Trithiocarbonate RAFT agents synthesis

The first example of nanogel synthesis by direct RAFT polymerization under precipitation/dis-persion polymerization condition was reported by An et al. in 2007 (Figure 54.27). Two types of poly(A,A -dimethylacrylamide)s (PDMAs) bearing a trithiocarbonate group were first synthesized by RAFT solution polymerization and were subsequently used as both stabilizers and RAFT agents for nanogel synthesis by RAFT precipitation/dispersion polymerization. These two types of... 

Postma et al. (2006) reported the synthesis of well-de ned polystyrene (PSt) with primary amine end groups through the use of phthalimide-functional RAFT agents. Styrene (St) polymerization with the RAFT agent, butyl phthalimidomethyl trithiocarbonate (P25-I), as shown in Scheme PI 1.25.1, was conducted at 110°C with thermal initiation in bulk and the following reaction conditions [RAFT]o = 0.0288 M and [St]o/[RAFT]o = 303, achieving 70% monomer conversion in 24 h to obtain RAFT PSt (P2S-II) with M = 22,400 g mol i and = 1.12. The polymerization was also successfully conducted at 60°C with AIBN... 

Scheme Pll.25.1 Synthesis of polystyrene with primary amine end group through the use of a phthalimide-functional RAFT agent for initiation, removal of trithiocarbonate end group by radical-induced reduction with BusSnH and hydrazinolysis of phthalimido end group. (Adapted from Postma et al., 2006.)...

VPr), and simifar monomers. Other RAFT agents may be required for soiubifity or compatibility with particular polymerization media or to provide specific end-group functionality. Hie rrse of bis- and multi-RAFT agents (see Section 3.07.3.4.4) permits the synthesis of polymers with complex architectmes. Symmetrical trithiocarbonates can be considered as a member of the class of bis-RAFT agents. 

Radical-induced decomposition of a bis(thioacyl) dtsw/-This is probably the most used method for the synthesis of RAFT agents requiring tertiary R groups. An example is the synthesis of the tertiary trithiocarbonate (Scheme 22). °° The source of radicals may also be an ATRP... 

Reaction of thiochloroformate with thiol The esterification of the appropriate thiol with a thiochloroformate (Scheme 28) has been used in the synthesis of phenyl xanthates and phenyl trithiocarbonates. This method was also used to synthesize the T-RAFT agent 173. " The thiochloroformate may be replaced with the corresponding imidazole to avoid use of thiophosgene. ... 

Use of a bis-RAFT agent allows the direct synthesis of triblock copolymers in a one-pot reaction. Bis-RAFT agents are described in Table 12 (bis-dithioesters). Table 16 (bis-trithiocarbonates), and Table 18 (bis-dithiocarbamates). The RAFT agent functionalities may be connected through the Z or R groups to give ABA (Scheme 35) or BAB blocks (Scheme 36), respectively. The limitations of the two forms... 

Scheme 6.12 ABA triblock synthesis from Z-connected bis-RAFT agents (w= 1) or symmetrical trithiocarbonates n = 0).

The synthesis of DAAmEP was conducted in three steps. The first step was a Michaelis-Arhuzov reaction between N-(2-bromoethyl)phthalimide and an excess of triethyl phosphite under reflux at 160 °C for 12 h. In the second step, the reaction between the resulting phthalimide and hydrazine led to the formation of (2-aminoethyl)phosphonic acid diethyl ester. The final step consisted of the reaction between the actyloyl chloride and the diethyl ester, which was achieved in the presence of poly(4-vinylpyridine), 2% crosslinked, to trap the hydrochloric acid produced during the acryloylation. The final DAAmEP monomer was obtained after purification by chromatography on silica gel. All intermediate products were characterized by H and P NMR. The H NMR spectrum of the DAAmEP monomer allowed validation of the expected chemical structure and as a consequence the synthetic pathway. RAFT homopolymerization of DAAmEP was carried out with two different trithiocarbonate chain transfer agents (see Scheme 2.6). 

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