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The morphology and thermal stability of different sectors in solution- and melt-grown crystals of star-branched polyesters with poly(ε-caprolactone) (PCL) arms, and of a reference linear PCL, have been studied by tapping-mode atomic-force microscopy (AFM). Real-time monitoring of melt-crystallization in thin films of star-branched and linear PCL has been performed using hot-stage AFM. A striated fold surface was observed in both solution- and melt-grown crystals of both star-branched and linear PCL. The presence of striations in the melt-grown crystals proved that this structure was genuine and not due to the collapse of tent-shaped crystals. The crystals of the star-branched polymers had smoother fold surfaces, which can be explained by the presence of dendritic cores close to the fold surfaces. The single crystals of linear PCL grown from solution showed earlier melting in the {100} sectors than in the {110} sectors, whereas no such sectorial dependence of the melting was found in the solution-grown crystals of the star-branched polymers. The proximity of the dendritic cores to the fold surface yields at least one amorphous PCL repeating unit next to the dendritic core and more nonadjacent and less sharp chain folding than in linear PCL single crystals; this evidently erased the difference in thermal stability between the {110} and {100} sectors. Melt-crystallization in thin polymer films at 53-55°C showed 4 times faster crystal growth along b than along a, and more irregular crystals with niches on the lateral faces in star-branched PCL than in linear PCL. Crystal growth rate was strictly constant with time. Multilayer crystals with central screw dislocation (growing with or without reorientation of the b-axis) and twisting were observed in both classes of polymers. [ABSTRACT FROM AUTHOR]

Cast, segmented polyetherurethanes with 30 and 50% hard-segment content (HSC), respectively, were studied by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Multi-phase segregation was observed in both samples on two levels (micro and nano) of structural organization. Spherulites with a prominent radial structure, built of branched fibrils and globules, were captured on the micrometer level. The use of AFM enabled us to investigate the nanostructure in the polyurethanes studied here. In the sample with low (30%) HSC, nano-scale phase separation was observed by AFM in areas outside the crystalline aggregates. The morphology in these domains exhibited short, rodlike hard domains embedded in the matrix of the soft segments. The other sample (50% HSC) contained four identifiable morphological features. These included spherulites, globules, bundles of lamellae, and nanophase-separated, rodlike hard domains, embedded in the soft-segment matrix. [ABSTRACT FROM AUTHOR]

The morphology of poly(propylene oxide) (PPO) crystals grown from the melt was investigated. The spherulites of the optically pure S polymers displayed a regular pattern of concentric rings as observed by polarizing optical microscopy, while the stereocopolymer developed irregularly banded, or non-banded spherulites depending on the degree of undercooling. The organization of the lamellar crystals within the spherulites was examined by means of atomic force microscopy (AFM). For all cases, the lamellar structures appeared to adopt an alternating flat or edge-on orientation. Examination of the morphology of single crystals in the melt of the stereocopolymer revealed truncated-lozenge crystals, which were elongated in shape. Results from crystallization kinetics, obtained by in situ AFM observations, showed that the elongated habit is related to differences in the growth rates of the {2 0 0} and {1 1 0} facets. Interestingly, the melt-grown RS-PPO crystals developed a curved asymmetrical three-dimensional shape. Based on these observations it can be proposed that the chiral nature of the chain is transmitted to higher structural levels of ordering in the crystal aggregates. [Copyright &y& Elsevier]