Synthesis of biphenyl polyesters derived from divanillic acid, and their thermal and mechanical properties

Abstract Four different symmetric dialkoxydivanillic acid monomers with different side-chain lengths, namely methoxy-, ethoxy-, propoxy-, and butoxy-divanillic acid monomers (MeDVA, EtDVA, PrDVA, and BuDVA) (side-chain carbon number; m = 1, 2, 3, and 4), were synthesized. Polymerizations of the DVA-based monomers with alkane diols with different alkyl carbon number (m’ = 4 and 6) were conducted with titanium tetraisopropoxide as a catalyst via bulk transesterification, and a series of DVA-based polyesters P(R′-RDVA) (m = 1, 2, 3, and 4, m’ = 4 and 6) were obtained. The weight-average molecular weight (Mw) of the polyesters reached 6.24 × 104 for poly(hexylene dibutoxydivanillate) [P(He-BuDVA)]. The obtained polyesters had high thermal stabilities with thermal degradation temperatures at 10% weight loss of ca. 380 °C on average. Differential scanning calorimetry showed that these DVA-based polyesters had no melting temperature and were amorphous. Their glass-transition temperatures varied from 19 to 89 °C, depending on the side-chain and diol-chain lengths. Cast films and melt-pressed films of the polyesters were obtained, and their mechanical properties were investigated by tensile testing. The P(Bu-BuDVA) and P(He-PrDVA) samples had maximum strengths of 15.8 and 7.5 MPa, respectively. The P(He-BuDVA) sample was highly stretchable. The maximum elongation without breakage of P(He-BuDVA) was 2300% and 400% elongation was recovered after release.