Mechanochemical transduction enables an extraordinary range of physiological processes such as the sense of touch, hearing, balance, muscle contraction, and the growth and remodelling of tissue and bone. Although biology is replete with materials systems that actively and functionally respond to mechanical stimuli, the default mechanochemical reaction of bulk polymers to large external stress is the unselective scission of covalent bonds, resulting in damage or failure. An alternative to this degradation process is the rational molecular design of synthetic materials such that mechanical stress favourably alters material properties. A few mechanosensitive polymers with this property have been developed; but their active response is mediated through non-covalent processes, which may limit the extent to which properties can be modified and the long-term stability in structural materials. Previously, we have shown with dissolved polymer strands incorporating mechanically sensitive chemical groups-so-called mechanophores-that the directional nature of mechanical forces can selectively break and re-form covalent bonds. We now demonstrate that such force-induced covalent-bond activation can also be realized with mechanophore-linked elastomeric and glassy polymers, by using a mechanophore that changes colour as it undergoes a reversible electrocyclic ring-opening reaction under tensile stress and thus allows us to directly and locally visualize the mechanochemical reaction. We find that pronounced changes in colour and fluorescence emerge with the accumulation of plastic deformation, indicating that in these polymeric materials the transduction of mechanical force into the ring-opening reaction is an activated process. We anticipate that force activation of covalent bonds can serve as a general strategy for the development of new mechanophore building blocks that impart polymeric materials with desirable functionalities ranging from damage sensing to fully regenerative self-healing.

There is growing interest in the use of mechanical energy to alter the molecular and supramolecular structure of polymers to create stress-responsive materials. 1a-l Chemical reactions that are accelerated by force remain poorly understood, and there is a need for the rapid discovery of new mechanophores (i.e., stress-sensitive units). Screening putative mechanophores, however, is a slow process that requires a high molecular weight polymer having a single testable unit positioned near the midpoint of the chain, the location where stress under elongation is greatest. Here we show that the required mechanophore-linked addition polymers are easily prepared using bifunctional initiators and a living polymerization method. The approach is demonstrated with benzocyclobutene 1k and spiropyran mechanophores that undergo stress-induced 4π and 6π electrocyclic ring opening, respectively. Mechanophore-linked addition polymers thus show considerable promise for rapidly identifying new mechanophores and will lead to a greater, molecular-level understanding of mechanochemical transduction in polymeric materials.Single electron transfer living radical polymerization (SET-LRP) 2 was employed for the synthesis of mechanophore-linked polymers, as this method has been shown to generate high molecular weight macromolecules with narrow polydispersity indices (PDIs). cis-1,2-Bis(R-bromopropionyloxy)-1,2-dihydrobenzocyclobutene (1), capable of initiating bidirectional SET-LRP, was synthesized and used to produce a series of benzocyclobutene (BCB)-linked PMAs (Scheme 1). Polymerizations were performed at room temperature in DMSO with Cu(0) catalyst and a hexamethylated tris(2-aminoethyl)amine (Me 6 TREN) ligand. Low (18 kDa), medium (91 kDa), and high (287 kDa) molecular weight BCB-linked PMAs (PMA-BCB-PMA) with PDIs around 1.3 were synthesized and used to investigate the ultrasound-induced electrocyclic ring opening reaction. Mechanochemical activation was analyzed by trapping the intermediate ortho-quinodimethide with UV-active N-(1-pyrene)-maleimide via cycloaddition (Scheme 1). 1k PMA end-functionalized with a BCB unit (PMA-BCB) was prepared as a mechanochemical control polymer since ultrasound-generated forces at the chain ends are minimal. Specifically, the monofunctional initiator cis-1-acetoxy-2-(R-bromopropionyloxy) 1,2-dihydrobenzocyclobutene was used to produce a PMA-BCB with a PDI of 1.3 and molecular weight of 190 kDa. This control polymer dispels the notion that the chemical changes are thermally induced, rather than the result of mechanical force.The BCB-containing polymers and PMA homopolymer were subjected to an acoustic field to probe for mechanical activity. Each polymer was dissolved in CH 3 CN with a large excess of N-(1-pyrene)maleimide and radical trap 2,6-di-tert-butyl-4-methylphenol (BHT) and exposed to pulsed sonication 3 for 45 min under Ar at 6-9°C. Aliquots were withdrawn at the beginning and end of each experiment and analyzed by analytical gel permeation chromatography (GPC) using a refractive index (RI) ...

No abstract

The ultrasound-induced scission of silver carbene coordination complexes with polytetrahydrofuran-functionalized N-heterocyclic carbene ligands is reported. In solution, scission is very efficient, with complete conversion within 10 min when the polymers have a molecular weight of 6.7 kDa. The mechanochemical origin of the scission is supported by the molecular weight dependence of the scission rate and by the low reactivity of the silver complex with low molecular weight ligands. The mechanochemical process at room temperature is much faster than thermal scission at 60 degreesC, which has a conversion of 30% in 18 h.

Steam-assisted gravity drainage (SAGD) is a mature technology for bitumen recovery from oil sands. However, it is an energy-intensive process that requires large amounts of steam to heat and mobilize bitumen. The purpose of this work is to develop ways to enhance SAGD performance through the use of organic base additives. The research is approached from three focus areas that supplement and guide each other: characterization tests, sand-pack floods, and computational simulation. A number of key mechanisms for enhancing oil recovery were identified, high-temperature additive characterization tests were developed, and promising alkalis were tested in porous media. Simulation was employed to history-match sandpack flood production data, in order to demonstrate the effect of an additive on the oil-water relative permeability. Based on these results, it was concluded that oxygenated organic bases had the most potential for improving bitumen recovery through reducing the oil-water interfacial tension (IFT) by increasing the pH of the system. These organic bases favorably modify the interfacial energies between the immiscible oil-water phases and enable them to flow easily through the porous media during production. Sand-pack flood tests have successfully demonstrated a 10%-15% improvement in bitumen recovery, over baseline, in the presence of IFT-reducing additives. Simulation results further showed that an IFT reduction had a positive impact on SAGD performance. This work demonstrates the potential of organic bases to improve not only SAGD, but other steam injection processes. Furthermore, a number of experimental methods were developed, tried, and tested during the course of this work. Keywords Heavy oil • Steam flood • Low interfacial tension • Wettability • Enhanced oil recovery • Organic bases List of symbols k rw Water relative permeability at S w k row Oil relative permeability at S w k rwro Water relative permeability at residual oil k rocw Oil relative permeability at connate water S w Water saturation S wc Connate water saturation S orw Residual oil saturation in the presence of water Z w Water Corey exponent Z ow Oil Corey exponent

Paraffins are linear and branched aliphatic molecules (ϾC18) present within crude oil. As crude oil cools upon exiting a well, the paraffins can gel or precipitate and ultimately cause pipelines to plug. The result is costly downtime in production as the pipelines are cleaned or repaired. One solution to address this challenge is chemical prevention, namely the use of wax inhibitors and pour point depressants.Traditionally wax inhibitors and pour point depressants are organic solvent-based materials that contain a low concentration of active inhibitor (approximately 5% active in a solvent such as toluene). In this work, newly developed high concentration (Ͼ30% active) aqueous-based wax inhibitors and pour point depressants will be discussed.These formulations are stable dispersions of active copolymers in water and can be freeze-protected to Ϫ40°C, enabling their use in arctic environments. There is also an advantage of reduced logistics costs, decreased storage space and the absence of flammable solvents. Additionally, the replacement of organic solvent with water makes these materials more environmentally friendly and less expensive to dilute during application. The physical properties and stability of these materials throughout a broad temperature range from Ϫ40°C to 125°C will be discussed. The performance of these innovative materials on various crude oils will also be presented. Up to a 30°C reduction in the pour point temperature was observed. This unique combination of properties and significant reduction in pour point temperatures is a novel advancement in flow assurance technology.

Steam injection is a widespread thermal enhanced oil recovery (EOR) method to increase oil mobility. The introduction of steam heats the reservoir, ultimately lowering oil viscosity and in turn enhancing heavy oil recovery. In the steam injection process, recovery of oil is limited by steam channeling due to reservoir heterogeneities. Early breakthrough implies that there is a large consumption of steam and incomplete reservoir drainage. Injection of surfactant with steam and a non-condensable gas such as nitrogen can generate foam in situ. Foam will redirect steam, increase apparent viscosity and reduce steam channeling. Although the technology is promising, it is not always economically attractive due to the large volumes that must be injected continuously, high adsorption of surfactant on reservoir rocks, and limited thermal stability of the surfactant. The opportunity exists to design steam foam surfactant formulations with improved performance at high temperature. In this paper, a systematic approach to screen surfactants for field applications at high temperature is presented. A feasibility test was conducted with the surfactant formulation (HSF-X) at target reservoir conditions to understand the thermal stability and adsorption behavior of the surfactant. Investigation found that the thermal decomposition and adsorption of the surfactant on sandstone rock under static conditions was mimimum at 200°C. In core flood testing conducted using silica sand and natural sandstone cores, foam generated by injecting N2 and HSF-X surfactant solution was able reduce steam mobility between 40 to 100 times at 100°C and 10 to 15 times at 200°C more compared to steam mobility in the absence of the foam. Finally oil recovery experiments at 200°C using silica sand cores indicated the ability of the HSF-X surfactant to foam in the presence of oil and enhance recovery of oil (a +20% increase in the original oil in place (OOIP) was observed).