Reversible Addition Fragmentation Transfer RAFT

To make further use of the azo-initiator, tethered diblock copolymers were prepared using reversible addition fragmentation transfer (RAFT) polymerization. Baum and co-workers [51] were able to make PS diblock copolymer brushes with either PMMA or poly(dimethylacrylamide) (PDMA) from a surface immobihzed azo-initiator in the presence of 2-phenylprop-2-yl dithiobenzoate as a chain transfer agent (Scheme 3). The properties of the diblock copolymer brushes produced can be seen in Table 1. The addition of a free initiator, 2,2 -azobisisobutyronitrile (AIBN), was required in order to obtain a controlled polymerization and resulted in the formation of free polymer chains in solution. 

A polyhedron silsesquioxane ladder polymer containing polymerizable components was prepared in a three-step process to address this concern. The process initially entailed preparing the reversible addition-fragmentation transfer (RAFT) ladder iniferter, polysilsesquioxane dithiocarbamate. This intermediate was then polymerized with methyl methacrylate at ambient temperature by irradiating with ultraviolet (UV) light and poly(si Isesquioxane-g-methyl methacrylate) was obtained. 

Uzulina, I., Kanagasapatty, S. and Claverie, J. (2000) Reversible addition fragmentation transfer (RAFT) polymerisation in emulsion. Macromol. Symp., 150, 33-8. 

Conversely it is possible to produce low-molar-mass oligomers or telomers by deliberately choosing an agent with a large value of Ca (e.g. methyl mercaptan, Ca 2x 10 in styrene), so that DP is reduced to 5 for a concentration of 0.001%. Further particular examples of chain transfer (e.g. to polymer to form branches) will be discussed later, together with the use of reversible-addition fragmentation transfer (RAFT) and other radical-mediated synthetic strategies. 

The fifty chapters submitted for publication in the ACS Symposium series could not fit into one volume and therefore we decided to split them into two volumes. In order to balance the size of each volume we did not divide the chapters into volumes related to mechanisms and materials but rather to those related to atom transfer radical polymerization (ATRP) and to other controlled/living radical polymerization methods reversible-addition fragmentation transfer (RAFT) and other degenerative transfer techniques, as well as stable free radical pol5mierizations (SFRP) including nitroxide mediated polymerization (NMP) and organometallic mediated radical polymerization (OMRP). 

Controlled Radical Polymerization (CRP) is the most recently developed polymerization technology for the preparation of well defined functional materials. Three recently developed CRP processes are based upon forming a dynamic equilibrium between active and dormant species that provides a slower more controlled chain growth than conventional radical polymerization. Nitroxide Mediated Polymerization (NMP), Atom Transfer Radical Polymerization (ATRP) and Reversible Addition Fragmentation Transfer (RAFT) have been developed, and improved, over the past two decades, to provide control over radical polymerization processes. This chapter discusses the patents issued on ATRP initiation procedures, new functional materials prepared by CRP, and discusses recent improvements in all three CRP processes. However the ultimate measure of success for any CRP system is the preparation of conunercially viable products using acceptable economical manufacturing procedures. 

The other CRP process to be disclosed in the 1990 s relies on degenerative transfer of an atom or group and is best exemplified by the reversible addition-fragmentation transfer (RAFT) process that employs dithioesters as chain-transfer agents which was introduced in 1998. (17-19)... 

There are several techniques for performing CRP, but the most popular and successful ones so far are as follows stable free radical (SFR) or nitroxide-mediated radical polymerization (NMRP) [44, 45, 49], atom transfer radical polymerization (ATRP) [50, 51], and degenerative transfer techniques, including particularly reversible addition-fragmentation transfer (RAFT) polymerization [3]. These are examined in some detail in the following sections. 

Controlled/ living radical polymerization (CLRP) processes are well-established synthetic routes for the production of well-defined, low-molecular weight-dispersity polymers [99]. The types of CLRP processes (initiator-transfer agent-terminator (INIFERTER), atom transfer radical polymerization (ATRP), nitroxide-mediated radical (NMRP) polymerization, reversible addition-fragmentation transfer (RAFT)) and their characteristics are described in Section 3.8 of Chapter 3 and in Section 14.8 of Chapter 14. 

Luo Y, Gu H (2007) Nanoencapsulation via interfaciaUy confined reversible addition fragmentation transfer (RAFT) miniemulsion polymerization. Polymer 48 3262-3272... 

It is of obvious interest to explore the use of other polymerization techniques that, being more tolerant to the experimental conditions and monomers, can produce amphiphilie azobenzene BCPs with no need for post reactions. Notably, Su et al. have reeently reported the synthesis of such an amphiphilic diblock copolymer with PAA as the hydrophilic block using reversible addition-fragmentation transfer (RAFT) polymerization (structure d in Fig. 6.2) (Su et al., 2007). Using RAFT, they prepared PAA capped with dithiobenzoate and used it as the macro-RAFT transfer agent to polymerize the hydrophobic azobenzene polymer successfully. It ean be expected that more amphiphilic azobenzene BCPs will be synthesized using the eontrolled radical polymerization techniques (ATRP and RAFT) because of their simplicity, versatility, and efficiency. 

Several acronyms are used to describe these polymerizations Reversible Addition-Fragmentation Transfer (RAFT), Group transfer polymerization, Ring Opening Metathesis Polymerization (ROMP), Group Transfer polymerization. 

Heterogeneous controlled radical polymerization Reversible addition fragmentation transfer (RAFT) process... 

Molecularly imprinted polymers (MIPs) that are capable of sensing specific organophosphorus compounds, such as pinacolyl methylphosphonate (PMP), by luminescence have been synthesized and characterized. The polymers have been synthesized using conventional free radical polymerization and using Reversible Addition Fragmentation Transfer (RAFT) polymerization. The RAFT polymers exhibited many advantages over conventional free radical processes but are more difficult to make porous. 

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