These chains are likely completely embedded in the building blocks and lack inter-block segments. The b1-chains probably contain one inter-block segment and are subdivided into b1a-and b1b-chains: b1a-chains have DP of 7–10 and b 1b-chains haveDP from 11 to 18. The b2-chains (DP 19–27) and b3-chains (DP > 28)are involved in the interconnection of three and four building blocks and contain therefore two and three inter-block segments