Method of making a distensible dilatation balloon using a block copolymer

A process of forming a dilatation balloon for a catheter comprising:

• a. providing a parison comprising a block polymer composition including a block copolymer having regions of (i) hard segments defined by regions of intermolecular chain interaction separated by (ii) soft segments regions in which individual polymer portions of chains have the ability to uncoil, said parison having a predetermined initial outer diameter, a predetermined wall thickness and a predetermined length;
• b. subjecting said parison to at least one axial stretch step and at least one radial expansion step at temperature T.sub.1 which is below the melting temperature of said block polymer composition to increase the diameter and length of said parison to at least three times the original diameter and at least two times the original length and to decrease the original wall thickness such that an expanded parison is formed having an internal diameter between about 6 and about 8 times an initial internal diameter of said parison and an outside diameter which is equal to or greater than 3 times an initial outside diameter of said parison;
• c. heating said expanded parison to a temperature T.sub.2 which is above T.sub.1 but below the melting temperature of said block polymer composition;
• and
• d. cooling said expanded parison to produce said balloon;
• wherein the ratio of said hard segments to said soft segments provides said balloon with (a) an elastic stress response not greater than 5.00, (b) a wall tensile strength of at least about 14000 psi and (c) a distensibility of between about 5% and about 20%.