[D] RNNs that don't require a fixed sequence length

Is there any research on RNNs that don't require a fixed sequence length? I'm looking for some key-words for a literature search. I am asking because, in my current project, I have seen quite devastating effects of padding. I would have fun thinking about ways to get around this.

Edit: I am aware that you only have to pad to the maximum length within a batch, but that still causes problems if your data vary widely in terms of sequence …

machinelearning