Preparation of the monomer

Vinyl acetate was originally prepared industrially by the reaction of acetylene with acetic acid or by oxidation of ethylene. 

The first reaction may be carried out either in the liquid or vapour phase although the liquid phase route is now commercially obsolete. In a typical liquid phase preparation, acetylene is passed through an agitated solution of glacial acetic acid and acetic anhydride containing mercuric sulphate, preferably formed in situ, in a finely divided state as catalyst. 

In a typical system the reaction vessel is at 75-80°C and the vinyl acetate formed is swept out into a condenser at 72-74°C by means of circulating excess acetylene. This prevents distillation of higher boiling components but allows the vinyl acetate and acetylene through. The former is separated out by cooling and the acetylene recycled. 

Vapour phase synthesis may be carried out by passing a mixture of acetylene and acetic acid through a reaction tube at 210-215°C. Typical catalysts for this reaction are cadmium acetate, zinc acetate and zinc silicate. The monomer in each of the above mentioned processes is purified by distillation. 

Purified monomer is usually inhibited before shipment by such materials as copper resinate, diphenylamine or hydroquinone, which are generally removed before polymerisation. The monomer is a sweet-smelling liquid partially miscible with water and with the following properties boiling point at 760mmHg, 72.5°C specific gravity at 20°C, 0.934 refractive index 1.395 vapour 

---

Numerous recipes have been pubUshed which describe the preparation of methacrylate homopolymer and copolymer dispersions (65,66). A typical process for the preparation of a 50% methyl methacrylate, 49% butyl acrylate, and 1% methacrylic acid terpolymer as an approximately 45% dispersion in water begins with the preparation of the monomer emulsion charge. 

The production process consists of the stages of preparation of the monomer and additive solutions elimination of the dissolved oxygen from the solutions polymerization compounding (i.e., stabilization and granulation) drying, crushing, and packing of the finished product. 

Hermann Staudinger, on developing a new and simple preparation of the monomer, studied the polymerization of isoprene as early as 1910 (42). Stimulated by the differences in physical properties between his synthetic rubber and natural rubber, he turned his full attention to the study of polymers. 

From the results presented in this chapter we can conclude that it is feasible to prepare sugar-based polymers analogous to the more qualified technological polymers - polyamides, polyesters, polyurethanes - with an enhanced hydrophilicity and degradability. However, in most cases, the high costs associated with the preparation of the monomers restrict the application of these polymers to biomedical applications and other specialized fields. More readily available monomers and simpler polymerization processes have to be found if sugar-derived polymers should compete with petrochemical-based polymers that are used in domestic applications. 

The synthesis of the j>. newington O-antigenic polysaccharide by the chemical polymerization pathway will be discussed as an example (J 6 J 7) The first and the most difficult task consists in the preparation of the monomer itself, i. e. , the properly functionalized, oligosaccharide repeating unit. The most usual approach is to introduce the required functions into the already-existing oligosaccharide molecule. 

If fatty alcohols with chain length equal to Or less than 16 carbon atmns are applied, the emulsion formed is relatively unstable. In order to get initiation in monomer droplets, the polymerization should then be carded out immadiately after preparation of the monomer emulsion. 

These amino acid anhydrides are usuaiiy made with phosgene. The use of dimethyi carbonate shouid be tested in the preparation of the monomers. Poiyaspartic acid can be made by heating aspartic acid without soivent to form a polysuccinimide which is then hydrolyzed (12.34).186 It can also be made directly from maleic anhydride and ammonia. It promises to be useful as a scale inhibitor in water, an antiredeposition agent in detergents, and such. Gamma-irradiation converts it to a biodegradable superabsorbent material that takes up 3400 g water per gram of dry polymer.187 (Most superabsorbent polymers are based on acrylamide, a neurotoxin.)... 

Methods for the preparation of the monomer are well-documented (12,13). Details of the procedures used in ESR studies have been published previously (14,15). 

The synthesis of alkyl-substituted mefa-linked PPEs was reported by Mullen and Bunz (Table 5, entries 7—9). The preparation of the monomers follows a route different from that of the hitherto mentioned ones (Scheme 11). Starting from 58,... 

The metal colloid preparations arc mostly based on reduction of metal ions in the presence of bulky anions (e.g. citrate and mercaptoethanesulfonatc), but also quaternary ammonium salts (e.g. tetraoctylammonium bromide) or polymers (e.g. poly(iV-vinylpyr-rolidone (PVP)) are used as stabilizers (Figure 7.2). Ionic species involved in the NP synthesis play a dual role of stabilizers for the metal particles and dopants for the polymer material. In some cases the synthesis of the metal NPs occurs under y-irradiation in the presence of the monomer, which stabilizes the metal particles [64—66,68]. A two-phase approach for the preparation of the monomer or eventually oUgomer-stabUized metal particles has been also suggested in the case of octylthiophen [57] and 3,4-ethylenediox-ythiophene (EDOT) [70,71]. 

The methods of preparation of the monomers are given in the references in Tables I-III. 

Emulsifiers. These serve several purposes in emulsion polymerization. Emulsifiers are needed for the preparation of the monomer emulsion and are also used later for stabilizing the final dispersion. The choice of the emulsifier, amount added, and the method of addition determines the particle size of the dispersion, which is typically in the range 50-1000 mm. 

The main experimental difficulty with cyanoacrv late characterization, as emphasized by Pepper (1978), is the extreme reactivity of the monomer and its sensitivity to apparently spontaneous pol merization, caused by traces of unknown initiators. To prevent this, commercial preparations of the monomer contain a few parts per million of undisclosed stabilizers (e.g. sulphur dioxide). If these stabilizers are removed, the monomers can be preserved only in the frozen state, and after liquifying, they polymerize to glassy solids of very high MW (10 -10 Da). 

The foregoing brief discussion clearly shows that polymers containing the biphenyl or the terphenyl unit generally present very attractive combinations of properties. These polymers range from amorphous and very tough to the highly crystalline, totally insoluble materials. As indicated earlier, the preparations of the monomers required to make these polymers frequently necessitate multistep tedious procedures with the result that the starting materials are often prohibitively expensive. 

Chains with molecular weight of 10000 and higher were easily obtained. Another way to create aromatic polyamide chains with pendant carboxylic acid groups involves the preparation of the monomer mixture... 

---