Selection of Starting Materials

For the synthesis of DPUR, a cycloaliphatic diisocyanate, isophorone diisocyanate (IPDI) from Fiiils, was used since unlike aromatic isocyanates, it does not result in yellowing of the coatings and films. The polyols used were polytetramethylene glycol (PTMG) with a MW of 2000 

Polymerisation of acrylic monomers was carried out according to the standard procedure using two different initiating systems  

The choice of initiating systems was made by considering their possible effect on particle morphology (see section 6.3.2). The other additives (emnlsifiers, protective colloids) were standard materials commonly used in emulsion polymerisation of acrylic monomers. 

It was assumed that three monomers would be used in this stndy methyl methacrylate, butyl acrylate and styrene. The possiblity of using styrene seemed to he especially interesting because of its very low cost compared to the other monomers. The other two monomers were selected for the significant differences in their polarity and solnhility in water that might affect the particle morphology and the T of poly(methyl methacrylate) and poly(butyl acrylate). Difunctional acrylate monomer (1,4-hntanediol dimethacrylate) was also used in some experiments since it encouraged the formation of an IPN strncture. 

Substances like carbon dioxide (generated from natural sources or synthetic routes) and methane gas (obtained from natural sources such as marsh gas) are available in abundance. These are considered as renewable starting materials. 

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Chemical Modification. The chemistry and synthetic strategies used in the commercial synthesis of cephalosporins have been reviewed (87) and can be broadly divided into ( /) Selection of starting material penicillin precursors must be rearranged to the cephalosporin nucleus (2) cleavage of the acyl side chain of the precursor (2) synthesis of the C-7 and C-3 side-chain precursors (4) acylation of the C-7 amino function to introduce the desked acylamino side chain (5) kitroduction of the C-3 substituent and 6) protection and/or activation of functional groups that may be requked. 

For a viable commercial process, the selection of materials and the choice of synthetic route is governed primarily by cost, not by overall yield. The selection of starting material is dictated usually by the desked C-3 substituent. For cephalosporins containing 3-acetoxymethyl or 3-(substituted)methyl such as 3-thiomethyl and 3-aminomethyl derived moieties, the most dkect synthetic route is from cephalosporin C, whereas pencillin V or G is the preferred starting material for the synthesis of the C-3 methyl cephalosporins. The three chemical transformations (2), (5), and 6) can potentially be carried out in a variety of ways, the precise sequence being determined by a balance of competing factors such as cost and optimization of yield (87). 

Selection of starting materials is always key for early development Starting materials should be readily available within a reasonable lead time. Cyclopentenone 27 was prepared by four different routes [6]. 

In the selection of starting material, one should be aware that there may be a variation in lignin composition depending on the part of a tree from which the wood is taken. Therefore, sapwood free of reaction wood should be used for the preparation of a reference lignin from a particular species. Size reduction and removal of extractives from the wood can be accomplished according to the directions given by Bjorkman (1956). 

Selection of starting material is crucial this considers not only the characteristics of the material, but also its origins and mode of use. 

Table 6X7 shows that the properties of hybrid dispersions prepared with additional crosslinking of acrylic/styrene polymer do not differ from the properties of dispersions of the same composition prepared without additional crosslinking. Also the properties of films made from both dispersions were very similar (see Table 6.28). However, lack of positive effects of additional crosslinking of the acrylic/styrene part of the hybrid may result from improper selection of starting materials for hybrid synthesis. Therefore, we intend to investigate this effect further in another study along with further studies on the effect of introducing double bonds to the polyurethane-urea part of the hybrid.

The mechanical and thermal properties of these polymers can also be varied over a wide range by the selection of starting materials with differing compositions and molecular weights. The tripolymerization of 3,9-h A(ethylidene 2,4,8,10-tetraoxaspiro[5,5]undecane) with mixtures of the rigid diol CDM and the flexible diol HD allows preparation of polymers with controlled glass transition temperature [40] (Fig. 55.6). Other thermal and mechanical properties for P(CDM -co-HD) copolymers are listed in Table 55.1. 

The strategies for dealing with potential migration of hazardous substances from recycled HDPE are essentially the same as with PET. First, a combination of the selection of starting materials and processing steps can be used to minimize the contamination levels that are present. The first company to obtain a letter of nonobjection from FDA for recycled HDPE in direct food contact was Union Carbide, which later sold the technology to Ecoplast, which also received a letter of nonobjection. ... 

Atom Economy. Usually, the synthesis and manufacture of chemical substances begins with the selection of starting materials. In an ideal chemical process, the amount of starting materials or reactants equals the amount of all products generated and no atoms are wasted. 

Another approach to making organic chemistry greener involves the way in which a reaction is carried out, rather than in the selection of starting material, reagents, or solvents. Microwave technology (see Technique 7, Section 7) can be used in some reactions... 

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