Lamellar assembly corresponding to transitions of positively to negatively birefringent spherulites in poly(ethylene adipate) with phenoxy

Surface morphology of positively or negatively birefringent spherulites in melt-crystallized neat poly(ethylene adipate) (PEA) vs. PEA blend with phenoxy was examined using atomic force microscopy (AFM), scanning electron microscopy, polarizing optical microscopy, thermal analysis, and wide-angle X-ray techniques. Their top-surface morphology in thin film forms was analyzed to fully expounded the lamellar assembly responsible for the opposite birefringence. Top-surface lamellar assemblies in positive/negative types of ringless spherulites (T _c = 0, 15, 20, 40 °C) and also alternating birefringence of double-ring-banded spherulite (T _c = 28 °C) of PEA/phenoxy blend were examined with AFM. From the results, spherulite’s positive and negative birefringence differs only in interior lamellar arrangements but not lattice geometries. Negative spherulites are composed of radially oriented edge-on lamellae, while positive spherulites are composed of bending/coiling edge-on lamellae. By contrast, the ring-banded spherulites can exhibit both negative and positive birefringence depending on the alternating radial and tangential lamellar arrangement. The addition of phenoxy into PEA could disrupt the regular lamellar bending and promote the singularity of edge-on lamellae; owing to that, the amorphous phenoxy induces looser arrangement of edge-on lamellae with phenoxy being in interlamellar/interfibrillar regions. The bulky linking pendent group phenoxy, with H-bonding capacity interacting with PEA, also disrupts the regularity of tangential–radial PEA lamellae to display a more zigzag pattern.     

Crystallization kinetics and melting behavior of metallocene short‐chain branched polyethylene fractions

Metallocene polyethylene (mPE) fractions are recognized as being more homogeneous with respect to short‐chain branch (SCB) distribution as compared with unfractionated mPEs. Differential scanning calorimetry and polarized optical microscopy (POM) were used to study the influences of SCB content on the crystallization kinetics, melting behavior, and crystal morphology of four butyl‐branched mPE fractions. The parent mPE of the studied fractions was also investigated for comparative purposes. mPE fractions showed a much simpler crystallization behavior as compared with their parent mPE during the cooling experiments. The Ozawa equation was successfully used to analyze the nonisothermal crystallization kinetics of the fractions. The Ozawa exponent n decreased from about 3.5 to 2 as the temperature declined for each fraction, indicating the crystal‐growth geometry changed from three‐dimensional to two‐dimensional. For isothermal crystallization, the fraction with a lesser SCB content exhibited a higher crystallization temperature (T_c) window. The results from the Avrami equation analysis showed the exponent n values were around 3 (with minor variation), which implied that the crystal‐growth geometry is pseudo‐three‐dimensional. Both of the activation energies for nonisothermal and isothermal crystallization were determined for each fraction with Kissinger and Arrhenius‐type equations, respectively. Double melting peaks were observed for both nonisothermally or isothermally crystallized specimens. The high‐melting peak was confirmed induced via the annealing effect during heating scans. The Hoffman–Weeks plot was inapplicable in obtaining the equilibrium melting temperature (T_m°) for each fraction. The relationship between T_c and T_m for the fractions is approximately T_m = T_c (°C) + 8.3. The POM results indicated that the crystals of parent or fractions formed under cooling conditions did not exhibit the typical spherulitic morphology as a result of the high SCB content. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 325–337, 2002     

Effects of amorphous poly(vinyl acetate) on crystalline morphology of poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid)

The amorphous and crystalline phase behavior, spherulite morphology, and interactions between amorphous poly(vinyl acetate) (PVAc) and poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) were examined using differential scanning calorimetry, polarized-light optical and scanning electron, atomic-force microscopy (DSC, POM, SEM, AFM), and small-angle X-ray scattering (SAXS). The PHBV/PVAc blend was found to be miscible with an almost linear T _g-composition relationship, indicating perfect homogeneity. Interaction parameter by melting point depression is a negative value of χ = −0.32, suggesting quite favorable interaction strength. With the intimate interaction between the amorphous PVAc and crystalline PHBV polymers, effects of PVAc on the spherulitic morphology of PHBV are quite significant. Owing to the higher T _g of PVAc (than that of PHBV), the spherulite growth rate of PHBV was depressed by increasing PVAc content in blends. Neat PHBV exhibits ring-banded spherulites when crystallized at T_c = 60 ~ 110^° C {T_{\rm{c}}} = {6}0\sim {11}0^\circ {\hbox{C}} ; however, with increasing PVAc content in the blends, the temperature range at which the PHBV/PVAc blends exhibit ring-banded spherulites remains similar but the regularity increases, and the inter-ring spacing significantly decreases. In addition, the spherulite size and ring-band patterns therein are strongly dependent on T _max (190 vs. 220 °C, respectively, for erasing prior nuclei), from which the blends were quenched to a T _c (60–110 °C) for crystallization. For PHBV/PVAc blends crystallized at the same T _c from different T _max, higher T _max tends to erase nuclei, leading to larger spherulites. However, such larger spherulites owing to higher T _max are not necessarily packed with thicker lamellae.     

Crystallization,morphology, and thermal behavior of poly(p‐phenylene sulfide)

This article deals with the structure, crystallization, morphology, and thermal behavior of poly(p‐phenylene sulfide) (PPS) with low‐molecular mass, probed by DSC, optical, and electron microscopy. The growth rates of spherulites were measured over the temperature range 235–275°C. A regime II–III transition was found at T = 250°C. The regime transition was accompanied by a morphological change from sheaflike structure to classical spherulites. The Avrami equation poorly described the isothermal crystallization of PPS, for the occurrence of mixed growth mechanisms and secondary crystallization, in agreement with the morphology and the thermal behavior. Two melting peaks were detected on DSC curves and attributed to the melting of crystals formed isothermally at T_c by primary and secondary crystallization. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 415–424, 2001     

Analysis of Polymorphism and Dual Crystalline Morphologies in Poly(hexamethylene terephthalate)

Summary: The polymorphisms in poly(hexamethylene terephthalate) (PHT), along with their associated melting and spherulite morphologies, were examined by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), and polarized‐light microscopy (PLM). The morphology and crystal cells were dependent on the temperature of crystallization. When melt‐crystallized at low temperatures (90–135 °C), PHT showed at least five melting peaks and two re‐crystallization peaks upon DSC scanning, and the samples displayed various fractions of both α and β crystals. However, only a single melting peak was obtained in PHT melt‐crystallized at 140 °C or above, which displayed a single type of β crystal. In addition, two different forms of spherulites were identified in melt‐crystallized PHT, with one being a typical Maltese‐cross spherulite containing the α crystal, and the other being a dendrite‐type packed mainly with the β crystal. This study provides timely evidence for a critical interpretation of the relationship between multiple melting and polymorphisms (unit cells and spherulites) in polymers, including semi‐crystalline polyesters.

WAXD diffractograms for PHT melt‐crystallized at 140 °C, revealing a single type of β‐crystal cell.     

Periodic extinction bands composed of all flat‐on lamellae in poly(dodecamethylene terephthalate) thin films crystallized at high temperatures

Using in‐house synthesized poly(dodecamethylene terephthalate) (P12T) as a model, periodic extinction‐banded spherulites melt‐crystallized at high T_cs (100–115 °C) are expounded in terms of growth mechanism. The extinction‐banded spherulites wildly differing from the usual blue/orange double ring‐banded spherulites are composed of all flat‐on discrete single‐crystalline lamellae packed like roof shingles (or fish scales) along the circularly curved bands and the lamellae in the extinction bands are flat with a lozenge shape with no continuous twisting at all. For P12T films of more than 10 µm crystallized at T_c = 105–115 °C, no periodic bands were seen, and all spherulites were ringless, where periodic growth precipitation of crystals to extinction does not occur until impingement. Extinction bands in the P12T spherulites with the inter‐ring spacing steadily decrease with decreasing film thickness, because for thinner films (submicrons to 2 µm), draining or depletion of available molten species takes place more frequently, leading to bands of smaller inter‐ring spacing. The petal‐like extinction bands are discussed and analyzed in detail using 3D AFM imaging. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 601–611     

Correlation of crack patterns and ring bands in spherulites of low molecular weight poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid)

Only a single type of circular circumferential crack is conventionally reported for poly(l-lactic acid) (PLLA). In this study, PLLA samples were found to exhibit as many as four crack types of different directions and patterns, which cannot be feasibly explained simply by the directional difference in coefficients of thermal expansion. Depending on crystallization temperature (T _c), PLLA crystallizes into ringless or ring-banded spherulites, whereas the crack patterns are dramatically different in these two types of spherulites. In ring-banded spherulites of PLLA crystallized at intermediate T _c, two uniquely different crack types are present: (1) twin circumferential cracks coinciding with the dark–bright and bright–dark boundary and (2) radial short-segmental voids coinciding on the bright bands in spherulites. The radial short-segmental cracks on the bright band of ring-banded spherulites may be caused by PLLA crystals of radial direction with various twisting that contract laterally upon cooling. Only circumferential cracks are present in PLLA crystallized into ringless spherulites, where concentric continuous circumferential cracks are present in the ringless spherulites at low T _c with finer lamellae, but discontinuous and irregular circumferential cracks are present in the ringless spherulites at high T _c with coarse lamellae. Although all cracks are triggered by cooling from T _c, all evidences indicate that the crack patterns and types are highly associated with the lamellar orientation, patterns, and coarseness in spherulites.     

Formation of interpenetrated spherulites based on miscible crystalline polymer blends

The morphology and formation process of interpenetrated spherulites of poly(butylene succinate)/poly(vinylidene choloride‐co‐vinyl chloride) (PBSU/PVDCVC) blends were investigated by confocal laser scanning microscopy (CLSM). CLSM images showed that the dense fibrils of PBSU spherulites penetrated into the sparse PVDCVC spherulites. For a blend with PBSU content 50% and crystallization temperature T_c = 368 K, the simultaneous growth of PBSU and PVDCVC spherulites was observed. After PBSU fibrils collided with PVDCVC spherulites, they kept growing through PVDCVC spherulites. For a blend with PBSU content 30% and T_c = 363 K, PBSU started to nucleate after PVDCVC spherulites filled the whole space.     

Melting behavior of isotactic polystyrene

The melting behavior of isotactic polystyrene, crystallized from the melt and from dilute solutions in trans-decalin, has been studied by differential scanning calorimetry and solubility measurements. The melting curves show 1, 2, or 3 melting endotherms. At large supercooling, crystallization from the melt produces a small melting endotherm just above the crystallization temperature T_c. This peak originates from secondary crystallization of melt trapped within the spherulites. The next melting endotherm is related to the normal primary crystallization process. Its peak temperature increases linearly with T_c, yielding an extrapolated value for the equilibrium melting temperature T_c° of 242 ± 1°C as found before. By self-seeding, crystallization from the melt could be performed at much higher temperature to obtain melting temperatures as high as 243°C, giving rise to doubt about the value of T_c° found by extrapolation. For normal values of T_c and heating rate, an extra endotherm appears on the melting curve. Its peak temperature is the same for both melt-crystallized and solution-crystallized samples, and independent of T_c, but rises with decreasing heating rate. From the effects of heating rate and partial scanning on the ratio of peak areas and of previous heat treatment on dissolution temperature, it is concluded that this peak arises from the second one by continuous melting and recrystallization during the scan.     

Poly(thiodiethylene adipate): Melting behavior,crystallization kinetics,morphology, and crystal structure

The melting behavior and crystallization kinetics of poly(thiodiethylene adipate) (PSDEA) were investigated with differential scanning calorimetry and hot‐stage optical microscopy. The observed multiple endotherms, commonly displayed by polyesters, were influenced by the crystallization temperature (T_c) and ascribed to melting and recrystallization processes. Linear and nonlinear treatments were applied to estimate the equilibrium melting temperature for PSDEA with the corrected values of the melting temperature. The nonlinear estimation yielded a higher value by about 9 °C. Isothermal crystallization kinetics were analyzed according to Avrami's treatment. Values of Avrami's exponent close to 3 were obtained, independently of T_c, in agreement with a crystallization process originating from predetermined nuclei and characterized by three‐dimensional spherulitic growth. As a matter of fact, space‐filling spherulites were observed by optical microscopy at all T_c's. The rate of crystallization became lower as T_c increased, as usual at a low undercooling, the crystallization process being controlled by nucleation. Moreover, the crystal structure of PSDEA was determined from powder X‐ray diffraction data by full profile fitting. A triclinic unit cell containing two polymer chains arranged parallel to the c axis was found. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 553–566, 2004     

Cracking in polylactide spherulites

A polylactide of high optical purity was crystallized between 100 and 140 °C, in‐between two glass slides, and its morphology was investigated by polarizing optical microscopy, scanning electron microscopy, and atomic force microscopy, during subsequent heating and cooling cycles between ?15 °C and the crystallization temperature. It was found that dark circular rings show up on cooling on top of the spherulites and represent cracks of about 300 nm in width. This phenomenon is completely reversible, and the heating–cooling curves are centered at about 56 °C, which coincide with the T_g of polylactide. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3308–3315, 2005     

Melt crystallization and morphology of poly(ε‐caprolactone)‐poly(ethylene glycol) diblock copolymers with different compositions and molecular weights

Ring opening polymerization of ε‐caprolactone was realized in the presence of monomethoxy poly(ethylene glycol) with M_n = 1000 and 2000, using Zn(La)₂ as catalyst. The resulting PCL‐PEG diblock copolymers with CL/EO repeat unit molar ratios from 0.2 to 3.0 were characterized by using DSC, WAXD, SEC, and ¹H NMR. The crystal phase of PCL blocks exist in all polymers, and the crystallization ability of PCL blocks increases with CL/EO ratio. PEG blocks are able to crystallize for copolymers with CL/EO below 1.0 only. Melt crystallization results were analyzed with Avrami equation. The Averami exponent n is around 3.0 in most cases, in agreement with heterogeneous nucleation with three dimensional growth. The morphology of the crystals was observed by using POM. Rod‐like crystals were found to grow in 1, 3 or 2, 4 quadrants for samples with low molecular weights. In the case of a copolymer with M_n,PEG = 2000 and M_n,PCL = 800, PEG blocks could crystallize and grow on PCL crystals after PCL finished to form rod‐like crystals, leading to formation of poorly or well structured spherulites. The spherulite growth rate (G) was determined at different crystallization temperatures (T_c) ranging from 9 to 49 °C. All the copolymers present a steady G decrease with increasing crystallization temperature due to lower undercooling. On the other hand, increase of CL/EO ratio leads to increase of G in the same T_c range. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 286–293, 2010     

Structure-property behavior of films containing disk spherulites: A model study

Thin films of a polyester of lactic and glycolic acid were prepared to give controlled amounts of disk spherulites. The spherulite contents ranged from zero to 100% and were accurately measured. The stress-strain properties of the films were then determined at 60°C, i.e., about 20°C above the glass transition temperature T_g. The mechanical behavior varied quite systematically with spherulite content and displayed little dependence on spherulite size. It was found that much of the mechanical data could be reasonably well described by a simple composite model. In addition, the yield strain as well as the strain to break could be principally coupled to the deformation of only the amorphous phase. SEM and optical microscopy studies supported the above conclusion, also demonstrating that the isolated spherulites adhered well to the amorphous matrix and behaved as stress concentrators in the system when the deformation temperature was above T_g.     

Crystallization behavior and morphology of poly(propylene terephthalate) copolymers containing neopenthyl glycol moieties

The melting behavior and the crystallization kinetics of random poly(propylene/neopenthyl terephthalate) copolymers (PPT‐PNT) were investigated by means of differential scanning calorimetry and hot‐stage optical microscopy. Multiple endotherms were evidenced in the PPT‐PNT samples, due to melting and recrystallization processes, similarly to PPT. By applying the Hoffman‐Weeks' method, the T_m° of the copolymers was derived. Baur's equation described well the T_m‐composition data. The isothermal crystallization kinetics was analyzed according to the Avrami's treatment. The introduction of NT units decreased the crystallization rate in comparison to pure PPT. Values of the Avrami's exponent close to three were obtained in all cases, regardless of T_c, in agreement with a crystallization process originating from predeterminated nuclei and characterized by three dimensional spherulitic growth. As a matter of fact, space‐filling spherulites were observed by optical microscopy at all T_cs. Banded spherulites were found for PPT‐PNT5 and PPT‐PNT10, the band spacing being affected by both T_c and composition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 818–830, 2008     

New insights into the multiple melting behaviors of the semicrystalline ethylene‐hexene copolymer: Origins of quintuple melting peaks

A semicrystalline ethylene‐hexene copolymer (PEH) was subjected to a simple thermal treatment procedure as follows: the sample was isothermally crystallized at a certain isothermal crystallization temperature from melt, and then was quenched in liquid nitrogen. Quintuple melting peaks could be observed in heating scan of the sample by using differential scanning calorimeter (DSC). Particularly, an intriguing endothermic peak (termed as Peak 0) was found to locate at about 45 °C. The multiple melting behaviors for this semicrystalline ethylene‐hexene copolymer were investigated in details by using DSC. Wide‐angle X‐ray diffraction (WAXD) technique was applied to examine the crystal forms to provide complementary information for interpreting the multiple melting behaviors. Convincing results indicated that Peak 0 was due to the melting of crystals formed at room temperature from the much highly branched ethylene sequences. Direct heating scans from isothermal crystallization temperature (T_c, 104–118 °C) were examined for comparison, which indicated that the multiple melting behaviors depended on isothermal crystallization temperature and time. A triple melting behavior could be observed after a relatively short isothermal crystallization time at a low T_c (104–112 °C), which could be attributed to a combination of melting of two coexistent lamellar stack populations with different lamellar thicknesses and the melting‐recrystallization‐remelting (mrr) event. A dual melting behavior could be observed for isothermal crystallization with both a long enough time at a low T_c and a short or long time at an intermediate T_c (114 °C), which was ascribed to two different crystal populations. At a high T_c (116–118 °C), crystallizable ethylene sequences were so few that only one single broad melting peak could be observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2100–2115, 2008     

Complex phase behavior and state of miscibility in Poly(ethylene glycol)/Poly(l‐lactide‐co‐ε‐caprolactone) Blends

A miscibility and phase behavior study was conducted on poly(ethylene glycol) (PEG)/poly(l ‐lactide‐ε‐caprolactone) (PLA‐co‐CL) blends. A single glass transition evolution was determined by differential scanning calorimetry initially suggesting a miscible system; however, the unusual T_g bias and subsequent morphological study conducted by polarized light optical microscopy (PLOM) and atomic force microscopy (AFM) evidenced a phase separated system for the whole range of blend compositions. PEG spherulites were found in all blends except for the PEG/PLA‐co‐CL 20/80 composition, with no interference of the comonomer in the melting point of PEG (T_m = 64 °C) and only a small one in crystallinity fraction (X_c = 80% vs. 70%). However, a clear continuous decrease in PEG spherulites growth rate (G) with increasing PLA‐co‐CL content was determined in the blends isothermally crystallized at 37 °C, G being 37 µm/min for the neat PEG and 12 µm/min for the 20 wt % PLA‐co‐CL blend. The kinetics interference in crystal growth rate of PEG suggests a diluting effect of the PLA‐co‐CL in the blends; further, PLOM and AFM provided unequivocal evidence of the interfering effect of PLA‐co‐CL on PEG crystal morphology, demonstrating imperfect crystallization in blends with interfibrillar location of the diluting amorphous component. Significantly, AFM images provided also evidence of amorphous phase separation between PEG and PLA‐co‐CL. A true T_g vs. composition diagram is proposed on the basis of the AFM analysis for phase separated PEG/PLA‐co‐CL blends revealing the existence of a second PLA‐co‐CL rich phase. According to the partial miscibility established by AFM analysis, PEG and PLA‐co‐CL rich phases, depending on blend composition, contain respectively an amount of the minority component leading to a system presenting, for every composition, two T_g's that are different of those of pure components. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014 , 52, 111–121     

Formation of new banded spherulites in polyimides

The crystalline morphology and structural development of aromatic polyimides during an optimum continuous thermal imidization procedure were examined by means of polarized optical microscopy and X‐ray diffraction. During thermal imidization, 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride/1,3‐diaminobenzene polyimide samples formed complicated spherulites, which, in addition to zigzag Maltese crosses, also showed concentric extinction rings, which are characteristic of banded spherulites. The factors affecting the formation of banded spherulites were studied. The initial imidization conditions dramatically affected the formation of the banded spherulite morphology: slow heating (0.5 °C/min) or fast heating (20 °C/min) led to relatively small polyimide spherulites and less identifiable extinction rings. The morphological features were also affected by the molecular weight of the polyimide: higher molecular weight samples showed typical banded spherulites, whereas low‐molecular‐weight samples formed degenerated banded spherulites. In all the spherulites formed in 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride/1,3‐diaminobenzene polyimides, special zigzag Maltese crosses, instead of normal Maltese crosses, were observed. The relationship between the imidization procedure and the spherulite morphology formation was also studied. X‐ray and Fourier transform infrared together revealed that after several minutes of thermal treatment, the crystallization was nearly complete, with a 42.5% degree of crystallinity; meanwhile, only some poly(amic acid) converted to the corresponding polyimide, with a 27% degree of imidization. The crystalline morphology and structure formed in the initial stage of the imidization process were maintained during the following imidization processing at an elevated temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1997–2004, 2005     

Changes in superstructure and mechanical properties of poly(ethylene‐2,6‐naphthalate) fibers with critical necking tension

Poly(ethylene‐2,6‐naphthalate) fibers were zone‐drawn under a critical necking tension (σ_c) defined as the minimum tension needed to generate a necking at a given drawing temperature (T_d). In the zone drawing under σ_c, the neck was observed from 110 to 160 °C. The superstructure in a neck zone induced at each T_d was studied. The σ_c value decreased exponentially with increasing T_d and dropped to a low level at a higher T_d. The draw ratio increased rapidly with T_d increasing above 90 °C, but the birefringence and degree of crystallinity decreased gradually. To study the molecular orientation in the neck zone, we measured a dichroic ratio (A_‖/A_?) of a C? O band at 1256 cm^?1 along a drawing direction in the neck zone with a Fourier transform infrared microscope. A_‖/A_? at T_d = 110 °C increased rapidly in the narrow neck zone, and that at T_d = 140 °C increased in the edge of the wide neck zone. Wide‐angle X‐ray diffraction patterns of the fibers obtained at T_d = 130 °C and lower showed three reflections due to an α form, but those at T_d = 140 and 150 °C had reflections due to the α form and a β form. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1629–1637, 2001     

High melting thermoplastic/epoxy resin blends: Influence of the curing reaction on the crystallization and melting behavior

The influence of the cure process and the resulting reaction‐induced phase separation (RIPS) on the crystallization and melting behavior of polyoxymethylene (POM) in epoxy resin diglycidylether of bisphenol A (DGEBA) blends has been studied at different cure temperatures (180 and 145 °C). The crystallization and melting behavior of POM was studied with DSC and the simultaneous blend morphology changes were studied using OM. At first, the influence of the epoxy monomer on the dynamically crystallized POM was investigated. Secondly, a cure temperature above the melting point of POM (T_cure = 180 °C) was applied for blends with curing agent to study the influence of resulting phase morphology types on the crystallization behavior of POM in the epoxy blends. Large differences between particle/matrix and phase‐inverted structures have been observed. Thirdly, the cure temperature was lowered below the melting temperature of POM, inducing isothermal crystallization prior to RIPS. As a consequence, a distinction was made between dynamically and isothermally crystallized POM. Concerning the dynamically crystallized material, a clear difference could be made between the material crystallized in the homogeneous sample and that crystallized in the phase‐separated structures. The isothermally crystallized POM was to a large extent influenced by the conversion degree of the epoxy resin. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2456–2469, 2007     

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