Intrinsic viscosity of poly(N-vinylcaprolactam) with varying the architecture

Abstract

Five CTA’s xanthate-type were synthesized and characterized and used in the controlled polymerization of N-vinylcaprolactam (NVCL) via reversible addition-fragmentation chain transfer (RAFT) polymerization. The CTA’s are linear (bifunctional), with three arms (from cholic acid or trimethylolpropane tris[poly(propylene glycol), amine terminated] ether), with six arms (from DPERT) and nine arms (from glycerol functionalized with cholic acid). Three of the synthesized CTA’s are reported for the first time. The intrinsic viscosity [η] and the Mark-Houwink-Kuhn-Sakurada (MHKS) constants were estimated in ethanol at 35 °C for each PNVCL polymer group. The η values for star-shaped polymers were lower compared with the linear analogues with similar molecular weights. Interestingly, the intrinsic viscosity values of two groups of polymers having three arms shown a noticeable difference, probably due to starting material used to prepare the CTA (rigid or flexible core). The MHKS exponents ranged from 0.68 to 0.82 indicates that all polymers behave as a flexible expanded conformation. The hydrodynamic diameter (Dh) of the polymers in ethanol solution was measured using DLS. The Dh values decreased significantly with the molecular weight (Mn) decreasing. The Dh values of linear polymers were higher compared with the stars one with similar molecular weights. Star-shaped PNVCL polymers containing cholane skeleton shown remarkable lower viscosity values.