posted on 2022-12-30, 21:10authored byYanlin Shi, Sung-Po R. Chen, George Fragkiadakis, Daniele Parisi, Virgil Percec, Dimitris Vlassopoulos, Michael J. Monteiro
The shape, breadth, and average molecular weight of the
overall
molecular weight distribution (MWD) largely define polymer properties.
In conventional free-radical polymerization, control over this distribution
is through the many competing kinetic pathways dominated by radical
termination events. “Living” radical polymerization
mechanistically minimizes these termination events, providing a facile
route to a desired Gaussian distribution with the distribution breadth
dependent upon the activity of the catalyst or modulating agent. However,
producing unusually shaped distributions can only be achieved through
modeling of the complex polymerization kinetics and invoking feeding
and other methods. Here, we construct square, slanted, and chair-like
MWDs by blending two to four polymers made using a low-reactive RAFT
agent with dispersities close to 2. The synthesis of these polymers,
unlike that of polymers made with high-reactive RAFT agents, is simple,
scalable, and importantly reproducible as the MWD is independent of
conversion, making this polymerization method virtually and kinetically
model-free. The blending method described here overcomes many of the
difficulties in producing unusually shaped MWDs and allows control
over the shape and breadth of the MWD. The concept further provides
a general synthetic strategy for studying important structure–property
relationships of polymers with desired processing and performance
characteristics. This is demonstrated by measurement and modeling
analysis of the linear viscoelastic properties of selected samples,
which provides a way to tailor the properties of polymers by controlling
the form of their MWD via blending. Unlike conventional approaches
analyzing the effects of the MWD, its actual shape is considered and
its effect on the properties is addressed.