Acknowledgments
3.3 Preparation and Characterization of Several Types of Functionally
3.3 Preparation and Characterization
3.3.2 Amorphous Polymer/Crystalline Polymer Miscible Blend
(Dissolution–Diffusion Method)
In the case of the PVC/PCL system [25], we obtained the optimum conditions when the graded polymer blend was prepared with a wider compositional gradient, similar to the PVC/PMMA system.
Figure 3.10 shows the PVC content of the samples for the direction of thickness, measured by the FTIR-ATR method. PVC decreased at about 70 mm from the petri glass side and decreased gradually until the surface of the air side, that is, about 240 mm apart from the petri glass side in both cases of the solution volume.
Th en, the change of Tg for the thickness direction of the blend fi lm was characterized by the DSC method (Figure 3.11) in the case of 0.364 ml/cm2 of solution volume. Tg decreased with the increase of the distance from the petri glass side, similar to the PVC content. Th us, the graded structure in the PVC content was confi rmed by the graded profi le in Tg.
Furthermore, the change of the PCL crystalline content was evaluated from that of the amount of the heat diff usion eff ect on the PCL crystalline, measured by the DSC method. Th e heat dif- fusion began to increase on the specimen aft er it was initially kept at 0 and then about 130 mm of the distance to the air side.
Th en, it increased immediately around about 180 mm. Th us, it was found that the graded structure in the PCL crystalline was formed in a distance of 130–240 mm. Th is means that the obtained graded PVC/PCL blend had both a gradient concentra- tion of the PVC and a gradient content of the PCL crystalline, as shown in Figure 3.12. Th e PCL content was about 30% for a dis- tance of 130 mm. Th is result corresponded to that of the PCL crystalline in a homogeneous PVC/PCL blend, which emerged in the case of the larger than 30% of the PCL [44]. It was further considered that the amorphous phase was made up of a miscible amorphous PVC/amorphous PCL blend. Finally, the PCL crys- talline phase decreased the closer it came to the surface of the air side again. Th is phenomenon occurred because the forming of the amorphous phase was more thermodynamically stable than that of the crystalline phase.
Th e graded structure of the PVC/PCL graded blend could be schematically illustrated in Figure 3.13.
Temperature (K) Graded structure 3
330 360 390 420 Graded structure 2
Graded structure 1
Exotherm
FIGURE 3.8 DSC curves of several types of PVC/PMMA blends.
Thickness direction
Chlorine content
20 μm
FIGURE 3.9 Chlorine content along the thickness of PVC/PHMA graded blend (×750).
J
J
J J J
J
J E
E
E E E
E E
E E E E
0 10 20 30 40 50 60 70 80 90 100
0 50 100 150 200 250
PVC content (%)
Distance from petri glass side (μm) J 0.182 ml/cm2
E 0.364 ml/cm2 Solution volume
FIGURE 3.10 Graded structures of the PVC/PCL graded blends mea- sured by the FTIR-ATR method.
E
E
E E E
E E
E E E E
0 10 20 30 40 50 60 70 80 90 100
0 50 100 150 200 250
PVC content (%)
Distance from petri glass side (μm) J Tg
E PVC content
J J J J J J
J
200 220 240 260 280 300 320 340 360
Tg (K)
FIGURE 3.11 Graded structures of PVC/PCL graded blends charac- terized by the DSC method.
3.3.3 Amorphous Polymer/Amorphous Polymer Immiscible Blend (Dissolution–Diffusion Method)
We attempted to prepare a graded PC/PS blend by the dissolu- tion–diff usion method [24], similar to the PVC/PMMA system.
In this case, the PS solution was poured onto the PC fi lm.
However, we did not obtain a graded structure, but obtained a homogeneous two-layer system, which was composed of about 50% and 0%–10% of PC, as shown in Figure 3.14. Next, the mac- rophase separation was observed in the former layer.
Th is result was thought to occur because of the following;
only three factors, dissolution rate, diff usion rate, and evapora- tion time, could aff ect the process in forming a graded structure of miscible blend. However, in forming the graded structure of an immiscible blend, three additional factors also played a role:
macrophase separation, surface roughness, and gravimetry, as shown in Figure 3.15. Especially, the macrophase separation may increase the size of the separated phases up to the size of the thickness in the prepared fi lm, resulting in a possible break in the formation of a strongly graded structure, when its concentration becomes higher by the evaporation of the solvent.
Th erefore, we attempted to prevent macrophase separation during graded structure formation by adding PS-b-PC block copolymer [45]
to the PS solution (PS-b-PC block copolymer/PS = 1/9). Th e copolymer may act as a compatibilizer by decreasing the interface energy of the phases. In this case, the PC segment content in the block copolymer was 46% (NMR measurement). It was found that the wide graded structure in the obtained PC/PS blend was formed in the distance range of 0–100 μm from the petri glass side (Figure 3.14).
Furthermore, we attempted to prepare a graded PC/PS blend by pouring the PC solution containing the block copolymer onto the PS fi lm. Figure 3.16 shows the change of the PC content for the direction of the fi lm thickness. A wide graded structure was formed and confi rmed not only, in the furtherest distance from, but also in the distance closest to the petri glass side. Th is result meant that surface roughness signifi cantly infl uenced the forming of the graded structure.
Th erefore, we were able to obtain the graded immiscible PC/PS blend by adding the PC-b-PS block copolymer. Th e graded structure assumed to be formed for the PC/PS graded blend could be schematically illustrated in Figure 3.17.
0 20 40 60 80 100 120 140 160
Heat of diffusion (J/g)
0 50 100 150 200 250
PVC content (%)
0 10 20 30 40 50 60 70 80 90
J 100
E
E E
E E E E
E J
J J
J J J
J J J J
Distance from petri glass side (μm) J PVC content
E Heat of diffusion
FIGURE 3.12 Graded structure of PVC/PCL graded blends (PCL crystalline).
PCL crystalline phase
PCL PVC
FIGURE 3.13 Schematic model of the PVC/PCL graded blend (graded structure).
E
E E
E
E
E J J J JJ J
J 0 J
10 20 30 40 50 60 70 80 90 100
0 20 40 60 80 100 120 140 160 180
PC content (%)
Distance from petri glass side (μm) E
J
PC -b-PS copol ymer/
PS(1/ 9) b lend PS o n l y
Type of solution
FIGURE 3.14 Graded structure of PC/PS graded blend with or without the PS-b-PC block copolymer.
FIGURE 3.15 Other factors that have an eff ect on forming graded structure in an immiscible blend.
(1) Effect of macro phase separations
(2) Effect of surface inclination
(3) Effect of gravitation
3.3.4 Amorphous Polymer/Crystalline Polymer Immiscible Blend
(Polymerization–Diffusion Method) In the case of the immiscible graded blend of the PBMA/PEO system [30], we obtained the optimum conditions in the prepara- tion by the polymerization–diff usion method. Figure 3.18 shows the PEO content of the samples for the direction of thickness, measured by the confocal Raman spectroscopy and the NMR methods. Th e data obtained by the NMR method were almost the same as those by the Raman method. It was found that the NMR method was available and so it was used. Figure 3.19 shows the GPC data of the layers around the thickness points (No. 1, 3, 5, 7 in Figure 3.18) as measured by NMR method. Th e peak cor- responding to the block copolymer (EO-b-BMA copolymer) became larger when the number of the points was larger. Th en, the molecular weight and the content of the block copolymer became larger as the number of points became larger, that is, the BMA content was larger (Table 3.2). It was considered to occur because the polymerization rate was larger with a larger amount of the BMA monomer.