Acidolysis is emerging as a promising method for recycling polyurethane foam (PUF) waste. Here, we present highly efficient acidolysis of PUFs with adipic acid (AA) by heating the reaction mixtures with microwaves. The influence of experimental conditions, such as reaction temperature, time, and amount of the degradation reagent, on the polyol functionality, molecular weight characteristics, the presence of side products, and the degree of degradation of the remaining PUF hard segments was studied by matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS), nuclear magnetic resonance (NMR), size-exclusion chromatography (SEC) coupled to a multidetection system, and Fourier transform infrared (FT-IR) spectroscopy. The purified recycled polyols were used for the synthesis of flexible PUFs. The morphology and mechanical properties of the PUFs show that the degree of functionalization of the polyol by the carboxylic end groups, which is higher for larger amounts of AA used to degrade the PUFs, significantly affects the quality and performance of the flexible PUFs from the recycled polyols.

Organocatalyzed ring-opening polymerization (ROP) of ε-caprolactone (CL) and 4,4′-bioxepanyl-7,7′-dione as a bislactone cross-linker was performed within the oil-in-oil high internal phase emulsions (HIPEs) at 50 °C. In this way, the cross-linked poly(ε-caprolactone) (PCL) polyHIPE foams of ∼85% porosity were synthesized. Thermomechanical properties of the prepared poly-HIPEs were studied and proved to greatly depend on a degree of PCL cross-linking. The melting and crystallization temperatures as well as the degree of crystallinity of PCL polyHIPE foams decrease with an increasing cross-linking degree. Semi-crystalline polyHIPEs demonstrate shape memory behavior with excellent shape fixity and shape recovery. At an appropriate degree of PCL crosslinking, the polyHIPE temporary shape can be fixed at room temperature, while a transition to the permanent shape occurs upon heating at 40 °C. Moreover, a two-way shape memory behavior of the PCL polyHIPEs under constant stress was observed.

Ring-opening polymerization of N-carboxyanhydrides was performed in oil-in-oil high internal phase emulsion to obtain well-defined macroporous synthetic polypeptides.

In this work, biodegradable macroporous stimuli-responsive polypeptide hydrogels based on L-glutamic acid (Glu) and its copolymers with equimolar amounts of L-phenylalanine (Phe) or L-lysine (Lys) were prepared by deprotection of the corresponding organogels under acidic conditions. The organogels were synthesized by ring-opening polymerization of Ncarboxyanhydride (NCA) derivatives of the corresponding α-amino acids in oil-in-oil high-internal phase emulsions (HIPEs) using the di-NCA derivative of L-cystine as a cross-linker. The organogels exhibit the typical interconnected porous polyHIPE morphology, which is completely preserved in the hydrogels after removal of the protecting groups of the Glu and Lys repeating units. The pHdependent behavior and mechanical properties of the obtained hydrogels were studied in buffer solutions with different pH values. At pH 7.5, P(Glu) and P(Glu-co-Phe) can be compressed to half their original height and both return to their initial state after unloading. By lowering the pH to 5.5, P(Glu) remains soft, while P(Glu-co-Phe) already becomes much stiffer. In contrast, for the P(Glu-co-Lys) hydrogel, high buffer uptake was observed only at high or low pH values, whereas at intermediate pH values, the low buffer uptake and the impaired ability to return to the original height are attributed to the attractive ionic interaction between the oppositely charged side groups. We have shown that by tuning the chemical composition of the polypeptides, the uptake, in vitro enzymatic degradation, and compression behavior of the hydrogels can be modulated.

Semi-interpenetrating polymer networks (semi-IPNs) were prepared by in situ simultaneous orthogonal polymerizations, where the linear poly(ε-caprolactone) (PCL) was synthesized by ring-opening polymerization of ε-caprolactone and the poly(styrene- co -divinylbenzene) (PS) network was formed by free-radical polymerization of styrene/divinylbenzene. Semi-IPNs were used as the precursors for the preparation of porous PS monoliths. To this end, the PCL domains were selectively removed by hydrolysis under basic conditions. By changing the amount of organocatalyst used for the ring-opening polymerization of ε-caprolactone, the relative polymerization kinetics of both monomers was varied, which has a pronounced effect on the morphology of thus-obtained PS frameworks.