable polyethylene-like properties. Hot-pressed films proved ductile materials (Young modulus Ey 60–110 MPa, elongation at break εb 670–1000%, ultimate tensile strength σb 8–10 MPa), while uniaxially oriented films proved very strong yet flexible materials (Ey 190–200 MPa, εb 160–350%, σb 43–66 MPa). Gas barrier properties were comparable to those of commercial polyolefins. Polyethers were resistant to hydrolysis, while polyesters depolymerized under alkaline conditions

Chemoselective Lactonization of Renewable Succinic Acid with Heterogeneous Nanoparticle Catalysts

The production of chemicals from renewable resources, resulting in the establishment of biorefineries, represents a challenge of increasing importance. Here we show that succinic acid, a C4 compound increasingly being produced on a kiloton scale by the microbial fermentation of sugar, can be selectively converted into a variety of important chemicals. Optimal performance in terms of activity, selectivity and reusability is observed with Al2O3-supported Pd nanoparticles, which mediate the selective, hydrogenative lactonization of succinic acid to γ-butyrolactone at >90% selectivity, even at high levels of conversion (<70%). Through a variety of kinetic, spectroscopic and microscopic studies, preliminary structure–activity relationships are presented, and the roles of the reaction conditions, the choice of metal and the nature of the support in terms of guiding the overall process selectivity, are also investigated. On a broader level, these studies demonstrate the suitability of succinic acid to act as a platform for renewable chemical production in future biorefineries

Epoxy-functionalised 4-vinylguaiacol for the synthesis of bio-based, degradable star polymers via a RAFT/ROCOP strategy

An epoxy derivative of a naturally occuring vinylphenolic compound, 4-vinylguaiacol (4VGEP), was used for the synthesis of a well-defined (Mw/Mn = 1.08–1.14), bio-based styrene-type polymer. Block copolymers of 4VGEP with styrene and diethylacrylamide were also prepared and used as macro-monomers in metal, and metal-free, ring-opening copolymerisation (ROCOP) with cis-4-cyclohexene-1,2-dicarboxylic anhydride to form ester cross-linked star polymers in high yields (82–90%), with narrow dispersity (Mw/Mn = 1.27–1.40). Finally, the selective degradation of the ester core of the styrene-based star was achieved under acidic conditions

Polymer-supported metal catalysts for the heterogeneous polymerisation of lactones

A series of metal complexes were immobilised onto an inert poly(styrene) (PS) support and utilised in the solvent free ring-opening polymerisation (ROP) of various lactones. PS-LHZnOAc, PS-LHSnOct and PS-LClSnOct were identified as the most successful heterogeneous catalysts for the ROP of L-lactide. Investigations by in situ ATR-FT-IR revealed conversions reaching ca. 90% in 6, 2.3 hours and 55 minutes, respectively, with excellent molecular weight control and dispersities (ĐM 1.15–1.17). Catalyst loadings as low as 15 ppm metal and TOF values of up to 810 h−1 could also be achieved. Higher molecular weights could be targeted (ca. 35 kDa) whilst maintaining low dispersities in comparison to the industrial standard. Catalyst reuse was also possible, with up to 7 reuse cycles, albeit accompanied by a progressive reduction in conversion. Energy-Dispersive X-ray (EDX) spectroscopy and Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) showed low metal content in the unpurified polymer (as low as 335 ppm, similar to what is found in polymer purified by classical methods), suggesting these systems as promising reusable catalysts for the industrial production of metal-free renewable polymers

Aluminum complexes of mono-pyrrolidine ligands for the con-trolled ring opening polymerization of lactide

In this paper we report the full characterization (solution-state NMR spectroscopy and solid-state structures) of a series of Al­(III) half-salan complexes and their exploitation for the ring-opening polymerization of <i>rac</i>-lactide. Depending on the ligand employed and stoichiometry of the complexation, structures of the form Al­(<b>X</b>)₂Me or Al­(<b>X</b>)­Me₂ were isolated. Interestingly Al­(<b>2</b>)₂Me and Al­(<b>2</b>)­Me₂ produce PLA with a strong isotactic bias (<i>P</i>_m up to 0.80), whereas all other complexes produced atactic PLA. This is in contrast to recent studies on similar salan ligand systems. PLAs with predictable molecular weights and narrow distributions were achieved. The results are discussed in terms of steric and electronic properties of the ligands