Vinyl homopolymers, copolymers

The nmr spectmm of PVAc iu carbon tetrachloride solution at 110°C shows absorptions at 4.86 5 (pentad) of the methine proton 1.78 5 (triad) of the methylene group and 1.98 5, 1.96 5, and 1.94 5, which are the resonances of the acetate methyls iu isotactic, heterotactic, and syndiotactic triads, respectively. Poly(vinyl acetate) produced by normal free-radical polymerization is completely atactic and noncrystalline. The nmr spectra of ethylene vinyl acetate copolymers have also been obtained (33). The ir spectra of the copolymers of vinyl acetate differ from that of the homopolymer depending on the identity of the comonomers and their proportion. 

Economic Aspects. Prices for PVAc polymers depend on the form of the polymer, ie, whether it is resin or emulsion, homopolymer or copolymer, as well as on the specific product. As of 1994, emulsion prices were 0.57— 0.86/wet kg of resin. Prices of VAE copolymer emulsions tend to be higher than those of the homopolymer priced at 0.97— 1.43/wet kg. Vinyl acryUc copolymers Hsted for 0.66— 0.88/wet kg of 55% soHds emulsion (138). Specialty copolymers generally have a premium price. These price ranges are for large shipments. 

Random copolymers of vinyl chloride and other monomers are important commercially. Most of these materials are produced by suspension or emulsion polymerization using free-radical initiators. Important producers for vinyl chloride—vinyUdene chloride copolymers include Borden, Inc. and Dow. These copolymers are used in specialized coatings appHcations because of their enhanced solubiUty and as extender resins in plastisols where rapid fusion is required (72). Another important class of materials are the vinyl chloride—vinyl acetate copolymers. Principal producers include Borden Chemicals Plastics, B. F. Goodrich Chemical, and Union Carbide. The copolymerization of vinyl chloride with vinyl acetate yields a material with improved processabihty compared with vinyl chloride homopolymer. However, the physical and chemical properties of the copolymers are different from those of the homopolymer PVC. Generally, as the vinyl acetate content increases, the resin solubiUty in ketone and ester solvents and its susceptibiUty to chemical attack increase, the resin viscosity and heat distortion temperature decrease, and the tensile strength and flexibiUty increase slightly. 

Commercial interest in poly(vinyl chloride) was revealed in a number of patents independently filed in 1928 by the Carbide and Carbon Chemical Corporaration, Du Pont and IG Farben. In each case the patents dealt with vinyl chloride-vinyl acetate copolymers. This was because the homopolymer could only be processed in the melt state at temperatures where high decomposition rates occurred. In comparison the copolymers, which could be processed at much lower temperatures, were less affected by processing operations. 

Vinyl chloride-vinyl acetate copolymers have lower softening points than the homopolymers and compounds and may be processed at lower temperatures than... 

Over 80% of the market is accounted for by suspension homopolymer, 13% by emulsion and paste-forming homopolymer, and the rest is mainly bulk homopolymer and vinyl chloride-vinyl acetate copolymer. In Western Europe about two-thirds of consumption is in the field of unplasticised PVC. 

PVA Formation Reaction. Poly(vinyl alcohol) is itself a modified polymer being made by the alcoholysis of poly(vinyl acetate) under acid or base catalysis as shown in Equation 1 (6.7). This polymer cannot be made by a direct polymerization because the vinyl alcohol monomer only exists in the tautomeric form of acetaldehyde. This saponification reaction can also be run on vinyl acetate copolymers and this affords a means of making vinyl alcohol copolymers. The homopolymer is water soluble and softens with decomposition at about 200°C while the properties of the copolymers would vary widely. Poly(vinyl alcohol) has been widely utilized in polymer modification because ... 

When measuring vinyl polymer tactlclty, one prefers the longest complete n-ad distribution available as well as the translated simplest comonomer distribution, possibly m versus r. An alternative exists to the m versus r distribution In the form of number average or mean sequence lengths. If any vinyl homopolymer Is viewed conceptually as a copolymer of meso and racemic dyads, mean sequence lengths can be determined for continuous runs of both meso and racemic configurations (32), that Is,... 

In addition to viewing a vinyl homopolymer conceptually as a copolymer of meso and racemic dyads, one may also consider the mean sequence length of "like" configurations (M). In this Instance, the polymer chain Is seen as a succession of different lengths of co-orlented configurations from one to "n", the longest sequence of like configurations, that Is,... 

Most naturally occurring polymers are largely homopolymers, but proteins and nucleic acids are copolymers composed of a number of different mers. While many synthetic polymers are homopolymers, the most widely used synthetic rubber, SBR, is a copolymer of styrene (S) and butadiene (B), with the R representing rubber. There are many other important copolymers. Here we will restrict ourselves to vinyl-derived copolymers. 

Cyclopolymerization of bifunctional monomers is an effective method of chirality induction. Optically active vinyl homopolymers and copolymers have been synthesized by using optically active distyrenic monomers (41) based on a readily removable chiral template moiety. Free-radical copolymerization of 41a with styrene and removal of the chiral template moiety from the obtained copolymer led to polystyrene, which showed optical activity ([Oc]365 -0.5-3.5°) (Scheme 11.6) [84], The optical activity was explained in terms of chiral (S,S)-diad units generated in the polymer chain through cyclopolymerization of 41a [85], Several different bifunctional monomers have been synthesized and used for this type of copolymerization [86-90]. 

The butadiene and butadiene-acrylic monomer systems polymerize when irradiated on PVC or vinyl chloride copolymer latex. The structure of the polymer obtained may be grafted if it can be proved that the copolymer properties are different from the blend properties. To elucidate the structure we studied a copolymer obtained by polymerizing butadiene-acrylonitrile on a PVC homopolymer lattice. Owing to practical reasons and to exclude the secondary effect of catalytic residues we used y radiation. However, we shall observe in a particular case the properties of peroxide-initiated graft copolymer. 

Ribbed helices (costal helices) are important in organic chemistry because linear polymers contain side chains as well as backbones. We may, then, discern not only the catenal helix of the backbone, but the intercostal helix formed by all of the ribs and the infracostal helicesof the individual side chains. The intercostal helix may be iterative (as in an isotactic head-to-tail vinyl polymer or homogeneous poly-a-amino acid) or non-iterative (as in a random copolymer, an atactic polymer or typical protein). The intracostal helices can best be analyzed as short-chain crooked lines, as in Section III. Important as costal helicity is, it is secondary to catenal helicity and we therefore limit our attention to the primary helicity, that of long chains. Indeed, we limit our attention to catenal helices having chain motifs of two atoms and two bonds as found in head-to-tail vinyl homopolymers ... 

Figure 13 Photoresponsive chiral vinyl homopolymers and copolymers.

The results obtained after having examined several latices are summarized in Figure 14. The values found for A do not differ significantly for the homopolymer ana the VeoVa copolymer. For the vinyl acetate copolymer the area is distinctly increased as a result of increased interface polarity (39). 

To illustrate this point consider the production of lacquers for PVC films and sheeting. Such lacquers contain a PVC homopolymer or low-acetate vinyl chloride-vinyl acetate copolymer, poly(methyl methacrylate), a plasticizer and perhaps some stabilizers, dulling agents (such as silica), pigments, and so on. Methyl ethyl ketone (MEK) is the solvent of choice because it gives the best balance of low toxicity, volatility, and low cost. Any other solvent is effectively... 

Blends. The type I reaction produces free radicals which, in the presence of oxygen, initiates photooxidation which also results in a decrease in the polymer molecular wei t. An indication of the relative importance of the type I reaction in these systems can be estimated from the amount of chain scission induced in a blend of the copolymers with homopolymer polystyrene. For these experiments, one part of 5% vinyl ketone copolymer was blended with four parts of styrene homopolymer to retain an overall ketone monomer concentration of 1%. 

Thermal stability of vinyl chloride copolymers is usually better than that of the homopolymer [27]. Some pyrolysis studies on PVC copolymers are reported in literature [28-32], A summary of several thermal stability studies of poiy(vinyl chloride) copolymers are indicated in Table 6.3.3. 

Available forms 102 Fine particle size, water-resistant homopolymer emulsion. 202 Fine particle size, water-resistant copolymer emulsion. 203 Vinyl-acrylic copolymer emulsion. 204 Vinyl copolymer emulsion. 

Solubility Characteristics of Today s Vinyl Chloride Homopolymers, Copolymers, and Terpolymers... 

Figure 3 shows the solubility characteristics of the vinyl acetate copolymers in MEK note the improved solubility over the homopolymers of vinyl chloride. Because these copolymers are still significantly less soluble than the metal adhesion terpolymers, one manufacturer has produced a copolymer not based on vinyl acetate (see Figure 3, high solubility copolymers). This copolymer is described in more detail in Figure 13. Copolymers are also available based on vinyl chloride-trifluorochloro-ethylene and vinyl chloride-vinylidene chloride.

---