In copolymerization reaction of two monomers

reactivity ratios r

1

and r

2

may vary in a wide range. Thus

correspondingto the different values

there are diverse kinds of the F

1

—f

1

curves. In most textbooks

the first step of the classification process is to compare the product of r

1

and r

2

(r

1

• r

2

) with the value 1. However

this indirect classification method might be opaque to some beginners. This article will provide a novel and fundamental strategy directly based on r

1

and r

2

value per se

followed by the discussion of diverse systems. We hope the classification could be helpful to polymer chemistry education as well as the frontier research.