Solvent fractionation of guayule rubber

A process for solvent fractionating a molecular weight rubber fraction from a guayule rubber source;

• comprising the steps of:
• forming a mixture of the guayule rubber source and a solvent system, said solvent system having an effective end ratio of polar to hydrocarbon solvents to yield a separation of a desired molecular weight rubber fraction, said organic polar solvent selected from the group consisting of an alcohol having from 1 to 8 carbon atoms, an ester having from 3 to 8 carbon atoms, a ketone having from 3 to 8 carbon atoms, an ether having from 2 to 8 carbon atoms, and combinations thereof, said hydrocarbon solvent selected from the group consisting of an alkane having from 4 to 9 carbon atoms, a cycloalkane having from 5 to 10 carbon atoms, an aromatic or an alkyl substituted aromatic having from 6 to 12 carbon atoms, and combinations thereof;
• and
• separating said resulting mixture and obtaining a molecular weight rubber fraction having a weight average molecular weight greater than that of said guayule rubber source.