Bicomponent moisture barrier poly(etherimide) ester films

Claim 1

A bicomponent film of a hydrophilic copolyester elastomer layer and a hydrophobic copolyester elastomer layer bonded together to permit differential transfer of water vapor and prevent buildup of moisture comprising: (A) a continuous layer of a hydrophilic copolyester elastomer 0.3-6 mil thick and having a water vapor transmission rate of at least 3500 gm.mil/m 2 /24 hrs according to ASTM E-96-66 (Procedure BW), said hydrophilic elastomer is a poly(etherimide) ester comprising the reaction product of one or more diols, one or more dicarboxylic acids, and one or more poly(oxyalkylene imide) diacids, said poly(oxyalkylene imide) diacid containing sufficient repeating units of ethylene oxide such that the resulting poly(etherimide) ester contains about 25-60 weight percent ethylene oxide units; (B) a continuous layer of a hydrophobic copolyester elastomer 0.05-6 mil thick and having a water vapor transmission rate of 400-2500 gm.mil/m 2 /24 hrs. according to ASTM E96-66 (Procedure BW) said hydrophobic elastomer is a copolyester selected from the group consisting of (i) a poly(etherimide) ester, as described hereinabove in (A), with the proviso that the poly(etherimide) ester elastomer contains no more than about 20 weight percent ethylene oxide units, and (ii) a segmented copolyester having a multiplicity of recurring long chain ester units and short chain ester units joined head-to-tail through ester linkages, said long chain ester units being represented by the formula ##STR8## and said short chain ester units being represented by the formula ##STR9## where G is a divalent radical remaining after the removal of terminal hydroxyl groups from a poly(alkylene oxide) glycol having an average molecular weight of about 400-3500, and the amount of ethylene oxide units incorporated in the segmented copolyester by the poly(alkylene oxide)glycol is not greater than about 20 weight percent based upon the weight of the copolyester; R is a divalent radical remaining after the removal of carboxyl groups from a dicarboxylic acid having a molecular weight less than about 300; D is a divalent radical remaining after removal of hydroxyl groups from a diol having a molecular weight less than about 250; said hydrophobic segmented copolyester has from about 25-80 weight percent short chain ester units; and, said bicomponent film of hydrophilic and hydrophobic layers has a separation ratio for water vapor of at least 1.2 as determined by ASTM E96-66 (Procedure BW).