A composition of matter comprising at least one compound of the formula: (a) z X X z; or (b) Q[ X z] m; wherein: (i) PS is a linear polymeric segment terminating with a methylene group at both ends of said segment, wherein said segment is derived from a polymer selected from the group consisting of: polyethylene oxide, poly(trimethyleneoxide), block or random copolymers of polyethylene oxide and polypropylene oxide, and triblock copolymers of polyethylene oxide and polypropylene oxide; (ii) X is selected from the group consisting of: CH 3-z, N, N(acetoacetamide)-CH 3-z, S-R 2 -N, S-R 2 -CH 3-z, NH-CH 3-z, and NH-R 2 -N, wherein R 2 is an alkylene group having from 1 to 5 carbon atoms; (iii) R is selected from the group consisting of: a direct bond, an alkylene group having from 1 to 5 carbon atoms, an alkylene ether group having up to a total of 6 backbone atoms, an alkyleneoxy urethane group of the formula R 4 O NHCH 2 wherein R 4 is a linear or branched alkylene group having 2 to 6 carbon atoms and R 4 is the group that is adjacent to X, and a C3 to C8 cycloalkylene group; (iv) Y is a functional group selected from the group consisting of: -NH 2, -SH, -CONHNH 2, acetoacetate, and -COR 1, wherein R 1 is OH or -N-hydroxysuccinimidyl; (v) Q is a core atom or molecule selected from the group consisting of: N, a polyol with the hydrogens removed from 3 or more of its OH groups, and N-R 3 -N, wherein R 3 is an alkylene group having 2-12 carbon atoms or a C3 to C8 cycloalkylene group; (vi) PA is a linear polymeric arm terminating with a methylene group at both ends of said arm, wherein said arm is derived from a polymer selected from the group consisting of: polyethylene oxide, poly(trimethyleneoxide), block or random copolymers of polyethylene oxide and polypropylene oxide, and triblock copolymers of polyethylene oxide and polypropylene oxide; (vii) z is 2 or 3 where X = CH 3-z, S-R 2 -CH 3-z, N(acetoacetamide)-CH 3-z or NH-CH 3-z and z is 2 where X = N, NH-R 2 -N, or S-R 2 -N; and (vii) m is 2 to 16; provided that if Y is acetoacetate or COR 1, wherein R 1 is N-hydroxysuccinimidyl, then X is not NH-CH 3-z, or NH-R 2 -N. (i) PS is a linear polymeric segment terminating with a methylene group at both ends of said segment, wherein said segment is derived from a polymer selected from the group consisting of: polyethylene oxide, poly(trimethyleneoxide), block or random copolymers of polyethylene oxide and polypropylene oxide, and triblock copolymers of polyethylene oxide and polypropylene oxide; (ii) X is selected from the group consisting of: CH 3-z, N, N(acetoacetamide)-CH 3-z, S-R 2 -N, S-R 2 -CH 3-z, NH-CH 3-z, and NH-R 2 -N, wherein R 2 is an alkylene group having from 1 to 5 carbon atoms; (iii) R is selected from the group consisting of: a direct bond, an alkylene group having from 1 to 5 carbon atoms, an alkylene ether group having up to a total of 6 backbone atoms, an alkyleneoxy urethane group of the formula R 4 O NHCH 2 wherein R 4 is a linear or branched alkylene group having 2 to 6 carbon atoms and R 4 is the group that is adjacent to X, and a C3 to C8 cycloalkylene group; (iv) Y is a functional group selected from the group consisting of: -NH 2, -SH, -CONHNH 2, acetoacetate, and -COR 1, wherein R 1 is OH or -N-hydroxysuccinimidyl; (v) Q is a core atom or molecule selected from the group consisting of: N, a polyol with the hydrogens removed from 3 or more of its OH groups, and N-R 3 -N, wherein R 3 is an alkylene group having 2-12 carbon atoms or a C3 to C8 cycloalkylene group; (vi) PA is a linear polymeric arm terminating with a methylene group at both ends of said arm, wherein said arm is derived from a polymer selected from the group consisting of: polyethylene oxide, poly(trimethyleneoxide), block or random copolymers of polyethylene oxide and polypropylene oxide, and triblock copolymers of polyethylene oxide and polypropylene oxide; (vii) z is 2 or 3 where X = CH 3-z, S-R 2 -CH 3-z, N(acetoacetamide)-CH 3-z or NH-CH 3-z and z is 2 where X = N, NH-R 2 -N, or S-R 2 -N; and (vii) m is 2 to 16;