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Crystallization behavior of PEO in blends of poly(ethylene oxide)/poly(2-vinyl pyridine)-b-(ethylene oxide) block copolymer.

INTRODUCTION

Polymer blends have been extensively studied due to their application for the development of materials with new chemical and physical properties [1-3]. Crystallization behavior and morphology developments of block copolymers have also been investigated widely in the last decades [4-9].

Studies on synthesis, characterization, isothermal crystallization, and spherulilic morphology of different types of copolymers can be found in the literature [4, 8, 10-13]. In multiblock copolymers, Petrova et al. [14] have reported the synthesis and thermal analysis of polyethylene oxide)-poly(caprolactone) (PEO/PCL) multiblock copolymers by differential scanning calorimetry (DSC). They found two melting peaks, reflecting the presence of two crystalline domains.

In semicrystalline block copolymers, high order superstructures such as spherulite and dendrite formation can be found [15]. The formation of spherulites can be affected by crystallization conditions. For this reason, the crystallization temperature is a very important factor to be taken into account for the superstructure formation in block copolymers. Albuerne et al. [4] studied the crystallization process of poly(p-dioxanone)-b-([epsilon]-caprolactone) diblock copolymer. They found that the copolymer exhibited banded spherulitic superstructure, that is, an extinction pattern between crossed polarizers under an optical microscope [16], caused by a zero birefringence effect was observed in studies of the spherulite formation. They discovered that this effect was progressively changed to spherical granular aggregates at lower supercooling temperatures. Hamley el al. [5] reported the crystallization behavior of poly(L-lactide)-b-([epsilon]-caprolactone) block copolymer, showing instantaneous nucleation with three dimensional superslructures according to the Avrami's indexes [17].

The majority of studies on polymer blends have focused on systems containing mainly homopolymers. Nevertheless, in the last years, the study of blends containing block copolymers has been a matter of current interest due to the versatility of chemical compositions of the samples that can allow to enhance interpolymer miscibilily and then miscibilily or at least compatibility, thus conducting to a material with new properties. Miscibility windows in these systems are very common and the phase behavior has been extensively studied and strongly discussed as a way to obtain new polymeric materials [18-20].

The aim of this work is the analysis of the thermal behavior and crystallization features of blends containing poly(ethylene oxide) (PEO) and a diblock copolymer of poly(2-vinylpyridine)-b-(ethylene oxide) (P2VP-b-PEO). The variations on crystallinity and changes in the morphology have been investigated using polarized optical microscopy (POM), thermogravimetric analysis (TGA), DSC, and atomic force microscopy (AFM). The effect of the chemical structure of the components on the crystallization process and on the compatibilization of the blends is also analyzed and discussed.

EXPERIMENTAL

Polymers

Poly(ethylene oxide) (PEO200M) with an average viscosimetric molecular weight, [M.sub.v] = 200,000 g/mol was purchased from Aldrich. Poly(ethylene oxide) (PEO40M) with weight average molecular weight, [M.sub.w] = 41,500 g/mol and [M.sub.w]/[M.sub.n] =1.14 was purchased from Fluka.

A poly(2-vinyl pyridine)-b-(ethylene oxide) block copolymer with number average molecular weight, [M.sub.n] = 80,000 g/mol, [M.sub.w]/ [M.sub.n] = 1.1 and 50% wt of P2VP was synthesized by anionic polymerization by Hadjichristidis and coworkers [10].

Preparation of Polymer Blends

A series of PEO and P2VP-6-PEO blends were prepared by solution casting using chloroform solutions. The polymer concentration in the solution was about 2% w/w and the polymer samples were dried under vacuum for 2 days.

Polarized Optical Microscopy

The isothermal crystallization of the blends was investigated using an Olympus BX60 polarized optical microscope equipped with a hot-stage Linkam THMS-600, TMS-93 temperature programmer, and CCD digital camera QImaging MP5. The films were prepared from the corresponding polymer blends in solution. Then each film was heated from room temperature to 120[degrees]C at which complete melting was observed. That temperature was maintained for 5 min and the sample was subsequently cooled at a rate of 40[degrees]C/min to the crystallization temperature (which was held constant). The growth of the spherulites was directly recorded and analyzed via software Qimaging QCapture pro.

Thermogravimethc Analysis

Thermal degradation of pure polymers, block copolymers and blends was measured with a Mettler Toledo TGA/SDTA 851 system. Thermograms were performed in the range 25-900[degrees]C at a scan rate of 20[degrees]C/min under nitrogen atmosphere.

Differential Scanning Calorimetry

Samples were encapsulated in aluminum pans under nitrogen atmosphere. A Mettler Toledo DSC 821 calorimeter was calibrated for lemperature and heat How using an indium standard.

Dynamic Experiments. Samples was heated from 25 to 120[degrees]C at 20[degrees]C/min and maintained at 120[degrees]C to erase all previous thermal history, after that it was cooled to - 100[degrees]C al the cooling rate of the 2.5[degrees]C/min to ensure crystallization of the sample. The [T.sub.g] and Tm were subsequently recorded at a heating rate of 20cC/min in a second scan.

Isothermal Crystallization Experiments. The samples were first heated to 120[degrees]C for 5 min to erase all previous thermal history, and then cooled at a rate of 40[degrees]C/min to the isothermal crystallization temperature ([T.sub.C]). The samples were held at [T.sub.C] for a constant period of 3 hr. Finally, a heating scan from [T.sub.C] up to complete melting was recorded at 10[degrees]C/min. Three crystallization temperatures were selected (40, 43, and 45[degrees]C).

Atomic Force Microscopy

AFM images were obtained operating in soft tapping mode with a scanning probe microscope (Nanoscope IIIa, Multimode from Digital Instruments) equipped with an integrated phosphorus doped tip/cantilever having a resonance frequency of around 180 kHz, from the same manufacturer.

The height and phase images were obtained under ambient conditions with typical scan speeds of 0.5-1 line/s, using a scan head with a maximum range of 16 * 16 [micro] [m.sub.2].

RESULTS AND DISCUSSION

The analysis by polarized light microscopy of polymers and blends was started establishing the sign of the birefringence. The sign of the birefringence was determined using a primary red filter ([lambda] plate) located diagonally between the crossed polarizers. When the spherulite is negative, its first and third quadrants are yellow-orange. The second and fourth ones are blue, being first quadrant that of the top in the right hand side of the polarized image. For a positive spherulite, the first and third quadrants are blue and the second and forth ones are yellow-orange, what is a common accepted interpretation [5, 21]. The sign of the birefringence is related to the orientation of the spherulite radius with the optical axis, that is, horizontal (positive) or perpendicular (negative).

[FIGURE 1 OMITTED]

Polarized optical pictures reported in Fig. 1 show spherulitic morphologies with a primary red filter for (a) PEO(40M), (b) P2VP-b-PEO copolymer, (c) 50% PEO(40M)/P2VP-b-PEO blend at 40[degrees]C, and (d) 50% PEO(40M)/P2VP-b-PEO blend at 45[degrees]C. Figure la shows that the sign of the birefringence in the spherulites is negative for the hornopolymer PEO(40M) taking into account the characteristic colors of Maltese Cross, when using a first order red ([lambda] plate) and the orientation of the spherulite radius with the optical axis is perpendicular. On the contrary, in Fig. lb, for the block copolymer, the sign of the birefringence is positive and the orientation of the spherulite radius with the optical axis is horizontal. For the 50% PEO(40M)/P2VP-b-PEO blend, as shown in Fig. lc, the sign of the birefringence changes, that is, the first and third quadrants are more yellow-orange than that for pure PEO(40M). A soft yellow-orange color with blue lines can be seen to be spread through the spherulite. Figure lc shows both signs of birefringence, what would indicate the presence of a mixture of both polymers (PEO and the copolymer). This result would suggest that both polymers have a distinct orientation. Figure Id is the image taken after crystallization at 45[degrees]C. It is possible to observe that blue and yellow-orange signals are spreading along the whole image. Therefore, this result suggests that when the crystallization process takes place at higher temperature (45[degrees]C; Fig. 1d), the blend shows a random-like distribution of the signals relative to the system crystallized at lower temperature.

Figure 2 shows the degradation profiles for PEO(40M)/ P2VP-b-PEO and PEO(200M)/P2VP-b-PEO blends. The profiles are represented as the first derivative of weight loss (weight %) with temperature (DTGA). The thermog-ravimelric profiles follow a single one-stage decomposition process for pure components and blends. The addition of the block copolymer P2VP-b-PEO to PEO(40M) (see Fig. 2a) increases the degradation temperature becoming the thermal stability of the blend very similar to that of the block copolymer P2VP-6-PEO. This behavior is similar irrespective of the molecular weight of the homopolymer, as can be seen in Fig. 2b (PEO200M). This behavior indicates that PEO(200M) degrades at lower temperature than PEO(40M) what could be due to the higher molecular mass. However, the peaks for blends are encounter at the same temperature irrespective of PEO molecular weight and are clearly higher than that the pure PEO, this behavior suggests that the interactions between the components in the blend thermally stabilize the pure PEO.

[FIGURE 2 OMITTED]

The crystallization of PEO was analyzed by DSC. The equilibrium melting temperature for crystalline PEO in the blend was estimated by the Hoffman and Weeks relationship [17]. The [T.sub.m] versus [T.sub.c] plots shows an extrapolation reasonably linear for all blend compositions at four distinct temperatures (see Fig. 3). Nevertheless, the analysis of the crystallization was performed only with three temperatures (40, 43, and 45[degrees]C).

[FIGURE 3 OMITTED]

Table 1 lists the values of the measured equilibrium melting temperatures ([T.sub.m][degrees]), melting temperatures ([T.sub.m]), crystallization temperature, and glass transition temperature for PEO(40M)/P2VP-b-PEO blends by determined by DSC. The addition of the block copolymer to PEO(40M) decreases the equilibrium melting temperature of the crystalline part of the blend. The exception is observed for the blend containing 80 wt% PEO(40M). This behavior is not observed in the melting temperature, what can be attributed to the fact that the equilibrium melting temperature is obtained only by the extrapolation from the Hoffman and Week plots, and can lead to an underestimation of the equilibrium melting temperature [22, 23]. The addition of the block copolymer to PEO(40M) decreases the melting and crystallization temperature of the crystalline part of the blend exhibiting an intermediate value to those for neat PEO and PEO block in the copolymer. The observed melting point depression can be attributed to morphological effects derived from the size and perfection of the crystalline regions, and the effects produced by the reduction of the amount of crystallizable polymer in the melt with increasing the copolymer content in the blend. This effect could produce a decrease of the driving force that favors the crystallization process [23, 24].

DSC measurements of the block copolymer and blends in the low temperature region show only one [T.sub.g] value (see Fig. 4; Tables 1 and 2). This behavior is a clear evidence of the interactions between PEO chains in the neat PEO and in the block copolymer, what is in agreement with the reported data for the miscibility of the components [25].

The [T.sub.g] of the homopolymer PEO(40M) is lower (-73[degrees]C, the [T.sub.g] value of PEO(40M) was obtained from literature)[26] than that of the copolymer (-42[degrees]C). As the copolymer content in the blend increases, the [T.sub.g] value of the blend increases and exhibits an intermediate value between those of the pure components, thus indicating that the blend behaves as a compatible one.
TABLE 1. [T.sub.m][degrees], [T.sub.m], [T.sub.c] and [T.sub.g]
values of PEO(40M)/P2VP-b-PEO blends.

System      [T.sub.m]     [T.sub.m]     [T.sub.c]     [T.sub.g]
             [degrees]    ([degrees]C)  ([degrees]C)  ([degrees]C)
            ([degrees]C)  Onset-Peak    Onset-Peak

PEO(40M)           66.0    61.7  66.7    51.5    49         -73
80% PEO            69.5    60.1  65.3    46.0  44.0         -63
50% PEO            65.5    59.0  64.0    41.3  38.8         -55
20% PEO            61.3    56.4  62.3    32.4  23.7         -45
P2VP-b-PEO         64.9    48.7  56.0    15.6  13.2         -42


Table 2 summarizes the results for [T.sub.m] [degrees], [T.sub.m], [T.sub.c], and [T.sub.g] obtained for PEO(200M)/P2VP-b-PEO blends by DSC. The melting and crystallization temperatures of the crystalline region decrease with addition of block copolymer, what is a similar behavior to that described for blends containing PEO(40M). For these blends, the [T.sub.g] value also increases as the content of the homopolymer PEO(200M) in the blend is lower (see Fig. 4). As the molecular weight of PEO increases from PEO(40M) to PEO(200M), the [T.sub.g] values of the blends also increase, as it can be seen in Tables 1 and 2. Therefore, it should be considered that the freedom to increase the cooperative motions to favor interactions of the chains is higher for PEO(40M) than for PEO(200M), due to the lower steric hindrance in the case of samples with lower molecular weight.
TABLE 2. [T.sub.m][degrees], [T.sub.m], [T.sub.c] and [T.sub.g]
results of PEO(200M)/P2VP-b-PEO

System      [T.sub.m]     [T.sub.m]     [T.sub.c]     [T.sub.g]
             [degrees]    ([degrees]C)  ([degrees]C)  ([degrees]C)
            ([degrees]C)  Onset-Peak    Onset-Peak

PEO(200M)          66.0    60.9  66.3    51.5  49.5         -73
80% PEO            66.5    57.1  63.7    44.4  41.4         -56
50% PEO            63.9    58.1  63.0    34.3  29.6         -51
20% PEO            63.9    55.7  61.7    20.6  14.6         -48
P2VP-b-PEO         64.9    48.7  56.0    15.6  13.2         -42


[FIGURE 4 OMITTED]

The spherulilic growth through crystallization of PEO on the block copolymer was studied by POM by analyzing the formation of the spherulites (see Fig. 5). The growth rate G ([micro]m/sec) was obtained by measurements of the spherulite diameter as function of time. The radius was found to increase linearly on time up to the point of impingement, indicating a constant growth rate throughout the crystallization process. The linearity of radius implies that the amorphous region, which is rejected from the growing PEO crystalline region, does not migrate away from the spherulitic growth front, but rather became trapped within the interfibrillar regions of the growing spherulites [27].

[FIGURE 5 OMITTED]

Tables 3 and 4 compile the results of (he growth rate G ([micro]m/sec) for PEO(40M)/P2VP-b-PEO and PEO(200M)/ P2VP-b-PEO blends. The value of growth rate of PEO is in the range expected according to the results found in the literature [28]. A diminishing of the grow rate of spherulites formation for blends can be observed as the copolymer content increases in the blends. It should be pointed out that this growth rate reduction is not related to changes in fluidity of the melt that may be of importance in blend systems showing a wide variation of [T.sub.g] with blend compositions [29], Nevertheless, the influence of P2VP block on the viscosity cannot be disregarded. In blends of PEO and P2VP-b-PEO, the variation of [T.sub.g] with the compositions is small (from -73 to -42[degrees]C). For this reason, the crystallization rate depression should be explained by the reduction of the driving force for crystallization due to changes in the equilibrium melting temperature and the dilution effects associated to a diminishing of the concentration of crystalline region in the crystal growth front.
TABLE 3. Crystallization growth rate G ([micro]m/sec) as a
function of homopolymer content in PEO(40M)/P2VP-b-PEO blends
at three isothermal crystallization temperatures.

System       40 [degrees]C  43[degrees]C  45[degrees]C


PEO(40M)           65.6            46.2          28.1
80% PEO            13.2            14.9           5.7
50% PEO            0.99            0.89          0.50
20% PEO            0.10            0.12          0.05
P2VP-b-PEO         0.01           0.008         0.006

TABLE 4. Crystallization growth rate G ([micro] m/sec) as a
function of homopolymer content in PEO(200M)/P2VP-b-PEO blends
at three isothermal crystallizalion temperatures.

System      40[degrees]C  43[degrees]C  45[degrees]C

PEO(200M)      55.9          29.7          20.2
80% PEO         5.5          1.92          0.37
50% PEO        0.40          0.20          0.18
20% PEO        0.06          0.03          0.03
P2VP-6-PEO     0.02         0.008         0.006


Growth rate of spherulite decreases as isothermal crystallization temperature in the blend is higher, as can be expected (as the temperature increases the number of active nucleus diminishes which are the responsible of the spherulites grow). When the molecular weight of the homopolymer in the blend increases, from PEO(40M) to PEO(200M), the grow rate of spherulite decreases. This behavior could be explained taking into account the restriction to diffusion with increasing the molecular weight.

POM observation at different blend composition shows small changes in the spherulite morphology. These results would suggest the existence of different crystalline structure as Cordova et al. [30] reported for the particular case of P2VP-PEO block copolymer. These changes could be attributed to the inhibition of secondary nucleation of PEO by the glass P2VP block.

Figure 6 shows the variation of crystallinity extent of PEO with the content of P2VP-b-PEO block copolymer. The crystallinity of PEO show in the Fig. 6 was calculated from crystallinity = [DELTA]H (measured)/[DELTA][H.sub.f],-, where the heat of fusion of 100% crystalline PEO is 196.6 J[g.sub.-1] [31]. The crystallinity of PEO(40M) is larger than that of PEO(200M) and decreases from 65 to 29% and from 56 to 29% for PEO(40M)/P2VP-b-PEO and PEO(200M)/ P2VP-b-PEO blends, respectively, as the composition of the diblock copolymer in the blend increases. This behavior should be a consequence of the higher degree of freedom in PEO(40M) than in PEO(200M) due lo the lower molecular weight.

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

However, the diminishing of the crystallinity with increasing the content in block copolymer is an expected result taken into account that blends contain increasing amount of block copolymer with lower crystallinity than that of the pure homopolymer.

The isothermal crystallization data obtained were fitted to the Avrami model [16], shown in Eq. 1.

[a.sub.c](t)= l-exp(-k[t.sup.n]) (1)

where [[alpha].sub.c] (t) is the relative crystalline fraction of the polymer as a function of time, k can be considered as an overall transformation rate constant, and n is the Avrami's index.

The Fig. 7 show the Avrami's indexes for the PEO200M/P2VP-b-PEO blends at 40[degrees]C and the Table 5 summarizes the results at three temperatures 40, 43, and 45[degrees]C. As a general trend, the index diminishes as PEO content in the blend decreases. Nevertheless, the general shape is similar for all the systems at the different temperature analyzed, and in the case of blends at 45[degrees]C, the values are more or less constant. Nevertheless, irrespective of the uncertainty of the data, the results suggest a two dimensional spherulitic growth with instantaneous nucleation, according to the data previously reported and generally accepted [5, 28]. It is necessary to take into account that the application of the Avrami's model has some limitations, particularly in the case of polymer blends; and therefore, it can be considered only as an approximation to take confidence about the kinetic of the crystallization of the blend [32].
TABLE 5. Avrami's indexes for PEO(200M)/P2VP-b-PEO blends.

System      40[degrees]C  43[degrees]C  45[degrees]C

PEO(200M)       5.1           1.9           4.9
80% PEO         2.8           2.5           2.4
50% PEO         2.3           2.3           2.4
20% PEO         2.0           2.3           2.1
P2VP-b-PEO      2.7           2.1           2.8


Avrami's indexes between 2 and 3 for the blends at 40[degrees]C are observed. In the case of 80 wt% PEO blend, the values of n are close to 3, what would indicate instantaneous spherulitic growth according to literature [17], However, in the case of 50 and 20 wt% PEO in the blend, the values of n are close to 2, what would suggest a two-dimensional spherulitic growth with instantaneous nucleation [17], With increasing isothermal crystallization temperature, the values of n for the blends are also close to 2 and 3. In the case of homopolymer PEO(200M), the value of n are close to 5. It has been reported a value of n = 5 for polystyrene, what suggests a three-dimensional conelike spherulitic growth [33].

Table 6 shows the Avrami's indexes for PEO(40M)/ P2VP-b-PEO blend. As a general observation, the Avrami's index increases as the PEO(40M) content decreases in the blend. At isothermal crystallization temperature of 40 C the n index changes from 1.6 to 2.7 as the PEO(40M) content decreases in the blend. As increasing isothermal crystallization temperature from 43 to 45C the values of n are also close to 2 and 3 for the blends. These results suggest a two dimension (2D) lamellar aggregates with instantaneous nucleation and three dimension (3D) instantaneous spherulitic growths, respectively. These results are widely reported and accepted [5, 17, 28]. These assumptions, therefore, could be accepted for PEO/P2VP-b-PEO blends, despite the scattering of the data relative to those of pure PEO. Nevertheless, the results for blends are inside the experimental error.
TABLE 6. Avrami's indexes for PEO(40M)/P2VP-b-PEO blends.

System      40[degrees]C  43[degrees]C  45[degrees]C

PEO(40M)        1.6           2.1           1.9
80% PEO         2.1           2.3           2.0
50% PEO         2.3           2.4           2.3
20% PEO         2.4           2.6           2.3
P2VP-b-PEO      2.7           2.1           2.8


To clarify the general crystallization behavior of the different blends and to know how the morphology of the blends is affected as the crystallization temperature changes, AFM measurements were performed. It seems reasonable to think that if the crystallization processes al different temperatures change the instantaneous crystallization in 2D or 3D, a change in the morphology should be expected.

The morphology of the PEO(200M)/P2VP-b-PEO blends after isothermal crystallization at 40 and 45[degrees]C was analyzed by AFM, Figs. 8 and 9. As shown in Fig. 8, AFM images of PEO(200M)/P2VP-b-PEO blends at 40[degrees]C. For the pure PEO(200M), spherulite formation with a lamellar crystal morphology alternating amorphous and crystalline phase is observed, in agreement with a reported work [34] (see Fig. 8a). As increasing the copolymer content in the blend, the morphologies show small changes. In the case of the blend containing 80 wt% PEO(200M) (Fig. 8b), it is possible to observe a lamellar crystal morphology with a sheaf-like lamellar arrangements [34] and in the case of 50 and 20 wt% PEO(200M) blends a lamellar crystal morphology with grains aggregation is observed (Fig. 8c, d). This morphology changes with the size and perfection of the crystalline part could be responsible of the depression in the equilibrium melting temperature as the copolymer content in the blends increases. This behavior is still enhanced as the molecular weight of the homopolymer in the blends decreases PEO(200M) to PEO(40M). This fact would be in agreement with the results obtained for the variation of crystallinity extent of PEO with the content of block copolymer. For sake of clarity images for PEO(40M) are not included.

[FIGURE 8 OMITTED]

[FIGURE 9 OMITTED]

When increasing the isothermal crystallization temperature from 40 to 45[degrees]C (see Fig. 9a-d) a diminishing in the lamellar thicknesses is observed for the blends. The degree of order after crystallization at 40[degrees]C diminishes relative to that at 45[degrees]C. For this reason the spherulites images after crystallization at 45[degrees]C can be observed as more homogenous than that after crystallization at 40[degrees]C. These results would be in agreement with the fact that at 45[degrees]C the blend spent more time to crystallize relative to that at 40[degrees]C and then a more "ordered" morphology is observed.

CONCLUSIONS

In this article, studies of the crystallization behavior and morphology in PEO/P2VP-b-PEO blends are reported. All the blends show the spherulite formation as can be seen by POM.

Thermogravimetric profiles show a single one-stage decomposition process for pure component and blends. The addition of the block copolymer to PEO increases the degradation temperature and the peak of the blends are encounter at the same temperature irrespective of the PEO molecular weight and is clearly higher than that the of pure PEO. This behavior suggests that the interactions between the components in the blend thermally stabilize the pure PEO.

The [T.sub.g] values of PEO(40M)/P2VP-b-PEO and PEO(200M)/P2VP-b-PEO blends exhibit an intermediate value between those of pure components and this value increases as the content of the homopolymer PEO decreases. This behavior is an evidence of the interactions between PEO chains in the neat PEO and in the block copolymer.

The addition of the block copolymer to PEO decreases the melting and crystallization temperature of the crystalline part of the blend, being the values in between those of the PEO domains in neat PEO and PEO block in the copolymer. This result may be attributed to a morphology effect, that is, the reduction of the crystalline region when the copolymer content in the blends increases.

A decreasing of the growing rate of spherulite for these blends as the copolymer content increased was observed. This may be due to the reduction of the driving force for crystallization because the changes in the equilibrium melting temperature and the dilution effect associated with a decreasing of the concentration of the crystalline part. When the molecular weight of the homopolymer in the blend increases from PEO(40M) to PEO(200M), the growth rate of spherulite decreases.

AFM images showed spherulites with lamellar crystal morphology for the homopolymer PEO in agreement with POM results. A lamellar crystal morphology with sheaflike lamellar arrangement is observed for 80 wt% PEO(200M) and a lamellar crystal morphology with grain aggregation is observed for 50 and 20 wt% blends. This behavior is still enhanced as the molecular weight of the homopolymer in the blends decreases PEO(200M) to PEO(40M). When increasing the isothermal crystallization temperature a diminishing in the lamellar thicknesses is observed for the blends.

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Correspondence to: Emilio Araneda; e-mail: ejaraned@uc.cl

Contract gram sponsor: Conicyt; contract grant number:

24090082. contract grant sponsor: Fondecyt; contract grant numbers:

N 1080026, N 1080007.

DOI 10.1002/pen.22183

Published online in Wiley Online Library (wileyonlinelibrary.com).

[c] 2011 Society of Plastics Engineers

Emilio Araneda, (1) Angel Leiva, (1) Ligia Gargallo, (1) Nikos Hadjichristidis, (2) Inaki Mondragon, (3) Deodato Radic (1)

(1.) Laboratorio de Quimica Fisica de Macromoleculas, Departamento de Quimica Fisica, Facultad de Quimica, Pontificia Universidad Catolica de Chile. Casilla 306, Correo 22, Santiago, Chile

(2.) Department of Chemistry, University of Athens, 15771 Panepistimiopolis Zografou, Athens, Greece

(3.) 'Materials + Technologies' Group, Dpto. Ingenierfa Quimica y M. Ambiente, Escuela Politecnica, Universidad Pais Vasco/Euskal Herriko Unibertsitatea Pza Europa 1. 20018 Donostia, San Sebastian, Spain
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Author:Araneda, Emilio; Leiva, Angel; Gargallo, Ligia; Hadjichristidis, Nikos; Mondragon, Inaki; Radic, Deo
Publication:Polymer Engineering and Science
Article Type:Report
Geographic Code:3CHIL
Date:May 1, 2012
Words:5069
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