Poly(butylene terephthalate) (PBT) vitrimers were prepared by reactive extrusion from industrial PBT thermoplastics using Zn(II)-catalyzed addition and transesterification chemistry. PBT thermoplastics are characterized by a high degree of crystallinity, high melting temperature and high crystallization rate, but right above their melting temperature their mechanical resistance disappear and they show a tendency to drip. We compared-OH and-COOH end-group additions on epoxies in the presence of two different catalysts, 2methyl imidazole (2-MI) and zinc acetyl acetonate (Zn(acac) 2). With 2-MI, chain extension reactions were efficiently catalyzed in a few minutes at 270 °C but no gelation was observed. With Zn(acac) 2 ,-COOH addition and transesterification led to efficient cross-linking within a few minutes at 270 °C. Such cross-linked material combines the crystalline properties of PBT and dimensional stability above the melting temperature. PBT materials cross-linked through epoxy-vitrimer chemistry are not soluble. However, compared with radiation cross-linked PBT, vitrimer PBT is processable and can be reshaped and recycled.

Network-coordinated Zn2+ ions activate carbonyls, promote alkoxides and hold reactants close to each other for transesterification.