A method for sealing downhole, comprising: disposing a seal in an opening downhole, wherein the seal has a gradient in glass transition temperature; heating the seal to a temperature greater than a minimum value of the glass transition temperature of the gradient; and applying pressure to an elastic portion of the seal for sealing the opening, wherein the seal comprises: a first portion including a crosslinked product of: a first crosslinked polymer; and a second crosslinked polymer different than the first crosslinked polymer; and a second portion including a polymer which is different than a constituent polymer in the first portion; and wherein the first crosslinked polymer comprises crosslinked polyphenylene sulfide, crosslinked polyphenylsulfone, crosslinked self-reinforced polyphenylene, crosslinked polyethersulfone, or a combination comprising at least one of the foregoing, and wherein the second crosslinked polymer comprises crosslinked polyphenylene sulfide, crosslinked polyphenylsulfone, crosslinked self-reinforced polyphenylene, crosslinked polyethersulfone, or a combination comprising at least one of the foregoing. disposing a seal in an opening downhole, wherein the seal has a gradient in glass transition temperature; heating the seal to a temperature greater than a minimum value of the glass transition temperature of the gradient; and applying pressure to an elastic portion of the seal for sealing the opening, wherein the seal comprises: a first portion including a crosslinked product of: a first crosslinked polymer; and a second crosslinked polymer different than the first crosslinked polymer; and a second portion including a polymer which is different than a constituent polymer in the first portion; and wherein the first crosslinked polymer comprises crosslinked polyphenylene sulfide, crosslinked polyphenylsulfone, crosslinked self-reinforced polyphenylene, crosslinked polyethersulfone, or a combination comprising at least one of the foregoing, and wherein the second crosslinked polymer comprises crosslinked polyphenylene sulfide, crosslinked polyphenylsulfone, crosslinked self-reinforced polyphenylene, crosslinked polyethersulfone, or a combination comprising at least one of the foregoing. a first portion including a crosslinked product of: a first crosslinked polymer; and a second crosslinked polymer different than the first crosslinked polymer; and a first crosslinked polymer; and a second crosslinked polymer different than the first crosslinked polymer; and a second portion including a polymer which is different than a constituent polymer in the first portion; and wherein the first crosslinked polymer comprises crosslinked polyphenylene sulfide, crosslinked polyphenylsulfone, crosslinked self-reinforced polyphenylene, crosslinked polyethersulfone, or a combination comprising at least one of the foregoing, and wherein the second crosslinked polymer comprises crosslinked polyphenylene sulfide, crosslinked polyphenylsulfone, crosslinked self-reinforced polyphenylene, crosslinked polyethersulfone, or a combination comprising at least one of the foregoing. wherein the first crosslinked polymer comprises crosslinked polyphenylene sulfide, crosslinked polyphenylsulfone, crosslinked self-reinforced polyphenylene, crosslinked polyethersulfone, or a combination comprising at least one of the foregoing, and wherein the second crosslinked polymer comprises crosslinked polyphenylene sulfide, crosslinked polyphenylsulfone, crosslinked self-reinforced polyphenylene, crosslinked polyethersulfone, or a combination comprising at least one of the foregoing.