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

Abstract

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...

Acrylamide modified poly(vinyl alcohol): crystalline and enhanced water solubility

“…The change in tacticity of PVA due to AAm modication is of special interest by the reason that PVA with higher tacticity, which has higher ability to form intermolecular hydrogen bond and crystals, leads to poor water solubility and eventually insolubility of PVA in hot water. 27,28 Though introducing AAm units into PVA chain to decrease the steric regularity of PVA chain, decreases of tacticity of AAm modied PVA samples were expected. To understand the change of tacticity due to AAm modication of PVA, isotactic and syndiotactic contents were determined in respective FT-IR scan using the following formulas: 29,30 Isotacticity ¼ À 78…”

“…Meanwhile, the tacticity conguration favours interchain hydrogen bonding, leading to high crystalline and consequently to poor water solubility. 28 Triggered by these researches, we carried out the investigation of the inuence of AAm units on tacticity and crystallinity of PVA, hoping that we can consequently enhance the water solubility of PVA. As previously discussed, tacticity and crystallinity have been successfully controlled by introducing AAm units, hence, the effects of the AAm units on water solubility (D%) of PVA is of particular interest in this section.…”

Synthesis of polyvinyl alcohol stereoblock copolymer via the combination of living cationic polymerization and RAFT/MADIX polymerization using xanthate with vinyl ether moiety

“…Typically, PVA cannot be synthesized directly from vinyl alcohol monomer, but it is synthesized by hydrolysis of poly(VAc) prepared from radical polymerization. On the other hand, PVA also can be obtained by hydrolysis of poly(TBVE) prepared by living cationic polymerization [36,37]. The combined block copolymer can be obtained by the combination of living cationic polymerization and RAFT/MADIX polymerization, and the stereoregularity of the polymer is essentially controlled as shown in Scheme 1.…”