Side Chain Molecular Weight Research Articles

Investigating the effects of the local environment on bottlebrush conformations using super-resolution microscopy.

The single-chain physics of bottlebrush polymers plays a key role in their macroscopic properties. Although efforts have been made to understand the behavior of single isolated bottlebrushes, studies on their behavior in crowded, application-relevant environments have been insufficient due to limitations in characterization techniques. Here, we use single-molecule localization microscopy (SMLM) to study the conformations of individual bottlebrush polymers by direct imaging. Our previous work focused on bottlebrushes in a matrix of linear polymers, where our observations suggested that their behavior was largely influenced by an entropic incompatibility between the bottlebrush side chains and the linear matrix. Instead, here we focus on systems where this effect is reduced: in solvent-swollen polymer materials and in systems entirely composed of bottlebrushes. We measure chain conformations and rigidity using persistence length (lp) as side chain molecular weight (Msc) is varied. Compared to a system of linear polymers, we observe greater flexibility of the backbone in both systems. For bottlebrushes in bottlebrush matrices, we additionally observed a scaling relationship between lp and Msc that more closely follows theoretical predictions. For the more flexible chains in both systems, we reach the edge of our resolution limit and cannot visualize the entire contour of every chain. We bypass this limitation by discussing the aspect ratios of the features within the super-resolution images.

Study on Dispersion, Adsorption, and Hydration Effects of Polycarboxylate Superplasticizers with Different Side Chain Structures in Reference Cement and Belite Cement.

To investigate the effects of Reference cement (RC) and Belite cement (LC) systems, different molecular structures of polycarboxylate ether (PCE) were prepared through the free radical polymerization reaction and designated as PC-1 and PC-2. The PCE was characterized and tested using a particle charge detector, gel permeation chromatography, a rotational rheometer, a total organic carbon analyzer, and scanning electron microscopy. The results showed that compared to PC-2, PC-1 exhibited higher charge density and better molecular structure extension, with smaller side-chain molecular weight and molecular volume. PC-1 demonstrated enhanced adsorption capacity in cement, improved initial dispersibility of cement slurry, and a reduction in slurry yield stress of more than 27.8%. LC, with its higher C2S content and smaller specific surface area compared to RC, could decrease the formation of flocculated structures, resulting in a reduction in slurry yield stress of over 57.5% and displaying favorable fluidity in cement slurry. PC-1 had a greater retarding effect on the hydration induction period of cement compared to PC-2. RC, which had a higher C3S content, could adsorb more PCE, leading to a greater retarding effect on the hydration induction period compared to LC. LC and PC-2, on the other hand, exhibited inhibition during the hydration acceleration period. The addition of PCE with different structures did not significantly affect the morphology of hydration products in the later stage, which was consistent with the trend of KD variation. This indicates that the analysis of hydration kinetics can better reflect the final hydration morphology.

Flowability, Strength, and Water Absorption of Mortars Containing Fly Ash and WRA Having Varying Main Chain Lengths

Within the scope of this study, the effect of the main chain length of polycarboxylate-based water-reducing admixture (WRA) on the fresh properties, compressive strength, and water absorption of mortar mixtures containing fly ash was investigated. Three WRAs with the same structure but different main chain lengths and resultantly different molecular weights were used. Effects of the admixtures on the properties of cementitious systems with 0, 15, 30, and 45 wt.% fly ash were investigated. Irrespective of the fly ash substitution level, the fluidity of the mixtures was improved when the admixture main chain length was increased up to a certain level. Possibly beyond a certain main chain length, the entanglement of too large main chains of the polymer to each other reduced the electrostatic effect of the polymer. Thus, the flow properties of the mixtures were affected negatively. The side chain molecular weight (length) of the admixtures was fixed (2,400 g/mol). However, the molecular weight of the admixtures was adjusted as 24, 48, and 71 kg/mol by changing the main chain length of the polymer. The admixture with 48 kg/mol molecular weight showed the best performance in terms of mortar fresh properties. However, the change in the length of the main chain of admixture did not have a considerable effect on the compressive strength and water absorption of the mortar. In addition, apart from the WRA admixture property, time-dependent flow and permeation properties of the mixtures were affected negatively by the increase in fly ash substitution level.

Tuning the micro-phase separation of the PES-g-PEG comb-like copolymer membrane for efficient CO2 separation

As a common CO2 separation membrane material, polyethylene glycol (PEG) with ether oxygen groups shows high dissolution selectivity to CO2. However, high molecular weight PEG has strong crystallinity, resulting in low gas flux, while the low molecular weight PEG has poor mechanical properties. Block copolymers containing PEG segments can address this challenge but are difficult to synthesize. In this work, a series of polyether sulfone (PES) comb-like copolymer with PEG side chains were prepared by the polycondensation followed by the thiol-ene click chemistry. By manipulating the density and length of PEG side chains (Mn = 550, 1000, 2000) to adjust the fine structure of the micro-phase separation, the gas separation performance of the PES-g-PEG membrane was optimized. The PES-g-PEG polymers have two glass transition temperatures (Tg), which are attributed to the PES main chain and PEG side chains. The Tg-PEG and Tg-PES difference (ΔTg) is highly correlated with the PEG side chain density and can be used to interpret the phase separation degree. The copolymer membrane with shorter PEG side chains achieved higher chain density and more developed micro-phase separation, which was facilitated by thermal annealing. As a result, PES A-g-PEG550 membrane shows the best gas separation performance with the CO2 permeability of 26.8 Barrer and the CO2/N2 selectivity of 27.6. The permeability variation with the microstructure of PES-g-PEG mostly relies on the side chain density rather than volume fraction or side chain molecular weight. We believe this study of the gas separation performance of the comb-like copolymer material is meaningful for the further application of membrane technology in CO2 capture and separation.

Effect of nonionic side chain length of polycarboxylate-ether-based high-range water-reducing admixture on properties of cementitious systems

Despite the large variations in the behaviors of water-reducing admixtures upon changes in their structures, most previous reports on the cement-admixture compatibility did not provide sufficient information on the structure of the admixture. Hence, the evaluation and generalization of the reports on the cement-admixture compatibility are challenging. In this study, three different polycarboxylate-ether-based water-reducing admixtures with the same free nonionic content, anionic/nonionic molar ratio, and main chain length and different side chain lengths were produced. The compatibility of these admixtures with a CEM I 42.5 R-type cement was investigated. In addition, an analysis of variance was performed on the experiment results to evaluate the contributions of the admixture type, admixture/cement ratio, and elapsing time to the Marsh funnel flow time, mini-slump, slump flow, and compressive strength. The water-reducing admixtures having long or short side chains reduced the initial flow characteristics of the cementitious systems. However, the admixture having the shortest side chain was better with regard to flow retention. The side chain length of the admixture did not have significant effects on the compressive strength and water absorption capacity of the mortar mixtures and mini-slump performances of the cement paste mixtures. Regarding the behaviors of the admixtures in the cementitious systems, an optimal admixture side chain molecular weight is proposed.

Effect of the polycarboxylate based water reducing admixture structure on self-compacting concrete properties: Main chain length

In this study, the effect of polycarboxylate ether-based water reducing admixture (WRA) main chain length on fresh state properties, compressive strength, ultrasonic pulse velocity (UPV) and water absorption capacity of self-compacting concrete (SCC) mixtures were investigated. Within this aim, three polycarboxylate ether-based high range WRAs with stabilized polyethylene oxide side chain molecular weight, free non-ionic content and constant anionic/non-ionic ratios, but different main chain length were synthesized. FTIR (Fourier transform infrared) and GPC (Gel Permeation Chromatography) analyzes were carried out to characterize admixtures. According to test results, the admixture requirement for reaching targeted main chain length in SCC increased and adsorption of admixture decreased in case the admixture main chain length is higher and lower than a certain value. However, time-dependent flow performance of the mixtures improved with the increase of admixture main chain length and a reverse situation was observed when the length was decreased. Similar behaviors were also observed in V funnel flow, L box and U box passing tests. While the admixture main chain length change affected early age strength, it showed no effect on the strengths of later ages. No considerable differences were observed in the 28-day water absorption, UPV and dynamic modulus of elasticity values of the mixtures with the change of admixture main chain length.

All-Acrylic Multigraft Copolymers: Effect of Side Chain Molecular Weight and Volume Fraction on Mechanical Behavior

We present the synthesis of poly(n-butyl acrylate)-g-poly(methyl methacrylate) (PnBA-g-PMMA) multigraft copolymers via a grafting-through (macromonomer) approach. The synthesis was performed using two controlled polymerization techniques. The PMMA macromonomer was obtained by high-vacuum anionic polymerization followed by the copolymerization of n-butyl acrylate and PMMA macromonomer using reversible addition–fragmentation chain transfer (RAFT) polymerization to yield the desired all-acrylic multigraft structures. The PnBA-g-PMMA multigraft structures exhibit randomly spaced branch points with various PMMA contents, ranging from 15 to 40 vol %, allowing an investigation into how physical properties vary with differences in the number of branch points and molecular weight of grafted side chains. The determination of molecular weight and polydispersity indices of both the PMMA macromonomer and the graft copolymers was carried out using size exclusion chromatography with triple detection, and the structural ...

Lignopolymers as viscosity-reducing additives in magnesium oxide suspensions

Lignopolymers are a new class of polymer additives with the capability to be used as dispersants in cementitious pastes. Made with kraft lignin cores and grafted polymer side-chains, the custom-synthesized lignopolymers were examined in terms of the molecular architecture for viscosity reducing potential in inert model suspensions. Lignin–poly(acrylic acid) (LPAA) and lignin–polyacrylamide (LPAm) have been found to vary the rheology of magnesium oxide (MgO) suspensions based on differences in chain architecture and particle–polymer interactions. A commercial comb-polymer polycarboxylate ester was compared to LPAA and LPAm at 2.7mg/mL, a typical dosage for cement admixtures, as well as 0.25mg/mL. It was found that LPAm was a more effective viscosity reducer than both LPAA and the commercial additive at low concentrations, which was attributed to greater adsorption on the MgO particle surface and increased steric dispersion from PAm side-chain extension. The influence of chain adsorption and grafted side-chain molecular weight on rheology was also tested.

Linear rheology and structure of molecular bottlebrushes with short side chains

We investigate the microstructure and linear viscoelasticity of model molecular bottlebrushes (BBs) using rheological and small-angle X-ray and neutron scattering measurements. Our polymers have short atactic polypropylene (aPP) side chains of molecular weight ranging from 119 g/mol to 259 g/mol and narrow molecular weight distribution (Mw/Mn 1.02–1.05). The side chain molecular weights are a small fraction of the entanglement molecular weight of the corresponding linear polymer (Me,aPP= 7.05 kg/mol), and as such, they are unentangled. The morphology of the aPP BBs is characterized as semiflexible thick chains with small side chain interdigitation. Their dynamic master curves, obtained by time-temperature superposition, reveal two sequential relaxation processes corresponding to the segmental relaxation and the relaxation of the BB backbone. Due to the short length of the side chains, their fast relaxation could not be distinguished from the glassy relaxation. The fractional free volume is an increasing function of the side chain length (NSC). Therefore, the glassy behavior of these polymers as well as their molecular friction and dynamic properties are influenced by their NSC values. The apparent flow activation energies are a decreasing function of NSC, and their values explain the differences in zero-shear viscosity measured at different temperatures.

On the Self-Assembly of Brush Block Copolymers in Thin Films

We describe a simple route to fabricate two dimensionally well-ordered, periodic nanopatterns using the self-assembly of brush block copolymers (brush BCPs). Well-developed lamellar microdomains oriented perpendicular to the substrate are achieved, without modification of the underlying substrates, and structures with feature sizes greater than 200 nm are generated due to the reduced degree of chain entanglements of brush BCPs. A near-perfect linear scaling law was found for the period, L, as a function of backbone degree of polymerization (DP) for two series of brush BCPs. The exponent increases slightly from 0.99 to 1.03 as the side chain molecular weight increases from ∼2.4 to ∼4.5 kg/mol(-1) and saturated with further increase in the side chain molecular weight due to the entropic penalty associated with the packing of the side chains. Porous templates and scaffolds from brush BCP thin films are also obtained by selective etching of one component.

PH-Responsive Films of Electrostatically Adsorbed Arborescent Copolymers

The adsorption of charged dendrigraft (arborescent) copolymers of different generations (G1, G2) and side chain molecular weights (Mn ≈ 5000 or 30,000) on silica surfaces in water, was monitored by the quartz crystal microbalance dissipation (QCM-D) technique. The topology of the adsorbed copolymers on mica was also investigated by AFM measurements. The PS-P2VP [polystyrene-graft-poly(2-vinylpyridine)] copolymers readily interact with a silica or mica surface and form a thin layer in acidic water (pH 2) due to the positively charged P2VP shell branches. The adsorbed arborescent PS-P2VP films expanded and collapsed reversibly in water upon cycling between low and high pH values, respectively. As the generation number increased, the density of copolymer molecules adsorbed onto the surface decreased due to stronger intermolecular electrostatic repulsions. The adsorption density also decreased significantly for copolymers with longer P2VP chains due to their more expanded conformation on the surface.

Constructing a Syntheses Table of the Standard Amino Acid Based on the PAM250 Matrix

It is well known that there are some similarities among various naturally occurring amino acids. The standard amino acids have been grouped by their general properties and the chemical structures of their side chains. In this paper we divided the molecular weight of amino acid into two parts: backbone molecular weight Mband side chain molecular weight Ms. We naturally grouped the amino acids into two sets according to the rate of Ms/ Mb. We developed a method to construct a syntheses table to reflect the relevant physicochemical properties based on the PAM250 matrix and successfully established an elegant table of the twenty amino acids. Our work proved that PAM250 matrix could be used not only in finding reasonable alignments but also in grouping similar amino acid.

An Approximation for the Intrinsic Viscosity of Brush-Shaped Polymers

The dependence of the intrinsic viscosity [η] on molecular weight and side-chain length for brush-shaped polymers is analyzed using a simplified expression for [η], in which a brush-shaped polymer is modeled as a linear chain with a contour length equal to that of the backbone of the brush-shaped chain and a repeat unit molar mass that includes the molar mass of the side chain. The treatment is used to estimate the ratio â/âref of the persistence length â of the brush-shaped chain relative to a reference chain as a function of side-chain molecular weight. Values of â/âref deduced for data on a series of brush-shaped polymers are found to be in good accord with values derived in a more complete treatment of the dependence of [η] on M based on the wormlike chain model. Estimates of â/âref are also given for a series of poly(alkyl methacrylate) chains as a function of the alkyl chain length, and the approximate expression is applied to the evaluation of the true molecular weight from the apparent molecular weight determined in a size exclusion chromatography analysis based on the calibration of the columns in terms of the molecular weight of a standard polymer.

Single Macromolecule Nanomechanical Design: Poly(2-hydroxyethyl methacrylate-g-ethylene glycol) Graft Copolymers of Varying Architecture

With the advent of nanotechnology, the behavior of individual polymer chains is increasingly being studied due to their potential to act as molecular springs, switches, sensors, shock absorbers, and motors. Single molecule force spectroscopy (SMFS) or “tensile testing” is a powerful technique that is fast enabling rational nanomechanical design of synthetic polymers for such applications.1-3 Recently, we reported the synthesis and characterization of a series of poly(2-hydroxyethyl methacrylate-g-ethylene glycol) or poly(HEMA-g-EG) neutral graft copolymers of varying macromolecular architecture with such functions in mind.3,4 For accurate SMFS experiments, a number of experimental factors were addressed,3,4 including (1) end-functionalization for strong and specific end-tethering to a planar substrate, (2) high enough molecular weight (preferably ∼100 kg/ mol) to enable long enough extensions beyond the nonspecific surface forces regime and clear observation of nanomechanical profiles, and (3) verification of low enough grafting densities after chemisorption to ensure probing of single molecules. The graft copolymers studied here were also designed to be water-soluble since aqueous solutions are typically much easier to work with than organic solvents in current nanomechanical devices and also, in the longer term, to enable the use of such polymers for biomedical applications. SMFS on poly(HEMA-g-EG)120K in aqueous solution was reported by us previously (Figure 1).3 The numerical subscript in the abbreviated polymer name label (referred to in the previous sentence) is the numberaverage molecular weight, Mn, of the graft copolymer in g/mol (as determined by 1H nuclear magnetic resonance (NMR)) “K” is an abbreviation for 1000. This particular graft copolymer had a poly(ethylene glycol) or PEG side-chain molecular weight, MWPEG, of 2080K, an average number of PEG chains per PHEMA (poly(2-hydroxyethyl methacrylate)) chain, NPEG, of ∼8, corresponding to a 1% molar ratio of PEG to HEMA (graft density), and a number-average degree of polymerization ratio of EG (ethylene glycol) to HEMA (2hydroxyethyl methacrylate), DPn,EG/DPn,HEMA, of 0.4. Poly(HEMA-g-EG)120K behaved similar to an extensible freely jointed chain5 with a statistical segment length, a, between 0.5 and 1.0 nm and segment elasticity, ksegment, between 5 and 15 N/m, both of which were largely insensitive to solution ionic strength. This relatively low value of the resisting force to extension suggested minimal noncovalent intramolecular interactions and that the PEG side chains were quite effective in causing local expansion of the PHEMA backbone and overcoming hydrophobic collapsing forces between the HEMA methyl groups. In this paper, we report the single molecule nanomechanical properties of a number of poly(HEMA-g-EG) graft copolymers with varying macromolecular architecture, in particular with DPn,EG/DPn,HEMA between 0 (PHEMA) and 1.8. Characterization data and corresponding schematics of the architecture of these polymers are given in Figure 2 of ref 4.

Survey on new printing ink pigments on the US market

Lignopolymers are a new class of polymer additives with the capability to be used as dispersants in cementitious pastes. Made with kraft lignin cores and grafted polymer side-chains, the custom-synthesized lignopolymers were examined in terms of the molecular architecture for viscosity reducing potential in inert model suspensions. Lignin–poly(acrylic acid) (LPAA) and lignin–polyacrylamide (LPAm) have been found to vary the rheology of magnesium oxide (MgO) suspensions based on differences in chain architecture and particle–polymer interactions. A commercial comb-polymer polycarboxylate ester was compared to LPAA and LPAm at 2.7 mg/mL, a typical dosage for cement admixtures, as well as 0.25 mg/mL. It was found that LPAm was a more effective viscosity reducer than both LPAA and the commercial additive at low concentrations, which was attributed to greater adsorption on the MgO particle surface and increased steric dispersion from PAm side-chain extension. The influence of chain adsorption and grafted side-chain molecular weight on rheology was also tested.

Dependence of the peptide amide III vibration on the phi dihedral angle.

Dependence of the peptide amide III vibration on the phi dihedral angle.

Solution Properties of Polymacromonomers Consisting of Polystyrene V. Effect of Side Chain Length on Chain Stiffness

Light scattering and viscosity measurements were made on cyclohexane and toluene solutions of a series of polymacromonomer samples consisting of polystyrene with 65 monomer units in each side chain to determine the z-average mean-square radius of gyration ‹s2›z and the intrinsic viscosity [η] as functions of the weight average molecular weight in a range from 2.9×105 to 8.6×106. The theta temperature for the polymacromonomer in cyclohexane was determined to be 34.5°C. The ‹s2›z data in this solvent at 34.5°C and toluene at 15°C (a good solvent) were quantitatively described by the wormlike chain with λ−1 (the Kuhn segment length)=36 nm and ML (the molecular weight per unit contour length)=25000 nm−1 in the former and with λ−1=75 nm and ML=25000 nm−1 in the latter. The molecular weight dependence of [η] in each solvent was also explained by this model chain when the end effect arising from side chains near the main-chain ends was taken into account. The above λ−1 values in the two solvents and the previous estimates for polystyrene polymacromonomers with shorter side chains were used to examine the dependence of the backbone stiffness on side chain length. It was found that λ−1 increases almost linearly with the side-chain molecular weight for both solvents but with a larger slope in toluene than in cyclohexane.

Density-Branching Relationships for LLDPE

Abstract Most commercially available LLDPE's are heterogeneous in the solid state, consisting of separate crystalline and amorphous phases. The crystalline phase may be considered as a solid solution of polyethylene itself and a miscible copolymer. This miscible copolymer can contain as little as 4+ branches/1000 C, depending on the comonomer. At higher comonomer contents, phase separation occurs. A semi-empirical relationship to predict densities of miscible copolymers relates the specific volume (reciprocal density) linearly with the degree of branching and the square root of the side chain molecular weight. It appears valid for comonomers from propylene to octene-1. At higher comonomer incorporations, there is no discernible comonomer effect; specific volume varies linearly with branchiness only. This relationship appears valid for comonomers from propylene to octadecene-1 (and their mixtures). It extrapolates to the EPR region. This model is consistent with previously reported studies of polyethylene crystallinity and copolymer phase separation.

Grafting of poly(vinyl pyrrolidone) onto gelatin and its application as synthetic plasma expander

Grafting of N-vinyl pyrrolidone onto gelatin is reported using α,α'-azobisisobutyronitrile as initiator. The effects of various variables like initiator concentration, monomer concentration, time and temperature are reported. These variables appreciably affect the percentage grafting, grafting efficiency and molecular weight of the grafted chain. The graft copolymers were characterized by i.r. spectroscopy and ninhydrin tests. Sulphathiazole was coupled to these graft copolymers using a diazotization technique. Blood compatibility of these graft copolymers of different side chain molecular weight was found to be satisfactory.

Thermal and swelling properties of polystyrene‐polyolefin blends

AbstractModel blends of glassy amorphous polystyrene and each of four different crystallizable and rubbery polyolefins of varying side‐chain molecular weight (polyethylene, polypropylene, poly(1‐butene), poly (4‐methyl‐1‐pentene)) have been prepared by melt extrusion of the polymeric components. Density measurements, differential scanning calorimetry (DSC), swelling measurements, and X‐ray diffraction have been performed on the extruded fibers. In all cases, over the entire range of blend composition, the polymeric blends are immiscible and incompatible. The DSC measurements indicated that the polystyrene Tg was not decreased after blending and that the small reductions in the crystallinity and melting point of the respective polyolefins was best explained by thermal and kinetic interference with homo‐crystallization of the respective polyolefins in the blends. The volumetric swelling and gravimetric sorption of n‐hexane in the various blends increased monotonically with polystyrene content. The companion experiments, relating axial swelling with polystyrene content, indicated that this particular mode of distension actually decreased with increasing polystyrene content. The composite results, including DSC, X‐ray, density, volumetric swelling and axial swelling suggest that the polystyrene phase is essentially microfibrillar and oriented in the direction of extrusion.