Atom Transfer Radical Polymerization of End-Functionalized Hydrogen-Bonding Polymers and Resulting Polymer Miscibility

Flexible Cages Enable Robust Supramolecular Elastomers

Advances in modern industrial technology continue to place stricter demands on engineering polymeric materials, but simultaneously possessing superior strength and toughness remains a daunting challenge. Herein, a pioneering flexible cage-reinforced supramolecular elastomer (CSE) is reported that exhibits superb robustness, tear resistance, anti-fatigue, and shape memory properties, achieved by innovatively introducing organic imide cages (OICs) into supramolecular networks. Intriguingly, extremely small amounts of OICs make the elastomer stronger, significantly improving mechanical strength (85.0 MPa; ≈10-fold increase) and toughness (418.4 MJ m-3; ≈7-fold increase). Significantly, the cooperative effect of gradient hydrogen bonds and OICs is experimentally and theoretically demonstrated as flexible nodes, enabling more robust supramolecular networks. In short, the proposed strengthening strategy of adding flexible cages effectively balances the inherent conflict between material strength and toughness, and the prepared CSEs are anticipated to be served in large-scale devices such as TBMs in the future.

Toughening of Glassy Supramolecular Polymer Networks

A modular approach for the design of two-component supramolecular polymer (SMP) networks is reported. A series of materials was prepared by blending two (macro)monomers based on trifunctional poly(propylene oxide) (PPO) cores that were end-functionalized with hydrogen-bonding 2-ureido-4[1H]pyrimidinone (UPy) groups. One monomer was based on a PPO core with a number-average molecular weight (M_n) of 440 g mol^-1. The SMP formed by this building block is a glassy, brittle material with a glass transition temperature (T_g) of about 86 °C. The second monomer featured a PPO core with an M_n of 3000 g mol^-1. The SMP formed by this building block adopts a microphase-segregated morphology that features a rubbery phase with a T_g of -58 °C and crystalline domains formed by the UPy assemblies, which act as physical cross-links and melt around 90-130 °C. Combining the two components allows access to microphase-segregated blends comprised of a rubbery phase constituted by the high-M_n cores, a glassy phase formed by the low-M_n component, and a crystalline phase formed by UPy groups. This allowed tailoring of the mechanical properties and afforded materials with storage moduli of 37-609 MPa, tensile strengths of 2.0-5.4 MPa, and melt viscosities of as low as 11 Pa s at 140 °C. The materials can be used as reversible adhesives.

Accurately Determining the Extent of Coupling in Post Polymerization Reactions of Polystyrene

Polymers prepared by controlled radical polymerization (CRP) can be employed in subsequent chain-end joining reactions, yet accurately assessing the extent of coupling in mechanistically unique paths is not straightforward. Precisely known mixtures of polystyrene standards were prepared and analyzed by gel permeation chromatography (GPC), mimicking the coupled product and precursor that could be present after a post-polymerization, chain-end joining reaction. The exactly known percentages of each polymer in the mixture allowed for comparison of the true "extent of coupling" (Xc) to that determined by a commonly used equation, which is based on number average molecular weights (Mn) of the precursor and coupled product. The results indicated that an improvement in accuracy could be achieved by instead using refractive index (RI) signal height ratios under the peak molecular weight (Mp) of each component, with all calculations being within 0.05 of the true Xc of the fabricated "product" mixture (compared to greater than 0.10 average error using the more established method) when the sample mixture had nominal molecular weights of 2500 and 5000 Da. Moreover, when "precursor" and "coupled" pairs mixed were not related as a simple doubling of molecular weight, the calculation method presented here remained effective at determining the content of the mixture, especially at higher Xc values (>0.45). This second case is important for experiments that may link polymer chains together with a spacer, such as a radical trap, a triazole, or even larger structure such as an oligomer.

Temperature-dependent crystalline structure and phase transition of poly(butylene adipate) end-functionalized by multiple hydrogen-bonding groups

The crystallization kinetics, crystalline structure and phase transition of UPy-functionalized poly(butylene adipate) were investigated. UPy functionalization facilitated the formation of α crystals.

Synthesis of end-functionalized hydrogen-bonding poly(lactic acid)s and preferential stereocomplex crystallization of their enantiomeric blends

A novel UPy-functionalized alcohol was synthesized and used to initiate the solvent-free ROP of lactide to attain UPy-functionalized PLLA and PDLA. The crystallization rate and stereocomplexation ability of UPy-functionalized PLLA/PDLA blends were promoted.

Alternating poly(lactic acid)/poly(ethylene-co-butylene) supramolecular multiblock copolymers with tunable shape memory and self-healing properties

PLA/PEB SMPs with tunable shape memory and self-healing properties were prepared by end functionalization of PLA–PEB–PLA with UPy units.

Synthesis and characterization of amphiphilic triblock Copolymers with Identical compositions but different block sequences

The amphiphilic triblock copolymers PAA-b-PS-b-PAA and PS-b-PAA-b-PS were synthesized by a combination of an atom transfer radical polymerization mechanism and a nitroxide radical coupling reaction or copper-catalyzed azide/alkyne click chemistry.