Poly acetal chemical structure

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]. 

Fig. 1 Chemical structures of the polymers commonly used for preparation of beads poly (styrene-co-maleic acid) (=PS-MA) poly(methyl methacrylate-co-methacrylic acid) (=PMMA-MA) poly(acrylonitrile-co-acrylic acid) (=PAN-AA) polyvinylchloride (=PVC) polysulfone (=PSulf) ethylcellulose (=EC) cellulose acetate (=CAc) polyacrylamide (=PAAm) poly(sty-rene-Wocfc-vinylpyrrolidone) (=PS-PVP) and Organically modified silica (=Ormosil). PS-MA is commercially available as an anhydride and negative charges on the bead surface are generated during preparation of the beads...

The CYPHER stent employs two nonerodible polymers polyethylene-co-vinyl acetate (PEVA) and poly-n-butyl methacrylate (PBMA), The combination of sirolimus and these two polymers constitutes the basecoat formulation that is applied to a stent treated with paryleneC. In addition, a drug-free topcoat of PBMA polymer is applied to control the release kinetics of sirolimus (59), making this a diffusion-controlled reservoir device. The chemical structure of the polymers used in the CYPHER stent is shown in Figure 4,... 

Fig. 6 Chemical structures of branched copolymers (x and y denote number averages of repeating units) a polyallylamine-gra/t-poly( /-methyl L-glutamate) (PAAx-g-PMLGluy, X = 175, y = 14), b poly(ethylene oxide)- Zoc/c-(branched-poly(ethylene imine)-gra/t-poly(y-benzyl L-glutamate)) (PEOx- -PEIy-g-PBLGlu2(o.4j+i) x = 113, y = 233, z = 0.2-2.9), and c poly(ethylene oxide)-MocA -([G-3]-dendritic poly(L-lysine)-acetal) (PEOx- -[G-3]-PALLys, x = 113, 227)...

Fig. 1. Chemical structures of barrier polymers, (a) Vinylidene chloride copolymers (b) hydrolyzed ethylene—vinyl acetate (EVOH) (c) acrylonitrile barrier polymers (d) nylon-6 (e) nylon-6,6 (f) amorphous nylon (Selar PA 3426), y = x + 2 (g) nylon-MXD6 (h) poly(ethylene terephthalate) and (i) poly(vinyl...

Lambe et al. (1978) studied the enhanced steric stabilization of polystyrene latices by poly(vinyl alcohol). This is included in this sub-section on copolymers because the samples studied were not fully hydrolysed. This means that the parent poly(vinyl acetate) from which they were derived was only partially (88%) hydrolysed (this is often accomplished by alcoholysis). The resultant polymer is not, however, a completely random copolymer because adjacent group effects influence the hydrolysis kinetics in such a way that some degree of blockiness is introduced. On average, these blocks consist of 2 ester groups to every 18 alcohol groups but blocks of average size 5-6 acetate groups are common. The chemical structure of the polymers should therefore formally represented by a structure intermediate between poly(vinyl acetate-6-vinyl dcohol) and poly(vinyl acetate-co-vinyl alcohol) rather than poly(vinyl alcohol) as such. The random (or statistical) copolymer can be prepared by partial reacetylation of fully hydrolysed poly(vinyl alcohol). 

Chart 1.1 Chemical structures of poly (vinyl acetate), PVAc poly (methyl methacrylate), PMMA polystyrene, PSt poly-(methyl vinyl ketone), PMVK poly(phenyl vinyl ketone), PPVK. 

Figure 2 Chemical structures of poly(vinyl acetate), PVAc, and poly(vinyl alcohol), PVA, used to...

When depropagation takes place at an elevated temperature, at a rate that is equal to the propagation in a free-radical polymerization, then the temperature of the reaction is a ceiling temperature (see Chap. 3). Termination can take place by disproportionation. Secmidary reactions, however, may occur in the degradation process depending upon the chemical structure of the polymer. Such side reactions can, for instance, be successive eliminations of hydrochloric acid, as in poly(vinyl chrolide), or acetic acid as in poly(vinyl acetate). 

Viscosity modifiers, usually referred to as thickeners, are used in varying concentrations throughout the range of sealants and adhesives. They span a diverse range of chemical structures. Some of the more commonly encountered thickeners include poly(alkyl methacrylates) - homo and/co-polymers poly(alkyl acrylates) - homo and/co-polymers polystyrene acry-lonitrile-butadiene-styrene co-polymers poly(vinyl acetate) fumaric or maleic acid-based polyesters. 

Fig. 6 Chemical structures of a poly(vinyl alcohol) and b poly vinyl acetate Source [17])...

Chemical nomenclature forms the alphabet of polymer science, (a) What is the chemical structure of it-poly(vinyl chloride)-WocA -cis-l,4-polyiso-prene (b) Poly(vinyl acetate) is totally hydrolyzed. What new polymer is formed What polymer is formed if the hydrolysis is only partial ... 

The question arises why cis-polyisoprene, different from poly(vinyl-acetate), shows in its dielectric spectrum the chain reorientation. The reason becomes clear when we look at the chemical constitution of polyisoprene, and focus in particular on the associated dipole moments. Figure 5.22 displays the chemical structure. The main point is that isoprene monomers are polar units which possess a longitudinal component p of the dipole moment, which always points in the same direction along the chain. As a consequence, the longitudinal components of the dipoles of all monomers become added up along the contour, giving a sum which is proportional to the end-to-end distance vector R. In the dielectric spectrum the kinetics of this total dipole of the chain is observable, hence also the chain reorientation as described by the time dependence R t). 

Figure 11.13 Chemical structure of some biodegradable synthetic polymers (a) poly(vinyl alcohol), (b) poly(vinyl acetate), and (c) poly(glycolic acid).

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