Reversible Lamellar Periodic Structures Induced by Sequential Crystallization/Melting in PBS-co-PCL Multiblock Copolymer

Upcycling poly(succinates) with amines to N-substituted succinimides over succinimide anion-based ionic liquids

The chemical transformation of waste polymers into value-added chemicals is of significance for circular economy and sustainable development. Herein, we report upcycling poly(succinates) (PSS) with amines into N-substituted succinimides over succinimide anion-based ionic liquids (ILs, e.g, 1,8-diazabicyclo[5.4.0]undec-7-ene succinimide, [HDBU][Suc]). Assisted with H2O, [HDBU][Suc]) showed the best performance, which could achieve complete transformation of a series of PSS into succinimide derivatives and corresponding diols under mild and metal-free conditions. Mechanism investigation indicates that the cation-anion confined hydrogen-bonding interactions among IL, H2O, ester group, and amino/amide groups, strengthens nucleophilicity of the N atoms in amino/amide groups, and improves electrophilicity of carbonyl C atom in ester group. The attack of the amino/amide N atom on carbonyl C of ester group results in cleavage of carbonyl C-O bond in polyester and formation of amide group. This strategy is also effective for aminolysis of poly(trimethylene glutarate) to glutarimides, and poly(1,4-butylene adipate) to caprolactone diimides.

Segmental mobility in sustainable copolymers based on poly(lactic acid) blocks built onto poly(butylene succinate) in situ

Two series of newly synthesized sustainable block copolymers based on poly(butylene succinate) (PBSu) and polylactide (PLA) were studied. The copolymers were synthesized by a ring-opening polymerization of PLA in the presence of two initial PBSu of low molar mass. We focused on the effects of the PBSu/PLA ratio (1/99 up to 15/85), chain length and initial PBSu length on the final thermal transitions in the copolymers with an emphasis on molecular mobility/dynamics and subsequently on crystallization. Both aspects are considered relevant to the final materials performance, as well as facilitation of polymer renewability. Calorimetry and dielectric spectroscopy were the main investigation tools. In the amorphous state (i.e., in which the direct effects of copolymer structure are assessable), the segmental mobility of neat PLA was significantly faster in the copolymers. Segmental mobility was monitored via the decrease in the calorimetric and dielectric (α relaxation) glass-transition temperatures, Tg and Tg,diel, respectively. The effect was systematic with an increase in the PBSu/PLA ratio, and was rationalized through the plasticizing role of PBSu (low-Tg component) and facilitated also by the simultaneous lowering of the chain length in the copolymers. Dielectric spectroscopy allowed evaluation of the dynamical fragility (cooperativity) of chains, which was strongly suppressed in the copolymers. This finding suggested an increase in free volume or a gradual increase of interchain distances. This phenomenon could favor the natural enzymatic degradation of the systems (compostability), which is limited in neat PLA. We recorded enhancement of nucleation and the crystalline fraction in the copolymers that was likely connected with faster chain diffusion. Further lowering of the Tg with the implementation of crystallization was noted (which seemed a controversial effect) but which indicated crystallization-induced phase separation.

Robust, Fully Biodegradable Films of Polyesters Realized by In Situ Formation of an Interconnected Multi-Nanolayer Structure under Extensional Flow

Multilayer structures are not only applied to manipulate properties of synthetic polymer materials such as rainbow films and barrier films but also widely discovered in natural materials like nacre. In this work, in situ formation of an interconnected multi-nanolayer (IMN) structure in poly(butylene adipate-co-terephthalate) (PBAT)/poly(butylene succinate) (PBS) cocontinuous blends is designed by an extensional flow field during a "casting-thermal stretching" process, combining the properties of two components to a large extent. Hierarchical structures including phase morphology, crystal structure, and lamellar crystals in IMN films have been revealed, which clearly identifies the crucial role of extensional flow. The oriented PBAT phase in the IMN structure can be beneficial to the epitaxial growth of PBS crystals onto the PBAT nanolayers, thus improving interfacial adhesions. Furthermore, intense extensional stress can also promote crystallinity and thicken the lamellar structure. Given such distinct features in the fully biodegradable films, a simultaneous enhancement in tear strength, tensile strength, and puncture resistance has been achieved. To the best of our knowledge, the tear strength of IMN films about 285.9 kN/m is the highest level in the previous works of this system. Moreover, the proposed fabrication way of the IMN structure is facile and scalable, which is highly expected to be an efficient strategy for development of structured biodegradable polymers with excellent comprehensive properties.

High Mechanical Properties of Stretching Oriented Poly(butylene succinate) with Two-Step Chain Extension

The structure, morphology, fracture toughness and flaw sensitivity length scale of chain-extended poly(butylene succinate) with various pre-stretch ratios were studied. PBS modification adopted from a multifunctional, commercially available chain-extension containing nine epoxy groups (ADR9) as the first step chain extension and hydroxyl addition modified dioxazoline (BOZ) as the second step. Time-temperature superposition (TTS) studies show that the viscosity increased sharply and the degree of molecular branching increased. Fourier transform infrared spectroscopy (FT-IR) confirm successful chain extension reactions. The orientation of the polymer in the pre-stretch state is such that spherulites deformation along the stretching direction was observed by polarized light optical microscopy (PLOM). The fracture toughness of sample (λ_fix = 5) is Γ ≈ 10⁶ J m^-2 and its critical flaw sensitivity length scale is Γ/W_c ≈ 0.01 m, approximately 5 times higher than PBS without chain-extension (Γ ≈ 2 × 10⁵ J m^-2 and Γ/W_c ≈ 0.002 m, respectively). The notch sensitivity of chain-extended PBS is significantly reduced, which is due to the orientation of spherulites more effectively preventing crack propagation. The principle can be generalized to other high toughness material systems.

Nucleobase-monofunctionalized supramolecular poly(l-lactide): controlled synthesis, competitive crystallization, and structural organization

Controlled synthesis, competitive crystallization, and crystallization-driven structural organization of thymine-monofunctionalized supramolecular poly(l-lactide).

Synthesis of multisegmented block copolymer by Friedel–Crafts hydroxyalkylation polymerization

Friedel–Crafts (FC) polycondensation of 1,4-dimethoxybenzene with 4-substituted benzaldehyde species was used to prepare telechelic oligomers and high-molar-mass multisegmented block copolymers.

Tailoring the degradation and mechanical properties of poly(ε-caprolactone) incorporating functional ε-caprolactone-based copolymers

Functional block copolymers (COPs) were synthesized through the ring-opening polymerization, and the effects of COPs on the hydrolytic & oxidative degradation and mechanical properties of PCL/COP composites were studied.