Modified siloxane composite membranes for heavy hydrocarbon recovery

A composite membrane comprising a polymer material that is selectively permeable to heavy hydrocarbons having three or more carbon atoms over methane, the polymer material comprising a first copolymer having a polysiloxane backbone according to formula (I):

• M-O-(A1)d-(A2)p-(A3)m-M (I)
• in which:
• each A1 is a dimethylsiloxyl monomer;
• each A2 is independently chosen from substituted methylsiloxyl monomers having formula (M1):
• each A3 is independently chosen from internal-network monomers having formula (M2):
• each Q is independently selected from the group consisting of —Si(R2)3, —Si(OR2)3, R3, R4, Z1, R5, and —(CH2)z—R5 in which z is an integer from 1 to 10;
• each R1 is independently chosen from a C5-C10 alkyl or phenyl;
• each R2 is independently a C1-C20 alkyl;
• each R3 is chosen independently from structures having formula (Q1):
• where each R6 is R4 or R5, and at least one R6 is R4;
• each R4 is chosen independently from structures having formula (Q2) or formula (Q3):
• where each y in formula (Q2) and formula (Q3) is an integer from 1 to 850;
• and
• each R5 is a crosslinking group having formula (X1):
• each Z1 is a crosslinking site to a second copolymer having a polysiloxane backbone;
• subscripts d, p, and m represent molar fractions of randomly arranged monomers A1, A2, and A3 in the polysiloxane backbone;
• p is from 0 to 0.50;
• when p is 0, at least one monomer A3 is —(CH2)z—R5;
• m is from 0.01 to 0.20;
• d+p+m≤1;
• and
• each M is a terminal silyl group.