If I have iambic pentameter but no rhyme pattern, can it still be a blank verse?
Iambic pentameter is also known as blank verse because it is a rhythm, so the simple answer is yes. Do not confuse rhythm and rhyme. Quite simplely, the rhythm of imabic pentameter is de DUM, de DUM, de DUM, de DUM de DUM.
Writers during the Elizabethean period used blank verse since it was closest to the rhythm of everyday speech. For example, "I asked for coffee but you gave me tea." In English, we usually use about ten syllables per breath.
Shakespeare was a master of blank verse and put the important words in the stressed position. For example, "In sooth I know not why I am so sad." (The opening lines of The Merchant of Venice.) Notice that the words sooth, know, why, am and sad are all in the stressed position.
Being the master that he was, Shakespeare would often break this rhythm once established as he needed. Classical actors have compared speaking Shakespeare to jazz.
Absolutely. In fact, blank verse is defined as poetry written in unrhymed iambic pentameter lines. Each iambic foot has an unstressed syllable follwed by a stressed syllable. A pentameter line, of course, has five of these feet.
Because blank verse sounds much like ordinary spoken Englsh, it has been used in famous poetry and drama. Shakespeare's Romeo and Juliet is written almost entirely in blank verse, for instance. And, modern poets such as Robert Frost have used blank verse. In his poem "Birches," for example, there is unrhymed iambic pentameter:
When I / see birch/ es bend / to left / and right
Across/ the lines / of straight / er dark /er trees
I like / to think /some boy's / been swing/ing them.