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1.
W. Lyoo C. Park J. Yeum B. Ji C. Lee S. Lee J. Lee 《Colloid and polymer science》2002,280(12):1075-1083
To prepare ultrahigh molecular weight (UHMW) poly(vinyl pivalate) (PVPi) with high conversion and high linearity for a precursor of syndiotacticity-rich UHMW poly(vinyl alcohol) (PVA), vinyl pivalate (VPi) was suspension polymerized using a low-temperature initiator, 2,2'-azobis(2,4-dimethylvaleronitrile) (ADMVN), and the effects of polymerization conditions on the polymerization behavior and molecular structures of PVPi and PVA prepared by saponifying PVPi were investigated. Suspension polymerization was slightly inferior to bulk polymerization in increasing the molecular weight of PVA. In contrast, the former was superior in increasing the conversion of the polymer. Suspension polymerization of VPi at 25 °C by controlling various polymerization factors proved to be successful in obtaining PVA of UHMW (number-average degree of polymerization (Pn): 14,700-16,700), high syndiotactic diad content (62%), and of high yield (ultimate conversion of VPi into PVPi: 85-90%). In the case of bulk polymerization of VPi under the same conditions, maximum Pn, conversion of 15,800-17,000, and 25-35% were obtained, respectively. The degree of branching was lower and the Pn and syndiotacticity were higher with PVA prepared from PVPi polymerized at lower temperatures. All PVAs from PVPi suspension-polymerized at 25 °C were fibrous, with a high degree of crystallinity and orientation of the crystallites. 相似文献
2.
Jeong Hyun Yeum Byung Chul Ji Chul Joo Lee Ji Youl Lee Sang‐Seob Lee Sam Soo Kim Joon Ho Kim Won Seok Lyoo 《Journal of polymer science. Part A, Polymer chemistry》2002,40(8):1103-1111
To prepare water‐soluble, syndiotacticity‐rich poly(vinyl alcohol) (PVA) microfibrils for various industrial applications, we synthesized syndiotacticity‐rich, low molecular weight PVA by the solution polymerization of vinyl pivalate (VPi) in tetrahydrofuran (THF) at low temperatures with 2,2′‐azobis(2,4‐dimethylvaleronitrile) (ADMVN) as an initiator and successive saponification of poly(vinyl pivalate) (PVPi). Effects of the initiator and monomer concentrations and the polymerization temperature were investigated in terms of the polymerization behaviors and molecular structures of PVPi and the corresponding syndiotacticity‐rich PVA. The polymerization rate of VPi in THF was proportional to the 0.91 power of the ADMVN concentration, indicating the heterogeneous nature of THF polymerization. The low‐temperature solution polymerization of VPi in THF with ADMVN proved to be successful in obtaining water‐soluble PVA with a number‐average degree of polymerization (Pn) of 300–900, a syndiotactic dyad content of 60–63%, and an ultimate conversion of VPi into PVPi of over 75%. Despite the low molecular weight of PVA with Pn = 800, water‐soluble PVA microfibrillar fibers were prepared because of the high level of syndiotacticity. In contrast, for PVA with Pn = 330, shapeless and globular morphologies were observed, indicating that molecular weight has an important role in the in situ fibrillation of syndiotacticity‐rich PVA. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1103–1111, 2002 相似文献
3.
Electrospinning fabrication and characterization of poly(vinyl alcohol)/montmorillonite/silver hybrid nanofibers for antibacterial applications 总被引:1,自引:0,他引:1
Jae Hyeung Park Mohammad Rezaul Karim In Kyo Kim In Woo Cheong Jong Won Kim Do Gyu Bae Jin Won Cho Jeong Hyun Yeum 《Colloid and polymer science》2010,288(1):115-121
Poly(vinyl alcohol) (PVA)/montmorillonite clay (MMT)/silver (Ag) nanoparticles have been electrospun for fabricating PVA/MMT/Ag
nanofiber in aqueous solutions. Since PVA is a water-soluble and biocompatible polymer, it is one of the best materials for
preparation of antibacterial nanofiber. MMT has been used as an inorganic filler to enhance properties of homopolymeric nanofiber.
The PVA/MMT/Ag nanofiber diameter increases with increasing contents of MMT clay and Ag nanoparticles. In preservation test,
the PVA/MMT/Ag nanofiber confirms an excellent antibacterial performance, elucidating for practical uses as a new preservative.
Moreover, the PVA/MMT/Ag nanofiber shows improved thermal properties. 相似文献
4.
Jae Hyeung Park Hyun Woo Lee Dong Keun Chae Weontae Oh Jae Deuk Yun Yulin Deng Jeong Hyun Yeum 《Colloid and polymer science》2009,287(8):943-950
Submicron fibers of the composite of poly(vinyl alcohol) (PVA), chitosan oligosaccharide [COS, (1→4)2-amino-2-deoxy-β-d-glucose], and montmorillonite clay (MMT) were prepared using electrospinning method with aqueous solutions. Scanning electron
microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), thermal gravimetric analyzer, and tensile strength
testing machine (Zwick) were utilized to characterize the PVA/COS/MMT nanofiber mats morphology and properties. The PVA/COS
ratio and MMT concentration play important roles in nanofiber mat properties. XRD and TEM data demonstrated that exfoliated
MMT layers were well-distributed within nanofiber. It was also found that the mechanical property and thermal stability were
increased with COS and MMT contents. 相似文献
5.
Nanofibers of the composite of pullulan (PULL), poly(vinyl alcohol) (PVA), and montmorillonite clay (MMT) were prepared using electrospinning method in aqueous solutions. Pullulan is an interesting natural polymer for many of its merits and good properties. Because of biocompatibility and non-toxicity of PVA, it could be used in numerous fields. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA) were done to characterize the PULL/PVA/MMT nanofibers morphology and properties. XRD patterns and FTIR data demonstrated that there were good interactions between PULL and PVA caused by possibly hydrogen bonds. Moreover, XRD data and TEM images indicated that intercalated and exfoliated MMT nanoplatelets can be obtained within the PULL/PVA/MMT nanofibers depending on the PULL/PVA blend ratios. Furthermore, the thermal stability and mechanical property (tensile strength) of PULL/PVA/MMT nanofibers could be enhanced more by exfoliated MMT nanoplatelets than intercalated structures of that nanoplatelets. 相似文献
6.
Mohammad Rezaul Karim Jeong Hyun Yeum 《Journal of Polymer Science.Polymer Physics》2008,46(21):2279-2285
Conducting polypyrrole (PPy)‐montmorillonite (MMT) clay nanocomposites have been synthesized by the in situ intercalative polymerization method. The PPy‐MMT nanocomposites are characterized by field‐emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), ultraviolet–visible (UV–vis) spectroscopy, thermogravimetric analysis (TGA), and Fourier‐transform infrared (FTIR) spectroscopy. XRD patterns show that after polymerization by the in situ intercalative method with ammonium persulfate and 1 M HCl, an increase in the basal spacing from 1.2 to 1.9 nm was observed, signifying that PPy is synthesized between the interlayer spaces of MMT. TEM and SEM micrographs suggest that the coexistence of intercalated MMT layers with the PPy macromolecules. FTIR reveals that there might be possible interfacial interactions present between the MMT clay and PPy matrix. The study also shows that the introduction of MMT clay results in thermal stability improvement of the PPy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2279–2285, 2008 相似文献
7.
Mohammad Rezaul Karim Jeong Hyun Yeum Min‐Young Lee Mu Sang Lee Kwon Taek Lim 《先进技术聚合物》2009,20(7):639-644
Sulfonated polyaniline‐silver (SPAni‐Ag) hybrid nanocomposites have been synthesized by the in situ reduction using a UV‐curing polymerization method without using any reducing or binding agent. An aqueous solution of aniline and orthoanilinic acid (OA) comonomers, a free‐radical oxidant and silver metal salts were irradiated by UV rays. Reduction of the silver salt in aqueous aniline and OA leads to the formation of silver particles which in turn catalyze the oxidation of comonomers to sulfonated polyaniline (SPAni). The resultant SPAni‐Ag nanocomposites were characterized by using different spectroscopy analyses like UV–visible (UV–Vis), X‐ray diffraction (XRD) and infrared spectroscopy. The absorption bands were revealed to be optically active and the peaks blue‐shifted due to the presence of metallic silver within the SPAni matrix. The XRD patterns displayed both the broad amorphous polymeric and sharp metallic peaks. Scanning electron microscopy and transmission electron microscopy of the nanocomposites showed a uniform size distribution with spherical and granular morphology. Thermogravimetric analysis revealed that the nanocomposites had a better thermal stability than the bulk SPAni. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
8.
W. Lyoo J. Yeum H. Ghim J. Park S. Lee J. Kim D. Shin J. Lee 《Colloid and polymer science》2003,281(5):416-422
To precisely identify the effect of the molecular weight of syndiotactic poly(vinyl alcohol) (s-PVA) on the water stability of a s-PVA/iodine complex film, we prepared four s-PVAs with similar syndiotactic diad (s-diad) contents of about 63% and with different number-average degrees of polymerization, Pn, of 900, 6,000, 10,000, and 17,000, respectively. The desorption behavior of iodine in the s-PVA/iodine complex film in water was investigated in relation to the solubility of s-PVA in water. The degree of solubility of a s-PVA film having different Pn in water at 80 °C was limited to about 0.3-10%, whereas the degrees of solubility of atactic PVA films with Pn of 6,000 and 10,000 were 100% at the same conditions. The degree of iodine desorption of the complex film decreased with increasing Pn of s-PVA. Especially, the degree of iodine desorption of a PVA drawn film having Pn of 17,000 was limited to 2%, regardless of soaking temperature from 40 to 80 °C. The desorption of iodine in water was strongly affected by the dissolution of PVA. In addition, the degree of iodine desorption of the drawn s-PVA/iodine film was larger than that of the undrawn one. 相似文献
9.
Minsoo Koo Jong-Seong Bae Seong Eun Shim Dongmin Kim Dae-Geun Nam Jae-Won Lee Gang-Woo Lee Jeong Hyun Yeum Weontae Oh 《Colloid and polymer science》2011,289(13):1503-1509
Polyimide–graphene composites (PIG) were prepared with variable amounts of graphene, and their thermal properties were analyzed
in films on substrates or sheet states. The thermal conductivities of PIG composite sheets gradually moved upwards with increase
of graphene loading. Coefficient of thermal expansion of composite sheet was higher in out-of-plane mode than in-plane mode.
The residual stress of a composite film was monotonously changed in accordance with the variation of temperature and lowered
with increase of graphene. In addition, the residual stress of a composite film reached to the initial stress value during
cooling process after heating. The stress profiles on further heating and cooling runs closely followed the stress profile
during the first cooing run. 相似文献
10.
Eun Mi Lee Hyun Woo Lee Jae Hyeung Park Young A. Han Byung Chul Ji Weontae Oh Yulin Deng Jeong Hyun Yeum 《Colloid and polymer science》2008,286(12):1379-1385
Poly(methyl methacrylate) (PMMA)/silver nanocomposite microspheres with unique multihollow structures were prepared by suspension
polymerization in the presence of dual dispersion agents. The addition of a lipophilic emulsifier, polyethylene glycol (30EO)
dipolyhydroxystearate (Arlacel P135), not only stabilized water-in-oil (W/O) emulsion, but also converted silver nanoparticles
from hydrophilic to lipophilic. When a suspension polymerization dispersion agent, poly(vinyl alcohol), was added to the above
W/O emulsion system, a water-in-oil-in-water suspension was formed with silver nanoparticles dispersed in the oil phase. The
suspension polymerization was carried out at low temperature with 2,2’-azobis(2,4-dimethylvaleronitrile) as the initiator.
When modified silver nanoparticles were added, the rate of polymerization increased slightly. High monomer conversion (about
85%) was obtained in spite of low polymerization temperature of 30 °C. Under controlled conditions, PMMA/silver microspheres
with various hollow structures were synthesized. The PMMA/silver microspheres with multihollow structure showed high antibacterial
ability. 相似文献