Cross-Linking of Poly(butylene terephthalate) by Reactive Extrusion Using Zn(II) Epoxy-Vitrimer Chemistry

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 disappears and they show a tendency to drip. We compared -OH and -COOH end-group additions on epoxies in the presence of two different catalysts: 2-methylimidazole (2-MI) and zinc acetylacetonate (Zn(acac)(2)). With 2-MI, chain extension reactions were efficiently catalyzed in a few minutes at 270 degrees 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 degrees 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.