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Lyoo, Won-Seok,Ha, Wan-Shik The Korean Fiber Society 2001 Fibers and polymers Vol.2 No.2
Vinyl acetate was polymerized in ultraviolet-ray initiated bulk system at low temperatures using 2,2-azobis(2,4-dimethylvaleronitrile) (ADMVN) or 2,2-azobis(isobutyronitrile) (AIBN) as the photoinitiator, respectively. High molecular weight (HMW) poly(vinyl alcohol) (PVA) having number-average degree of polymerization ($P_n$) of 3,900-7,800 and syndiotactic diad (S-diad) content of 52.5-54.0% could be prepared by complete saponification of synthesized linear poly(vinyl acetate) (PVAc) having $P_n$ 5,900-9,400 obtained at conversion of below 30%. $P_n$ of PVA using ADMVN was larger than that of PVA using AIBN. On the other hand, conversion of the former was smaller than that of the latter, and it was found that the initiation rate of the ADMVN was lower than that of AIBN. This could be explained by a fact that the rate of photolysis of AIBN is faster than that of ADMVN due to the higher quantum yield or dissociation rate constant of AIBN than that of ADMVN. The $P_n$, syndiotacticity, and whiteness of PVA from PVAc polymerized at lower temperatures were superior to those of PVA from PVAc polymerized at higher temperatures.
Room Temperature Polymerization of N-vinylcarbazole in Tetrahydrofuran
Lyoo, Won-Seok,Kwak, Jin-Woo,Noh, Seok-Kyun,Kim, Dae-Heum,Lee, Jinwon,Kim, Nakjoong,Park, Ki-Hong,Lee, Chul-Joo The Korean Fiber Society 2004 Fibers and polymers Vol.5 No.2
N-Vinylcarbazole (VCZ) was solution-polymerized in tetrahydrofuran (THF) at 25, 35, and $45^{\circ}C$ using a room temperature initiator, 2,2'-azobis(2,4-dimethylvaleronitrile) (ADMVN); the effects of amount of solvent, polymerization temperature, and initiator concentration were investigated. On the whole, the experimental results corresponded to predicted ones. Room polymerization temperature using ADMVN proved to be successful in obtaining poly(N-vinylcarbazole) (PVCZ) of high molecular weight with small temperature rise during polymerization, nevertheless of free radical polymerization by azoinitiator. The polymerization rate of VCZ in THF was proportional to the 0.47 power of ADMVN concentration. The molecular weight was higher and the molecular weight distribution was narrower with PVCZ polymerized at lower temperatures. For PVCZ prepared in THF at $25^{\circ}C$ using ADMVN concentration of 0.00005 mol/mol of VCZ, weight-average molecular weight of 221,000 was obtained, with polydispersity index of 2.05, and degree of lightness converged to about 99%.
Lyoo, Won Seok,Yeum, Jeong Hyun,Park, Joo Min,Kwak, Jin Woo,Kim, Joon Ho,Kim, Sam Soo,Ji, Byung Chul,Noh, Seok Kyun Wiley Subscription Services, Inc., A Wiley Company 2005 Journal of applied polymer science Vol.96 No.4
<P>To precisely identify the effect of molecular weight of atactic poly(vinyl alcohol) (a-PVA) on the durability and polarizing efficiency (PE) of a-PVA/dye polarizing film, we prepared two (a-PVA)s with similar syndiotactic diad contents of 54.0%, degrees of saponification of 99.9%, and with different number-average degrees of polymerization [(P<SUB>n</SUB>)s] of 1700 and 4000, respectively. Through a series of experiments, it was found that molecular weight of a-PVA had a significant influence on the durability of a-PVA/dye film in heat and humidity conditions (relative humidity of 80% and temperature of 90°C). That is, both desorption of dye in a-PVA/dye film and transmittance of film decreased with increasing molecular weight of PVA. The change of PE (durability) of a-PVA/dye film in heat and humidity conditions was limited to about below 5%. The change of PE of PVA/dye film having P<SUB>n</SUB> of 4000 especially was limited to 1%, whereas that of a-PVA/iodine film with P<SUB>n</SUB> of 4000, was almost 80% under the same condition. Also, transmittance of the drawn a-PVA/dye film was far higher than that of the undrawn one. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 967–974, 2005</P>
Lyoo, Won Seok,Yeum, Jeong Hyun,Kwon, Oh Wook,Shin, Dong Soo,Han, Sung Soo,Kim, Byoung Chul,Jeon, Han Yong,Noh, Seok Kyun Wiley Subscription Services, Inc., A Wiley Company 2006 Journal of applied polymer science Vol.102 No.4
<P>To identify the effect of blend ratios of syndiotacticity-rich poly(vinyl alcohol) (s-PVA)/atactic PVA (a-PVA) having similar number-average degrees of polymerization (P<SUB>n</SUB>)s of 4000 and degrees of saponification (DS)s of 99.9% on the rheological properties of s-PVA/a-PVA/water solutions, water-soluble s-PVA and a-PVA with different syndiotactic diad contents of 58.5 and 54.0%, respectively, were prepared by bulk copolymerization of vinyl pivalate and vinyl acetate (VAc) and solution polymerization of VAc, followed by saponifying the corresponding copoly(vinyl pivalate/vinyl acetate) and poly(vinyl acetate). The blend ratios played a significant role in rheological behavior. Over the frequency range of 10<SUP>−1</SUP>–10<SUP>2</SUP> rad/s, s-PVA/a-PVA blend solutions with larger s-PVA content show more shear thinning at similar (P<SUB>n</SUB>)s and (DS)s of polymer, suggesting that PVA molecules are more readily oriented as s-PVA content increases. Yield stress is higher for s-PVA/a-PVA blend solutions with larger s-PVA content at similar (P<SUB>n</SUB>)s and (DS)s of polymer. This indicates that more domains with internal order are produced at larger s-PVA content in s-PVA/a-PVA blend solutions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3934–3939, 2006</P>
Lyoo, Won-Seok,Noh, Seok-Kyun,Yeum, Jeong-Hyun,Kang, Gu-Chan,Ghim, Han-Do,Lee, Jinwon,Ji, Byung-Chul The Korean Fiber Society 2004 Fibers and polymers Vol.5 No.1
To obtain high molecular weight (HMW) poly(methyl methacrylate) (PMMA) with high conversion, methyl methacrylate (MMA) was polymerized in suspension using a room temperature initiator, 2,2'-azobis(2,4-dimethylvaleronitrile) (ADMVN), and the effects of polymerization conditions on the polymerization behavior of MMA and the molecular parameters of PMMA were investigated. On the whole, the experimental results well corresponded to the theoretically predicted tendencies. These effects could be explained by a kinetic order of ADMVN concentration calculated by an initial rate method and an activation energy difference of polymerization obtained from the Arrhenius plot. Suspension polymerization at 25℃ by adopting ADMVN proved to be successful in obtaining PMMA of HMW (number-average degree of polymerization (P/sub n/): 30,900-36,100) and of high yield (ultimate conversion of MMA into PMMA: 83-93 %) with diminishing heat generated during polymerization. The P/sub n/ and lightness were higher and polydispersity index was lower with PMMA polymerized at lower temperatures.