Nonspherical microparticles and method therefor

A method for producing polymeric microparticles having a prolate spheroidal shape which method comprises:

• dispersing spherical particles of a polymeric material having a glass-to-rubber transition temperature or melting point above room temperature into a second material capable of forming an elastic polymer matrix, said elastic polymer matrix and said polymeric material having similar elastic properties but dissimilar chemical properties;
• forming the dispersion of spherical particles into a shape and reacting the matrix-forming material with a crosslinking reagent to form a shaped particle/matrix composite material comprising an elastic polymer matrix surrounding the spherical particles;
• cutting the particle/matrix material into strips;
• heating the strips to a temperature greater than the glass-to-rubber transition temperature, or melting point of said spherical particles;
• applying a uniaxial strain to the strips to uniaxially extend the strip and the spherical polymer particles surrounded by the polymer matrix;
• cooling the strips while maintaining the strips uniaxially extended;
• treating the strips to selectively effect dissolution of the elastic polymer matrix and release of the particles;
• and
• separating and recovering said particles from the chemical degradation medium, whereby prolate spheroidal particles are obtained.

A method for producing polymeric microparticles having an oblate spheroidal shape which method comprises:

• dispersing spherical particles of a polymeric material having a glass-to-rubber transition temperature or melting point above room temperature into a second material capable of forming an elastic polymer matrix, said elastic polymer matrix and said polymeric material having similar elastic properties but dissimilar chemical properties;
• forming the dispersion of spherical particles into a shape and reacting the matrix-forming material with a crosslinking reagent to form a shaped particle/matrix composite material comprising an elastic polymer matrix surrounding the spherical particles;
• cutting the particle/matrix material into strips;
• heating the strips to a temperature greater than the glass-to-rubber transition temperature or melting point of said spherical particles;
• applying an equal biaxial strain to the strips to biaxially extend the strip and the spherical polymer particles surrounded by the polymer matrix;
• cooling the strips while maintaining the strips biaxially extended;
• treating the strips to selectively effect dissolution of the elastic polymer matrix and release of the particles;
• and
• separating and recovering said particles from the chemical degradation medium, whereby oblate spheroid particles are obtained.

A method for producing polymeric monodisperse microparticles having an ellipsoidal shape which method comprises:

• dispersing spherical particles of a polymeric material having a glass-to-rubber transition temperature or melting point above room temperature into a second material capable of forming an elastic polymer matrix, said elastic polymer matrix and said polymeric material having similar elastic properties but dissimilar chemical properties;
• forming the dispersion of spherical particles into a shape and reacting the matrix-forming material with a crosslinking reagent to form a shaped particle/matrix composite material comprising an elastic polymer matrix surrounding the spherical particles;
• cutting the particle/matrix composite material into strips;
• heating the strips to a temperature greater than the glass-to-rubber transition temperature or melting point of said spherical particles;
• applying an unequal biaxial strain to the strips to biaxially extend the strip and the spherical polymer particles surrounded by the polymer matrix;
• cooling the strips while maintaining the strips biaxially extended;
• treating the strips to selectively effect dissolution of the elastic polymer matrix and release of the particles;
• and
• separating and recovering said particles from the chemical degradation medium, whereby ellipsoidal particles are obtained.