Lamellar thickening in nascent poly(acrylonitrile) upon annealing

No systematic study has been reported on the lamellar thickening in atactic poly(acrylonitrile) (PAN) upon annealing because PAN, in the form of solution‐cast films or their drawn products, generally shows no small‐angle X‐ray scattering (SAXS) maximum corresponding to the lamellar thickness. In this work, PAN crystals were precipitated during the thermal polymerization of acrylonitrile in solution. The nascent PAN film, obtained by the filtration of the crystal suspension, exhibited a clear SAXS maximum revealing the lamellar structure. The lamellar thickening upon annealing of the nascent PAN films was studied in the temperature range 100–180 °C, where the degradation was minimal, as confirmed by the absence of an IR absorption band at 1605 cm⁻¹ ascribed to the cyclized nitrile groups. Above 190 °C, the degradation of the samples was significant, and the SAXS became too broad to determine the scattering maximum. The long period was significantly affected by the annealing time (t_a) and the temperature (T_a). Depending on t_a, three stages were observed for the lamellar thickening behavior. The lamellar thickness stayed constant in stage I (t_a = 0.5–3 min, depending on T_a), rapidly increased in stage II (t_a = 0.5–8 min), and stayed at a constant value characteristic for each T_a at yet longer t_a's in stage III. The lamellar thickness characteristic for T_a increased rapidly with increasing T_a at 165 °C (or higher), which was 152 °C lower than the estimated melting temperature of PAN (T_m = 317 °C). A possible mechanism for such lamellar thickening in PAN far below the T_m is discussed on the basis of the enhanced chain mobility in the crystalline phase above the crystal/crystal reversible transition at 165–170 °C detected by differential scanning calorimetry and wide‐angle X‐ray diffraction. The structural changes associated with annealing are also discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2571–2579, 2000     

Polymer single crystals of poly(4-hydroxybenzoate). II. A contribution to crystal structure and polymorphism

Electron diffraction has been used to investigate the structure of a wide range of as-polymerized crystals of poly(4-hydroxybenzoate) [systematic name: poly(1,4-oxybenzoyl)]. The chemical composition and the degree of polymerization (DP) have been varied and some samples have been thermally treated. At room temperature two crystalline modifications with orthorhombic unit cells coexist. The chains adopt a 2₁ helical conformation in both forms, but there are differences for oligomer and polymer crystals. Oligomers of low DP have an extended chain-conformation, whereas in polymers a shortening of the repeat distance along the chain is observed as a function of both the DP and the crystallization conditions. From the most extensive data sets we have derived the lattice parameters a = 7.52, b = 5.70, and c = 12.49 Å for polymer crystals of phase I, and the subcell parameters for oligomer crystals of phase II a = 3.77, b = 11.06, and c = 12.89 Å. Both phases contain two chains per unit cell. In addition to modifications I and II several defect structures exist the unit cells of which contain more than two chains. At temperatures which depend on the degree of polymerization, a phase transition to a third modification takes place. The large difference between the densities of phase III as compared to both phase I and II suggests that torsional degrees of freedom exist in phase III which allow a certain mobility of the phenyl and ester groups. This mobility enables the end groups of adjacent layers in interlamellar regions of oligomer crystals to undergo transesterification reactions and therefore to increase the molecular weight of the samples.     

Morphological investigations on the nanostructured poly(vinylidene fluoride)/polyamide 11 blends by high-shear processing

Nanostructured poly(vinylidene fluoride) (PVDF)/polyamide 11 (PA 11) blends of various compositions were prepared using a high-shear extruder. The lamellar morphology of the nanoblends consisting of two crystalline constituents was investigated by transmission electron microscopy (TEM) and temperature-variable small-angle X-ray scattering (SAXS). The average lamellar long period and the thickness of the amorphous part for the high-shear-processed blends were larger than those for the low-shear-processed sample, indicating the molecular incorporations between PVDF and PA 11 upon high-shear processing. A novel scattering peak, corresponding to the long period of 25.2 nm, is observed when the SAXS measurements were carried out at a temperature between the melting points of PVDF and PA 11. The structural change with time at high temperature was investigated in situ by SAXS. It was found that the intensity of the new peak increased with time at high temperature and the peak position slowly shifted in the low-angle direction, indicating a gradual increase of the long period for PA 11 crystals upon annealing. The novel scattering peak originates from the enlarged PA 11 lamellar long period in the nanodomain because the peak cannot be observed for the same blends prepared by low-shear-processing. It is considered that the melt PVDF chains are gradually diffused into the galleries of PA 11 lamellae in the PA11 nanodomain, which enlarged the long period of PA 11 because of the more favorable interaction at high temperature. The chain diffusion can only occur from the interface between the PVDF and PA 11 phases, and therefore, almost no change was observed for the long period of bulk PA 11 crystals in the nanoblend.     

Effect of miscible polymer diluents on the development of lamellar morphology in poly(oxymethylene) blends

The development of lamellar morphology in poly(oxymethylene) (POM) and its miscible blends was studied by synchrotron time-resolved small-angle X-ray scattering (SAXS), during primary and secondary crystallization at temperatures near 150°C. The blends contained two different diluents: poly(vinyl 4-hydroxy styrene) [common name poly(vinyl phenol), (PVP)], which had a high glass temperature (T_g = 150°C), and styrene-co-hydroxy styrene oligomer (PhSO), which had a low glass temperature (T_g = −37°C). The SAXS data were analyzed by correlation function analysis to extract several lamellar parameters: long period (L), lamellar crystalline thickness (lc), amorphous layer thickness (la), and invariant (Q). The variation in Q defined the region where spherulites quickly grew and filled the entire space, and was referred to as the primary crystallization dominant regime. A rapid drop in L and lc was observed at early times, and this can be explained by defective lamellar stacks filling in space between primary stacks, as secondary crystals form during the nominal primary crystallization dominant regime. Lamellar thickening with time in the long-time secondary crystallization region was observed in neat POM and the blend with 10 % low T_g diluent, while this process was inhibited with the high T_g diluent due to the higher T_g of the interlamellar species. A decrease in la at long times confirmed the lamellar thickening. We refer to the lamellar thickening process as a type of secondary crystallization. Interlamellar inclusion or trapping was detected to different degrees with the high T_g diluent, while exclusion was found for the low T_g diluent. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3115–3122, 1999     

Lamellar‐level morphology induced by combined crystallization and liquid–liquid demixing in a poly(ethylene terephthalate)/poly(ethylene‐2,6‐naphthalate) blend

The lamellar‐level morphology of an extruded poly(ethylene terephthalate) (PET)/poly(ethylene‐2,6‐naphthalate) (PEN) blend was investigated with small‐angle X‐ray scattering (SAXS). Measurements were made as a function of the annealing time in the melt and the crystallization temperature. The characteristic morphological parameters at the lamellar level were determined by correlation function analysis of the SAXS data. At a low crystallization temperature of 120 °C, the increased amorphous layer thickness was identified in the blend, indicating that some PEN was incorporated into the interlamellar regions of PET during crystallization. The blend also showed a larger lamellar thickness than pure PET. A reason for the increase in the lamellar thickness might be that the formation of thinner lamellar stacks by secondary crystallization was significantly restricted because of the increased glass‐transition temperature. At high crystallization temperatures above 200 °C, the diffusion rates of noncrystallizable components were faster than the growth rates of crystals, with most of the noncrystallizable components escaping from the lamellar stacks. As a result, the blend showed an interfibrillar or interspherulitic morphology. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 317–324, 2002     

Lamellar cluster structure formation resulting from interchain interaction in a novel aromatic polyimide based on PMDA monomer

The aggregation structure of a novel polyimide ( PIM ‐ 6 ) with six methylene flexible spacing groups in biphenyl side chain synthesized by the traditional two‐step imidisation process was investigated by polarized light microscope (PLM), small angle X‐ray scattering (SAXS), wide angle X‐ray scattering (WAXS), and molecular simulation approach. The agreement between the experimental data and simulation result reveals that due to the predominant interchain interaction, each three backbones stack together to form a distinct lamellar cluster with side chains packed inside dispersedly. The thickness of the lamellar cluster is about 16.0 A°, corresponding to a strong peak at 5.5° in SAXS pattern. As the backbone is not perfectly parallel to each other in each lamellar cluster, the distance between each backbone ranges from 5.8 to 8.8 A° possibly relating to the weak peak at 9.8° in WAXS pattern. Meanwhile, no birefringence or apparent phase texture has been observed by PLM indicating an amorphous nature in this film. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Morphology of homogeneous copolymers of ethylene and 1‐octene. III. Structural changes during heating as revealed by time‐resolved SAXS and WAXD

The structural changes of two linear polyethylenes, LPEs, with different molar mass and of two homogeneous copolymers of ethylene and 1‐octene with comparable comonomer content but different molar mass were monitored during heating at 10 °C per minute using synchrotron radiation SAXS. Two sets of samples, cooled at 0.1 °C per minute and quenched in liquid nitrogen, respectively, were studied. All LPEs display surface melting between room temperature and the end melting temperature, whereas complete melting, according to lamellar thickness, only occurs at the highest temperatures where DSC displays a pronounced melting peak. There is recrystallization followed by isothermal lamellar thickening if annealing steps are inserted. The lamellar crystals of slowly cooled homogeneous copolymers melt in the reverse order of their formation, that is, crystals melt according to their thickness. Quenching creates unstable crystals through the cocrystallization of ethylene sequences with different length. These crystals repeatedly melt and co‐recrystallize during heating. The exothermic heat due to recrystallization partially compensates the endothermic heat due to melting resulting in a narrow overall DSC melting peak with its maximum at a higher temperature than the melting peak of slowly cooled copolymers. With increasing temperature, the crystallinity of quenched copolymers overtakes the one of slowly cooled samples due to co‐recrystallization by which an overcrowding of leaving chains at the crystal surfaces is avoided. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1975–1991, 2000     

Crystal structure,morphology, and phase transitions in aromatic polyimide oligomers. 3. Poly(1,4-phenyleneoxy-1,3-phenylene pyromellitimide)

An aromatic polyimide oligomer, poly(1,4-phenyleneoxy-1,3-phenylene pyromellitimide) (PMDA-3,4'-ODA), was synthesized from pyromellitic dianhydride (PMDA) and 3,4'-oxydianiline (3,4'-ODA) via a melt-polymerization method. This method permits growth of PMDA-3,4'-ODA lamellar crystals and the crystal structure can be studied via electron diffraction (ED) and wide-angle x-ray diffraction (WAXD) experiments. Our structure analysis indicates that this polyimide possesses a two-chain orthorhombic crystal lattice with dimensions of a = 0.848, b = 0.562, and c = 3.365 nm. It has also been found that poly(amic acid) precursors with little imidization possess the same ab lateral lattice packing, but statistical departure from the ordered packing along the c-direction. Upon increasing the degree of imidization through annealing at elevated temperatures, the order along the c-axis was progressively enhanced. Increasing the annealing temperature caused the dimensions of the a- and the b-axes to expand while the crystal correlation lengths decreased laterally. Simultaneously the dimension of the c-axis shrinks with an increase of the crystal correlation length along the chain direction. Crystal morphological study via transmission electron microscopy (TEM) indicates a mainly lamellar crystal texture with different thicknesses depending upon the polymerization conditions. The end lamellar surface is usually smooth. After annealing at elevated temperatures, the lamellar end surfaces become rough, which may be due to chain motion along the c-axis. The annealed PMDA-3,4'-ODA lamellar crystals still show a large amount of defects. © 1994 John Wiley & Sons, Inc.     

Synchrotron SAXS and WAXS Studies on Changes in Structural and Thermal Properties of Poly[(R)‐3‐hydroxybutyrate] Single Crystals during Heating

Summary: The annealing and melting behavior of poly[(R)‐3‐hydroxybutyrate] (P(3HB)) single crystals were followed in real time by synchrotron small‐ (SAXS) and wide‐angle X‐ray scattering (WAXS) measurements. The real‐time SAXS measurements revealed that the P(3HB) single crystal exhibits a discontinuous increase of lamellar thickness during heating. The structural changes as observed by SAXS and WAXS were in response to the thermal properties of single crystals characterized by differential scanning calorimetry.

A series of two‐dimensional small‐angle X‐ray scattering patterns of P(3HB) single crystal mats during the lamellar thickening process.     

Perfectly Controlled Lamella Thickness and Thickness Distribution: A Morphological Study on ADMET Polyolefins

Summary: Lamella thickness distribution (LTD) plays a critical role in determining the mechanical properties of polyethylene. LTD is predominantly governed by the intermolecular chemical composition distribution, but intrachain heterogeneity also results in a broadened LTD. Polyethylene synthesized by acyclic diene metathesis (ADMET) contains pristine microstructures free from inter and intrachain heterogeneity and therefore represent ideal models to investigate these phenomena. The crystalline structures of ADMET polyethylene with ethyl or n-hexyl branches every 21^st backbone carbon (EB21and EO21, respectively) were characterized by transmission electron microscopy (TEM), small X-ray scattering and wide angle X-ray diffraction (SAXS and WAXD), and differential scanning calorimetry (DSC). The samples were crystallized for various periods at temperatures near the DSC crystallization peak temperatures: 10 °C for EB21 and 0 °C for EO21. TEM observation exhibited that EB21 displays straight lamellar crystals with axialitic organization and an average thickness of about 55 Å. This corresponds to twice the ethylene sequence length between branches, suggesting that one lamellar stem spans three branches and includes one ethyl branch within the lamella. The lamella thickness distribution was very narrow compared with that of the cross-fraction of ethylene/1-butene copolymer prepared via Ziegler-Natta polymerization. Similarly it was found from the same characterization methods that EO21 also displays a narrow lamella thickness distribution albeit with thinner lamellae, averaging 25–26Å thick. Judging from this lamella thickness, EO21 is considered to have a lamella stem composed of a single ethylene sequence between two braches, suggesting that the n-hexyl branch is entirely excluded from a crystalline phase.     

The microstructure of poly(vinyl chloride) as revealed by x-ray and light scattering

Small-angle x-ray scattering (SAXS) and wide-angle x-ray scattering (WAXS) as well as small-angle light-scattering (SALS) techniques have been applied to investigate the microstructure of a number of commercial poly(vinyl chloride) (PVC) samples. From the wide-angle x-ray scattering, crystallinity and crystal size parameters have been determined. The crystallinity of the samples investigated range from 5% to 10%. Superstructure parameters such as crystallite thickness, distribution functions of crystallite and amorphous thicknesses, and size of ordered regions have been obtained by an analysis of the SAXS curves using the cluster model. The crystallinity agrees well with the WAXS crystallinities indicating that most of the crystals are lamellar shaped, though some rodlike entities are present in the sample as is shown by the small-angle light scattering. From the SAXS analysis, the microstructure is described as clusters of lamella stacks which are identical with the subprimary particles. Their size is determined to be 220–240 Å. Emulsion type PVC also contains lamellar-shaped crystals. The superstructure, however, of this type of PVC is different from that of mass or suspension-polymerized material. The SAXS curve does not reveal any correlation between the crystals.     

Annealing of polypropylene films crystallized from a highly extended melt

Thin films of isotactic polypropylene were drawn from the melt at a very high rate of extension. Transmission electron micrographs of this material reveal fibrous crystals lying along the draw direction. The chain axis and fiber axis are identical. Dark field micrographs show a dark/light modulation along the fiber axis. Annealing at temperatures below 110°C produces no qualitative change in the electron microscope observations. Annealing between 110 and 150°C produces gradual dominance of lamellar crystals, oriented normal to the draw direction. Small-angle x-ray scattering (SAXS) data exhibit a strong streaking normal to the fiber axis, in broad agreement with the observed fibrosity. A Bragg peak along the draw directions shows that the modulation observed microscopically is a density modulation. The absence of second-order maxima and the dependence of the SAXS peak on treatment temperature strongly suggest that the axial modulation is a spinodal decomposition of the material into crystalline and amorphous regions.     

Single crystals of cellulose IVII: Influence of the cellulose molecular weight

The influence of the degree of polymerization (DP) of cellulose was evaluated in the preparation of micron-sized cellulose IV_II lamellar crystals in order to ascertain whether a regular chain-folded morphology could develop during their growth. For this purpose, sharp fractions of cellulose acetate were collected by preparative gel permeation chromatography. Aliquots of these fractions were deacetylated and crystallized in dilute solutions containing water, methylamine, and DMSO, and held at 150°C under pressure. Well-developed cellulose IV_II lamellar crystals were obtained with fractions of DP 22–24 whereas higher-DP material gave polycrystalline aggregates. This behavior indicates that large lamellar crystals of cellulose IV_II can be obtained only with unfolded short cellulose chains. The occurrence of chain-folded crystals with high–DP cellulose samples cannot be demonstrated.     

Anisotropic swelling of doubly oriented nylon-11 with a lamellar structure

Rolled smaples of nylon-11 annealed in formic acid (90%) at 80°C remain doubly oriented and have the same allotropic form as filter mats of single crystals. the basal planes of the crystals are parallel to (00l) planes. the long spacing is larger than in filter mats. Experimental swelling results obtained on such samples are discussed on the basis of two extreme models, the lamellar and the switchboard models. The long spacing d_y and the length of the sample (along 0Y) change reversibly by the same proportion during swelling. Insertion of solvent between lamellae is invoked to explain such changes of dimension. As linear swelling ratios computed from macroscopic dimensions and SAXS measurements can reach 100%, lamellar crystals are only bonded by a few chains. The large increase of the SAXS intensity observed when annealed doubly oriented samples of nylon-11 are wetted with allylic alcohol cannot be explained on the basis of the switchboard model but only with a three-phase lamellar model. These three phases are the crystalline phase, the fold region, and a dilute solution of polymer in the swelling agent.     

Thickness-dependent Orientation Structure in Poly（ethylene oxide） Multi-layer Crystals

Poly(ethylene oxide) multi-layer crystals were obtained and the re-crystallization behavior was studied to give insight into how melt thickness and temperature affect the lamellar orientation. For a special re-crystallization temperature, there exists a critical transition thickness range for the occurrence of edge-on lamellar orientation. Below the critical thickness, only flat-on lamellae were observed. While above the critical thickness, both flat-on and edge-on lamellae were found and the proportion of the edge-on lamellae increases with thickness. At low re-crystallization temperatures(below 30 °C), the critical transition thickness gradually increases from about 15 nm to 35 nm when the re-crystallization temperature was increased from 20 °C to 30 °C. However, when the re-crystallization temperature is above 30 °C, the critical transition thickness becomes constant. Our results demonstrated that the lamellar orientation could be specially modified by changing the melt thickness and re-crystallization temperature.     

一个低分子量聚氧化乙烯从亚稳态的折叠链片晶向稳态的伸直链片晶转化增厚过程的研究

报道分子量为5000的聚氧化乙烯(PEO)从熔融态淬火到液氮温度后形成的两次链折叠(2-FC)片晶增厚过程的研究结果.在升温和恒温条件下,采用小角X射线散射(SAXS)在位地跟踪了2-FC片晶增厚成一次链折叠(1-FC)和进一步成为伸直链(EC)片晶的增厚过程.通过对SAXS数据以及它们的一维相关函数的数据的分析,发现在52℃以下,2-FC片晶主要增厚为1-FC片晶;在52℃以上,2-FC片晶则主要增厚为EC片晶;在58℃到EC片晶的熔点的温度区域里,已经形成的1-FC片晶还会熔融,完全转化为EC片晶.利用偏光显微镜(PLM)和扫描电子显微镜(SEM)观察晶体的形貌,比如球晶,获得的研究结果表明,没有发生大范围的晶体破坏后再形成的变化,也就是说片晶的增厚过程是一个发生在球晶内部的薄片晶熔融后转化为厚片晶的过程.     

Salt‐induced microphase separation of amorphous dendritic poly(ethylene oxide)‐block‐linear polystyrene copolymers

We prepared two block copolymers 1 and 2 consisting of a third‐generation dendron with poly(ethylene oxide) (PEO) peripheries and a linear polystyrene (PS) coil. The PS molecular weights were 2000 g/mol and 8000 g/mol for 1 and 2 , respectively. The differential scanning calorimetry (DSC) data indicated that neither of the block copolymers showed glass transition, implying that there was no microphase separation between the PEO and PS blocks. However, upon doping the block copolymers with lithium triflate (lithium concentration per ethylene oxide unit = 0.2), two distinct glass transitions were seen, corresponding to the salt‐doped PEO and PS blocks, respectively. The morphological analysis using small angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM) demonstrated that a hexagonal columnar morphology was induced in salt‐doped sample 1‐Li⁺ , whereas the other sample ( 2‐Li⁺ ) with a longer PS coil revealed a lamellar structure. In particular, in the SAXS data of 2‐Li⁺ , an abrupt reduction in the lamellar thickness was observed near the PS glass transition temperature (T_g), in contrast to the SAXS data for 1‐Li⁺ . This reduction implies that there is a lateral expansion of the molecular section in the lamellar structure, which can be interpreted by the conformational energy stabilization of the long PS coil above T_g. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2372–2376, 2010     

Stretching temperature and direction dependency of uniaxial deformation mechanism in overstretched polyethylene

In order to elucidate microscopic deformation behavior at different locations in isotropic semicrystalline polymers, the structural evolution of a preoriented high‐density polyethylene sample during tensile deformation at different temperatures and along different directions with respect to the preorientation was investigated by means of combined in situ synchrotron small‐angle X‐ray scattering (SAXS) and wide‐angle X‐ray diffraction (WAXD) techniques. For samples stretched along preorientation, two situations were found: (1) at 30 °C, the sample broke after a moderate deformation, which is accomplished by the slippage of the microfibrils; (2) at 80 and 100 °C, fragmentation of original lamellae followed by recrystallization process was observed resulting in new lamellar crystals of different thickness depending on stretching temperature. For samples stretched perpendicular or 45° with respect to the preorientation, the samples always end up with a new oriented lamellar structure with the normal along the stretching direction via a stress‐induced fragmentation and recrystallization route. The thickness of the final achieved lamellae depends only on stretching temperature in this case. Compared to samples stretched along the preorientation direction, samples stretched perpendicular and 45° with respect to the preorientation direction showed at least several times of maxima achievable stress before macroscopic failure possibly due to the favorable occurrence and development of microdefects in those lamellar stacks with their normal parallel to the stretching direction. This result might have significant consequence in designing optimal procedure to produce high performance polyethylene products from solid state. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 716–726     

Annealing during polymerization of crystalline poly(ethylene terephthalate)

Melt-crystallized poly(ethylene terephthalate) and etched oligomer lamellae from the same polymer have been annealed under vacuum at temperatures between 200 and 260°C and times between 3 and 48 hr. The annealed samples were analyzed through determination of viscosity-average molecular weight, x-ray low-angle spacing, density, heat of fusion, and variation of melting point with heating rate. In all cases it could be shown that the crystal lamellar surfaces remained chemically reactive. Chain folds and chain ends in the surface were converted by chemical reaction to tie molecules between different crystals or different locations on the same lamella.     

Lamellar morphology and equilibrium melting temperature of syndiotactic polystyrene in β‐crystalline form

Lamellar morphology and thickness of syndiotactic polystyrene (sPS) samples melt‐crystallized at various temperatures were probed using transmission electron microscopy (TEM) and small‐angle X‐ray scattering (SAXS). In addition, the melting temperature and enthalpy of the crystallized samples were characterized with differential scanning calorimetry. Under appropriate thermal treatments, all the samples investigated in this study were crystallized into β′ crystal modification, as revealed by wide‐angle X‐ray diffraction. From the SAXS intensity profiles, a scattering peak (or shoulder) associated with lamellar features as well as the presence of anomalous scattering at the zero‐scattering vector were evidently observed. The peculiar zero‐angle scattering was successfully described by the Debye–Bueche model, and subtraction of its contribution from the raw intensity profiles was carried out to deduce the intensity profile merely associated with the lamellar feature. The lamellar thickness obtained from Lorentz‐corrected intensity profiles in this manner agrees with that measured from the TEM images, provided that the two‐phase model is applied. On the basis of the Gibbs–Thomson equation, the modest estimations of equilibrium melting temperature and the surface free energy of the fold lamellar surface are 292.7 ± 2.7 °C and 20.2 ± 2.6 erg/cm², respectively, when lamellar thicknesses measured by TEM are applied. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1626–1636, 2002