  We present a method of constructing rate-compatible polar codes that are
capacity-achieving with low-complexity sequential decoders. The proposed code
construction allows for incremental retransmissions at different rates in order
to adapt to channel conditions. The main idea of the construction exploits the
common characteristics of polar codes optimized for a sequence of successively
degraded channels. The proposed approach allows for an optimized polar code to
be used at every transmission thereby achieving capacity.
