Formaldehyde monomer polymerization

Acetals. Acetal resins (qv) are polymers of formaldehyde and are usually called polyoxymethylene [9002-81-7]. Acetal homopolymer was developed at Du Pont (8). The commercial development of acetal resins required a pure monomer. The monomer is rigorously purified to remove water, formic acid, metals, and methanol, which act as chain-transfer or reaction-terminating agents. The purified formaldehyde is polymerized to form the acetal homopolymer the polymer end groups are stabilized by reaction with acetic anhydride to form acetate end groups (9). 

Fig. 9.10. Mechanism of the proton-catalyzed polymerization of monomeric formaldehyde (top), formalin (middle) and 1,3,5-trioxane (F bottom) to give polyformaldehyde ("paraformaldehyde" H), respectively. The carboxonium ions A, B, C, E etc. play a central role. They are transformed into each other through the nucleophilic reaction of a formaldehyde monomer on the respective carboxonium carbon atom. Analogously, E and formaldehyde continue to react to yield a high-molecular carboxonium ion that is intercepted by (traces of) water to furnish the final neutral product H.

Only in two reports are there claims that the chains formed in a cationic polymerization are exclusively macrozwitterions when formaldehyde is polymerized by BF351) and vinyl ethers by TCNQ31). Neither of these polymerizations fit the criteria of an ideal macrozwitterion polymerization set out above. If cationic polymerizations of this type are to be successfully studied an initiator system must be developed which will generate macrozwitterions in a simple fashion from nucleophilic monomers. The organic chemical literature indicates the form such an initiator could take. 

Polyformaldehyde can also be prepared by polymerization of trioxane, the cyclic trimer of formaldehyde. Trioxane polymerizes by ring opening polymerization and cationic initiators are the only effective initiators. Formaldehyde is always present when trioxane is polymerized because the growing polyoxymethylene chains by depropagation may lose one monomer unit, which is formaldehyde not trioxane. In spite of the fact that formaldehyde plays an (as yet incompletely understood) role in trioxane polymerization, which is a cyclic ether polymerization like dioxolane or tetrahydrofurane [5], trioxane will not be discussed in this review. 

When a few percent of formic acid was added to gaseous formaldehyde at about 500 mm pressure a rapid polymerization was observed, the velocity was some hundredfold greater than with pure formaldehyde. It appeared that formic acid was a powerful initiator of formaldehyde polymerization under these conditions. The polymerization was confined to the surface of the vessel and the kinetics were those of a heterogeneous system. Because of the much faster formaldehyde polymerization promoted by formic acid the purity of the formaldehyde became less important. The erratic results of earlier investigators were best explained by varying degrees of purity of earlier preparations of formaldehyde monomer. 

Triallylcyanurate comonomer, high temp, plastics Hydroxyethyl-s-triazine comonomer, high-performance resin m-Phenylenedimaleimide comonomer, hydrophobic acrylics N-t-Octylacrylamide comonomer, ionomeric polymers Sodium vinyl sulfonate comonomer, melamine-formaldehyde resins Guanidine carbonate comonomer, monomer polymerization 4-Vinylcyclohexene comonomer, nitrile rubber m-Divinylbenzene Vinylidene chloride monomer... 

Commercial polymerization of acetal homopolymer starts with anhydrous formaldehyde monomer from formaldehyde solution. Water is evaporated from the aqueous solution, forming paraformaldehyde, poly-oxymethylene, and hemiformal, which are purified and thermally decomposed to form anhydrous formaldehyde [6]. Methanol and formic acid are removed, either by freeze-trapping at a temperature just above the boiling temperature of formaldehyde or by washing with a nonvolatile polyol [6]. The anhydrous formaldehyde is fed into a reactor containing the inert hydrocarbon solvent, initiator, and dispersant, where the... 

In some polycondensations, new functional groups are created by reactions of the monomers. Thus, methylol end groups are formed by the initial reactions of formaldehyde with other monomers, and their condensation reactions shown in the last two rows of Table 3.1 occur in later stages of formaldehyde/urea and formaldehyde/phenol polymerizations (see Section 3.3.4). 

Crosslinked under acid using cellulose crosslinking agents such as dialdehyde and aldehyde (formaldehyde). It polymerizes and crosslinks with a vinyl monomer and crosslinking agent (methylene bis acrylamide) using the tree radical initiator. 

The reaction conditions can be varied so that only one of those monomers is formed. 1-Hydroxy-methylurea and l,3-bis(hydroxymethyl)urea condense in the presence of an acid catalyst to produce urea formaldehyde resins. A wide variety of resins can be obtained by careful selection of the pH, reaction temperature, reactant ratio, amino monomer, and degree of polymerization. If the reaction is carried far enough, an infusible polymer network is produced. 

Uses. Furfuryl alcohol is widely used as a monomer in manufacturing furfuryl alcohol resins, and as a reactive solvent in a variety of synthetic resins and appHcations. Resins derived from furfuryl alcohol are the most important appHcation for furfuryl alcohol in both utihty and volume. The final cross-linked products display outstanding chemical, thermal, and mechanical properties. They are also heat-stable and remarkably resistant to acids, alkaUes, and solvents. Many commercial resins of various compositions and properties have been prepared by polymerization of furfuryl alcohol and other co-reactants such as furfural, formaldehyde, glyoxal, resorcinol, phenoHc compounds and urea. In 1992, domestic furfuryl alcohol consumption was estimated at 47 million pounds (38). 

I ovolac Synthesis and Properties. Novolac resins used in DNQ-based photoresists are the most complex, the best-studied, the most highly engineered, and the most widely used polymers in microlithography. Novolacs are condensation products of phenoHc monomers (typically cresols or other alkylated phenols) and formaldehyde, formed under acid catalysis. Figure 13 shows the polymerization chemistry and polymer stmcture formed in the step growth polymerization (31) of novolac resins. 

Fig. 13. Polymerization chemistry of phenol—formaldehyde condensation synthesis of novolac resia. The phenol monomer(s) are used ia stoichiometric excess to avoid geUation, although branching iavariably occurs due to the multiple reactive sites on the aromatic ring.

Formaldehyde reacts with the hydrogen on the a-carbon of the fatty acid from which the oxazoline was formed to yield a vinyl monomer which can be polymerized or utilized for synthesis (4). Thus, esters of the oxazoline formed from TRIS AMINO undergo the reaction... 

Ammonia is used in the fibers and plastic industry as the source of nitrogen for the production of caprolactam, the monomer for nylon 6. Oxidation of propylene with ammonia gives acrylonitrile (qv), used for the manufacture of acryHc fibers, resins, and elastomers. Hexamethylenetetramine (HMTA), produced from ammonia and formaldehyde, is used in the manufacture of phenoHc thermosetting resins (see Phenolic resins). Toluene 2,4-cHisocyanate (TDI), employed in the production of polyurethane foam, indirectly consumes ammonia because nitric acid is a raw material in the TDI manufacturing process (see Amines Isocyanates). Urea, which is produced from ammonia, is used in the manufacture of urea—formaldehyde synthetic resins (see Amino resins). Melamine is produced by polymerization of dicyanodiamine and high pressure, high temperature pyrolysis of urea, both in the presence of ammonia (see Cyanamides). 

Thermosetting Reactive Polymers. Materials used as thermosetting polymers include reactive monomers such as urea—formaldehyde, phenoHcs, polyesters, epoxides, and vinyls, which form a polymerized material when mixed with a catalyst. The treated waste forms a sponge-like material which traps the soHd particles, but not the Hquid fraction the waste must usually be dried and placed in containers for disposal. Because the urea—formaldehyde catalysts are strongly acidic, urea-based materials are generally not suitable for metals that can leach in the untrapped Hquid fractions. Thermosetting processes have greater utiHty for radioactive materials and acid wastes. 

A waterborne system for container coatings was developed based on a graft copolymerization of an advanced epoxy resin and an acryHc (52). The acryhc-vinyl monomers are grafted onto preformed epoxy resins in the presence of a free-radical initiator grafting occurs mainly at the methylene group of the aHphatic backbone on the epoxy resin. The polymeric product is a mixture of methacrylic acid—styrene copolymer, soHd epoxy resin, and graft copolymer of the unsaturated monomers onto the epoxy resin backbone. It is dispersible in water upon neutralization with an amine before cure with an amino—formaldehyde resin. 

The mechanism of ion polymerization in formaldehyde crystals proposed by Basilevskii et al. [1982] rests on Semenov s [1960] assumption that solid-phase chain reactions are possible when the arrangement of the reactants in the crystal prepares the configuration of the future chain. The monomer crystals capable of low-temperature polymerization fulfill this condition. In the initial equilibrium state the monomer molecules are located in the lattice sites and the creation of a chemical bond requires surmounting a high barrier. However, upon creation of the primary dimer cation, the active center shifts to the intersite, and the barrier for the addition of the next link... 

The polybenzoxazines (PBZs) provide a new class of phenolic resins that were first described by Ishida in 1998 (Ref. 15). Synthesis of the resins involves three components a phenol, a primary amine and formaldehyde. The first stage involves the formation of a multifunctional benzoxazine monomer Figure 23.30 a)). The monomer can then be ring-opened at elevated temperatures (160-220 C) to yield a polymeric stmcture (Figure 23.30(b)). 

Alkyl 2-(hydroxymethyl)acrylates are versatile functionalized monomers and synthetic building blocks. Conventional preparations employ the Baylis-Hillman reaction which involves the addition of formaldehyde to the parent acrylate ester, catalyzed by l,4-diazabicyclo[2.2.2]octane (DABCO). These reactions typically take several days at room temperature, but can be achieved within minutes in the CMR and MBR (Scheme 2.4). Rapid heating under pressure prevents loss of formaldehyde. Subsequent cooling limits hydrolysis of the product, as well as dimerization and polymerization [33],... 

Substance made of giant molecules formed by the union of simple molecules (monomers) for example, polymerization of ethylene forms a polyethylene chain, or condensation of phenol and formaldehyde (with production of water) forms phenol-formaldehyde resins. 

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