Processing additives are a special group of chemicals included in rubber formulations to facilitate the flowability of the resultant compounds. Their addition generally affects the cured properties of the subsequent rubber composites, and fine-tuning of the compound formulation is therefore required. In this work, an attempt has been made to address this issue through the preparation of new bio-based processing additives capable of promoting the mixing of the rubber compound while at the same time enhancing mechanical properties following curing. A significant decrease in the mixing energy at the first stage of mixing (~10%) has been observed by substituting only a small percentage of the conventional petroleum-derived process oil with aminated epoxidized soybean oil. Concomitantly, it is found that this aminated epoxidized soybean oil promotes rubber curing and increases the tensile strength of the final composite by ~20% compared to the control.

While polyhydroxyurethanes (PHUs) have been offered as "greener" alternatives to conventional polyurethanes (PUs) for ∼15 years, their low molecular weights, high hydrophilicity, and water uptake limit practical utility. In this study, we directly address these limitations by coupling pendant hydroxyl groups in tailored thermoplastic PHUs with 1,4-phenylenediboronic acid to form tough, robust PHU vitrimers, whose enhanced viscoelastic properties and reduced moisture sensitivity significantly differentiate them from existing linear and vitrimeric PHUs. Three families of PHU vitrimers incorporate either dioxaborolane or dioxazaborocane moieties based on aromatic or aliphatic amines. A fundamental comparison of structure-property relationships confirmed that dioxazaborocanes stabilized by aliphatic nitrogen atoms improve thermal and hydrolytic stability, as demonstrated through direct observations via solid-state NMR. In contrast to aromatic nitrogens, aliphatic nitrogens form N→B dative bonds, reducing chain mobility and increasing T _g. This significantly enhances mechanical performance (+65-170% tensile strength, +125-300% break strain, ∼4-11× increase in tensile toughness) vs the parent PHUs and allows the resulting vitrimers to maintain their viscoelastic properties even at elevated humidity levels. Moreover, these N-stabilized dioxazaborocane PHU vitrimers are readily recyclable, both mechanically (up to at least 3×) and chemically (using ethanol/NaOH_aq), without loss of performance.

Conventional methods for synthesizing thermoplastic polyurethanes (TPUs) typically rely on isocyanates and tin-based catalysts, both of which pose significant environmental and safety risks. To mitigate these issues, alternative routes for synthesizing nonisocyanate polyurethanes (NIPUs) have been explored since the 1980s. However, most reported approaches yield polymers with molecular weights below 35 kg/mol and only a few exceptions reaching 50–70 kg/mol, often requiring oligomeric monomers or postmodification. This limitation has been a major barrier to the broader application and production of NIPUs. In this study, we demonstrate a direct polyaddition strategy for synthesizing high-molecular-weight poly(hydroxyurethane)s (PHUs, a subclass of NIPUs) from low-mass difunctional monomers without relying on macromonomers, oligomers, catalysts, or postcondensation/modification steps. The key to this achievement was the rational design of the monomers. The reactivity of cyclic carbonates was enhanced by incorporating aromatic rings into the structure of 7,7,7′,7′-tetramethyl-6,6′,7,7′-tetrahydro-5,5′-spirobi[indeno[5,6-d][1,3]dioxole]-2,2′-dione. Model reactions of this bis(cyclic carbonate) with secondary amines revealed that steric and electronic effects are decisive with alicyclic secondary amines markedly outperforming their linear analogues. Further pairing of activated aromatic bis(cyclic carbonate) with alicyclic secondary diamines enabled nearly quantitative monomer conversion under mild, catalyst-free conditions (at 50 °C), yielding linear PHUs with a record-high degree of polymerization (DP_n) of up to 220 and a number-average molecular weight (M_n) of 105 kg/mol. This strategy was further extended to another aromatic cyclic carbonate, 5,5′-(9H-fluorene-9,9-diyl)bis(benzo[d][1,3]dioxol-2-one), producing PHUs with M_n values of up to 100 kg/mol.