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1.
Polyurethanes were synthesized using the high functional 4,4′‐diphenylmethane diisocyanate (MDI), polyester polyol, and 1,4‐butane diol. The synthesized polyurethanes were analyzed using differential scanning calorimeter (DSC), dynamic mechanical thermal analysis (DMTA), Fourier transform infrared (FTIR) spectrometer, and swelling measurement using N,N′‐dimethylformamide. From the result of thermal analysis by DSC and DMTA, single Tgs were observed in the polyurethane samples at all the formulated compositions. From this result, it is suggested that the polyurethanes synthesized in this study have crosslinked structure rather than the phase‐separated segmented structure because of the high functionality (f = 2.9) of the MDI. By annealing the polyurethane samples using DSC, the Tgs were increased by 4.7∼16.0°C at the various annealing temperatures. From the results of FTIR and swelling measurement of polyurethanes, it is suggested that the increase of Tg of the polyurethanes by annealing is not due to increase of the hydrogen bond strength but mainly due to the increase of the crosslink density. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 624–630, 2000  相似文献   

2.
A reduction in the glass‐transition temperature (Tg) was found for polyolefins chemically crosslinked by peroxide. This tendency, which was observed for low‐density and high‐density polyethylenes, was also validated for their blends with Ethylene Vinyl Acetate copolymer. It is proposed that the constrained crystallization process, as a result of a restriction imposed on the chain packing by the chemical crosslinks, results in an increasing net free volume in the amorphous phase and hence reduces Tg. The Tg depression becomes greater with increasing crosslink density, whereas at the same time, the degree of crystallinity and consequently the density of the system decreases with an increase in the peroxide content. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1654–1660, 2007  相似文献   

3.
Hydroxypropyl lignin-based thermosetting polyurethanes were synthesized with excess hexamethylene diisocyanate (HDI) and tolylene diisocyanate (TDI) by solution casting. Four polyethylene glycols (PEG) of molecular weight 400, 600, 1000, and 4000 were mixed with lignin polyol to incorporate different proportions of soft segment into the network prior to crosslinking. Neither thermal nor mechanical and limited small angle x-ray scattering (SAXS) analysis provided distinct evidence for phase separation and microstructure formation. The study examines the effect of the soft segment in relation to chain length and weight contribution on the thermal and mechanical properties of the final networks. A significant sensitivity of glass transition temperature (Tg), of swelling in DMF, and of the mechanical properties to soft segment content was observed. Some of this sensitivity must, however, be attributed to differences in crosslink density since the polyol to diisocyanate weight ratio was kept constant throughout the synthesis series. The magnitude of the change of the different properties was found to be influenced by both glycol content and glycol molecular weight. The Tg of the network decreased from 105°C to as low as 38°C (HDI), and from 158°C to 70°C (TDI), with incorporation of up to 17.8% glycol, and it was greater with lower molecular weight glycols than with higher ones at any weight fraction. Swelling in DMF increased as expected with soft segment content. Mechanical properties were affected most if HDI and lower molecular weight glycols were used. The uniformity in structure, reduction in brittleness, and considerable improvement in mechanical properties with inclusion of minor PEG contents indicates that lignin-based network polyurethanes can be synthesized with controllable performance characteristics.  相似文献   

4.
Polydimethylsiloxane polyurethane (PDMS‐PU), which was synthesized from PDMS as the soft segment, was blended into a variety of ester‐ or ether‐based soft‐segment waterborne polyurethanes with different concentrations to investigate the crystallization, thermal, and physical properties of the membrane formations. According to X‐ray analysis, the ether‐based PUs, synthesized from soft segments of poly(propylene glycol) (PPG1000) or poly(ethylene glycol) (PEG2000), were found to have maximum crystallinity at a 5% blending ratio of PDMS‐PU, but the ester‐based PU, synthesized from soft segments of polycaprolactone (PCL1250), had decreased crystallinity at a 5% blending ratio. Differential scanning calorimetric analysis revealed that the Tg,s values of PUs were highest when the blending ratio of PDMS‐PU was 5%–10%, except for PU from PCL1250. Moreover, ether‐based PUs showed maximum Tm,h values, but the Tm,h of the ester‐based PU was greatly reduced when PU with PCL1250 was blended with PDMS‐PU. In addition, the PU from PEG2000 had the highest melting entropy. Mechanical property analysis showed that the stress of ether‐based PUs would be increased when PUs were blended with a small amount of PDMS‐PU and that the stress of PU from poly(tetramethylene glycol) (PTMG1000) increased to its greatest value (20–30 MPa). On the other hand, the ester‐based PU, from PCL1250 blended with PDMS‐PU, would have reduced stress. On the whole, the stress and strain of PU from PEG1000 had excellent balance. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 210–221, 2006  相似文献   

5.
Electron beam, thermal free radical, and cationic complexation mechanisms have been employed to investigate crosslinking in selected polyphosphazenes. In polyphosphazenes functionalized with o‐allylphenol to facilitate free radical crosslinking, maximum crosslink density was achieved after 10 min at 130°C utilizing benzoyl peroxide as an initiator. Electron beam radiation was found to give an increased crosslink density with increased dose. The dose–crosslink density relationship observed for a aryloxyphosphazene terpolymer PPXP also was seen in poly[bis(2,2′‐(methoxyethoxy)ethoxy)phosphazene] (MEEP). However, with two lots of a fluoroalkoxyphosphazene an initial crosslink density was achieved at a lower electron beam exposure with no additional crosslink density observed with increasing dose. These measurements are observations of net crosslinking, which is the result of crosslinking processes balanced by chain scission processes. DSC revealed that neither thermal‐ nor electron beam‐initiated crosslinking cause any significant change in the Tg of the polymer. Metal ion complexation with MEEP consistently gave Tg values that were higher than MEEP. The Tg values measured for both MEEP and the lithium‐complexed MEEP were unaffected by electron beam irradiation. These data suggest the location of lithium complexation may be at the nitrogen lone electron pair on the backbone, representing a new mechanism of lithium complexation in phosphazenes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 55–66, 2000  相似文献   

6.
Poly(ethylene succinate) (PES), poly(butylene succinate) (PBS), and PES‐rich copolyesters were synthesized using an effective catalyst, titanium tetraisopropoxide. PES was blended with minor amounts of PBS for the comparison. The compositions of the copolyesters and the blends were determined from NMR spectra. Their thermal properties were studied using a differential scanning calorimeter (DSC), a temperature modulated DSC (TMDSC), and a thermogravimetric analyzer. No significant difference exists among the thermal stabilities of these polyesters and blends. For the blends, the reversible curves of TMDSC showed a distinct glass‐rubber transition temperature (Tg), however, the variation of the Tg values with the blend compositions was small. Isothermal crystallization kinetics and the melting behavior after crystallization were examined using DSC. Wide‐angle X‐ray diffractograms (WAXD) were obtained for the isothermally crystallized specimens. The results of DSC and WAXD indicate that the blends have a higher degree of crystallinity and a higher melting temperature than those of the corresponding copolymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010  相似文献   

7.
In this study, melt intercalation method is applied to prepare poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG)‐plasticized PLA nanocomposite films including 0, 3, and 5% organoclay (Cloisite 30B) using a laboratory scale compounder, which is connected to a microcast film device. To evaluate the nanomorphology and the dispersion state of the clays, X‐ray diffraction (XRD) and transmission electron microscopy (TEM) are conducted. Tensile tests are performed to characterize the mechanical behavior of the films. Biodegradation rate is determined by degradation tests in composting medium. Differential scanning calorimeter (DSC) is applied to observe the thermal behavior of the films. XRD and TEM show that the exfoliation predominantly occurrs in plasticized PLA nanocomposites, whereas unexfoliated agglomerates together with exfoliated clays are observed in the nonplasticized PLA. Tensile tests indicate that the addition of 3% clay to the neat‐PLA does not affect the strength; however, it enhances the modulus of the nanocomposites in comparison to neat‐PLA. Incorporation of 3% clay to the plasticized PLA improves the modulus with respect to PLA/PEG; on the other hand, the strain at break value is lowered ~ 40%. The increase in the rate of biodegradation in composting medium is found as in the order of PLA > PLA/PEG > 3% Clay/PLA/PEG > 5% Clay/PLA/PEG > 3% Clay/PLA. DSC analysis shows that the addition of 3% clay to the neat PLA results in an increase in Tg. The addition of 20% PEG as a plasticizer to the neat‐PLA decreases Tg about 30°C, however incorporation of clays increases Tg by 4°C for the plasticized PLA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009  相似文献   

8.
This paper describes the experimental findings of the study of a series of PU/epoxy composites, which formed interpenetrating networks and have shape-memory properties. The morphological variation for different chemical compositions and the influences of morphology on mechanical performance and shape-memory behavior are discussed. Length and mass fraction of polyethylene glycol (PEG) units are chosen as the key parameters in this study. The molecular weight of PEG was varied from 400 (as such PEG units are unable to crystallize) to 1500, 4000, and 6000, which are crystallizable. It was shown that the crystallization of PEG units is the key parameter, which determines the mechanical performance and shape-memory behavior of PU/epoxy composites in this study. DMTA results show the linear dependence of glass transition temperature and tensile strength, elongation, and other mechanical parameters on the amount of PEG in PU/epoxy composites independently of the amount of PEG unit lengths. The maximal value of shape fixation rate was achieved for 30–40 mass percentage of PEG 4000 (4.5 × 10−2 s−1 at Tg + 20°C) or PEG 6000(4.1 × 10−2 s−1 at Tg + 20°C) in PU/epoxy composites.  相似文献   

9.
Poly(lactic acid) PLA was plasticized with low molecular weight poly(ethylene glycol) PEG‐200 to improve the ductility of PLA, while maintaining the plasticizer content at maximum 10 wt%. Low molecular weight of PEG enables increased miscibility with PLA and more efficient reduction of glass transition temperature (Tg). This effect is enhanced not only by the low molecular weight but also by its higher content. The tensile properties demonstrated that the addition of PEG‐200 to PLA led to an increase of elongation at break (>7000%), but a decrease of both tensile strength and tensile modulus. The plasticization of the PLA with PEG‐200 effectively lowers Tg as well as cold‐crystallization temperature, increasing with plasticizer content. SEM micrographs reveal plastic deformation and few long threads of a deformed material are discernible on the fracture surface. The use of low molecular weight PEG‐200 reduces the intermolecular force and increases the mobility of the polymeric chains, thereby improving the flexibility and plastic deformation of PLA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4576–4580, 2013  相似文献   

10.
This study develops a simple copolymerization/crosslinking technique to control the swelling and mechanical properties of hyaluronic acid‐based hydrogels. Because of the widespread acceptance of poly(ethylene glycol) in biomedical applications, functionalized oligomers of ethylene glycol (EG) were used as comonomers to crosslink methacrylated hyaluronic acid (MHA). The swelling degree, shear and elastic moduli, and fracture properties (stress and strain) of the gels were investigated as a function of the crosslinking oligomer length and reactive group(s). It was hypothesized that acrylated oligomers would increase the crosslink density of the gels through formation of kinetic chains by reducing the steric hindrances that otherwise may limit efficient crosslinking of hyaluronic acid into gels. Specifically, after crosslinking 13 wt % MHA (47% degree of methacrylation) with 0.06 mol % of (EG)n‐diacrylate, the swelling ratio of the MHA gel decreased from 27 to 15 g/g and the shear modulus increased from 140 to 270 kPa as n increased from 1 to 13 units. The length and functionality (i.e., acrylate vs. methacrylate) of the oligomer controlled the crosslink density of the gels. The significant changes in the gel properties obtained with the addition of low levels of the PEG comonomer show that this method allows precise tuning of the physical properties of hyaluronic acid (HA) gels to achieve desired target values for biomedical applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42009.  相似文献   

11.
Plasticization of medical grade poly‐L ‐lactide (PLLA) by addition of polyethylene glycol (PEG) with various molar masses has been evaluated as means of producing low stiffness matrices for bioresorbable scaffolds for soft‐tissue engineering applications. As reported previously, the Tg of injection molded specimens of the PLLA/PEG blends decreased strongly with PEG content, so that at PEG contents of 15 and 25 wt % it became significantly lower than normal human body temperature, implying an essentially rubber‐like mechanical response in vivo. The degree of crystallinity of the moldings also increased strongly with PEG content, reaching a maximum of about 60 wt % at 25 wt % PEG. Moreover, after the immersion in phosphate‐buffered saline for 5 days in 37°C to simulate conditions in vivo, the moldings with the highest PEG contents showed increased water uptake and, for relatively low molar mass PEG, significant mass loss, associated with phase separation and leaching of the PEG. Blends with relatively low PEG contents also showed large increases in their degree of crystallinity. The implications of these changes for the in vivo performance of the blends and their potential for development as matrices for bioresorbable scaffolds are discussed in the light of results from a series of PLLA/PEG copolymers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011  相似文献   

12.
The glass transition temperature (Tg) of poly(phenylene sulfide) (PPS) with various crystalline fractions has been studied using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The DSC measurements show that Tg can be observed from the heating curves for the PPS sample with very low crystallinity, and no Tg is observed when the crystallinity is over 8%. DMA indicates that crystallinity has an important effect on molecular chain segment motion of PPS. When the crystallinity, Xc, of PPS is over 38%, there is only one chain segment motion, which mainly results from the crystalline chain vibration; while three different chain segment motions occur for PPS samples with lower crystallinity (Xc < 26%), which are amorphous chain segment motion, crystalline chain segment motion and constrained amorphous chain segment motion. Tg of PPS is mainly caused by the amorphous chain segment motion which is independent of the crystallinity, while the relaxation temperature corresponding to crystalline chain motion shifts to lower temperature as the crystallinity increases. The reduction of the relaxation temperature can be attributed to the disorder‐order transition of amorphous chains for PPS with lower crystallinity. © 2012 Society of Chemical Industry  相似文献   

13.
A series of phosphorus‐containing, wholly aromatic thermotropic copolyesters from acetylated 2‐(6‐oxide‐6H‐dibenz〈c,e〉〈1,2〉oxa phosphorin‐6‐yl)‐1,4‐dihydroxy phenylene, p‐acetoxybenzoic acid, terephthalic acid, and isophthalic acid were prepared by melting polycondensation. The structure and basic properties of the polymers, such as the glass‐transition temperature (Tg), melting temperature (Tm), thermal stability, crystallinity, and liquid crystallinity, were investigated with Fourier transform infrared, elemental analysis, differential scanning calorimetry (DSC), thermogravimetric analysis, wide‐angle X‐ray diffraction, and hot‐stage polarizing optical microscopy. The copolyesters had relatively high Tg values ranging from 183 to 192°C. The Tm values obtained from DSC curves for samples P‐20 and P‐25 were 290 and 287°C, respectively (where the number in the sample name indicates the molar fraction of the phosphorus‐containing monomer in the reactants). The initial flow temperatures of other samples observed with hot‐stage polarizing microscopy were 271–290°C. The 5% degradation temperatures in nitrogen ranged from 431 to 462°C, and the char yields at 640°C were 41–52%. All the copolyesters, except P‐40, were thermotropic and nematic. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1278–1284, 2002  相似文献   

14.
In this study, a random copolymer of acylamide and acrylic acid [poly(AAm‐co‐AA)] was prepared by a redox copolymerization method of their aqueous solutions. The effects of initial AAm/AA mole ratio, PEG 4000 content, and N,N′‐methylenebisacrylamide concentration on swelling behavior were investigated in water. Average molecular weights between crosslinks, percentage swelling, swelling equilibrium values, and diffusion/swelling characteristics (i.e., the structure of network constant, the type of diffusion, the initial swelling rate, swelling rate constant) were evaluated for every hydrogel systems. The hydrogels showed mass swelling capabilities in the range 789–1040% (for AAm/AA hydrogels), 769–930% (for AAm/AA hydrogels in the presence of PEG 4000), and 716–1040% (for AAm/AA hydrogels containing different concentrations of the crosslinker). The swelling capabilities of the hydrogels decreased with the increasing AA, PEG 4000, and crosslinker concentrations. The diffusion of water into AAm/AA hydrogels was found to be a non‐Fickian type. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1289–1293, 2004  相似文献   

15.
This study used in situ polymerization to prepare polyethylene terephthalate (PET) nanocomposites incorporating Ethoquad‐modified montmorillonite (eMMT), unmodified hectorite (HCT), or phenyl hectorite (phHCT) particles to study the impact of platelet surface chemistry and loading on thermal, mechanical, and gas barrier properties. eMMT platelets reduced the PET crystallization rate without altering the ultimate degree of crystallinity. In contrast, HCT and phHCT platelets accelerated the polymer's crystallization rate and increased its crystallinity. DMA results for thermally‐quenched samples showed that as T increased past glass transition temperature (Tg), HCT and phHCT nanocomposites (and control PET) manifested precipitous drops in G′ followed by increasing G′ due to cold crystallization; in contrast, eMMT nanocomposites had much higher G′ values around Tg. This provides direct evidence of eMMT reinforcement in thermally‐quenched eMMT nanocomposites. These results suggest that eMMT has a strong, favorable interaction with PET, possibly through Ethoquad‐PET entanglement. HCT and phHCT have a fundamentally different interaction with PET that increases crystallization rate and Tg by 11 to 17°C. Water barrier improvement in eMMT nanocomposites agrees with previously published oxygen barrier results and can be rationalized in terms of a tortuous path gas barrier model. POLYM. ENG. SCI., 52:1888–1902, 2012. © 2012 Society of Plastics Engineers  相似文献   

16.
Diglycidyl ether of 9,9‐bis(4‐hydroxyphenyl) fluorene (DGEBF) monomer was successfully synthesized and characterized in detail. The crystal structure of DGEBF was measured by single‐crystal X‐ray diffraction analysis. Curing kinetics of DGEBF with 4,4‐diaminodiphenyl sulfone (DDS), thermal properties, and decomposition kinetics were investigated using nonisothermal differential scanning calorimetry (DSC) according to Kissinger, Ozawa and Crane methods. The glass transition temperature (Tg), thermal properties of cured polymer were estimated by DSC, dynamic mechanical analysis, and thermogravimetric analyses. Epoxy value of DGEBF monomer up to theoretical value leads to higher crosslink density of cured polymers. The cured DGEBF/DDS system exhibited obvious higher Tg and better thermal stability compared to those of DGEBF/diamine systems reported previously. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010  相似文献   

17.
A comparison of the thermal properties of two classes of poly(D,L ‐lactic‐glycolic acid) multiblock copolymers is reported. In particular, the results of differential scanning calorimetry, and thermogravimetric analysis of copolymers containing poly(ethylene glycol) (PEG) or diol‐terminated poly(ϵ‐caprolactone) (PCDT) segments are described. The influence of the chemical structure and the length of PEG and PCDT on thermal stability, degree of crystallinity and glass transition temperature (Tg ) is discussed. Finally, an evaluation of the hydrolytic behavior in conditions mimicking the physiological environment is reported. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1721–1728, 2000  相似文献   

18.
Benzylated waste pulps (PBzs) were synthesized from treated waste pulp (Pulp), and benzyl chloride with phase transfer catalyst (PTC), and graft copolymers (PBz‐g‐LA) were synthesized from PBzs and L‐lactic acid (LA). Thermal properties, solubility, crystallinity, and biodegradability of the obtained PBzs and graft copolymers were investigated. PBzs with the degree of substitution (DS) higher than 1.5 showed Tg and Tm in DSC measurement. All PBz‐g‐LA exhibited no Tm. However, the graft copolymers obtained from lower DS PBzs having no Tg, exhibited Tg. The solubility of PBzs enhanced with increasing DS, and the crystallinity of PBzs reduced with increasing DS because of hydrophobicity and steric effect of benzyl groups. The solubility of graft copolymers was similar to that of original PBzs. Biodegradation tests for PBzs, Pulp, and graft copolymers were performed using cellulase in 0.1 M acetate buffer solution (pH 5.5) at 37°C. All samples showed biodegradability though the biodegradation rate decreased with increasing DS of PBz. In PBz‐g‐LA, the initial biodegradation rate was faster than that of original PBz because of hydrolysis of LA units. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2658–2664, 2004  相似文献   

19.
The effects of the species and content of a swelling agent on the molecular weight of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) synthesized in an aqueous medium were studied. It was found that the molecular weight of PPO increases after introducing a certain amount of the swelling agent during the oxidative polymerization of 2,6‐dimethylphenol (DMP). Tg of the PPO/swelling agent mixture decreases with the increase of the swelling agent content, and the relation between Tg of the PPO/swelling agent mixture and the swelling agent content obeys Fox equation. After the introduction of the swelling agent during the oxidative polymerization of DMP, the molecular weight of PPO is correlated with Tg of the PPO/swelling agent mixture and it was revealed that Tg plays an important role in the molecular weight of PPO synthesized in the aqueous medium. The same molecular weight of PPO can be obtained only if Tg of the PPO/swelling agent mixture is the same, no matter what kind of swelling agent is introduced during the oxidative polymerization of DMP. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers  相似文献   

20.
The unusual amino acid l ‐3,4‐dihydroxyphenylalanine (DOPA), which was found in mussel adhesive protein, was recognized as crucial element for the adhesive of mussel. In this work, the synthesis of thermoresponsive and photocrosslinkable bioadhesive with ternary networks prepared by incorporating dopamine acrylamide (DAM) and N‐isopropylacrylamide (NIPAAm) into a crosslinked network based on poly(ethylene glycol)‐triacrylate (PEG‐TA) was reported. The effects of DAM and NIPAAm on polymerization kinetics, swelling kinetics, adhesion strength, thermomechanical properties, and cytotoxicity assays were systematically evaluated. The results showed that DAM could affect photopolymerization kinetics of terpolymer due to inhibitory effects of the catechol. The terpolymer has not only strong adhesion strength which was better than that of the commercial fibrin adhesives (0.05 MPa), but also the good humid‐resistant property. The thermoresponsive properties of the system were investigated by the measurement of swelling kinetics. The equilibrium swelling ratio of gels was obviously higher at 25°C than at 37°C. The thermomechanical properties of terpolymer indicated that the presence of the catechol moiety increased significantly the glass transition temperature (Tg) and crosslink density of ternary network. The results of cytotoxicity of gels indicated that terpolymer were biocompatible and less cytotoxicity towards the growth of mouse fibroblast cells (L929 cells). The obtained products could have the potential to serve as the bioadhesive in the future. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41102.  相似文献   

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