Stereospecificityand Dynamic Viscoelasticityof Polyvinyl Alcohol

Nagai, Akihiko; Takayanagi, Motowo

doi:10.1246/nikkashi1898.68.5_836

Cited by 12 publications

(11 citation statements)

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“…22 It resulted from a reduction of intermolecular forces in crystals, and this reduction takes place with thermal expansion of the PVA unit cells. 19,21 As previously reported, successive intramolecular hydrogen bonding is formed for all OH groups along the chains in the crystalline region for the HI-PVAs.…”

Section: Comparison Of Hi-pva S-pva and A-pva Filmssupporting

confidence: 61%

“…The major dispersion ( a ) observed at around 70 C is attributable to the onset of micro-Brownian motion (i.e., glass transition) of the polymer chains in the non-crystalline region, as judged from the sharpness of the dispersion reflected in the large decrease of E 0 at around 70 C. The a dispersion seen at around À10 C can be assigned to the local twisting motion of non-crystalline chains. 19 The c and c dispersions, seen at around 140 C and 220 C, occurs at temperatures well above the glass transition temperature and are attributable to the motion in the crystallites. [20][21][22][23] The decrease of E 0 at around 70 C ( Figure 1) can be used as a measure of the intensity of the a dispersion (glass transition).…”

Section: Resultsmentioning

confidence: 97%

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Highly Isotactic Poly(vinyl alcohol) Derived from tert-Butyl Vinyl Ether V. Viscoelastic Behavior of Highly Isotactic Poly(vinyl alcohol) Films

Ohgi

Sato

Watanabe

et al. 2006

Polym J

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ABSTRACT:Dynamic viscoeasticity of poly(vinyl alcohol) with high isotacticity (HI-PVA, mm ¼ 0:78), being derived from tert-butyl vinyl ether, was investigated to compare with that of syndiotactc PVA (S-PVA, mm ¼ 0:14) and commercial atactic PVA (A-PVA, mm ¼ 0:22). In the non-crystalline region, the a (local twisting motion) and a (micro-Brownian motion) dispersions occurring at around À10 C and 70 C were nearly the same, in both magnitude and location, for the HI-PVA and S-PVA having an almost identical degree of crystallinity. On the other hand, in the crystalline region, the c and c dispersions of HI-PVA were somewhat different from those of ordinary PVAs. The c dispersion (local motion in crystals due to defects) was clearly observed for HI-PVA but not for S-PVA and A-PVA. The c dispersion (axial motion of the chain in the crystal lattices) was observed for all PVA films but its temperature increased in the order of HI-PVA > S-PVA > A-PVA, which well corresponded to the order of the melting temperature and 13 C spin-lattice relaxation time (T 1C ) of each stereoregular PVA. These differences may be attributed to a difference of the magnitude of intermolecular and/or intramolecular hydrogen bonding in the crystals of respective PVAs. Specifically, the successive intramolecular bonding in the HI-PVA crystal appears to reduce the magnitude of the intermolecular bonding thereby allowing the chain to exhibit the c motion. This successive bonding would also stiffen the chain backbone thereby increasing the c dispersion temperature. [doi:10.1295/polymj.PJ2005235] KEY WORDS Highly Isotactic Poly(vinyl alcohol) / Stereoregular Polymerization / Viscoelasticity / Many efforts have been made for synthesis of stereoregular poly(vinyl alcohol)s (PVAs) being rich in syndiotactic or isotactic sequences 1-3 and changes of their physical properties with the stereoregularity, possibly reflecting changes in the inter-and intramolecular hydrogen bonding, have been extensively investigated. A series of radical-polymerized poly(vinyl ester)s was utilized to synthesize syndiotactic PVAs, and the relationships between stereoregularity and physical properties of PVA have been examined. 1-3Isotactic PVAs were synthesized successfully from poly(vinyl ether)s such as poly(benzyl vinyl ether) (PBzVE), 4,5 poly(tert-butyl vinyl ether) (PtBVE), 6,7 and poly(trimethyl silyl vinyl ether) (PVOSi), 8,9 and their physical properties were also investigated. 1,3Despite the above efforts, the stereoregularity still remained at a low level of the mm fraction (¼ 0:70) even for so-called isotactic PVA (LI-PVA) derived from PVOSi.9,10 Recently, we studied the cationic polymerization of tBVE with boron trifluoride diethyl etherate (BF 3 . OEt 2 ) and successfully prepared the PVAs having the highest isotacticity so far reported. [10][11][12] We found interesting features of these highly isotactic PVAs (HI-PVAs) being different from those of LI-PVA and ordinary atactic PVA (A-PVA). 10,13,14 In particular, we compared the melting temperature T m , degree...

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Section: Comparison Of Hi-pva S-pva and A-pva Filmssupporting

confidence: 61%

Section: Resultsmentioning

confidence: 97%

Highly Isotactic Poly(vinyl alcohol) Derived from tert-Butyl Vinyl Ether V. Viscoelastic Behavior of Highly Isotactic Poly(vinyl alcohol) Films

Ohgi

Sato

Watanabe

et al. 2006

Polym J

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“…The dynamic mechanical properties of PVA have been previously investigated in detail, 21,22 and it was reported that the pure PVA has as many as five mechanical relaxations around Ϫ60, 35, 80, and other two above 100°C.…”

Section: Dma Analysismentioning

confidence: 99%

“…In the present study, the designation of the relaxations in the tan ␦ curve was borrowed from Takayanagai et al 21,22 In Figure 4, the elastic modulus (EЈ) and tan ␦ curve of the dry PVA and wet PVA (c.a. 5 wt % of water) are plotted against temperature, in the temperature range of Ϫ20 to 260°C.…”

Section: Dma Analysismentioning

confidence: 99%

On the viscoelastic properties of poly(vinyl alcohol) and chemically crosslinked poly(vinyl alcohol)

Park

Ruckenstein

2001

J of Applied Polymer Sci

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Poly(vinyl alcohol)(PVA) films chemically crosslinked with glutaraldehyde(GA) in the presence of HCl were prepared by casting from aqueous solutions. The PVA and PVA gels were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA); their swelling characteristics and tensile strength were also determined. The DSC results for the gels displayed depressions of the melting and crystallization temperatures, as well as a decrease of the heat of fusion, when compared to those of PVA free of crosslinker. The DMA analysis revealed that: (1) The glass transition temperature of the wet PVA was lower than that of the dry one, indicating that the water had a plasticizing effect.(2) The gels had a lower glass transition temperature than PVA. (3) The glass transition temperature of the wet gels increased with increasing crosslink density. Possible explanations are provided for these observations. Whereas the thermogravimetric curves of PVA exhibited a single degradation peak, two degradation peaks were detected for the crosslinked PVA. The wet PVA and PVA gels displayed lower tensile strengths and higher elongations than the dried ones.

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“…11 Shiragashi et al showed, using X-ray analysis, that the relaxation of PV A in the range of 140°C can be assigned to mild secondary transition of the crystal phase caused by local molecular motion. 12 The line plotted of E' shows a plateau above the glass transition region (1Xa relaxation region).…”

Section: Dynamic Viscoelasiticity Of Pva-69mentioning

confidence: 99%

Poly(vinyl alcohol) with High Diad-Syndiotacticity and High Melting Point

Fukae

Yamamoto

Fujita

et al. 1997

Polym J

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KEY WORDSPoly(vinyl alcohol) I High Syndiotacticity I Vinyl Pivalate I Crystal Melting I Dynamic Viscoelasticity I Physical properties and new industrial applications of poly( vinyl alcohol) (PV A) with high syndiotacticity have become of interest in recent years.PV A with diad-syndiotacticity of 63% was prepared from an initiator-free photo-emulsion polymerization of vinyl pivalate (VP) followed by saponification of the resulting poly( vinyl pivalate) (PVP), 1 and its characteristics were much different from those of the usual one. 2 During the course of study, radical polymerization of VP in various solvents was examined and non polar solvents were favorable for syndiotactic propagation. 3 Lower temperatures give rise to higher syndiotacticity in radical polymerization of vinyl esters, 4 and even a slight difference in tacticity of PV A substantially affects physical properties.In the present work, to get PV A of higher syndiotacticity, radical polymerization of VP at -40°C using n-hexane as a solvent was tried, and PVA with diad-syndiotacticity of 69% was obtained via saponification of PVP.Although many investigations regarding PV A having high syndiotacticity have been reported, most were carried out using PV A derived from poly( vinyl trifluoroacetate). The preparation of PVA with syndiotacticity of 64%, given by radical polymerization of vinyl trifluoroacetate (VTFAc) at -40°C in n-hexane, was reported. 5 As for PV A having the highest syndiotacticity in radical polymerization, syndiotacticity of 67% has been shown by Yamaura et a!. This was based on the radical polymerization of VTF Ac at -20°C in toluene and quoted as a reference. No detailed information concerning physical properties can be given.PVA having the highest syndiotacticity (ca. 74%), derived from poly(vinyl trimethylsilyl ether) by cationic polymerization process, has been reported. 6 However, there is no description of physical properties. EXPERIMENTAL Preparation of PVAFifty milliliters (0.34 mol) of VP, 200 ml of n-hexane and 17.3 mg (0.11 mmol) of !Y.,!Y.'-azobisisobutyronitrile were placed in a Pyrex Kjeldahl flask. After degassing the mixture, the flask was sealed under vacuum and the mixture was irradiated with a high pressure mercury lamp for 10 days. The mixture was poured into a mixture of methanol and water (4: 1, v/v), and the precipitated PVP was collected by filtration and dried in vacuo at 60°C. Polymerization of VP gave PVP in 70% conversion.PVP was saponified to give PVA as previously reported. 7 PV A was filtered, washed with methanol and dried in vacuo at 60°C. MeasurementThe 1 H NMR spectrum was recorded on a JEOL JNM EX270 at 60°C using dimethyl sulfoxide (DMSO)-d6 as a solvent. Tacticity of PV A was determined by evaluating triplet spectrum of hydroxyl proton in a tactic structure. 8 Resonances are ascribed to triad-syndiotactic (4.1lppm), heterotactic (4.35ppm), and isotactic (4.52 ppm) sequences. Tactic contents were calculated from relative ratios of integrated values of split peaks. Triadtacticity was converted to d...

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Stereospecificityand Dynamic Viscoelasticityof Polyvinyl Alcohol

Cited by 12 publications

References 0 publications

Highly Isotactic Poly(vinyl alcohol) Derived from tert-Butyl Vinyl Ether V. Viscoelastic Behavior of Highly Isotactic Poly(vinyl alcohol) Films

Highly Isotactic Poly(vinyl alcohol) Derived from tert-Butyl Vinyl Ether V. Viscoelastic Behavior of Highly Isotactic Poly(vinyl alcohol) Films

On the viscoelastic properties of poly(vinyl alcohol) and chemically crosslinked poly(vinyl alcohol)

Poly(vinyl alcohol) with High Diad-Syndiotacticity and High Melting Point

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