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1.
Copolymers (polyoxymethylene) were prepared by cationic copolymerization of 1,3,5‐trioxane (TOX) with 1,3‐dioxolane (DOX) in the presence of Maghnite‐H+ (Mag‐H+) in solution. Maghnite is a Montmorillonite sheet silicate clay, with exchanged protons to produce Mag‐H+. Various techniques, including 1H‐NMR, 13C‐NMR, FT‐IR spectroscopy, and Ubbelohde viscometer were used to elucidate structural characteristics properties of the resulting copolymers. The influence of the amount of catalyst, of dioxolane (DOX), temperature, solvent, and time of copolymerization on yield and on intrinsic viscosity of copolymers was studied. The yield of copolymerization depends on the amount of Mag‐H+ used and the reaction time. We also propose mechanisms involved in the synthesis of copolymer (polyoxymethylene). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010  相似文献   

2.
The copolymerization of carbon dioxide, allyl glycidyl ether, and cyclohexene oxide catalyzed by the system consisting of Y(CF3CO2)3, Zn(Et)2, and pyrogallol in the solvent of 1, 3‐dioxolane was performed in this study. The IR, 1H NMR, and 13C‐NMR spectra, as well as the elemental analysis, indicated that the resulting copolymer was an alternating polycarbonate possessing more than 90% of carbonate units. The molecular weight could be as high as 1.5 × 105, and the polydispersity index was 4.5. The resultant polycarbonate was found to effectively react with 3‐(trimethoxysilyl)propyl methacrylate via a free radical reaction to result in a precursor used in the sol‐gel process to synthesize a polycarbonate‐silica nanocomposite. The nanocomposites were characterized by SEM, 29Si NMR, TGA, DSC, and UV–Vis. Silica particles with size less than 100 nm were found to disperse uniformly in the nanocomposites. It was also found that the thermal properties were dependent on the content of cyclohexene carbonate units. Both the thermal and mechanical properties of the resultant nanocomposites could be adjusted with silica content, while the transparency was comparable to the base copolymer even at high silica contents. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 750–757, 2005  相似文献   

3.
Polyamide‐6 (PA‐6)/clay (modified montmorillonite) hybrid was synthesized by melt blending at high shear stress. 27Al‐NMR of solid state shows that the clay is not modified after melt blending. Using wide‐line 1H‐NMR and TEM, it is demonstrated that the nanocomposite exhibits mainly an exfoliated structure. It is shown that the modified montmorillonite induces the crystallization of PA‐6 predominantly in γ‐form. The presence of clay in PA‐6 increases the polymer crystallization temperature, and decreases its melting point. These phenomena show that a certain number of interactions develop near the reinforcing material, and that the latter plays a particular role of nucleating agent. However, the crystallization is not spherulitic and the assumption of macromolecular orientation in the vicinity of the clay is demonstrated by the observations carried out in DSC and AFM. These particular properties of orientation will have a particular importance on the mechanical behavior of the nanocomposite material. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2416–2423, 2002  相似文献   

4.
The crystallization of poly(ethylene oxide) (PEO) in the presence of silica nanoparticles (SiO2 NPs) was investigated in terms of heterogeneous nucleation of SiO2 NPs using polarizing optical microscopy and differential scanning calorimetry. The content and surface functionality of SiO2 NPs were considered as the main factors affecting crystallization, and the effect of annealing time and temperature was also examined. The SiO2 NPs acted as heterogeneous nucleates during the crystallization process, thereby enhancing the nucleation density and limiting the spherulitic growth rate. A kinetics study of non‐isothermal crystallization showed that the crystallization rate of 5 wt% SiO2/PEO nanocomposite was ca 2.1 times higher than that of neat PEO. In addition, among various surface‐functionalized SiO2 nanoparticles, alkyl‐chain‐functionalized SiO2 NPs were favorable for achieving a higher crystallization rate due to the enhanced compatibility between the SiO2 NPs and PEO chains. © 2012 Society of Chemical Industry  相似文献   

5.
Poly{[α‐maleic anhydride‐ω‐methoxy‐poly(ethylene glycol)]‐co‐(ethyl cyanoacrylate)} (PEGECA) copolymers were prepared by radical polymerization of macromolecular poly(ethylene glycol) monomers (PEGylated) and ethyl 2‐cyanoacrylate in solvent. The structures of the copolymer were characterized by Fourier‐transform infrared (FTIR) and proton nuclear magnetic resonance (1H‐NMR). The morphology and size of the PEGECA nanoparticles prepared by nanoprecipitation techniques were investigated by transmission electron microscopy (TEM) and photon correlation spectroscopy (PCS) methods. The results show that the PEGECA can self‐assemble into highly stable nanoparticles in aqueous media, and inner core and outer shell morphology. The size of the nanoparticles was strongly influenced by the solvent character and the copolymer concentration in the organic solvents. A hydrophobic drug, ibuprofen, was effectively incorporated into the nanoparticles, which provides a delivery system for ibuprofen and other hydrophobic compounds. Copyright © 2005 Society of Chemical Industry  相似文献   

6.
The thermooxidative degradation of poly(oxymethylene) copolymer (CPOM‐Y) powder was studied in air in 150°C. The effect of the sequence distribution of degraded poly(oxymethylene) (POM) samples on the thermal decomposition behavior was investigated with 1H‐NMR and gas chromatography/mass spectrometry. The results showed that the degradation process of CPOM‐Y could be divided into three stages with a gradually increasing degradation rate. The change in the sequence molar fractions agreed with the fact that the ethylene oxide (EO) units had higher thermal stability, and the degradation of POM was due to the decomposition of formal units. At the beginning, CPOM‐Y tended to split off formaldehyde, starting at the chain ends, some of which were not ended by EO units. In stage 2, the thermooxidation of POM occurred in the amorphous phase. In stage 3, no obvious rules for the changes in the sequence contents were obtained from NMR results, and this indicated further random chain scission and unzipping occurring heavily in the crystalline bulk. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 577–583, 2004  相似文献   

7.
Microspheres consisting of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) polymer matrix and calcium phosphate (Ca‐P) nanoparticles were made using the solid‐in‐oil‐in‐water (S/O/W) emulsion solvent evaporation technique. Amorphous Ca‐P nanoparticles with the calcium to phosphate ratio of 1.5 were relatively well distributed in microspheres. The nonisothermal crystallization behavior of Ca‐P/PHBV nanocomposite with different Ca‐P contents (0–20%) was studied through differential scanning calorimetry using different cooling rates. During nonisothermal crystallization, the presence of Ca‐P nanoparticles resulted in an increase in crystallization rate and the nucleation activity of the nanocomposite also increased with increasing Ca‐P content. Various models were applied to investigate nonisothermal crystallization kinetics. All approaches, except for the Ozawa model, could successfully describe the nonisothermal crystallization behavior of PHBV and Ca‐P/PHBV nanocomposite. The effective activation energy for nonisothermal crystallization was calculated using the differential isoconversional method proposed by Friedman. The morphology of PHBV spherulites in nanocomposite was also studied using polarized optical microscopy. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers  相似文献   

8.
In this article, polyimide (PI)/silica nanocomposite nanofoams were prepared by solid‐state foaming using supercritical CO2 as foaming agent. To control the cell size and morphology of the PI/silica foam, the silica nanoparticles as nucleating agent were in situ formation from TEOS via sol‐gel process, which make the silica nanoparticles homogeneously dispersed in PI matrix. The resulting PI/silica nanocomposite nanofoams were characterized by scanning electron microscopy (SEM), the image analysis system attached to the SEM and dielectric properties measurements. In PI/silica nanocomposite nanofoams, one type of novel morphology was shown that each cell contained one silica nanoparticle and many smaller holes about 20–50 nm uniformly located in the cell wall. This special structure could visually prove that the nucleation sites during foaming were formed on the surface of nucleating agents. Compared with those of neat PI foam, the cell size of PI/silica nanocomposite nanofoams was smaller and its distribution was narrower. The dielectric constant of PI/silica nanocomposite nanofoams was decreased because of the incorporation of the air voids into the PI/silica nanofoams. While the porosity of PI/silica nanocomposite nanofoam film was 0.45, the dielectric constant of the film (at 1 MHz) was reduced from 3.8 to about 2.6. Furthermore, the dielectric constant of PI/silica nanofoam films remained stable across the frequency range of 1×102~1×107 HZ. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42355.  相似文献   

9.
In a previous article, we reported the preparation and characterization of a nanocomposite of poly(L ‐lactic acid) (PLLA) and silica via the in situ melt polymerization of L ‐lactic acid in the presence of acidic silica sol. In this study, the isothermal crystallization and melting behaviors of a PLLA/silicon dioxide (SiO2) nanocomposite with 5 wt % well‐dispersed SiO2 nanoparticles (PLLASN5) and pure PLLA were comparatively studied with differential scanning calorimetry and polarized optical microscopy. The SiO2 nanoparticles acted as nucleation agents in the PLLA matrix and enhanced its nucleation rate and overall crystallization rate, especially at high crystallization temperatures. However, no deleterious effect on the crystal morphology or crystallinity was observed. The crystals that formed at a low temperature were imperfect; therefore, double melting peaks occurred during the second heating scan because of melt recrystallization. With the crystallization temperature increasing, the crystals became increasingly perfect; as a result, the low melting peak increased and shifted to a higher temperature. The existence of SiO2 nanoparticles had no effect on the equilibrium temperature of the PLLA matrix. Pure PLLA and PLLASN5 have the same equilibrium temperature of 171.5°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009  相似文献   

10.
The downstream processing of 1,3‐propanediol fermentation broth using flocculation, reactive extraction, and reactive distillation was studied. Cellular debris and soluble protein in the broth were flocculated by combined use of chitosan and polyacrylamide at optimal concentrations of 150 ppm and 70 ppm, respectively; the soluble protein in the broth decreased to 0.06 g L?1, and the recovery ratio of the supernatant liquor to broth was greater than 99%. 1,3‐Propanediol and other alcohols were extracted from the supernatant liquor by reacting with butyraldehyde. In a four‐stage countercurrent extraction with the volume ratio of the extraction solvent to the aqueous phase being 20:100, more than 99% 1,3‐propanediol acetal (2‐propyl‐1,3‐dioxane) and 2,3‐butanediol acetal (2‐propyl‐4,5‐dimethyl‐1,3‐dioxolane) were recovered from the aqueous phase; 35% of the glycerol acetals were recovered. The acetals produced were hydrolyzed in a reactive distillation column using the strongly acidic cation‐exchange resin as catalyst, the bottom product obtained was a mixture of 1,3‐propanediol (407 g L?1), 2,3‐butanediol (252 g L?1), glycerol (277 g L?1), and glycerol acetals (146 g L?1). Copyright © 2005 Society of Chemical Industry  相似文献   

11.
To improve the crystallization rate and melt strength of polylactide (PLLA), nano‐size amino silica grafted by four‐arm PLLA (4A‐PLLA) with different molecular weight was synthesized. 1H nuclear magnetic resonance proved that 4A‐PLLA had been grafted onto the surface of SiO2 successfully, and the grafting ratios and the degradation behaviors of the grafted SiO2 nanoparticles (g‐SiO2) were studied. When the grafted silica was introduced into PLLA matrix, the crystallization rate and melt strength of composites were found to be improved and the length of grafted chain played an important role. The extension rheology indicated that long grafted 4A‐PLLA on the surface of SiO2 was more efficient in enhancing the elongational viscosity of PLLA, owing to the stronger interactions between the grafted chains and the matrix. The crystallization behavior of ungrafted silica filled composite was similar to that of neat PLA, while g‐SiO2 played a role of nucleating agent. The crystallinities and the crystallization rates of the composites depended on the content of g‐SiO2 and the grafted chain length of 4A‐PLLA, especially the latter. Longer grafted chain acted as nucleation site in the matrix and significantly improved the crystallization behaviors of PLLA. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45675.  相似文献   

12.
In this study, cationic ring opening in situ copolymerization of 1,3,5-trioxane (TOX) and 1,3-dioxolane (DOX) occurred during bulk polymerization in the presence of phosphotungstic acid as a catalyst. In another part of the study, copolymerization occurred in the presence of retarder tetrahydrofuran (THF), and its effect on the crystallization and thermal stability of the samples was also investigated. The findings from 1HNMR spectrometry indicated that the synthesized samples of random acetal copolymer are comprised of an independent oxyethylene unit in an oxymethylene main-chain sequence. The findings from DSC indicated that crystallinity decreases with increasing comonomer content. Furthermore, the sample with retarder revealed greater crystallinity than the samples without retarder. From TGA results, it was revealed that the sample with retarder caused a larger quantity of comonomer to enter the chain and increased the thermal stability compared to the samples without retarder.  相似文献   

13.
Diblock copolymers with different poly(ε‐caprolactone) (PCL) block lengths were synthesized by ring‐opening polymerization of ε‐caprolactone in the presence of monomethoxy poly(ethylene glycol) (mPEG‐OH, MW 2000) as initiator. The self‐aggregation behaviors and microscopic characteristics of the diblock copolymer self‐aggregates, prepared by the diafiltration method, were investigated by using 1H NMR, dynamic light scattering (DLS), and fluorescence spectroscopy. The PEG–PCL block copolymers formed the self‐aggregate in an aqueous environment by intra‐ and/or intermolecular association between hydrophobic PCL chains. The critical aggregation concentrations of the block copolymer self‐aggregate became lower with increasing hydrophobic PCL block length. On the other hand, reverse trends of mean hydrodynamic diameters were measured by DLS owing to the increasing bulkiness of the hydrophobic chains and hydrophobic interaction between the PCL microdomains. The partition equilibrium constants (Kv) of pyrene, measured by fluorescence spectroscopy, revealed that the inner core hydrophobicity of the nanoparticles increased with increasing PCL chain length. The aggregation number of PCL chain per one hydrophobic microdomain, investigated by the fluorescence quenching method using cetylpyridinium chloride as a quencher, revealed that 4–20 block copolymer chains were needed to form a hydrophobic microdomain, depending on PCL block length. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3520–3527, 2006  相似文献   

14.
《Polymer Composites》2017,38(1):61-67
Organo‐silica nanoparticles were prepared by sol–gel technique of triethoxyvinylsilane (VTES) in aqueous solution. The vinyl groups located on the surface of organo‐silica were used to induce the polymerization process and the encapsulation into styrene‐butyl acrylate copolymer emulsion. The prepared latex samples were characterized using FTIR, 1HNMR, UV–visible, thermal analysis, field emission‐SEM and TEM. Results of TGA revealed that nanosilica has retarded the decomposition of nanocomposite polymers with at least 10°C higher than that of pure emulsions. DSC has shown an increase in the nanosilica ratio up to 5% which leads to a dramatic decrease in the glass transition (T g) of nanocomposite polymer due to the formation of silica nanoparticles homopolymer. DMTA results indicated that the storage modulus of pure polymer is less than nanocomposite, which proves the reinforcing role of nanosilica in the matrix of polymer. Water resistance and UV‐blocking ability have improved by introducing the nanosilica into the matrix of prepared polymer. POLYM. COMPOS., 38:61–67, 2017. © 2015 Society of Plastics Engineers  相似文献   

15.
The crystallization behavior of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) induced by two kinds of nucleating agents, boron nitride (BN) and talc, was investigated by differential scanning calorimetry, polarized optical microscopy and X‐ray diffraction. Both BN and talc have good nucleating ability in the crystallization of PHB and PHBV. From these results, combined with molecular weight measurement by gel permeation chromatography, the mechanism of nucleation by BN and talc in the crystallization of PHB and PHBV has been proposed. BN acts as a nucleating agent itself and initiates nucleation in the crystallization of PHB and PHBV. Talc acts in a different way. It reacts as a chemical reagent with the molten chains of PHB/PHBV, while the reaction product acts as the true nucleating agent, which lowers the crystallization barriers of PHB and PHBV. 1H NMR spectroscopy provides evidence for the reaction between PHB and talc and supports the proposed nucleation mechanism. Copyright © 2005 Society of Chemical Industry  相似文献   

16.
Biodegradable copolymers of 2‐methylene‐1,3‐dioxepane (MDO) and styrene (ST) were synthesized by free‐radical copolymerization using di‐t‐butyl peroxide (DTBP) as the initiator. The copolymers containing ester units were characterized by Fourier transform infrared (FTIR), 1H‐NMR, and 13C‐NMR spectroscopy. Their molecular weight and polydispersity index were determined by gel permeation chromatography (GPC). In vitro enzymatic degradation of poly(MDO‐co‐ST) was performed at 37°C in phosphate buffer solution (PBS, pH = 7.4) in the presence of Pseudomonas lipase or crude enzyme extracted from earthworm. The experiment showed that incorporating ester units into C? C backbone chain of polystyrene would result in a biodegradable copolymer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1146–1151, 2007  相似文献   

17.
Novel amphiphilic ABA‐type poly(D ‐gluconamidoethyl methacrylate)‐b‐polyurethane‐b‐poly(D ‐gluconamidoethyl methacrylate) (PGAMA‐b‐PU‐b‐PGAMA) tri‐block copolymers were successfully synthesized via the combination of the step‐growth and copper‐catalyzed atom transfer radical polymerization (ATRP). Dihydroxy polyurethane (HO‐PU‐OH) was synthesized by the step‐growth polymerization of hexamethylene diisocyanate with poly(tetramethylene glycol). PGAMA‐b‐PU‐b‐PGAMA block copolymers were synthesized via copper‐catalyzed ATRP of GAMA in N, N‐dimethyl formamide at 20°C in the presence of 2, 2′‐bipyridyl using Br‐PU‐Br as macroinitiator and characterized by 1H‐NMR spectroscopy and GPC. The resulting block copolymer forms spherical micelles in water as observed in TEM study, and also supported by 1H NMR spectroscopy and light scattering. Miceller size increases with increase in hydrophilic PGAMA chain length as revealed by DLS study. The critical micellar concentration values of the resulting block copolymers increased with the increase of the chain length of the PGAMA block. Thermal properties of these block copolymers were studied by thermo‐gravimetric analysis, and differential scanning calorimetric study. Spherical Ag‐nanoparticles were successfully synthesized using these block copolymers as stabilizer. The dimension of Ag nanoparticle was tailored by altering the chain length of the hydrophilic block of the copolymer. A mechanism has been proposed for the formation of stable and regulated Ag nanoparticle using various chain length of hydrophilic PGAMA block of the tri‐block copolymer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013  相似文献   

18.
A series of poly(5,5‐dimethyl‐1,3‐dioxan‐2‐one)‐block‐methoxy poly(ethylene glycol) (PDTC‐b‐mPEG) copolymers were synthesized by the ring‐opening polymerization of 5,5‐dimethyl‐1,3‐dioxan‐2‐one (DTC) in bulk, using methoxy poly(ethylene glycol) (mPEG) as initiator without adding any catalysts. The resulting copolymers were characterized by Fourier transform infrared spectra, 1H NMR and gel permeation chromatography. The influences of some factors such as the DTC/mPEG molar feed ratio, reaction time and reaction temperature on the copolymerization were investigated. The experimental results showed that mPEG could effectively initiate the ring‐opening polymerization of DTC in the absence of catalyst, and that the copolymerization conditions had a significant effect on the molecular weight of PDTC‐b‐mPEG copolymer. In vitro drug release study demonstrated that the amount of indomethacin released from PDTC‐b‐mPEG copolymer decreased with increase in the DTC content in the copolymer. © 2013 Society of Chemical Industry  相似文献   

19.
The heat‐resistant copolymer of N‐phenylmaleimide (NPMI)–styrene (St)–maleic anhydride (MAH) was synthesized in xylene at 125°C with di‐tert‐butyl diperoxyterephthalate as an initiator. The characteristics of the copolymer were analyzed by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy (1H‐NMR and 13C‐NMR), gel permeation chromatography, and elemental analysis. The 13C‐NMR results show that the copolymer possessed random sequence distribution; this was also supported by the differential scanning calorimetry experiment, in which a single glass‐transition temperature (Tg) of 202.3°C was observed. The thermal stability and degradation mechanism of the copolymer were investigated by thermogravimetric analysis. Using the Kissinger equation and Ozawa equation, we proved a nucleation controlling mechanism with an apparent activation energy of 144 kJ/mol. Blends of acrylonitrile–butadiene–styrene with the NPMI–St–MAH copolymer with various contents were prepared with a twin‐screw extruder processes. The mechanical and thermal properties of the materials, such as the tensile and flexural strength, Tg's, and Vicat softening temperatures, were all enhanced with the addition of the modifier, whereas the melt flow index decreased. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012  相似文献   

20.
ABA‐type triblock copolymers derived from 4,4'‐(hexafluoroisopropylidene)diphthalicanhydride‐2,3,5,6‐tetramethyl‐1,4‐phenylenediamine (6FDA‐TeMPD) and methacryl phenyl polyhedral oligomeric silsesquioxane (MPPOSS) were synthesized by atom transfer radical polymerization. The chemical structure of the synthesized ABA‐type triblock copolymer was confirmed by 1H NMR, 13C NMR, 29Si NMR and Fourier transform infrared analyses. The ratios of 6FDA‐TeMPD and MPPOSS determined by TGA were 94/6, 85/15, 77/23, 68/32, 57/43 and 31/69. The film density of the ABA‐type triblock copolymer films did not conform to the mixing rule because of polyimide (PI) chain aggregation. Based on contact angle and water uptake analyses, the hydrophobicity of the ABA‐type triblock copolymer film was determined to be higher than the theoretical value because of POSS cage effects and PI chain aggregation. The gas permeability coefficient of the ABA‐type triblock copolymer decreased compared with that of PI because of aggregation of PI chains and inhibition of solubility decreases by substitutes with high affinity. ABA‐type triblock copolymer CO2/H2 separation performance increased compared with that of PI. The ABA‐type triblock copolymer derived from PI and MPPOSS can be described as a polymer material with higher hydrophobicity and higher CO2/H2 selectivity than PI. © 2015 Society of Chemical Industry  相似文献   

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