Expanding the scope of atom transfer radical polymerization with low catalyst concentrations.

摘要

Several aspects of ARGET and ICAR ATRP were examined. The effect of copper catalyst concentration on molecular weight distribution during an ICAR ATRP was investigated using Predici software, and next confirmed experimentally. Similarly, the effect of free radical initiator concentration on polymerization rate of an ICAR ATRP was investigated using Predici software, and next confirmed experimentally. All simulations were performed using ICAR ATRP as a model, but similar effects were observed experimentally using ARGET ATRP. The synthesis of block copolymers using ARGET and ICAR ATRP was performed for a system with otherwise poor initiation efficiency. The poor initiation efficiency of the macroinitiator was overcome by performing the chain extension step in the presence of St, a less active comonomer. The synthesis of block copolymers in a one-pot process starting from the presence of air was also achieved using ARGET ATRP with a large excess of reducing agent to account for oxidation of catalyst by air. Block copolymers with a broad molecular weight distribution in one block were also synthesized using ARGET ATRP. It was observed that a different morphology was obtained for a block copolymer with broad molecular weight distribution in one block as compared to its analog with narrow molecular weight distribution in the same block. ARGET ATRP was also used to improve the synthesis of star polymers by allowing for precise control over radical concentration during polymerization (by controlling reducing agent concentration). At the beginning of star synthesis, radical concentration was kept low to prevent star-star termination reactions. At later stages of star synthesis (after star molecules of larger size were obtained), radical concentration could be increased as star-star termination would be decreased due to steric hinderance. In another study, ICAR ATRP was used to reach high molecular weight polystyrene. With ICAR ATRP, less catalyst-based termination reactions occur as copper concentration is low, and therefore higher molecular weight polystyrene could be obtained. It was also demonstrated that very high molecular weight polymethacrylates and polystyrene could be obtained by going to very high pressure. At high pressure, termination reactions are suppressed while propagation is enhanced, therefore full conversion can be attained of polymerizations with high targeted degrees of polymerization (leading to high molecular weight). Finally, the effectiveness of various copper-removal techniques were studied, together with the effect that these techniques have on chain end functionality of a polystyrene.