Synthesizing Monofunctionalized Polycyclopentene with Chain Transfer Agents during ROMP

Abstract

This thesis investigated the selective creation of polycyclopentene (PCP) macromers via addition of chain transfer agents (CTAs) during ring-opening metathesis polymerization (ROMP). The ROMP of cyclopentene (CP) with a Mo-based catalyst had previously been optimized to produce living-like conditions, making this system attractive due to the low levels of acyclic metathesis.

We first verified the use of the chain transfer equation, originally derived for steady-state free-radical polymerization (FRP), and found that the expression applied in our system due to (1) complete initiation, (2) constant [CTA]/[M] at low conversion, and (3) inactivity of the bound alkylidene state to transfer. Using the chain transfer equation, we then determined CT values for 1-pentene (0.79+-0.04), styrene (0.18+-0.01), and divinylbenzene (DVB, 0.27+-0.02). Sophisticated end group analysis of CTA products was achieved with MALDI-ToF (matrix-assisted laser desorption/ioniziation time-of-flight) mass spectroscopy, a “soft” ionization technique that produces Dalton-resolution peaks for polymer chains. Proton nuclear magnetic resonance spectroscopy in conjunction with MALDI-ToF confirmed that the PCP synthesized with DVB afforded mono-functional polycyclopentene (PCP) with styryl reactivity at one end.

This PCP macromer was copolymerized with styrene via FRP. Both intrinsic viscosity and UV detection confirmed the presence of comb-like PS bearing approximately 20 wt% PCP teeth. Indeed, the intrinsic viscosities of the PS homopolymer and comb copolymer were plotted against molecular weight and fit to a power law to produce the Mark-Houwink parameters (K = 0.014+-0.002 ml/g and a = 0.707+-0.011 for the PS homopolymer and K = 0.013+-0.004 ml/g and a = 0.703+-0.026 for the comb). As expected, the comb copolymer shows a lower intrinsic viscosity at a given molecular weight. Thus, we demonstrate the successful creation of styryl-capped mono-functional PCPs, which yielded PS-backbone comb copolymers.