Atom transfer radical polymerization crosslinking

This was utilized by Tian et al. to prepare a new elass of liquid erystal homopolymers of poly ll-[4- (3-ethoxycarbonyl- eoumarin- 7-oxy)-earbonyl-phenyloxy]-undecyl methacrylate containing a eoumarin moiety as a photo-crosslinkable unit. The preparations included polymers of various chain lengths. Also, liquid crystalline-coil diblock and liquid crystalline-coil-liquid crystalline triblock copolymers with polystyrene as the coil segment were formed. The polymers were reported to have been synthesized with the aid of atom transfer radical polymerization. The dimerization of the eoumarin moieties takes place upon irradiation with light of > 300 nm to yield crosslinked network structures. 

Mu B, Shen RP, Liu P (2009) Crosslinked polymeric nanocapsules from polymer brushes grafted silica nanoparticles via surface initiated atom transfer radical polymerization. Colloid SurfB 74 511-515... 

Even with the successes of these methods, synthesis of selective membrane skins with minimal (< 50 nm) thicknesses is still difficult. Balachandra et at [47] described the use of room-temperature atom transfer radical polymerization (ATRP) from a substrate to synthesize two types of ultrathin ( 50 nm) polymer skins crosslinked poly(ethylene glycol dimethacrylate) (PEGDMA) and linear poly(2-hydroxyethyl methacrylate) (PHEMA). 

Mu, B. and Liu, P. (2012). Temperature and pH dual responsive crosslinked polymeric nanocapsules via surface-initiated atom transfer radical polymerization. Reactive and Functional Polymers, 72,983-989. 

Each of these reactions and their reverse reactions may, in fact, be involved in major reaction pathways in coal conversion. Reaction 10, for instance, is expected to be a key step in H-transfer and aromatization, reaction 11 can lead to crosslinking and polymerization while reaction -11 breaks up complex molecules, and reaction 12 should provide a steady source of free radicals in many pyrolytic systems even in the absence of weak covalent bonds (vide infra). Furthermore, these free radicals contain weak C-H bonds that may rupture to yield H atoms, which can in turn lead to breaking of C-C or C-0 bonds through aromatic displacement reactions (reaction 5). 

During the following half-century, polymer chemists learned that curing or drying oleoresinous paints in the presence of heavy metal salts ( driers ) and air involved forming hydroperoxides on the carbon atoms adjacent to the ethylenic bonds in the unsaturated oils. In the accepted mechanism, the carbon-carbon double bond shifts to a conjugated configuration, and the peroxide is transferred to another monoallylic carbon atom. Polymerization proceeds via a radical chain mechanism to produce a crosslinked insoluble film. 

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