wherein the group enclosed within parenthesis represents an amino acid or an amino acid derivative, R2 is a C1-C6 alkyl, R3, R4 and R5 can be the same or different and each is an organic group, q is an integer greater than one, and p is an integer greater than 0; X and Y are both free of a hydrogen-bond donor; R1 is selected from the group consisting of hydrogen, a C1-C6 alkyl and an aryl, and n i