Polyacetals aldehyde polymers

Carbonyl addition-substitution n. Step-growth polymerization schemes based on carbonyl addition-substitution reactions are almost entirely concerned with reaction of aldehydes step-growth polymers prepared by this type of reaction include polyacetals, phenolformaldehyde polymers, ureaformaldehyde polymers, and melami-neformaldehyde polymers. 

Aldehyde polymers have also been important for the understanding of polymer stability, the recognition of the importance of end groups for polymer stability, reaction on polymers by end capping and the limitation of thermal and acidolytic stability of polyacetal chains. (3)... 

Similar polyacetals were prepared by BASF scientists from CO-aldehydic aUphatic carboxyUc acids (189,190) and by the addition of poly(hydroxycarboxyhc acid)s such as tartaric acid to divinyl ethers (191) as biodegradable detergent polymers. 

Cationic initiators can also polymerize aldehydes. For example, BF3 helps produce commercial polymers of formaldehyde. The resulting polymer, a polyacetal, is an important thermoplastic (Chapter 12) ... 

By organic chemistry formalism, polyacetals are reaction products of aldehydes with polyhydric alcohols. Polymers generated from aldehydes, however, either via cationic or anionic polymerization are generally known as polyacetals because of repeating acetal linkages. Formaldehyde polymers, which are commercially known as acetal resins, are produced by the cationic ring opening polymerization of the cyclic trimer of formaldehyde, viz., trioxane [29-30] (Fig. 1.5). 

Ethylene glycol in the presence of an acid catalyst readily reacts with aldehydes and ketones to form cyclic acetals and ketals (60). 1,3-Dioxolane [646-06-0] is the product of condensing formaldehyde and ethylene glycol. Applications for 1,3-dioxolane are as a solvent replacement for methylene chloride, 1,2-dichloroethane, 1,1,1-trichloroethane, and methyl ethyl ketone as a solvent for polymers as an inhibitor in 1,1,1-trichloroethane as a polymer or matrix interaction product for metal working and electroplating in lithium batteries and in the electronics industry (61). 1,3-Dioxolane can also be used in the formation of polyacetals, both for homopolymerization and as a comonomer with formaldehyde. Cyclic acetals and ketals are used as protecting groups for reaction-sensitive aldehydes and ketones in natural product synthesis and pharmaceuticals (62). 

Polyacetals form a different subclass of compounds with oxygen in the backbone chain. In this group are included polymers that contain the group -0-C(R2)-0- and can be formed from the polymerization of aldehydes or ketones. A typical example of a polymer from this class is paraformaldehyde or polyformaldehyde or polyoxymethylene (CH20)n. Polyoxymethylene can be prepared by anionic catalysis from formaldehyde in an inert solvent. Acetylation of the -OH end groups of the polymeric chain is common since it improves the thermal stability of the polymer. Some results reported in literature regarding thermal decomposition of these polymers are indicated in Table 9.2.1 [1]. 

The polymerization of aldehydes to give polyacetal is readily undertaken anionically in the presence of base, due to the susceptibility of formaldehyde to nucleophilic attack (Odian, 1991) as shown in Scheme 1.25. It should be noted that the resulting polymer is thermally unstable and stabilization is achieved by an esterification reaction of the unstable hemiacetal end groups after polymerization. 

The main application fields of aldehyde scavengers are PET (more specifically wafer bottles made from PET), and polyacetals such as POM or polymers synthesized from formaldehyde such as urea-formaldehyde resins. 

The polymerization of the carbonyl group in aldehydes yields polymers, referred to as polyacetals, since they contain the acetal repeating structure... 

An acetal (e.g., 3 Figure 13.1) can be prepared by the equilibrium reaction of two equivalents of an alcohol and one equivalent of a compound possessing an aldehyde (or ketone to generate a ketal). The hemiacetal intennediate 2 is hydrolytically labile to both base and acid, but the resulting acetal product 3 is only labile to hydrolysis at acidic pH values. When polyacetals are prepared by acid catalysis, it is important to remove or neutrahze any residual add to ensure the polymer is stable enough to isolate and for storage. 

Polyacetals that have been examined for biomedical applications are often prepared by step or condensation polymerizations. Utilizing a diol monomer and an aldehyde to prepare a polymer requires removal of 1 equivalent of water per acetal (Figure 13.1). Acetal exchange reactions can be used where the small molecule is an alcohol with a lower boiling point than water... 

Y. Wang, H. Morinaga, A. Sudo, T. Endo, Synthesis of amphijdiilic polyacetal by polycondensation of aldehyde and polyethylene glycol as an acid-labile polymer for controlled release of aldehyde, J. Polym. Sd. A Polym. Chem. 49 (2011) 596-602. 

Polymers of aldehydes are commonly termed polyacetals (or acetal resins) since their structure resembles that of polymers obtained by the acetal-forming reaction between aldehydes and diols ... 

Since the most important commercial polymers of aldehydes are based on formaldehyde, the term polyacetal (or acetal resin) is commonly used as applying solely to polymers of formaldehyde. 

This book is a useful guide for the industrial, and academic chemist as well as students studying polymer chemistry which involve ureas, melamines, benzoguanamine/aldehyde resins (amino resins-aminoplasts), phenol/aldehyde condensates, epoxy resins, silicone resins, alkyd resins, polyacetals/polyvinyl acetals, polyvinyl ethers, polyvinylpyrrolidones, polyacrylic acids and polyvinyl chloride. 

Cationic polymerization of cyclic acetals yields polyacetals, that is, polymers containing acetal bonds -OCR R O- in the main chain (the class name polyacetals should not be confused with the name poly (vinyl acetal )s, which is the class name for a group of polymers that are products of the reaction between poly (vinyl alcohol) and an aldehyde). Homopolymers of cyclic acetals are at the same time perfectly alternating copolymers composed of oxymethylene and oxyalkylene units, as shown for DXL polymerization in Scheme 2. 

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