Search

Various substituted dioxythiophenes bearing 3,4-propylenedioxythiophenes (ProDOT) and 3,4-ethylenedioxythiophene (EDOT) moieties successfully undergo Pd-catalyzed direct C–H arylation to yield π-conjugated polymers. The effects of palladium catalysts, phosphine ligands or additives, and functional groups on this facile polycondensation approach are investigated. Polymers from alkoxy-substituted ProDOT are synthesized with reasonable molecular weight (Mn = 6100–9600) and low PDI (1.3–1.9). Four substituted EDOT with alkoxy or protected functional groups also undergo direct C–H arylation polycondensation to yield corresponding polymers. The obtained polydioxythiophenes exhibit UV–vis absorptions ranging from 480 to 590 nm, and these conjugated polymers are electroactive and reversibly switched between the oxidized and neutral states upon applying potentials.

The effects of poly(vinylidene fluoride) (PVDF) component on the crystallization kinetics, crystalline structure, phase transition, and morphology of polymorphic poly(butylene adipate) (PBA) in their miscible PVDF/PBA binary blends have been investigated. The polymorphism of PBA can be regulated upon blending with PVDF. The incorporated PVDF faciliates the formation of PBA α-crystal, which is probably attributed to the thermodynamic and kinetic contributions. From the crystallization kinetics, it was found that a small amount of PVDF acts as a nucleating agent and can accelerate the crystallization of PBA, while a large amount of PVDF hinders the crystallization of PBA due to the confinement effect. In addition, the addition of PVDF greatly accelerates the β- to α-form phase transition of PBA upon annealing the PBA β-form at higher tmeperataure (48 °C). However, the large amount of PVDF decelerates the phase transition to a certain extent. The possible reasons for these phenomena were also proposed.

The factors influencing the crystalline structure of polymorphic polymer have been investigated for random copolyester, poly(hexamethylene adipate-co-butylene adipate) (P(HA-co-BA)). P(HA-co-BA) ex...

The crystalline phase of random poly(hexamethylene sebacate-co-hexamethylene adipate) (P(HSe-co-HA)) was studied by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXD), and small-angle X-ray scattering (SAXS). From the quantitative analysis of the comonomer composition in the crystalline phase and the finding of the change both in the WAXD patterns and in the d-spacing values of some planes in the HA composition (CHA) of 60 mol % < CHA < 70 mol %, the occurrence of isodimorphism was confirmed for P(HSe-co-HA). As the secondary comonomer unit content in the crystalline phase decreased with increasing crystallization temperature, it was concluded that the cocrystallization of the HSe and HA units in the crystal of P(HSe-co-HA) is affected by kinetics. From SAXS analysis, the lamella thickness of P(HSe-co-HA) was found to rely on the comonomer unit inclusion behavior in the PHSe or PHA type crystal. Application of the Sanchez−Eby model ...

The effects of miscible blending on the crystallization kinetics and crystalline structure of poly(l-lactide) (PLLA) were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), Fourier transform infrared (FTIR) spectroscopy, and wide-angle X-ray diffraction (WAXD). It was confirmed that the blends of PLLA and poly(d,l-lactide) (PDLLA) are miscible at all compositions. Due to the dilution effect, the crystallization of PLLA was hindered with the presence of PDLLA. The PLLA/PDLLA blends show the irregular or ring-banded spherulites. The polymorphic behavior of PLLA is influenced by the miscible blending with PDLLA. FTIR and WAXD data indicates that the formation of the α-form crystals of PLLA is favored in the blends. With incorporation of 50 wt % PDLLA, the critical temperature for the formation of α′- and α-form crystals decreases from ∼110 (of neat PLLA) to ∼80 °C. The factors affecting the formation of the PLLA α′- and α-form crystals were discussed from the thermod...

Effects of physical aging temperatures (Ta 40 and 50 °C) and times (ta 0−840 h) on the crystallization kinetics as well as induction periods of poly(l-lactide) (PLLA) have been studied by differential scanning calorimetry (DSC) and time-resolved Fourier transform infrared (FTIR) spectroscopy. The crystallization rate of PLLA increases considerably after the physical aging process. According to the DSC analysis, the crystallization temperature (Tc) of the nonisothermal crystallization and the crystallization half-time (t1/2) in the isothermal crystallization decrease nearly logarithmically with ta in the investigated ta region. With increasing Ta, both the Tc and t1/2 values decrease. Polarized optical microscopy (POM) observation revealed that the nucleation of PLLA becomes faster and the nucleation density increases significantly with physical aging. Besides, the crystallization induction period of PLLA shortens with aging. It was found that the FTIR spectral intensity changes of the conformation-sensiti...

The enthalpy relaxation behavior of poly(l-lactide) (PLLA) below glass transition temperature (Tg) and its effects on the mechanical properties were studied using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and tensile test. Both the enthalpy loss (δH) and peak endothermic temperature (Tp) in the glass transition region show a linear increase with the logarithm of aging time (ta). On the basis of DSC results, the kinetics of the enthalpy relaxation process were analyzed, and the kinetic parameters of PLLA were obtained: relaxation rate of enthalpy at 40 °C βH = 1.77 J g-1 per decade, and apparent activation energy Δh* = 1107 kJ mol-1. Besides, analysis on the kinetic of enthalpy relaxation for poly(dl-lactide) (PDLLA) shows that the Δh* value of PDLLA is similar to that of PLLA. Moreover, it was found that the strength and modulus of PLLA increase gradually; on the contrary, the toughness reduces dramatically during the physical aging. The yield strength and tensi...

A set of water-soluble dendronized polyfluorenes bearing peripheral charged amino groups were synthesized by two steps: (1) Suzuki polycondensation of dendritic macromonomers carrying peripheral B...

The crystalline structure of biodegradable poly(3-hydroxypropionate) (PHP) has been found to quite depend on the molecular weight (MW) and crystallization conditions. In particular, a new crystal form (the δ-form) has been successfully prepared by casting and optimal melt-crystallizing the low-MW PHP. The overwhelming growth of the δ-form in the cast low-MW PHP possibly arises from the conformational restriction of the intramolecular interaction between terminal groups. As for the melt-crystallization of low-MW PHP, the temperature of the melt (Tf) and the crystallization temperature (Tc) jointly decide the crystalline structure. It has been found that the Tf-dependent nucleation of the δ-form competes with Tc-dependent nucleation of the β- and γ-form and then plays a very important part in the Tf- and Tc-dependent polymorphism of PHP. With the aid of the FTIR analysis and the conformation prediction, the δ-form PHP are suggested to take on the 21 helix conformation rather than the trans one adopted by th...

The nucleation effects of α-cyclodextrin (α-CD) and its inclusion complexes (ICs) with poly(e-caprolactone) (PCL), poly(ethylene glycol) (PEG), and poly(butylene succinate) (PBS) on the crystallization of PCL, PEG, and PBS were investigated by differential scanning calorimetry (DSC) and polarized optical microscopy. The formations of ICs of α-CD with PCL, PEG, and PBS were characterized by DSC, Fourier transform infrared spectroscopy, wide-angle X-ray diffraction (WAXD), and solution 1H NMR. The WAXD studies showed that all of the α-CD-ICs adopt a channel structure. Both DSC and 1H NMR results suggested that the polymer chains were partially complexed by α-CDs. Thus, the polymer chains in the bulk phase can contact not only the exterior of the α-CD macrocycle but also the end parts of polymer chains protruding from the α-CD cavity and/or the free chain segments uncovered by α-CD, when the α-CD-IC as a nucleating agent is added into the polymers. Therefore, the difference in the interfacial interaction bet...

Using wide-angle X-ray diffraction, high-resolution solid-state 13C NMR (SNMR), attenuated total reflection infrared (ATR/IR), and Fourier transform infrared (FTIR) spectrometry, we investigated the crystalline structure and morphology of melt-crystallized poly(3-hydroxypropionate)s (PHPs). The melt-crystallization of the β-form crystal and that of the γ-form crystal are found to be favored respectively thermodynamically at higher temperature and kinetically at lower one. In addition, the PHPs with higher molecular weight more readily crystallize into the γ-form crystal. In this way, the polymorphism leads to the bimodal growth behavior for PHP spherulites, attending by a discontinuously temperature-dependent morphology phenomenon. PHP chains take on a similar conformation (the trans) in both type crystals but are packed with different efficiency. In the γ-form, the tighter packing of the atoms along the a axis make the adjacent chains strongly interact with each other, resulting in the crystal field spli...

The crystallization behavior of the poly(ethylene oxide) (PEO) component in poly(butylene succinate) (PBS)/PEO blends with the middle PEO content was investigated as a function of isothermal crystallization temperature of the PBS component (TIC,PBS) using differential scanning calorimetry (DSC). It is found that the crystallization behavior of the PEO component in these blends is significantly affected by TIC,PBS. Small-angle X-ray diffraction (SAXS) measurements were performed to explore the origin of the TIC,PBS dependence of crystallization of PEO component. On the basis of the SAXS measurements and the results of our previous work [Macromolecules 2004, 37, 3337−3345], it is suggested that TIC,PBS controls the location distribution of the PEO component in the blends after the crystallization of the PBS component and thus significantly affects the crystallization behavior of PEO.

The miscibility, morphology, and crystallization behavior of the blend of poly(ethylene oxide) (PEO) and poly(butylene succinate) (PBS) have been investigated using differential scanning calorimetr...

The effect of intermolecular hydrogen bonding on the crystallization kinetics and the morphology of poly(e-caprolactone) (PCL)/4,4‘-thiodiphenol (TDP) blends with TDP content 0−20 wt % has been investigated by differential scanning calorimetry, polarizing optical microscopy, X-ray measurements, and in situ FT-IR. The equilibrium melting point ( ) of PCL in the PCL/TDP blends decreases with increasing the TDP content, suggesting the miscibility of the blends as expected when strong hydrogen bonding is involved. Following the depression of and the increase of glass transition (as reported in our previous works), the half-time of crystallization and the spherulite growth rate rapidly decrease with increasing TDP content. By small-angle X-ray scattering measurement, obvious extralamellar segregation of TDP was detected, the extent of which increased with increasing TDP content. The inter-spherulite segregation of TDP was also observed by a polarizing optical microscope and FT-IR microscope. For a given compos...

Effects of annealing conditions and molecular weight (MW) on the crystalline phase transition in poly(l-lactide) (PLLA) were studied by wide-angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC). The disordered crystal (α′-form) of PLLA was found to transform into the α one during annealing process at elevated temperatures. The α′-to-α transition is quite dependent on the annealing period (ta: 0−1440 min) and annealing temperature (Ta: 120−160 °C). With increasing Ta, the polymorphic transition progresses much more rapidly. The α′-to-α transition is mainly involved by the slight rearrangement of the chain conformation (especially related to the side groups) and packing manner in the unit cell to the more energy-favorable state, corresponding to the reduction of unit cell dimension. Besides, it was proposed that the α′-to-α transformation mainly proceeds by the direct solid−solid transition mechanism. Moreover, it was found that MW affec...