Chain-end chemical modification

The use of thiol compounds as transfer agents exclusively leads to monofunctional oligomers. To achieve bifunctionality requires a chain-end modification. Fock et al. [20-23] developed a new method based on the chemical chain-end modification of polymethacrylate telomers. These were previously obtained by telomerization reaction in the presence of mercaptoethanol or thioglycolic acid as transfer agents. The chemical modification can be summarized in two strategies  

Selective saponification leading to hydroxy-telechelic oligomethacrylates. 

Selective transesterification of the chain-end ester groups leading to carboxy-telechelic oligomethacrylates. 

In a second step, the transesterification of the terminal ester group is possible by using 3-methylpentanediol. Owing to a steric effect, the reaction becomes selective, and it is possible to obtain a functionality very close to 2. The telechelic structure was evidenced by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) analysis. The telechelic oligomers were then reacted with 1,6-hexanediisocyanate to increase the molecular weight of the oligomers. 

The acid functionality was obtained in the range 1.95-2.05 by acido-basic titration. 

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