Hydroxyl group reactions architecture

As seen in Scheme 5.1, preparation of the IG polymer in this synthesis involved the ROP of cCL and subsequent chain-end modification. Conversion of the terminal hydroxyl group to two hydroxyl functions enabled further ROP to the 2G polymer. The IG polymer synthesized by this procedure was a 6-arm star-branched PcCL. The target dendrimer-like star-branched polymer was obtained as a 2G polymer by the second iteration and possessed a minimum architectural unit. One more repetition of the synthetic sequence involving the two reaction steps resulted in a 3G dendrimer-like star-branched PaCL. The 3G polymer possessed six branches at the core and two branches at the junctions in both the 2G- and 3G-based layers, composed of 42 arm segments (6 (IG) + 12 (2G) + 24 (3G) = 42). The observed M value was 96 000 g/mol, close to the theoretical value, and the molecular-weight distribution was not narrow, but an acceptable value of 1.14. 

The modification of polymers can be readily conducted by chemical coupling reactions when the chain to be modified possesses groups such as vinyl, hydroxyl, or azide [23], etc. The Diels-Alder reaction between a diene and a dienophile, discovered by Otto Diels and Kurt Alder in 1928 [24], is the most important example of click chemistry. These robust and efficient click coupling reactions have been widely exploited in the construction of tailor-made functional polymeric materials with complex molecular architectures... 

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