Vinyl acetate segments

The elastic repulsion hypothesis has arisen from the studies using partially hydrolysed poly(vinyl alcohol) as stabilizer. In this instance, no interactional groups are apparently necessary on the surface of the colloidal particles, presumably because the blocks of poly(vinyl acetate) segments, which are nominally insoluble in water, anchor the poly(vinyl alcohol) stabilizing moieties to the surface. Of course, poly(vinyl alcohol) is a decidedly atypical... 

Stabilizer, not just to the poly(vinyl alcohol) moieties. Yet it is these latter moieties which presumably impart stability. The presence of the nominally insoluble poly(vinyl acetate) segments would be expected to depress the observed value of the -temperature. The conclusion emerges that just because the observed UCFT is greater than the putative 0 -temperature of the copolymer, this does not necessarily imply that the true. -temperature of the homopolymeric poly(vinyl alcohol) moieties is exceeded. It follows that the existence of enhanced steric stabilization with partially hydrolysed poly(vinyl alcohol) has not yet been established unequivocally, although its occurrence does seem highly likely. Unfortunately, it is not possible to use the method of Comet and van Ballegooijen (1966) to determine the actual fl -temperature of fully hydrolysed poly(vinyl alcohol) because its crystallinity and insolubility renders the method both inoperative and invalid. 

The fraction of bound segments

was found to be ca 0-1 for the poly(vinyl alcohol) and zero (within experimental error) for the poly(oxyethylene) tails. The value of

0-l for poly(vinyl alcohol) is consistent with the assumption that most of the poly(vinyl acetate) segments, (present in the overall molecule at a mole fraction of ca 0-12) are in trains at the latex particle surface. 

When the vinyl acetate segments were hydrolyzed, a gel material was formed from the surfactant, which was expanded in volume by a factor of about 5. Upon drying, the gel turned into a hard rabber sealant material (Fig. 6.1.2(a)), which has a closed structure (Fig. 6.1.2(b)) and a surface that is very adherent to glass. 

A great many polymers appear to form films having a flat molecular configuration. Thus various polyesters [7] gave extrapolated areas of about 2.5 m /mg corresponding to about the calculated 60-70 area per segment, or mono-layer Sickness of 3-5 A. A similar behavior was noted for poly(vinyl acetate)... 

Poly(vinyl alcohol) can be derived from the hydrolysis of a variety of poly(vinyl esters), such as poly(vinyl acetate), poly(vinyl formate), and poly(vinyl ben2oate), and of poly(vinyl ethers). However, all commercially produced poly(vinyl alcohol) is manufactured by the hydrolysis of poly(vinyl acetate). The manufacturing process can be viewed as one segment that deals with the polymeri2ation of vinyl acetate and another that handles the hydrolysis of poly(vinyl acetate) to poly(vinyl alcohol). 

Another important feature of some random copolymers is the abihty to achieve miscibility in either a homopolymer or a second random copolymer. This "copolymer effect" has been shown empirically for quite some time, eg, PVC is miscible with random copolymers of ethylene and vinyl acetate (52). Such systems are effective because repulsions between the dissimilar segments in the copolymer are enough to overcome the repulsions between these segments and those of the second component in the mixture. In other words, in the above example, the ethylene units "hate" vinyl acetate units more than either of them "hate" PVC. Thus there is a net negative interaction energy and the two materials are miscible (53). 

In a previous paper (15) the segment density of PVA adsorbed on PS latex in water was presented and it was noted that H Cgans was at the extremity of the s.a.n.s. profile. Calculating <5 assuming a value of a of 0.5 nm gives 13 nm in contrast to the experimental value of 18 nm. The discrepancy here is much smaller than in the case of PE0. This effect is difficult to interpret without further theoretical work but may be attributable to the fact that the PVA chain is less flexible than PEO and that the block structure (PVA is a random block copolymer of vinyl acetate. 12%, and vinyl alcohol) makes the formation of tails less likely. 

The EVA polymer emulsions contain crystalline segments resulting from ethylene linkages. In addition to ethylene and vinyl acetate, a carboxylic comonomer is used, such as acrylamide or versa tic acid vinyl ester. The polymers have crystalline melting point of 50-90°C. 

Instead, the distribution of vinyl acetate and ethylene in the copolymer is a major factor. A sufficient level of amorphous ethylene vinyl acetate polymer segments is needed in order to provide adhesion to a substrate. Further, a sufficient level of crystalline ethylene polymer segments is needed to provide the proper balance of heat seal characteristics and non-blocking. 

Although the manufacture and sale of adhesives is a worldwide enterprise, the adhesives business can be characterized as a fragmented industry. The 1987 Census of Manufacturers obtained reports from 712 companies in the United States, each of which considers itself to be in the adhesives or sealants business only 275 of these companies had more than 20 employees. Phenolics, poly(vinyl acetate) adhesives, rubber cements, and hot-mclt adhesives arc the leading products in terms of monetary value. These products are used primarily in llie wood, paper, and packaging industries. The annual growth rate of the adhesives market is 2.3%, and individual segments of the market are expected to grow faster than this rate. 

In the absence of solvent, the influence of the surface on the segmental mobility can be deduced by measuring the temperature dependence of the spectral line shape in the presence and absence of the surface. The temperature dependence of bulk poly(vinyl acetate) is shown in Figure 3, and of bulk polystyrene... 

Internal plasticizers are synthesized by copolymerization of suitable monomers. Polymeric non-extractable plasticizers, mostly copolymers having substantially lower glass transition temperatures due to the presence of plasticizing ( soft ) segments such as poly(ethylene-co-vinyl acetate) with approximately 45 % vinylacetate content, ethylene-vinyl acetate-carbon monooxide terpolymer, or chlorinated PE, are available for rather special applications in medicinal articles (Meier, 1990). In this case, the performance of the internally plasticized polymers is the principal advantage. However, copolymerization may account for worse mechanical properties. A combination with external plasticizers may provide an optimal balance of properties. For example, food contact products made from poly(vinylidene chloride) should have at most a citrate or sebacate ester based plasticizers content of 5 % and at most 10 % polymeric plasticizers. 

As shown in part A of Table IV, fg increases slightly with PTMG MW, while decreases. A similar trend was observed with low molecular weight polymers of poly(vinyl acetate) and polystyrene (6). It is reasoned that the molecular weight dependence of fg arises because longer soft segment length requires more volume to accommodate the increased number of conformations available to such a chain. 

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