Vinyl acetate structure

PVC materials are often defined to contain 50% or more vinyl chloride units by weight. PVC is generally a mixture of a number of additives and often other units, such as ethylene, propylene, vinylidene chloride, and vinyl acetate. Structurally similar products, but with differing properties, are made from the chlorination of PE but almost all PVC is made from the polymerization of vinyl chloride. Typical homopolymers are about 400-1000 units long. 

A further class of ethylene-vinyl acetate copolymer exists where the vinyl acetate content is of the order of 3 mole %. These materials are best considered as a modification of low-density polyethylene, where the low-cost comonomer introduces additional irregularity into the structure, reducing crystallinity and increasing flexibility, softness and, in the case of film, surface gloss. They have extensive clearance as non-toxic materials. 

As already mentioned in previous sections ethylene may also be copolymerised with several non-hydrocarbon polymers. Some of these copolymers are elastomeric and they also have a measure of oil resistance. Two monomers used commercially are vinyl acetate and, the structurally very similar, methyl acrylate ... 

It was found that the amount of chlorine that could be removed (84-87%) was in close agreement to that predicted by Flory on statistical grounds for structure Figure 12.10(a). It is of interest to note that similar statistical calculations are of relevance in the cyclisation of natural rubber and in the formation of the poly(vinyl acetals) and ketals from poly(vinyl alcohol). Since the classical work of Marvel it has been shown by diverse techniques that head-to-tail structures are almost invariably formed in addition polymerisations. 

In addition to homopolymers of varying molecular and particle structure, copolymers are also available commercially in which vinyl chloride is the principal monomer. Comonomers used eommercially include vinyl acetate, vinylidene chloride, propylene, acrylonitrile, vinyl isobutyl ether, and maleic, fumaric and acrylic esters. Of these the first three only are of importance to the plastics industry. The main function of introducing comonomer is to reduce the regularity of the polymer structure and thus lower the interchain forces. The polymers may therefore be proeessed at much lower temperatures and are useful in the manufacture of gramophone records and flooring compositions. 

Poly(vinyl acetate) is an atactic material and is amorphous. Whilst the structure of polyfvinyl alcohol) is also atactic the polymer exhibits crystallinity and has essentially the same crystal lattice as polyethylene. This is because the hydroxyl groups are small enough to fit into the lattice without disrupting it. 

Several authors have discussed the ion exchange potentials and membrane properties of grafted cellulose [135,136]. Radiation grafting of anionic and cationic monomers to impart ion exchange properties to polymer films and other structures is rather promising. Thus, grafting of acrylamide and acrylic acid onto polyethylene, polyethylene/ethylene vinyl acetate copolymer as a blend [98], and waste rubber powder [137,138], allows... 

One of the most dramatic examples of a solvent effect on propagation taken from the early literature is for vinyl acetate polymerization.78,79 Kamachi el al.n reported a ca. 80-fold reduction in kp (30aC) on shifting from ethyl acetate to benzonilrile solvent (Table 8.1). Effects on polymer structure were also reported. Hatada ef a m conducted a H NMR study on the structure of the PVAc formed in various solvents. They found that PVAc (M n 20000) produced in ethyl acetate solvent has 0.7 branches/chain while that formed in aromatic solvents is essentially unbranched. 

A cobalt(II)-chitosan chelate has been prepared by soaking a chitosan film in C0CI2 aqueous solution. The chitosan chelated Co(II) through both oxygen and nitrogen atoms in the chitosan chain. The tetracoordinated, high-spin Co(II)-chitosan chelate could be used as a catalyst, and the polymerization of vinyl acetate was carried out in the presence of Na2S03 and water at pH 7 and normal temperature. The polyvinyl acetate possessed a random structure [114,115]. 

Chattopadhyay S., Chaki T.K., and Bhowmick A.K., New thermoplastic elastomers from poly(ethyle-neoctene) (engage), poly(ethylene-vinyl acetate) and low-density polyethylene by electron beam technology structural characterization and mechanical properties. Rubber Chem. TechnoL, 74, 815, 2001. Roy Choudhury N. and Dutta N.K., Thermoplastic elastomeric natural rubber-polypropylene blends with reference to interaction between the components. Advances in Polymer Blends and Alloys Technology, Vol. 5 (K. Finlayson, ed.), Technomic Publishers, Pensylvania, 1994, 161. 

Chattopadhyay, S., Chaki, T.K., Bhowmick, A.K., Gao, G.J.P., and Bandyopadhyay, S., Structural characterization of electron-beam crosslinked thermoplastic elastomeric films from blends of polyethylene and ethylene-vinyl acetate copolymers, J. Appl. Polym. Sci., 81, 1936, 2001. 

If the condensation proceeds far enough, a network structure is easily formed. Similarly, copolymerization of a little divinyl adipate with vinyl acetate yields a nonlinear polymer in which chains of bifunctional vinyl acetate units are bridged, or cross-linked, by the tetrofunctional divinyl adipate units, as indicated on the following page, where the divinyl adipate unit is enclosed between vertical dashed lines ... 

Ethylene vinyl acetate has also found major applications in drug delivery. These copolymers used in drug release normally contain 30-50 wt% of vinyl acetate. They have been commercialized by the Alza Corporation for the delivery of pilocarpine over a one-week period (Ocusert) and the delivery of progesterone for over one year in the form of an intrauterine device (Progestasert). Ethylene vinyl acetate has also been evaluated for the release of macromolecules such as proteins. The release of proteins form these polymers is by a porous diffusion and the pore structure can be used to control the rate of release (3). Similar nonbiodegradable polymers such as the polyurethanes, polyethylenes, polytetrafluoroethylene and poly(methyl methacrylate) have also been used to deliver a variety of different pharmaceutical agents usually as implants or removal devices. 

Poly(vinyl alcohol) has the structure 10.67. Poly(vinyl acetate) is the fully esterified derivative of polyfvinyl alcohol), in which the -OH groups are replaced by -OCOCH3 groups. As indicated in Table 10.5, commercial polyvinyl sizes are effectively copolymers of polyfvinyl acetate) and polyfvinyl alcohol) that vary in the degree of saponification of the ester groups. These products may comprise 100% of either polymer, or combinations of the two monomers in any proportions. Crotonic acid (2-butenoic acid), widely used in the preparation of resins, may also be a component. This compound exhibits cis-trans isomerism (Scheme 10.17). The solid trans form is produced readily by catalysed rearrangement of the liquid cis isomer. 

Coleman and Sivy also used an infrared transmission cell to undertake degradation studies under reduced pressure on a series of poly(acrylonitrile) (ACN) copolymers [30-33]. Thin films prepared from a polymer were mounted in the specially designed temperature-controlled cell mounted within the infrared spectrometer. The comparative studies were made on ACN copolymers containing vinyl acetate [30,32], methacrylic acid [30,31] and acrylamide [30,33]. The species monitored was the production of the cyclised pyridone structure. This was characterised in part by loss of C=N stretch (vC = N) intensity at 2,240 cm-1 accompanied by the appearance and increase in intensity of a doublet at 1,610/1,580 cm-1. 

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. 

Several polymer and random copolymers of fluoroalkyl acrylates have been studied,76 including (1) Poly-1,1-dihydroperfluoroheptylacrylate (PFHA), (2) copolymer of 1,1-dihydroperfluoroheptylacrylate (PFHA) with acrylic acid (PFHA-AA, 1 1), and (3) copolymer of the monoester of 1,1-dihydroperfluor-oheptyl alcohol and maleic acid (PFHM) with vinyl acetate (PFHM-VA, 1 1). The average degree of polymerization was found to be about ten for all the polymers tested. The tendency of polymers to form well-ordered two-dimensional structures on the water surface was demonstrated. Polymers were deposited as... 

PVA in, 25 617 setting speed of, 25 579-580 smectites application, 6 697t solution, 1 532-534 structural, 1 534-545 styrenic block copolymers in, 24 714 use of latex in, 14 711-712 vinyl acetate polymers in, 25 578-583 viscosity of, 25 581 water-borne, 25 475 Adhesive systems, microencapsules in, 16 460... 

Poly(vinyl alcohol) (PVA) is a polymer of great interest because of its many desirable characteristics specifically for various pharmaceutical, biomedical, and separation applications. PVA has a relatively simple chemical structure with a pendant hydroxyl group (figure la). The monomer, vinyl alcohol, does not exist in a stable form, rearranging to its tautomer, acetaldehyde. Therefore, PVA is produced by the polymerization of vinyl acetate to poly(vinyl acetate) (PVAc) followed by the hydrolysis to PVA (figure 2). Once the hydrolysis reaction is not complete, there are PVA with different degrees of hydrolysis (figure lb). For practical purposes, PVA is always a co-polymer of vinyl alcohol and vinyl acetate [1]. 

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