Starting from common monounsaturated fatty acids, a strategy is revealed that provides ultra long aliphatic a,w difunctional building blocks by a sequence of two scalable catalytic steps that virtually double the chain length of the starting materials. The central double bond of the a,w dicarboxylic fatty acid self metathesis products is shifted selectively to the statistically much disfavored a,b position in a catalytic dynamic isomerizing crystallization approach. "Chain doubling" by a subsequent catalytic olefin metathesis step, which overcomes the low reactivity of this substrates by using waste internal olefins as recyclable co reagents, yields ultra long chain a,w difunctional building blocks of a precise chain length, as demonstrated up to a C 48 chain. The unique nature of these structures is reflected by unrivaled melting points (T m = 120 8 8C) of aliphatic polyesters generated from these telechelic monomers, and by their self assembly to polyethylene like single crystals.

Starting from common monounsaturated fatty acids, a strategy is revealed that provides ultra long aliphatic a,w difunctional building blocks by a sequence of two scalable catalytic steps that virtually double the chain length of the starting materials. The central double bond of the a,w dicarboxylic fatty acid self metathesis products is shifted selectively to the statistically much disfavored a,b position in a catalytic dynamic isomerizing crystallization approach. "Chain doubling" by a subsequent catalytic olefin metathesis step, which overcomes the low reactivity of this substrates by using waste internal olefins as recyclable co reagents, yields ultra long chain a,w difunctional building blocks of a precise chain length, as demonstrated up to a C 48 chain. The unique nature of these structures is reflected by unrivaled melting points (T m = 120 8 8C) of aliphatic polyesters generated from these telechelic monomers, and by their self assembly to polyethylene like single crystals.