The T’s measured by DMA for SPE/TA(1/1) and SPE/QC(1/1.2) were 95 °C and 86 °C, respectively, whose values were much lower than that of the cured conven­tional DGEBA (>100 °C). Therefore, when industrially available and inexpensive SPE is combined with a bio-based phenolic hardener, the hardener having a lower hydroxy value and a higher aromatic content than TA should be used. Vanillin (VN) is contained in essential oil of clove or vanilla, and is also prepared from bio-based
eugenol or guaiacol. In this section, the synthesis of a bio-based novolac is exam­ined by the reaction of PG and VN.26 As a result of the spectral analyzes of the ob­tained reaction product, it was found that pyrogallol-vanillin calixarene (PGVNC) mainly composed of guaiacyl pyrogallol[4]arene is formed. Although aryl pyro — gallol[4]arenes synthesized by the reactions of pyrogallol with benzaldehyde, p — methylbenzaldehyde and p-methoxybenzaldehyde, etc., are known compounds, their calixarenes have attracted little attention because of the very poor solubility in common solvents.7879 In contrast, the PGVNC can be easily used as building blocks of polymeric materials because of the good solubility to some organic solvents.

The reaction of PG and VN in the presence of p-toluenesulfonic acid gave PGVNC as a pale purple powder in 51% yield (Fig. 4.35). The obtained PGVNC was soluble to tetrahydrofuran, Ж. Ж-dimethylformamide and dimethylsulfoxide, and insoluble to water, methanol, ethanol, acetone, chloroform, ethyl acetate and hexane. Fig. 36 shows a FD-MS spectrum of PGVNC. A strong peak of m/z 1040 (C56H48O20:4PG+4 VN-4H2O) corresponds to a calix[4]arene, guaiacyl pyrogallol[4] arene. Other peaks at m/z 520, 398, 262 and 126 correspond to (C28H24O10: 2PG+2 VN-2H2O), (C22H22O7: PG+2 VN-2O), (C14H14O5: PG+VN-O) and (C6H6O3: PG), respectively. Although the peak of m/z 520 corresponds a calix[2]arene, the struc­ture would not be possible because of highly strained structure. From the MS spec­trum of PGVNC, we could not decide whether the peaks other than 1040 are the fragment peaks of guaiacyl pyrogallol[4]arene or due to the compounds contained in PGVNC.

Figure 4.37 shows the ‘H-NMR spectrum of PGVNC measured in J6-DMSO. Although novolac derivatives prepared from phenols and aldehydes generally show complex spectral patterns because of different substitution positions of benzene ring and degree of polymerization, PGVNC showed a simple spectral pattern, suggest­ing the formation of a single product with a symmetrical structure. Almost the main ‘H-signals can be assigned to the protons of guaiacyl pyrogallol[4]arene. The ‘H signals at 7.89 (s, 4H), 7.70 (s, 2H), 7.63 (s, 2H), 7.43 (s, 4H) and 7.19 (s, 4H) are assigned to the protons of phenolic hydroxy groups of PGVNC, because the ‘H signals disappeared by the H-D exchange by the addition of D2O. The fact that two separated hydroxy protons are observed at 7.70 (s, 2H) and 7.63 (s, 2H) in­dicates that there are two pairs of hydroxy groups with a different conformation. The ‘H signals of guaiacyl group were observed at 6.33 (d, 4H, Hb, J = 8.0 Hz), 6.17 (s, 4H, Hd), 6.10 (d, 4H, Hc, J = 8.0 Hz). The ‘H-signals of pyrogallol ring were observed at 6.06 (s, 2H, Ha) and 5.58 (s, 2H, Ha), indicating that there are two kinds of pyrogallol rings with a different conformation, and that thermodynami­cally stable rctt (cis-trans) isomer is preferentially formed. Although the ‘H NMR spectral data of aryl pyrogallol[4]arenes have not yet been reported because of the very poor solubility, the reported NMR data of acylated aryl pyrogallol[4]arenes in CDCl3 resemble those of PGVNC.78 The stable conformation of the PGVNC with rctt configuration was calculated by MM2. Fig. 38 shows the calculated structure of the rctt PGVNC. The four-pyrogallol units in the calixarene ring were divided into two groups with two pyrogallol rings at almost perpendicular direction and other two pyrogallol rings nearly in horizontal position. The stretching direction of two perpendicular pyrogallol rings is opposite. One pyrogallol ring is upper standing and the other is upside down. The four side gauiacyl groups are also divided two groups with two neighboring guaiacyl groups at left side, while other two-guaiacyl groups locating at right side. For acylated ^-methylphenyl pyrogallol[4]arene and acrylated ^-methoxyphenyl pyrogallol[4]arene, similar structure is confirmed by the X-ray crystal structure analysis.78