The sequence length‐distribution in eutectoid copolymers as obtained from an analysis of the melting process

Abstract

Thermodynamics of eutectoid copolymers is based on the assumption that the co‐units are eutectic units. At low concentration of one of these units (non‐crystallizable units, nc‐units), crystallizable sequences (c‐sequences) are formed. Segregation of the eutectic units leads to lamella‐shaped extended c‐sequence crystals, the thickness distribution of which is controlled by the c‐sequence length‐distribution (“structure‐c‐sequence length relationship”). According to thermodynamics the lamellar crystals have to melt selectively and consecutively with respect to their mean thickness. For eutectoid copolymers it is, therefore, possible to deduce the c‐sequence length‐distribution from a thermodynamic analysis of the whole melting process. A computer‐aided method of analyzing differential scanning calorimetry measurements is applied to various semicrystalline copolymers (low‐density polyethylene (LDPE), vicinal‐chlorinated polyethylene, copolymers with OCH2 units). Theoretical structure parameters (crystallinity, mean crystal thickness) and small‐angle X‐ray scattering (SAXS) ‐pattern computed from the c‐sequence length‐distribution are shown to be in good accord with the experimental data. The universal features of the crystallization behaviour of eutectoid copolymers are emphasized. The influence of topochemical reactions onto the distribution of the eutectic co‐units of copolymers containing oxymethylene units is discussed.

Chain-structure-superstructure relations in eutectoid copolymers

“…Solid solutions are formed, the properties of which are in accordance with thermodynamics [1][2][3][4][5]. Solid solutions are formed, the properties of which are in accordance with thermodynamics [1][2][3][4][5].…”

“…The model of the inhomogeneous microphase [4,5,16,17] As nc-chain-units are squeezed out of the crystal lattice longitudinal defect layers come into existence. For thermodynamic reasons the disparity in e-sequence lengths within the crystallized micro-phase cannot exceed a maximum value which is defined by…”

“…The normalization condition holds xc + x,c = 1 (4) where Xne is the mol fraction of the no-units. The normalization condition holds xc + x,c = 1 (4) where Xne is the mol fraction of the no-units.…”

“…The molar crystallinity is for example given by [2][3][4][5]17] (12) with Ymax as the longest c-sequence in q~(y). The molar crystallinity is for example given by [2][3][4][5]17] (12) with Ymax as the longest c-sequence in q~(y).…”

“…The sequence-length distribution [4] Application of thermodynamics of eutectoid copolymers yields the possibility to deduce the c-sequence-length number distribution from a computeraided analysis of caloric melting-curves. This is possible because IMPs melt selectively in respect to their thickness.…”