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Polypeptides, as the synthetic analogues of natural proteins, are an important class of biopolymers that are widely studied and used in various biomedical applications. However, the preparation of polypeptide materials from the polymerization of N-carboxyanhydride (NCA) is limited by various side reactions and stringent polymerization conditions. Recently, we report the cooperative covalent polymerization (CCP) of NCA in solvents with low polarity and weak hydrogen-bonding ability (e.g., dichloromethane or chloroform). The polymerization exhibits characteristic two-stage kinetics, which is significantly accelerated compared with conventional polymerization under identical conditions. In this Account, we review our recent studies on the CCP, with the focus on the acceleration mechanism, the kinetic modeling, and the use of fast kinetics for the efficient preparation of polypeptide materials. By studying CCP with several initiating systems, we found that the polymerization rate was dependent on the secondary structure as well as the macromolecular architecture of the propagating polypeptides. The molecular interactions between the α-helical, propagating polypeptide and the monomer played an important role in the acceleration, which catalyzed the ring-opening reaction of NCA in an enzyme-mimetic, Michaelis–Menten manner. Additionally, the proximity between initiating sites further accelerated the polymerization, presumably due to the cooperative interactions of macrodipoles between neighboring helices and/or enhanced binding of monomers. A two-stage kinetic model with a reversible monomer adsorption process in the second stage was developed to describe the CCP kinetics, which highlighted the importance of cooperativity, critical chain length, binding constant, [M]0, and [M]0/[I]0. The kinetic model successfully predicted the polymerization behavior of the CCP and the molecular-weight distribution of resulting polypeptides. The remarkable rate acceleration of the CCP offers a promising strategy for the efficient synthesis of polypeptide materials, since the fast kinetics outpaces various side reactions during the polymerization process. Chain termination and chain transfer were thus minimized, which facilitated the synthesis of high-molecular-weight polypeptide materials and multiblock copolypeptides. In addition, the accelerated polymerization enabled the synthesis of polypeptides in the presence of an aqueous phase, which was otherwise challenging due to the water-induced degradation of monomers. Taking advantage of the incorporation of the aqueous phase, we reported the preparation of well-defined polypeptides from nonpurified NCAs. We believe the studies of CCP not only improve our understanding of biological catalysis, but also benefit the downstream studies in the polypeptide field by providing versatile polypeptide materials.
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A Comprehensive, Multidimensional First‐Principles Model for Free‐Radical Photopolymerizations in Bulk and Thin Films
Abstract Decades of advances in understanding and simulating the polymerization kinetics and structural evolution that arises in free‐radical photopolymerizations of multifunctional monomers are combined into a single, first‐principles 3D model. The model explicitly accounts for polymerization features including diffusion‐controlled kinetics, oxygen inhibition, light attenuation, chain‐length dependent termination, reaction‐diffusion termination, heat transfer, composition and conversion‐dependent material properties, crosslinking effects, and species diffusion. Using the homopolymerization of 1,6‐hexanediol diacrylate as a model system, a minimum of two kinetics experiments performed at different initiation rates are required to fit model parameters. The model accurately predicts known relationships regarding oxygen inhibition, light intensity, and curing temperature for samples of different geometries and boundary conditions. The emphasis of the results herein is placed on the interactions between polymerization features, motivating the importance of a model that accommodates these features all in one simulation. The model is shown to be robust in its handling of thermal boundary conditions, alternative polymerization techniques or mechanisms, and characteristics of 3D voxel formation. The model in this work provides a useful tool for property prediction in a wide variety of applications, most notably coatings, dental materials, industrial photocuring processes, additive manufacturing, and holography, where complex interactions of the various features of polymerization play a substantial role.
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- Award ID(s):
- 1808484
- PAR ID:
- 10489880
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Functional Materials
- Volume:
- 34
- Issue:
- 22
- ISSN:
- 1616-301X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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