The aqueous solution properties of alkylene oxide polymers and copolymers are related to their interaction with water. In an attempt to better understand this behavior, differential scanning calorimetry has been employed to measure phase changes and water binding in solutions of polyethylene glycol (PEG), polypropylene glycol (PPG), and a 50/50 random copolymer of ethylene oxide and propylene oxide. PEG (Mn = 3510) forms a crystalline eutectic with water at 0.48 weight fraction of polymer. The liquidus curve for water can be fit accurately using the Flory–Huggins expression for solute activity with an interaction parameter of 0.05. PPG and the random copolymer do not crystallize and thus do not form a crystalline eutectic. Based on decreases in the heat of fusion of free water with added polymer, PEG binds more water than the copolymer which binds more water than PPG. The estimated hydration numbers per polymer segment are 1.5 for PPG, 2.3 for the copolymer, and 2.7 for PEG. 相似文献
A series of high molecular weight copolymers based on poly(L-lactic acid) (PLLA) as the biodegradable aliphatic segments,
poly(butylene terephthalate) (PBT) as the rigid aromatic segments and hydrophilic poly(ethylene glycol) (PEG) as the soft
segments were synthesized with the aim of developing novel polymer materials which could combine high physical properties
with good biodegradability. Via direct melt polycondensation of terephthalic acid (TPA), 1,4-butanediol (BDO), poly(L-lactic
acid) oligomer (OLLA) and PEG, biodegradable aliphatic/aromatic copoly(ester-ether)s, poly(butylene terephthalate-co-lactate-co-ethylene
glycol) (PBTLG), were prepared. The effect of the introduction of PEG soft segments on the synthesis, mechanical properties
and thermal stabilities as well as the degradation behaviors of the final copolymers was investigated. When the PEG units
were incorporated into the polymer main-chains, the weight-average molecular weight of the copolymers increased from 53,700 g/mol
to 177,000 g/mol and the tensile strength (σ) improved by nearly two times from 6.5 MPa to 12.8 MPa for PBTLG1000-0.5. The
glass-transition temperature (Tg) gradually decreased from 26.9 °C down to −5.5 °C and a depression of melting temperature was observed with the increase
of PEG content. According to the in vitro hydrolytic degradation observation, all of the copolymers underwent significant
degradation in phosphate buffer solution at 37 °C and the water absorption as well as the degradation rate of PBTLGs displayed
a strong dependency on the PEG content. 相似文献
Plasticization of semicrystalline poly(l-lactide) (PLA) with a new plasticizer - poly(propylene glycol) (PPG) is described. PLA was plasticized with PPG with nominal Mw of 425 g/mol (PPG4) and 1000 g/mol (PPG1) and crystallized. The plasticization decreased Tg, which was reflected in a lower yield stress and improved elongation at break. The crystallization in the blends was accompanied by a phase separation facilitated by an increase of plasticizer concentration in the amorphous phase and by annealing of blends at crystallization temperature. The ultimate properties of the blends with high plasticizer contents correlated with the acceleration of spherulite growth rate that reflected accumulation of plasticizer in front of growing spherulites causing weakness of interspherulitic boundaries. In PLA/PPG1 blends the phase separation was the most intense leading to the formation of PPG1 droplets, which facilitated plastic deformation of the blends that enabled to achieve the elongation at break of about 90-100% for 10 and 12.5 wt% PPG1 content in spite of relatively high Tg of PLA rich phase of the respective blends, 46.1-47.6 °C. Poly(ethylene glycol) (PEG), long known as a plasticizer for PLA, with nominal Mw of 600 g/mol, was also used to plasticize PLA for comparison. 相似文献
Segmented poly(urethane–urea)s have been synthesized with mixed soft segments of ultra-low monol content poly(propylene glycol) (PPG) and tri(propylene glycol) (TPG) which allows the fabrication of quality elastomers without crosslinking. The narrow molecular weight distribution of the ultra-low monol content PPG polyols allows for the probing of the influence of the low molecular components of the molecular weight distribution through the inclusion of low molecular homologs of PPG such as TPG. Structure–property relationships for these materials were investigated as average soft segment molecular weight was varied by blending 8000 g/mol PPG with TPG to achieve molecular weights of 2500, 2000, and 1500 g/mol. Morphological features such as microphase separation, interdomain spacing and interphase thickness were quantified and revealed with SAXS. AFM was utilized to verify the microphase separation characteristics inferred by SAXS. The thermal and mechanical behavior was assessed through applications of DMA, DSC, and conventional mechanical tests. It was found that as the average soft segment molecular weight was decreased through the addition of TPG, the interdomain spacing distinctly increased contrary to the trend seen for decreasing soft segment molecular weight in PPG based systems without TPG. Additionally, the inclusion of TPG in the poly(urethane–urea) formulations resulted in the formation of larger hard domains as evidenced by AFM. These results and supporting evidence from DMA, DSC, birefringence, and mechanical testing led to the conclusion that TPG apparently acts more as a chain extender as well as, or in contrast to, a soft segment. 相似文献
Abstract Oil palm empty fruit bunch (EFB)-polyurethane (PU) composites were produced. The effects of the isocyanate (NCO)/glycol (OH) ratio, glycol type, and mixtures (polyethylene glycol PEG 400 (Mw 400) and polypropylene glycol PPG 400 (Mw 400)) on the flexural properties were investigated. The NCO/OH ratio had a significant effect on the flexural properties of the EFB-PU composites. Composites made with PEG 200 exhibited higher flexural properties than with PEG 400 and PPG 400. The flexural properties were also found to be influenced by the PPG 400/PEG 400 ratio. 相似文献
The structural requirements for the preparation of polyether polyol/Na+‐montmorillonite nanocomposites, which are used in polyurethane/NaMMT nanocomposites, were evaluated using X‐ray diffraction, thermogravimetric analysis and shear viscosity behavior. Nanocomposites based on homopolyetherols: poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), polytetrahydrofuran (PTHF), block‐type copolyetherols and a SAN‐grafted polymer polyol were prepared. Intercalation was observed only with oxyethylene (EO) units containing polyetherols. The amount of the intercalated polyetherol ranged from 15 to 30 wt.‐%. EO‐sequences of 5 to 6 units proved to be sufficient for intercalation, which suggests a crown‐ether type complexation of interlayer cations.
The application of polyurethanes (PUs) on breathable waterproof fabric coatings requires a balance of water vapor permeability (WVP) and water resistance which can be achieved by tailoring hydrophilic and hydrophobic segments. PU prepolymers were prepared from isophorone diisocyanate, dimethylol butanoic acid, and a mixture of various ratios of amphiphilic PPG2050 (copolymer of ethylene oxide and propylene oxide with –OH end groups) and hydrophobic poly(tetramethylene ether glycol) (PTMEG). After neutralization with triethylamine, the prepolymers were chain-extended with ethylene diamine/1,4-butanediol (1:1 by molar). The WVP values of the fabric coatings prepared using various waterborne PUs were very similar (910–990 g/m2 × 24 h). When waterborne PUs prepared using a mixture of PPG2050 and PTMEG were employed for the textile coatings, the resulting PU-coated textiles exhibited excellent waterproof properties (>10,000 mm H2O). The textile coatings prepared from PPG2050/PTMEG-based waterborne PUs were significantly more waterproof than those prepared from poly(ethylene glycol) (PEG)/poly(propylene glycol) (PPG)/PTMEG-based waterborne PU. This is probably due to a more even distribution of hydrophobic segments in the PUs, even though the WVP values of the PEG/PPG/PTMEG-based PU coatings were considerably smaller than those of the PPG2050/PTMEG-based PU coatings. 相似文献
Data reported for the autoxidation of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) in solution at relatively long reaction times were analyzed. A relatively simple and a more general kinetic scheme with corresponding rate expressions were used. It was found that the more general scheme gave somewhat more satisfactory agreement between calculated and observed values of several reaction variables. Limitations in the applications of both schemes to PEG and PPG autoxidations are mentioned. 相似文献
Poly(trimethylene terephthalate)/poly(propylene glycol) (PTT/PPG) copolymers with different PPG molecular weights (400–4,000?g?/mol) were successfully synthesized and characterized. Double melting endotherms during isothermal melt crystallization were observed by differential scanning calorimetry. Middle-temperature melting endotherms in all copolymers were stronger than that in PTT homopolymer and became smaller with the increasing PPG molecular weight. Nonisothermal crystallization kinetics of all samples were analyzed by Ozawa and Mo models. Polarized optical microscopy micrographs revealed that ring-banded spherulitic morphology was relatively easier to be observed in copolymers with higher PPG molecular weight at lower crystallization temperature, and PPG molecular weight nearly had no influence on the band spacing. 相似文献
The application of polyurethanes (PUs) on breathable waterproof fabric coatings requires a balance of water vapor permeability (WVP) and water resistance which can be achieved by tailoring hydrophilic and hydrophobic segments. PU prepolymers were prepared from isophorone diisocyanate, dimethylol butanoic acid, and a mixture of various ratios of amphiphilic PPG2050 (copolymer of ethylene oxide and propylene oxide with –OH end groups) and hydrophobic poly(tetramethylene ether glycol) (PTMEG). After neutralization with triethylamine, the prepolymers were chain-extended with ethylene diamine/1,4-butanediol (1:1 by molar). The WVP values of the fabric coatings prepared using various waterborne PUs were very similar (910–990 g/m2 × 24 h). When waterborne PUs prepared using a mixture of PPG2050 and PTMEG were employed for the textile coatings, the resulting PU-coated textiles exhibited excellent waterproof properties (>10,000 mm H2O). The textile coatings prepared from PPG2050/PTMEG-based waterborne PUs were significantly more waterproof than those prepared from poly(ethylene glycol) (PEG)/poly(propylene glycol) (PPG)/PTMEG-based waterborne PU. This is probably due to a more even distribution of hydrophobic segments in the PUs, even though the WVP values of the PEG/PPG/PTMEG-based PU coatings were considerably smaller than those of the PPG2050/PTMEG-based PU coatings. 相似文献
Pressure-volume-temperature properties were measured for polymer solutions of poly(propylene glycol) (PPG)+anisole, polymer blends of PPG+poly(ethylene glycol methyl ether) (PEGME), and the blends of PPG+PEGME and poly(ethylene glycol) (PEG)+PPG with anisole at temperatures from 298.15 to 348.15 K and pressures up to 50 MPa. The Tait equation represents accurately the pressure effect on the liquid densities over the entire pressure range. The excess volumes change from positive to negative as increasing the mole fraction of PPG in the binary systems of PPG+anisole and PPG+PEGME. The volumetric data of the related binary systems were correlated with the Flory-Orwoll-Vrij and the Schotte equations of state to determine the binary parameters. By using these determined binary parameters, both equations predicted the specific volumes of the polymer blends with anisole to average absolute deviations of better than 0.13%. 相似文献