Controlled Synthesis of a Homopolymer Network Using a Well-Defined Single-Component Diels–Alder Cyclopentadiene Monomer

Abstract

Cyclopentadiene is known for its high reactivity and propensity to dimerize, making monomer synthesis and polymerization notoriously challenging. In fact, despite its long history and compelling chemistry, only two reports have appeared in the literature since the first attempt to homopolymerize cyclopentadiene by Staudinger in 1926. Herein, we present a strategy not only to synthesize, isolate, and homopolymerize a well-defined tetracyclopentadiene monomer but also to de-cross-link the network homopolymer. Mechanical properties are also investigated, including creep–recovery, shape memory, and tensile behaviors. Interestingly, the tensile test reflects a tough and elastic material, in contrast to prior Cp-based homopolymer networks. This work provides a versatile platform to access and study new cyclopentadiene-based and better-defined homopolymer networks with potential applications ranging from shape memory polymers to degradable thermosets.

Molecular Clogging Organogels with Excellent Solvent Maintenance, Adjustable Modulus, and Advanced Mechanics for Impact Protection

“…The measured cross-link density of the cross-linked polymer network is often lower than the theoretical value due to possible defects in the cross-link network and incomplete reaction of the monomers. [35] The experimental M c of the polyurea network measured by DMA is 994 g mol −1 , which is very close to the theoretical M c of 876 g mol −1 (876/994 = 88%), indicating fewer defects within the network and a more homogeneous network topology. This high degree of homogeneity of the polyurea network may be related to fast polyaddition reaction between the amino and the isocyanate.…”

“…The variation of its storage modulus E′, loss modulus E″ and loss coefficient (tan 𝛿) as a function of temperature was measured. (Figure S1, Supporting Information) The average molecular weight of the chain segments between the crosslinking sites, Mc, can be calculated by using the following equation: [35]…”

Diels–Alder Photoclick Patterning of Extracellular Matrix for Spatially Controlled Cell Behaviors

“…Without an available maleimide to undergo the click reaction, the uncaged Cp on the protein surfaces can slowly dimerize, [ 30 ] potentially increasing the material stiffness and driving ERK signaling. [ 31 ] Given the rapid reaction kinetics of the maleimide‐Cp cycloaddition, we anticipated that negligible Cp dimerization would occur in our patterned surfaces.…”

“…Remarkably, activated ERK was sustained through the entire duration of the experiment (6 h, Videos S1−S3, Supporting Information) suggesting that our EGF-functionalized ECM is resistant to receptor-level negative feedback that reduces pathway activity after activation with soluble ligands. [28,29] Without an available maleimide to undergo the click reaction, the uncaged Cp on the protein surfaces can slowly dimerize, [30] potentially increasing the material stiffness and driving ERK signaling. [31] Given the rapid reaction kinetics of the maleimide-Cp cycloaddition, we anticipated that negligible Cp dimerization would occur in our patterned surfaces.…”

Enantioselective Total Synthesis of (+)-Pedrolide

“…Of the potential candidates considered, , we were particularly attracted to C(7)-metalated norbornadiene derivative VI . The lithiated species would readily be accessed and, additionally, recent reports suggest mild ways of unmasking the cyclopentadiene, which we could examine in a complex setting …”