Effective Chain Transfer Research Articles

Synthesis of functionalized hyperbranched polyethylene with high density polar groups using triarylnaphthyl iminopyridyl palladium catalysts

The 8-arylnaphthalenyl substituent is widely used as an effective chain transfer retarding substituent in late-transition-metal-catalyzed ethylene (co)polymerization. In this contribution, we introduce a new class of palladium catalysts based on 2,4,8-triarylnaphthyliminopyridyl ligands to provide an effective shield on the axial site of the active center. This results in the production of high molecular weight polyethylene or functionalized polyethylene. The palladium catalysts exhibit moderate polymerization activity (104 g mol−1 h−1) in ethylene polymerization. The resulting polyethylene has high molecular weights (16.8–60.8 kg/mol) and high branching densities (90–96/1000C). These catalysts are highly efficient for ethylene and MA copolymerization, enabling access to high molecular weight functionalized polyethylene with a remarkable MA incorporation ratio (9.21–21.00 mol%) under very mild conditions. According to the 13C NMR analysis, it was found that the polyethylene and E-MA copolymers were hyperbranched. In comparison to previously reported iminopyridine palladium catalysts with similar structures, catalysts in this work demonstrated reduced activity and exhibited a relatively high molecular weight, alongside achieving the highest insertion ratio in ethylene (co)polymerization.

Visible Light Photoiniferter Polymerization for Dispersity Control in High Molecular Weight Polymers.

The synthesis of polymers with high molecular weights, controlled sequence, and tunable dispersities remains a challenge. A simple and effective visible-light controlled photoiniferter reversible addition-fragmentation chain transfer (RAFT) polymerization is reported here to realize this goal. Key to this strategy is the use of switchable RAFT agents (SRAs) to tune polymerization activities coupled with the inherent highly living nature of photoiniferter RAFT polymerization. The polymerization activities of SRAs were in situ adjusted by the addition of acid. In addition to a switchable chain-transfer coefficient, photolysis and polymerization kinetic studies revealed that neutral and protonated SRAs showed different photolysis and polymerization rates, which is unique to photoiniferter RAFT polymerization in terms of dispersity control. This strategy features no catalyst, no exogenous radical source, temporal regulation by visible light, and tunable dispersities in the unprecedented high molecular weight regime (up to 500 kg mol-1 ). Pentablock copolymers with three different dispersity combinations were also synthesized, highlighting that the highly living nature was maintained even for blocks with large dispersities. Tg was lowered for high-dispersity polymers of similar MWs due to the existence of more low-MW polymers. This strategy holds great potential for the synthesis of advanced materials with controlled molecular weight, dispersity and sequence.

Mechanistic Insight into Anion‐Binding Catalytic Living Cationic Polymerization

AbstractExploiting non‐covalent interactions to catalyze challenging ionic polymerizations is an ambitious goal but is in its infancy. We recently demonstrated non‐covalent anion‐binding catalysis as an effective methodology to enable living cationic polymerization (LCP) of vinyl ethers in an environmentally benign manner. Here, we further elucidate the structure‐reactivity relationships of the elaborately designed seleno‐cyclodiphosph(V)azanes catalysts and the roles of anion‐binding interactions by a combined theoretical DFT study and experimental study. The investigation suggests that the distinct cis‐cyclodiphosph(V)azane framework combined with “selenium effect” and electron‐withdrawing 3,5‐(CF3)2‐Phenyl substitution pattern in catalyst enables a critical contribution to accessing excellent stability, anion affinity and solubility under polymerization conditions. Thus, the catalyst could leverage anion‐binding interactions to precisely control reversible and transient dormant‐active species equilibrium, allowing it to dynamically bind, recognize and pre‐organize propagating ionic species and monomer, thereby facilitating efficient chain propagation and minimizing irreversible chain transfer events under mild conditions. The more in‐depth understanding of the mechanism for anion‐binding catalytic LCP reported herein should help to guide future catalyst design and to extend this concept to broader polymerization systems where ionic species serve as crucial intermediates.

Mechanistic Insight into Anion-Binding Catalytic Living Cationic Polymerization.

Exploiting non-covalent interactions to catalyze challenging ionic polymerizations is an ambitious goal but is in its infancy. We recently demonstrated non-covalent anion-binding catalysis as an effective methodology to enable living cationic polymerization (LCP) of vinyl ethers in an environmentally benign manner. Here, we further elucidate the structure-reactivity relationships of the elaborately designed seleno-cyclodiphosph(V)azanes catalysts and the roles of anion-binding interactions by a combined theoretical DFT study and experimental study. The investigation suggests that the distinct cis-cyclodiphosph(V)azane framework combined with "selenium effect" and electron-withdrawing 3,5-(CF3 )2 -Phenyl substitution pattern in catalyst enables a critical contribution to accessing excellent stability, anion affinity and solubility under polymerization conditions. Thus, the catalyst could leverage anion-binding interactions to precisely control reversible and transient dormant-active species equilibrium, allowing it to dynamically bind, recognize and pre-organize propagating ionic species and monomer, thereby facilitating efficient chain propagation and minimizing irreversible chain transfer events under mild conditions. The more in-depth understanding of the mechanism for anion-binding catalytic LCP reported herein should help to guide future catalyst design and to extend this concept to broader polymerization systems where ionic species serve as crucial intermediates.

Removable Pressure-Sensitive Adhesives Based on Acrylic Telomer Syrups

Removable pressure-sensitive adhesives (PSAs) are used in the production of self-adhesive materials such as protective films, masking tapes or biomedical electrodes. This work presents a new and environmentally friendly method of obtaining this type of adhesive materials, i.e., photochemically induced free radical telomerization. Adhesive binders to removable PSAs, i.e., the photoreactive acrylic telomer syrups (ATS) were prepared from n-butyl acrylate, acrylic acid, and 4-acrylooxybenzophenone. Tetrabromomethane (CBr4) or bromotrichloromethane (CBrCl3) were used as the telogens. ATS was modified with unsaturated polybutadiene resin and a radical photoinitiator. Adhesive compositions were coated onto a carrier and UV cross-linked. The effects of the chemical nature of telomers (i.e., terminal Br or Cl atoms) and their molecular weight (K-value), as well as the cross-linking degree on adhesive properties of PSAs, were studied. It was found that with the increase in telogen content in the system, the dynamic viscosity of ATS and K-value of acrylic telomers decrease, and the conversion of monomers increases. CBr4 turned out to be a more effective chain transfer agent than CBrCl3. Moreover, telomers with terminal Br-atoms (7.5 mmol of CBr4), due to slightly lower molecular weights and viscosity, showed a higher photocrosslinking ability (which was confirmed by high cohesion results at 20 and 70 °C, i.e., >72 h). Generally, higher values of the temperature at which adhesive failure occurred were noted for PSAs based on ATS with lower telogen content (7.5 mmol), both CBr4 and CBrCl3. The excellent result for removable PSA was obtained in the case of telomer syrup Br-7.5 crosslinked with a 5 J/cm2 dose of UV-radiation (adhesion ca.1.3 N/25 mm, and cohesion > 72 h).

Unusual Effect of α-olefins as Chain Transfer Agents in Ethylene Polymerization over the Catalyst with Nonsymmetrical Bis(imino)pyridine Complex of Fe(II) and Modified Methylalumoxane (MMAO) Cocatalyst.

Ethylene polymerization with bis(imino)pyridlyiron precatalysts generally produces linear polyethylene (PE) even with the presence of α-olefins because α-olefins are not incorporated into polymeric products. Interestingly, α-olefins, such as hexene-1 or butene-1, have been found to act as effective chain transfer agents in the ethylene polymerization promoted by nonsymmetrical bis(imino)pyridyliron complexes with modified methylalumoxane (MMAO), resulting in higher catalytic activities with higher amounts of polymers with lower molecular weights, and, more importantly, narrower molecular weight distributions of the resultant polyethylenes (PE). This phenomenon confirms the assistance of α-olefins in the chain-termination reaction of iron-initiated polymerization and regeneration of the active species for further polymerization. Besides higher activities of the catalytic system, the formation of linear PE with trans-vinylene terminal groups and lower molecular weights are explained. The observation will provide a new pathway for enhancing catalytic activity and improving the quality of polyethylenes obtained by regulation of molecular weights and molecular weight distribution.

Dual Function of β-Hydroxy Dithiocinnamic Esters: RAFT Agent and Ligand for Metal Complexation.

The reversible addition-fragmentation chain-transfer (RAFT) process has become a versatile tool for the preparation of defined polymers tolerating a large variety of functional groups. Several dithioesters, trithiocarbonates, xanthates, or dithiocarbamates have been developed as effective chain transfer agents (CTAs), but only a few examples have been reported, where the resulting end groups are directly considered for a secondary use besides controlling the polymerization. Herein, it is demonstrated that β-hydroxy dithiocinnamic esters represent a hitherto overlooked class of materials, which are originally designed for the complexation of transition metals but may as well act as reversible CTAs. Modified with a suitable leaving group (R-group), these vinyl conjugated dithioesters indeed provide reasonable control over the polymerization of acrylates, acrylamides, or styrene via the RAFT process. Kinetic studies reveal linear evolutions of molar mass with conversion, while different substituents on the aromatic unit has only a minor influence. Block extensions prove the livingness of the polymer chains, although extended polymerization times may lead to side reactions. The resulting dithiocinnamic ester end groups are still able to form complexes with platinum, which verifies that the structural integrity of the end group is maintained. These findings open a versatile new route to tailor-made polymer-bound metal complexes.

Dithiocarbamates as Effective Reversible Addition-Fragmentation Chain Transfer Agents for Controlled Radical Polymerization of 1-Vinyl-1,2,4-triazole.

Narrow dispersed poly(1-vinyl-1,2,4-triazole) (PVT) was synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization of 1-vinyl-1,2,4-triazole (VT). AIBN as the initiator and dithiocarbamates, xanthates, and trithiocarbonates as the chain transfer agents (CTA) were used. Dithiocarbamates proved to be the most efficient in VT polymerization. Gel permeation chromatography was used to determine the molecular weight distribution and polydispersity of the synthesized polymers. The presence of the CTA stabilizing and leaving groups in the PVT was confirmed by 1H and 13C NMR spectroscopy. The linear dependence of the degree of polymerization on time confirms the conduct of radical polymerization in a controlled mode. The VT conversion was over 98% and the PVT number average molecular weight ranged from 11 to 61 kDa. The polydispersity of the synthesized polymers reached 1.16. The occurrence of the controlled radical polymerization was confirmed by monitoring the degree of polymerization over time.

Living Aqueous Microemulsion Polymerization of Ethylene with Robust Ni(II) Phosphinophenolato Catalysts.

Due to chain transfer events being competitive with chain growth, ethylene polymerization by P,O-chelated Ni(II) complexes usually affords low molecular weight polymers or oligomers. We now show that appropriately bulky substituted phosphinophenolato Ni(II) can polymerize in a living fashion, virtually devoid of chain transfer. Aqueous polymerizations with microemulsions of [κ2-P,O-2-(2-(2',6'-(MeO)2C6H3)C6H4)(Ph)P-6-(3',5'-(CF3)2C6H3)C6H3O-NiMe(pyridine)] (3) at 30 °C yield polyethylenes with narrow molecular weight distributions (Mw/Mn 1.02 to 1.34) and ultrahigh molecular weights (up to 2 × 106) in the form of aqueous nanoparticle dispersions. Catalyst stability and activity are maintained up to 70 °C in water.

PET-RAFT single unit monomer insertion of β-methylstyrene derivatives: RAFT degradation and reaction selectivity.

Reversible addition-fragmentation chain transfer (RAFT) single unit monomer insertion (SUMI) of β-methylstyrene derivatives into diverse RAFT agents presented fast reaction kinetics, but significant degradation of the SUMI products occurred due to a hydrogen abstraction reaction. Fortunately, such degradation can be suppressed through appropriate design of initial RAFT agents attributed to effective chain transfer and selective photoactivation.

Aluminum Alkyls as Highly Active Catalytic Chain Transfer Agents

AbstractDuring the production of free radical initiated low‐density polyethylene (LDPE), it was discovered that the addition of low levels of alkyl aluminum compounds caused the molecular weight of the LDPE to drop precipitously. Further investigation demonstrated that aluminum‐alkyl compounds are among the most effective chain transfer agents ever utilized. It was also shown that polymer chains, which transfer to Al alkyl species, contain almost exclusively vinyl terminated end groups. A catalytic chain transfer mechanism is proposed in which chain transfer occurs from a growing polymer chain to an aluminum center followed by beta hydride elimination to produce a vinyl terminated polymer chain and a new aluminum hydride bond. This new aluminum hydride bond can then undergo further chain transfer reactions. This is the first time such a catalytic chain transfer mechanism has been reported. As little as 10–20 mol ppm aluminum alkyl species decreased the degree of polymerization by a factor of 2 resulting in chain transfer constant (Cs) values as high as 1000–2000. Density functional theory (DFT) study elucidated the catalytic cycle of triethylaluminum (TEA). It is discovered that, depending on the reaction conditions, TEA can serve as a conventional as well as catalytic chain transfer agent.

Coordinative Chain Transfer Polymerization of Butadiene with Functionalized Aluminum Reagents.

Functionalized aluminum alkyls enable effective coordinative chain transfer polymerization with selective chain initiation by the functionalized alkyl. (ω‐Aminoalkyl)diisobutylaluminum reagents (12 examples studied) obtained by hydroalumination of α‐amino‐ω‐enes with diisobutylaluminum hydride promote the stereoselective catalytic chain growth of butadiene on aluminum in the presence of Nd(versatate)3, Cp*2Nd(allyl), or Cp*2Gd(allyl) precatalysts and [PhNMe2H+]/[B(C6F5)4 −]. Carbazolyl‐ and indolylaluminum reagents result in efficient molecular weight control and chain initiation by the aminoalkyl rather than the isobutyl substituent bound to aluminum. As confirmed for (3‐(9H‐carbazol‐9‐yl)propyl)‐initiated polybutadiene (PBD), for example, by deuterium quenching studies, polymer chain transfer by β‐hydride transfer is negligible in comparison to back‐transfer to aluminum.

Coordinative Chain Transfer Polymerization of Butadiene with Functionalized Aluminum Reagents

AbstractFunctionalized aluminum alkyls enable effective coordinative chain transfer polymerization with selective chain initiation by the functionalized alkyl. (ω‐Aminoalkyl)diisobutylaluminum reagents (12 examples studied) obtained by hydroalumination of α‐amino‐ω‐enes with diisobutylaluminum hydride promote the stereoselective catalytic chain growth of butadiene on aluminum in the presence of Nd(versatate)3, Cp*2Nd(allyl), or Cp*2Gd(allyl) precatalysts and [PhNMe2H+]/[B(C6F5)4−]. Carbazolyl‐ and indolylaluminum reagents result in efficient molecular weight control and chain initiation by the aminoalkyl rather than the isobutyl substituent bound to aluminum. As confirmed for (3‐(9H‐carbazol‐9‐yl)propyl)‐initiated polybutadiene (PBD), for example, by deuterium quenching studies, polymer chain transfer by β‐hydride transfer is negligible in comparison to back‐transfer to aluminum.

Sol–Gel Transition-Accompanied Radical Polymerization Initiated by Two Primary Radicals

When irradiation generates two radicals capable of initiating chain growth with different rate constants for chain transfer, two polymerization routes with different average chain length emerge. These pathways are not mixed in the initial part of the ballistic growth. Their mixing in chain transfer events is accompanied by transition from ballistic to diffusion growth. In the sol–gel transition region, the routes are spatially separated if the chain transfer depends on the rotational mobility of the reactants and decreases with increasing viscosity as the resulting oligomers accumulate. As an example, the polymerization of tetrafluoroethylene in solutions of silanes and oxysilanes is considered.

Alcohol mediated degenerate chain transfer controlled cationic polymerisation of para-alkoxystyrene

In this report we demonstrate methanol as an effective degenerative chain transfer agent to control the cationic polymerisation (initiated by triflic acid) of electron rich p-alkoxy-styrenes, such as p-methoxystyrene (p-MOS).

One-Pot Synthesis of Ion-Containing CO2-Based Polycarbonates Using Protic Ionic Liquids as Chain Transfer Agents

An analysis of the construction of ion-containing CO2-based polycarbonates via metal-catalyzed immortal copolymerization of propylene oxide (PO) and carbon dioxide in the presence of protic ionic liquids (ILs) as chain transfer agents is described. The reactions were catalyzed by the binary (salen)CoO2CCF3/onium salt system in the absence of added solvent. On the basis of the results of this study, which includes 1H NMR and MALDI-TOF-MS data, it is clear that the role of the protic IL in this process is dominated by its anion. When the anion of the protic ionic liquid is nucleophilic, such as chloride, the protic ionic liquid acts as a cocatalyst in the reaction system for epoxide ring opening, and the chain transfer reaction initiated by the cation is completely suppressed. However, when the anion of the protic ionic liquid is non-nucleophilic, such as BF4–, the protic ionic liquid acts as an effective chain transfer agent to afford IL-based polycarbonates by rapid and reversible chain transfer processes...

Polymers containing amino bis(methylene phosphonic acid) groups for scale inhibition

PurposeThe purpose of this paper is to prepare poly[allyl amino bis(methylene phosphonic acid)-ran-acrylic acid]s by two different routes. In the first route, poly(allyl amine-ran-acrylic acid)s were produced by radical copolymerization of a mixture of ally amine and acrylic acid, then converted into poly[allyl amino bis(methylene phosphonic acid)-ran-acrylic acid]s by the Mannich reaction with a mixture of formaldehyde and phosphonic acid. In the second route, allyl amino bis(methylene phosphonic acid) monomer was synthesized and copolymerised with acrylic acid. The aim of this work is to produce low-molecular-weight copolymer with the low amount of nitrogen and phosphorous having better scale inhibiting performance than commercial low-molecular-weight poly(acrylic acid)s.Design/methodology/approachPoly(allyl amine-ran-acrylic acid)s were prepared by radical copolymerisation of a mixture of ally amine and acrylic acid, and the molecular weight of copolymers was regulated by using an effective chain transfer compound and the formed copolymer was reacted with a mixture of formaldehyde and phosphorous acid. Allyl amino bis(methylene phosphonic acid) monomer was prepared and then copolymerised with acrylic acid using radical initiators.FindingsPoly[allyl amino bis(methylene phosphonic acid)-ran-acrylic acid] produced with both routes, especially low-molecular weight ones have better anti-scaling performance than low-molecular-weight commercial poly(acrylic acid).Research limitations/implicationsBy using an excess of formaldehyde and phosphonic acid, a limited increase in the conversion of amine groups of poly(allyl amine-ran-acrylic acid) to amino methylene phosphonic acid groups was achieved, so unreacted amine groups were always present in the structure of the final copolymers.Practical implicationsThe low-molecular-weight poly[allyl amino bis(methylene phosphonic acid)-ran-acrylic acid] may be used as a better anti-scaling polymer in industry.Social implicationsThe low-molecular-weight poly[allyl amino bis(methylene phosphonic acid)-ran-acrylic acid] is an alternative polymer for scale inhibition in the water boilers.Originality/valueThe low-molecular-weight poly[allyl amino bis(methylene phosphonic acid)-ran-acrylic acid] copolymers containing both carboxylic acid and amino bis(methylene phosphonic acid) are more effective anti-scaling additives than poly(acrylic acid)s in water boilers.

Surface‐initiated nitroxide‐mediated polymerization of sodium 4‐styrene sulfonate from latex particles

ABSTRACTIn this study, we report the use of a double‐headed dialkoxyamine trithiocarbonate (I) capable of acting as chain transfer agent via reversible addition‐fragmentation chain transfer polymerization or as initiator via nitroxide‐mediated polymerization. It is worth mentioning that I was revealed as an effective dual chain transfer agent in the synthesis of multiblock copolymers via bulk and emulsion processes. In this article, we report the employing of I in dispersed systems to obtain amphiphilic multiblock copolymers and latexes. In this case, a water soluble macroagent of PAA previously synthetized was used in disperse media using a mixture of methanol/water (70:30, w/w). Stable latexes were obtained via polymerization‐induced self‐assembly and surface‐initiated polymerization of SSNa from alkoxyamine‐functionalized latex PAA‐b‐PS‐b‐PAA was also obtained © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 437–444

Cellulose nanocrystals grafted with polyacrylamide assisted by macromolecular RAFT agents

Graft modification is an excellent way to prepare cellulose nanocrystals (CNCs) with various functions. In this work, different water-soluble macro reversible addition fragmentation chain transfer (macroRAFT) agents were used to mediate grafting of polyacrylamide with cellulose nanocrystals. Fourier-transform infrared spectroscopy, 13C solid-state nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy, and elemental analysis were used to characterize the presence of polyacrylamide and quantify its content on the modified cellulose nanocrystals. The results show that two amphiphilic macroRAFTs, namely St5AA14RAFT and St7AA14RAFT, increased the weight ratio of polyacrylamide on the modified cellulose nanocrystals, whereas a corresponding hydrophilic macroRAFT (AA14RAFT) impeded growth of the polymer chains on the cellulose nanocrystals. Examination of the structure of the graft products and the cleaved polyacrylamide chains revealed that the amphiphilic macroRAFTs were involved in the graft reaction through effective chain transfer, thereby increasing the weight ratio of polyacrylamide on the modified CNCs.

Free Radical Polymerization Behavior of the Vinyl Monomers from Plant Oil Triglycerides

A one-step method of plant oil direct transesterification was used to synthesize new vinyl monomers from sunflower (SFM), linseed (LSM), soybean (SBM), and olive (OVM) oils. The degree of unsaturation in plant oil fatty acids was used as a criterion to compare the free radical polymerization behavior of new monomers. The number-average molecular weight of plant oil-based homopolymers synthesized in toluene in the presence of AIBN at 75 °C varies at 11 000–25 000 and decreases as follows: poly(OVM) > poly(SFM) > poly(SBM) > poly(LSM), corresponding to increasing degree of unsaturation in the monomers. Rate of polymerization depends noticeably on the degree of unsaturation in monomers. Due to the allylic termination, chain propagation coexists with effective chain transfer during polymerization. The obtained values of CM (ratio of chain transfer and propagation rate constants) depends on monomer structure as follows: CM(LSM) > CM(SBM) > CM(SFM) > CM(OVM). 1H NMR spectroscopy shows that the fraction of the r...