Postpolymerization Modification of Hydroxyl-Functionalized Polymers with Isocyanates

The postpolymerization functionalization of hydroxyl-group terminated polymers (M-n in the range of 1000-6000 g mol(-1)) such as poly(ethylene glycol) (PEG), poly(N-isopropylacrylamide) (PNIPAM), poly(N,N-dimethylacrylamide) (PDMAM), and poly(tert-butyl acrylate) (PtBA) with a wide range of functional isocyanate derivatives such as azobenzene, and anthracene has been investigated. It was shown by H-1 and C-13 NMR, GPC, Fourier transform infrared spectroscopy (FTIR), and electrospray ionization mass spectrometry (ESI-MS) that a high degree of end-group conversion, typically >98%, with little or no formation of side products can be achieved at ambient temperature. PNIPAM, PDMAM, PtBA, and PHEAM polymers have been obtained by reversible addition-fragmentation chain transfer (RAFT) radical polymerization from a hydroxyl-group containing chain transfer agent (CTA). The formation of the carbamate has been shown to be compatible with the trithiocarbonate end-group of the RAFT polymers. Additionally, this approach allows for the direct functionalization of RAFT polymers without the need of additional steps such as deprotection or aminolysis of the CTA. This route was subsequently used for the preparation of a variety of side-chain functional polymers from poly(N-hydroxyethyl acrylamide) (PHEAM). Three different high yielding methods have been employed to prepare the isocyanates (R-NCO). Either amino or carboxylic acid precursors have been converted into the desired R NCO or hydroxyl group moieties have been reacted with an excess of 1,6-hexamethylene diisocyanate (HDI) to statistically form the monofunctional product.