Independent Control of Elastomer Properties through Stereocontrolled Synthesis

Abstract

In most synthetic elastomers,c hanging the physical properties by monomer choice also results in ac hange to the crystallinity of the material, which manifests through alteration of its mechanicalperformance.Using organocatalyzed stereospecific additions of thiols to activated alkynes,h igh-molarmass elastomers were isolated via step-growth polymerization. The resulting controllable double-bond stereochemistry defines the crystallinity and the concomitant mechanical properties as well as enabling the synthesis of materials that retain their excellent mechanical properties through changing monomer composition. Using this approacht oe lastomer synthesis,f urther end group modification and toughening through vulcanization strategies are also possible.The organocatalytic control of stereochemistry opens the realm to an ew and easily scalable class of elastomers that will have unique chemical handles for functionalization and post synthetic processing.Nature has evolved the ability to create large and complex molecules in which the precise control over the spatial arrangement of the atoms is critical to their performance.The three-dimensional control over the arrangement of bonds is as important to the function and behavior of molecules as any other factor and is critical to the structure-function relationships that govern the role of arange of molecules.While the effect of stereochemistry on functionality is probably best known in the examples of small molecule drugs such as thalidomide (one enantiomer is effective against morning sickness,t he other is teratogenic) or naproxen (one enantiomer is used to treat arthritis pain, the other causes liver poisoning with no analgesic effect), it is less well-studied with respect to materials design.Elastomeric materials are applied widely to demanding applications on account of their inherent reversible deformation behavior. Many synthetic elastomer materials are tri-or multi-block copolymers that are based on the concept of an amorphous-crystalline or hard-soft phase-separated system in which organization of the hard and soft domains endows the strong but elastic properties upon the materials.[1] While these materials have found widespread application, changes to the monomers or stoichiometry designed to elicit ac hange in physical properties also alter the chain packing and hence the mechanical properties of the materials.I nterestingly,n atural rubber and gutta percha are homopolymers of poly(cisisoprene) and poly(trans-isoprene) respectively.W hile these materials differ by only the double bonds of the backbone,the superior elastomeric properties of natural rubber [2] are attributed to the enhanced chain packing afforded by its stereochemical orientation.[3] While the design principles to control crystallinity and the associated mechanical properties in these materials are clear,the inability to incorporate awide range of functional groups in ac ontrolled manner or rationally define the chain end functionality limits the applications of both these materials a...

Stereocontrolled Acyclic Diene Metathesis Polymerization

“…DSC revealed a clear influence of cis-alkene content on thermal transitions as depicted in the thermograms in Fig. 5d-f, which is in line with reports by Buchard 39 and Dove and Becker 3,40 . In addition to small variations of glass transition temperatures (Tg), striking differences in crystalline behavior were observed.…”

Concomitant control of mechanical properties and degradation in resorbable elastomer-like materials using stereochemistry and stoichiometry for soft tissue engineering

“…This behavior is consistent with a more elastic material that is expected from the interruption of crystallinity through the introduction of ester groups into the main chain that disrupt chain packing and increase chain mobility. These findings were confirmed via differential scanning calorimetry (DSC) which showed that increasing %cis without altered succinate content increased the glass transition temperature in line with results from our previous work 5,29 . Significantly, the materials exhibit high thermal stability and the onset of degradation temperatures exceeds 350°C.…”

“…Until now, no synthetic resorbable elastomer or elastomer-like polymer system have afforded independent control of mechanical properties and degradation de novo 2 . We recently reported the first metal-free, stereocontrolled step-growth polymerization via a nucleophilic thiol-yne addition which yielded a series of thermally-processable elastomers in which the mechanical properties were controlled by the double bond stereochemistry 5,29 . The double bond stereochemistry (% cis) in each thiol-yne step growth polymer was tuned based on solvent polarity and organic base which is able to preferentially direct the thiol addition to the cis stereochemistry.…”

“…Future studies for these materials will observe the effects of degradation and associated inflammation for the slower degrading variants. Many recent findings have noted the importance of fine-tuning degradation rates to match regeneration rates for optimal tissue growth and mechanical reinforcement as needed throughout healing 2,24,29,41 . Significantly, this study has shown significant tissue growth into non-functionalized bulk implants where inflammation and granuloma formation was limited.…”

Divergent Catalytic Strategies for the Cis/Trans Stereoselective Ring-Opening Polymerization of a Dual Cyclic Carbonate/Olefin Monomer

“…13 Becker and Dove reported an organocatalytic stereocontrolled synthesis of unsaturated polyesters, resulting in a tunable cis/trans ratio, crystallinity, and mechanical properties. 14 Postpolymerization catalysis was also exploited to isomerize poly(propylene maleate) into poly(propylene fumarate) toward 3D printing and medical applications. 15−17 The ability to drastically change polymer properties through cis/trans isomerization, e.g.…”