Comb Stars by the Divergent Approach

1 Comb Stars by the Divergent Approach (Schappacher and Deffteux, 2005) 

This lower average branch number could be explained either by incomplete initiation of the CEVE polymerization by the 4 acetal ends of the precursor and/or by some termination or transfer during the propagation reaction. It is difficult at this stage, using SEC or other conventional analytical techniques, to further identify the nature of the side reactions that predominantly occur during the star synthesis. 

The main molecular characteristics of the 4-arm comb star polystyrene are collected in Table 21.2. The Mw Ri(app)ls ratio, which is related to the volume contraction due to branching is 0.19 for the star comb versus 0.29 for the linear comb of same structure. These very low values agree with the highly branched chain architecture of the comb polymers on which is superposed the volume contraction related to the comb star architecture. The radius of gyration (/ g) and hydrodynamic radius (/ h) of the star comb on the one hand are very close to each other as are and of the corresponding one-branch linear comb polymer. They are equal to 45 nm, in THE at 25 °C for the star comb M = 9 000 000 g/mol) and 25 nm for the similar linear comb (M = 2 700 000 g/mol) in the same conditions. 

4 arms 3-1-1 degen. 2-1-2 degen. 3 arms 2-1-1 degen. eq. to 2 arms one arm 

This suggests that beside secondary initiation resulting from hydrolyzed TMSI, a fraction of the linear PCEVE chains may come from transfer reactions. The overall impact of these different processes (incomplete initiation, transfer or termination) reduces the efficiency of the synthesis of symmetric 4-arm stars to 47%, the other 53% having one or several structural defects (lower number of branches, degenerated branch). 

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