Long Branching in Poly(vinyl acetate) and Poly(vinyl alcohol). V. Determination of the Long-Chain Branching in Poly(vinyl alcohol).

Abstract

ABSTRACT:Long branching in poly(vinyl alcohol) (PV A) was quantitatively determined from measurements of the intrinsic viscosity and gel-permeation chromatography of derived poly(vinyl acetate) (PVAc) according to Kurata's method. The average number of branch points per unit molecular weight, .Aa, was observed to lie in the range of 10-6-10-5 for PV A obtained from PV Ac polymerized at 60°C in bulk. The tendency for the values of .Aa to increase with the increase in the conversion of polymerization of the parent polymer was found to be in close agreement with that expected from the kinetic equation proposed in our previous paper.KEY WORDS Long Branching I Poly(vinyl alcohol) 1 Poly(vinyl acetate) I Gel-Permeation Chromatography I Intrinsic Viscosity I Branching Parameter 1In previous papers 1 ' 2 the formation of longchain branches in poly(vinyl alcohol) (PYA) was kinetically analyzed. It was clarified that the long branches in PV A are exclusively formed by the chain transfer to polymer and that the amount of the branch increases as the conversion increases and as the polymerization temperature rises. As a result, the amount of long branches in PV A derived from bulk polymerization of vinly acetate at 60°C is predictable from kinetic equations. However, the quantitative determination of long-chain branches for a given PV A specimen has not been reported so far. A method has been proposed for estimating the degree of branching from the elution curve of GPC and the intrinsic viscosity of unfractionated samples. Drott, et al., 3 ' 4 determined long branches in polyethylene using this method. Kurata, et al., 5 -7 also reported the same method independently, and discussed the limit of reliability by showing an example of the application to branched polystyrene. In the present paper, the amount of long-chain branches in PV A was determined by means of Kurata's method, 5-7 and the results were compared with those expected * Leave of absence from Department of Polymer Science, Kyungpook National University, Korea. 196 from the kinetic scheme proposed in our previous work. 2 EXPERIMENTAL MaterialsVinyl acetate was purified according to the previous paper. 2 Tri-n-butylborane was distilled under reduced pressure (bp, 90-91 oq9 mmHg), and 2,2' -azobisisobutyronitrile (AIBN) was recrystallized from methanol. Benzene was dried over CaC12 and distilled through a Widmer column twice. Methanol and tetrahydrofuran were distilled through a Widmer column. Polymerization of Vinyl AcetatePolymerization of vinyl acetate at ooc was carried out in the following way. To 21.9 g of vinyl acetate and 8.1 g of methanol contained in a 50-ml Shlenk tube kept at ooc were added 0.23 ml of tri-n-butylborane (0.5 mol% to monomer) and 1 ml of oxygen as initiators under an atmosphere of nitrogen. The polymerization was quenched at conversion lower than 10% by the addition of 1 ml of 5-% methanolic solution of hydroquinone. The contents were concentrated and poured into n-hexane to precipitate poly(vinyl acetate) (PVAc). The precipitated pol...