Free-radical grafting glycol

Poly( ethylene oxide)-block-poly (propylene oxide)-hZock-poly(ethylene oxide)-g-poly(acrylic acid) (PEO-fc-PPO-fc-PEO-g-PAA, Pluronic-PAA) graft copolymers were synthesized by free radical grafting copolymerization of acrylic acid monomers onto PEO-h-PPO-h-PEO (Pluronic F127) and the aqueous solution properties were characterized by Bromberg [133, 134]. Chiu et al. [135] reported on the micellization of (non-ionic) poly(stearyl methacrylate)-gra/f-poly(ethylene glycol) graft copolymers. 

Acrylic acid and derivatives have been free radically grafted onto the backbone of biodegradable polycaprolactone and poly(lactic-co-glycolic acid). These functionalized biocompatible materials are useful as drug delivery agents. 

Wang used reactive-extrusion polymerization with 2,5-di-methyl-2,5-di-t-bu-tylperoxy hexane to prepared a graft copolymer, (11), by free radically grafting polyethylene-glycol malonic acid onto the biodegradable substrate of poly((3-hydroxybutyrate-co- p-hydroxy valerate). 

This technique is based in the fact that when cellulose is oxidized by ceric salts such as ceric ammonium nitrate Ce(NH4)2(N03)6 free radicals capable of initiating vinyl polymerization are formed on the cellulose. However, the possibility remains that the radical formed is an oxygen radical or that the radical is formed on the C-2 or C-3 instead of the C-6 carbon atom. Another mechanism, proposed by Livshits and coworkers [13], involves the oxidation of the glycolic portion of the an-hydroglucose unit. Several workers [14,15], however, have found evidence for the formation of some homopolymer. In the ceric ion method free radicals are first generated and are then capable of initiating the grafting process [16-18]. 

PEG molecules which are relatively nontoxic and capable of reducing the interaction between the blood components and man-made materials, can be also tethered to a polymer surface through surface grafting. This has been achieved by free-radical polymerization of methacrylate monomers carrying a pendant PEG chain [71-73]. For instance, the surface of a PU film was subjected to UY-induced graft polymerization of methoxy-PEG methacrylate monomers with numbers of ethylene glycol (EG) units of 4, 9, and 23 [74]. As shown in Fig. 14, the monomer with the shortest PEG length of only 4 EG... 

TABLE 1. Biodegradable poly[(lactic-co-glycolic acid) substrates free radically functionalized with grafted acrylic acid or 2-hydroxylethyl acrylate. 

Graft copolymers were prepared by both classical strategies, that is, from enzymatically obtained macromonomers by subsequent chemical polymerization and by enzymatic grafting from hydroxyl functional polymers. Kalra et al. studied the synthesis of PPDL graft copolymers from macromonomers, which were obtained by the enzymatic ROP of pentadecalactone (PDL) from hydroxyethyl methacrylate (HEMA) and polyethylene glycol) methacrylate (PEGMA) [40]. Subsequently graft copolymers were obtained by free radical polymerization of the macromonomers. A similar approach was published by Srivastava for the HEMA-initiated enzymatic ROP of CL and subsequent free radical polymerization [41]. 

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