Coupling polymer termini

Thiol-ene coupling was also used for the end-functionaHzation of PNIPAM in an analogous study conducted by the groups of Lowe and Hoyle [55]. In this case, PNIPAM was prepared by RAFT polymerization, followed by the aminolysis of the thiocarbonylthio end group to produce a terminal thiol simultaneous Michael addition with aUyl methacrylate yielded the alkene mono end-functional PNIPAM. The polymer terminus was then modified via a radical thiol-ene dick reaction with three different mercaptans to afford a series of PNIPAM polymers with varied LCSTs (Scheme 30.5). 

Coupling of allyl group to the terminus of another polymer... 

The Liquid-Phase Method (LPS) developed by Mutter and Bayer combines the advantages of a polymer-supported technique with those of a synthesis carried out under homogmeous reaction conditions. The C-terminal amino acid is coupled to a mono- or bifiinctional poly(ox thyl )e) (POE-M, POE), and the extension of the peptide towards the N-terminus takes place step by step. Unlike the solid-phase method, the LPS aisures coupling and deprotection in homogeneous solution. Excess low-molecular reagents are removed by precipitation of the POE-peptide with diethyl ether ch- by crystallization from ethanol or methanol. 

For modular synthesis of ABC-type triblock copolymer, two successive CuAAC reactions have to be performed on the central polymer chain (B block). To accomplish this, the B block polymer having both azide and acetylene end groups (heterotelechelic B) has to be used and, moreover, one of the termini has to be protected in order to prevent linear chain extension (cf Scheme P12.2.1) or formation of cyclic products (Scheme P12.4.1). In a straightforward methodology, the terminal acetylene moiety on B is protected and the azide terminus is used to carry out the rst coupling reaction to join the preformed A or C block. Next, the acetylene moiety is to be deprotected to make it available for the second coupling reaction to join the remaining C or A block. 

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