Competitive Copolymerization: Access to Aziridine Copolymers with Adjustable Gradient Strengths

Abstract

Competitive copolymerization gives access to gradient copolymers with simple one-step and one-pot strategies. Due to the living nature of the sulfonyl-aziridine polymerization, gradient copolymers can be obtained with low dispersities and adjustable molar masses. The combination of different sulfonyl activating groups allowed to fine-tune the reactivity difference of the comonomers and thus an exact adjustment of the gradient strength. Sulfonyl-activated aziridines are to date the only monomer class providing access to gradient copolymers with reactivity ratios ranging from (1 ≤ r 1 ≤ 2; 1 ≥ r 2 ≥ 0.5) for statistical or soft gradient copolymers to block copolymers (r 1 ≥ 20, r 2 ≤ 0.02), only by adjusting the electron-withdrawing effect of the activation groups: the reactivity ratios were calculated by different models for a library of eight comonomers. This library was further used to classify between hard, medium, and soft gradients. From the data obtained from the monomer library, it was possible to predict polymerization rate coefficients (k p ) for aziridines, which were not prepared so far: correlation of the shifts in the 13 C NMR spectra, the Hammett parameters and secondary parameters such as calculated lowest unoccupied molecular orbital (LUMO) levels of the monomers and the natural charge at the electrophilic carbon, etc., were used to predict (co)monomer reactivity and the resulting gradient strength. We believe that our findings allow us to access tailored gradient copolymers with a controlled monomer sequence distribution depending on the chemical control of comonomer reactivity. With these systematic data on activated aziridines, also more complex copolymer structures can be predicted and prepared. Such materials might find application as linear polyethylenimine derivatives to act as functional polyelectrolytes, or predesigned compatibilizers and surface-active gradient copolymers by a predictable one-step copolymerization.

C5 and C6 Polymerizations by Anion Migrated Ring-Opening of 1-Cyclopropylvinylbenzene and 1-Cyclobutylvinylbenzene

“…The particular reactivity ratio of comonomers is the essential factor in regulating the sequence structure of monomer units during chain growth polymerization. For general polymerization systems ( r 1 × r 2 > 0), sequence regulation of monomer units cannot be realized, and only block or statistical (random and gradient) sequence distributions can be prepared. ,− Recently, Kamigaito et al proposed a strategy to obtain sequence-defined vinyl polymers containing two double bonds in the main chain via ROMP of template ring monomers, and the polymer subsequently treated by hydrogenation resulted in methylene/styrene/acrylate/styrene/ethylene (i.e., SASEM) as the repeating units in the hydrogenation product . ROMP of 4-phenylcyclopentene (4PCP) has also been investigated, and quantitative homogeneous hydrogenation of P4PCP results in a precision E/S copolymer with a C5 skeleton (i.e., SEM) .…”

Synthesis of poly-α/β-peptides with tunable sequence via the copolymerization on N-carboxyanhydride and N-thiocarboxyanhydride

“…When THF was used as the solvent for copolymerization on a mixture of a-NCA and b-NTA, using Boc-a-L-Lys NCA and Bn-b 3 -LCHG NTA as the model, we found no significant gradient separation in compositional profile of two amino acid subunits within the poly-a/b-peptide chain, though Boc-a-L-Lys NCA have a slightly higher reactivity than Bn-b 3 -LCHG NTA according to the kinetic plot of residual monomer (Figures 3A-3C) and instantaneous copolymer composition F a-NCA (Figures 3C and S19). (Gleede et al, 2019) This copolymerization proceeded close to ''ideal copolymerization'' (r a-NCA 3 r b-NTA = 0.93, r a-NCA 3 r b-NTA = 1 means ideal copolymerization) (Yasir et al, 2020), which in combination with the instantaneous copolymer composition F a-NCA revealed that the resulting poly-a/b-peptide was a random-like copolymer and the b-amino acid residue has a nearly even distribution along poly-a/b-peptide chain (Figure 3C) (Yasir et al, 2020). Poly-a/b-peptides have proven to be important mimics and modifications of nature polypeptides, such as host defense peptide (HDP), to effectively improve the stability upon enzymatic degradation and therapeutic potential (Konai et al, 2018;Schmitt et al, 2004Schmitt et al, , 2007.…”

Anionic Ring-Opening Polymerizations of N-Sulfonylaziridines in Ionic Liquids

“…Sulfonylaziridines are intriguing as monomers as they are able to polymerize under less stringent conditions than are typically associated with anionic polymerizations. − In 2018, Wurm reported that the anionic ring-opening polymerization of methylsulfonylaziridines proceeds in wet DMF . The presence of water in the AROP of sulfonylaziridine is possible because the p K a of the sulfonylamides is comparable to that of water, and hydroxide is a poor nucleophile for sulfonylaziridine-ring opening.…”