3.3. Reactivity Ratio Determination

Fineman-Ross and Kelen-Tüdös presented methods to calculate the reactivity ratio values (r_nBA and r_CyA), and thus, a variety of different monomer feed ratios (f_CyA) were explored. Limiting the copolymerization at a low conversion (<10%) allowed to determine the instantaneous copolymer composition (F_CyA) [32]. Copolymerization equation (Equation (1)) correlated the monomer feed (f_CyA and f_nBA) and copolymer composition (F_CyA and F_nBA) to the reactivity ratios (r_CyA and r_nBA)

Fineman-Ross method rearranged Equation (1) to afford linearization expression of reactivity ratios (Equation (2)).

where G and H are

Therefore, Equation (2) can also be converted to

where G and H were readily determined by monomer feed and copolymer composition at different monomer conversions calculated from ¹H NMR spectroscopy. Based on Equation (3), a linear relationship was generated through plotting G against H, where −r₂ and r₁ corresponding to the intercept and slope of the linear relationship, respectively. However, Fineman-Ross method resulted in a local concentration of data points. To solve this problem, Kelen-Tüdös method distributed data points evenly through adding an arbitrary correction factor α to modify Equation (3) to Equation (4).

where η, ξ, and α are

Therefore, a new linear relationship was applied with −r_nBA/α and r_CyA corresponding to the intercept and slope of the curve, respectively.