Condensation polymerisation formaldehyde

Urea formaldehyde /alkyd blends Sloving Condensation polymerisation Aromatic hydrocarbons and alcohols Fairly good Fairly good Very good Good Fair Water white Gives white finishes of excellent colour... 

Melamine formaldehyde polymer is formed by the condensation polymerisation of melamine and formaldehyde. 

The polymers can be categorised as formaldehyde containing and formaldehyde free and as thermoset or thermoplastic resins. Typical formaldehyde containing resins are melamine formaldehyde sulfonamide resins, where the sulfonamide is ortho and para toluenesulfonamide. The sulfonamide, which is a solvent for the dye, undergoes a condensation polymerisation with formaldehyde and melamine, the latter acting as a cross-linking agent. Non-formaldehyde, thermoplastic resins are usually polyamides and polyesters. 

UF is made by the condensation polymerisation of urea and formaldehyde. Although it has been widely used for closures (mainly in pastel shades), use is now in decline due to wadless thermoplastic systems. Density 1.47-1.52. 

PF is made by the condensation polymerisation of phenol and formaldehyde. Due to the volatile and toxic/irritant nature of formaldehyde, this is usually fixed with ammonia giving hexamine. Polymerisation of hexamine and phenol not only produces phenol formaldehyde but may release residues of phenol, formaldehyde or ammonia. In certain cases some residues may remain in the moulding and be released into the product. As with UF, PF is mainly used for closures but due to the fact that the material is naturally dark, it is used for dark or deep colours. PF is generally more resistant to heat and moisture than UF. Both UF and PF are used with a range of fillers, e.g. wood flour, synthetic fibre. Density 1.25-1.45. General pharmaceutical applications have now reduced. 

Linseed oil fatty amides were reacted with melamine or tartaric acid to obtain melamine or tartaric acid-modified poly (ester amide). This was cured at room temperature by poly(styrene co-maleic anhydride) or butyl-ated melamine formaldehyde in different weight percentages (30-80%) to obtain a highly thermostable surface coating material. Similarly, piperazine-modified fatty amide was prepared from A,A-bis(2-hydroxyethyl) linseed oil fatty amide and piperazine by condensation polymerisation. The poly(ester amide) resin was cured with butylated melamine-formaldehyde... 

Step-growth condensation copolymerisations give rise to additional experimental difficulties, with respect to the former reactions studied, due to the continuous release of e.g. water. Indeed, the evaporation of water produced by the reaction may obscure the detection of the cure process and prohibit a reliable quantification of the reaction heat and the reaction conversion. To illustrate how condensation polymerisations can be studied by MTDSC, the post-cure condensation reactions of melamine-formaldehyde (MF) resins will be discussed [91]. 

Phenolics Phenol and resorcinol formaldehyde adhesives cure by condensation polymerisation with the elimination of water, and therefore require high curing pressures. They are normally available as two-component systems consisting of a paste resin and a liquid hardener. Traditional uses include wood bonding and plywood fabrication, but nowadays phenolics, especially modified phenolics, are also used in structural bonding of metals and plastics. 

Strictly speaking, vulcanisation is a type of polymerisation that is comparable to what is called addition polymerisation. The definition of this is that two different raw materials, rather than one and the same raw material, combine in chains to form macromolecules, as is the case - for example - with polyurethanes (see [1], p. 316). If there are by-products, water in particular, as is the case with Galalith (from casein and formaldehyde) or nylon (from hexamethylene diamine and adipic acid), this is called condensation polymerisation instead (cf. [1], pp. 175, 315-316 and [10], p. 15) (see Appendix 1). 

The initial step of the polymerisation process is reaction of the amine groups with formaldehyde to generate methylol units, as illustrated in Reaction 1.9. Further heating of the polymer then leads to a variety of reactions. For example, the methylol groups can undergo self-condensation (Reaction 1.10). 

These reversible polymerisations of aldehydes are to be distinguished from the condensations which they can also undergo. Thus formaldehyde is converted by quite weak alkalis (Ca(OH)2, CaC03) into glycollic aldehyde and glyceraldehyde, and further into a mixture of hexoses (Butlerow, 0. Loew) from which E. Fischer isolated the so-called... 

If the monomers are bifunctional, as in the above example, then a linear polymer is formed. Terminating monofunctional groups will reduce the average degree of polymerisation. Polyfunctional monomers, such as glycerol and phthalic acid, are able to form branching points, which readily leads to irreversible network formation (see Chapter 9). Bakelite, a condensation product of phenol and formaldehyde, is an example of such a space-network polymer. Linear polymers are usually soluble in suitable solvents and are thermoplastic - i.e. they can be softened by heat without decomposition. In contrast, highly condensed network polymers are usually hard, are almost completely insoluble and thermoset - i.e. they cannot be softened by heat without decomposition. 

As far as calix[4]pyrrole-based materials are concerned, particular emphasis should be placed on the production of chelating resins. Those obtained by the condensation reaction of calix[4]pyrrole and formaldehyde in the presence of formic acid offer potential for their use as extracting agents for fluoride removal from water. Their advantage relies on the fact that a single-step procedure is required for polymerisation. However, research in this area is in a preliminary stage. Much work needs to be done to establish the full capacity of these materials to take up fluoride from water, the kinetics of the process, and the optimum experimental conditions for fluoride extraction. Although, their ability to extract fluoride reaches a value of 88% from solutions of tetra-n-butylammonium fluoride... 

The formation of polymer build-up in polymerisation reactors and the routes towards minimising polymer buildup are described. The antifouling action of Evicas 90, a naphthol/formaldehyde condensate, is demonstrated and the main factors influencing the formation of polymer build-up and the effectiveness of antifouling agents are outlined. 10 refs. 

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