Replacing conventional synthetic polymers with biodegradable ones, such as aliphatic polyesters, is part of the solution of increasing plastic waste. However, the less than ideal physical properties of current commercial products have impeded their wider application. Incorporating the aromatic terephthalate unit into the main chain of aliphatic polyesters and producing new aliphaticaromatic copolyesters seems a promising strategy for combining biodegradability with good physical performance. In this project we propose to study one of such copolymers, poly(butylene succinate co- butylene terephthalate). The monomer sequence distribution has been found to be critical to the crystallization and biodegradability of the copolymers. However, what has not been addressed is the distribution of the comonomer units between crystalline and amorphous regions and, where two crystal forms coexist, the apportioning of comonomers between them. With a combination of WAXS and WANS, we expect to gain information on the longitudinal disorder of the BS groups incorporated into the BT matrix. Similarly the change in diffuse scatter would tell us about the d4-BS groups excluded from the crystals.