SynopsisMolecular weight distributions, long chain branching frequency, and solution viscosities of samples of commercial poly(viny1 alcohol) (PVA) are reported. The PVA was fully reacetylated to poly(viny1 acetate) (PVAc) for characterizations by size exclusion chromatography using a low angle light scattering detector. The Mark-Houwink constants for PVAc in toluene were determined to be K = 0.106 cm3 g-' and a = 0.59, at 25°C. Long chain branching frequency in the commercial PVAs studied was small and was little affected by polymer molecular weight. Some 95% or more of the branches in these species were short. Aqueous solutions at 10% (w/v) of PVA were Newtonian. The polymers examined differed in chemical composition, molecular weight distributions, and mean block lengths of vinyl acetate residues. Variations in a single characteristic, like a solution or intrinsic viscosity, cannot be used to deduce structural differences between PVAs.
INTRODUCTIONThe principal characteristics that determine the physical and technological properties of polymers are chemical composition, molecular weight distribution, and branching character. Poly(viny1 acetate) (PVAc) and its derivative poly(viny1 alcohol) (PVA) are not exceptions. Fine differences in PVA microstructure reflect structural variations in the precursor PVAc and in the reaction system used to convert the PVAc to PVA. These differences are often not reflected in the results of commercial quality control tests, but they can be very important in the performance of PVA as a protective colloid in emulsion and suspension polymerizations..We have earlier' reported on the characterization of the molecular architecture of commercial PVAs. Polymer samples were analyzed by 13C nuclear magnetic resonance spectroscopy and by differential scanning calorimetry to measure tacticity, chemical composition, branch frequency, and mean run lengths of vinyl acetate and alcohol units.Further characterization procedures are reported and discussed in this article. Parameters measured here include molecular weight distribution, long chain branching, intrinsic viscosities, and aqueous solution viscosities and unsaturation in the polymer backbone.Mark-Houwink constants for linear PVAc in toluene are also reported. This report and its predecessor' provide a critical survey of procedures that are thought to give reliable and fairly comprehensive characterizations of the chemical structure of commercial PVAs.
EXPERIMENTALSix commercial partially hydrolyzed PVA samples, referred to as A to F inclusive, were used in this study. These materials have been described earlier. '
Acetylation ProcedureThe following reacetylation procedure was used for all of the six partially hydrolyzed PVA samples under investigation. Five grams of the polymer was placed in a round bottom flask. The flask was purged with nitrogen gas for about 10 mins. Fifty milliliters of a 2:l pyridine/acetic anhydride solution were added to the reaction vessel, and the contents were heated on a steam bath at 93-94"C, with stirr...
