UV radiation, grafting

Parquet P, Padeste C, Solak HH, Gursel SA, Scherer GG, Wokaun A. Extreme UV radiation grafting of glycidyl methacrylate nanostructures onto fluoropolymer foils by RAFT-mediated polymerization. Macromolecules 2008 41(17) 6309-16. 

The first method, although effective, was soon abandoned for safety reasons, while the use of chromic acid has been largely discontinued. The other two have remained the most widely used pre-treatments, not only for LDPE but also for high-density polyethylene (HDPE) and polypropylene (PP). Other methods have been found to be effective, but for reasons of cost, safety or convenience, they have not been widely used. The pre-treatments include fuming nitric acid, potassium permanganate, ammonium peroxydisulphate, ozone, fluorine, peroxides, UV radiation, grafting of polar monomers, plasmas (see Plasma pretreatment), electrochemical oxidation (see Electrochemical pre-treatment of polymers) and the use of solvent vapours. The corona, flame and plasma methods and the use of trichloroethylene are now discussed briefly the latter is included because it involves a different mechanism. 

The reaction between Cell—O radical and vinyl monomers leads to the formation of grafted cellulose. In the presence of photosensitizers generally used as photoinitiators, such as benzophenone and phenylace-tophenone derivatives, the photoinitiator absorbs the UV radiation and transforms to its singlet (S ) and then triplet (T ) states. After that it may decompose into free radicals or transfer its energy to cellulose or any other molecules in the system. Take benzophenone as an example ... 

Graft polymerization can also be achieved by irradiation with ultraviolet radiation, often in the presence of a photosensitizer such as benzophenone or benzoin [Guthrie et al., 1979 Tazuke and Kimura, 1978], Photolytic grafting is similar to radiation grafting, except that the depth of penetration by UV is far less than by ionizing radiation. 

In the simultaneous method, which is the one most commonly used, the substrate is irradiated while in direct contact with the monomer. The monomer can be present as a vapor, liquid, or solution. This grafting process can occur via free radial or ionic mechanism. With the simultaneous method, the formation of homopol5mier is unavoidable, but there are several systems to minimize it. The advantage of this method is that both monomer and substrate are exposed to the radiation source and both form reactive sites. The other two techniques rely upon rupture of the bond to form reactive sites, and therefore require higher radiation doses. Thus, the simultaneous method is more suitable for substrates sensitive to radiation. The simultaneous method can utilize UV radiation besides EB source. Logically, the UV irradiation requires a photoinitiator or sensitizer to achieve an acceptable level of grafting. 

The energy associated with UV light is in competence with the chemical bond energies associated with any two atoms [104]. Hence, UV radiation often has the potential for retention of the properties of monomers and polymers while the other surface grafting techniques, which use ionisation radiation, cause damage to the substrate polymer due to excessive degradation. 

Both UV and ionizing radiation grafting procedures were modifications of previously reported methods (7,13). Monomers were purchased from Monsanto Chemicals (Australia) Limited and Polysciences Incorporated. Inhibitor was removed prior to reaction by passing the monomer down a column of activated alumina (13). All solvents were AR grade and used without further purification. 

Photolithography on the basis of the cationic graft-polymerization uses an inert polymer film containing a PAQ coated onto a wafer. Exposing the photoresist to the UV radiation generates acid on its surface, to which a vapor-phase silicon-containing monomer is grafted. RIE in O2 is used as a final step. ° ... 

Novel Additives for Enhancing UV and Radiation Grafting of Monomers to Polymers and Use of These Copolymers as Ion Exchange Resins... 

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