Molecular weight distributions (MWD) have a substantial impact on a diverse set of polymer physical and rheological properties, from processability and stiffness to many aspects of block copolymer microphase behavior. The precise MWD compositions of these polymers can be modularly controlled through temporal initiation in anionic polymerizations by metered addition of a discrete initiating species. With the technique described in this work, we identify initiator addition profiles through theoretical modeling which can be used to prepare any desired arbitrary MWD. This kinetic model reproduces experimental MWDs with high fidelity. Our modeling strategy incorporates a detailed kinetic description of polymer initiation and propagation, including the association and dissociation equilibria of the living polymer chain ends. We simplify the kinetic model by incorporating the aggregation phenomena into an effective propagation rate constant k p , allowing it to vary with the polymer chain length ( i ). Importantly, this model also yields the ability to predict MWDs at any arbitrary value of monomer conversion during the polymerization. Lastly, we simulate MWDs for a variety of new, yet unmeasured, initiator addition profiles, demonstrating the predictability of this approach.
This content will become publicly available on February 15, 2023
A general model for the ideal chain length distributions of polymers made with reversible deactivation
Polymer molecular weight, or chain length distributions, are a core characteristic of a polymer system, with the distribution being intimately tied to the properties and performance of the polymer material. A model is developed for the ideal distribution of polymers made using reversible activation/deactivation of chain ends, with monomer added to the active form of the chain end. The ideal distribution focuses on living chains, with the system having minimal impact from irreversible termination or transfer. This model was applied to ATRP, RAFT, and cationic polymerizations, and was also used to describe complex systems such as blended polymers and block copolymers. The model can easily and accurately be fitted to molecular weight distributions, giving information on the ratio of propagation to deactivation, as well as the mean number of times a chain is activated/deactivated under the polymerization conditions. The mean number of activation cycles per chain is otherwise difficult to assess from conversion data or molecular weight distributions. Since this model can be applied to wide range of polymerizations, giving useful information on the underlying polymerization process, it can be used to give fundamental insights into macromolecular synthesis and reaction outcomes.
- Publication Date:
- NSF-PAR ID:
- 10319502
- Journal Name:
- Polymer Chemistry
- Volume:
- 13
- Issue:
- 7
- ISSN:
- 1759-9954
- Sponsoring Org:
- National Science Foundation
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