Mechanochemical Degradation of Denpols: Synthesis and Ultrasound-Induced Chain Scission of Polyphenylene-Based Dendronized Polymers

Peterson, Gregory I.,Bang, Ki-Taek,Choi, Tae-Lim American Chemical Society 2018 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.140 No.27

<P>New polyphenylene-based dendronized polymers (denpols), exhibiting extended and rigid conformations, were prepared using ring-opening metathesis polymerization (ROMP). Their mechanochemical degradation was explored in ultrasound-induced elongational flow fields. Degradation rate constants were obtained for polyphenylene-based denpols, of varying generation, across a degree of polymerization (DP) range of ∼100-600. In general, it was found that larger side chains led to increased degradation rates and that the rate enhancement was proportional to the natural log of persistence length (Ln(<I>l</I><SUB>p</SUB>)) or the square root of monomer molecular weight (<I>M</I><SUB>mon</SUB><SUP>0.5</SUP>). These relationships led to the generation of “master curves” in which the rate constant trends for each polymer series converged, enabling accurate prediction of degradation rate constants for related polymers bearing long alkyl chains or ester-type dendrons. Furthermore, we observed evidence for, and used computational modeling to support, polymer chains undergoing multiple scissions during a single elongation event, leading to faster degradation of daughter fragments that come from parent polymers with large side chains.</P> [FIG OMISSION]</BR>

Multimechanophore Graft Polymers: Mechanochemical Reactions at Backbone-Arm Junctions

Peterson, Gregory I.,Lee, Jaeho,Choi, Tae-Lim American Chemical Society 2019 Macromolecules Vol.52 No.24

<P>Typical multimechanophore polymers (MMPs) are comprised of numerous mechanophores (force-responsive moieties) distributed throughout the backbone of linear polymers. We have developed a new MMP design based on graft polymers with mechanophores linking each arm to the backbone. By utilizing maleimide-anthracene cycloadducts, polymeric species containing anthracene were released from the parent polymer, enabling facile quantification of mechanophore activation. With pulsed ultrasound experiments, we observed that mechanophore activation was dependent on the arm length (a faster rate with longer arms), and we observed that 85% of the polystyrene (PS) arms underwent scission (64% specifically at the mechanophore site) for a graft polymer with 23 kDa arms. Solid-state activation was also investigated with hand-grinding experiments. Fast reactions were observed, with up to 96% of PS arms undergoing scission and 70-75% of mechanophores being activated, for all arm lengths studied. Multimechanophore graft polymers provide important insight into the distribution of forces in topologically complex polymers and may enable the development of new mechanoresponsive materials.</P> [FIG OMISSION]</BR>

Synthesis of Functional Polyacetylenes via Cyclopolymerization of Diyne Monomers with Grubbs-type Catalysts

Peterson, Gregory I.,Yang, Sanghee,Choi, Tae-Lim American Chemical Society 2019 Accounts of chemical research Vol.52 No.4

<P><B>Conspectus</B></P><P>Metathesis cyclopolymerization (CP) of α,ω-diynes is a powerful method to prepare functional polyacetylenes (PAs). PAs have long been studied due to their interesting electrical, optical, photonic, and magnetic properties which make them candidates for use in various advanced applications. Grubbs catalysts are widely used throughout synthetic chemistry, largely due to their accessibility, high reactivity, and tolerance to air, moisture, and many functional groups. Prior to our entrance into this field, only a few examples of CP using modified Grubbs catalysts existed. Inspired by these works, we saw an opportunity to expand the accessibility and utility of Grubbs-catalyzed CPs. We began by exploring CP with popular and commercially available Grubbs catalysts. We found Grubbs third-generation catalyst (G3) to be an excellent catalyst when we used strategies to stabilize the propagating Ru carbene, such as decreasing the polymerization temperature or using weakly coordinating solvent or ligands. Controlled living polymerizations were demonstrated using various 1,6-heptadiyne monomers and yielded polymers with exclusively 5-membered rings (via α-addition) in the polymer backbone. The strategy of stabilizing the Ru carbene was also critical to successful CP with Hoveyda-Grubbs second-generation (HG2) and Grubbs first-generation (G1) catalysts. We found that decomposed Ru species were catalyzing side reactions which could be completely shut down by decreasing the reaction temperature or using weakly coordinating ligands. While HG2 generally led to uncontrolled polymerizations, we found it to be an effective catalyst for monomers with very large side chains. G1 displayed broader functional group tolerance and thus broader monomer scope than G3. We next looked at our ability to change the regioselectivity of the polymerization by using <I>Z</I>-selective catalysts which favor β-addition and the formation of 6-membered rings in the polymer backbone. While modest β-selectivity could be obtained using Grubbs Z-selective catalyst at low temperatures, we found that by using one of Hoveyda and co-workers’ catalysts with decreased carbene electrophilicity, we could achieve exclusive formation of 6-membered rings. We also pursued alternative routes to achieve 6+-membered rings in the polymer backbone by using diyne monomers with increased distance between alkynes. We found that optimizing the monomer structure for CP was an effective strategy to achieve controlled polymerizations. By using bulky substituents (maximizing the Thorpe-Ingold effect) and/or using heteroatoms (shorter bonds) to bring the alkynes closer together, controlled living CP could be achieved with various 1,7-octadiyne and 1,8-nonadiyne monomers. Finally, we took advantage of several inherent properties of controlled CP techniques to prepare polymers with advanced architectures and nanostructures. For instance, the living nature of the polymerization enabled production of block copolymers, the tolerance of very large substituents enabled production of dendronized and brush polymers, and the insolubility or crystallinity of some monomers was utilized for the spontaneous self-assembly of polymers into various one- and two-dimensional nanostructures. Overall, the strategies of stabilizing the propagating Ru carbene, modulating the selectivity and reactivity of the Ru carbene, and enhancing the inherent reactivity of monomers were key to improving the utility and performance of CP with Grubbs-type catalysts. The insight provided by these studies will be important for future developments of CP and other metathesis polymerizations utilizing ring-closing steps.</P> [FIG OMISSION]</BR>

Mechanochemical Degradation of Monodisperse Cyclic Polymers in Solution and Solid States

노진경,Gregory I. Peterson,최태림 한국고분자학회 2022 한국고분자학회 학술대회 연구논문 초록집 Vol.47 No.2

Controlled Living Cascade Polymerization To Make Fully Degradable Sugar-Based Polymers from <small>D</small>-Glucose and <small>D</small>-Galactose

Bhaumik, Atanu,Peterson, Gregory I.,Kang, Cheol,Choi, Tae-Lim American Chemical Society 2019 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.141 No.31

<P>Monomers derived from glucose and galactose, which contain an endocyclic alkene (in the sugar ring) and a terminal alkyne, underwent a cascade polymerization to prepare new polymers with the ring-opened sugar incorporated into the polymer backbone. Polymerizations were well-controlled, as demonstrated by a linear increase in molecular weight with monomer-to-initiator ratio and generally narrow molecular weight dispersity values. The living nature of the polymerization was supported by the preparation of a block copolymer from two different sugar-based monomers. The resulting polymers were also fully degradable. They underwent fast and complete depolymerization to small molecules under acidic conditions.</P> [FIG OMISSION]</BR>