Copolymer Molecular Weight Research Articles

Structural Color for Additive Manufacturing: 3D-Printed Photonic Crystals from Block Copolymers.

The incorporation of structural color into 3D printed parts is reported, presenting an alternative to the need for pigments or dyes for colored parts produced through additive manufacturing. Thermoplastic build materials composed of dendritic block copolymers were designed, synthesized, and used to additively manufacture plastic parts exhibiting structural color. The reflection properties of the photonic crystals arise from the periodic nanostructure formed through block copolymer self-assembly during polymer processing. The wavelength of reflected light could be tuned across the visible spectrum by synthetically controlling the block copolymer molecular weight and manufacture parts that reflected violet, green, or orange light with the capacity to serve as selective optical filters and light guides.

Influence of Biodegradable Polymer Properties on Antifouling Paints Activity.

The development of new antifouling paints requires understanding the parameters involved in antifouling activity and to develop new analytical tools for their evaluation. A series of biodegradable poly(ε-caprolactone-co-δ-valerolactone) copolymers varying by molecular weight and composition were synthesized, characterized and formulated as antifouling paints. The physico-chemical properties such as hydration, degradation, erosion and lixiviation of paints were studied. Microfouling (bacteria and microalgae) was observed by microscopic observations in a short delay, whereas macrofouling colonization was observed by visual inspection during one year. The antifouling activity of paints was modified by varying the composition and molecular weight of copolymer. The crystallinity appears to play a major role in antifouling activity, however the involvement of other properties such as hydration, degradation or erosion remains difficult to understand. Confocal laser scanning and scanning electron microscopes were used for the evaluation of antifouling paints. Results show that microalgae seem to be a pertinent indicator of antifouling activity.

Tuning the phase separated morphology and resulting electrical conductivity of carbon nanotube filled PαMSAN/PMMA blends by compatibilization with a random or block copolymer

The mechanism governing the electrical properties for phase separating blends containing multiwall carbon nanotubes (MWNTs) is unravelled by tuning the compatibilization efficiency. Thereto, compatibilization by interfacially segregated block and random copolymers (cp) of poly(styrene-random/block-methyl methacrylate)(PS-r/b-PMMA) was achieved in phase separating blends of poly[(α-methyl styrene)-co-acrylonitrile]/poly(methylmethacrylate) (PαMSAN/PMMA) undergoing spinodal decomposition. A systematic study of the effects of copolymer architecture and molecular weight on the percolating network of selectively localized MWNTs is performed. Effective compatibilization is achieved with block cp irrespective of the ability of the blocks to entangle, whereas for random cp only long random cp having the ability to effectively entangle with the homopolymers are as efficient as long block cp. With increasing copolymer concentration, an increase and subsequent saturation of the electrical conductivity is attained. This originates from an increased connectivity and refinement of the MWNT laden PαMSAN phase, as confirmed by optical microscopy and the linear viscoelastic response of the blends. An effective compatibilizer led to an interfacial tension mediated suppression of an interfacial coarsening of the PαMSAN phase during phase separation, subsequently leading to percolation of MWNTs selectively localized in the PαMSAN phase. Furthermore, the copolymer having the ability to promote the development of a percolated network of MWNTs also allowed the network to be formed at a lower copolymer concentration as compared to that of blends with copolymers leading to restricted improvement in the connectivity of MWNTs. Our robust and simple procedure to tune the blend morphology via the efficiency of the compatibilizers can be used to achieve a synergistic increase in conducting properties.

Expansion characteristics of expandable styrene/methyl methacrylate copolymer particles: The effects of copolymer molecular weight and particle size

Spherical foamable particles were synthesized by suspension polymerization of methyl methacrylate and styrene in the presence of a blowing agent. When the surrounding temperature was high enough to vaporize the blowing agent and soften the polymer shell, the particles were expanded due to pressure difference across the shell. The effects of initiator and crosslinker concentration on the particle size, average molecular weight, and molecular weight distribution of synthesized copolymer, pentane content and expansion properties (density, residual pentane, and dimensional stability of pre-expanded beads) of expandable particles were investigated. The results showed that the expansion behavior of the particles was dependent on molecular weight of the matrix polymer and size of the synthesized particles. In a constant copolymer molecular weight, the pre-expanded bead density decreased with increasing of particle size whereas it increased with molecular weight in a constant particle size. Moreover, the crosslinker improved dimensional stability of the pre-expanded beads.

Copolymerization of ethylene with norbornene or 1-octene using supported ionic liquid systems

Copolymerization of ethylene with norbornene (E/NB) and ethylene with 1-octene (E/Oct) is performed using supported ionic liquid (SIL) systems, in which metallocene (Cp2VCl2) or post-metallocene [VCl2(salenCl2)] vanadium catalysts are immobilized in pyridinium chloroaluminate ionic liquid supported on silica. The studied SIL catalysts show higher activities as well as stability than their non-supported analogues. In addition, higher activities and better comonomer incorporation are observed for norbornene (above 30 mol%). The comonomer incorporation has considerable influence on copolymer molecular weight (Mw), melting temperature, crystallinity degree, and microstructure of the copolymers. Molecular-weight distribution is relatively narrow (1.5 ≤ Mw/Mn ≤ 3.0), which indicates the presence of single-site catalyst systems.

Systematic Investigations of Ligand Steric Effects on α-Diimine Palladium Catalyzed Olefin Polymerization and Copolymerization

In the Brookhart type α-diimine palladium catalyst system, it is highly challenging to tune the polymer branching densities through ligand modifications or polymerization conditions. In this contribution, we describe the synthesis and characterization of a series of α-diimine ligands and the corresponding palladium catalysts bearing both the dibenzhydryl moiety and with systematically varied ligand sterics. In ethylene polymerization, it is possible to tune the catalytic activities ((0.77–8.85) × 105 g/(mol Pd·h)), polymer molecular weights (Mn: (0.2–164.7) × 104), branching densities (25–116/1000C), and polymer melting temperatures (amorphous to 98 °C) over a very wide range. In ethylene–methyl acrylate (E–MA) copolymerization, it is possible to tune the catalytic activities ((0.3–8.8) × 103 g/(mol Pd·h)), copolymer molecular weights (1.1 × 103–79.8 × 103), branching densities (30–119/1000C), and MA incorporation ratio (0.4–13.8%) over a very wide range. The molecular weights and branching densities could also be tuned in α-olefin polymerization. The tuning in polymer microstructures leads to significant tuning in polyethylene mechanical properties and the surface properties of the E–MA copolymer.

Stimuli-responsive coil-rod-coil block copolymers synthesized by using a bis-alkoxyamine-functionalized poly(para-phenylene) macro initiator

The preparation of coil-rod-coil block copolymers possessing a rigid poly(para-phenylene) middle segment surrounded by either temperature- or pH-responsive blocks is described. First, the bis-alkoxyamine terminated macro initiator was synthesized using microwave-accelerated Suzuki polycondensation (SPC). Afterwards the macro initiator was applied for the nitroxide-mediated radical polymerization (NMRP) of N-isopropyl acrylamide (NIPAAm) and 2-vinyl pyridine (2VP), respectively, to attach defined thermo- or pH-sensitive blocks. Macro initiator and block copolymer molecular weight and molecular weight distribution determinations were conducted via size exclusion chromatography (SEC). In addition 1H NMR spectroscopy was used to determine block ratios and molecular weights complementary. Further block copolymer characterization was performed by DSC, AFM, SEM measurements as well as turbidity and titration experiments. Critical transition values were found to be little different than for respective homo polymers.

Direct Synthesis of Functionalized High‐Molecular‐Weight Polyethylene by Copolymerization of Ethylene with Polar Monomers

AbstractThe introduction of even a small amount of polar functional groups into polyolefins could excise great control over important material properties. As the most direct and economic strategy, the transition‐metal‐catalyzed copolymerization of olefins with polar, functionalized monomers represents one of the biggest challenges in this field. The presence of polar monomers usually dramatically reduces the catalytic activity and copolymer molecular weight (to the level of thousands or even hundreds Da), rendering the copolymerization process and the copolymer materials far from ideal for industrial applications. In this contribution, we demonstrate that these obstacles can be addressed through rational catalyst design. Copolymers with highly linear microstructures, high melting temperatures, and very high molecular weights (close to or above 1 000 000 Da) were generated. The direct synthesis of polar functionalized high‐molecular‐weight polyethylene was thus achieved.

Direct Synthesis of Functionalized High-Molecular-Weight Polyethylene by Copolymerization of Ethylene with Polar Monomers.

The introduction of even a small amount of polar functional groups into polyolefins could excise great control over important material properties. As the most direct and economic strategy, the transition-metal-catalyzed copolymerization of olefins with polar, functionalized monomers represents one of the biggest challenges in this field. The presence of polar monomers usually dramatically reduces the catalytic activity and copolymer molecular weight (to the level of thousands or even hundreds Da), rendering the copolymerization process and the copolymer materials far from ideal for industrial applications. In this contribution, we demonstrate that these obstacles can be addressed through rational catalyst design. Copolymers with highly linear microstructures, high melting temperatures, and very high molecular weights (close to or above 1 000 000 Da) were generated. The direct synthesis of polar functionalized high-molecular-weight polyethylene was thus achieved.

Smart dendrimer-based nanogel for enhancing 5-fluorouracil loading efficiency against MCF7 cancer cell growth

Nano-carriers are not only evaluated as a novel kind of drug delivery, but also expected to bypass the critical bottleneck of conventional cancer chemotherapeutics. Among them, thermo-sensitive nanogel draws much attention due to its efficacy in the loading and release of hydrophobic drugs. In the study, we developed a promising thermosensitive polymer-grafted dendrimer to enhance drug-loading efficiency, which was prepared from conjugation of thermo-sensitive carboxylic-terminated poly(N-isopropylacrylamide) polymer (PNIPAM) with polyamidoamine (PAMAM) dendrimer (G3.0). The obtained copolymer structure and molecular weight were confirmed by proton nuclear magnetic resonance ( 1 H NMR) and gel permeation chromatography (GPC), respectively. Morphology of the nanocarrier was observed around 120–150 nm by transmission electron microscopy (TEM) and 200 nm by dynamic light scattering (DLS). The nanocarrier exhibited the higher drug loading (DL = 7.79%) and entrapment efficiency (EE = 42.25%) of 5-FU compared to PAMAM dendrimer G3.0 (DL = 2.25% and EE = 11.52%). In-vitro test, the 5-FU-loaded in PAMAM G3.0–PNIPAM could release approximately 40% of the encapsulated drug at pH = 7.4 after 5 days tracking, while the cumulative anticancer drugs achieved nearly two-fold increase (around 75%) at pH 5.5 during the same time. Moreover, the cytotoxicity assay results also indicated that the drug-loaded nanocarrier exhibited a significant growth inhibition of the MCF-7 cancer cell. The obtained resulted possibly offered a great potential of the nanocarrier which may be utilized in delivering other anticancer drugs or dual drugs for chemotherapy in future.

Effect of sulfonation degree on molecular weight, thermal stability, and proton conductivity of poly(arylene ether sulfone)s membrane

Direct copolymerization of sulfonated and non-sulfonated difluorodiphenyl sulfones as dihalide monomers with hydroquinone and also 4,4′-(4,4′-sulfonylbis-(1,4-phenylene)bis(oxy)) diphenol as diols led to preparation of two series of poly(arylene ether sulfone)s. Copolymers with different degrees of sulfonation (40, 50 and 60%) were synthesized in order to evaluate their potential for fuel cell application. 1H-NMR, FT-IR, and mass spectroscopy were used for characterization of prepared monomers and copolymers. Differential scanning calorimetry and thermogravimetric analysis were applied for investigation and comparison of the thermal properties of copolymers. Laser light scattering (LLS) was employed to calculate zeta potential, conductivity, and molecular weight of copolymers. Copolymers were obtained in high and sufficient molecular weight that was basic need to reach reasonable physical and thermal properties for applications as fuel cell membrane. The effect of similar structural repeating units with different sizes on the final properties of sulfonated poly(ether sulfone)s was investigated to compare their potential in fuel cell membrane.

Vanadium(III)–catalyzed copolymerization of ethylene with norbornene: Microstructure at tetrad level and reactivity ratios

Vanadium(III) complex bearing PMePh2 ligand has been synthesized, fully-characterized and investigated for homo- and co-polymerization of ethylene with norbornene, in combination with aluminum compounds, i.e., methylaluminoxane (MAO) and Et2AlCl. The results are carefully compared with those obtained with VCl3(THF)3 and VCl3 in the presence and absence of ethyltrichloroacetate (ETA), and free phosphine. VCl3(PMePh2)2 was likely activated through a dissociative mechanism where the dissociation of the labile phosphine ligand was the first and possibly the rate-determining step. The activity of VCl3(THF)3 was slightly higher than that of VCl3(PMePh2)2 likely due to a different competition of re-insertion rate of dissociated ligand compared to the insertion/coordination of (co)monomers. Copolymers obtained at low norbornene feedstock concentration from VCl3(THF)3, showed greater non-uniformity in terms of composition distribution with respect to those from VCl3(PMePh2)2 because of a more pronounced compositional drift in the semi-batch polymerization process. This strongly affects the copolymer’s thermal properties, the copolymers from VCl3(PMePh2)2 exhibiting higher Tgs. The effect of PMePh2 and THF ligand on reactions responsible for chain growth termination, affecting the copolymers molecular weight, is discussed. Control over the norbornene incorporation and molecular weight of the resultant copolymers proved to be possible by changing the polymerization temperature, and ETA loading.In addition, ad-hoc. experiments, designed to ensure the uniformity of the catalytic copolymerization process even in the presence of the observed relevant (and unavoidable) compositional drift were performed, and copolymers microstructure and catalytic mechanisms were thoroughly investigated. Due to the peculiar features of the catalytic systems, these studies could be performed only after appropriate modifications to well established methods were developed. As a by-product of these investigations, general and original computational methods are proposed, whose applicability goes beyond the cases treated here.

Drug Release Kinetics and Mechanism from PLGA Formulations

The release kinetics of indomethacin (IND) and hydrochlorothiazide (HCT) from drug/PLGA formulations with different copolymer composition and molecular weight of PLGA were measured in vitro by using a rotating disk system (USP II). The release mechanism of IND and HCT from their PLGA formulations was analyzed using a chemical‐potential‐gradient model combined with the Perturbed‐Chain Statistical Associating Fluid Theory (PC‐SAFT). Furthermore, the release kinetics of IND and HCT from the PLGA formulations with different copolymer composition and molecular weight of PLGA were correlated and predicted in good accordance with the experimental data. It was found that the chemical‐potential‐gradient model combined with the PC‐SAFT helped to understand the drug release mechanism from the drug/PLGA formulations. It also well correlated and predicted the drug release kinetics as function of copolymer composition and molecular weight of PLGA as well as of drug type. It helps to save time and costs for determination of the long‐term drug release kinetics, especially for sustained drug release as obtained from the drug/PLGA formulations in this work. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4055–4065, 2016

Symmetrical Permeable Membranes Consisting of Overlapped Block Copolymer Cylindrical Micelles for Nanoparticle Size Fractionation

Free-standing symmetrical porous membranes consisting of uniform cylindrical micelles were prepared from a polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymer following a process combining self-assembly and nonsolvent-induced phase separation (SNIPS). The fabricated membranes displayed an impressive ultrastructure by the overlapping of the cylindrical micelles throughout the whole membrane profile (∼65 μm). The effects of copolymer molecular weight and membrane-formation condition on membrane morphology were investigated and discussed in detail. It was concluded that the cylindrical micellar membranes could be obtained in a wide window of fabrication conditions as low molecular weight of PS-b-P4VP was used as the raw material. The permeation tests indicated that the water permeability of the symmetrical membranes reached 400 L/(h m2 bar) in neutral condition, which was comparable to that of the block copolymer (BCP) isoporous membrane reported in the literature. Significantly, the permea...

Isolating the Effect of Molecular Weight on Ion Transport of Non-Ionic Diblock Copolymer/Ionic Liquid Mixtures

The effects of molecular weight and microdomain orientation on the ionic conductivities of poly(styrene-b-methyl methacrylate) diblock copolymer/1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (SM/IL) mixtures are assessed through complementary experimental and theoretical techniques. Small-angle X-ray scattering revealed that SM/IL mixtures have anisotropic lamellar morphologies, preferentially oriented parallel to the casting substrate. A method for quantifying the morphology factor, or microdomain orientation within the Sax–Ottino model, using 2-D SAXS data is presented and applied to SM/IL mixtures. Ionic conductivity increases by up to an order of magnitude with a 2-fold increase in molecular weight, even when accounting for the morphology type, composition, microdomain orientation, and PMMA/IL glass transition temperature. Self-consistent field theory calculations predict a nonuniform solvent distribution in PMMA/IL microdomains, suggesting that polymer mobility and ion transport are reduced near PS–PMMA microdomain interfaces. Thus, the increase in ionic conductivity with increasing block copolymer molecular weight is associated with having fewer PS–PMMA/IL interfaces per unit volume.

Biodegradation of poly(aspartic acid-lysine) copolymers by mixed bacteria from natural water

Poly(aspartic acid-lysine) copolymers (PAL), as an alternative product to traditional water treatment agents, was developed based on poly(aspartic acid) through microwave-assisted synthesis of aspartic acid and lysine. Its biocompatibility and performance in inhibiting scale and corrosion are determining factors in its application. In this paper, biodegradability of PAL was investigated by carbon dioxide evolution tests. The degradation ratio of PAL on day 10 and day 28 respectively reached 35.01% and 80.00%, which indicated that PAL was a degradable water treatment agent. PAL is superior to polyacrylic acid and phosphonic carboxylic acid in biodegradability. With the increase in the addition ratio of lysine in copolymerization process and the decrease in the molecular weight of copolymer, the biodegradability of PAL was significantly enhanced. In addition, the incubation period before the biodegradation was shortened. The result showed that Cu2+ could decrease the degradation rate through inhibiting enzymatic activities.

Diblock Polyelectrolytic Copolymers Containing Cationic Iron and Cobalt Sandwich Complexes: Living ROMP Synthesis and Redox Properties.

Diblock metallopolymer polyelectrolytes containing the two redox-robust cationic sandwich units [CoCp'Cp](+) and [FeCp'(η(6)-C6 Me6)](+) (Cp = η(5)-C5 H5; Cp' = η(5)-C5H4-) as hexafluorophosphate ([PF6](-)) salts are synthesized by ring-opening metathesis polymerization using Grubbs' third generation catalyst. Their electrochemical properties show full chemical and electrochemical reversibilities allowing fine determination of the copolymer molecular weight using Bard-Anson's electrochemical method by cyclic voltammetry.

Patterning at the 10 nanometer length scale using a strongly segregating block copolymer thin film and vapor phase infiltration of inorganic precursors.

In this work, we demonstrate the use of self-assembled thin films of the cylinder-forming block copolymer poly(4-tert-butylstyrene-block-2-vinylpyridine) to pattern high density features at the 10 nm length scale. This material's large interaction parameter facilitates pattern formation in single-digit nanometer dimensions. This block copolymer's accessible order-disorder transition temperature allows thermal annealing to drive the assembly of ordered 2-vinylpyridine cylinders that can be selectively complexed with the organometallic precursor trimethylaluminum. This unique chemistry converts organic 2-vinylpyridine cylinders into alumina nanowires with diameters ranging from 8 to 11 nm, depending on the copolymer molecular weight. Graphoepitaxy of this block copolymer aligns and registers sub-12 nm diameter nanowires to larger-scale rectangular, curved, and circular features patterned by optical lithography. The alumina nanowires function as a robust hard mask to withstand the conditions required for patterning the underlying silicon by plasma etching. We conclude with a discussion of some of the challenges that arise with using block copolymers for patterning at sub-10 nm feature sizes.

Phenylboronic acid based polymeric micelles for mucoadhesive anterior segment ocular drug delivery.

Event Abstract Back to Event Phenylboronic acid based polymeric micelles for mucoadhesive anterior segment ocular drug delivery. Ben Muirhead1, Graeme Prosperi-Porta2 and Heather Sheardown1 1 McMaster University, Biomedical Engineering, Canada 2 University of Calgary, Cumming School of Medicine, Canada Introduction: Despite poor performance, topical drops are by far the most widely used therapy for many ocular diseases. Static barriers including tight junctions of the conjunctiva, the hydrophobic corneal epithelium and hydrophilic corneal stroma, and dynamic barriers including the rapid tear turnover, lacrimal drainage, and the vasculature and lymphatics of the conjunctiva all conspire to prevent the majority of topically applied therapeutics from reaching their site of action. Only 5% of topically administered drug reaches the anterior structures of the eye, while less than 1% reach the posterior[1]. Consequently, drugs delivered via eye drop are massively overdosed, resulting in undesirable systemic exposure and extreme waste (>99% for many glaucoma medications). We propose the use of mucoadhesive self-assembling micelles as a solution to the obvious problems facing topical ocular drug delivery. Phenylboronic acid (PBA) is a synthetic molecule with a strong affinity for mucin due to its ability to complex with 1,2-cis-diols. PBA has an extensive pedigree in biomedical engineering, including as part of an ocular delivery scheme for cyclosporine A (CycA)[2]. Thus, a series of block copolymer micelles incorporating mucoadhesive PBA into their outer shells was developed capable of targeted drug delivery to ocular tissues. Method and Materials: pLA-b-p(MAA-PBA) copolymers were synthesized by RAFT polymerization and contained a spectrum of PBA mole percentages. The resultant copolymer was isolated by precipitation into 10 times excess of cold anhydrous diethyl ether and further purified by repeated precipitation into diethyl ether from tetrahydrofuran two additional times. Copolymer composition and molecular weight were determined using proton nuclear magnetic resonance. Micelles were formed by precipitation into purified water from acetone. Micelle size was determined using dynamic light scattering. Mucoadhesion was determined using Surface Plasmon Resonance with bovine mucin and simulated tear fluid. CycA release from micelles was determined using high performance liquid chromatography (HPLC). Results: DLS determined the diameter and polydispersity (PDI) of the micelles. Micelle diameter is dependent on the PBA content in the micelle corona and ranges from 35nm to 65nm in diameter as the mole percentage of PBA is increased from 0% to 30%. The PDI in all cases was acceptable, with a maximum value of 0.29. CycA was entrapped within the LMP micelles by dissolving both components in acetone followed by addition into purified water at a ratio of 20 mg copolymer to 3 mg CycA. All micelles showed entrapment efficiencies greater than 99.8% and excellent release characteristics. SPR showed an unambiguous relationship between the molde percentage of PBA and mucoadhesion. After a standard battery of cell viability testing which showed no adverse reaction using human corneal epithelial cells, these micelles were tested in vivo using Sprague-Dawley rats by dropping their eyes for a period of 10 days, showing excellent biocompatibility. Conclusions: Mucoadhesive micelles offer significant potential to increase the efficacy of topically applied ophthalmic drugs by decrease the dosage, frequency of dose, and off-target systemic toxicity. We have synthesized a series of poly(L-lactide)-b-poly(methacrylic acid-co-phenylboronic acid) copolymer micelles with varying amounts of phenylboronic acid which show excellent mucoadhesivity, drug release characteristics, and biocompatibility.

Acrylate copolymers as impact modifier for epoxy resin

P(BA-GMA) (PBG), having various molecular weights, was synthesized by in situ polymerization of butyl acrylate (BA) and glycidyl methacrylate (GMA), and further used as a modifier to improve the comprehensive properties of the epoxy curing system. The copolymers were characterized by gel permeation chromatography (GPC). The effects of various molecular weights of copolymers on the mechanical properties, thermal performance, and phase behavior of the curing system were carefully evaluated. The experimental results of differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) showed that glass transition temperature decreased and the tan δ peak shifted to a lower temperature with decreasing molecular weight of copolymer. Mechanical properties analysis of curing films showed that the impact strength and fracture toughness increased significantly upon the addition of PBG, indicating good toughness of the modified epoxy resins. From scanning electron microscopy (SEM) studies of the fracture surfaces of ER/PBG systems, the fracture behavior of epoxy matrix was changed from brittleness to toughness.