A high level of control over the photoinitiated RAFT polymerization of vinyl acetate (VAc) was achieved using a specifically designed xanthate, S-2-cyano-2-propyl-O-ethyl xanthate (CPEC), which acted as a radical source and a chain transfer agent simultaneously. Unlike other RAFT processes, the present system did not use any additional radical initiator, while achieving greater control over the polymerization than the photoiniferter process. The molecular weight of the resulting polymer could be modulated by changing the initial [VAc]0/[CPEC]0 ratio, but the control over the polymerization was lost with a very low initial [VAc]0/[CPEC]0 ratio. The intensity of UV irradiation affected the polymerization by reducing the induction period and increasing the rate of polymerization but did not affect the molecular weight of the resulting polymer.

Chemotherapy is a widely adopted method for the treatment of cancer. However, its use is often limited due to side effects produced by anti-cancer drugs. Therefore, various drug carriers, including polymeric micelles, have been investigated to find a method to overcome this limitation. In this study, alginate-based, self-assembled polymeric micelles were designed and prepared using alginate-g-poly(N-isopropylacrylamide) (PNIPAAm). Amino-PNIPAAm was chemically introduced to the alginate backbone via carbodiimide chemistry. The resulting polymer was dissolved in distilled water at room temperature and formed self-assembled micelles at 37 °C. Characteristics of alginate-g-PNIPAAm micelles were dependent on the molecular weight of PNIPAAm, the degree of substitution, and the polymer concentration. Doxorubicin (DOX), a model anti-cancer drug, was efficiently encapsulated in alginate-g-PNIPAAm micelles, and sustained release of DOX from the micelles was achieved at 37 °C in vitro. These micelles accumulated at the tumor site of a tumor-bearing mouse model as a result of the enhanced permeability and retention effect. Interestingly, DOX-loaded alginate-g-PNIPAAm micelles showed excellent anti-cancer therapeutic efficacy in a mouse model without any significant side effects. This approach to designing and tailoring natural polymer-based systems to fabricate nanoparticles at human body temperature may provide a useful means for cancer imaging and therapy.

A photoinitiation process was investigated to develop a rapid and well-controlled RAFT polymerization method applied to vinyl acetate (VAc) using methyl (ethoxycarbonothioyl)sulfanyl acetate (MESA) and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide as the RAFT agent and photoinitiator, respectively. MESA was selected as the photochemically inert RAFT agent to minimize photolysis of the thiocarbonylthio groups during polymerization. Poly(vinyl acetate) with a prespecified well-controlled molecular weight (MW) and a narrow MW distribution was successfully synthesized. The polymerization reaction proceeded as a living polymerization and was remarkably rapid compared with approaches that use thermally initiated processes with a very short induction period. A detailed kinetic study of the mechanism underlying the polymerization reaction, however, revealed that the chain ends containing xanthate moieties were not perfectly stable upon UVirradiation, and they generated radicals via homolytic cleavage. This reaction appeared to proceed by a combination of a degenerative transfer RAFT mechanism and a dissociation-combination mechanism.

Performance requirements for extreme UV ͑EUV͒ resists will require the development of polymer platforms. A challenge in designing photoresists for EUV wavelengths is the selection of molecular structures that have minimal absorbance. For example, elements that are commonly used in photoresists at other wavelengths, such as oxygen and fluorine, are highly absorbing at ϳ13 nm making them problematic for EUV applications. In order to provide a tool for EUV resist design, this article presents a study of the absorbance of common photoresist structures and compares it to theoretical estimates of resist absorbance based on composition and density. On this basis, several potential structures suitable for EUV resists are assessed.

Fluorinated polymers form an interesting class of materials with a wealth of unique properties including self-assembly, remarkably low surface energies, low absorbance to 157 nm UV light, and solubility in supercritical carbon dioxide. As a result many fluorinated polymers are of use in advanced technology applications. We review some of our work on the synthesis and characterization of block copolymers with fluorinated side chains, with special emphasis on surfaces formed using these polymers. The use of fluorinated polymers as photoresists for 157 nm lithography, with the possibility for processing in environmentally friendly supercritical carbon dioxide is also discussed.