Method for casting ultrathin methylpentene polymer membranes

DETAILED DESCRIPTION OF THE INVENTION AND MANNER AND PROCESS OF MAKING AND USING IT Film-forming MPP-containing compositions suitable for use in the practice of this invention include, in general, any methylpentene homopolymer (PMP) or interpolymer of methylpentene with one or more other monomers interpolymerizable therewith, including graft and block interpolymers and the like, capable of formation into substantially hole-free films by solvent casting.
Blends of any of the foregoing with up to about 100 or more parts, preferably from 1 to about 25 parts, per 100 parts of the MPP-containing polymer, of one or more PSPC interpolymers are generally preferred.
Preferably, the MPP polymer composition included as part of the casting system employed in this invention is not soluble in the film-support liquid; is not highly swollen by the film-support liquid; and is soluble in a normally liquid solvent.
The preferred MPP composition herein is a 4-methylpentene-1 homopolymer having a weight average molecular weight (M.
sub.
W) of about 140,000 and commercially available from Mitsui, Inc.
of Tokyo, Japan, under the trademark TPX, grade RT-20.
PSPC interpolymers suitable for use in MPP-containing blends in the practice of this invention include repeating units desirably comprising bisphenol-A carbonate (BAC) units and dimethylsiloxane (DMS) units, preferably wherein the BAC and DMS units are present in blocks.
Block interpolymers of BAC and DMS and methods for the preparation thereof are described in U.
S.
Pat.
No.
3,189,662-Vaughn, Jr.
, (incorporated herein by reference).
The BAC-DMS interpolymers may be alternating, random block polymers of the -ABABA- type in which the blocks are polydisperse.
Such interpolymers may be represented by the formula below and may include other interpolymerized monomer units (not shown): ##STR1## Additional teachings are provided in U.
S.
Pat.
No.
3,419,634 - Vaughn and U.
S.
Pat.
No.
3,419,635 - Vaughn on the preparation of silicone/polycarbonate copolymers.
The PSPC interpolymer M