Poly melting endotherms

The DSC technique enables crystalline materials to be characterised by their melting point. Additives that come into this category include hydrocarbon waxes and poly(tetrafluoroethylene) (PFTE) lubricant. The presence of PTFE in low friction acetal mouldings can be established from the detection of the PTFE melting endotherm at 320°C. 

Poly(oxymethylene), POM, is a polymer with well-known melting behavior [56]. Fibrous, extended chain crystals can be produced by crystallization during polymerization, as described in Figs. 3.104 and 3.105. These extended-chain crystals can superheat on melting due to their slow melting rate, as is also seen for extended-chain crystals of polyethylene in Fig. 6.21. The DSC melting endotherms in Fig. 6.92 start for all heating rates at about the same temperatures, but the peak- and melt-end... 

Polyurethane (PU) PV membranes were reported by Schauer et al. (1999). PU membranes were prepared by the reaction of toluene-2,4-diisocyanate with hydroxyl-terminated oligomers. Oligomers were either liquid polybutadiene (PB) (MW 3000) or propylene oxide-based PEs (MW 420 and 4800). The prepared membranes were used in PV of binary mixtures of water-EtOH, water-dioxane, and EtOH-toluene, respectively. Membranes obtained from the polymer quatemized poly[3-(N, N -dimethyl)aminopropylamide-co-acrylonitriles] showed selective separation of water from aqueous EtOH solution by PV (Yoshikawa et al. 1991). The separation factor toward water reached over 15,000. Membrane performance showed a good correlation to membrane polarity. DSC melting endotherms of the water-swoUen membranes were studied to clarify the state of water in the membrane. The resnlts suggested that there were two states of water in the membrane bound and free. The higher the fraction of bound water in the membrane, clearly, the more preferentially was water permeated. 

Linear increases in crystallinity with increasing MWNT concentration of a MWNT/poly(vinyl alcohol) (PVA) composite were observed in DSC melting endotherms. This suggested that each CNT had a discrete crystalline polymer layer associated with it, which was supported by evidence from SEM imaging [69]. Indeed, others have observed polymer... 

Figure 2.43. A full DSC curve of quenched (amorphous) poly(ethylene terephthalate) recorded at a heating rate of 10°C/min the glass transition (at 80°C) is followed by cold crystallization and melting of crystals formed in nonisothermal cold crystallization. The baseline during the transition was drawn to show that the crystallization process lasts to the beginning of melting. Endotherm is down. (Menczel, tmpnbhshed results.)...

Fig. 13.7. Heat flux during heating of poly(ethylene terephthalate) (PET) at a constant rate in a differential scanning calorimeter (DSC), showing changes in specific heat at Tg, crystallization exotherm at Tc, and melting endotherm at I m.

Journal of Applied Polymer Science 81, No. 11, 12th Sept.2001, p.2779-85 RIGID AMORPHOUS PHASE AND LOW TEMPERATURE MELTING ENDOTHERM OF POLY(ETHYLENE TEREPHTHALATE)... 

Fig. 1. Variation of the glass transition and crystallization temperatures of poly(di-/ -alkyl itaconate)s plotted as a function of the number of carbon atoms in one side chain. Single Tg (O) Tg ( ) Tg ( ) melting temperatures (A) poly(di-oleyl itaconate) Tg (V) small melting endotherm ( ). ("Reproduced from J.M.G. Cowie, Z. Haq, I.J. McEwen, and J. Velickovic, Polymer, 22, 327 (1981), by permission of the publishers, Buttenvorth and Co. (Publishers) Ltd. "). 

Poly (2,6-dimethyl-1,4-phenylene oxide) is a semicrystalline polymer and contains veiy low crystalline phase after membrane formation. It has a broad melting endotherm at 245 °C. However, its selectivity for gases is relatively low. Industrial Membrane Research Institute of University of Ottawa has been working on the application of PPO membranes for gas separation and characterization of the membranes by modem techniques. ... 

The role of sequence selection during the isothermal crystallization of random type copolymers can be monitored by means of differential scanning calorimetry. (21-24) The evolution of the melting endotherms with the time of crystallization shows some unique features. An example of this development is shown in Fig. 10.17 for a hydrogenated poly (butadiene) with 2.3 mol percent branch points crystallized at 89.8 °C.(24) In this experiment the fusion process was initiated from the... 

Other hand, when an equimolar mixture of 2,5-DSP and l OEt is recrystallized from benzene, yellow crystals, comprising 2,5-DSP and l OEt in a molar ratio of 1 2, deposit. In the DSC curve of this crystal, a single endothermic peak is observed at 166°C, which is different from the melting point of either 2,5-DSP (223°C) or l OEt (156°C). Furthermore, the X-ray powder diffraction pattern of the crystal is quite different from those of the homocrystals 2,5-DSP and l OEt. Upon irradiation the cocrystal 2,5-DSP-l OEt affords a crystalline polymer (77i h = 1.0 dl g in trifluoroacetic acid). The nmr spectrum of the polymer coincides perfectly with that of a 1 2 mixture of poly-2,5-DSP and poly-1 OEt. In the dimer, only 2,5-DSP-dimer and l OEt-dimer are detected by hplc analysis, but the corresponding cross-dimer consisting of 2,5-DSP and l OEt is not detected at all (Hasegawa et al., 1993). These observations by nmr and hplc indicate that the photoproduct obtained from the cocrystal 2,5-DSP-l OEt is not a copolymer but a mixture of poly-2,5-DSP and poly-l OEt in the ratio 1 2. 

An X-ray diffraction study of PHA-10UND= showed that this PHA was amorphous however, the DSC thermogram of the polymer showed a small but clear endotherm at approximately 38 °C. The glass transition temperature of PHA-10UND= is approximately - 46 °C which is significantly lower than those of the poly(nHAMCL)s. Both the melting temperature and the glass transition tempe-... 

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