Polymerization Of Polar Vinyl Monomers Research Articles

Lewis Pair RAFT Polymerization of Methacrylates on-Water: Evidence of Radical Propagation Mechanism

Abstract The Lewis pair (LP) composed of PPh3 and Cu(OTf)2 on-water is a newly emerging catalytic system for polymerization of polar vinyl monomers. Herein, we report the additive effect of the reversible addition–fragmentation chain transfer (RAFT) agents on the polymerization of six methacrylate monomers with various hydrophilicities. The polymerization control by the RAFT agents proved that this LP polymerization involves a radical propagating mechanism.

Mechanistic Insight into the Stereoselective Cationic Polymerization of Vinyl Ethers.

The control of the tacticity of synthetic polymers enables the realization of emergent physical properties from readily available starting materials. While stereodefined polymers derived from nonpolar vinyl monomers can be efficiently prepared using early transition metal catalysts, general methods for the stereoselective polymerization of polar vinyl monomers remain underdeveloped. We recently demonstrated asymmetric ion pairing catalysis as an effective approach to achieve stereoselective cationic polymerization of vinyl ethers. Herein, we provide a deeper understanding of stereoselective ion-pairing polymerization through comprehensive experimental and computational studies. These findings demonstrate the importance of ligand deceleration effects for the identification of reaction conditions that enhance stereoselectivity, which was supported by computational studies that identified the solution-state catalyst structure. An evaluation of monomer substrates with systematic variations in steric parameters and functional group identities established key structure-reactivity relationships for stereoselective homo- and copolymerization. Expansion of the monomer scope to include enantioenriched vinyl ethers enabled the preparation of an isotactic poly(vinyl ether) with the highest stereoselectivity (95.1% ± 0.1 meso diads) reported to date, which occurred when monomer and catalyst stereochemistry were fully matched under a triple diastereocontrol model. The more complete understanding of stereoselective cationic polymerization reported herein offers a foundation for the design of improved catalytic systems and for the translation of isotactic poly(vinyl ether)s to applied areas.

Fast and Regioselective Polymerization of para-Alkoxystyrene by Palladium Catalysts for Precision Production of High-Molecular-Weight Polystyrene Derivatives

Polymerization of polar vinyl monomers by a coordination–insertion approach is a topic of fundamental importance to the field of polymer synthesis. Herein, we initially report the coordination–inse...

Highly Syndioselective Coordination (Co)Polymerization of ortho-Fluorostyrene

Coordination (co)polymerization of polar vinyl monomers is a theoretical challenge of polymer science, of which monomers bearing a polar group close to the reaction double bond are rather difficult...

Self-Activated Coordination Polymerization of Alkoxystyrenes by a Yttrium Precursor: Stereocontrol and Mechanism

Coordination–insertion polymerization of polar vinyl monomers has always been a challenging subject since the Lewis basic polar groups are usually poisonous to the Lewis acidic metal centers of the catalysts. In this paper, we report the coordination polymerization of the unmasked polar alkoxystyrenes (AOS), including o-methoxystyrene (oMOS), o-ethoxystyrene (oEOS), o-n-propoxystyrene (oPOS), o-n-butoxystyrene (oBuOS), o-benzyloxystyrene (oBnOS), and 5-phenyl-2-methoxystyrene (Ph-MOS), by using the cationic quinolyl anilido yttrium alkyl species that was inert to styrene polymerization. In addition, the styrenic monomer bearing two polar groups, 4-fluoro-2-methoxystyrene (FMOS), was also polymerized since the presence of the additional polar fluorine group did not block the interaction between the ortho-oxygen and yttrium center. In contrast, the o-(tert-butyldimethyl)silyloxystyrene (oSiOS), where the ortho-oxygen atom was prevented from coordinating to the yttrium center by the sterically bulky −SiMe2tB...

Polar-Group Activated Isospecific Coordination Polymerization of ortho-Methoxystyrene: Effects of Central Metals and Ligands.

Stereoselective polymerization of polar vinyl monomers has been a long-standing challenge because the employed transition-metal catalysts are easily poisoned by polar groups of monomers. In this contribution, a series of β-diketiminato rare-earth metal complexes 1-5 (L1-5 Ln(CH2 SiMe3 )2 (THF)n , Ln=Gd-Lu, Y, and Sc) were successfully synthesized. In combination with AliBu3 and [Ph3 C][B(C6 F5 )4 ], complexes 1 c(Tb)-1 g(Tm) exhibited high activities and excellent isoselectivities for the polymerization of ortho-methoxystyrene (oMOS), in which, the polar methoxy group of oMOS did not poison but activated the polymerization through σ-π chelation to the active species together with the vinyl group. Moreover, the large Gd-attached precursor 1 b showed a higher activity, albeit with a slightly decreased isoselectivity. The small Sc-attached precursor 1 i was completely inert. Meanwhile, the spatial steric arrangement and the coordination mode of the β-diketiminato ligand could clearly affect and even block oMOS polymerization. This work sheds new light on the coordination polymerization of polar monomers.

Cationic Zirconocene‐Mediated Catalytic H‐Shuttling Polymerization of Polar Vinyl Monomers: Scopes of Catalyst, Chain‐Transfer Agent, and Monomer

SummaryThis study investigates the characteristics of the recently developed catalytic H‐shuttling polymerization (HSP) of polar vinyl monomers mediated by cationic zirconocenium catalysts, through examining the scopes of chain transfer agent, catalyst, and monomer. Amongst the three classes of chain transfer agents (metal hydrides, metal aryl/alkyls, organics) investigated for the MMA polymerization catalyzed by Cs‐ligated catalyst 1, the Lewis acid B(C6F5)3, metal hydrides MH (M = K, Na, Li) and the organic PhNMe2 promote efficient catalytic polymerization, while metal alkyls such as Et3Al and Et2Zn serve only as the scavenger and/or monomer activator and thus do not promote chain transfer. In the presence of 5 equivalents of KH, both Cs‐ligated catalyst 1 and achiral C2v‐ligated catalyst 3 promote catalytic MMA polymerization through effective chain transfer, whereas C2‐ligated catalyst 2 shows no chain transfer. Of several other conjugated polar vinyl monomers investigated, including acrylamides and α‐methylene‐γ‐butyrolactones, only N,N‐diphenylacrylamide (DPAA) exhibits catalytic polymerization behavior. Thus, in the presence of enantiopure pre‐catalyst (S,S)‐4 and excess B(C6F5)3, DPAA is polymerized catalytically and asymmetrically to optically active poly(DPAA) with a narrow MWD of 1.02.

Synthesis of Pyridine- and 2-Oxazoline-Functionalized Vinyl Polymers by Alane-Based Frustrated Lewis Pairs

Reported herein is the first example of polymerization of polar vinyl monomers bearing the C=C–C=N functionality by Frustrated Lewis pairs (FLPs). In particular, FLPs based on Al(C6F5)3 and N-heterocyclic carbenes rapidly convert 2-vinyl pyridine and 2-isopropenyl-2-oxazoline into medium to high molecular weight, N-functionalized vinyl polymers. Activated monomer-alane adduct 1 and initiated zwitterionic intermediate 2 have been isolated and structurally characterized, providing strong evidence for the proposed bimolecular, activated monomer polymerization mechanism.

High‐Speed Living Polymerization of Polar Vinyl Monomers by Self‐Healing Silylium Catalysts

This contribution describes the development and demonstration of the ambient-temperature, high-speed living polymerization of polar vinyl monomers (M) with a low silylium catalyst loading (≤ 0.05 mol % relative to M). The catalyst is generated in situ by protonation of a trialkylsilyl ketene acetal ((R)SKA) initiator (I) with a strong Brønsted acid. The living character of the polymerization system has been demonstrated by several key lines of evidence, including the observed linear growth of the chain length as a function of monomer conversion at a given [M]/[I] ratio, near-precise polymer number-average molecular weight (M(n), controlled by the [M]/[I] ratio) with narrow molecular weight distributions (MWD), absence of an induction period and chain-termination reactions (as revealed by kinetics), readily achievable chain extension, and the successful synthesis of well-defined block copolymers. Fundamental steps of activation, initiation, propagation, and catalyst "self-repair" involved in this living polymerization system have been elucidated, chiefly featuring a propagation "catalysis" cycle consisting of a rate-limiting C--C bond formation step and fast release of the silylium catalyst to the incoming monomer. Effects of acid activator, catalyst and monomer structure, and reaction temperature on polymerization characteristics have also been examined. Among the three strong acids incorporating a weakly coordinating borate or a chiral disulfonimide anion, the oxonium acid [H(Et(2)O)(2)](+)[B(C(6)F(5))(4)](-) is the most effective activator, which spontaneously delivers the most active R(3)Si(+), reaching a high catalyst turn-over frequency (TOF) of 6.0×10(3) h(-1) for methyl methacrylate polymerization by Me(3)Si(+) or an exceptionally high TOF of 2.4×10(5) h(-1) for n-butyl acrylate polymerization by iBu(3)Si(+), in addition to its high (>90 %) to quantitative efficiencies and a high degree of control over M(n) and MWD (1.07-1.12). An intriguing catalyst "self-repair" feature has also been demonstrated for the current living polymerization system.

Effect of Polymer Tacticity on the Performance of Poly(N,N-dialkylacrylamide)s as Kinetic Hydrate Inhibitors

Kinetic hydrate inhibitors (KHIs) are water-soluble polymers designed to delay gas hydrate formation in upstream gas and oilfield operations. Most classes of KHI polymers that have been discovered are vinylic polymers made by radical polymerization of vinyl monomers, giving atactic polymer structures. Atactic polymers may not be optimal for KHI performance. However, metallocene-mediated stereospecific coordination polymerization of polar vinyl monomers to stereoregular polymers can be carried out to give syndiotactic and isotactic polymers of certain monomers with molecular-weight control. This was carried out for several poly(N,N-dialkylacrylamide)s. We have carried out structure II gas hydrate KHI ramping tests in high-pressure autoclaves on the poly(N,N-dialkylacrylamide)s. Clearly, polymer tacticity does affect the performance of this class of polymers. Isotactic polyacryloylpyrrolidine (PAP) gave shorter induction times than atactic PAP. Assuming that the primary nucleation inhibition mechanism is perturbation of the water structure, these observations can be rationalized in that the side groups in isotactic PAP are more crowded together than in atactic PAP, which results in less water perturbation for the isotactic PAP and, therefore, less effect on disrupting hydrate nucleation. However, isotactic PAP gave longer periods of slow hydrate crystal growth than atactic PAP. This could be rationalized by considering that the isotactic PAP has a higher concentration of side groups along one side of the polyvinyl backbone than atactic PAP, which may give it better adsorption onto the growing hydrate crystal surfaces. All three different tacticity poly(N,N-dimethylacrylamide)s (PDMAA)s were poorer nucleation inhibitors than the PAPs. Syndiotactic PDMAA gave, on average, longer induction times than isotactic or atactic PDMAA. This can be rationalized by the fact that the syndiotactic polymer has alternating up and down dimethylamide side groups, giving the best surface/volume ratio for this polymer tacticity and, therefore, the best perturbation of the water structure. Again, this is assuming that is the dominant nucleation inhibition mechanism. The isotactic PDMAA clearly gave shorter slow crystal growth periods than the syndiotactic polymer, while the atactic polymer gave the longest times. For the isotactic polymer, this is the opposite of the results that we obtained with the PAPs, in which the isotactic polymer gave the longest hydrate slow growth periods.

ChemInform Abstract: Coordination Polymerization of Polar Vinyl Monomers by Single‐Site Metal Catalysts

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Catalyst-Site-Controlled Coordination Polymerization of Polar Vinyl Monomers to Highly Syndiotactic Polymers

This contribution reports a combined synthetic, kinetic, mechanistic, and theoretical/computational study of the recently discovered catalyst-site-controlled coordination polymerization of polar vinyl monomers [such as methyl methacrylate (MMA) and N,N-dimethylacrylamide (DMAA)] into highly syndiotactic polymers. Among the 12 C(s)-ligated ansa-cyclopentadienyl (Cp)-R(2)E(C,Si)-fluorenyl (Flu) group 4 metallocene catalyst systems examined-which varied in metal center, anion structure, bridging atom and substituents, and ligand substitution pattern-cationic ansa-metallocene ester enolate catalyst 6(+)[B(C(6)F(5))(4)](-), derived from the activation of the precatalyst [Ph(2)C(Cp)(2,7-(t)Bu(2)-Flu)]Zr[OC(O(i)Pr)=CMe(2)](2) with [Ph(3)C][B(C(6)F(5))(4)], stood out as the best catalyst in all aspects of the MMA polymerization at room temperature, including the highest activity (1554 h(-1) TOF), efficiency (98% I*), syndiotacticity (94% rr), and control (predicted number-average molecular weight and 1.14 molecular weight distribution). Kinetic and mechanistic results are consistent with a catalyst-site-controlled, monometallic coordination-addition mechanism, involving fast intramolecular addition within the catalyst-monomer complex leading to the resting eight-membered ester enolate chelate, followed by the rate-limiting ring-opening of the chelate to regenerate the active species. This work has also uncovered several unique features of this polymerization system that are in marked contrast to the propylene polymerization by analogous C(s)-ligated cationic alkyl catalysts: a constant syndiotacticity of PMMA produced over a wide polymerization temperature range (i.e., from 0 degrees C, 94% rr to 25 degrees C, 94% rr to 50 degrees C, 93% rr); insensitivity of its high activity, degree of control, and stereoselectivity to solvent polarity and structure of weakly coordinating anions; and deviation from a pure site-control mechanism at high [MMA]/[catalyst] ratios. Computational results provide theoretical support for the proposed monomer-assisted, catalyst-site epimerization, after an enantiofacial mistake, to a thermodynamically more stable resting state, which accounts for the observed higher than expected [mr] contents based on a pure site-controlled mechanism. DFT calculations rationalize why the Ph(2)C< bridged catalyst 6 exhibits higher stereoselectivity than other catalysts with the Me(2)C< or Me(2)Si< bridge: the bridge rigidity pushes the eta(3)-bound Flu ligand closer to the growing chain and the monomer, thereby increasing DeltaE(stereo) between the competing transition states for the addition of a monomer molecule to the opposite (correct and wrong) enantiofaces of the enolate growing chain. The relative polymerization activity of this catalyst series is shown to correlate with the relative energetics of the back-biting of the penultimate unit and ion-pair formation.

Coordination Polymerization of Polar Vinyl Monomers by Single-Site Metal Catalysts

Coordination Polymerization of Polar Vinyl Monomers by Single-Site Metal Catalysts

Transformation of polymerization of polar vinyl monomers by discrete and hybrid metal catalysts

Chiral metallocene cations, discrete main group anions, dually active ion pairs and nucleophile/electrophile pairs have been utilized to transform the polymerization of polar vinyl monomers from one type to another. These discrete or hybrid catalysts have enabled the development of five types of such polymerizations, including stereospecific and living coordination polymerization, asymmetric coordination polymerization, single-site anionic polymerization, bimolecular polymer-transfer polymerization, and diastereospecific ion-pairing polymerization.

Structure and Hydrodynamical Properties of Heteroarm Star‐Shaped C60 Fullerene‐containing Polymers

Multifunctional initiator with six active centers for anionic polymerization of polar vinyl monomers based on hexaadduct of polystyryllithium with C60 fullerene was obtained. Star‐shaped polymers with fullerene C60 as branching center and polystyrene and poly‐(2‐vinylpyridine) arms were synthesized using anionic polymerization techniques; the conditions of modification of macroinitiator (hexaadduct of polystyryllithium with fullerene C60) were varied. Translational diffusion and viscometry in benzene solutions were used to determine molecular masses and functionality (f) of heteroarm molecules. It was shown that during the formation of heteroarm macromolecules, the determining stage is the process of modification of hexaadduct with 1.1‐diphenylethylene. If the synthesis is performed under the conditions when the elimination of “living” polystyrene chains from hexaadduct‐precursor is possible, heteroarm polymers have, on average, four arms of polystyrene and four arms of poly‐(2‐vinylpyridine). When the synthesis is performed under optimized conditions in nonpolar medium, star‐shaped molecules with total number of arms close to 12 were obtained.

Metallocene-Mediated Asymmetric Coordination Polymerization of Polar Vinyl Monomers to Optically Active, Stereoregular Polymers

Asymmetric coordination polymerization of 13 acrylamide and methacrylate monomers of four different classes has been investigated using chiral ansa-zirconocenium ester enolate catalyst (S,S)-(EBI)Zr+(THF)[OC(OiPr)═CMe2][MeB(C6F5)3]− [(S,S)-1), EBI = C2H4(η5-Ind)2] and its enantiomer (R,R)-1. This polymerization system is built upon four advanced features of polymerization including living, stereospecific, coordination, and asymmetric core elements, thus efficiently converting prochiral N,N-diaryl acrylamides at ambient temperature to optically active, stereoregular polymers with solution-stable, single-handed helical secondary structures. Kinetic studies show that the polymerization of N,N-diaryl acrylamides by 1 proceeds via a monometallic, coordination-conjugate addition mechanism. Investigation into polymer chain-length effects on optical activity of the chiral polymers reveals two opposite trends, depending on the polymer secondary structure (i.e., helical vs random coil conformation). Examination of the polymerization scope shows that the formation of optically active poly(acrylamide)s due to solution-stable helical conformations with an excess of one-handed helicity is dictated by the sterics and rigidity of the monomer repeat units; while diaryl acrylamides can readily achieve such conformations, unsymmetrically substituted diaryl acrylamides give the chiral polymers with much higher optical activity than the symmetrically substituted ones. It is also possible for N,N-dialkyl acrylamides to lead to chiral helical polymers. Extensive asymmetric block copolymerization studies of MMA with acrylamides and other methacrylates have also been carried out, producing optically active, high-molecular-weight methacrylate-b-acrylamide stereoblock copolymers in which the acrylamide block can be either helical or nonhelical; in sharp contrast, all high-molecular-weight methacrylate-b-methacrylate di- or triblock copolymers produced by the enantiomeric catalysts 1 are optically inactive.

Intermediacy of Radicals in Rearrangement and Decomposition of Metal−Alkyl Species: Relevance to Metal-Mediated Polymerization of Polar Vinyl Monomers

The neutral compound [2,3-bis(2,6-diisopropylphenylimino)butane]Pd(CH2CH2CH2CO2Me)(X) (X = Cl, Br) undergoes “reverse” chain walking to form [2,3-bis(2,6-diisopropylphenylimino)butane]Pd(CH(CO2Me)C...

Diametrically opposite trends in alkene insertion in late and early transition metal compounds: relevance to transition-metal-catalyzed polymerization of polar vinyl monomers.

Variable-temperature 1H NMR studies of the reaction of cationic (alpha-diimine)Pd-alkyl complexes with alkenes are presented. The studies reveal that vinyl bromide coordinates to the Pd(II)-Me complex followed by migratory insertion and beta-bromo elimination, to generate free propene. Propene further reacts to give beta-agostic Pd(II)-tert-butyl species. From the reactions with vinyl bromide, stable chloro-bridged dicationic Pd complex was isolated and characterized. For a series of alkenes (CH2=CHX), the rate for migratory insertion decreases as follows: X = CO2Me > Br > H > Me.

Polymerization of Polar Vinyl Monomers by Cobalt Complex-Alkylaluminum Compound

Polymerization of Polar Vinyl Monomers by Cobalt Complex-Alkylaluminum Compound

Polymerization of Polar Vinyl Monomers with Novel Cobalt-based Catalyst

Abstract Cobalt-based complex CH3C(CH2PPh2)3Co(BH4) (1) polymerized polar vinyl monomers like acrylonitrile (AN) and methyl methacrylate (MMA) without any cocatalysts. The molecular weight of the poly(AN) was fairly high at around 500 × 103. It was concluded that the polymerizations did not proceed with radical polymerization mechanism based on the copolymerization results with styrene. The obtained poly(AN) had an atactic structure.