Reversible Addition−Fragmentation Chain Transfer Polymerization in Microemulsion

Abstract

We have conducted reversible addition−fragmentation chain transfer (RAFT) polymerization of n-hexyl methacrylate solubilized in a microemulsion using dodecyltrimethylammonium bromide as surfactant and 2-cyanoprop-2-yl dithiobenzoate (1) as the RAFT agent. The resulting latex particles are stable and much smaller, ranging from 18 to 30 nm depending on the mole ratio of RAFT agent 1 to the free radical initiator, 2,2‘-azobis(2-amidinopropane) hydrochloride (V50), than those produced by conventional microemulsion polymerization. The molecular weight increases linearly with conversion, and the polydispersity remains low when the number of RAFT agent molecules used is in excess of the initial number of swollen micelles. The RAFT technique can be successfully used in microemulsion polymerization to produce stable dispersions of small particles containing low molecular weight polymers. This is believed to be the first report of RAFT polymerization in microemulsion.

Block copolymer synthesis by controlled/living radical polymerisation in heterogeneous systems

“…72, 73 An intrinsic feature of all CLRP in dispersed systems is the fact that within small particle sizes, such as in microemulsions, there can be an intrinsic broadening effect on the molecular weight distribution due to a statistical variation in the number of control agents between particles. 74 This is closely related to the phenomenon of compartmentalisation, 75,76 which refers to the physical confinement of reactants to nano-size spaces, and is typically observed for particles with d <100 nm. Compartmentalisation can cause problems depending on the specific conditions/system, but may also lead to improvements in both control and livingness.…”

Polimerização RAFT em Miniemulsão

“…Dessa forma, o uso da técnica de polimerização RAFT oferece inúmeras vantagens para a síntese de polímeros para aplicações biotecnológicas [15,17] , dentre as quais podem ser citados quatro principais pontos: (i) a possibilidade do uso de uma grande variedade de monômeros e solventes [7,18] ; (ii) o uso da técnica RAFT possibilita também a síntese de polímeros com diversos tipos de arquitetura molecular [7,16] ; (iii) o fato da técnica de polimerização RAFT ter sido adaptada para uso em diferentes sistemas de polimerização [34,[142][143][144] , incluindo a miniemulsão direta [34,35] e inversa [52] ; e (iv) a baixa toxicidade de alguns agentes RAFT empregados nas polimerizações [145,146] . Isso possibilita o uso da técnica RAFT na síntese de nanogéis biodegradéveis e com partículas menores que 200 nm, utilizando um sistema de miniemulsão inversa, por exemplo [23] .…”

Microstructure, Kinetics, and Transport in Oil‐in‐Water Microemulsion Polymerizations

“…The partitioning of chain transfer agents in reversible addition-fragmentation chain transfer (RAFT) microemulsion polymerization has been shown to impact the degree of control imparted to the polymerization. [20] In atom transfer radical polymerization (ATRP), the hydrophobicity of the ligand and the copper complex are crucial parameters for controlling the polymerization. [21] Oil-in-Water Microemulsion Polymerization Kinetics…”

“…However, uncertainties in the reaction mechanism remain, particularly with respect to possible termination of the intermediate macroRAFT radicals. Recently, Liu et al have successfully incorporated RAFT into the microemulsion polymerization of hexyl methacrylate [20] to produce stable latex nanoparticles that contain polymers of controlled molecular weight and low polydispersity. As the concentration of the chain transfer agent cyanoprop-2-yl dithiobenzoate (CPDB) increased, the rate of polymerization decreased and the percent conversion at the rate maximum shifted first to higher conversions than the predicted value of 39% from the Morgan model, and then to lower conversions.…”