Chester A Thayer

US Patent:

53747437, Dec 20, 1994

Filed:

Sep 30, 1993

Appl. No.:

8/128433

Inventors:

Chester A. Thayer - Wilmington DE
Harold E. Bellis - Wilmington DE

Assignee:

E. I. Du Pont de Nemours and Company - Wilmington DE

International Classification:

C07D31900

US Classification:

549274

Abstract:

A process for preparing lactide or glycolide from a lactic acid oligomer or glycolic acid oligomer is disclosed where the molecular weight of the synthesis reactor residue is controlled to no more than 1. 2 times that in the feed. The process is carried out at 130. degree. to 280. degree. C. and preferably 180. degree. to 210. degree. C. using from 1 to 6 weight percent catalyst in the oligomer feed to the synthesis reactor. The catalysts are tin or tin compounds, yttrium or rare earth metal compounds, or antimony compounds which are known as alphahydroxycarboxylic acid cyclic dimerization or polymerization catalysts.

US Patent:

54477573, Sep 5, 1995

Filed:

Mar 7, 1994

Appl. No.:

8/206377

Inventors:

Allan Cairncross - Hockessin DE
Chester A. Thayer - Wilmington DE

Assignee:

E. I. Du Pont de Nemours and Company - Wilmington DE

International Classification:

B41C 114

US Classification:

427510

Abstract:

Polymeric ledges on a metal stencil screen are made using a polymeric layer which is partially removed by a developer solution.

US Patent:

50432443, Aug 27, 1991

Filed:

Sep 10, 1990

Appl. No.:

7/580229

Inventors:

Allan Cairncross - Hockessin DE
Chester A. Thayer - Wilmington DE

Assignee:

E. I. du Pont de Nemours and Company - Wilmington DE

International Classification:

G03C 554

US Classification:

430247

Abstract:

A process is described for defined etching of holes using a sliver mask formed by silver diffusion transfer imaging.

US Patent:

55738150, Nov 12, 1996

Filed:

May 30, 1995

Appl. No.:

8/454487

Inventors:

Allan Cairncross - Hockessin DE
Chester A. Thayer - Wilmington DE

Assignee:

E. I. Du Pont de Nemours and Company - Wilmington DE

International Classification:

C08J 704

US Classification:

427504

Abstract:

Polymeric ledges on a metal stencil screen are made using a polymeric layer which is partially removed by a developer solution.

US Patent:

53227638, Jun 21, 1994

Filed:

May 6, 1992

Appl. No.:

7/879211

Inventors:

Allan Cairncross - Hockessin DE
Chester A. Thayer - Wilmington DE

Assignee:

E. I. Du Pont de Nemours and Company - Wilmington DE

International Classification:

G03F 700
G03F 712
G03C 500
G03C 800

US Classification:

430308

Abstract:

A process for making a metal ledge on one side of a metal screen involves exposing through the stencil screen a photoresist layer, removing unexposed photoresist areas, plating the metal stencil screen where the unexposed photoresist has been removed and removing the exposed photoresist.