Catalysis as an Enabling Science for Sustainable Polymers

In the paper

“Among potential candidates, aliphatic polyesters and polycarbonates are promising materials due to their renewable resources and excellent biodegradability.”

In the paper

“However, the amount of landfill space available for discarded plastic wastes is finite.”

In the paper

“Even under the most highly optimized circular materials economies, some fraction of the products will eventually end up in the environment.”

In the paper

“While considerable research has focused on replacing petroleum raw materials with renewable sources and developing biodegradable or recyclable polymers that minimize waste disposal, 16 ultimately the point of maximum leverage 44 is the socioeconomic system that has led to our current model of resource utilization.”

In the paper

“Life-cycle assessment has been used to assess the environmental impacts resulting from the production, use, and disposal of a polymer product (see section 1.5.2) but the results are variable across studies with quantification being strongly tied to modeling assumptions and feedstock choice.”

In the paper

“However, while biodegradable plastics can mitigate some of the environmental consequences of plastics that find their way into the environment, it is only one of the several end-of-life strategies to minimize the environmental impact of plastics.”

In the paper

“Thus, while many petrochemically-based polymers are recyclable, the current rates of plastics recycling are exceedingly low (<10%) and, on a volume basis, are not keeping pace with the increased volumes of production.”

In the paper

“To mitigate the environmental impact of plastics that end up in the environment, these plastics should be biodegradable.”

In the paper

“As the chemical composition of renewable resources are quite different from those derived from petroleum-based resources, new scientific and technological innovations are needed for the development of efficient catalytic strategies for converting these resources into platform chemicals, monomers, polymers, and products that can be produced economically on a scale sufficient for commodity materials”

In the paper

“Incineration of recovered plastic provides a potential source of energy, 39 but generates CO2; moreover, rigorous purification and process controls are needed to insure that the hazardous substances are not released into the atmosphere.”

In the paper

“LCA provides a standardized methodology to compare different product choices, and identifies unintended environmental trade-offs between impact categories.”

In the paper

“Support from public and government including favorable policy and legislation is the key stimulator for technological innovations on sustainable polymers and for businesses and customers to transition towards more sustainable products.”

In the paper

“Several other reviews discuss the topic from the end-of-use perspective, covering different families of recyclable and biodegradable polymers.”

In the paper

“Catalysis presents an enabling tool to facilitate the development of sustainable polymers.”

In the paper

“It is arguably not the optimal end-of-life option in that the energy invested to create these materials is wasted and provides benefit only to the microbes.”

In the paper

“Although there is no direct correlation between a plastic's ability to biodegrade and the resource from which is derived, many biomass-derived polymers have oxygen-rich backbones and are thus more readily degraded than the all-carbon backbones of most petroleum-based polymers.”

In the paper

“New strategies are needed for the selective depolymerization of plastics either to their constituent monomers or other useful intermediates that could be used as resources for other chemical processes”

In the paper

“One of the most significant challenges is that the plastics of modern society are quite remarkable materials; more sustainable alternatives will have to meet a high bar in terms of the cost and performance in order to be economically competitive.”

In the paper

“Oilseed crops such as soybean, rapeseed, and oil palm are the major supply of oils at present, but algae has turned up as a cheaper alternative due to its non-food nature, fast production and recycle rate, and low use of production inputs.82”

What the sources say

• Not checked yetcites [82] source

In the paper

“Transition to non-food sources such as lignocellulosic biomass is an important direction to lower the production costs [78][79][80] and to avoid resource competition with the food supply.”

What the sources say

• Not checked yetcites [78] source
• Not checked yetcites [79] source
• Not checked yetcites [80] source

In the paper

“Succinic acid is used in the production of bio-based PBS; it is also a versatile precursor for monomers such as 1,4-butanediol (BDO), g-butyrolactone (g-BL), maleic anhydride, and maleic acid.91”

What the sources say

• Not checked yetcites [91] source

In the paper

“Fatty acids obtained from transesterification of plant oils have been a long-standing biofeedstock for polymer production.25,98”

What the sources say

• Not checked yetcites [25] source
• Not checked yetcites [98] source

In the paper

“Second, the conversion of these renewable monomers to polyesters and polycarbonates can be achieved via a variety of polymerization methods, which enables diverse backbone structures and side-chain functionalities that in turn give rise to versatile physical properties of these polymers.”

In the paper

“In the last decade, a number of synthetic bio-derived plastics have been commercialized.”

In the paper

“While the sustainability of a polymer should be considered on a systems level that encapsulate a variety of factors in its feedstock, synthesis, and end-of-use options, two important criteria are the use of renewable feedstock and the degradability or recyclability of the polymer.”

In the paper

“The conversion of renewable feedstocks to monomers focuses on two directions: to replace the existing petroleum-derived monomers with their renewable counterparts, and to develop new bio-derived monomers and polymers with unique structures and properties that current commodity plastics do not have.”

In the paper

“Although bio-based polymers save non-renewable resources and generally emit less greenhouse gases for their production, studies have shown that they may exert higher environmental impacts in the categories of eutrophication and stratospheric ozone depletion.”

In the paper

“For example, in 2014 only 1.7 megatons of more than 300 megatons of polymers produced globally were bio-derived, of which the three main products were PLA, biopolyethylene, and bioPET.”

In the paper

“Alternatively, these are attractive candidates for feedstock recycling as the polymerization thermodynamics are not as exergonic as those of conventional commodity plastics (PE, PS, PVC).”

In the paper

“They are not only key monomers for various commodity polyesters and polycarbonates, but also serve as a platform for a multitude of highvalue added products by means of chemical and biological transformations.77”

What the sources say

• Not checked yetcites [77] source

In the paper

“Among the families of polymers that can be both renewable and degradable (upper right quadrant), polyesters and polycarbonates have attracted the most attention, with a great many of them been successfully used as substitutes for plastics of petroleum origin.”

In the paper

“Poly(ethylene furandicarboxylate) (PEF) produced from FDCA is regarded as a renewable substitute for PET.104”

What the sources say

• Not checked yetcites [104] source

In the paper

“One important example is PLA produced from starch-rich crops such as corn; for example, that developed by Natureworks LLC under the brand name Ingeo TM .60”

In the paper

“Adipic acid, a monomer used for the production of nylon, polyurethane, and polyesters, is one of the most important diacids in industry and ~2.5 million tons are produced annually from petrochemicals.96”

What the sources say

• Not checked yetcites [96] Bohnet M., 2003

In the paper

“The role of catalysis in these conversions is critical and many research efforts are focusing on developing green catalytic processes with high efficiency and low cost.[84][85][86]”

What the sources say

• Not checked yetcites [84] source
• Not checked yetcites [85] source
• Not checked yetcites [86] source

In the paper

“They have met several key principles outlined for a sustainable polymer (section 1.3), which enables a potentially cyclic model of resource utilization.”

In the paper

“Traditional polymers are derived from fossil fuels and are non-degradable in nature (lower left quadrant), whereas sustainable polymers are sourced from renewables and can readily degrade in the environment.”

In the paper

“In this analysis, biopolymers such as polylactide (PLA) and polyhydroxyalkanoate (PHA) were ranked the highest based on green design metrics but in the middle of the LCA rankings whereas petroleum polymers such as PE and PP were ranked the highest in the LCA rankings but in the middle of green design rankings.”

In the paper

“Another common renewable resource is plant oil, which is converted to fatty acids and glycerol for biodiesel and oleochemical production.16,25,81”

What the sources say

• Not checked yetcites [16] source
• Not checked yetcites [25] source
• Not checked yetcites [81] source

In the paper

“This allows a faster rate of resource regeneration than resource consumption.”

In the paper

“Since the two metrics focus on different aspects of sustainability, the evaluation based on these metrics can give different results.”

In the paper

“As summarized in Figure 2, synthetic plastics on the market can be classified into four categories according to their feedstock renewability and polymer degradability.”

In the paper

“Sugar fermentations to produce these polyols are also feasible although it cannot yet compete with the chemical reduction economically.[149][150][151]”

What the sources say

• Not checked yetcites [149] source
• Not checked yetcites [150] source
• Not checked yetcites [151] source

In the paper

“The coupling of diols with CO2 occurred at 25 °C and ambient pressure, affording cyclic carbonates in 40-70% yields.”

What the sources say

• Not checked yetcites [202] source

In the paper

“The use of halide is crucial for the conversion, highlighting the importance of the leaving group.”

In the paper

“Lactic acid is a well-recognized bio-based chemical, currently produced from starch crops via bacteria fermentation.91”

What the sources say

• Not checked yetcites [91] source

In the paper

“Recently, Buchard reported an efficient two-step procedure using DBU as the base in the first step to activate the hydroxyl group toward carbonylation and NH3/TsCl in the second step to facilitate the cyclization.202”

What the sources say

• Not checked yetcites [202] source

In the paper

“However, the yields of these processes are typically low, which makes them hard to compete with the current petroleum-based synthesis.”

What the sources say

• Not checked yetcites [158] Dischert, W.; Colomb, C.; Soucaille, P.Fermentation Process for Producing Glycolic Acid. U.S. 20120178136A1, 2012.
• Not checked yetcites [159] source

In the paper

“This second step requires the use of a selective catalyst, typically tin octoate, 156 and continuous removal of lactide (e.g. by distillation) to achieve good yield.”

What the sources say

• Not checked yetcites [156] source

In the paper

“Dehydrative condensation of CO2 and alcohols is the most straightforward and green route to dialkyl carbonates but the reaction is severely limited by the unfavorable equilibrium.”

In the paper

“The most successful cyclic ester derived from biomass is lactide (LA), the monomer for commodity polylactides (PLAs).”

In the paper

“These monomers can undergo polymerizations at both the alkene and ester site, making them potential substitutes for petroleum-based polyacrylates and polyesters.176,177”

What the sources say

• Not checked yetcites [176] source
• Not checked yetcites [177] source

In the paper

“Ethylene glycol (EG), a component for PET, is traditionally produced from petroleum-based ethylene, via the intermediate ethylene oxide.”

In the paper

“Another promising route is the hydrogenolysis of sugarderived polyols (glycerol, xylitol, sorbitol) catalyzed by supported transition-metal catalysts, mostly Ru, Cu, Ni, under basic conditions.126,127 This process provides a direct and potentially cheaper route to EG but is complicated by the concurrent generation of other polyols, like propylene glycol (PG).”

What the sources say

• Not checked yetcites [126] source
• Not checked yetcites [127] source

In the paper

“The shape-selective property of zeolites enables high selectivity for LA (~79% at full conversion), devoid of racemization and side-product formation.”

What the sources say

• Not checked yetcites [157] source

In the paper

“Both steps are time-and energy-intensive owing to their reliance on high temperatures and vacuum.”

In the paper

“Their syntheses typically involve elaborate protecting group chemistry, which compromises the atom economy and production cost of these monomers.”

In the paper

“Since furfural is industrially produced from lignocellulose on a scale of 400 kilotons a year, this provides a potentially cheaper route to FDCA.115”

What the sources say

• Not checked yetcites [115] source

In the paper

“The thermodynamics of this dehydrative cyclization reaction is unfavorable, similar to the synthesis of dialkyl carbonate from CO2. 184”

What the sources say

• Not checked yetcites [184] source

In the paper

“The development of petroleum-based plastics has been driven by the innovations in catalytic petrochemistry and polymerization methods.”

In the paper

“Due to the wide availability of diols, diacids or hydroxy acids, SGP provides easy access to polyesters and polycarbonates with diverse backbone structures and side-chain functionalities.”

In the paper

“Most bio-derived epoxides are prepared by catalytic epoxidation of alkene group present in a renewable substrate.”

In the paper

“Epichlorohydrin (ECH), an important industrial chemical produced on a 1.8 million tons scale annually, can be derived from glycerin through a two-step reaction.208,209”

What the sources say

• Not checked yetcites [208] source
• Not checked yetcites [209] source

In the paper

“In addition, the removal of by-products, water or alcohol, from the polycondensation reactions necessitates the use of high temperatures and often times vacuum conditions, which makes this approach very energy-intensive.218”

What the sources say

• Not checked yetcites [218] Odian G., 2004 source

In the paper

“The traditional way of synthesizing polyesters and polycarbonates is by step-growth polymerization.”

In the paper

“Although these approaches use cheap, safe, and renewable feedstocks and operate under relatively mild conditions, the generation of stoichiometric wastes and the moderate yields of these reactions limit their atomic efficiencies.”

In the paper

“Similarly, the effective uses and transformations of renewable feedstocks to sustainable polymers rely on the development of innovative and green catalytic chemistries.”

In the paper

“Since the water by-product is expelled out of the hydrophobic interior of micelles, this reaction can proceed effectively at low temperature (40-80 °C) and 1 atm.”

In the paper

“The use of a chemoselective catalyst is critical to eliminate the need for tedious and uneconomical protection chemistry 239,240 and to enhance the product specificity.”

What the sources say

• Not checked yetcites [239] source
• Not checked yetcites [240] source

In the paper

“Among different metals, bismuth triflate (Bi(OTf)3) has received particular attention due to its low toxicity (Bi 3+ is among the least toxic heavy metal ions), low cost, and stability.234”

What the sources say

• Not checked yetcites [234] source

In the paper

“They can be produced on a large scale from CO, or potentially from CO2. 183,184”

What the sources say

• Not checked yetcites [183] source
• Not checked yetcites [184] source

In the paper

“The development of catalytic processes that can operate at lower temperatures will reduce the energy input, and thus increase the sustainability of the step-growth synthesis.”

In the paper

“The pendant hydroxyl groups not only enable post-polymerization functionalization but also provide a handle to tailor the crystallinity of these aliphatic polyesters.242”

What the sources say

• Not checked yetcites [242] source

In the paper

“To date, the activity of organocatalysts for SGP and the molecular weights of the resulting polyesters and polycarbonates are not yet comparable to the most efficient metal catalysts.”

In the paper

“The direct coupling of CO2 and diols is severely limited by the reaction equilibrium and requires an effective dehydration system.”

In the paper

“Further modification of the resulting unsaturated polyesters by Michael addition yielded polyesters with different substituents dangling of the backbone, which provided a means to tune the thermal property of the materials.233”

What the sources say

• Not checked yetcites [233] source

In the paper

“For the step-growth synthesis of polycarbonates, the replacement of hazardous phosgene with more renewable and eco-friendly carbonyl reagents is a subject of intensive research.”

In the paper

“High yields (> 90%) and high molecular weights (Mn in the range of 10-40 kDa) were achieved for a variety of diols and dihalides substrates.”

What the sources say

• Not checked yetcites [265] source

In the paper

“While the ROP of fivemembered cyclic carbonates is enthalpically disfavored, six-and seven-membered cyclic carbonates (6CCs, 7CCs) can undergo facile and controlled ROP under mild conditions.”

In the paper

“Four-, six-, and seven-membered rings are favorable for ROP due to their large ring strains while five-membered lactones such as γ-butyrolactone (γ-BL) exhibits a less favorable enthalpy of polymerization and is usually considered as nonpolymerizable.277”

What the sources say

• Not checked yetcites [277] source

In the paper

“The synthetic versatility of 6CCs allows the incorporation of a wide range of functional groups to the resulting polycarbonates, which has led to a versatile material platform for biomedical applications.”

What the sources say

• Not checked yetcites [282] source

In the paper

“With the proper choice of an initiating/catalytic system, ROP of cyclic esters and carbonates can be performed under mild conditions (room temperature, ambient pressure) to give high yield and 100% atom economy, which makes ROP a highly efficient and green route for the synthesis of polyesters and polycarbonates.”

In the paper

“Quantitative conversions of diols were achieved under 5 MPa CO2 but the molecular weights of the obtained polycarbonates were extremely low (Mn < 1700 Da).”

What the sources say

• Not checked yetcites [263] source

In the paper

“Similar limitations on ring size exist for cyclic carbonates.”

In the paper

“In another study, Du employed CH2Cl2 as the dihalide and condensed it with various diols and 1 atm of CO2 to give polymers with Mn up to 11 kDa (Scheme 5e).266”

What the sources say

• Not checked yetcites [266] source

In the paper

“The N-substitution not only enhances the ring strain but also provides a synthetic handle to introduce functionality to these polycarbonates.”

What the sources say

• Not checked yetcites [283] source
• Not checked yetcites [284] source

In the paper

“Only moderate yields (< 60%) and low molecular weights (Mn up to 6 kDa) were achieved.”

What the sources say

• Not checked yetcites [261] source
• Not checked yetcites [262] source

In the paper

“In addition, catalytic processes performed at mild temperature, low catalyst loading, and solvent-free conditions are particularly attractive from a sustainability standpoint.”

In the paper

“As depicted in Scheme 6, intramolecular chain transfer such as cyclization (kcy) and backbiting (kbb) of chain end onto an internal ester group leads to the formation of cyclic polyesters; intermolecular chain transfer (transesterification) results in chain scrambling (ksc) and broadens the molecular weight distribution.”

What the sources say

• Not checked yetcites [273] Duda A., 2009

In the paper

“Some of these catalysts show not only extremely high reactivity (TOF > 1000 h -1 ) but also high regio-/stereoselectivity for the ROP of asymmetric monomers.”

In the paper

“The aggregation of alkali metal salts, lithium in particular, often complicates the polymerization kinetics.287”

What the sources say

• Not checked yetcites [287] source

In the paper

“Simple metal alkoxides and carboxylates such as tin octoate are cheap and convenient catalysts for ROPs and are used industrially to produce PLA.”

In the paper

“The most commonly used catalysts for ROP are transition and posttransition metal complexes, which mediate the ROP through a “coordination-insertion” type mechanism (Scheme 7).289”

What the sources say

• Not checked yetcites [289] source

In the paper

“However, when it comes to selectivity, especially stereoselectivity, those well-defined single-site metal catalysts with ancillary ligands are more competent.”

In the paper

“The ancillary ligand has proven to be an important element in ROP catalysis to fine tune the electronic and steric properties of the metal center and to control the selectivity of polymerization.”

In the paper

“Aluminum complexes supported by SALEN-type ligands [301][302][303][304][305][306][307][308][309] are some of the most stereoselective catalysts for the ROP of racemic LA but their low reactivities (typical reaction conditions: Al loading >1 mol%, 70-130 °C, and long reaction time) limit their applicability.”

What the sources say

• Not checked yetcites [301] source
• Not checked yetcites [302] source
• Not checked yetcites [303] source

In the paper

“Unlike the previous case, the two monomers exhibited orthogonal reactivity with one being completely inactive during the polymerization of the other.”

What the sources say

• Not checked yetcites [320] source

In the paper

“PHAs are naturally produced by various bacteria (section 3.3) but only isotactic microstructures are made biologically.317”

What the sources say

• Not checked yetcites [317] source

In the paper

“Among all chiral monomers, the stereoselective ROP of lactide has been most extensively studied because of the important application of PLAs.”

In the paper

“This provides new possibilities for engineering the properties and applications for these plastics.”

In the paper

“Rare-earth metal catalysts supported by phosphasalen ligands (such as Ln-phosSALEN in Figure 8) displayed both high reactivity and stereoselectivity (Pi up to 0.84 at 25°C) with the ability to produce high molecular weight isotactic PLAs (Mn > 100 kDa) with extremely narrow polydispersities (Ð <1.1).310,311”

What the sources say

• Not checked yetcites [310] source
• Not checked yetcites [311] source

In the paper

“They found that the reduced form was much more active towards LA than CL while the oxidized form had the opposite selectivity.”

What the sources say

• Not checked yetcites [319] source

In the paper

“Given that many cyclic esters and carbonates monomers derived from plants contain stereocenters, the stereoselective ROP is an important aspect for the controlled synthesis of sustainable polymers.”

In the paper

“No appreciable amount of ether linkage was detected in the resulting polymers, indicating the absence of decarboxylation reaction.”

What the sources say

• Not checked yetcites [297] source

In the paper

“End-group analysis revealed an imidazolium enol-like chain end of the final polymers, indicative of an intramolecular proton transfer within the zwitterionic intermediates generated from the nucleophilic addition of NHOs to the monomer (Scheme 11D).”

What the sources say

• Not checked yetcites [335] source

In the paper

“Organic acids such as sulfonic or phosphoric acid can catalyze the polymerization through electrophilic activation of monomers.”

In the paper

“Typical nucleophilic organocatalytic ROP is subject to a trade-off between rate and selectivity: the most active catalysts, i.e.NHCs, TBD, tend to promote side reactions such as chain transfer and epimerization especially at high conversions while the most selective systems, such as TU/amines, suffer from slow kinetics.”

In the paper

“While non-substituted NHOs (at the exocyclic carbon, NHO-1,3) were ineffective for ROP due to catalyst deactivation (Scheme 11C), NHO bearing dimethyl substituents (NHO-2) proved highly active for the ROP of LA and VL.334”

What the sources say

• Not checked yetcites [334] source

In the paper

“Under the same conditions, the ROP of VL is fast but poorly controlled due to the more significant enolate-based initiation.”

What the sources say

• Not checked yetcites [334] source

In the paper

“The high activity and the ability to operate through different polymerization mechanisms make NHO an attractive motif for future catalyst design and optimization.”

In the paper

“They found that the dizinc acetate catalyst (Zn-OAc) was an excellent catalyst for the ring-opening copolymerization of epoxide and CO2 but not for the ROP of CL.”

What the sources say

• Not checked yetcites [322] source

In the paper

“In the presence of an alcohol initiator, the ROP of 50 equiv.L-LA by as low as 0.2 mol% NHO-2 reached quantitative conversion in less than a minute, resulting in PLAs with low molecular weight distributions (Ð <1.2).”

What the sources say

• Not checked yetcites [334] source

In the paper

“Since the pioneering work of Hedrick in 2001, 324 the application of organic catalysts to ROP has witnessed significant progress in the last 15 years and this field has grown to the point that it now provides a powerful and, in some cases, better alternative to the use of traditional metal-based catalysts.325,326”

What the sources say

• Not checked yetcites [324] source
• Not checked yetcites [325] source
• Not checked yetcites [326] source

In the paper

“These ionic catalysts are prepared by simple deprotonation of the neutral ureas or thioureas.”

What the sources say

• Not checked yetcites [321] source
• Not checked yetcites [336] source

In the paper

“The diversity in mechanistic pathways not only provides new opportunities for enhancing the rate and selectivity of polymerization but also enable the synthesis of polymer architectures that are difficult to access by metal-mediated processes.”

In the paper

“These systems have proven especially selective for chain propagation over transesterification, affording narrowly dispersed polyesters and polycarbonates.”

In the paper

“While low stereo-control at ambient temperature has been a long-standing problem for organocatalytic ROP, recent advances in catalyst design have demonstrated the potential of organocatalysts to rival the state-of-the-art metal catalysts.”

In the paper

“Chen developed a bifunctional catalyst that combines b-isocupreidine, a previously reported chiral ROP catalyst with low enantioselectivity (kL/kD = 4.4), 340 and a chiral thiourea based on the binaphthyl scaffold.341”

What the sources say

• Not checked yetcites [340] source
• Not checked yetcites [341] source

In the paper

“The urea anions are more active than the corresponding thiourea anions, with the ability to polymerize all tested monomers in just seconds (<12s) with excellent control on molecular weight distributions (Ð =1.06 ~ 1.14).336”

What the sources say

• Not checked yetcites [336] source

In the paper

“The most active one, a trisurea/MTBD, is approximately 100 times faster than mono-TU/MTBD for the ROP of CL, with equally good control on molecular weights and molecular weight distributions (Ð < 1.05).”

What the sources say

• Not checked yetcites [337] source
• Not checked yetcites [338] source

In the paper

“exo-PRO exhibited a strong preference for L-LA and the ROP of rac-LA by this catalyst at 50% conversion generates a highly isotactic PLAs with Pm up to 0.96 at 25 °C.342”

What the sources say

• Not checked yetcites [342] source

In the paper

“Kiesewetter reported a series of bis-and tris-(thio)urea based H-bond donors (Scheme 13), which exhibited dramatic rate acceleration compared to the mono-TU/amine systems, yet retaining the high selectivity for propagation over transesterification. 337,338”

What the sources say

• Not checked yetcites [337] source
• Not checked yetcites [338] source

In the paper

“The rate acceleration is proposed to arise from an “activated (thio)urea” mechanism in which each additional (thio)urea moiety enhances the acidity via intramolecular H-bond activation (Scheme 13), supported by DFT calculations.”

What the sources say

• Not checked yetcites [337] source
• Not checked yetcites [338] source

In the paper

“While these catalysts can show good reactivities, they lack sufficient control on the polymerizations and the structures of the active species are ill-defined.”

What the sources say

• Not checked yetcites [353] source
• Not checked yetcites [354] source
• Not checked yetcites [355] source

In the paper

“One obvious advantage of epoxide/CO2 copolymerization is the utilization of CO2 as a monomer.”

In the paper

“While the field of epoxide/CO2 copolymerization is quite mature, with several technologies been commercialized, the progress in epoxide/cyclic anhydride copolymerization is more recent.211,343”

What the sources say

• Not checked yetcites [211] source
• Not checked yetcites [343] source

In the paper

“Depending on the epoxide, this method enables 30-50% of a polymer's mass to be derived from CO2, with the rest derived from cheap platform petrochemicals, or potentially from renewable biomass.”

In the paper

“Upcycling of waste gases such as CO2 to useful and valuable plastics has long been of interest to researchers, and the ROCP of epoxides and CO2 represents one of the most successful examples of CO2 utilization in polymer synthesis.83,[344][345][346][347][348][349][350][351][352]”

What the sources say

• Not checked yetcites [83] source
• Not checked yetcites [344] source
• Not checked yetcites [345] source

In the paper

“Because 5CCs are thermodynamically stable and cannot be re-incorporated into the chains, this elimination causes irreversible loss of yield.”

In the paper

“One appealing aspect of the ROCP approach is the common availability and structural diversity of epoxide and cyclic anhydride monomers, which can be easily prepared from olefins and dicarboxylic acids, respectively.”

In the paper

“Chain propagation proceeds by the alternative insertion of epoxide and CO2 (or cyclic anhydride) to the metal-oxygen chain end, which leads to the desired formation of polycarbonate (or polyesters) backbones.”

What the sources say

• Not checked yetcites [344] source

In the paper

“In most cases, a nucleophilic cocatalyst is used to increase the activity of the metal complexes, the most common ones being bis(triphenylphosphine) iminium salts ([PPN]X) and 4-dimethylaminopyridine (DMAP).”

What the sources say

• Not checked yetcites [343] source

In the paper

“On the other hand, the exploitation of chain transfer phenomenon enables immortal polymerization conditions, where the chain transfer agents are added in large excess compared to the catalyst to increase the polymerization rate and control the molecular weight of products.360”

What the sources say

• Not checked yetcites [360] source

In the paper

“Some epoxides and anhydrides can be prepared from biomass (Figure 7) such as limonene oxide (from terpene) 365,366 and maleic anhydride (from furfuraldehyde) 138 , which are attractive monomers for fully renewable aliphatic polyesters and polycarbonates.”

What the sources say

• Not checked yetcites [365] source
• Not checked yetcites [366] source
• Not checked yetcites [138] source

In the paper

“PHAs are produced by a variety of microorganisms as a carbon and energy storage material in times of unbalanced nutrient availability.376”

What the sources say

• Not checked yetcites [376] source

In the paper

“Collectively, these bacteria have led to the biosynthesis of over 150 different types of PHA copolymers.385”

What the sources say

• Not checked yetcites [385] source

In the paper

“However, this is the longest path for building a circular flow of the plastics (Scheme 17), and the energy and environmental prices paid to build the chemical complexity of monomers are completely lost during the degradation processes.”

In the paper

“Recycling is one of the most important end-of-use options to reduce the environmental impacts and resources depletion of plastics.”

In the paper

“In addition, while efficient processes have been developed, sophisticated purification and process controls are needed to insure that the hazardous substances are not released into the atmosphere.41”

What the sources say

• Not checked yetcites [41] Francis R., 2017

In the paper

“Depending on the organism and the conditions of growth, the molecular weight of PHBs can vary from 50,000 Da to over a million Da. 384”

What the sources say

• Not checked yetcites [384] Bugnicourt E., 2015

In the paper

“The methanotrophic bacteria that produce PHAs can be found at wastewater treatment plants, which are often geographically close to sources of waste methane.375,381,382”

What the sources say

• Not checked yetcites [375] source
• Not checked yetcites [381] source
• Not checked yetcites [382] source

In the paper

“Additionally, many epoxides and cyclic anhydrides contain unsaturated moieties that can be utilized for post-polymerization modifications and crosslinking, 211 which increases the range of architectures and functionalities that can be achieved through the ROCP method.”

What the sources say

• Not checked yetcites [211] source

In the paper

“PHAs are an important class of biodegradable plastics commonly used for packaging, bottles, cutlery, furniture, biomedical implants, drug delivery vehicles, and animal food supplements.[371][372][373][374]”

What the sources say

• Not checked yetcites [371][372][373][374]

In the paper

“Terpolymerization of epoxide, cyclic anhydride, and CO2 is a facile strategy for the onepot synthesis of poly(ester-carbonate), 211,343 a class of biodegradable polymers that have garnered considerable interest due to their possible superior properties than pure polyesters and polycarbonates.”

What the sources say

• Not checked yetcites [211] source
• Not checked yetcites [343] source

In the paper

“The majority (> 70%) of recycled PET (rPET) is used for production of lower-grade products, mainly polyester fibers, and only a small fraction (~10%) is used for closed-loop bottle-to-bottle recycling.394”

What the sources say

• Not checked yetcites [394] Data from Noone A., Collected PET bottles, Proceedings of 13th International Polyester Recycling Forum, 2008.

In the paper

“According to the National Association for PET Container Resources (NAPCOR), ~30.1% PET plastic bottles were mechanically recycled in 2015 in the United States.393”

What the sources say

• Not checked yetcites [393] NAPCOR Recycling Rate Reports. http://www.napcor.com/PET/pet_reports.html(accessed May 8, 2017).

In the paper

“Since the ability to substitute recycled plastic for virgin polymer depends on the purity of the recovered plastic feed, mechanical recycling of rigid plastic bottles consisting of a single polymer are much simpler and more economical than those multi-layer and multi-component packages.”

In the paper

“Since closed-loop mechanical recycling requires the polymers to be effectively separated from sources of contaminations (other plastics, metals, pigments, adhesives, etc.) and stable during reprocessing (grinding, melting), the only postconsumer plastic wastes that have routinely been recycled in a closed-loop fashion are clear PET bottles and more recently HDPE bottles.388”

What the sources say

• Not checked yetcites [388] source

In the paper

“The most challenging step is sorting/ separation, which limits the type of polymers that can be recycled and also determines the quality of recyclates.”

In the paper

“In the first step, PET was depolymerized using isosorbide to oligomers, which were chain extended by succinic acid in the second step to form a novel copolyester (Scheme 18).”

What the sources say

• Not checked yetcites [414] source

In the paper

“Computational studies revealed that this reaction proceeds by the nucleophilic attack of the metal carbonate on the PC and the evolution of CO2 gas as the by-product.”

What the sources say

• Not checked yetcites [417] source

In the paper

“The alcoholysis of PLAs have been achieved under different conditions [433][434][435][436] and the efficiency of these processes is highly condition-dependent.”

What the sources say

• Not checked yetcites [433][434][435][436]

In the paper

“Monobutyltin oxide was identified as the most active catalyst for both steps and resulted in minimal discoloration.”

What the sources say

• Not checked yetcites [415] source

In the paper

“These mechanisms are supported by the fact that when the OH chain end is capped via acetylation, the degradation rate significantly decreases and the relatively slow random chain scission become dominant.428”

What the sources say

• Not checked yetcites [428] source

In the paper

“They found that PPC was less susceptible to degradation in acidic medium than PCL and PLA, with increased degradation rate as PPC << PLA < PCL.”

What the sources say

• Not checked yetcites [425] source

In the paper

“Although the two mechanisms operate simultaneously during hydrolysis, several studies have found that the chainend scission is significantly faster than the random backbone cleavage.424,426,427”

What the sources say

• Not checked yetcites [424] source
• Not checked yetcites [426] source
• Not checked yetcites [427] source

In the paper

“In contrast, PPC was more readily hydrolyzed in basic conditions, with increased degradation rate being PCL << PLA < PPC.”

What the sources say

• Not checked yetcites [425] source

In the paper

“The rate of water diffusion depends on the hydrophobicity of the polymer and its shape or surface area while the intrinsic degradation kinetics is affected by the pH 421 and temperature of the medium 422 as well as the molecular weight 423 and microstructures of the polymer.424”

What the sources say

• Not checked yetcites [421] source
• Not checked yetcites [422] source
• Not checked yetcites [423] source

In the paper

“While at acidic pH the hydrolysis proceeds through a preferential scission of the end groups and spits out one lactic acid unit at a time, the base catalyzed hydrolysis proceeds preferentially via a backbiting process from the OH chain end leading to the formation of lactide, which is eventually hydrolyzed to lactate.”

What the sources say

• Not checked yetcites [421] source
• Not checked yetcites [424] source
• Not checked yetcites [428] source

In the paper

“The computational investigation showed that stoichiometric amounts of metal carbonate is needed for the reaction to proceed to completion, but insights provided by investigating the mechanism also led them to develop a catalytic process using 12 mol% K2CO3 with lower reaction efficiency.”

What the sources say

• Not checked yetcites [417] source

In the paper

“The acid-or base-catalyzed hydrolysis of aliphatic polyester and polycarbonates has also been widely explored, the results of which have been used to guide the design and application of these polymers for therapeutic delivery and medical implants.418”

What the sources say

• Not checked yetcites [418] Kumar M. N. V. R., 2016

In the paper

“The use of Bu2Sn(OMe)2 or NaOH facilitated a nearly quantitative depolymerization to CL, while Ti(O i Pr)4 gave almost equal amounts of CL and its cyclic dimer.”

What the sources say

• Not checked yetcites [454] source

In the paper

“It was shown that both the depolymerization rate and selectivity increased with Sn concentration.[447][448][449]”

What the sources say

• Not checked yetcites [447][448][449]

In the paper

“Acetylation of the OH chain end significantly increased the polymer stability and impeded the thermal recycling, consistent with an unzipping mechanism initiated from the OH chain end.444”

What the sources say

• Not checked yetcites [444] source

In the paper

“For Sn < 20 ppm, the degradation proceeded mainly via random intra-and intermolecular ester exchange, generating a significant amount of diastereomers and cyclic oligomers.448”

What the sources say

• Not checked yetcites [448] source

In the paper

“Compared to the traditional bulk production of lactate esters based on the esterification of lactic acid 441,442 , these catalytic alcoholyses of PLAs provide a number of advantages, including starting materials derived from PLA wastes, reduced reaction time and high yield, simple purification, and retention of stereochemistry.”

What the sources say

• Not checked yetcites [441] source
• Not checked yetcites [442] Martino-Gauchi, G.; Teissier, R.Continuous Esterification Process for the Preparation of Ethyl Lactate from Lactic Acid and Ethanol. U.S. Patent 20060041165 A1, 2004.