The obvious answer is to determine the sequence distribution using 13C NMR. A low tech approach might be to use thermogravimetric analysis to examine depolymerisation, but this will have to be "calibrated" with copolymers with known sequence distributions.

You may also be able to use advanced gel permetation chromatography GPC / size exclusion chromatography SEC. The intrinsic viscosity may be able to reveal the difference in structure, see for example https://theanalyticalscientist.com/issues/0116/analysis-of-different-of-plaplga-polymer-samples-using-a-gpcsec-system/

As mentioned earlier, NMR is a common technique. However, the type of monomers, the polymerization conditions, etc. may be able to tell you something in advance. Also after the polymer is made, you may want to examine it with methods such as DSC and DMTA looking for transitions related to multiphase or single phase copolymers, although this is not always providing answers if the material shown single phase chracteristics.