Crystallization behaviour of poly(N-methyldodecano-12-lactam) Part 2. Recrystallization

The recrystallization process of poly(N-methyldodecano-12-lactam) MPA has b een studied by differential scanning calorimetry (DSC), wide- and small-ang le X-ray scattering (WAXS, SAXS) and Raman spectroscopy. During this irreve rsible process, the primary crystalline structure with a melting temperatur e of about 324 K is transformed to the higher-ordered final structure melti ng at 335 K. Isothermal recrystallization has an optimum at 327-329 K. Duri ng recrystallisation, no change in crystalline modification takes place; ho wever, crystallinity is increased from 30 to 35% (by WAXS) and the long per iod rises from 10.0 to 11.2 nm. The MPA sample recrystallized at 327 K and relaxed at laboratory temperature shows the melting point of 338.8 K. Cryst allization/recrystallization of MPA is a diffusion-controlled kinetic proce ss dependent on molecular weight and the rate of temperature changes. On th e molecular level, the crystallization/recrystallization processes taking p lace in MPA can be interpreted as being directed by two conformational tran sitions in MPA molecules, namely the trans/cis transition on the C-N bond a nd the gauche/trans transition of the C-C sequences. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.