Functionalized Cyclic Polymers and Network Gels

Abstract

Cyclic polymers exhibit different solution and bulk properties compared to their linear analogs of the same molecular weight, such as smaller hydrodynamic volumes and higher glass transition temperatures (T g ). Polymers having boron-centered Lewis acids as pendent groups have utility in sensors, biomaterials, and dynamic covalent materials. Conventional and controlled radical polymerization are the most common routes to synthesize polymers with pendent boronate ester and boronic acid functional groups. Herein, we expand the synthetic repertoire available for their synthesis by reporting the preparation of cyclic poly(4ethynylphenylboronate ester) (c-PEPB) by ring-expansion polymerization (REP) of 4-ethynylphenylboronate ester using a pincersupported tethered tetra-anionic tungsten alkylidene complex. The polymers were successfully characterized and compared to their linear analogs using light scattering measurements, solution viscometry, and thermal analysis. In all cases, the polymer interrogation experiments reveal key differences attributed to the cyclic topology. Deprotection of the polymeric boronate esters was performed by transesterification with methylboronic acid to furnish cyclic poly(4-ethynylphenyl boronic acid) (c-PEPB−OH). The reversible reaction of boronic acids with 1,2-and 1,3-diols to form boronate esters was used to cross-link c-PEPB−OH with a polyol crosslinker to form gels from cyclic polymers.

Tethered Alkylidenes for REMP from Carbon Disulfide Cleavage

“…The expected ratio range under θ conditions ( a = 0.5) between 0.65 , and 0.58 ± 0.01 . Experimental results are consistent, ranging from ∼0.4 to ∼0.8, ,− depending on the molecular weight , and the polymer–solvent system. , …”

Polysquaramides

“…CANs, distinguished by their bond exchange mechanism, are divided into dissociative and associative types. Dissociative CANs, when triggered by stimuli (e.g., heat or light), have their cross-links break down into reactive components that diffuse and then recombine, regenerating the network. − Whereas associative CANs (i.e., vitrimers) break and reform cross-links simultaneously through an associative intermediate, where a reactive group within the network swaps with an existing cross-link. − …”