High-Purity Discrete PEG-Oligomer Crystals Allow Structural Insight

Catalyst-Free Synthesis of Covalent Adaptable Network (CAN) Polyurethanes from Lignin with Editable Shape Memory Properties

Here a new strategy of catalyst-free direct synthesis of covalent adaptable network polyurethanes (LPUs) from lignin with editable shape memory effect is reported. Using unmodified lignin, PEG, and isocyanate under the condition of the isocyanate index less than 1.0 (NCO/OH<1.0), a variety of LPUs are obtained. When NCO/OH=0.8, a stable cross-linked network can be formed (ex. the gel content of LPU50-0.8 was 98±0.3 %). The activation energy (E_a ) value of LPUs is similar to that of polyhydroxyurethanes (PHUs), at around 110 kJ mol^-1 . With an increase of lignin content, the LPUs show a transition from ductile fracture to brittle fracture mode. And the mechanical properties of LPUs are significantly enhanced after extrusion processing, with the maximum modulus reaching 649±26 MPa and the maximum toughness up to 9927±111 kJ m^-3 . The improvement in mechanical properties is due to the homogenization of complex cross-linked network under the powerful external force of the extruder and the lignin that originally was free in the system participated in the exchange reactions. Moreover, LPUs can also be prepared continuously in one step by using an extruder as the reactor. In addition, LPU50-0.8 has an editable shape memory effect. This study develops a novel method for the synthesis of LPU from lignin with NCO/OH<1.0, showcasing new possibilities for value-added utilization of lignin, and expands the bio-based products portfolio from biomass feedstock to help meet future green manufacturing demands.

Programmed and Sequential Disassembly of Multi-responsive Supramolecular Protein Nanoassemblies: A Detailed Mechanistic Investigation

The rational design of a multi-responsive protein-based supramolecular system that can predictably respond to more than one stimulus remains an essential but highly challenging goal in biomolecular engineering. Herein, we report a novel chemical method for the construction of multi-responsive supramolecular nanoassemblies using custom-designed facially amphiphilic monodisperse protein-dendron bioconjugates. The macromolecular synthons contain a globular hydrophilic protein domain site-specifically conjugated to photo-responsive hydrophobic benzyl-ether dendrons of different generations through oligo(ethylene glycol) linkers of defined length. The size of the protein nanoassemblies can be systematically tuned by choosing an appropriate dendron or linker of defined length. Exposure of protein nanoassemblies to light results in partial rather than complete disassembly of the complex. The newly formed protein nanoparticle no longer responds to light but could be disassembled into constitutive monomers under acidic conditions or by further treatment with a small molecule. More interestingly, the distribution ratio of the assembled versus disassembled states of protein nanoassemblies after photochemical reaction does not depend on dendron generation, the nature of the linker functionality or the identity of the protein, but is heavily influenced by the linker length. In sum, this work discloses a new chemical method for the rational design of a monodisperse multi-responsive protein-based supramolecular system with exquisite control over the disassembly process.

Solid Phase Stepwise Synthesis of Polyethylene Glycols

Polyethylene glycol (PEG) and derivatives with eight and twelve ethylene glycol units were synthesized by stepwise addition of tetraethylene glycol monomers on a polystyrene solid support. The monomer contains a tosyl group at one end and a dimethoxytrityl group at the other. The Wang resin, which contains the 4-benzyloxy benzyl alcohol function, was used as the support. The synthetic cycle consists of deprotonation, Williamson ether formation (coupling), and detritylation. Cleavage of PEGs from solid support was achieved with trifluoroacetic acid. The synthesis including monomer synthesis was entirely chromatography-free. PEG products including those with different functionalities at the two termini were obtained in high yields. The products were analyzed with ESI and MALDI-TOF MS and were found close to monodispersity.

Effect of soft segment molecular weight on the glass transition, crystallinity, molecular mobility and segmental dynamics of poly(ethylene oxide) based poly(urethane–urea) copolymers

The effect of poly(ethylene oxide) (PEO) soft segment molecular weight (M_n= 2000, 4600, 8000 g mol⁻¹) molecular mobility and segmental dynamics of a series of polyurethane–urea copolymers (PU) was investigated by dielectric relaxation spectroscopy.

Beyond PEG2000: synthesis and functionalisation of monodisperse PEGylated homostars and clickable bivalent polyethyleneglycols

A new strategy to access highly monodisperse, heterobifunctional linear polyethylenglycols (PEGs) has been designed. This was built around unidirectional, iterative chain extension of a 3-arm PEG homostar. A mono-(4,4'-dimethoxytriphenylmethyl) octagol building block, DmtrO-EG8-OH, was constructed from tetragol. After six rounds of chain extension, the monodisperse homostar reached the unprecedented length of 56 monomers per arm (PEG2500). The unique architecture of the synthetic platform greatly assisted in facilitating and monitoring reaction completion, overcoming kinetic limitations, chromatographic purification of intermediates, and analytical assays. After chain terminal derivatisation, mild hydrogenolytic cleavage of the homostar hub provided heterobifunctional linear EG56 chains with a hydroxyl at one end, and either a toluene sulfonate, or a tert-butyl carboxylate ester at the other. A range of heterobifunctional, monodisperse PEGs was then prepared having useful cross-linking functionalities (-OH, -COOH, -NH2, -N3) at both ends. A rapid preparation of polydisperse PEG homostars, free of multiply cross-linked chains, is also described. The above approach should be extendable to other high value oligomers and polymers.

Synthesis of poly(ethylene oxide) approaching monodispersity

Polydispersity in polymers hinders fundamental understanding of their structure-property relationships and prevents them from being used in fields like medicine, where polydispersity affects biological activity. The polydispersity of relatively short-chain poly(ethylene oxide) [(CH2CH2O2)n; PEO] affects its biological activity, for example, the toxicity and efficacy of PEOylated drugs. As a result, there have been intensive efforts to reduce the dispersity as much as possible (truly monodispersed materials are not possible). Here we report a synthetic procedure that leads to an unprecedented low level of dispersity. We also show for the first time that it is possible to discriminate between PEOs differing in only 1 ethylene oxide (EO) unit, essential in order to verify the exceptionally low levels of dispersity achieved here. It is anticipated that the synthesis of poly(ethylene oxide) approaching monodispersity will be of value in many fields where the applications are sensitive to the distribution of molar mass.

A structured monodisperse PEG for the effective suppression of protein aggregation

Part of the solution: A PEG with a discrete triangular structure exhibits hydrophilicity/hydrophobicity switching upon increasing temperatures, and suppresses the thermal aggregation of lysozyme to retain nearly 80 % of the enzymatic activity. CD and NMR spectroscopic studies revealed that, with the structured PEG, the higher-order structures of lysozyme persist at high temperature, and the native conformation is recovered after cooling.