The synthesis of copolyesters via interchange reactions of polypivalolactone (PPVL) with several compounds was studied. The synthetical procedures are two-stage melt processes: in the first stage ester bonds in the polymer chain are cleaved and new groups are incorporated in the polymer chain, while in the second step condensation of the end-groups formed occurs. For the synthesis of copolymers, three procedures were used, with tetrabutyl orthotitanate as a catalyst. PPVL was heated with equimolar mixtures of bisphenol-A diacetate (BPAac) and terephthalic acid (TA), but no copolymers were formed; instead, polycondensation of BPAac with TA occurred, leaving the PPVL unaffected. From PPVL and mixtures of BPAac and dimethyl terephthalate (DMT) polymers were obtained which contained a significant amount of copolymeric sequences. However, most of the polymeric chains consisted of PPVL and poly(bisphenol-A terephthalate) blocks. Random copolymers with thermal stability were obtained after heating PPVL with bisphenol-A polycarbonate and DMT. The latter process was studied in detail by IR, DSC, and solubility and selective degradation tests. Based on the results of these studies, the reactions occurring during the three procedures were discussed.
Tijsma, E. J., van der Does, L., Bantjes, A., Vulić, I., & Buning, G. H. W. (1993). Pivalolactone, 2: Copolyester synthesis via interchange reactions with polypivalolactone. Makromolekulare Chemie, 194(194), 2807-2825. https://doi.org/10.1002/macp.1993.021941015