Sequential Monomer Addition Research Articles

Conjugated Copolymers of Poly(arylenevinylene)s: Synthesis by Ring-Opening Metathesis Polymerization, Film Morphology, and Resonant Luminescence from Microspheres

A series of copolymers of poly(arylenevinylene)s have been prepared by ring-opening metathesis polymerization (ROMP) of cyclic conjugated monomers composed of cyclopentadithiophene, bis(thienyl)benzothiadiazole, or bithiophene using a second-generation Grubbs catalyst and the sequential monomer addition technique. The spectroscopic, electrochemical, and morphological properties of these polymers are tailored by changing the chemical structures and fractions of the monomers. The polymers self-assemble to form microspheres (diameter: 2–5 μm), which act as whispering-gallery-mode optical resonators.

Hierarchical Fractal Assemblies from Poly(ethylene oxide- b-lysine- b-leucine).

Poly(ethylene oxide43- b-lysine62- b-leucine72) (wherein subscripts denote the degree of polymerization) was synthesized via ring-opening polymerization of N-carboxyanhydrides using an amine-terminated poly(ethylene oxide) macroinitiator, with polypeptide blocks produced by sequential monomer addition. Infrared and circular dichroism spectroscopy indicated that the peptide blocks in this polymer formed α-helices in the solid and solution states, respectively. In the aqueous solution, this polymer self-assembled into spherical micelles with a hydrodynamic radius of approximately 90 nm at concentrations between 0.05 and 0.20% w/w and pH values between 2 and 6.5. Upon preparation of transmission electron microscopy (TEM) grids, the micelles at pH 2 underwent hierarchical assembly to produce fractal assemblies, whereas small clusters were observed for micellar solutions at pH 6.5. Cryogenic-TEM of solutions showed spherical micelles, and dynamic light scattering showed no large (∼1 μm) aggregates in the solution, which suggests that fractal formation was a result of the drying process, and that fractals were not present in the solution. This system provides a facile route to nanostructured surfaces, which can be used for applications such as modulating cell adhesion or promoting the growth of neurons.

A strategy combining quantitative reactions and reversible-covalent chemistry for sequential synthesis of sequence-controlled polymers with different sequences

A new strategy combing quantitative reactions and reversible-covalent chemistry is proposed for sequential synthesis of a series of sequence-controlled polymers with different sequences. Using a Michael addition reaction between acrylate and thiol, an aminolysis reaction of five-membered cyclic dithiocarbonate and a thiol substitution reaction of bromomaleimide and thiol, AB-, AB'C- and AB'CD-sequenced molecules are synthesized via AB, AB'C and AB'CD sequential monomer additions, respectively. These three molecules all have furan-protected maleimido group at one end, and the other end of AB-, AB'C- and AB'CD-sequenced molecules is amine, thiol and anthracene groups, respectively. Due to the fact that the furan-protected maleimido group can be efficiently transformed to maleimide group at high temperature via retro Diels-Alder reaction, AB-, AB'C- and AB'CD-sequenced molecules polymerize into sequence-controlled polymers with corresponding sequences at 120 °C. Through this strategy, the synthesis of molecular modules does not require separation and purification, and sequence-controlled polymers with specific sequence can be synthesized in a one-pot process via adding different monomers and adjusting reaction condition.

Syntheses and properties of ABA, CBA, and CBC triblock copolymers based thermoplastic elastomers with glassy (A), elastomeric (B), and crystalline (C) blocks

In this contribution, we describe the syntheses, characterization, and properties of ABA, CBA and CBC triblock copolymers with glassy (A), elastomeric (B), and crystalline (C) blocks. These three hard-soft-hard triblock copolymers were prepared via living ring-opening metathesis copolymerization by use of Grubbs third generation catalyst through one-pot sequential monomer addition and subsequent hydrogenation. These hard-soft-hard triblock copolymers based thermoplastic elastomers have been analyzed by proton NMR, differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), IR, and transmission electron microscopy (TEM). The mechanical properties of these triblock copolymers were also measured by monotonic and step cyclic tensile test. Compared with the ABA triblock copolymer, the CBC triblock copolymer containing highly crystalline hard end-blocks shows enhanced tensile strength and the best elastic recovery of 90.8%. The hybrid CBA triblock copolymer displays much improved elongation, which is almost twice as long as the other two TPEs, and excellent elastic recovery of 87.0%.

Controlled living anionic polymerization of cyanoacrylates by frustrated Lewis pair based initiators.

A hydrogenated frustrated Lewis pair ([TMPH+][HB(C6F5)3 -]) promotes controlled living ionic polymerization of cyanoacrylates. Controlled growth of various homopolymeric CAs through sequential monomer addition has been achieved, in addition to CA block copolymers with controlled block sequences for the first time in the long history of these materials.

Halide-free neodymium phosphate based catalyst for highly cis-1,4 selective polymerization of dienes.

Neodymium-based Ziegler–Natta type catalytic systems are known to produce polydienes with high cis-1,4 content. It is generally believed that in Ziegler–Natta catalytic systems, a halide or pseudohalide, whether in the catalyst itself or a separate source, is required for the success of the polymerization. In this work, we have synthesized an unusual halide-free neodymium diethyl phosphate catalyst for diene polymerization. This neodymium complex combined with triisobutylaluminum (TIBA), formed a binary catalytic system and was used to polymerize β-myrcene. The catalytic system displays high stereospecificity and produces poly(β-myrcene) with 96% cis-1,4 content and a relatively narrow molecular weight distribution (Mw/Mn = 1.80). Also, kinetic studies indicated the catalytic system gives a pseudo-living polymerization. The block copolymer poly(β-myrcene)-b-poly(isoprene) was successfully synthesized by sequential monomer addition, further demonstrating the pseudo-living nature of polymerization with the neodymium diethyl phosphate catalyst.

Synthesis and characterization of isotactic poly(p-hydroxystyrene)- block-1,4-trans-polybutadiene by sequential monomer addition using titanium complex with an [OSSO]-type Bis(phenolate) ligand

Herein, we demonstrated the synthesis and characterization of a well-defined diblock copolymer consisting of isotactic poly(p-hydroxystyrene) (iP(p-HOS)) and 1,4-trans-polybutadiene (1,4-trans-PBD), iP(p-HOS)-b-1, 4-trans-PBD, by the combination of sequential monomer addition and deprotection. Isospecific living polymerization of p-tert- butyldimethylsilyloxystyrene and living trans-1,4-polymerization of 1,3-butadiene were catalyzed by 1, 4-dithiabutandiyl-2, 2ʹ-bis(6-cumenyl-4-methylphenoxy) titanium dichloride (complex 1) activated by methylaluminoxane (MAO) at room temperature to provide highly stereospecific isotactic poly(p-tert-butyldimethylsilyloxystyrene) (iP(p-TBDMSOS)) and 1,4-trans-polybutadiene (1,4-trans-PBD) with narrow molecular weight distribution. Furthermore, the iP(p-TBDMSOS)-b-1, 4-trans-PBD was prepared via sequential monomer addition in the presence of complex 1 and MAO. The deprotection of the iP(p-TBDMSOS) block was promoted by concentrated hydrochloric acid to produce iP(p-HOS)-b-1, 4-trans-PBD. In addition, the resultant diblock copolymer and intermediate polymers were characterized by gel permeation chromatography, nuclear magnetic resonance and differential scanning calorimeter.

Confinement driven crystallization of ABA crystalline-soft-crystalline block copolymers synthesized via RAFT mediated miniemulsion polymerization

Waterborne ABA block copolymers of stearyl acrylate (SA) and 2-ethylhexyl acrylate (2EHA) containing crystalline A block and soft middle B block, were synthesized via two-step reversible addition fragmentation chain transfer (RAFT) polymerization, using S,S-dibenzyl trithiocarbonate (DBTTC) bifunctional RAFT agent. First, miniemulsion polymerization was used for the synthesis of the crystalline domains. Then in the second step 2EHA was fed to the system as a pre-emulsion and soft domains were formed. For the sake of simplicity sequential monomer addition was performed without any removal of the unreacted monomer in the first step. Thermal properties of the obtained block copolymers were investigated by means of DSC, which revealed reduced crystallinity by the formation of the block copolymers compared to the crystallinity of the polySA initial block. Morphological properties were studied by means of microscopic techniques after film formation at different conditions. Lamellar phase separation induced by confined crystallization in the particles was shown in the films dried at room temperature. Particle coalescence and higher ordering of the lamellar structure was obtained upon film annealing above the melting temperature of the crystalline domains and the structure obtained was comparable with the one of films casted from THF solution, indicating that equilibrium morphology was already obtained by annealing. Mechanical properties studied using DMTA revealed two transition temperatures and reduced storage modulus as the length of the middle block and casting temperature of the film was increased.

Ultrafast phosphazene‐promoted controlled anionic polymerization of styrenic monomers

ABSTRACTThe anionic polymerization of styrenic monomers with phosphazene bases as promoters, utilizing “seeding” technique in a nonpolar solvent and at room temperature was studied. In all experiments, the phosphazene base (t‐BuP4, t‐BuP2, and t‐BuP1) was added in an equimolar amount to the organolithium initiator after the formation of oligomers (2 min) by conventional anionic polymerization. When t‐BuP4 was used, the polymerization of styrene and 4‐methylstyrene was extremely fast (100 % conversion within 5 min) and the final homopolymers exhibited narrow molecular weight distribution and controlled molecular characteristics. Likewise, when weaker bases were employed, the polymerization was also controlled but showing slower reaction rate. To examine the “livingness” of this system, block copolymers were synthesized by sequential monomer addition. Further studies were conducted in order to extend this novel method to the anionic polymerization of dienes. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 456–464

Fabrication of well‐defined shape memory graft polymers derived from biomass: An insight into the effect of side chain architecture on shape memory properties

ABSTRACTFully sustainable shape memory polymers (SMPs) derived from ethyl cellulose (EC, derived from cellulose), tetrahydrofurfuryl methacrylate (THFMA, derived from furfural), and lauryl methacrylate (LMA, derived from fatty acids) were prepared via “grafting from” atom transfer radical polymer (ATRP). The “grafting from” ATRP strategy allows to fabricate SMPs with EC as a backbone, and LMA and THFMA copolymer as a side chain. By utilizing the one‐pot and sequential monomer addition approach, two types of SMPs with random/semi‐block side chain architectures were obtained, respectively. Random/semi‐block side chain architecture of SMPs was confirmed by DSC, DMA, SAXS, and TEM. The presence of microphase separation in the SMPs with semi‐block side chain architecture provided two distinct thermal transitions, which was needed for triple‐shape memory behavior. Shape memory study showed that SMPs with semi‐block side chain architecture exhibited excellent triple‐shape memory property, and also had higher shape recovery speed and shape recovery ratio than those with random side chain architecture. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1711–1720

Block-Stereoblock Copolymers of Poly(ϵ-Caprolactone) and Poly(Lactic Acid).

A magnesium complex of the type {ONNN}Mg-HMDS wherein {ONNN} is a sequential tetradentate monoanionic ligand is introduced. In the presence of an alcohol initiator this complex catalyzes the living and immortal homopolymerization of the lactide enantiomers and ϵ-caprolactone at room-temperature with exceptionally high activities, as well as the precise block copolymerization of these monomers in a one-pot synthesis by sequential monomer addition. Copolymers of unprecedented microstructures such as the PCL-b-PLLA-b-PDLA and PDLA-b-PLLA-b-PCL-b-PLLA-b-PDLA block-stereoblock microstructures that feature unique thermal properties are readily accessed.

Block–Stereoblock Copolymers of Poly(ϵ‐Caprolactone) and Poly(Lactic Acid)

AbstractA magnesium complex of the type {ONNN}Mg‐HMDS wherein {ONNN} is a sequential tetradentate monoanionic ligand is introduced. In the presence of an alcohol initiator this complex catalyzes the living and immortal homopolymerization of the lactide enantiomers and ϵ‐caprolactone at room‐temperature with exceptionally high activities, as well as the precise block copolymerization of these monomers in a one‐pot synthesis by sequential monomer addition. Copolymers of unprecedented microstructures such as the PCL‐b‐PLLA‐b‐PDLA and PDLA‐b‐PLLA‐b‐PCL‐b‐PLLA‐b‐PDLA block–stereoblock microstructures that feature unique thermal properties are readily accessed.

One-Step Block Copolymer Synthesis versus Sequential Monomer Addition: A Fundamental Study Reveals That One Methyl Group Makes a Difference

Block copolymers of polyisoprene and polystyrene are key materials for polymer nanostructures as well as for several commercially established thermoplastic elastomers. In a combined experimental and kinetic Monte Carlo simulation study, the direct (i.e., statistical) living anionic copolymerization of a mixture of isoprene (I) and 4-methylstyrene (4MS) in nonpolar media was investigated on a fundamental level. In situ 1H NMR spectroscopy enabled to directly monitor gradient formation during the copolymerization and to determine the nature of the gradient. In addition, a precise comparison with the established copolymerization of isoprene and styrene (I/S) was possible. Statistical copolymerization in both systems leads to tapered block copolymers due to an extremely slow crossover from isoprene to the styrenic monomer. For the system I/4MS the determination of the reactivity ratios shows highly disparate values with rI = 25.4 and r4MS = 0.007, resulting in a steep gradient of the comonomer composition. Th...

Neodymium‐based catalysts bearing phosphate ligands for ring‐opening polymerization of ɛ‐caprolactone

ABSTRACTNeodymium‐based catalysts coordinated with phosphate ligands (NdCl3·3L), where L = triethyl phosphate (TEP) or tris(2‐ethylhexyl) phosphate (TEHP), were synthesized. The ring‐opening polymerizations (ROP) of ɛ‐caprolactone (ɛ‐CL) with these catalysts in the presence of benzyl alcohol initiator were performed, yielding polymers with well‐defined molecular weights and relatively narrow polydispersity index (PDI = 1.22–1.65). In situ NMR analysis of the reaction between NdCl3·3TEP and benzyl alcohol indicated that ROP proceeds through a coordination‐insertion mechanism. The end groups of the resultant polymers were determined using MALDI‐ToF mass spectrometry and NMR spectroscopy. The quasi‐living nature of this catalytic system was demonstrated by kinetic studies and the successful synthesis of the block copolymer poly(ɛ‐caprolactone)‐block‐poly(l‐lactide) by sequential monomer addition. Kinetic studies revealed that the catalyst with the bulkier TEHP ligand increased the rate of ROP of ɛ‐CL as compared to the TEP ligand. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1289–1296

Tandem Functionalization in a Highly Branched Polymer with Layered Structure.

A hyperbranched polymer with multilayer structure was developed to demonstrate the possibility of highly efficient tandem functionalization reactions at different domains within one nanostructured platform. The polymer scaffold was constructed by chain-growth copper-catalyzed azide-alkyne cycloaddition polymerization of three functional monomers with sequential monomer addition in one pot. Subsequent reactions with different monomer units resulted in efficient functionalization of each segment with construction of a highly sophisticated polymer structure by a robust procedure. As a proof of concept, the ability of this polymer structure to quantitatively load six species of guest molecules through three different types of conjugation reactions was demonstrated.

Palladium Nanoparticles within Core-Cross-Linked Polymer Gels for Suzuki Coupling Reactions: from Monomers to Ready-to-Use Catalysts in Two-Steps

This study shows that polymer nanogels (well-defined cross-linked nanoparticles behaving as highly hydrated unimolecular objects) are suitable capping agents for palladium nanoparticle catalyst systems. In spite of the structurally complex nature of the catalysts, it was possible to go from acrylate-based monomers to ready-to-use and recyclable catalysts in only two-steps. First, nanogels were synthesized by activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) method with sequential addition of monomers. Then, in the second step, palladium acetate was reduced to obtain ready-to-use catalysts (ca. 25 nm nanogel structures containing ca. 7 nm palladium nanoparticles). The catalytic activity was confirmed in p -nitrophenol (Nip) reduction and Suzuki cross-coupling reactions. The observed rate constants (kobs) for Nip reduction were in the range of 0.8-10.0 × 10-2 s-1 depending on the polymeric capping agent structure, with the highest value being found for nanogel-based systems. These composite catalysts also mediated the cross-coupling Suzuki reaction providing the expected products in quantitative yields under relatively mild conditions after 4 h at 50 oC. The simplicity of catalyst preparation protocol that ensures excellent activity and the low concentration of polymer applied during the synthesis are a step forward in terms of environmental and economic prospects.

Regioselective living polymerization of allylcyclohexane and precise synthesis of hydrocarbon block copolymers with cyclic units

Regioselective living polymerization of allylcyclohexane was catalyzed by a bulky α-diimine nickel catalyst. Well-defined hydrocarbon block copolymers with cyclic units were constructed by sequential monomer addition.

Synthesis and self-assembly of a novel amphiphilic diblock copolymer consisting of isotactic polystyrene and 1,4-trans-polybutadiene-graft-poly(ethylene oxide).

Herein, a novel amphiphilic diblock copolymer consisting of isotactic polystyrene (iPS) and 1,4-trans-polybutadiene-graft-poly(ethylene oxide) (1,4-trans-PBD-g-PEO), iPS-b-(1,4-trans-PBD-g-PEO), was synthesized by the combination of living coordination copolymerization and graft copolymerization. iPS-b-1,4-trans-PBD was firstly synthesized via sequential monomer addition in the presence of 1,4-dithiabutandiyl-2,2′-bis(6-cumenyl-4-methylphenoxy) titanium dichloride (complex 1) activated by triisobutyl aluminum modified methylaluminoxane (MMAO). Moreover, hydroboration of double bonds in the 1,4-trans-PBD blocks were performed with 9-borabicyclo[3.3.1]nonane (9-BBN) and subsequent oxidation by NaOH/H2O2 to form hydroxyls. Consequently, PEO was grafted into the hydroxylated 1,4-trans-PBD block in terms of ring-opening polymerization of ethylene oxide with potassium/naphthalide as initiatior. We also described solvent-evaporation-induced self-assembly of iPS-b-1,4-trans-PBD in n-dodecane and iPS-b-1,4-trans-PBD-g-PEO in aqueous solution, which were selective solvent for 1,4-trans-PBD and for 1,4-trans-PBD-g-PEO blocks, respectively. In these cases, tetrahydrofuran (THF) was used as good and volatile solvent. These resultant iPS-containing diblock copolymers could self-assemble into spherical nano-micelles with an iPS core as amorphous agglomeration or a very low degree of crystallinity resulting from slow crystallization rate and nanoconfinement. In addition, after isothermal crystallization of iPS in the micellar cores self-assembled in n-dodecane at 120 °C for 3 hours, the micellar morphology changed from sphere-like to platelet-like. It was believed that isothermal crystallization of iPS induced the deformation of the micelles.

Quaternized poly (poly(ethylene glycol)methyl ether methacrylate)-b-poly (2-(dimethylamino)ethyl methacrylate) as block copolymers by sequential monomer addition: Dispersion of copper phthalocyanine

We synthesized poly(poly(ethylene glycol)methyl ether methacrylate)-b-poly(2-(dimethylamino)ethyl methacrylate) (p(PEGMA-b-DMAEMA)) by sequential addition of monomers and its quaternized products (p(PEGMA-b-(DMAEMA-co-QDMAEMA)) from the reaction with benzyl chloride for dispersion of copper phthalocyanine (CuPc). The structure of block copolymers was characterized by 1H NMR and GPC analysis. The block copolymers were investigated for their dispersion performance of CuPc in propylene glycol monomethyl ether acetate. The dispersion states of CuPc by dispersants were studied using dynamic light scattering.

Hydrocarbon‐Soluble Piperazine‐Containing Dilithium Anionic Initiator for High Cis‐1,4 Isoprene Polymerization

AbstractThe synthesis of 1,4‐bis[4‐(1‐phenylethenyl)benzyl] piperazine and subsequent reaction with sec‐butyllithium enables a novel piperazine‐containing difunctional organolithium initiator for the living anionic polymerization of isoprene. Piperazine provides a polar unit within the difunctional initiator, promoting ion dissociation and miscibility with hydrocarbon solvents, and enabling the formation of well‐defined polyisoprene homopolymers with predictable molecular weights and controlled microstructure. In situ Fourier transform infrared spectroscopy monitors the dilithium initiator formation and the anionic polymerization of isoprene, revealing kinetic insight into this synthetic method. Furthermore, sequential monomer addition with styrene affords poly(styrene‐block‐isoprene‐block‐styrene) triblock copolymers with controlled molecular weights and narrow polydispersities. This novel initiator facilitates the synthesis of thermoplastic elastomers with desired cis‐1,4 microstructure in polydienes.