Recently proposed adaptive platooning strategies for connected automated vehicles are able to address uncertain parameters of the vehicles in the platoon (uncertain driveline time constants), but are limited to acyclic interaction like lookahead interaction. This restrains from augmenting platooning protocols with synchronized merging maneuvers, where cyclic communication is needed and creates algebraic loops that require well posedness of the inputs. We propose an adaptive protocol for synchronized merging in the cyclic communication scenario. The protocol exploits a set of adaptive control strategies, designed to cope with uncertain driveline time constants. Well-posedness of the control inputs is proven in a distributed way (using information from neighboring vehicles) in spite of uncertainty and cyclic communication. The proposed strategy is shown in a benchmark merging scenario.