Solvent Dependency in the Synthesis of Multiblock and Cyclic Poly(2-oxazoline)s

Abstract

Multiblock copolymers as well as cyclic polymers exhibit unique physical properties and are being utilized in various applications. However, the synthesis of such polymers is quite challenging because there is a delicate balance in achieving either structure. Here, we report a surprising solvent dependence on the cyclization and step-growth reactions of poly­(2-alkyl 2-oxazoline)­s. Additionally, other important parameters such as catalyst concentration, polymer concentration, and temperature were investigated, and their influences on the obtained ratio between step-growth and cyclization polymers are discussed. Step growth of a telechelic poly­(2-ethyl 2-oxazoline) macromonomer yielded a multiblock polymer containing, on average, eight repeating units. Moreover, reaction conditions in order to favor cyclization over step-growth polymerization were optimized for poly­(2-fatty acid-2-oxazoline). Finally, using the optimized conditions, an up to 80:20 cyclization/step-growth polymer mixture was obtained at a relatively high polymer concentration (50 mg/mL).

Macrocyclization efficiency for poly(2-oxazoline)s and poly(2-oxazine)s

“…Interestingly, these new signals differ between PnPropOx 20 and PnPropOzi 20 . In agreement with data from previous studies, 1,9,11 CuAAC of PnPropOx 20 results in a distinct signal group between 4.50 and 4.60 ppm. However, CuAAC of PnPropOzi 20 results in a broader signal group between 4.30 and 4.70 ppm.…”

“…Whilst effective, an inherent challenge is the interdependency of reaction parameters such as solvent, batch volume, and reagents, which dictate the cyclization efficiency, making optimization on a case-by-case basis necessary. 10,11 Conversely, post-reaction separation of the cyclized product from by-products, unreacted starting materials, [12][13][14][15][16] solvents, as well as other reagents employed during the reaction 17 can be time and labour-intensive. Despite these synthetic challenges, the interest in cyclic polymers is ever increasing.…”

“…4,18 However, insight into the impact of reaction conditions on the cyclization efficiency of PAOx remains limited to a single recent report by the group of Becer, investigating the effect of solvent on the macrocyclization reaction. 11 To understand the cyclization mechanism in more detail and to work towards the scale-up of these cyclic polymers, a methodological approach is needed. Hence, in the current study, the influence of batch volume, catalyst equivalents, molecular weight, polymer addition method and polymer backbone on the cyclization efficiency has been investigated to provide deeper insight into the influence of synthetic parameters on the cyclization reaction.…”

Synthesis of well-defined cyclic glycopolymers and the relationship between their physical properties and their interaction with lectins

“…To enable the intramolecular cyclization of the polymer main chain by "click" reaction, the RAFT agent was modified with an azide moiety on the "R" group. [23][24][25][26] The [DMA]/[Man] monomer ratio was set at 9 : 1 to avoid steric hindrance of the bulky glycounits during the cyclization reaction. The target degrees of polymerization (DP) were 50 and 100.…”

“…S17 and Table S2 †). 26 To purify the cyclic polymers, the oligomeric by-products were removed by cycled SEC separation (Fig. S18 and S19 †).…”