Foamed polymer for use as dielectric material

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a foamed polymer having a pore size less than about 1000 .
ANG.
made by the steps of: (a) forming a copolymer comprising a matrix polymer and a thermally decomposable polymer which thermally decomposes at a temperature below the decomposition temperature of the matrix polymer; (b) heating said copolymer to a temperature which is at or above the decomposition temperature of the thermally decomposable polymer and below the decomposition temperature of the matrix polymer to form said foamed polymer.
The copolymer which is formed in the process of making the foamed polymer of the present invention is preferably a block copolymer preferably of the ABA type where A represents the thermally decomposable polymer.
Preferably, the block copolymer is formed by reacting one or more monomers to form the matrix polymer which couples with one or more oligomers which constitute the thermally decomposable portion of the copolymer.
The matrix polymer may also be preformed before coupling with the thermally decomposable oligomer.
The thermally decomposable polymer may also be formed from one or more monomers.
It will be known to those skilled in the art that various other types of block copolymers or graft copolymers can also be utilized in forming the polymers of the present invention.
Oligomers used in forming the copolymer have a molecular weight (Mn) which is large enough to enable the oligomer to be formed into a film generally from about 1000 to 20,000 preferably 2500 to 10,000.
The oligomer is preferably soluble in organic film forming solvents.
Suitable oligomers for forming the thermally decomposable polymer include poly(propylene oxide), poly(methyl methacrylate), and aliphatic polycarbonates e.
g.
poly(propylene carbonate) and poly(ethylene carbonate).
Other suitable oligomers for forming the copolymer will be known to those skilled in the art.
In the preferred embodiment of the present invention the oligomer has only one reactive site to enable the formation of the block ABA copolymer