Polyfunctional starters

The general polymerisation of an alkylene oxide, initiated by a polyfunctional starter, is ... 

The polymerisation of PO and EO, initiated by polyfunctional starters, to make short chain polyether polyols is a reaction that is strongly dependent on diffusion. The consumption rate of PO or EO is given by two simultaneous factors the rate of the chemical reaction in the liquid phase and the efficiency of the monomer mass transfer from the gaseous phase to liquid phase (see details in section 4.1.5). The PO (or EO) consumption rate, considering the mass transfer, is described by equation 13.27 [45-50] ... 

Figure 17.3 Chemical transformations of starch and D-glucose into polyols that can be used as polyfunctional starters for polyether polyols synthesis...

Representative PCL are the diols of MW of 2000-4000 daltons, used in hydrolytically stable PU elastomers. The diols used as starters are DEG, 1,4 butanediol and NPG. The melting point of PCL, of MW of 2000 daltons, is in the range of 40-60 °C and of MW of 1000 daltons in the range of 30-40 °C. If a polyfunctional polyol is used as a starter, polyfunctional PCL polyols are obtained. Thus, by polymerisation of CPL initiated by trimethylolpropane (reaction 8.32) a polyester triol is obtained and initiated by pentaerythritol, a polyester tetraol is formed. It is interesting that some low MW PCL triols with a MW of 300-900 daltons are liquid at room temperature (melting points in the range of 6-16 °C). The viscosities of PCL polyols, at 60 °C, are 40-1600 mPa-s, depending on the polyol structure. 

Fatty acids are built from acetyl CoA as a starter and several molecules of malo-nyl CoA (D 3) by fatty acid synthase, as is shown schematically in Fig. 52. In yeast the enzymes involved are located on two polyfunctional proteins. It is still unclear whether similar polyfunctional enzymes exist in other organisms. 

The flavane ring system is formed by the polyfunctional protein chalcone synthase from one molecule of a cinnamoyl CoA ester and 3 molecules malonyl CoA. The enzyme isolated from parsley (Petroselinum hortense) reacts with p-coumaroyl CoA and caffeoyl CoA as starter molecules (A 3.1). It uses the CoA esters as immediate substrates for the condensation reaction and contains neither an acyl carrier domain nor pantetheine. 

---