Poly(ethylene terephthalate)-polyethylene block copolymer architecture effects on interfacial adhesion and blend compatibilization

In this study, poly(ethylene terephthalate)-block-polyethylene (PET-PE) multiblock copolymers (MBCPs) with block molar masses of ~4 or 7 kg mol⁻¹ and either alternating or random block sequencing, and a PE-PET-PE triblock copolymer (TBCP) of comparable total molar mass, were synthesized. To explore the effect of molecular architecture on compatibilization, both MBCPs and TBCPs were blended into 80/20 wt/wt mixtures of PET/linear low-density PE (LLDPE). Compatibilization was remarkably efficient for all MBCP types, with the addition of 0.2 wt% yielding blends nearly as tough as PET homopolymer. Addition of MBCP also significantly decreases LLDPE dispersed phase sizes compared to PET/LLDPE neat blends, as much as 80% in as-mixed blends and by a factor of 10 in post-mixing thermally annealed samples. Conversely, the TBCP was less efficient at decreasing domain sizes of the blends and improving the mechanical properties, requiring loadings of 1 wt% to produce comparably tough blends. Peel tests of PET/BCP/LLDPE trilayer films showed that both MBCPs and TBCP all improve interfacial strength over a PET-PE bilayer film by two orders of magnitude; however, when the BCPs were preloaded into LLDPE, only the MBCP containing films showed strong adhesion highlighting their potential utility as adhesive agents in multilayer films.