Entropy-driven Ring-opening Metathesis Polymerization Research Articles

Orthogonally deconstructable and depolymerizable polysilylethers via entropy-driven ring-opening metathesis polymerization.

The synthesis of novel polysilylethers via entropy-driven ring-opening metathesis polymerization (ED-ROMP) of cyclic bifunctional silyl ether-based monomers is reported. These polymers display good thermal stability and ultra-low Tg (-88 °C). Moreover, they are rapidly deconstructable via the cleavage of the silicon-oxygen linkages with acid or fluoride triggers, and they were partially depolymerizable by the addition of exogenous metathesis catalyst. Analysis of the deconstructed polymer products provided insight into the polymer microstructure, showing that the ED-ROMP process was regiorandom. Altogether, this work offers a new class of deconstructable polymers with a range of potential applications.

High molar mass poly(ricinoleic acid) via entropy-driven ring-opening metathesis polymerization

High molar mass poly(ricinoleic acid) was synthesized via entropy-driven ring-opening metathesis polymerization of mono-, di- and mixed macrolactones of ricinoleic acid using a Grubbs second-generation catalyst and fully characterized.

Influence of Short-Range Scrambling of Monomer Order on the Hydrolysis Behaviors of Sequenced Degradable Polyesters

The extent to which small changes in monomer sequence affect the behaviors of biological macromolecules is studied regularly, yet the dependence of bulk properties on small sequence alterations is underexplored for synthetic copolymers. Investigations of this type are limited by the arduous syntheses required, lack of scalability, and scarcity of examples of polymer systems that are known to exhibit sensitive sequence/property dependencies. Our group has previously explored the hydrolysis behaviors of a library of sequenced poly(lactic-co-glycolic acid)s and found a strong correlation with the L–G sequence. To investigate the degree to which properties are dominated in this system by relatively short-range sequence changes, we have incorporated precisely sequenced and mildly “scrambled” L–G oligomers into cyclic macromonomers and subjected them to entropy-driven ring-opening metathesis polymerization, a method that we have recently shown produces polymers with molecular weight control and sequence preserv...

Sequence-Controlled Polymers Through Entropy-Driven Ring-Opening Metathesis Polymerization: Theory, Molecular Weight Control, and Monomer Design.

The bulk properties of a copolymer are directly affected by monomer sequence, yet efficient, scalable, and controllable syntheses of sequenced copolymers remain a defining challenge in polymer science. We have previously demonstrated, using polymers prepared by a step-growth synthesis, that hydrolytic degradation of poly(lactic- co-glycolic acid)s is dramatically affected by sequence. While much was learned, the step-growth mechanism gave no molecular weight control, unpredictable yields, and meager scalability. Herein, we describe the synthesis of closely related sequenced polyesters prepared by entropy-driven ring-opening metathesis polymerization (ED-ROMP) of strainless macromonomers with imbedded monomer sequences of lactic, glycolic, 6-hydroxy hexanoic, and syringic acids. The incorporation of ethylene glycol and metathesis linkers facilitated synthesis and provided the olefin functionality needed for ED-ROMP. Ring-closing to prepare the cyclic macromonomers was demonstrated using both ring-closing metathesis and macrolactonization reactions. Polymerization produced macromolecules with controlled molecular weights on a multigram scale. To further enhance molecular weight control, the macromonomers were prepared with cis-olefins in the metathesis-active segment. Under these selectivity-enhanced (SEED-ROMP) conditions, first-order kinetics and narrow dispersities were observed and the effect of catalyst initiation rate on the polymerization was investigated. Enhanced living character was further demonstrated through the preparation of block copolymers. Computational analysis suggested that the enhanced polymerization kinetics were due to the cis-macrocyclic olefin being less flexible and having a larger population of metathesis-reactive conformers. Although used for polyesters in this investigation, SEED-ROMP represents a general method for incorporation of sequenced segments into molecular weight-controlled polymers.

Cis-Selective Metathesis to Enhance the Living Character of Ring-Opening Polymerization: An Approach to Sequenced Copolymers.

The hydrolytic behavior and physical properties of a polymer are directly related to its constituent monomer sequence, yet the scalable and controllable synthesis of sequenced copolymers remains scarcely realized. To address this need, an enhanced version of entropy-driven ring-opening metathesis polymerization (ED-ROMP) has been developed. An unprecedented level of control is obtained by exploiting the kinetic and thermodynamic differences in the metathesis activity of cis- and trans-olefins embedded in large, unstrained macrocycles. First-order rate kinetics were observed, and polymer molecular weights were found to be proportional to catalyst loading. Computational analysis suggests that incorporation of a cis-olefin into the monomer backbone both introduces a thermodynamic driving force and increases the population of metathesis-active conformers. This approach offers a generally applicable method for enhancing living character in ED-ROMP.

Precision Aliphatic Polyesters via Segmer Assembly Polymerization.

Precise structure-property relation of a biodegradable polymer (e.g., aliphatic polyester) is anticipated only if monomer units and chiral centers are arranged in a defined primary sequence as a biomacromolecule. An emerging synthetic methodology, namely segmer assembly polymerization (SAP), is introduced in this paper to reveal the latest progress in polyester synthesis. Almost any periodic polyester envisioned can be synthesized via SAP using a programed linear or cyclic monomer. In this context, the macroscopic properties of a biodegradable polymer are fundamentally determined by microstructural information through a bottom-up approach. It can be highlighted that SAP ideally combines the precision of organic synthesis and the high efficiency of a polymerization reaction. Previously reported strategies including nucleophilic displacement, polyesterification, cross-metathesis polymerization (CMP), ring-opening polymerization (ROP), ring-opening metathesis polymerization (ROMP) and entropy-driven ring-opening metathesis polymerization (ED-ROMP) are critically reviewed in this paper to shed light on precision synthesis of aliphatic polyesters via SAP. Emerging yet challenging, SAP is a paradigm which reflects the convergence of organic and polymer chemistries and is also an efficient pathway to microstructural control. The current status, future challenges and promising trends in this realm are analyzed and discussed in this overview of the state-of-the-art.

Metathesis polymerization of cystine-based macrocycles

Entropy-driven ring-opening metathesis polymerization (ED-ROMP) of cystine-based macrocycles yields multifunctional poly(ester-amine-disulfide-alkene)s.

An entropy-driven ring-opening metathesis polymerization approach towards main-chain liquid crystalline polymers

In this manuscript, an entropy-driven ring-opening metathesis polymerization (ED-ROMP) approach is applied for the first time in producing main-chain liquid crystalline polymers by polymerizing a macrocyclic olefin monomer.

Sequence-Controlled Copolymers Prepared via Entropy-Driven Ring-Opening Metathesis Polymerization.

A new general synthetic approach to sequenced macromolecules was developed and applied to the synthesis of polymers comprising lactic acid (L), glycolic acid (G), and ε-caprolactone (C)-derived monomer units. The new method employs entropy-driven ring-opening metathesis polymerization (ED-ROMP) to prepare copolymers with embedded sequences and controlled molecular weights. Cyclic macromonomer precursors were prepared by ring-closing metathesis of ethylene glycol (Eg)-linked sequenced oligomers bearing terminal olefins. ED-ROMP of the resulting macrocycles using Grubbs' second generation catalyst yielded poly(CL-Eg-LC-Oed), poly(CLL-Eg-LLC-Oed), poly(LGL-Eg-LGL-Oed), and poly(LGL-Eg-LGL-Hed) (Oed = octenedioc acid; Hed = hexenedioc acid). Hydrogenation produced the saturated sequenced copolymers. Molecular weight was well-controlled and could be adjusted by varying the monomer-to-catalyst ratio. Mns of 26-60 kDa were obtained (dispersities = 1.1-1.3). The methodology proved general for three different sequences and two olefinic metathesis groups.

Self-assembly and ring-opening metathesis polymerization of a bifunctional carbonate–stilbene macrocycle

A carbonate–stilbene bifunctional macrocycle was readily synthesized, and its assembly was studied by crystallization from several solvents. The macrocycle displayed columnar assembly from less polar solvents (THF and CH2Cl2), while a more compact structure was observed from 9 : 1 CH2Cl2–acetone. All structures displayed organization through the C–H⋯O hydrogen bonding motif as well as through aryl stacking interactions. Upon dissolution and treatment with Grubbs’ II catalyst, this 30-membered ring underwent entropy-driven ring-opening metathesis polymerization (ED-ROMP) to give a precisely linear alternating A–B–A–B copolymer. This design of a single macrocyclic building block allows the formation of supramolecular self-assembly in the solid-state while affording a linear alternating polymer from solution.

Shape Memory Polymers Based on Naturally-Occurring Bile Acids

Naturally occurring bile acids are ideal building blocks for a new generation of biomaterials displaying low systemic toxicity and engineered properties. Herein we report the synthesis of bile acid-based polyesters using entropy-driven ring-opening metathesis polymerization (ED-ROMP) and characterization of the structure of the resulting polymers. The materials synthesized display high molecular weights (Mn above 100000), typical of ED-ROMPs. The mechanical and responsive behavior of these bile acid-based polyesters (BAPs) is studied by dynamic mechanical analysis (DMA) and thermomechanical cycling. Although BAPs are amorphous thermoplastics, they display typical rubber-like elasticity with tunable mechanical behavior, glass transitions close to body temperature, and outstanding shape memory properties. By introducing small changes in the chemical structure of BAPs (amide bonds or additional hydroxyl groups), we were able to correlate the materials’ stiffness, their Tg and shape recovery temperature to th...

Entropy-driven ring-opening olefin metathesis polymerizations of macrocycles

The curious entropy-driven ring-opening metathesis polymerization (ED-ROMP) of macrocyclic olefins is highlighted. From early proof-of-principle reports through current state-of-the-art studies with an inclination towards materials applications, the known examples of these uncommon polymerizations are surveyed. The underpinnings of why these reactions work, what is and what is not to be expected and the prevailing practical measures to be taken to favor ED-ROMPs are discussed.

Main-Chain Bile Acid Based Degradable Elastomers Synthesized by Entropy-Driven Ring-Opening Metathesis Polymerization

Dehnübungen: Abbaubare thermoplastische Elastomere wurden durch entropiegesteuerte Ringöffnungsmetathesepolymerisation von Gallensäure-Makrocyclen erhalten. Die Streckmoduln der Polyester entsprechen Werten für Elastin und andere weiche Gewebe wie Haut, Knorpel oder die Aorta. Durch ihre mechanischen Eigenschaften bieten sie sich als Kandidaten für biomedizinische Anwendungen an. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2001/2006/z602096_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.