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1.
Liquid crystalline (LC) poly(ethylene terephthalate-co-2(3)-chloro-1,4-phenylene terephthalate) (50/50, mole/mole) [PECPT] was synthesized and blended with polycarbonate (PC).
LC properties of PECPT and thermal, morphological, and rheological behaviors of the PECPT/PC blend were studied. PECPT showed
the nematic LC phase and much longer relaxation time than poly(ethylene terephthalate) (PET). The apparent melt viscosity
of PECPT was one third of that of PET. An abrupt torque change was observed during the blending process due to the orientation
of LC domains. For the blends containing 10∼30 wt% of PECPT, the complex viscosities were higher than that of PC. As PECPT
content increases above 40 wt%, shear thinning was observed. The lowest complex viscosity was obtained at 40∼50 wt%. Transesterification
of PECPT and PC was confirmed by the selective chemical degradation of carbonate groups in PC. 相似文献
2.
Poly(trimethylene terephthalate) (PTT)/poly(ethylene naphthalate) (PEN) blends of various compositions were prepared by the
solution-blending and melt-blending methods. The changes in miscibility and crystallization behaviors of the blends upon thermal
treatment above the melting temperature of the blends at 280°C were investigated by using DSC, DMA,1H NMR, and SAXS analyses. Without any thermal treatment, the blend systems were not miscible, and the thermal transitions,
such as glass transition, cold crystallization, and crystal melting of the individual components were observed in the DSC
and DMA analyses. With thermal treatment, though, they became miscible as the thermal transitions of each component disappeared
and single glass transition peaks were observed in the thermal analysis. The chain randomness determined using1H NMR spectroscopy revealed that thermal treatment at 280°C for more than 30 min brought about transesterification reactions
between the PTT and PEN segments resulting in an increase in their miscibility. These results were confirmed by the small
angle X-ray analysis conducted to determine the long period (L), the thickness of the crystalline lamella stack (l
c
), and the thickness of the amorphous region (l
a
). After short thermal treatment, the melt-blended sample followed the values for the individual components. However, with
extended thermal treatment, the blend became homogeneous, possessing different crystalline morphologies which resulted in
different values ofL, l
c
, andl
a
. 相似文献
3.
In this study, we evaluated the effect of the molecular weight of the polymer on electrospun poly(ethylene terephthalate)
(PET) nonwovens, and their mechanical properties as a function of the linear velocity of drum surface. Polymer solutions and
electrospun PET nonwovens were characterized by means of viscometer, tensiometer, scanning electron microscope (SEM), wide
angle X-ray diffraction measurement (WAXD) and universal testing machine (UTM). By keeping the uniform solution viscosity,
regardless of molecular weight differences, electrospun PET nonwovens with similar average diameter could be obtained. In
addition, the mechanical properties of the electrospun PET nonwovens were strongly dependent on the linear velocity of drum
surface. From the results of the WAXD scan, it was found that the polymer took on a particular molecular orientation when
the linear velocity of drum surface was increased. The peaks became more definite and apparent, evolving from an amorphous
pattern at 0 m/min to peaks and signifying the presence of crystallinity at 45 m/min. 相似文献
4.
Phase behavior and spinodal phase separation kinetics in binary blends of a random copolymer of vinylidene fluoride and trifluoroethylene
(75/25) [P(VDF/TrFE)] and poly(1,4-butylene adipate) (PBA) have been investigated by means of optical microscopic observation
and time-resolved light scattering. The blends exhibited a typical lower critical solution temperature (LCST)∼34 °C above
the melting temperature of the P(VDF/TrFE) crystals over the entire blend composition range. P(VDF/TrFE) and PBA were totally
miscible in the temperature gap between the melting point of P(VDF/TrFE) and the LCST. Temperature jump experiments of the
3/7 P(VDF/TrFE)/PBA blend were carried out on a light-scattering apparatus from a single-phase melt state (180 °C) to a two-phase
region (205∼215 °C). Since the late stage of spinodal decomposition (SD) is prevalent in the 3/7 blend, SD was analyzed using
a power law scheme. Self-similarity was preserved well in the late stage of SD in the 3/7 blend. 相似文献
5.
The kinetic parameters, including the activation energyE, the reaction ordern, and the pre-exponential factorZ, of the degradation of the copolymers based on the poly(L-lactide) (PLLA) or poly(p-dioxanone-co-L-lactide) (PDO/PLLA) and diol-terminated poly(ethylene glycol) (PEG) segments have been evaluated by the single
heating methods of Friedman and Freeman-Carroll. The experimental results showed that copolymers exhibited two degradation
steps under nitrogen that can be ascribed to PLLA or PDO/PLLA and PEG segments, respectively. However, copolymers exhibited
almost single degradation step in air. Although the values of initial decomposition temperature were scattered, copolymers
showed the lower maximum weight loss rate and degradation-activation energy in air than in nitrogen whereas the higher value
of temperature at the maximum rate of weight loss was observed in air. 相似文献