Sensing the melting transition of semicrystalline polymers via a novel fluorescence technique

In this study, we have developed a new, simple, and versatile fluorescence technique for probing the melting transitions of semicrystalline thermoplastics. With this approach, fluorescent probes are incorporated into a semicrystalline polymer, either by physical doping or covalent labeling, and their T-dependent fluorescence intensity data exhibit a stepwise decrease nearby T_m because of the reduced restriction of intramolecular motion when crystals start to melt. Interestingly, the first derivative of the obtained T-dependent fluorescence intensity data can reveal more details of the melting transition, e.g., the onset and endset of the melting transition as well as the peak melting temperature. The melting point values determined by fluorescence agree well with those characterized by conventional differential scanning calorimetry. This fluorescence technique can be applied with various types of fluorescent probes and generalized to many semicrystalline thermoplastics, while maintaining excellent sensitivity to melting transitions. Our fluorescence technique represents an easy and contact-free melting point characterization approach that may allow for novel location-specific T_m investigations within heterogeneous polymeric systems (e.g., multilayer films and composites).