Summary: Two types of spherulites, extinction‐ring and Maltese‐cross, in poly(ethylene adipate) (PEA) were identified, isolated, and separately characterized using DSC and polarized‐light optical microscopy (POM). Ring‐band spherulites in PEA occurred only in a very narrow temperature range roughly between 25 and 30 °C, while Maltese‐cross spherulites at 35 °C and above or at 20 °C and below. Thermal behavior of ring‐spherulites is interpreted, analyzed, and compared to that of Maltese‐cross spherulites. The thermal behavior, like the morphology, was found to be significantly different between these two types of spherulites. Among the three multiple melting peaks in PEA, the highest P3 is proven to be related to melting of lamellae in the ring‐band spherulites; P1 and P2, whose relative extent of overlapping is dependent on the temperature of crystallization, are related to melting of lamellae in the regular ringless spherulites. This study has provided urgent and timely evidence for one major step further in the interpretation of relationships between the thermal behavior, melting, and extinction‐ring versus Maltese‐cross spherulites in semi‐crystalline polymers.DSC curves (10 °C · min−1, scanned from where the trace begins) for: (a) ring‐spherulites in PEA crystallized at 30 °C for 90 min, (b) sample‐(a) heated to 50 °C for 1 min, and (c) sample‐(a) heated to 50 °C, then quenched to 20 °C.magnified imageDSC curves (10 °C · min−1, scanned from where the trace begins) for: (a) ring‐spherulites in PEA crystallized at 30 °C for 90 min, (b) sample‐(a) heated to 50 °C for 1 min, and (c) sample‐(a) heated to 50 °C, then quenched to 20 °C.

Multiple melting peaks in some semicrystalline polymers such as poly(trimethylene terephthalate) (PTT) have caused some difficulty in estimating accurately the equilibrium melting points. PTT forms a miscible blend with amorphous poly(ether imide) (PEI); for comparison purposes, a miscible system of a fixed composition (PTT/ PEI of weight ratio ϭ 9/1) was determined. PTT and its miscible blend both exhibited dual melting peaks (labeled as low and high peaks: T m,L , T m,H ), and the first peaks (T m,L ), not the second peak (T m,H ), should be used for extrapolation. The equilibrium melting temperatures (T m 0 ) of neat PTT and its blend PTT/PEI (9/1) were 245.2 and 242.4°C, respectively, by the linear Hoffman-Weeks treatment using the corrected values of T m,L (i.e., values obtained using a heating rate close to zero). Linear and nonlinear treatments led to a significant difference in estimated T m 0 , and the relative validity of these two methods is discussed. The nonlinear estimate yielded a higher value by about 27.3°C for neat PTT and 23.1°C for the PTT/PEI (9/1) blend, respectively (also the correction in T m,L at the same condition mentioned previously). Results showed melting depression in miscible PTT/PEI (9/1). In addition, the T m 0 value of neat PTT was higher than that of PTT/PEI (9/1) owing to much thicker and more-perfect crystals in neat PTT.

A new aryl polyester, poly(pentamethylene terephthalate) (PPT) with five methylene groups in the repeat unit, was synthesized. Its multiple‐melting behavior and crystal structure were analyzed with differential scanning calorimetry and wide‐angle X‐ray diffraction. In addition, the spherulitic/lamellar morphology of melt‐crystallized PPT was investigated. Typical Maltese‐cross spherulites (with no rings) were seen in melt‐crystallized PPT at low temperatures (70–90 °C), but ring patterns were seen in PPT crystallized only at temperatures ranging from 100 to 115 °C, whereas rings disappeared with crystallization above 120 °C. The mechanisms of the rings in PPT were explained with several coordinated directional changes (wavy changes, twisting changes, and combinations) in the lamellae during growth. Scanning electron microscopy, in combination with atomic force microscopy, further proved that the ringed spherulites originated from the aggregation of sufficient numbers of edge‐on lamellar crystals; the radial‐growth edge‐on/flat‐on lamellae could be twisted and/or waved to form realistic band patterns. A postulated model properly described a possible origin of the ring bands through combined mechanisms of waving (zigzagging) and twisting (spiraling) of the lamellae during crystallization. Superimposed twisting and/or wavy models during crystallization were examined as examples. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4421–4432, 2004

This study demonstrates and discusses ternary miscibility in a three-polymer blend system based on balanced binary interactions. A truly miscible ternary blend comprising poly(e-caprolactone) (PCL), poly(benzy1 methacrylate) (PBzMA), and poly(viny1 methyl ether) (PVME), was discovered and reported. Miscibility with phase homogeneity (excluding the PCL crystalline domain) in a wide composition range has been demonstrated using criteria of thermal transition behavior, cloud point, and microscopy characterization. At ambient temperature, the three-polymer ternary system is completely miscible within the entire composition range (i.e., no immiscibility loop). However, at slightly elevated temperatures above the ambient, phase separation readily occurred in this originally miscible ternary blend. A quite low "lower critical solution temperature" (LCST) near 75°C was found for the ternary blend, which is much lower than any of those for the binary pairs. Balanced interactions with no offsetting A x among the three binary pairs were a key factor leading to a ternary miscible system.