Universal iterative strategy for the divergent synthesis of dendritic macromolecules from conventional monomers by a combination of living radical polymerization and irreversible TERminator multifunctional INItiator (TERMINI)

A new synthetic concept named TERMINI that stands for irreversible TERminator Multifunctional INItiator is reported. Suitable combinations of TERMINI and living polymerizations provide access to strategies for the design and synthesis of unprecedented complex molecular and macromolecular architectures from a diversity of commercial monomers. TERMINI represents a masked multifunctional initiator designed to quantitatively and irreversibly interrupt a chain organic reaction or a living polymerization. After demasking, the TERMINI repeat unit enables the quantitative reinitiation, in the presence or absence of a catalyst, of the same or a different living polymerization or a chain organic reaction in more than one direction, thus becoming a branching point. The demonstration of this concept was made by using a combination of metal-catalyzed living radical polymerization (LRP) and (1,1-dimethylethyl)[[1-[3,5-bis(S-phenyl 4-N,N'-diethylthiocarbamate)phenyl]ethenyl]oxy]dimethylsilane as TERMINI, to elaborate a novel iterative divergent method for the synthesis of dendritic macromolecules based on methyl methacrylate (MMA).     

Synthesis of dendrimers through divergent iterative thio‐bromo “Click” chemistry

The development of a novel nucleophilic thio‐bromo “Click” reaction, specifically base‐mediated thioetherification of thioglycerol with α‐bromoesters, is reported. Combination of this thio‐bromo click reaction with subsequent acylation with 2‐bromopropionyl bromide provides an iterative two‐step divergent growth approach to the synthesis of a new class of poly(thioglycerol‐2‐propionate) (PTP) dendrimers. This approach is demonstrated in the rapid preparation of four generation (G1–G4) of PTP dendrimers with high‐structural fidelity. The isolated G1–G4 bromide‐terminated dendrimers can be used directly as dendritic macroinitiators for the synthesis of star‐polymers via SET‐LRP. Additionally, the intermediate hydroxy‐terminated dendrimers are analogs of other water‐soluble polyester and polyether dendrimers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3931–3939, 2009     

Implications of monomer and initiator structure on the dissociative electron‐transfer step of SET‐LRP

The heterolytic dissociation process associated with the activation of Single Electron‐Transfer Living Radical Polymerization is examined through the use of energy profile modeling. Monomer and initiator structure is correlated with the approximate activation barriers, energies of electrostatic ion‐radical pair formation, and stability of ion‐radical pair generated from the counteranion halide leaving group and the radical atom with partial positive charge density induced by its electron‐withdrawing substituent. Energy profiles permit access not just to one, but to all local minima, in the dissociation pathway and the identification of a global minimum. The location and energy of this global minimum allows for the placement of various initiators and dormant propagating macroradicals on the spectrum between stepwise and concerted dissociative electron‐transfer. The barrier for the activation step for alkyl‐halides derived from acrylates, vinyl halides, and styrenes, as well as from initiators bearing electron‐withdrawing groups is decreased in comparison to relatively more electron‐rich alkyl halides. This rate enhancement is explained through the sticky dissociative model wherein electron‐transfer is accelerated by the formation of strong ion‐radical pairs between radicals with partial positive charge density and their counteranion leaving group. Greater electron‐withdrawing capacity of the alkyl halide substituent increases the stability of the ion‐radical pair, reduces its equilibrium bond length, and accelerates electron‐transfer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5663–5697, 2008     

Soluble polyarylenes containing alternating binaphthylene and biphenylene structural units

This article describes the synthesis of a novel series of soluble polyarylenes containing alternating binapthylene and biphenylene structural units. They were obtained by the cation-radical polymerization of bis(1-naphthyl) biphenyls. The following monomers were synthesized and polymerized : 4,4′-bis(1-naphthyl) biphenyl ( 9 ), 3,3′-bis(1-naphthyl) biphenyl ( 10 ), 2,2′-bis(1-naphthyl)biphenyl ( 11 ), and 2,5-bis(1-naphthyl)biphenyl ( 14 ). All polymerizations were performed in nitrobenzene using FeCl₃ as oxidant. Polymers with number average molecular weights of up to 4000 g/mol were obtained.     

Functionalization of the active chain ends of poly(vinyl chloride) obtained by single‐electron‐transfer/degenerative‐chain‐transfer mediated living radical polymerization: Synthesis of telechelic α,ω‐di(hydroxy)poly(vinyl chloride)

The chloroiodomethyl chain ends of poly(vinyl chloride) (PVC) obtained by the single‐electron‐transfer/degenerative‐chain‐transfer mediated living radical polymerization of vinyl chloride initiated with iodoform were quantitatively functionalized by the reaction with 2‐allyloxyethanol (CH₂?CHCH₂OCH₂CH₂OH). This reaction was performed in dimethyl sulfoxide at 70 °C and was catalyzed by sodium dithionite/sodium bicarbonate. The resulting product is the first example of telechelic PVC [α,ω‐di(hydroxy)PVC]. A possible mechanism for this reaction was suggested. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1255–1260, 2005