PVAC dispersions table

One can read letters through the porous PVA-PVAc film in benzene, but one cannot do so in cyclohexane nor in the case of the blank. This is supported by the fact that the refractive indices of benzene are close to that of PVA, but the refractive index of cyclohexane is far from that of PVA. When the porous film was dipped in a mixed solvent of benzene and cyclohexane (8.0 2.0 in weight), it became semi-transparent. To make this point clearer, the refractive index and the dispersive power of polymers and organic solvents were measured. The results are shown in Table 3, which shows that the refractive index of PVA is near that of benzene and that the dispersion power of aliphatic compounds is lower than that of aromatic compounds. 

The chromatograms of the several injected PVAc samples were corrected for axial dispersion (8-11) and number and weight average diameters were estimated. The resulting distributions and diameter averages showed that the latex samples from the batch runs were "almost monodispersed (8). This was further supported by the fact that estimated average diameters were very close to the "peak" average diameters (Table III). 

We have studied the dispersibility of several pure PVAc-styrene graft copolymers with one PS branch in various selective solvents mainly at room temperature5. The experiment was done with two kinds of dried samples one was recovered from a tetrahydrofuran solution by pouring it into water and the other from a benzene solution which was poured into n-hexane. Let us refer to the former sample as A and the latter sample as B. Due to the difference in solubility of each polymer sequence in those solvents, sample A is supposed to have approximately such a microstructure that PVAc chains are extended and PS chains collapsed, while sample B has the inverse structure. A similar tendency was also pointed out by Merrett12. The results are summarized in Table 2. 

Table 2. Dispersibility of PVAc-styrene graft copolymers in various solvents from dried samples at room temperature graft copolymer/solvent = 1/100 (w/v)...

The water dispersions of PVAc were prepared under nitrogen atmosphere using a semi-batch emulsion polymerization technique, in a four-neck kettle equipped with a mechanical stirrer, an inlet for feeding streams and a reflux condenser. The reagent amounts, the reaction conditions and the yields for each preparation are reported in Table 5. Solids content, pH and viscosity were measured and reported in Table 5. 

Mechanical properties, water and solvent resistance of the polymer films obtained from the water dispersions and tensile strengths of the adhesive joints were evaluated (entries 14-18, Table 6). These results were compared with those obtained for a formulation containing the PVAc homopolymer (entry 19, Table 6) and for a PVAc homopolymer/linseed oil blend (entry 20, Table 6). 

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