Melting behavior of polymorphic MDI/BD-block TPU investigated by using in-situ SAXS/WAXS and FTIR techniques. Hydrogen bonding formation causing the inhomogeneous melt

Polymer Testing

Elmar Pöselt¹  Berend Eling²  Zongbao Wang²  Zeyu Wang³  Xuke Li³ 

[1] Corresponding author.;BASF Polyurethanes GmbH, Elastogranstrasse 60, 49448, Lemförde, Germany;Ningbo Key Laboratory of Specialty Polymers, School of Materials Science and Chemical Engineering, Ningbo University, Ningbo, 315211, PR China;

关键词: TPU;    MDI/BD block;    Inhomogeneous melt;    WAXS;    SAXS;    FTIR;   

DOI  :  

来源: DOAJ

【 摘 要 】

MDI/BD hard segment based TPUs exhibit two distinct polymorphs, form I and form II, when it is solution-cast at 60 and 145 °C. Form I shows paracrystalline features, whereas form II typically shows semi-crystalline spherulitic structures with birefringence. The melting behavior of these two forms is investigated using in-situ FTIR and simultaneous in-situ SAXS and WAXS techniques. The long spacing of form I is smaller than that of form II with increasing the temperature up to 200 °C, as the thermal expansion increases the size of the hard and soft domains and therefore also the length of the long spacing. Partial melting of the hard domains above 200 °C increases the long spacing while the hard domains that survive in the melt reorganize into larger domains. As the size increment above 200 °C of form I is larger than that of form II, the long spacing of form I becomes larger than that of form II. The presence of significant H-bonding between the urethane carbonyl CO and the amide N–H and the diffuse scattering confirm the inhomogeneous melt containing tiny MDI/BD hard block aggregates. The presence of these aggregates in the melt may influence the crystallization behavior of the MDI/BD hard blocks during cooling.

【 授权许可】

Unknown