Hollow fiber membranes with nucleating agent and methods of making and using the same

A method of making an asymmetric hollow fiber membrane comprising:

• providing a substrate resin and a skin layer resin,
• the substrate resin including a first semi-crystalline thermoplastic polyolefin (co)polymer and a nucleating agent in an amount effective to achieve nucleation,
• the skin layer resin including a second semi-crystalline thermoplastic polyolefin (co)polymer derived by polymerizing at most 98 wt. % of 4-methyl-1-pentene monomer
• with at least 2 wt. % of linear or branched alpha olefin monomers selected from the group consisting of ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, isobutylene, vinylcyclohexane, 3-ethyl-1-pentene, 1,3-methyl-1-pentene, cyclobutene, cyclopentane, 2-norbornene, 3-methyl-2-norbornene, 5-methyl-2-norbornene, tetracyclododecene, methyltetracyclododecene, dimethyltetracyclo-dodecene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-eicosene, or a combination thereof,
• optionally wherein the first thermoplastic polyolefin (co)polymer is compositionally different from the second thermoplastic polyolefin (co)polymer;
• co-extruding the substrate resin and the skin layer resin to form an asymmetric hollow fiber membrane precursor;
• and
• stretching the asymmetric hollow fiber membrane precursor to form an asymmetric hollow fiber membrane having a porous substrate comprised of the substrate resin and comprising a plurality of pores, and a skin layer comprised of the skin layer resin overlaying the porous substrate,