Polyvinyl acetate branching

The method outlined above for characterizing branched polymers will hereafter be referred to as the molecular weight and branching distribution (MWBD) method. In the following sections, its application to the long chain branching in polyvinyl acetate and high pressure low density polyethylene will be demonstrated. 

In order to estimate the branching factor e for polyvinyl acetate we have analyzed the SEC data obtained on sample PVAc-E4 using the MWBD method with various e values. This sample was synthesized under kinetically controlled conditions (isothermal, T = 60°C, [AIBN] = 10"5 g-mole/1, conversion level of 48.5 percent). The SEC measurements were made at 25°C in tetrahydro-furan. The Mark-Houwink coefficients used for linear polyvinyl acetate are those suggested by Graessley (21), namely K = 5.1 x 10"5 dl/gm and a = 0.791. The whole polymer M, Mj, and B j values obtained are listed in Table II. 

The MWBD method also requires an independent measure of the branching structure factor e. For our analysfs of polyvinyl acetate, it was obtained by comparing M and Bf values calculated from SEC data, analyz d using the MWBD method and various epsilons, and the Mfj and Bj values predicted by Graessley s (21) kinetic model. An epsilon value of 1.0 was found to fit best. 

To illustrate the utility of the MWBD method, a series of commercial polyvinyl acetates and low density polyethylenes are analyzed. Either kinetic models or 13c nuclear magnetic resonance results are used to estimate the branching structural parameter. 

This is just the first example of how the ADMET reaction can be used to model branching behavior and precisely control the structure in olefin-based polymer backbones. Other polymers under study include polyalcohols, polyvinyl acetates, and ethylene-styrene copolymers. The ultimate goal of this research is to be able to define, or even predict, crystallization limits and behavior for many polymers, some of which have not yet been prepared in a crystallized form. 

Polyvinyl Acetate. Two polyvinyl acetate samples (PVAc 1 and PVAc 3) also were analyzed. Both samples have been shown to be branched by Hamlelec (50) by a SEC/LALLS study. Table 8 shows the results obtained from SEC/Vlscometry along with some of the available data. It is seen that the intrinsic viscosity values for... 

Figure 17. Plot of log [ril vs. log M for a Branched Polyvinyl Acetate (PVAc) (Aldrich 18250-8 Lot 3).

Light Scattering Characterization of Branched Polyvinyl Acetate... 

Branching effects of polyvinyl acetate (PVAc) were... 

Long,V.C. Thesis The effect of branching on the dilute solution and bulk properties of polyvinyl acetate. University of Michigan 1958. 

Fig. 25. Guinier plot of the soft sphere model. The numbers denote the number of branching shells the filled and open circles are lightscattering results from polyvinyl acetate (PVAc) microgels in methanol at 20 °C at A0 = 546 nm and 436 nm, respectively. The dot-dash line corresponds to the Rayleigh-Gans behavior of hard spheres, i.e. no Mie scattering93)...

The synthesis of branched polyvinyl acetate was based on the same method carboxyl-ended material was transformed to acid chloride with thionyl chloride and condensed with a linear copolymer of vinyl alcohol and vinyl acetate (155, 156). 

The synthesis of branched chain polyvinyl acetates. Makromol. 

Chain Free radical Polybutadiene Polyethylene (branched) Polyisoprene Polymethylmethacrylate Polyvinyl acetate Polystyrene... 

The formation of the first branch is shown, but it is clear that the trunk may have more than one branch it is also likely that the primary branch has second, third, etc., branches. As early as 1940, Blaikie and Crozier reported that PVA obtained from polyvinyl acetate has a lower degree of polymerization than the parent acetate [17]. Further investigation was carried out by McDowell and Kenyon [18] and Staudinger and Warth [19]. 

Osugi [20], Inoue, and Sakurada [21], and Wheeler et al. [22] pointed out that the drop in the DP of polyvinyl acetate by saponification is due to the cutting of branches at the acetyl groups of polyvinyl acetate. The evidence for this mechanism is found in Figure 4.3, where an example of the dependence of the DP of polyvinyl acetate and alcohol on the conversion is shown. 

As for the position of hydrogen abstraction, chain transfer to dead polymers may occur, in principle, not only at carbon atom (1) but also at (2) and (3) [22]. It is, however, necessary to remember that branches at carbon atoms (2) and (3) cannot be cut by saponification to convert polyvinyl acetate to PVA. 

A change in the DP of polyvinyl acetate and alcohol with the progress of saponification shows no indication of the presence of branches that cannot be cut in the saponification. It may be that the transfer to carbon at (2) and (3) occurs far less frequently than it does at carbon atom (1). 

The degree of polymerization of polyvinyl acetate drops more or less by the hydrolysis or methanolysis, and PVA of a lower DP is obtained. This is because branches of polyvinyl acetate formed by the chain transfer to acetyl groups of dead polymers are cut at the point of hydrolysis or methanolysis simultaneously with deacetylation, as described in the discussion of chain transfer to dead polymer. 

As already mentioned, multibranched polyvinyl acetate is produced by the chain transfer to acetyl groups of dead polyvinyl aeetate, but all these branches are cut off by the deacetylation. If chain transfer occurs at a carbon atom on the main chain, it is certain that the branch connected directly to the main chain carbon atom will not be broken to result in the long branches. There are some papers that insist on the chain transfer to the main chain carbon atoms however, there is no experimental evidence to show the existence of a main chain branch [58-60]. The main chain transfer probably occurs, but its rate is much lower than the rate of transfer to the acetyl group. 

The formation of a short branch in polyvinyl acetate, as in the case of high-pressure polymerization of ethylene, by the backbiting intramolecular radical transfer is also operative [61] ... 

With loose structures of linear molecules the exponent for instance to cellulose nitrate in acetone, precipitated by water, to Polyvinyl acetate in toluene, precipitated by a methanol-water mixture-, and to the methyles-ters of polymethacrylic acid in benzene, precipitated by cyclohexane With compact spherical particles we must expect n-values in the neighbourhood of 2/3, since in this case only the outer surface of the particles is subject to the action of the medium. Examples can be found in some proteins. Finally, if the long-chain molecule shows a pronounced ramification or if the randomly kinked structure is comparatively close-packed, n may assume values between 0.7 and 1. This is shown for instance, by branched polystryrene h by acetyl-starch and by glycogene An accurate check on the value of n, however, is usually impossible. Husemann s experiments with glycogene, for instance, can be equally well described by n = 2/3 as by n — J (Fig. 5). This is due to the fact that the value of P in this method is not unlimited. In practice the upper limit of the molecular weight lies in the neighbourhood of 5.10, the lower limit lies in the further to be noted that the constant b in equation... 

EVA copolymers have low crystallinity because the acetate branches interfere with crystallization. These resins are characterized by increased flexibility and resilience over a wide temperature range and by improved clarity. EVA copolymers are widely used as a nonplasticizer alternative for polyvinyl chloride (PVC) applications. These copolymers also have higher moduli than standard elastomers and are preferable in that they are more easily processed without the need to vulcanize. 

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