An overview on 12-polyurethane: Synthesis, structure and crystallization

The knowledge on linear aliphatic polyurethanes n-PUR has increased significantly due to a series of works made in these last years and published in recent literature An overview of 12-polyurethane (12-PUR) embracing its synthesis thermal properties crystal structure and crystallization is given in this paper The purpose is to provide a representative example able to reflect comprehensively the state of the art reached for the whole family The synthesis of 12-PUR was accomplished in good yield and with acceptable molecular weight from 12-amino-1-dodecanol by applying a two-step method without isolation of the isocyanate alcohol precursor 12-PUR is a semicrystalline polymer with an equilibrium melting temperature of 157 C. It adopts a layered crystal structure similar to the a-form of nylons with chains in fully-extended conformation and arranged in hydrogen-bonded sheets in the antiparallel mode This structure is thermally stable up to melting and is unable to undergo Brill transition 12-PUR crystallized from dilute solution affording well-shaped lamellar crystals with a thickness of 8-9 nm and from the melt yielding either banded or fibrillar spherulitic textures displaying negative birefringence Isothermal crystallization of 12-PUR from the melt took place with heterogeneous nucleation while both crystallization rate and the finally attained crystallinity degree were highly depending on crystallization temperature (C) 2010 Elsevier Ltd All rights reserved