Structure analysis of copolymers

The homogeneous redox peaks of the copolymers are a first hint that copolymers were formed. 

The most advanced method to determine the polymer structure is solid-state NMR spectroscopy. For the details of this method one must refer to the special literature. As an example, the application of double quantum magical angel spinning (DQ MAS) NMR spectroscopy to determine the structure of copolymers of 3-methylthiophene and ethyl-3-thiophene acetate (ETA) will be described.  

The data in Table 11.4 show that the peak positions of the homopolymers are shifted in the spectrum of the copolymer. There is also the overlap of the a- and c-type protons in the spectrum of the copolymer. This indicates that the copolymer is a random copolymer rather than a block copolymer. The other argument for a random copolymer is the missing peak from b-type protons in the spectrum of the copolymer. 

But the real information on the structure is provided by two-dimensional double quantum H NMR (2D DQ NMR) experiments. This method gives information about double quantum coherence through dipole coupling, which is a strong indication of spatial proximity. In general, there is no distinction between intra- and inter-chain interactions. 

Peak assignment and relative peak intensities of poly-(3-methylthiophene) (PMT), poly-(ethyl-3-thiophene acetate) (PETA), and of the corresponding copolymer 

---