Elastomer synthesis controlled radical polymerization

Several other methods for controlled radical polymerization have been developed and should be applicable to elastomer synthesis (Matyjaszewski, 1998, 2000). One of the other most important systems for controlled radical polymerization is atom transfer radical polymerization (ATRP) (Matyjaszewski and Xia, 2001). A transition metal (Mt) catalyst participates in an oxidation-reduction equilibrium by reversibly transferring an atom, often a halogen, from a dormant species (initiator or polymer chain) as shown below. 

Here, we report on the synthesis and characterization of PMMA-poly(/i-butylacrylate)-PMMA (MBuM) symmetric triblock copolymers, as a new family of thermoplastic elastomers. These compounds have be prepared by a novel route based on controlled radical polymerization [4]. Compared to classical anionic living polymerization [5], this new route, sketched in Scheme la, appears particularly appealing since the triblock copolymers are prepared in a two-step process instead of the usual three steps required in anionic polymerization. In the latter case, as butylacrylate cannot be polymerized via a living process, the MBuM symmetric triblocks have to be synthesized by sequential copolymerization of er butylacrylate (tBuA) and MMA followed by the transalcoholysis of the tBu esters with n-butanol... 

A controlled free radical polymerization technique was also used, namely, atom transfer radical polymerization (ATRP), to synthesize ATE on the basis of ABA triblock copolymers (Fig. 11.3b) (Cui et al., 2004). The triblock copolymer was designed to have a rubbery midblock of poly(n-butyl acrylate) (PnBA) and two end blocks of poly 6-[4-(4-methoxyphenylazo)phenoxy]hexyl methacrylate) (PAzoMA) that is azo-SCLCP. For synthesis, a dibromo initiator, namely, l,l -biphenyl-4,4 -bis(2-bromoisobutyrate), can first be used to prepare the dibromo PnBA macroinitiator, which is then used to polymerize the azobenzene methacrylate monomer to yield the two end blocks of PAzoMA. This ATE is different from azo-SCLCP-grafted SBS. It is a thermoplastic elastomer, in which... 

Moineau, G., et al. (2000). Synthesis of fully acrylic thermoplastic elastomers by atom transfer radical polymerization (ATRP). 2. Effect of the catalyst on the molecular control and the rheological properties of the triblock copol5mers. Macromol. Chem. Phys., 20/(11) 1108-1114. 

Controlled/living radical polymerisation (CRP) is currently a fast developing area in polymer synthesis and it allows preparation of many advanced polymeric materials, including thermoplastic elastomers, surfactants, gels, coatings, biomaterials, materials for electronics and many others. 

The synthesis of elastomers by step, chain, and ring-opening polymerizations is reviewed. These reactions are characterized as to the process variables which must be controlled to achieve the synthesis and crosslinking of an elastomer of the required structure. Both radical and ionic chain polymerizations are discussed as well as the structural variations possible through copolymerization and s tereoregularity. 

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