Macromers efficiency

Although there are other unsaturated compounds that will undergo addition-elimination with free radicals, the benzyl ketene acetal XIV appears to be the most active double bond as far as rate of addition is concerned and the most efficient as far as regards to the extent of elimination is concerned. A comparison with the list of chain transfer agents listed in the Polymer Handbook (23) indicated that only the sulfur compounds appear to be more effective than XIV. Hydrolysis of the end-capped oligomer gives a macromer that is terminated with a carboxylic acid group. 

The dispersions obtained by copolymerisation of styrene with ACN, with low ACN content (ACN being around 25-30% in the monomer mixture), are more difficult to stabilise. For such low ACN content polymer polyols, or for polymer polyols based exclusively on styrene, more efficient NAD are necessary. These are discussed in the next chapters, i.e., macromers (reactive NAD) and nonreactive NAD. 

It was observed experimentally that the trans isomer of maleic structures the fumaric ester structures, are more reactive in copolymerisation with ACN and styrene than the maleic esters. The maleic esters (cis isomers, of structure 6.12) were rearranged to form fumaric esters (trans isomers, of structure, shown in Figure 6.4), in the presence of specific catalysts such as calcium salts of organic acids (calcium naphthenate [55], calcium octanoate [55]) or morpholine [55]. The resulting very efficient and reactive macromer structure of the fumaric ester type is shown in Figure 6.5. 

A direct method to obtain an efficient macromer useful as NAD for polymer dispersion stabilisation is the PO homopolymerisation or random PO-EO copolymerisation initiated by fumaric acid and catalysed by DMC catalyst [53] ... 

Although side-group mobility is obviously needed for efficient bonding, the majority of macromers are synthesized with side groups that have short spacers and are... 

Catalyst Macromer Amount of Catalyst,% Total Conv.,% Grafting Efficiency%... 

Table 3 shows that in the copolymerization of macromer with ethylene oxide different types of catalyst attained different grafting efficiencies, which was calculated by the following equation ... 

If the macromer were not isolated from the polymerization system, but used directly, both conversion and grafting efficiency became lower. 

Figure 6 shows how the molecular weight of the macromer affects grafting efficiency. As molecular weight of the macromer increases, grafting efficiency decreases. This is attributed to the increase of viscosity and steric... 

Figure 6. Effect of molecular weight or concentration of the macromer on grafting efficiency.

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