Biodegradable ultra-pH sensitive polymers

A polymer of the formula:

• wherein:
• R1 is hydrogen, alkyl(C≤8), substituted alkyl(C≤8), or a thiol reactive group;
• m is an integer from 1 to 8;
• p and q are each independently 1, 2, or 3;
• x is an integer from 10 to 200;
• y is an integer from 20 to 200;
• z is an integer from 0 to 200;
• wherein the monomer of either y or z is randomly distributed in the polymer;
• X1, X2, X1′, and X2′ are each independently O or NRa, wherein:
• Ra is alkyl(C≤6) or substituted alkyl(C≤6);
• R2 and R2′ are each independently hydrogen, alkyl(C≤8), or substituted alkyl(C≤8);
• R3 is hydrogen, alkyl(C≤8), or substituted alkyl(C≤8);
• X3 and X3′ are each independently O or NRb, wherein:
• Rb is hydrogen, alkyl(C≤6), or substituted alkyl(C≤6);
• L and L′ are each independently a group of the formula:
• —X4—S(O)n—X5—
• wherein:
• n is 0, 1, or 2;
• X4 of L is —CH2CH2— and is attached via X3;
• and
• X5 of L is alkanediyl(C≤8) or substituted alkanediyl(C≤8);
• and
• Y1, Y2, Y1′, and Y2′ are each independently alkyl(C≤12), substituted alkyl(C≤12), alkenyl(C≤12), or substituted alkenyl(C≤12);
• or Y1 and Y2 or Y1′ and Y2′ are taken together and are alkanediyl(C≤12), alkenediyl(C≤12), or a substituted version of either group;
• or a pharmaceutically acceptable salt thereof.