Radical initiated double ring-opening polymerization

Scheme 2.5 Unsaturated polyester formation with low volume shrinkage by radical initiated double ring-opening polymerization [23].

In contrast, here a bifunctional initiator is employed and the polymerization order of the two blocks is inverted In a first step, the styrene block is synthesized by atom transfer radical polymerization (ATRP) followed by the addition of lactide via the recently developed organocatalytic ring-opening polymerization, as depicted in Fig. 3.1 [4, 5]. This synthesis route reduces the involved steps and enables a simplified and time-efficient preparation of copolymers with different block compositions. Importantly, both polymerization techniques offer precise and robust control over the copolymer composition, which is an essential requirement to reliably target the double-gyroid s narrow location in phase space [6]. 

Summary A double-headed initiator was synthesized yielding two functional groups for the initiation of the nickel mediated ring-opening polymerization of y-benzyl-L-glutamate-N-carboxyanhydride and controlled radical polymerization of vinyl monomers via ATRP or NMP. Well-defined block copolymers combining polypeptides and synthetic polymers were obtained. 

Lactide polymerization with the addition of tin octoate is proposed via the coordination—insertion mechanism, as shown in Figure 2.10 (Henton, et al., 2005). The tin catalyst initiates the ring-opening reaction by attacking the nearest double-bond oxygen of the lactide. The hydroxyl and nucleophilic species simultaneously react with the ring-opened radical and finally... 

The first route relies on the ROP of cyclic ketene acetals [1-3]. The electron-rich double bond is prone to react with radicals and electrophiles. Therefore, this class of monomers undergoes cationic and radical polymerization. For example, radical initiators react with the double bond to provide a new tertiary radical (Fig. 2). Two distinct mechanisms of polymerization can then take place direct vinyl polymerization or indirect ring opening of the cycle accompanied by the formation of a new radical, which is the propagating species (Fig. 2). The ester function is formed... 

The addition of the growing radical to the double bond is analogous to the first step of 1-5 addition, but apparently conformational restraints caused by the cyclobutane ring prevents normal cyclopropyl ring opening. Instead a hydrogen shift resulting in a resonance-stabilized radical takes place. The possibility of initial thermal isomerization followed by polymerization was excluded because monomer 13 when heated in the presence of DPPH did not isomerize or lymerize. 

Acrylic acid, methacrylic acid, or maleic acid ring opening of epoxidized PBD give access to hydroxyl esters with an a,p-unsaturated double bond next to a carbonyl group. The acrylic derivatives are much more reactive in radical polymerizations than the double bonds of PBD. Peroxide-initiated copolymerization of PBD with acrylic esters and styrene proceeds readily to give hard and tough resins... 

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