Copolymer Molecular Weight Research Articles

Tailoring Uniform Copolymer Composition Distribution via Policy II RAFT Solution Copolymerization of Styrene and Butyl Acrylate

AbstractControlled radical polymerization (CRP) is regarded as a powerful method to design various chain structures. Semibatch monomer feeding strategies in CRP are widely used for targeting the polymer products with desired copolymer composition distribution (CCD) and molecular weight distribution, which define the properties of polymer materials. In this work, the uniform CCD in reversible addition–fragmentation transfer (RAFT) solution copolymerization is targeted via model‐based semibatch Policy II. A RAFT solution copolymerization model is first developed and correlated with batch styrene (St) and butyl acrylate (BA) copolymerization experimental data. St/BA copolymers having three different uniform compositions are produced by the comonomer feeding Policy II. Heat and concentration analysis prove feasibility of the policy. Simulation results show that the uniform CCD can be achieved by both Policy II and Policy I, compared with starved feeding and constant feeding. Policy II gives higher and more steady rates than Policy I.

Effect of polymer chain architecture on the aqueous solution properties of amphiphilic copolymers: A study of poly(N-vinylpyrrolidone-co-vinyl laurate)

The synthesis and aqueous solution properties of copolymers comprised of N- vinylpyrrolidone (NVP) and vinyl laurate (VL) with three different architectures is reported. By using reversible addition-fragmentation chain-transfer (RAFT) polymerization, statistical, forced gradient, and block copolymers were synthesized with varying compositions and molecular weights. Surface tension, critical micelle concentrations (CMCs) and micelle size were determined, and related to copolymer composition, molecular weight and architecture. It was observed that more block-like polymer architectures produced from the block copolymerizations and forced gradient copolymerizations were likely to self-assemble in solution, indicating that the degree and placement of the hydrophilic (NVP) and hydrophobic (VL) monomer units are important in predicting solution behavior of such copolymers.

Synthesis, structure and behavior of vanadium(III) diphosphine complexes in the homo- and co-polymerization of ethylene with norbornene: the ligand donor strength and bite angle make the difference

A series of vanadium(III) complexes containing diphosphine ligands of the type R2P(CH2)2PR2 [R = Me (dmpe, 1a), R = Et (depe, 1b), R = Ph (dppe, 1c)] were synthesized by reacting VCl3(THF)3 with 1.3 equiv. of the corresponding ligand. The molecular structures of 1a and 1b were determined by X-ray crystallography, revealing that both are dimers of the type [VCl3(dmpe)]2(μ-P,P′-dmpe) and [VCl3(depe)]2(μ-P,P′-depe), respectively, having one chelating diphosphine ligand, and an additional diphosphine bridging the two vanadium metals. Upon activation with diethylaluminum chloride (Et2AlCl) and in the presence of ethyltrichloroacetate (ETA) the complexes exhibited good activity in the polymerization of ethylene, affording linear, semicrystalline polymers with melting temperatures of about 135 °C. All the complexes (1a–1c) showed from good to excellent activity in the copolymerization of ethylene with norbornene. The resultant copolymers are mainly alternating with a uniform composition and a norbornene incorporation depending on the ligand employed. The substituents at the phosphorus atoms strongly affect the catalytic activity, which increased in the order 1a <1b < 1c with increasing the ligand donor strength, and the comonomer incorporation, while no significant differences were observed in terms of copolymers microstructure and molecular weight. The results are carefully compared with those obtained with the monodentate phosphine VCl3(PMePh2)2 complex and VCl3(THF)3. Overall, we found that the use of diphosphine ligands gave less active catalysts likely because PMePh2 and THF ligands are weakly coordinated to the metal, but (co)polymers with higher molecular weight due to the ability of chelating diphosphines to stabilize the electron-deficient catalytic intermediate, thus reducing the rate of β–hydrogen elimination and subsequent chain-transfer.

Self-Assembly of Amphiphilic Statistical Copolymers and Their Aqueous Rheological Properties

A range of poly(n-butyl methacrylate-stat-methacrylic acid) [P(BMA-stat-MAA)] statistical copolymers of various compositions and molecular weights ranging from 5 to 30 kDa were prepared using either reversible addition–fragmentation chain transfer (RAFT) solution copolymerization or conventional free radical polymerization in isopropanol (IPA). On dilution with water, these amphiphilic copolymers self-assembled to form spherical nano-objects as confirmed by small-angle X-ray scattering (SAXS) and transmission electron microscopy. Various structural models were examined to extract information regarding the mean nano-object size and morphology. It is found that nano-object radii are independent of copolymer molecular weight but depend on the copolymer composition: the smaller the amount of MAA units in the copolymer chains, the larger the nano-objects that are formed. Combined SAXS and aqueous electrophoretic measurements indicated that most of the MAA units are located at the nano-object surface. Furthermore, SAXS and rheology measurements were used to monitor the effect of solvent composition on the copolymer morphology both at a fixed copolymer concentration (either 1 or 25 wt %) and also for a gradual variation in copolymer concentrations (from 1 to 40 wt %) when adding water to the initial copolymer solution in IPA. These studies revealed that the copolymers are present in solution as molecularly dissolved Gaussian chains when the solvent composition is IPA-rich. However, the copolymer chains self-assemble into spherical nano-objects when the solvent composition is water-rich. At intermediate solvent compositions, SAXS analysis confirmed the formation of an interconnected nano-object network, which accounts for the apparently anomalous increase in solution viscosity on dilution indicated by rheology measurements.

Thermoresponsive poly(2-oxazoline) homopolymers and copolymers in aqueous solutions studied by NMR spectroscopy and dynamic light scattering

Structural changes during temperature-induced phase transition in D2O solutions of poly(2-ethyl-2-oxazoline) (PEOx) and P(EOx-grad-2-methyl-2-oxazoline (MOx)) copolymers were investigated by 1H NMR methods in combination with dynamic light scattering. NMR spectra showed that in PEOx solutions on molecular level structures formed during gradual heating are preserved during subsequent cooling. Phase transition in solutions of P(EOx-grad-MOx) copolymers as revealed by NMR exists irrespective the solution is turbid or nonturbid at higher temperatures. In contrast to PEOx homopolymers it is very broad, virtually independent of the copolymer composition and molecular weight, and reversible with some hysteresis. Reduced intensities of cross-peaks in NOESY spectra of copolymer solutions at elevated temperatures are mainly due to the changed mobility of copolymer segments. In all investigated solutions two types of water, “free” and “bound” with long and very short spin–spin relaxation times T2, respectively, were detected in the transition region and above the transition. The existence of two T2 components shows that exchange between “bound” and “free” water is slow regarding T2 values.

Organocatalyzed ring-opening copolymerization of α-bromo-γ-butyrolactone with ε-caprolactone for the synthesis of functional aliphatic polyesters – pre-polymers for graft copolymerization

ABSTRACTDiphenyl phosphate (DPP) was exploited as an organocatalyst to synthesize copolymers by ring-opening polymerization with α-bromo-γ-butyrolactone (αBrγBL) and ε-caprolactone (εCL) as monomers and polyethylene glycol (PEG) as initiator. The conversion rates of monomers and molecular weights of copolymers synthesized under different conditions were determined by 1H-NMR. The 1H-NMR results showed that the copolymers of αBrγBL and εCL initiated by PEG (PEGCB) were successfully synthesized and the conversions of εCL were relatively high (＞70%), while the conversions of αBrγBL were relatively low (＜26%). The highest molar ratio of αBrγBL to εCL units in these copolymers is 0.17, when the copolymerization was carried out at 100℃ for 17h.The bromine atoms hanged on the chain of the copolymers PEGCB provide a good opportunity to construct graft copolymers via atom transfer radical polymerization (ATRP). The subsequent grafting of 2-(dimethylamino)ethyl methacrylate (DMAEMA) was conducted by using PEGCB3 as macroinitiator, CuBr/N,N’,N’,N”,N”- pentamethyldiethylenetriamine (PMDETA) as catalysts and toluene/anisole as solvents via ATRP. According to the analysis of 1H-NMR, the grafting efficiency, grafting ratio and grafting frequency were 22.4%, 160.7% and 1133.8, respectively.

Improving the antifouling properties of polypropylene surfaces by melt blending with polyethylene glycol diblock copolymers

ABSTRACTProtein‐resistant polyethylene‐block‐poly(ethylene glycol) (PE‐b‐PEG) copolymers of different molecular weights at various concentrations were compounded by melt blending with polypropylene (PP) polymers in order to enhance their antifouling properties. Phase separation of the PE‐b‐PEG copolymer and its migration to the surface of the PP blend, was confirmed by attenuated total reflectance–Fourier transform infrared, X‐ray photoelectron spectroscopy, and static water contact angle measurements. Enrichment of PEG chains at the surface of the blends increased with increasing PE‐b‐PEG copolymer concentration and molecular weight. The PP blends compounded with PE‐b‐PEG copolymer having the lowest molecular weight (875 g mol−1), at the lowest concentration (1 wt %), gave the lowest bovine serum protein adsorption (30% less) compared to that of neat PP. At higher concentrations (5 and 10 wt %), and higher molecular weights (920, 1400, and 2250 g mol−1), the PE‐b‐PEG copolymers leached‐out resulting in protein adsorption comparable to that of neat PP. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46122.

Influence of Polyethylene Glycol Unit on Palladium- and Nickel-Catalyzed Ethylene Polymerization and Copolymerization.

The transition-metal-catalyzed copolymerization of olefins with polar functionalized co-monomers represents a major challenge in the field of olefin polymerization. It is extremely difficult to simultaneously achieve improvements in catalytic activity, polar monomer incorporation, and copolymer molecular weight through ligand modifications. Herein we introduce a polyethylene glycol unit to some phosphine-sulfonate palladium and nickel catalysts, and its influence on ethylene polymerization and copolymerization is investigated. In ethylene polymerization, this strategy leads to enhanced activity, catalyst stability, and increased polyethylene molecular weight. In ethylene copolymerization with polar monomers, improvements in all copolymerization parameters are realized. This effect is most significant for polar monomers with hydrogen-bond-donating abilities.

Influence of Polyethylene Glycol Unit on Palladium‐ and Nickel‐Catalyzed Ethylene Polymerization and Copolymerization

AbstractThe transition‐metal‐catalyzed copolymerization of olefins with polar functionalized co‐monomers represents a major challenge in the field of olefin polymerization. It is extremely difficult to simultaneously achieve improvements in catalytic activity, polar monomer incorporation, and copolymer molecular weight through ligand modifications. Herein we introduce a polyethylene glycol unit to some phosphine‐sulfonate palladium and nickel catalysts, and its influence on ethylene polymerization and copolymerization is investigated. In ethylene polymerization, this strategy leads to enhanced activity, catalyst stability, and increased polyethylene molecular weight. In ethylene copolymerization with polar monomers, improvements in all copolymerization parameters are realized. This effect is most significant for polar monomers with hydrogen‐bond‐donating abilities.

Polymer type and molecular weight dictate the encapsulation efficiency and release of Quercetin from polymeric micelles

Flavonoids such as quercetin (QCT) represent a diverse class of natural compounds with unique therapeutic potential in cancer and inflammatory diseases. However, their clinical efficacy is hindered by poor aqueous solubility and stability. This study describes the in vitro evaluation of QCT-encapsulated polymeric micelles based on methoxy polyethylene glycol-b-poly(D,L-lactide) (mPEG-PLA) and methoxy polyethylene glycol-b-poly(e-caprolactone) (mPEG-PCL) copolymers as a drug delivery platform for QCT. The copolymers were synthesized in different molecular weights (MWs) of the hydrophobic blocks to investigate the effect of polymer type and MW on the micelle properties. All copolymers exhibited critical micelle concentrations (CMCs) in the micromolar range or lower and produced QCT-loaded micelles with particles sizes < 100 nm. mPEG5K-PLA3K, with the highest predicted compatibility with QCT as indicated by the Flory-Huggins interaction parameter, was able to achieve the highest loading capacity and encapsulation efficiency. Drug loading also exhibited a strong correlation with the hydrophilic-lipophilic balance (HLB) of the copolymers. In vitro release of the micelles followed a biphasic profile, with an initial burst phase followed by a controlled release phase, and showed a clear dependence on drug-copolymer compatibility and copolymer MW. This work represents the first report on the use of mPEG-PLA micelles to encapsulate QCT. It also emphasizes the importance of tuning formulation variables as they influence the properties of polymeric micelles for the design of a successful nanomedicine for QCT and similar drugs.

Nanoformulation and characterization of nomilin with different poly (lactic-co-glycolic acid) resomers and surfactants for the enhanced inhibition of α-amylase and angiotensin-converting-enzyme

To overcome the solubility and bioavailability challenges of nomilin, we have formulated and characterized a nanoparticle-based delivery system. Nomilin nanoparticles were prepared with poly (lactic-co-glycolic acid) (PLGA) resomers of different co-polymer composition and molecular weights with two surfactant, didodecyl dimethyl ammonium bromide (DMAB) and pluronic F-68 (PF-68) at three nomilin loading levels (30%, 40% and 50%) through modified emulsion diffusion evaporation technique. The smallest mean particle sizes, 135–188nm, were obtained with DMAB as the surfactant. The PLGA (50:50) polymer exhibited a slow release pattern in all loading levels, except 40% loading with PF-68. Significantly higher in vitro inhibition of α-amylase and angiotensin-converting enzyme activity was observed with nomilin-loaded PLGA nanoparticles as compared to pure nomilin. Thus, nomilin nanoparticles can be explored for understanding the various biological properties using in vivo studies.

The Origin of Hierarchical Structure Formation in Highly Grafted Symmetric Supramolecular Double-Comb Diblock Copolymers.

Involving supramolecular chemistry in self-assembling block copolymer systems enables design of complex macromolecular architectures that, in turn, could lead to complex phase behavior. It is an elegant route, as complicated and sensitive synthesis techniques can be avoided. Highly grafted double-comb diblock copolymers based on symmetric double hydrogen bond accepting poly(4-vinylpyridine)-block-poly(N-acryloylpiperidine) diblock copolymers and donating 3-nonadecylphenol amphiphiles are realized and studied systematically by changing the molecular weight of the copolymer. Double perpendicular lamellae-in-lamellae are formed in all complexes, independent of the copolymer molecular weight. Temperature-resolved measurements demonstrate that the supramolecular nature and ability to crystallize are responsible for the formation of such multiblock-like structures. Because of these driving forces and severe plasticization of the complexes in the liquid crystalline state, this supramolecular approach can be useful for steering self-assembly of both low- and high-molecular-weight block copolymer systems.

Universal Bioinert Control of Polystyrene Interfaces via Hydrophobic‐Driven Self‐Assembled Surface PEGylation with a Well‐Defined Block Sequence

This work proposes a new molecular insight of interfacial design in the control of antifouling performance for the versatile biofoulants, including proteins, blood cells, tissue cells, and bacteria. A self‐assembled bioinert interface with universal fouling resistance to general biofoulants via hydrophobic‐driven surface PEGylation is presented. The study systematically discriminates the optimum PEGylated block polymer configuration and hydrophobic/hydrophilic segmental ratio enabling to optimize the surface coverage by the bioinert moieties, thus ensuring the best resistance to biofouling. For similar copolymer molecular weights and similar polystyrene (PS)/poly(ethylene glycol) methacrylate (PEGMA), the coating density obtainable is the highest if a random copolymer is used, while it is the lowest with a triblock copolymer. That measured with a diblock copolymer lies in between. Random copolymers offer more numerous anchoring possibilities than diblock copolymers, while they are importantly fewer if triblock copolymers are used. For similar total number of hydrophilic blocks, the diblock copolymer is more efficient to resist larger cells (leukocytes, fibroblasts) while the triblock is better to promote mitigate biofouling by smaller molecules or cells (proteins, platelets, red blood cells). The length of the hydrophilic PEGylated block seems to dominate fouling resistance of large biofoulants.

Structure and properties of ethylene/propylene copolymers synthesized with bis(2,4,7-trimethylindenyl)zirconium dichloride activated by methyl aluminoxanes containing different amount of trimethylaluminum

Ethylene/propylene copolymerization was catalyzed under the same conditions with unbridged metallocene bis(2,4,7-trimethylindenyl)zirconium dichloride (Cat.1) activated by aluminoxane type cocatalysts having different content of trimethylaluminum (TMA). Chain structure of the copolymers was characterized by 13C NMR and thermal analysis on copolymer fractions separated based on crystallinity. Changing the cocatalyst from commercial methylaluminoxane (MAO, containing both free TMA and bond TMA) to dried MAO (dMAO, containing only bond TMA) and BHT-treated MAO (BMAO, containing almost no TMA) caused only slight differences in polymerization activity and moderate increase in copolymer molecular weight, but marked differences in copolymer chain structure. The copolymers produced using MAO (sample 1) and dMAO (sample 2) as cocatalysts contain high amount of fractions with very low propylene content and almost isolated propylene units. The copolymer produced using BMAO as cocatalyst (sample 3) has very broad composition distribution, but its fraction with the highest crystallinity has much higher content of PP dyads than the crystalline fractions of the other two samples. This sample has the lowest crystallinity among the three samples. Phase morphology and tensile properties of the copolymer changed markedly when different cocatalyst was used. Tensile properties of sample 1 and 2 were similar to mixtures of elastomer and crystalline plastic materials, but tensile properties of sample 3 were more or less like a thermoplastic elastomer. Influences of TMA on the micro scale environment of active centers were considered the main reason for the effects of cocatalyst on copolymer structure and properties.

Side-Arm Control in Phosphine-Sulfonate Palladium- and Nickel-Catalyzed Ethylene Polymerization and Copolymerization

A series of phosphine-sulfonate ligands bearing various side-arm substituents were designed and prepared. The corresponding Pd(II) complexes [κ2-(P,O)-2-(PPhAr)-1-benzenesulfonato]Pd(Me)(dmso) (Pd1, Ar = o-MeO-C6H4; Pd2, Ar = o-PhO-C6H4; Pd3, Ar = o-(2,6-Me2-C6H3)O-C6H4; Pd4, Ar = o-PhSO2-C6H4) and Ni(II) complexes [κ2-(P,O)-2-(PPhAr)-1-benzenesulfonato]NiPh(PPh3) (Ni1, Ar = o-MeO-C6H4; Ni2, Ar = o-PhO-C6H4; Ni3, Ar = o-(2,6-Me2-C6H3)O-C6H4; Ni4, Ar = o-PhSO2-C6H4) were prepared and applied in ethylene polymerization and ethylene–polar monomer copolymerization. Catalysts Pd2, Pd3, Ni2, and Ni3 are moderately active in ethylene polymerization (activity up to 8.7 × 105 g mol–1 h–1), generating polyethylene with high molecular weights (Mn up to 105100) and high melting temperatures (Tm up to 131.6 °C). The two palladium catalysts can also initiate efficient copolymerization of ethylene with methyl acrylate, allyl cyanide, and allyl acetate. Most importantly, high copolymer molecular weights (Mn between 21600...

Dielectric Properties of Phase-Separated Blends Containing a Microcapacitor Network of Carbon Nanotubes: Compatibilization by a Random or Block Copolymer

The mechanisms governing the dielectric blend properties at different length scales for phase separating blends with multiwall carbon nanotubes (MWNTs) are unravelled by tuning the microstructure. Thereto, compatibilization by interfacially segregated block copolymers (bcp) and random copolymers (rcp) of poly(styrene-random/block-methyl methacrylate) (PS-r/b-PMMA) was achieved in phase-separating blends of poly[(α-methylstyrene)-co-acrylonitrile] and poly(methyl methacrylate) (PαMSAN/PMMA) undergoing spinodal decomposition. In our recent work, we elucidated the effects of copolymer architecture and molecular weight on the percolating network of selectively localized MWNTs. Only short bcp and long rcp/bcp improved the connectivity and refinement of the PαMSAN phase laden with MWNTs and the resulting conductivity. In the present work, we study the effects of copolymer type, architecture, and concentration on the dielectric properties. We demonstrate a concurrent increase of the interfacial capacitance and decrease of the interfacial resistance of MWNTs with entrapped PαMSAN upon effective compatibilization. This is attributed to the increasing amount of connected parallel microcapacitor RC elements formed by the network of adjacent MWNTs enclosing a thin dielectric layer of PαMSAN. At high frequencies (above 1 MHz) the electrons hop between the neighboring MWNTs, whereas at intermediate frequencies, the electrons of the MWNTs tunnel through the barriers imposed by the entrapped PαMSAN. The physical characteristics of the microcapacitor network, namely the thickness of the microcapacitors and the volume fraction of entrapped PαMSAN contributing to the microcapacitor network, are estimated by describing the dielectric relaxation time and strength using the fluctuation induced tunneling model and the interlayer model, respectively. Combining the knowledge of the aforementioned parameters allows to describe the evolution of the total interfacial capacitance of the microcapacitor assembly as a function of copolymer type and concentration. Our robust and simple procedure to tune the MWNT microcapacitor network in polymer blends via the efficiency of the compatibilizer can be used to achieve a synergistic increase in the dielectric properties at different length scales.

Double alkyl chain copolymers as flow improvers for heavy oil

ABSTRACTAs flow improvers for heavy crude oil, two oil-soluble copolymers (DM-S-VA, DA-S-VA) were successfully synthesized and characterized by 1H NMR and GPC. A rich alkyl chain and appropriate molecular weight of copolymer play fundamental role in viscosity reduction of heavy oil. Furthermore, synergistic effect of surfactants on polymers can promote the viscosity reduction, and the best formulation can increase the viscosity reduction rate to 78% to oil A. Comparing with the apparent viscosity of the different heavy oil mixing system in a wide shear rate range (0.1–200 s−1), the results show good stability and viscosity reducing effect.

Controlling final morphologies of two-step polymerization induced phase separated blends of trimethylolpropane triacrylate/acrylate copolymer through copolymer molecular weight

Effect of molecular weight of a thermoplastic copolymer on final morphology of polymerization induced phase separation of trimethylolpropane triacrylate/copolymer blends have been studied. Two acrylate copolymers, ACHM and ACLM, mainly based on methyl methacrylate, butyl acrylate and styrene were synthesized with high and low molecular weight, respectively. Final morphology of TMPTA/ACHM and TMPTA/ACLM blends were investigated by optical microscopic observation of ensemble of surface and bulk phase separation status points of view. Image analysis were done to provide related characteristic length scales.Polymerization induced phase separation of TMPTA/ACHM and TMPTA/ACLM resulted in different final morphologies with different characteristic length scales, which was attributed to the kinetic effect of the copolymer chains mobility during two-step phase separation induced during the thermal history and UV-irradiation periods.

Dodecyl methacrylate and vinyl acetate copolymers as viscosity modifier and pour point depressant for lubricating oil

The article presents application of homo polymer of dodecyl methacrylate (DDMA) and its copolymers with vinyl acetate (VA) as multifunctional additives for lubricant formulation. Homo polymer of DDMA and five copolymers of DDMA with VA at different molar ratios were synthesized by free radical polymerization method using azobisisobutyronitrile (AIBN) as initiator. The characterization of the polymers was carried out through FTIR, NMR and GPC (gel permeable chromatography) analysis. The performance of all the polymers as viscosity index improver (VII) or viscosity modifier and pour point depressant (PPD) additive in two different base oils (mineral) were evaluated. The mechanism of action of the polymers as pour point depressant was studied by photo micrographic analysis. Rheological study of the formulated lubricant was also carried out and reported. The thermal stability of the polymers was determined by thermogravimetric analysis (TGA). It was found that thermal stability, VI and molecular weights of copolymers are higher than the homopolymer which showed better PPD property.

Direct Synthesis of Branched Carboxylic Acid Functionalized Poly(1-octene) by α-Diimine Palladium Catalysts.

In this work, we studied propylene polymerization using some α-diimine palladium catalysts with systematically varied ligand sterics. In propylene polymerization, the ligand steric effect exhibits significant variations on the catalytic activity, polymer molecular weight, and branching density. However, the regio control for the polymer microstructure is poor. Furthermore, copolymerization of 1-octene with the highly challenging and biorenewable comonomer acrylic acid was investigated. High copolymer molecular weights and high comonomer incorporation ratios could be achieved in this system. This study provides a novel access for the direct synthesis of branched carboxylic acid functionalized polyolefins.