Some basic aspects of flame resistance of polymeric materials

It is reported that thin films of polyimide are efficiently etched in air at pulsed excimer laser wavelengths of 248, 308, and 351 nm. Etch rate versus incident fluence data are found to obey a Beer–Lambert etching relation. Sharp laser fluence thresholds for significant etching are found to correlate with the wavelength‐dependent absorption coefficient. The absorbed energy density required to initiate significant etching is found, within experimental error, to be independent of the wavelengths examined. It is felt that this information demonstrates the predominantly thermal nature of the laser etching mechanism. Additionally, infrared spectroscopy and coupled gas chromatography/mass spectroscopy were used to identify several gases evolved during pulsed laser etching of polyimide in both air and vacuum.

Excimer laser etching of polyimide

This review article deals with aromatic polyimides that are processable from the melt or soluble in organic solvents. Conventional aromatic polyimides represent the most important family of heat resistant polymers, but they cannot be processed in the melt, and their application in the state of soluble intermediates always involves a hazardous step of cyclo-dehydration and elimination of a non-volatile polar solvent. A major effort has therefore been devoted to the development of novel soluble and/or melt-processable aromatic polyimides that can be applied in the state of full imidation. The structural factors conducive to better solubility and tractability are discussed, and representative examples of monomers showing favourable structural elements have been gathered and listed with the chemical criteria. Experimental and commercial aromatic polyimides are studied and evaluated by their solubility, transition temperatures and thermal resistance. An example is also given of the methods of computational chemistry applied to the study and design of polyimides with improved processability.

Processable Aromatic Polyimides

A chemically amplified positive resist composition capable of giving a resist film excellent in adhesion to a substrate; excellent in various resist performance characteristics such as dry etching resistance, sensitivity and resolution; and comprising a resin (X) which, per se, is insoluble or slightly soluble in alkali but becomes soluble in alkali due to an action of acid, and has a polymeric unit (a) derived from 3-hydroxy-1-adamantyl(meth)acrylate and a polymeric unit (b) derived from β-(meth)acryloyloxy-γ-butyrolactone wherein the lactone ring may optionally be substituted by alkyl; and an acid generating agent (Y).

Chemically amplified positive resist composition

Direct polycondensation in ionic liquids

New linear polymers

Bovine teeth that were treated with acidulated fluoride before and after etching with phosphoric acid produced adhesive bonds with fissure sealers that were lower than those of untreated controls. Human teeth from an area of high natural fluoridation were shown to be extremely resistant to etching with citric and phosphoric acids.

Sealing of Developmental Pits and Fissures : III. Effects of Fluoride on Adhesion of Rigid and Flexible Sealers

Esters are prepared by reaction of acyl halides and alcohols or hydroxyalkyl esters and acid halides in the presence of a tertiary amine and polar aprotonic solvents. Bis(2-methacrylatoethyl) phthalate is prepared by the reaction of phthaloyl chloride with 2-hydroxyethyl methacrylate in pyridine and acetone. Bis-phenol-A-bis(2-methacrylatoethyl)ether is prepared from 2,2-bis[4-(2-hydroxyethoxy)phenyl]-propane and methacryl chloride in acetone.

Donald Stoffey

Papers

New linear polymers

Sealing of Developmental Pits and Fissures : III. Effects of Fluoride on Adhesion of Rigid and Flexible Sealers

Process for preparing esters