Reversible melting in nanophase-separated poly (oligoamide-alt-oligoether)s and its dependence on sequence length, crystal perfection, and molecular mobility

The degree of reversibility of the melting of multiblock copolymers of alte rnating oligoamides and oligoethers was investigated with respect to the co mposition and molecular mass of the blocks. The analysis was conducted with temperature-modulated calorimetry, and it revealed different degrees of re versibility of the melting process that depended on the block length, cryst al perfection, and molecular mobility. For the oligoamide blocks, the amoun t of crystal that melts and crystallizes reversibly during quasi-isothermal analysis increases with decreasing molar mass, and shorter amide sequences form poorer crystals that have a higher tendency toward reorganization. Re organization of the oligoamides is also favored by the presence of the more mobile oligoether units. Reversible melting of the oligoether segments is influenced by the presence of glassy and crystalline oligoamide blocks in t he adjacent nanophases. Because of the segmented nature of the copolymers, the oligoether segments are not free to flow as in an isotropic melt but ar e anchored to the oligoamide surfaces with different degrees of restriction that change the local equilibrium of melting and recrystallization. A comp arison of the copolymers with the corresponding homopolymers provides infor mation about the role of molecular nucleation and mobility in the reversibi lity of melting. (C) 2001 John Wiley & Sons, Inc.*.