Bio‐basedbenzoxazine from renewableL‐tyrosine: Synthesis, polymerization, and properties

Abstract

Developing thermosets derived from renewable sources is of great importance. In this work, a fully bio-based benzoxazine monomer, 3,6-bis ((3-(furan-2-ylmethyl)-3,4-dihydro-2H-benzo[e][1,3]oxazin-6-yl)methyl)piperazine-2,5-dione (TCDPF), is conveniently synthesized from L-tyrosine cyclic dipeptide (TCDP), furfurylamine and paraformaldehyde. The chemical structure of TCDPF is confirmed by nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy (FT-IR) techniques. The curing behavior of TCDPF is investigated by differential scanning calorimetry and in situ FT-IR techniques. After temperatureprogrammed curing, the thermomechanical property and thermal stability of the resulting TCDPF polymer (PTCDPF) are evaluated by dynamic mechanical analysis and thermogravimetric analysis techniques, respectively. It is found that PTCDPF have excellent comprehensive performance such as high glass transition temperature (T g = 322 C), high thermal degradation temperature (T 5% = 342 C, T 10% = 395 C in N 2 atmosphere), and high char yield (CY = 51.3% at 800 C in N 2 atmosphere). The results demonstrate that L-tyrosine is a promising bio-based raw material for preparing high performance polybenzoxazines.

Synthesis of new biobased benzoxazine through green strategy and its polybenzoxazine resin with high thermal resistance and mechanical strength

“…Up‐to‐date, only one Green‐Bz was reported its 𝐸 𝑎 values (Kissinger method: 115.9 kJ/mol, Ozawa method: 118.9 kJ/mol), 18 which are higher than the data of CT‐fa . For biobased benzoxazines synthesized with nongreen solvents, their 𝐸 𝑎 values ranged from 92.3 to 165.2 kJ/mol (Kissinger method), or from 95.4 to 164.8 kJ/mol (Ozawa method), 26,27,29–31,48,52,57,71 so it is reasonable to state that CT‐fa has low 𝐸 𝑎 , and the curing reaction of CT‐fa is easier to be activated.…”

“…Based on the FTIR spectra of CT‐fa and poly(CT‐fa) (Figure 7), the percentage of furan groups involved in curing reactions is found to be 69.8% using the semi‐quantitative equation (Equation 3), indicating that the furan groups have bigger possibility of acting as ring‐opening crosslinking sites of the oxazine ring (route B) than the neighboring sites of the phenolic hydroxyl group (route A). Therefore, the obtained poly(CT‐fa) contains fewer suspending groups, this is beneficial to enhance the thermal stability 48 …”

“…Among the literature that reported benzoxazine resins based on green strategies, 9–27,29–31,47–72 only three of them reported static mechanical properties of the resins (Table S1), however, these resins do not show high thermal resistance ( T g ≤ 193 °C, T di ≤ 381 °C). Figure 10B shows the stress–strain curve of poly(CT‐fa) , from which poly(CT‐fa) is known to have excellent tensile strength (51.60 ± 0.27 MPa), tensile modulus (3.32 ± 0.03 GPa) and elongation at break (1.95 ± 0.02%).…”

“…Up-to-date, only one Green-Bz was reported its E a values (Kissinger method: 115.9 kJ/mol, Ozawa method: 118.9 kJ/mol), 18 which are higher than the data of CT-fa. For biobased benzoxazines synthesized with nongreen solvents, their E a values ranged from 92.3 to 165.2 kJ/mol (Kissinger method), or from 95.4 to 164.8 kJ/mol (Ozawa method), 26,27,[29][30][31]48,52,57,71 so it is reasonable to state that CT-fa has low E a , and the curing reaction of CT-fa is easier to be activated. Figure 7 gives the FTIR spectrum of poly(CT-fa), there are typical vibration peaks reflecting C O C and oxazine ring, which are not found in the spectrum of CTfa (Figure 1), while there is the characteristic peak of OH (around 3400 cm À1 ), proving that CT-fa has undergone ring-opening reaction to form a crosslinked structure.…”

“…Therefore, the obtained poly(CT-fa) contains fewer suspending groups, this is beneficial to enhance the thermal stability. 48 The asymmetric peak of the tanδ-temperature curve is divided into two symmetric peaks, of which the corresponding peak temperatures are thought to be glass transition temperatures (T g1 , T g2 ) of different phases. Specifically, T g1 and T g2 are 281 C and 320 C, respectively.…”