Copolyamides, based on 1,12-dodecanedicarboxylic acid and different ratios of 1,2-ethylenediamine and piperazine, i.e., PA2,14-co-pip,14 as well as the homopolymers PA2,14 and PApip,14 are studied. Incorporation of the piperazine component in the homopolymer PA2,14 reduces the number of hydrogen bonds. This provides a unique opportunity to investigate the influence of hydrogen bonding on the origin of the Brill transition and chain mobility within polymer crystals. Time-resolved conformational, structural, and morphological changes during heating are followed by FTIR spectroscopy, WAXD, and SAXS. The findings are that from 0 to 62 mol % of piperazine the Brill transition occurs in the same temperature region. The transformation is triggered by the conformational changes in the methylene sequences of the main chain, followed by twisting in the methylene sequences next to the amide group. This results in enhanced chain mobility along the c-axis, causing lamellar thickening. For 80 mol % of piperazine and higher, no Brill transition is observed. However, conformational changes in the methylene sequences of the main chain occurs, triggering lamellar thickening. © 2006 American Chemical Society.