RAFT polymerization molar mass

The temperature optimization for the RAFT polymerization of EAA revealed an optimum reaction temperature of 70 °C. Block copolymers with a poly(methyl acrylate) (PMA), a poly(n-butyl acrylate) (PnBA), a PMMA, or a poly(A,A-dimethyl aminoethyl methacrylate) (PDMAEMA) first block and a poly(l-ethoxyethyl acrylate) (PEEA) second block were successfully synthesized in an automated synthesizer. The synthesis robot was employed for the preparation of 16 block copolymers consisting of 25 units of the first block composed of PMA (exp. 1 ), PnBA (exp. 5-8), PMMA (exp. 9-13), and PDMAEMA (exp. 13-16) and a second block of PEEA consisting of 25, 50, 75, or 100 units, respectively. The first blocks were polymerized for 3 h and a sample from each reaction was withdrawn for SEC analysis. Subsequently, EAA was added and the reactions were continued for 12 h. The molar masses and PDI values of the obtained block copolymers are shown in Fig. 15. 

With the development of controlled radical polymerization techniques like nitroxide-mediated radical polymerization (NMRP), atom transfer radical polymerization (ATRP), and reversible addition fragmentation chain transfer (RAFT) polymerization (see Section 3.2), the field of linear glycopolymers has significantly flourished, especially as control of molar mass and monomer sequence has become available, even for functionalized monomers. This enables incorporation of new and more complex glycomonomers as well as allows controlled dispersity, end group functionality, and monomer sequences in block, star-shaped, and graft copolymers, and eventually... 

Rieger and coworkers [332] reported a surfactant free RAFT emulsion polymerization of butyl acrylate and styrene using poly(A,iV-dimethylacrylamide) trithiocarbonate macromolecular transfer agent. They observed that the polymerizations were fast and controlled with molar masses that matched well the theoretical values and low polydispersity indexes. Monomer conversions close to 100% were reached and the polymerizations behaved as controlled systems, even at 40% solids contents. The products were poly(lV,lV-dimethyl acrylamide)-b-poly(/i-butyl acrylate) and poly(Al,Al-dimethylacrylamide)-b-polystyrene amphiphilic diblock copolymers formed in situ. 

The final system that is worth mentioning in this chapter on LRP in emulsion is the use of 1,1-diphenylethylene (DPE) (127). DPE adds to a growing radical and forms a radical with a reactivity too low for propagation. The exact mechanism is not elucidated, but the incorporation of DPE leads to a chain that allows chain extension or block copolymer formation. More or less similar to what was described about the xanthates in RAFT polymerization, here also the molar mass distributions are relatively broad. The greatest advantage of DPE-mediated polymerization is the fact that it results in minimal disturbance of the polymerization process. The product latex does not contain any unusual extractable material (like the catalyst in ATRP), or polymer-bound colored moieties (like the thiocar-bonylthio compound in RAFT). The obvious drawback is the limited control over chain architecture, and the limited understanding of the mechanistic details. 

Automatic continuous online monitoring of polymerization joins other techniques to study and quantify RAFT polymerization kinetics under different conditions [75-77]. The utility of the technique for monitoring RAFT polymerization and to chart changes in kinetics and molar mass evolution as the concentration of RAFT agent is varied was recently demonstrated [78]. 

RAFT in emulsion polymerization The development of RAFT in true emulsion polymerization processes was more challenging than in miniemulsion. A general difficulty of RAFT in aqueous dispersed systems, and particularly emulsion polymerization, is related to the need for a radical initiator in conjunction with the RAFT agent. Consequendy, it is not always easy to control the locus where reversible transfer will take place, and this may have important and sometimes deleterious consequences on the control over molar mass and MMD. Again, the most important parameters to consider are both the water solubility and the reactivity of the chain transfer agent. 

In an analogous manner, copolymers were produced by RAFT polymerization using monomer 7 as comonomer with N-isopropylacrylamide (NIPAAM) (Scheme 12). Thiolactone contents of the final polymers were determined via H-NMR spectroscopy and elemental analysis. The polymers used for the PPM exhibited thiolactone contents between 23 and 32 mol%, with molar masses in the range of 10-20 kDa and low dispersities (D= 1.2-1.3) [52]. 

Guo et al. synthesized a series of block-type amphiphilic copolymers via copolymerization of methacrylate end-capped oligo-urethane and MPS via the sol-gel process [167]. After hydrolysis and condensation of the copolymer precursors (self-assembled in the form of spherical micelles), polyurethane-silica hybrid materials with excellent thermal stability and mechanical properties were obtained. Etmimi et al. synthesized PS-GO nanocomposites via surface RAFT-mediated miniemulsion polymerization [155]. The molar mass and dispersity of PS in the nanocomposites were dependent on the amount of RAFT-grafted GO in the system. The PS-GO nanocomposites were of exfoliated morphology, and their thermal stability and mechanical properties were dependent on the modified GO content and better than those of neat PS polymer. Salami-Kalajahi et al. studied the effect of pristine nanoparticle loading on the properties of PMMA-silica nanocomposites prepared... 

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