Tacticity of PVA

In short, the PVA/P(3HB) blend is compatible in the amorphous phase and the compatibility between them depends on the tacticity of PVA. 

The PVA in Fig. 6a used in this experiment was purchased from Nacalai Tesque, Inc. and is atactic with a degree of polymerization of 2.0 x 10 and a degree of saponification of 99-100 mol%. As the polymer backbone of PVA is formed by the polymerization of vinyl acetate (Fig. 6b) before saponification, the tacticity of PVA... 

Fig. 21 a Tacticity of PVA, b concentration profiles on four polymer phase and c change range of the amount of syndiotactic structure (Reprinted from [17])... 

Fig. 19.16. CRAMPS spectra of PVA films with different tacticities measured at room temperature (Ref. [53]).

PVA samples with different tacticities, such as isotactic (iso-), atactic (at-) and syndiotactic (syn-) ones were used. The degree of polymerization, and the fractions of mm, mr and rr triads, are shown in Table 20.2, where m and r indicate the meso and racemic dyads, respectively. The CP/MAS NMR spectra for the three kinds of PVA gels with different tacticity (9% of polymer concentration) are shown in Fig. 20.7. As described in Section 20.4.1, the CH peaks are composed of both the three sharp peaks corresponding to the triad configurations (mm, mr and rr) and the three broad peaks (I, II and III at about 77, 71 and 65 ppm, respectively). 

In the CP/MAS NMR spectrum for the iso-PVA gel (Fig. 20.7(A)), peak I, together with three sharp peaks for the triad configurations, is obviously observed while peaks II and III are not so obvious. However, in the spectra for the at-PVA and syn-PVA gels shown in Figs. 20.7(B) and 20.7(C), respectively, peaks II and III are observed together with peak I. The signal areas for each of the configurations may reflect the fractions of the triad tacticity of the main chain of the PVA gel. 

Study of the effect of PVA tacticity on the cis and tmns configuration in poly(vinyl formal) close cousin of PVB DMSO as solvent TMS standard... 

Similar to caustic alkali, mineral acid is also effective in catalyzing the reaction. The use of acid, however, does not have any advantage and, often, partly water-insoluble PVA is obtained. Polyvinyl esters of higher fatty acids and aromatic esters were studied, but, from the viewpoint of fiber-making, no advantage in using esters other than acetate has been reported. The tacticity of polyvinyl esters and ethers is discussed in Section 4.3.1. 

By contrast, other polymers such as polyolefins and PVA form immiscible blends with HKL. In fact, phase separation is observed in fibers produced from the thermal spinning of HKL and PP. The fiber spinning properties of several PP samples having various melt viscosities and tacticities were examined. Most of the HKL/PP blends show poor or bad fiber spinnability. However, excellent fiber spinning was achieved with PP samples having a thermal viscosity comparable to the HKL. 

Different hydrogen-bonded states of OH groups in poly(vinyl alcohol) (PVA) films with different tacticities have been characterized by H combined rotation and multiple pulse spectroscopy (CRAMPS),solid-state NMR and 2D (2D) H- C HETCOR analyses. 

Fig. 20.2 shows the NMR spectra for the PVA in (A) the solution (B-D) gel and (E) solid states as measured by solution and solid-state NMR methods [16]. The NMR spectrum for the PVA aqueous solution obtained by the solution C NMR method (Fig. 20.2(A)) shows each of the signals for the CH and CH2 carbons split into multiple peaks due to its stereochemical configuration. The triply split peaks for the CH carbon are assigned to the mm, mr and rr triads from high frequency [17-19] and, furthermore, each of the triad peaks splits into pentad peaks. The split peaks for the CH2 carbon come from tetrad tacticity. In the solution NMR spectrum for the PVA gel shown in Fig. 20.2(B), the signal for the CH carbon splits into three peaks due to triad tacticity. The signals for the CH and CH2 carbon become broader as compared with those for the PVA solution. This is caused by the...

The NMR measurement was made on PVA solutions at low temperature in order to clarify the mechanism of gel formation by freeze-thaw cycles [16]. The C CP/MAS NMR spectrum for the PVA solution was measured at -50°C by going from room temperature to -50°C (Fig. 20.6). The signals for the CH group shows that instead of the three peaks, which arise from the splitting by tacticity, peaks I, II and III appear. The result shows that in the PVA solution at -50°C, some hydroxyl groups form hydrogen bonds as in the PVA gel and so the crosslinked structure is formed in the PVA solution. This means that the gel formation is induced in going from room temperature to -50°C. 

Kobayashi et al. [21] are concerned with the effect of the tacticity on the amount of the crosslinked region for the PVA gel. In this study, the three... 

Table 20.2. The characterization of three PVA samples with different tacticities...

This polymer is included here to illustrate the effect of parent PVA tacticity on the ring conformation of the acetal. ... 

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