The crystallization and crystalline structure of syndiotactic-polypropylene (sPP) and syndiotactic-poly(1-butene) (sPB) blend containing 10 (Bl-10), 25 (Bl-25), 50 (Bl-50), 75 (Bl-75), and 90 (Bl-90) wt% of sPB, have been investigated by means of differential scanning calorimetry (DSC), FT-IR, and wide-angle X-ray diffraction (WAXD) analyses. The melt-crystallization behavior of the blend samples was studied by DSC on the cooling process at constant rates. Bl-50, Bl-75, and Bl-90 showed lower crystallization temperatures than the neat sPP. sPP in Bl-75 showed the lowest crystallization rate among the blend samples. Bl-90 showed a two-phase molten state, and sPP in Bl-90 crystallized via two-stepprocess. Time evolution of FT-IR spectroscopy at room temperature detected conformational transformation of the sPP polymer chain in the blend samples of Bl-50 and Bl-75. The absorption peaks intensity in the FT-IR spectra derived from the helical conformations in the crystalline phase decreased, and the planar zigzag conformations in the amorphous and mesophase phases decreased over the crystallization time. The time evolution of the WAXD profile of Bl-90 indicated that sPP in the blend accelerated the crystallization of sPB. The crystallized Bl-10, Bl-25, and Bl-50 samples showed diffraction peaks in WAXD profiles and melting endothermic peak in DSC profiles derived from only the sPP crystal. The crystallinity and melting temperature of sPP in the crystallized Bl-10, Bl-25, and Bl-50 samples were almost independent of the sPB content. Both the crystalline structure of sPP and sPB were detected in Bl-75 and Bl-90. Bl-75 showed the lowest crystallinity and melting temperature of sPP among the blend samples.
Development of transition metal catalysts for olefin polymerizations has enabled us to synthesize highly syndiotactic poly(α-olefin)s with narrow molecular weight and composition distributions [
The Cs-symmetrical syndio-selective metallocene catalysts also promote copolymerization of olefins effectively. The copolymerization of propylene with other olefins is one of the useful methods to control the crystalline structure and properties of sPP [
Polymer blends of sPP with other crystalline polyolefins, such as isotactic-polypropylene (iPP) [
As mentioned above, syndiotactic-poly(propylene-co-1-butene) forms the isomorphous crystal. Both the syndiotactic-poly(propylene-co-1-butene) [
sPP and sPB were synthesized by polymerization of the corresponding monomer with a syndio-selective zirconocene catalyst, isopropylidene(cyclopentadienyl)(9-fluorenyl)zirconiumdichloride, using methylaluminoxane as a co-catalyst, according to the literature [
sPP and sPB (total 1 g) were dissolved in a 15 mL of o-dichlorobenzene at 160˚C and stirred for 30 min. The heated polymer solution was slowly poured into a large excess of methanol with stirring to precipitate the polymer blend. The blend sample was filtered and dried in vacuo at 30˚C for 6 h. The sPB contents in the blends are 10 (Bl-10), 25 (Bl-25), 50 (Bl-50), 75 (Bl-75), and 90 (Bl-90) wt%.
The crystallization process was traced with a Rigaku DSC 8230. The blend samples were heated from room temperature to 180˚C at a heating rate of 10˚C/min and kept for 10 min, and cooled to 20˚C at the desired cooling rate under nitrogen atmosphere. The samples for FT-IR measurement were melted at 200˚C and pressed under 10 MPa pressure in a mold of 0.2 mm thickness, and rapidly cooled to room temperature by quenching into water. The IR spectra were measured using a FT-IR 800S (Shimadzu) or a Nexus 470 FT-IR (Thermo Nicolet).
The blend samples were melted at 200˚C and pressed under 10 MPa pressure in a mold of 5 mm radius with 1 mm thickness, followed by quenching in water at room temperature. The samples were stored at room temperature for 4 weeks to prepare crystallized samples. The WAXD patterns of the crystallized samples were recorded on a Shimadzu XD-D1 using Cu Kα radiation. The differential scanning calorimetry (DSC) measurement of the crystallized polymers was investigated by a Shimadzu DSC-50 at a heating rate of 10˚C/min from room temperature to 200˚C under nitrogen atmosphere.
The crystallization process of sPP in the blend samples was traced by the DSC measurement from 180˚C to 20˚C on the constant cooling rate of 3, 6, 12, or 24˚C/min.
Bl-90 showed the bimodal exothermic peaks in the DSC profiles. A Tc of Bl-90 detected at the higher temperature was almost same to that of the neat sPP. The result indicates that a portion of sPP would form isolate crys-
Cooling rate ˚C/min | sPP | Bl-10 | Bl-20 | Bl-50 | Bl-75 | Bl-90 | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Tc ˚C | t1/2a s | Tc ˚C | t1/2a s | Tc ˚C | t1/2a s | Tc ˚C | t1/2a s | Tc ˚C | t1/2a s | Tc ˚C | t1/2a s | |
3 | 110.0 | 3.2 | 110.0 | 3.2 | 110.0 | 3.0 | 107.9 | 3.0 | 100.8 | 3.2 | 107.9, 96.7 | 3.2 |
6 | 104.7 | 1.8 | 104.7 | 1.9 | 104.8 | 2.0 | 102.7 | 1.8 | 94.2 | 2.3 | 102.5, 88.7 | 2.0 |
12 | 99.2 | 0.98 | 99.0 | 1.0 | 99.0 | 1.1 | 97.0 | 1.0 | 87.4 | 1.4 | 96.0, 81.6 | 1.1 |
24 | 96.3 | 0.75 | 96.0 | 0.83 | 95.5 | 0.80 | 93.4 | 0.77 | 83.4 | 1.0 | 92.0, 74.2 | 0.53 |
a: The half time of crystallization.
tals in Bl-90. Compatibility of sPP and sPB at the molten state was observed with with hot-stage microscopy at 200˚C. The blend samples of Bl-10, Bl-25, Bl-50, and Bl-75 showed the miscible molten phase. On the other hand, the micro graphs of Bl-90 indicated the texture derived from the two-phase separation. The crystallization from the two-phase separated molten state should induce the complex crystallization process and form the two kinds of crystals of sPP in Bl-90.
The half time of the crystallization (t1/2), t at X(t) = 0.5, of the blend samples on the constant cooling rates is summarized in
Supahol investigated kinetics of non-isothermal crystallization of sPP by various macro kinetic models, and found that Ozawa model was suitable to study the crystallization kinetics of sPP [
on a constant cooling rate ϕ of polymers can be analyzed by the following Equation (1), developed by Ozawa [
where χ represents the cooling crystallization function and n represents Avrami exponent. The Avrami exponent of sPP in the blend samples was determined by the slope of the plots between ln|ϕ| and ln{–ln[1 – X(t)]} at theconstant temperatures.
T ˚C | sPP | Bl-10 | Bl-20 | Bl-50 | Bl-75 | Bl-90 | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
n | r2 | n | r2 | n | r2 | n | r2 | n | r2 | n | r2 | |
106 | 5.14 | 0.97 | ||||||||||
104 | 3.67 | 0.96 | 4.35 | 0.99 | 4.05 | 0.97 | 4.92 | 0.97 | ||||
102 | 2.82 | 0.96 | 3.51 | 0.99 | 3.20 | 0.97 | 3.67 | 0.98 | ||||
100 | 2.77 | 0.99 | 2.83 | 0.99 | 2.75 | 0.99 | 2.94 | 0.98 | 4.80 | 0.98 | 5.12 | 0.77 |
98 | 2.32 | 0.99 | 2.38 | 0.99 | 2.57 | 0.99 | 4.66 | 0.99 | 2.43 | 0.89 | ||
96 | 3.81 | 0.99 | 1.60 | 0.96 | ||||||||
94 | 3.43 | 0.99 | 1.11 | 0.99 | ||||||||
92 | 0.79 | 0.83 |
n: Avrami exponent, r2: Corresponding correlation of the plots.
The crystallization process of the blend samples at room temperature was traced by FT-IR spectroscopy to study the structure transformation of sPP and sPB in the blend samples for long period. The FT-IR spectra of sPP, Bl-10, and Bl-25, did not show any time change. The results indicate that the structures of the crystalline, mesophase, and amorphous phase of sPP in the samples should be fixed within a short period approximately 2 min.
The FT-IR spectroscopy detects the helical conformation and the planar zigzag conformation in the amorphous phase and mesophase of sPP. The peak intensity at 1153 cm−1, derived from planar zigzag conformations in
the amorphous phase, of the Bl-50 and Bl-75 samples decreased with increasing the crystallization time. The absorption peaks derived from the planar zigzag and the helical conformations in the mesophase are detected at 963 and 977 cm−1, respectively [
All the crystallized blend samples (crystallization for 120 min) showed lower R(A963/A977) values than that of the neat sPP. The FT-IR spectra cleared that the decrease of the absorbance intensity at 963 cm−1 (A963), derived from planar zigzag conformations of the mesophase phase, caused the decrease of the R(A963/A977) values in the blend samples. Bl-75 showed the lowest R(A963/A977) value among the blend samples. These results indicate that sPB prevents the formation of the planar zigzag conformations in the mesophase formed on the cooling process from the miscible molten state. The R(A963/A977) value of Bl-90 was larger than that of Bl-75, due to the isolated crystallization of sPP and sPB from the phase-separated molten state.
Slow crystallization of sPB in Bl-90 makes it possible to trace the crystallization process by WAXD.
Sample | sPB wt% | sPP | sPB | TmPPa ˚C | HmPPb J/g | TmPBa ˚C | HmPBb J/g | |||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
2θ (˚) | 2θ (˚) | |||||||||||
(200) | (010) | (200) (122) | I200/I010c | (200) | (110) | (210) | ||||||
sPP | 0 | 12.3 | 15.9 | 20.5 | 1.41 | 147.7 | 42.3 | |||||
Bl-10 | 10 | 12.3 | 15.9 | 20.5 | 1.12 | 147.0 | 41.2 | |||||
Bl-25 | 25 | 12.3 | 15.9 | 20.5 | 1.05 | 147.0 | 40.8 | |||||
Bl-50 | 50 | 12.3 | 15.9 | 20.5 | 1.03 | 146.8 | 40.4 | |||||
Bl-75 | 75 | 12.3 | 15.9 | 20.5 | 0.93 | 10.5 | 142.0 | 30.5 | 37.9 | 4.8 | ||
Bl-90 | 90 | 11.9 | 10.5 | 15.3 | 19.1 | 144.5 | 32.8 | 39.3 | 10.4 | |||
sPB | 100 | 10.4 | 15.2 | 19.0 | 44.7 | 9.6 |
a: Melting temperature derived from sPP (TmPP) or sPB (TmPB), b: Heat of fusion derived from sPP (ΔHmPP) or sPB (ΔHmPB) determined by DSC, c: Intensity ratio of the diffraction peaks derived from (200) and (010) planes of sPP crystal.
only the sPB crystal at around 2θ = 10.5˚, 15.3˚, and 19.1˚ but a weak peak derived from the (200) planes of sPP at 2θ = 11.9˚, as shown in
The crystallization and crystalline structure of the sPP-sPB blends were successively investigated with the WAXD, DSC, and FT-IR measurements. The WAXD patterns and the DSC profiles showed that the large amount of sPP in the blend samples in Bl-10, and Bl-25 prevented the crystallization of sPB. The crystallization behavior and thermal properties of sPP in those blend samples were not affected by sPB. The Tcs of sPP in Bl-50, Bl-75, and Bl-90 were lower than that of the neat sPP. The Tm and ΔHm of sPP in Bl-75 were the lowest among the blend samples. A part of sPP in Bl-90 formed the isolate crystals, and induced the heterogeneous two-step crystallization. The portion of planar zigzag conformations in the mesophase and amorphous phase of sPP in Bl-50, and Bl-75 gradually decreased with increasing the crystallization time. The ratio of the planar zigzag conformation to the helical (t2g2)2 conformation of sPP in the mesophases decreased with increasing of the sPB content in the blend samples, except Bl-90. sPB could be crystallized in Bl-75 and Bl-90.
More detailed studies, especially transmission electron microscopic study and solid NMR spectroscopy, of the crystalline structure of the blend samples are now being carried out, and the results will be reported elsewhere.