Chain Extension Reaction Research Articles

Catalyzing PET-RAFT Polymerizations Using Inherently Photoactive Zinc Myoglobin.

Protein photocatalysts provide a modular platform to access new reaction pathways and affect product outcomes, but their use in polymer synthesis is limited because co-catalysts and/or co-reductants are required to complete catalytic cycles. Herein, we report using zinc myoglobin (ZnMb), an inherently photoactive protein, to mediate photoinduced electron/energy transfer (PET) reversible addition-fragmentation chain transfer (RAFT) polymerizations. Using ZnMb as the sole reagent for catalysis, photomediated polymerizations of N,N-dimethylacrylamide in PBS were achieved with predictable molecular weights, dispersity values approaching 1.1, and high chain-end fidelity. We found that initial apparent rate constants of polymerization increased from 4.6×10-5 s-1 for zinc mesoporpyhrin IX (ZnMIX) to 6.5×10-5 s-1 when ZnMIX was incorporated into myoglobin to yield ZnMb, indicating that the protein binding site enhanced catalytic activity. Chain extension reactions comparing ZnMb-mediated RAFT polymerizations to thermally-initiated RAFT polymerizations showed minimal differences in block copolymer molecular weights and dispersities. This work enables studies to elucidate how protein modifications (e.g., secondary structure folding, site-directed mutagenesis, directed evolution) can be used to modulate polymerization outcomes (e.g., selective monomer additions towards sequence control, tacticity control, molar mass distributions).

Catalyzing PET‐RAFT Polymerizations Using Inherently Photoactive Zinc Myoglobin

AbstractProtein photocatalysts provide a modular platform to access new reaction pathways and affect product outcomes, but their use in polymer synthesis is limited because co‐catalysts and/or co‐reductants are required to complete catalytic cycles. Herein, we report using zinc myoglobin (ZnMb), an inherently photoactive protein, to mediate photoinduced electron/energy transfer (PET) reversible addition‐fragmentation chain transfer (RAFT) polymerizations. Using ZnMb as the sole reagent for catalysis, photomediated polymerizations of N,N‐dimethylacrylamide in PBS were achieved with predictable molecular weights, dispersity values approaching 1.1, and high chain‐end fidelity. We found that initial apparent rate constants of polymerization increased from 4.6×10–5 s−1 for zinc mesoporpyhrin IX (ZnMIX) to 6.5×10–5 s−1 when ZnMIX was incorporated into myoglobin to yield ZnMb, indicating that the protein binding site enhanced catalytic activity. Chain extension reactions comparing ZnMb‐mediated RAFT polymerizations to thermally‐initiated RAFT polymerizations showed minimal differences in block copolymer molecular weights and dispersities. This work enables studies to elucidate how protein modifications (e.g., secondary structure folding, site‐directed mutagenesis, directed evolution) can be used to modulate polymerization outcomes (e.g., selective monomer additions towards sequence control, tacticity control, molar mass distributions).

Synthetic Approaches to and Structures of Diplatinum Polyynediyl Complexes trans,trans‐[(C6F5)(R3P)2Pt(C≡C)nPt(PR3)2(C6F5)] With Odd Numbers of Triple Bonds; Avoiding Complicating Ethynediyl Extrusions

AbstractReactions of trans‐(C6F5)(p‐tol3P)2Pt(C≡C)nSiEt3 (PtC2nSi; n=5, 7, 9) and excess PtCl in the presence of wet n‐Bu4N+ F− (to effect protodesilylation) under Sonogashira‐type conditions (CuCl, base, other additives) afford the title compounds PtC10Pt, PtC14Pt, and PtC18Pt in 42–32 % yields. A four‐fold substitution of the phosphine ligands in PtC10Pt by PEt3 affords Pt'C10Pt’ (78 %), and a Sonogashira reaction of Pt'C2H and Pt'Cl affords Pt'C2Pt’ (68 %). The analogous reaction with PtC2Si and PtCl is unsuccessful, presumably for steric reasons. The crystal structures of PtC10Pt, PtC14Pt, Pt'C10Pt′, and Pt'C2Pt’ exhibit a number of interesting trends and features. Certain sp chain extension reactions that lead to or employ the precursors PtC10Si, PtC12Si, PtC14Si, and PtC18Si sometimes give byproducts derived from C2 loss, and possible origins are discussed. Related phenomena have been reported by others in the course of synthesizing extended conjugated polyynes.

Interfacial compatibilization of fully biodegradable polylactic acid/polybutylene adipate terephthalate blends for improved mechanical and physical performance

Environmental problems, such as plastic pollution and global warming, are motivating researchers worldwide to seek sustainable biodegradable polymers that would replace the nonbiodegradable ones. Polylactic acid (PLA) has emerged as one of the most promising alternatives due to its superior mechanical and thermal qualities compared to other types of biopolymers. However, PLA has some inherent deficiencies such as its brittleness and rigidity, which limit its further use. This study investigates the toughening effect of different amounts of polybutylene adipate terephthalate (PBAT) on PLA, and the compatibilization effect of ADR, a chain extender, on the PLA/PBAT blends. The results indicate that PBAT can significantly enhance the flexibility and toughness of PLA. PLA and PBAT can react with ADR to form PLA-g-PBAT copolymers thereby increasing the compatibility of these two polymers. The tensile strength, elongation at break and impact strength of the PLA/PBAT/ADR blends are all increased due to the increased compatibility. The chain extension reaction can promote the formation of a better crystalline structure in the PLA/PBAT blends, which leads to the increase of the Tm of PLA. Besides, the hydrophilicity of PLA can be adjusted by blending with PBAT, and the hydrophilicity of the blends with blend ratios of 75:25, 50:50 and 25:75 can also be enhanced after the addition of ADR.

Ultraviolet-induced controlled radical polymerization using titanium dioxide nanoparticles via the reversible addition–fragmentation chain transfer process

Abstract Herein, we report the ultraviolet (UV)-induced controlled radical polymerization facilitated by titanium dioxide nanoparticles and trithiocarbonate derivatives, serving as photocatalysts and chain transfer agents, respectively. The polymerization proceeded through a reversible addition–fragmentation chain transfer (RAFT) process. The resulting polymers exhibited well-controlled molecular weights and relatively low polydispersity. Additionally, the chain extension reaction via UV-induced RAFT polymerization using titanium dioxide nanoparticles yielded higher molecular weight polymer products.

Dual role of epoxidized soybean oil (ESO) as plasticizer and chain extender for biodegradable polybutylene succinate (PBS) formulations

This work reports the effect of 1–5 wt% epoxidized soybean oil (ESO) addition on the thermal, mechanical, and morphological properties of polybutylene succinate (PBS). ESO acts as a chain extender as well as a mild plasticizer of PBS. N-methylimidazole (NMI) is used as a catalyst to promote the reaction between PBS and ESO, and thermal, rheological, and spectroscopic analyses demonstrate increased viscoelastic properties, compatibility, crystallinity and thermal stability of the melt reacted formulations. In the presence of NMI, storage modulus (G’) values two orders of magnitude higher than that of pure PBS are achieved, confirming the completion of the chain extension reaction. A drastic refinement of the biphasic structure of the blend is observed, with the formation of a homogenous structure where ESO is well incorporated into the matrix. Finally, tensile tests reveal enhanced mechanical performance in the blends reacted in the presence of NMI. These findings pave the way for the development of a versatile family of materials which could find potential application in sustainable biodegradable packaging.

All-Inorganic sp-Chain Ligands: Isoelectronic B/N Analogues of E. O. Fischer's Alkynylcarbynes.

Borylation of a tungsten-bound N2 ligand and halide abstraction provides access to a cationic complex with an unprecedented linear NNBR ligand. This complex undergoes [3+2] cycloaddition with azides, and an unexpected chain-extension reaction with an iminoborane, leading to a complex with a five-atom B/N chain. These two [NNBR]-containing complexes, inorganic analogues of E. O. Fischer's alkynylcarbynes, are very rare examples of molecules containing all-inorganic chains of sp-hybridized atoms.

Phosphorus/Bromine Synergism Improved the Flame Retardancy of Polyethylene Terephthalate Foams.

Polyethylene terephthalate (PET) foams have the characteristics of being lightweight and high strength, as well as offering good heat resistance, minimal water absorption, etc., and they have been widely used in the wind power field. In addition, they are being promisingly applied in automotive, rail, marine, construction, and other related fields. Therefore, the flame retardancy(FR) of PET foams is an issue that requires investigation. The addition of flame retardants would affect the chain extension reaction, viscoelasticity, and foamability of PET. In this study, zinc diethyl hypophosphite (ZDP) and decabromodiphenylethane (DBDPE) were used to form a synergistic FR system, in which ZDP is an acid source and DBDPE is a gas source, and both of them synergistically produced an expanded carbon layer to improve the flame retardancy of PET foams. The ratio of ZDP and DBDPE is crucial for the carbon yield and the expansion and thermal stability of the char layers. At the ZDP/DBDPE ratios of 9/3 and 7/5, the thickness of the char layers is about 3-4 mm, the limiting oxygen index (LOI) values of FR modified PET are 32.7% and 33.6%, respectively, and the vertical combustion tests both reached the V-0 level. As for the extruded phosphorous/bromine synergism FR PET foams, ZDP/DBDPE ratios of 3:1 and 2:1 were applied. As a result, the vertical combustion grade of foamed specimens could still reach V-0 grade, and the LOI values are all over 27%, reaching the refractory grade.

Synthesis and properties of novel degradable polyglycolide-based polyurethanes

Graphical abstract Polyglycolide-based polyurethane was synthesized via chain extension reaction. As the hard segment content increases, its thermal stability and mechanical properties are improved; and the weight loss rate in PBS solution is reduced.

High melt viscosity, low yellowing, strengthened and toughened biodegradable polyglycolic acid via chain extension of aliphatic diisocyanate and epoxy oligomer

Poly(glycolic acid) (PGA) is a biodegradable plastic with excellent degradation rate, barrier properties, and heat resistance. However, its low melt viscosity and narrow processing temperature severely limit its application. To overcome these drawbacks, the aromatic diisocyanates TDI and MDI, aliphatic diisocyanate HDI, and multifunctional epoxy oligomer ADR were used as the chain extender to modify PGA. The PGA/HDI shows a faster chain extension reaction rate and significantly less yellowing than PGA/TDI or PGA/MDI. The combined use of HDI and ADR to modify PGA can produce long chain branched/crosslinked structures, resulting in a significant increase in melt viscosity, with complex viscosity two orders of magnitude higher than that of pure PGA and minimal yellowing. The T-5% of PGA/HDI/ADR is 45 °C higher than that of pure PGA, and its crystallization temperature, crystallization rate and melting temperature are significantly decreased, suggesting that it has a wider processing temperature window. Moreover, the tensile and flexural strength of PGA/HDI/ADR are 113.8 MPa and 216.8 MPa, respectively, an increase of 25% and 26% over pure PGA, while the elongation at break and impact strength increase to 9.5% and 11.6 KJ/m2, respectively, 42% and 176% higher than pure PGA.

Controlled Polymerization of N‐Vinyl Imidazole, N‐Vinyl Pyrrolidone, and N‐Vinyl Carbazole with Dithiocarbamates toward High Molar Mass Polymers

AbstractAchieving control over the polymerization of less activated monomers like N‐vinyl carbazole (NVC), N‐vinyl pyrrolidone (NVP), and N‐vinyl imidazole (NVIm) to produce high molar mass polymers poses a significant challenge. To accomplish this, eight different dithiocarbamate‐based reversible addition–fragmentation chain transfer (RAFT) agents are synthesized and employed to polymerize NVIm, NVC, and NVP in order to understand and establish a suitable agent for their controlled polymerization to achieve high molar mass polymers. Chain end presence of these RAFT‐derived polymers is established through 1H NMR studies. Further, these active chain ends are used for chain extension reactions to prepare block copolymers. Synthesized RAFT agents 04, 05, 06, and 08 that are bearing primary leaving groups (methyl 2‐acetate, ethyl 2‐acetate, tert‐butyl 2‐acetate, and cyanomethane) display moderate to good control over the polymerization of NVIm and NVC. Among these, RAFT agent‐08 with cyanomethane leaving group produces poly(NVIm) and poly(NVC) with the highest molar masses of 44 670 Da (1.52) and 53 620 Da (1.4), respectively. Interestingly, RAFT agents bearing both secondary and primary leaving groups show good control over the NVP polymerization. Notably, RAFT agent‐02 with ethyl‐2‐propionate leaving group yields poly(NVP) with the highest molar mass of 89 450 Da and dispersity of 1.43.

Development of PCR primers enabling the design of flexible sticky ends for efficient concatenation of long DNA fragments.

We developed chemically modified PCR primers that allow the design of flexible sticky ends by introducing a photo-cleavable group at the phosphate moiety. Nucleic acid derivatives containing o-nitrobenzyl photo-cleavable groups with a tert-butyl group at the benzyl position were stable during strong base treatment for oligonucleotide synthesis and thermal cycling in PCR reactions. PCR using primers incorporating these nucleic acid derivatives confirmed that chain extension reactions completely stopped at position 1 before and after the site of the photo-cleavable group was introduced. DNA fragments of 2 and 3 kbp, with sticky ends of 50 bases, were successfully concatenated with a high yield of 77%. A plasmid was constructed using this method. Finally, we applied this approach to construct a 48.5 kbp lambda phage DNA, which is difficult to achieve using restriction enzyme-based methods. After 7 days, we were able to confirm the generation of DNA of the desired length. Although the efficiency is yet to be improved, the chemically modified PCR primer offers potential to complement enzymatic methods and serve as a DNA concatenation technique.

Preparation of rigidity toughness balance and stable poly(glycolic acid) based on chain extension reaction

AbstractAs a completely degradable material, poly(glycolic acid) (PGA) has excellent rigidity, barrier properties, degradability and biocompatibility. However, the inherent brittleness and easily hydrolysable characteristics limit its widespread application. Herein, we introduced chain extension ADR to modify PGA to ameliorate these defects. The results showed that ADR could react with PGA to form “comb‐like” and “cross‐linked” chain extension structures resulting in the improvement of complex viscosity and formation of gel. Because of the chain entanglement of chain extension structures, the toughness of modified PGA was improved (which was verified by the impact strength value of 4.3 kJ/m2 that was about 126% of virgin PGA) without sacrificing its rigidity. Furthermore, the hydrolysis results indicated that the representative PGA/1.0ADR had better hydrolysis stability, it had more complete morphology and slower degradation rate than virgin PGA in the 17‐day hydrolysis experiment. Apart from better toughness and hydrolysis stability, there was also improvements in crystallization performance, the sample PGA/1.0ADR endowed with higher crystallization peak temperature (2.3°C higher than virgin PGA) and lower crystallization activation energy. In short, this work prepared a kind of modified PGA with rigidity toughness balance and better hydrolysis stability, which could expand the application range of PGA‐based materials.

Design and fabrication of bio-based functional composite materials with antibacterial, antioxidant, and improved mechanical properties based on poly (butylene adipate-co-terephthalate) (PBAT) for food packaging

The PBAT/epoxy chain extender (ADR-4468) film, with its competitive pricing, excellent biodegradability, and outstanding mechanical properties, stands out. Through experimental design, quercetin (QR) with antibacterial and antioxidant properties was effectively grafted onto the epoxy chain extender (ADR-4468), resulting in the successful synthesis of the functional modifier A-QR. PBAT composite films containing different weight percentages (0.2, 0.4, 0.6, 0.8, and 1% w/w) of A-QR were prepared using extrusion blow molding technology. QR and ADR are chemically bonded together, forming a strong and tightly knit composite. The composites exhibit excellent composite effects and outperform single-component blends, reducing A-QR migration, improving mechanical properties, and enhancing the barrier properties of the composite film. Structural, mechanical, and water barrier properties, antibacterial and antioxidant properties, as well as freshness preservation effects of the film, were analyzed. A-QR and PBAT formed a cross-linked network structure through chain extension reactions. Tensile strength increased from 19.7 MPa to 37.9 MPa, representing a 92.4% improvement. Antioxidant activity reached up to 65%. It exhibited excellent antibacterial activity against Staphylococcus aureus and Escherichia coli. The maximum total migration was only 0.7 mg/dm2, significantly below the specified overall migration limit (OML). PBAT/A-QR films successfully extended the shelf life of bananas, strawberries, apples, and oyster mushrooms due to their excellent antioxidant, antibacterial, and water barrier properties.

Phenanthroline Derivatives as Efficient Organic Photocatalysts for Visible‐Light‐Mediated PET‐RAFT Polymerization

Comprehensive SummaryPhenanthroline is an excellent and stable π‐electron acceptor with a large conjugated chromophore. Phenanthroline derivatives are widely used in adsorption, photodegradation, solar cells, biology, and so on. At present, there are still limited organic molecules utilized to efficiently photocatalyze reversible‐deactivation radical polymerization (RDRP). Therefore, the design of organic photocatalysts (OPCs) for RDRP remains a challenge. Herein, according to the strategy of combining the donor groups and weak acceptor groups, donor‐acceptor (D‐A) type OPCs based on phenanthroline were utilized for the first time in photoinduced electron transfer‐reversible addition‐fragmentation chain transfer (PET‐RAFT) polymerization. 1,10‐Phenanthroline‐5‐amine (Aphen) with a donor group‐amino was screened out for efficacious photo‐controlled radical polymerization under blue light for various monomers with conjugated and unconjugated structures with high monomer conversion and well‐defined narrow dispersity polymers (Đ < 1.20). Controllable homo‐polymers and block copolymers were successfully realized by chain extension reaction and block copolymerization of structurally diverse monomers.

Cardanol derivatives as compatibilizers for strengthening and toughening polylactic acid/bamboo fiber bio‐composites

AbstractThe application of bamboo fibers (BFs) as a reinforcing filler in polylactic acid (PLA) is hindered by their poor compatibility owing to the intrinsic hydrophilia of BFs and the hydrophobicity of PLA. To solve this issue, cardanol (CD) and epoxidized cardanol glycidyl ether (ECGE) were used as compatibilizers to strengthen and toughen PLA/BF bio‐composites, to the best of our knowledge, preparing PLA/BF/CD and PLA/BF/ECGE bio‐composites. The impact strengths of the synthesized bio‐composites increased from 7.75 to 23.75 and 7.75 to 23.95 kJ/m2, respectively, compared with that of a PLA/BF composite without compatibilizer. The investigation of the mechanical properties, crystallization, fractured surface morphology, and solvent stress‐cracking resistance properties revealed that the toughening mechanism of the PLA/BF/CD bio‐composites are mainly based on the plasticization of CD, which results in high impact toughness but low tensile strength. Moreover, the modification with ECGE improves the impact and tensile strengths of the bio‐composite owing to the following factors: (1) the epoxy groups of ECGE generate strong interactions with the BF surface and PLA to form an enhanced interfacial structure; (2) when present at high concentrations, chain extension reaction between ECGE and PLA to increase the molecular chain entanglement of PLA; and (3) upon curing and crosslinking, ECGE forms an entangled network structure that toughens the matrix.

Dl-Methionine-Mediated Reversible Deactivation Radical Polymerization of Styrene and Methyl Methacrylate.

Reversible deactivation radical polymerization (RDRP) is a facile and highly efficient technique for the synthesis of well-defined polymer with precise structure. dl-Methionine (Met) as a RDRP control agent is described and assessed for RDRP of styrene (St) and methyl methacrylate (MMA) with AIBN as radical initiator at 75°C, which enables excellent control of this polymerization. The addition of dl-Methionine significantly decreased the dispersity (Đ) of the polymers for both monomers and first-order linear kinetic plots of polymethyl methacrylate (PMMA) are observed in DMSO. Considering the heat resistance of dl-Methionine, kinetic studies indicate that polymerization develops at a faster rate at higher reaction temperature (100°C) with the same dl-Methionine content. Well-defined polymethyl methacrylate-block-polystyrene (PMMA-block-PSt) is successfully achieved by the chain extension reaction that demonstrates the high end fidelities of this polymerization approach. The system allows the use of dl-Methionine, a rich source and easily synthesized agent, to mediate RDRP strategy.

Improving flame retardancy and mechanical properties of polyamide 6 induced by multiple reactions among flame retardants and matrix

A bio-based flame retardant TFD was synthesized using tyrosine (Tyr), furfural and 9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) which was used in polyamide 6 (PA6) to modify its flame retardancy. A bio-based chain extender EDPDO which was obtained by epoxidation of the reaction product between phenylphosphonic dichloride and magnolol, was used to regulate the mechanical properties of PA6. TFD endows PA6 with a UL-94 V0 rating at the content of 12 wt%. If TFD and EDPDO were premixed and incorporated into PA6, 8 wt% TFD and 1 wt% EDPDO are needed for PA6 to display a UL-94 V0 rating. Moreover, the mechanical properties were improved. The tensile strength of PA6 containing 8 wt% TFD and 2 wt% EDPDO is 97 MPa which is 21 MPa higher than that of PA6. The TFD reduces the molecular weight of PA6, while the chain extension reactions increase the molecular weight to a certain extent. In addition, the adhesion among the char particles is so poor that some small char particles volatilize into the gas phase to form smoke. The improved flame retardancy in UL-94 test is mainly caused by the melting-away effect.

Chain-Extendable Crosslinked Hydrogels Using Branching RAFT Modification.

Functional crosslinked hydrogels were prepared from 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA). The acid monomer was incorporated both via copolymerization and chain extension of a branching, reversible addition-fragmentation chain-transfer agent incorporated into the crosslinked polymer gel. The hydrogels were intolerant to high levels of acidic copolymerization as the acrylic acid weakened the ethylene glycol dimethacrylate (EGDMA) crosslinked network. Hydrogels made from HEMA, EGDMA and a branching RAFT agent provide the network with loose-chain end functionality that can be retained for subsequent chain extension. Traditional methods of surface functionalization have the downside of potentially creating a high volume of homopolymerization in the solution. Branching RAFT comonomers act as versatile anchor sites by which additional polymerization chain extension reactions can be carried out. Acrylic acid grafted onto HEMA-EGDMA hydrogels showed higher mechanical strength than the equivalent statistical copolymer networks and was shown to have functionality as an electrostatic binder of cationic flocculants.

Enhanced heat resistance and expansion ratio of biodegradable poly (lactic acid)/poly (butylene adipate-co-terephthalate) composite foams via synergistic effect of nucleating agent and chain extension

Abstract Environmentally friendly foams have been studied extensively to handle the plastic pollution caused by disposable tableware. Herein, biodegradable poly (lactic acid) (PLA) – poly (butylene adipate-co-terephthalate) (PBAT) composites were first fabricated by melt blending, in which a reactive chain extender (ADR) was incorporated to enhance the interfacial compatibility and melt strength, a nucleating agent (TMC) was applied to improve the crystallinity. Subsequently, the foaming behavior of the composites was investigated via supercritical CO2 foaming. Specifically, a spherulite and shish-kebab-like nanoporous structure was observed from PLA and PLA/TMC foams, respectively, when the soaking temperature was far below melting temperature. With an increase of foaming temperature, the unmelted completely crystals served as physical cross-linking points, also contributing to a high melt strength. Combined with chain extension reaction of ADR, the PLA–PBAT/ADR/TMC foams showed the largest cell diameter and expansion ratio, which were 19 μm and 8.9, respectively. Furthermore, the heat resistance of PLA–PBAT/ADR/TMC foams was also significantly improved, owing to the high crystallinity induced by TMC. Consequently, the composite foams with superior heat resistance and toughness were obtained to broaden its application as biodegradable disposable tableware for hot food.