Walter Raymond Hertler

Synthesis of reactive-ended acrylic polymers by group transfer polymerization: initiation with silyl ketene acetals

Abstract Living methacrylate polymers are obtained at room temperature and above by initiation with ketene silyl acetals in the presence of a soluble bifluoride catalyst. During the polymerization, a trialkylsilyl group is transferred from the living chain end to incoming monomer. The new procedure has thus been named group transfer polymerization (GTP). Monodisperse polymers with predetermined molecular weights as high as 100,000 can be obtained by adjusting the monomer/initiator ratio. Telechelic poly(methyl methacrylate) with hydroxy or carboxy ends can be obtained by using an initiator containing a protected hydroxy or carboxy group and coupling the resulting living polymer.

Phase behavior of random and ABC triblock methacrylic polyampholytes with poly(vinyl alcohol) in water: effect of pH and salt

Abstract ABC triblock and random methacrylic polyampholytes of molecular weight 4,000 g mol −1 with various base-neutral-acid compositions were examined for their phase separation behavior, each in an aqueous mixture with poly(vinyl alcohol) of molecular weight 10,000 g mol −1 . Potassium chloride concentration and solution pH were varied and the phase behavior was mapped on the pH-(KCl) space. The block copolymers presented a much broader phase separation region than the random copolymers. This difference may reflect the effect of the structure of the block copolymers which leads to the formation of micelles in solution. The two-phase region of the block copolymers extended over the whole range of potassium chloride concentrations employed in this study, from 0.0 to 0.75 M, and covered the pH range from two pH units below the polyampholyte isoelectric point up to two units above, with the exception of the points at alkaline pH without added salt. The two-phase region of the random copolymers extended from 0.0 to 0.1 M KCl and covered at most one unit in pH, centered near the isoelectric point. The two-phase region of the block copolymers comprised two regimes: the low salt concentration regime characterized by a compact polyampholyte precipitate in equilibrium with a low-viscosity poly(vinyl alcohol) phase; the high salt concentration and alkaline pH regime characterized by two coexisting low-viscosity phases. The one-phase region of the block copolymers extended in the acidic pH range and covered the whole salt concentration range. The ion type effect on the phase behavior of block polyampholytes was related to the position of the ion in the Hofmeister series: high concentrations of salt of low salting out ability resulted in a transition from a two- to a one-phase system.

A positive, chemically amplified, aromatic methacrylate resist employing the tetrahydropyranyl protecting group

In this article we describe the synthesis, properties, and lithographic behavior of a new class of chemically‐amplified, positive‐tone, aromatic methacrylate resists incorporating the tetrahydropyranyl protecting group bound to base‐solubilizing carboxylic acid moieties. Copolymers containing equimolar amounts of benzyl methacrylate and tetrahydropyranyl methacrylate were prepared by free radical and group transfer polymerization (GTP). Photogenerated sulfonic acids formed from covalent ester or ionic salt precursors were used to remove the acid labile tetrahydropyranyl (THP) group by heating after exposure. The resulting copolymers of benzyl methacrylate (BMA) and methacrylic acid (MAA) are extremely soluble in aqueous base solutions when the MAA concentration exceeds 38 mol %, thus affording positive tone patterns. We have studied these copolymer resists and find them to have high sensitivity (<30 mJ/cm2) when formulated with aromatic sulfonate or trifluoromethyl sulfonate sensitizers. Contrast is greater than 2 and submicrometer patterns in 1 μm thick films are resolved. Resolution is significantly influenced by the sensitizer, post exposure heating and development conditions. Molecular weight distribution appears to have little effect on the lithographic properties. Resolution presently is limited by resist adhesion which remains to be optimized. Plasma etching resistance to conditions used to etch Al is 1.8 times less than for hard‐baked HPR‐206 photoresist, but can be improved to a value of 1.5 by postexposure thermolysis. Improvements are needed before this type of chemically‐amplified resist is able to meet all deep‐UV lithographic requirements. However, it appears quite promising for other lower resolution (≫1 μm), thick‐film‐imaging applications which will be the subject of future papers.

Advances in phototackification

A direct single-layer negative-working phototackification system with application to 4-color half-tone proofing has been invented. It makes use of chemical amplification and is based on photo-induced microphase separation in an initially non-tacky miscible blend of acid-labile and tacky polymers. Factors which influence tack generation are discussed. The system has been sensitized both in the UV for conventional analog proofing and in the near-IR for digital proofing.