Microcellular foams

A process for synthesizing a foam in a single reactor comprising the steps of:

• (a) mixing a monomer which is capable of polymerizing with a comonomer capable of effecting a crosslinking reaction with the monomer in a near-critical fluid at a temperature below the boiling point of the near-critical fluid;
• (b) pressurizing the reactor and increasing the temperature of the reactor to a point below a critical temperature of the near-critical fluid;
• (c) polymerizing the monomer with the comonomer in the near-critical fluid for a time sufficient to effect a synthesis of primary particles in the near-critical fluid, a rate of an interaction between the near-critical fluid and the monomer and the comonomer effecting a separation the primary particles just before a gelation occurs, thereby forming a microcellular crosslinked copolymer network;
• (d) drying the microcellular crosslinked copolymer network by raising the temperature to a point above the supercritical temperature of the near-critical fluid, thereby transforming the near-critical fluid into a supercritical fluid, yet below a temperature which might degrade the microcellular crosslinked copolymer network;
• (e) venting the supercritical fluid from the reactor to permit collection of a microcellular crosslinked copolymer foam having a cell size which is less than 10 .mu.m.

A process for synthesizing a microcellular polymer foam in a diluent comprising the steps of:

• (a) polymerizing a multifunctional monomer with at least one primary and at least one secondary reaction site, capable of propagating a polymerization reaction with the primary reaction site, yet also capable of effecting a crosslinking reaction with the secondary reaction site in a solvent and a non-solvent at a temperature and a time sufficient to effect a synthesis of primary particles in the solvent and non-solvent, a rate of an interaction between the solvent and the non-solvent effecting a separation of the primary particles just before a gelation occurs, thereby forming a crosslinked network;
• (b) adding a near-critical fluid to a reactor containing the crosslinked copolymer network;
• (c) venting the reactor to allow a portion of the near-critical fluid to escape the reactor while maintaining a quantity of the near-critical fluid to totally immerse the crosslinked network;
• (d) repeating process steps (b) and (c) until the solvent and the non-solvent in the crosslinked network is removed and replaced with the near-critical fluid;
• (e) increasing a reactor temperature above a critical-point value for the near-critical fluid thereby transforming the near-critical fluid into a supercritical fluid, yet below a temperature which might degrade the crosslinked network, for a sufficient period of time to effect a permeation of the voids in the crosslinked network;
• and
• (f) venting the near-critical fluid until an internal pressure in the reactor approximates an ambient pressure to permit collection of a microcellular crosslinked homopolymer foam having a cell size which is less than 10 .mu.m.

A process for synthesizing a microcellular polymer. foam in a supercritical fluid in a single reactor comprising the steps of:

• (a) adding a multifunctional monomer with at least one primary and at least one secondary reaction site, capable of propagating a polymerization reaction with the primary reaction site, yet also capable of effecting a crosslinking reaction with the secondary reaction site in a near-critical fluid at a temperature below the boiling point of the near-critical fluid;
• (b) pressurizing the reactor and increasing the temperature of the reactor to a point above the boiling point of the near-critical fluid yet below a critical temperature of the near-critical fluid;
• (c) polymerizing the monomer in the near-critical fluid for a time sufficient to effect a synthesis of primary particles in the near-critical fluid, a rate of an interaction between the near-critical fluid and the monomer effecting a separation the primary particles just before a gelation occurs, thereby forming a microcellular crosslinked polymer network;
• (d) drying the crosslinked network by raising the temperature to a point above a supercritical temperature of the near-critical fluid thereby transforming the near-critical fluid into a supercritical fluid, yet below a temperature which might degrade the microcellular crosslinked copolymer network;
• (e) venting the supercritical fluid from the reactor to permit collection of a microcellular crosslinked homopolymer foam having a cell size which is less than 10 .mu.m.