Lignin derivative vanillin when coupled with diamines and diethyl phosphite followed by reaction with echichlorohydrin yields high-performance flame retardant epoxy resins. Biorenewable and environment-friendly flame retardant alternatives to bisphenol A epoxy resins (having plenty of applications such as coatings, adhesives, composites, etc.) have captured great attention due to their ecological and economic necessity. Vanillin, an industrial scale monoaromatic compound from lignin, is a promising sustainable candidate for high-performance polymers, while synthesis of diepoxies is challenging. Meanwhile, bio-based epoxy resins combining high performance and excellent fire resistance are more difficult to be achieved. In this paper, two novel bio-based epoxy monomers EP1 and EP2 were synthesized by one-pot reaction containing Schiff base formation and phosphorus–hydrogen addition between vanillin, diamines, and diethyl phosphite, followed by reacting with epichlorohydrin. Their reactivities are similar to bisphenol A epoxy resin DGEBA. After curing they showed excellent flame retardancy with UL-94 V0 rating and high LOI of ∼32.8%, which was due to the outstanding intumescent and dense char formation ability. Meanwhile, it was found that the cured vanillin-based epoxies had exceedingly high T gs of ∼214 °C, tensile strength of ∼80.3 MPa, and tensile modulus of ∼2709 MPa, much higher than the cured DGEBA with T g of 166 °C, tensile strength of 76.4 MPa, and tensile modulus of 1893 MPa; the properties of vanillin-based epoxies are easy to be regulated by using different “coupling” agentsdiaminesduring the synthesis process.

still susceptible to fatigue fracture during multiple-cycle mechanical loads, exhibiting fatigue threshold (i.e., the minimal fracture energy required for crack propagation under cyclic loads) below 100 J m −2 . [5][6][7] Therefore, the long-term reliability has substantially hampered the in practical utility of hydrogels and hydrogel-based devices, and remains a key challenge in these fields.On the contrary, biological tissues, such as skeletal muscles, tendon and cartilage, are well known for not only their superior strength, modulus, toughness, but also long-term robustness. [8][9][10] For example, skeletal muscles can sustain a high stress (i.e., 1 MPa) over millions cycles per year without fracture, exhibiting fatigue thresholds (i.e., the minimal fracture energy required for crack propagation under cyclic loads) over 1000 J m −2 , despite their high water content (≈80%). [8,11] Such unrivalled fatigue-resistance originates from their hierarchically-arranged collagen fibrillar micro/nanostructures. [10] Despite bioinspired construction of structural materials has been promising for the design of fatigue-resistant hydrogels, [12][13][14][15][16][17] how to produce hydrogel materials with unprecedented fatigue-resistance in a universal and viable manner still remains an open issue. More recently, fatigue-resistant hydrogels have been fabricated by engineering the crystalline domains, [12][13][14] fibril structures, [15,16] or mesoscale phase separation. [17] Ice-templated freeze-casting strategy has been utilized as a powerful technology to impart Nature builds biological materials from limited ingredients, however, with unparalleled mechanical performances compared to artificial materials, by harnessing inherent structures across multi-length-scales. In contrast, synthetic material design overwhelmingly focuses on developing new compounds, and fails to reproduce the mechanical properties of natural counterparts, such as fatigue resistance. Here, a simple yet general strategy to engineer conventional hydrogels with a more than 100-fold increase in fatigue thresholds is reported. This strategy is proven to be universally applicable to various species of hydrogel materials, including polysaccharides (i.e., alginate, cellulose), proteins (i.e., gelatin), synthetic polymers (i.e., poly(vinyl alcohol)s), as well as corresponding polymer composites. These fatigueresistant hydrogels exhibit a record-high fatigue threshold over most synthetic soft materials, making them low-cost, high-performance, and durable alternatives to soft materials used in those circumstances including robotics, artificial muscles, etc.

Birefringent ring-banded spherulites with radial periodic variation of thicknesses were grown from poly(ε-caprolactone) (PCL) solutions under conditions for which the solution concentration was held constant during the whole development of the morphology. The as-grown ring-banded spherulites were investigated by optical (OM) and atomic force (AFM) microscopies, by transmission electron microscopy (TEM) of samples sectioned parallel to the plane of film, and also by electron diffraction (ED) and grazing incidence X-ray diffraction (GIXD) techniques. The results indicate that the concentric rings in the birefringent ring-banded spherulites, as well as those in the nonbirefringent ring-banded spherulites, are a manifestation of periodic variation of thicknesses along the radius. The development of the ring-banded spherulites with radial periodic variation of thicknesses is due to periodic diffusion-induced rhythmic growth associated with periodical change in the concentration gradient in polymer solution with constant concentration. The morphological features reflect the competition between the diffusion flux of polymer chains in solution, J, and spherulitic growth with radial growth velocity, V, which can be characterized by the parameter δ ) J/V. The effects of crystallization conditions, including polymer molecular weight, initial solution concentration, and solvent evaporation rate, on the formation of ring-banded spherulites with radial periodic variation of thicknesses were studied.