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This work examined the miscibility, crystallization kinetics, and melting behavior of melt‐mixed poly(trimethylene terephthalate) (PTT)/poly(ethylene‐co‐cyclohexane 1,4‐dimethanol terephthalate) (PETG) blends. Differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction techniques were used to approach the goals. The single composition‐dependent glass‐transition temperatures of the blends and the equilibrium melting temperature (T) depression of PTT in the blends indicated the miscible characteristic of the blend system at all compositions. T of pure PTT, determined with a conventional extrapolative method, was 525.8 K. Furthermore, the Flory–Huggins interaction parameter was estimated to be −0.38. The dynamic and isothermal crystallization abilities of PTT were hindered by the incorporation of PETG. A complex melting behavior was observed for pure PTT and its blends. The observed complex melting behavior resulted mainly from the recrystallization and/or reorganization of the originally formed crystals during the heating scans. For the samples crystallized under the same conditions, the degree of recrystallization and/or reorganization declined with increasing PETG contents in the blends. The preliminary results obtained from the DSC experiments suggested that untraceable interchange reactions occurred in the studied blends. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2264–2274, 2003

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Three commercial metallocene-catalyst synthesized short-chain branched polyethylene (SCBPE) samples with similar molecular weights and molecular weight distributions were investigated in terms of their molecular structural (comonomer sequences and compositions) inhomogeneity and crystal morphology. Two of these samples [SCBPE(B1) and SCBPE(B2)] contained different ratios of a butene comonomer (20.7 and 26.8 SCB/1000 carbons, respectively), while the third sample, SCBPE(H), contained a branched hexane comonomer (7.8 SCB/1000 carbons). A linear PE fraction was also investigated for comparison. Differential scanning calorimetry (DSC) results indicate that multiple-step isothermal (thermal segregation) experiments lead to multiple endothermic melting processes in these SCBPEs during heating, a phenomenon that was not observed in the linear PE. Wide-angle X-ray diffraction (WAXD) experiments show that all of these SCBPEs possess an orthorhombic crystal lattice with different crystallinities. Linear coefficients of thermal expansion along both the a-and b-axes of the PE crystals were also determined using WAXD at different temperatures. This lateral lattice expansion is critically associated with the comonomer size and composition ratio of the SCB series. Small-angle X-ray (SAXS) scattering results of the thermal segregated samples obtained during heating required a differential scattering data treatment. It was found that the long period for each isothermal crystallization step was different and increased with increasing temperature. By increasing the comonomer composition at a constant temperature, the long period was also increased, although the thickness of the crystal lamellae decreased. This was due to an increase of the noncrystalline layer thickness between two neighboring lamellae. The crystalline morphology was observed under transmission electron microscopy (TEM). During multiple-step isothermal crystallization, the crystalline morphology exhibited a clearly separated lamellar domain texture. All of the experimental results presented suggest that a phase separation occurs during multiple-step crystallization due to the inhomogeneity that exists in these SCBPE molecular structures. These samples may thus possess an intermolecular heterogeneity in comonomer composition and sequence.

The thermal properties and phase morphology of poly(L‐lactide) (PLLA)‐based blends have been studied. Two poly(ethylene glycol)s (PEGs) with molecular weight (MW) of about 1,500 (1.5k) g/mol and 2,000,000 (2M) g/mol, respectively, were used as counterparts. The blends were annealed at a preselected temperature of 200 °C for either 2 min or 30 min before the characterizations. Both PEGs were determined to enhance the crystallizability of PLLA. After a 2‐min process of annealing, the PEG(1.5k)'s crystallization efficiency on PLLA has been noted to increase with the increase of its content. Conversely, PEG(2M)'s crystallization efficiency declined with the increase of its content. Extending the annealing time has evidently changed the PEGs' crystallization effect on PLLA. Moreover, the PEG(1.5k) has, to a greater extent, brought about the depression of PLLA's melting temperature by increasing its content, and this depression increased with the annealing time. The blends exhibited lower thermal stability than those of the parent components, particularly for the PEG(1.5k)‐included system with a higher PEG content. Regardless of the annealing time, the PEG(1.5k)‐included blends have shown homogeneous melt morphology under light microscope, whereas the PEG(2M)‐included blends have displayed phase‐separated melt morphology. In addition to the composition, PEG's MW and annealing time influence the crystalline morphology of the blends. The ringed PLLA spherulites have appeared mostly in the 2‐min annealed PEG(1.5k)‐included blends. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1497–1510, 2009