Semi-synthetic polymers

The first polymers were developed in 1862, known as semi-synthetics and formed a technological bridge between natural (those produced by trees, plants and insects) and fully synthetic polymers. Semi-synthetic plastics were made by treating a natural material chemically to modify its properties, usually with the aim of producing a mouldable product. In 1909, the first fully synthetic polymer was produced by reacting two chemicals (monomers) together. 

Some of the products formed are functional ingredients in their own right, such as high fmctose syraps, cefuroxime etc. Others are intermediates that can be either freely traded, such as acrylamide as a pre-polymer and 6-APA and p-hydroxyphenylglycine as precursors of semi-synthetic antibiotics. Alternatively some intermediates tend to be used in-house by the company producing them such as fS)-2-chloropropanoate and L-tert-leucine. 

During World War II a large amount of research was carried out in seeking fully synthetic polymeric materials which could substitute a semi-synthetic polymer such as nitrocellulose. This research was connected with the immense development of plastics chemistry, which began shortly before World War II and is still advancing at a great pace. 

Synthetic polymer materials are so ubiquitous in modem life that we now take them for granted. But, the first commercially significant, completely synthetic plastic was only introduced at the beginning of the 20th century. This was Bakelite, invented by Leo Baekeland and a short account of his contributions will form the subject of one of our Polymer Milestones in the next chapter. The introduction of this new material was preceded by roughly 40 years of the development of what can be called semi-synthetics based on chemically modified forms of cellulose. 

A useful synthesis (ref.ll)of patchouli alcohol, an important fragrant constituent of patchouli oil, from (+)-camphor, that onetime important natural product which was employed as a plasticiser for nitrocellulose (itself a semi-synthetic polymer), was complicated by structural revision of the sesquiterpene alcohol. Dihydrocarvone (14) obtained by saturation of the ring double bond in carvone, a major constituent of oil of spearmint has been employed for two very different sesquiterpenes, the ketone campherenone (15) and the alcohol, occidentalol (16). In the first case an enol acetate was converted to a bicyclic intermediate by earlier established methodology and the route emulated a plausible biogenetic sequence giving racemic campherenone (ref.12) as shown. Any chirality in (14) is apparently lost. 

For some applications, a refractive index is important. A match between the particle size of some barium grades and the refractive index of matrix material allows the formulation of products with desirable optical properties. A series of synthetic barium sulfates is produced by Sachtleben Chemie which have particle sizes between 4 and 10 pm. If the particle size of these barium sulfates is well coordinated with the refractive index of the matrix polymer, semi-opacity combined with translucency results. This permits the foimulation of a light disperser in lampshades or in illuminated advertising displays. The coirect particle size can be calculated from the equation d = (lOOn - 141)/2, where n is the refractive index of the resin and d the particle size of barium sulfate. 

Preparation of semi-synthetic polymers. Cellulose plastics, particularly cellulose nitrate and acetates, were the most commercially-important semi-synthetics, and have been used to prepare photographic films, textile fibres and lacquers. 

The development of improved separational processes for obtaining pure (mixed) cardanol and cardol from technical CNSL has encouraged experimentation in chemical instead of polymer uses for these component phenols as well as for anacardic acid, by extraction from natural CNSL. Some of the earlier chemistry has been reviewed (ref. 2). Most of the more recent uses particularly for cardanol, but also cardol and anacardic add, stem from the conception of their semi-synthetic applications as readily available replenishable resources (refs. 278, 279). As with CNSL, the reactions considered in this section are concerned with the hydroxyl group of the side chain and substitution in the ring. 

A complete list of semi-synthetic heparinoids is outside the scope of this article. Products of sulfation of neutral polysaccharides include sulfates of starch, cellulose, - - xylan, dextran, " guaran, and synthetic polymers of o-glucose. A somewhat closer simulation of the structure of heparin was attempted by sulfating polysaccharides containing amino sugars or uronic acids or both, such as chitin and chitosan, " and the corresponding N-formyl, N-(car-boxymethyl), O-(carboxymethyl), and 5-carboxylated - deriva-... 

Semi-synthetic and synthetic polymers are also used as thickening agents. Such are carboxymethyl cellulose (87,6] and polyacrydamide (73) respectively. 

In conventional tabletting, powder particles are made to adhere with binding materials (granulation). Generally, the solutions of natural, semi-synthetic, or synthetic polymers are used for granulation (solutions of gelatine, cellulose ethers, and polyvinyl alcohol). 

In the mid twenties several circumstances permitted a revised orientation of both content and style of areas of research at the Central Research Laboratory. In 1925 the Technical Committee (TEA) of I.G. Farben discussed the possibilities for producing artificial fibres. At this time, I.G. Farben was the second largest producer of artificial fibres in Germany. Therefore polymer chemistry became more important for the company at the same time as dyestuffs chemistry lost its former position. However, the science of synthetic, semi-synthetic and natural polymers was not yet established in the same way as structural chemistry was for organic dyestuffs, pharmaceuticals, and intermediates. Colloid chemists regarded substances such as cellulose, silk, and wool as... 

Plastics are semi-synthetic or synthetic materials which can be manipulated to form films, fibres, foams or three-dimensional olgects. Natural polymers from plants, insects and animals are not discussed in this book. Synthetic paints, synthetic textiles and photographic film contain plastics but will not be discussed in this book because their conservation is the focus of specialist publications (Chiantore and Rava, 2005 Learner, 2005 Timar-Balazsy and Eastop, 1998 Lavedrine et al., 2003). Plastics are based on polymers, also known as macromolecules, which are large molecules made by joining together many smaller ones. The chemical and physical properties of liquid polymers are modified with additives and shaped to convert them into solids with dimensionally stable forms. 

Although we consider plastics to be new materials, only semi-synthetic and synthetic plastics are modem (Table 2.1). Naturally occurring polymers, those formed by plants, trees, insects and animals, were first documented as coatings and waterproofing agents in the form of bitumen, referred to as slime in the Old... 

Semi-synthetic plastics are natural polymers which have been treated chemically to modify their properties with the aim of producing physically stable, mouldable products. The Swiss chemist, Schonbein, unwittingly prepared the first semi-synthetic polymer by treating paper (cellulose) with a mixture of nitric and sulphuric acids in 1846. The resulting cellulose nitrate was soluble in organic liquids and was softened by heat. It was highly flammable and only thought to be useful as an explosive, which was named gun cotton . 

Cellulose-based plastics, particularly cellulose nitrate and acetates, were the most commercially important semi-synthetics up to the 1940s and were used as the base for photographic film, textile fibres, moulded goods and in lacquers. Naturally occurring polymer cellulose in the form of cotton linters or wood pulp is chemically treated to increase its solubility. Cellulose has a high molecular weight of between 100000 and 500000 and an empirical formula C0H1OO5. Casein-formaldehyde is the only protein-based moulded plastic that achieved commercial success. It is based on cow s milk and is still produced in very small quantities for specialist items such as hand-coloured buttons. 

It is easier to characterize unknown material if its historical and technological backgrounds are known. The development of semi-synthetic polymers in the second half of the nineteenth century can be followed using patents (Fernandez-Villa and Moya, 2005). Development of cellulose nitrate was prompted by the need to find substitutes for natural materials including tortoiseshell, ivory and ebony, which were very expensive. By 1858, approximately 8 per cent of British patents concerned the synthesis or moulding of semi-synthetics. 

For more recent synthetic polymers, interviews with the artist can provide information about materiak and technique used, although they do not always replace analysis. The date of manufacture or, if unavailable, the date of collection, can provide a starting point in the identification of plastics. If a plastic was manufactured before around 1905, it is likely to be a semi-synthetic or natural material, rather than a fully synthetic plastic. The period between 1939 and 1960 saw a dramatic increase in production of polystyrene, poly (vinyl chloride), nylon, acrylics and polyethylene and the phasing out of semi-synthetics. If a plastic was manufactured before the 1940s, it could not have been shaped by injection moulding, recognized by a small imperfection due to the filling hole. 

Traces of metals are present in most polymers as a result of processing in stainless steel reaction vessels, being transported in metal containers and shaping in metal moulds or rolling between metal rollers. Many metal ions catalyze oxidation by accelerating decomposition of hydroperoxides at room temperature. Observation of plastics materials in museums suggests that copper is a highly effective catalyst for semi-synthetic materials such as cellulose nitrate and... 

Dash, M. Chiellini, F. Ottenbrite, R.M. Chiellini, E. Chitosan—A versatile semi-synthetic polymer in biomedical applications. Prog. Polym. Sci. 2011,36 (8), 981-1014. 

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