ELASTOMERS WITH EXCEPTIONAL ELONGATION
Nanocomposites exhibiting elongation exceeding about 2000%, elastic recovery, and tensile strength exceeding 2.5 MPa are described. A method these elastomers involves performing a catalyzed step growth polymerization of a heterobifunctional siloxane macromonomer compounded with at least about 15 wt % surface passivated silica nanoparticles. The macromonomer has a degree of polymerization of at least about 40 and the silica nanoparticles have nominal diameters of less than about 50 nm.
1 . A polysiloxane nanocomposite elastomer, wherein the elastomer exhibits an elongation exceeding about 2000% and a tensile strength exceeding about 2.5 MPa.
2 . The elastomer according to claim 1 , wherein the elastomer is a catalyzed step growth polymerization product of a heterobifunctional silicone macromonomer compounded with at least about 15 wt % surface passivated silica nanoparticles.
3 . The elastomer according to claim 2 , wherein the macromonomer has a degree of polymerization of at least about 40.
4 . The elastomer according to claim 2 , wherein the surface passivated nanoparticles have nominal diameters of less than about 50 nm.
5 . The elastomer according to claim 2 , wherein the macromonomer is compounded with about 15 to 45 wt % of the silica.
6 . The elastomer according to claim 1 , wherein the elastomer has a molecular weight Mw of at least about 1,000,000.
7 . The elastomer according to claim 1 , wherein the elastomer exhibits elastic recovery.
8 . The elastomer according to claim 2 , wherein the macromonomer comprises hydride and vinyl termini.
9 . The elastomer according to claim 1 , wherein the elastomer has no apparent covalent crosslinking to a level of about 2 ppm.
10 . A method for forming a nanocomposite elastomer exhibiting an elongation exceeding about 2000% and a tensile strength exceeding about 2.5 MPa, the method comprising performing a catalyzed step growth polymerization of a heterobifunctional siloxane macromonomer compounded with at least about 15 wt % surface passivated silica nanoparticles to form the nanocomposite elastomer, wherein the macromonomer has a degree of polymerization of at least about 40 and the silica nanoparticles have nominal diameters of less than about 50 nm.
11 . The method according to claim 10 , wherein the nanocomposite elastomer has a molecular weight Mw of at least about 1,000,000.
12 . The method according to claim 10 , wherein the nanocomposite elastomer has no apparent covalent crosslinking to a level of about 2 ppm.
13 . The method according to claim 10 , comprising performing the polymerization using a platinum catalyst.
14 . The method according to claim 13 , wherein the catalyst is present in an amount of no more than about 100 ppm.
15 . The method according to claim 10 , wherein the nanocomposite elastomer exhibits elastic recovery.
16 . The method according to claim 10 , wherein the macromonomer is compounded with about 15 to 45 wt % of the silica.
17 . The method according to claim 10 , wherein the macromonomer comprises hydride and vinyl termini.