Propogation of clematis from cuttings can be difficult depending on the variety you are attempting to propagate. Generally speaking, cuttings are not taken from plants when they are in bloom because the chance of getting them to root is severely impaired when they are blooming. Following is a link to propagating clematis from cuttings for you to peruse and find a wealth of info on the subject.

Here is a link that might be useful: clematis propagation from cuttings.