The mechanical properties of polymers are highly dependent on the mobility of the underlying chains. Changes in polymer architecture can affect inter‐ and intramolecular interactions, resulting in different chain dynamics. Herein, an enhancement in the mechanical properties of poly(butylmethacrylate) is induced by folding the polymer chains through covalent intramolecular crosslinking (CL). Intramolecular CL causes an increase in intramolecular interactions and inhibition of intermolecular interactions. In both the glassy and rubbery states, this molecular rearrangement increases material stiffness. In the glassy state, this molecular rearrangement also leads to reduced failure strain, but surprisingly, in the rubbery state, the large strain elasticity is actually increased. An intermediate intramolecular CL degree, where there is a balance between intra‐ and intermolecular interactions, shows optimal mechanical properties. Molecular dynamics simulations are used to confirm and provide molecular mechanisms to explain the experimental results.

Chemical cross-linking of polymer chains is a powerful means for tailoring the thermomechanical properties of bulk plastics. Nonetheless, upon cross-linking, processability is reduced as the plastic becomes thermoset. Here, molecular dynamics simulations are used to study the effects of intramolecular chemical cross-linking on chain topology and thermomechanical properties of a bulk, thermoplastic polymer. Polyethylene (PE)-like plastics are assembled purely from chains which have undergone a set level of intrachain cross-linking (to form single chain polymer nanoparticles, SCPNs). We have analyzed the chain topology at an equilibrated state in terms of chain unfolding and entanglement by radius of gyration and primitive path, respectively. The extents of both chain unfolding and chain entanglement were found to decrease with increasing intrachain cross-linking ratio. By applying simulated cooling, uniaxial tension, and uniaxial compression, we characterized the thermomechanical properties at the glassy state. The simulated mechanical testing shows that the bulk polymer becomes stiffer, stronger, and more brittle as the intrachain cross-linking ratio is increased. We observe that the failure of the SCPN-based bulk polymers is a consequence of separation between SCPNs. This study successfully elucidates the effect of intramolecular cross-linking on the thermomechanical properties at bulk, as a clear correlation is shown between the amount of covalent intrachain collapse and interchain interactions.

The mechanical properties of an amorphous polymer are a consequence of the inter- and intramolecular interactions which are typically similar. Yet, polymers can be made with covalent intramolecular cross-links, leading to stronger intramolecular interactions. Here, a study on the effect of this intramolecular cross-linking on the mechanical properties of a glassy polymer is shown. A linear poly­(methyl methacrylate) with defined size was cross-linked at different ratios and assembled into solid samples by solvent casting. Mechanical testing indicates that intramolecular cross-linking does not affect the mechanical properties at the elastic region but does influence these properties at the plastic region. Interestingly, intramolecular cross-linking leads to different effects than “regular” interchain cross-linking. The results are consistent with a reduction in chain entanglement, reducing toughness and to a lesser extent strength.

INTRODUCTION Noncovalent interactions such as hydrogen bonds, hydrophobic interaction, and metal-ligand interactions (neutral and ionic) enable networks in both natural systems 1,2 and synthetic materials. [3][4][5][6] These noncovalent networks can potentially mimic classical covalent network behaviors such as elastic recovery from large deformation and swelling in the presence of good solvents, 7,8 while boasting appealing properties such as self-healing, 9,10 processability, 11,12 energy absorption, 13 self-assembly, 14 and stimuli responsiveness. 15,16 This combination of covalent-like and dynamic properties is accomplished by tuning the dynamics of the network connections. Metallopolymers in particular have attracted much attention in the past two decades due to their possible mechanical properties, synthetic methodologies, and processing. 17,18 Metallopolymers are highly customizable since in addition to normal polymer control knobs such as monomer selection, molecular weight and architecture, metallopolymers can be differentiated by where the metal complexes are bound in the polymer architecture (i.e., as crosslinkers, side chain substituent, or part of a linear backbone), and by the type of metal cation and ligand chemistry. 17The strength of the metal complex to resist breaking under mechanical force has been shown to strongly influence the mechanical behavior of metallopolymers. [19][20][21] It was demonstrated that by clever design of supramolecular polymers, metallopolymers synthesized with different metals 19,20,22 or different ligands 21,23 presented diverse organometallic interactions that lead to different stiffness, toughness, and viscoelastic dissipation. These distinct mechanical behaviors can also be controlled by external stimuli. The groups of Holten-Andersen and Meyer showed how changing metal-ligand interactions in metallo-hydrogels by changing the pH, 8 the oxidation state of the metals with UV exposure, 24 or electrochemically 25,26 allowed control over mechanical properties. Recently, Manners et al. showed that polarity and coordination ability of a solvent dictate the dynamic nature of metal-ligand interactions in a poly-nickelocene solution. 27 Here we present an innovative material system in which the addition of copper(II) to a linear elastomer increases strength and decreases ductility through the formation of metal-ligand bonds that behave in a covalent-like manner. Unlike covalent crosslinks, however, the copper-based crosslinks can be weakened and even removed with proper choice of ligands, enabling full thermoplastic-like processing. Furthermore, we show in our final portion that ligands can be incorporated within the solid-state material, essentially removing or making the crosslinks mechanically dynamic, increasing toughness, and enabling self-healing. In contrast to much of the previous work in this field, our polymers are solid even without the metal-ligand bonds, making the dynamic behavior regime, and its applications distinct.Our design strategy for creating an elastomer...

The nanoscale morphologies of block copolymer (BCP) thin films are determined by chain architecture. Experimental studies of thin film blends of different BCP chain types have demonstrated that blending can stabilize new motifs, such as coexistence phases. Here, we deploy coarse-grained molecular dynamics (MD) simulations in order to better understand the self-assembly behavior of BCP blend thin films. We consider blends of lamella- and cylinder-forming BCP chains, studying their morphological makeup, the chain distribution within the morphology, and the underlying polymer chain conformations. Our simulations show that there are local concentration deviations at the scale of the morphological objects that dictate the local structure, and that BCP chains redistribute within the morphology so as to stabilize the structure. Underlying these effects are measurable distortions in the BCP chain conformations. The conformational freedom afforded by BCP blending stabilizes defects and allows coexistence phases to appear, while also leading to kinetic trapping effects. These results highlight the power of blending in designing the morphology that forms.