Scheme 1. Chemical Structures of the Molecules Used in This Study: (a) UPy-Modified Polycaprolactone (M_n,PCL = 2 kDa); (b) Bifunctional UPy Poly(ethylene glycol) (M_n,PEG = 2 kDa); (c) Bifunctional PEG_10KdiUPy (M_n,PEG = 10 kDa); (d) Monofunctional UPyPEG (M_n,PEG = 5 kDa).