Composition Drift Research Articles

Correction: Avoiding compositional drift during the RAFT copolymerization of N-(2-hydroxypropyl)methacrylamide and N-acryloxysuccinimide: towards uniform platforms for post-polymerization modification

Correction for ‘Avoiding compositional drift during the RAFT copolymerization of N-(2-hydroxypropyl)methacrylamide and N-acryloxysuccinimide: towards uniform platforms for post-polymerization modification’ by John Moraes et al., Polym. Chem., 2015, 6, 3245–3251.

Control of particle size by feed composition in the nanolatexes produced via monomer-starved semicontinuous emulsion copolymerization

Conventional batch and semicontinuous emulsion copolymerizations often produce large particles whose size cannot be easily correlated with the comonomer feed compositions, and are to some degree susceptible to composition drift. In contrast, we found that copolymer nanolatexes made via semicontinuous monomer-starved emulsion copolymerizations are featured with an average nanoparticle size being controlled by the feed composition, a high conversion achieved, and a high degree of particle composition uniformity. This was achieved because the rate of particle growth, during nucleation, was controlled by the rate of comonomer addition, and the copolymer composition, surfactant parking area on the particles, and nucleation efficiency determined by the comonomer feed composition. Two model systems, methyl methacrylate/styrene and vinyl acetate/butyl acrylate, with significant differences in water solubility were studied. Monomers were added to the aqueous solution of sodium dodecylsulfate and potassium persulfate at a low rate to achieve high instantaneous conversions.

Estimating Monomer Sequence Distributions in Tetrapolyacrylates

Recently Ting et al. [ACS Macro Lett. 2013, 2, 770−774] described the syntheses of acrylic tetrapolymers with controlled molecular weights and tetramonomer compositions. Relative reactivity ratios of all monomer pairs were determined and used in the Walling–Briggs terminal copolymerization model along with Skeist’s equations to address the expected compositional drift in the monomer feed ratios. The anticipated control of monomer incorporation based on this approach was verified experimentally on several tetrapolyacrylates synthesized by RAFT polymerization, which additionally controlled their molecular weights. Their “new and simple paradigm combining both predictive models provides complementary synthetic and predictive tools for designing macromolecular chemical architectures with hierarchical control over spatially dependent structure–property relationships for complex applications” is extended here to the derivation of expected monad compositions, and diad, triad, and tetrad monomer sequence distributions. These were obtained directly from the comonomer reactivity ratios determined experimentally by Ting et al. Our motivation was twofold: (i) The similar chemical structures of the four acrylate monomers they selected (methyl, 2-carboxyethyl, 2-hydroxypropyl, and 2-propylacetyl acrylate) render the experimental determination of sequence distributions in the resulting tetrapolyacrylates problematic. (ii) Because they are spatially dependent structural parameters, the sequence distributions of monomer diads, triads, tetrads, etc., in co-, tri-, tetrapolymers, etc., are generally expected to correlate more closely with their properties than their overall compositions.

Deterministic Modeling of Copolymer Microstructure: Composition Drift and Sequence Patterns

AbstractA concept of a population balance is applied to study evolving structures of propagating linear copolymer chains. As a result, a general numerical toolbox was developed capable to handle various copolymerization mechanisms utilizing two‐dimensional distributions as means of system description. The method was applied to free radical copolymerization of styrene–acrylonitrile explaining peculiar bimodality in chain length distribution observed for asymmetrical initial monomer ratios.

Preparation and characterization of narrow compositional distribution polyampholytes as potential biomaterials: Copolymers of N‐(3‐aminopropyl)methacrylamide hydrochloride (APM) and methacrylic acid (MAA)

ABSTRACTThis article describes the preparation and solution properties of a series of polyampholytes composed of N‐(3‐aminopropyl)methacrylamide hydrochloride (APM) and methacrylic acid (MAA). In particular, conditions were found where the copolymers could be formed with little or no drift in composition over the course of polymerization to quite high conversions. The compositional drift, common to many copolymerizations, was limited by adjusting the reactivity of MAA through control of its degree of ionization (i.e., pH). As revealed by potentiometric measurements and changes in 1H NMR spectra, the solution pH drifted over the course of some polymerizations. This was ascribed to changes in the pKa values of the ammonium and carboxylate groups upon incorporation in the copolymer. The pH drift led to a change in degree of MAA ionization, and hence the relative reactivities of APM and MAA, but this effect could be minimized by using a buffer. Precipitation, which occurred during some polymerizations, could be prevented, in some cases, by the addition of salt or an organic cosolvent. Even in cases where precipitation could not be prevented, it was found that the copolymer was still formed with minimal compositional drift. The solubility of the resulting polyampholytes in aqueous solution was found to depend on their composition, as well as pH, ionic strength and temperature. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 353–365

On the causes of rising gross ecosystem productivity in a regenerating clearcut environment: leaf area vs. species composition.

Clearcutting a forest ecosystem can result in a drastic reduction of stand productivity. Despite the severity of this disturbance type, past studies have found that the productivity of young regenerating stands can quickly rebound, approaching that of mature undisturbed stands within a few years. One of the obvious reasons is increased leaf area (LA) with each year of recovery. However, a less obvious reason may be the variability in species composition and distribution during the natural regeneration process. The purpose of this study was to investigate to what extent the increase in gross ecosystem productivity (GEP), observed during the first 4 years of recovery in a naturally regenerating clearcut stand, was due to (i) an overall expansion of leaf area and (ii) an increase in the canopy's photosynthetic capacity stemming from either species compositional shifts or drift in physiological traits within species. We found that the multi-year rise in GEP following harvest was clearly attributed to the expansion of LA rather than a change in vegetation composition. Sizeable changes in the relative abundance of species were masked by remarkably similar leaf physiological attributes for a range of vegetation types present in this early-successional environment. Comparison of upscaled leaf-chamber estimates with eddy-covariance-based estimates of light-response curves revealed a broad consistency in both maximum photosynthetic capacity and quantum yield efficiency. The approaches presented here illustrate how chamber- and ecosystem-scale measurements of gas exchange can be blended with species-level LA data to draw conclusive inferences about changes in ecosystem processes over time in a highly dynamic environment.

A Detailed Model on Kinetics and Microstructure Evolution during Copolymerization of Ethylene and 1-Octene: From Coordinative Chain Transfer to Chain Shuttling Polymerization

We introduce a theoretical model based upon the kinetic Monte Carlo (KMC) simulation approach capable of quantifying chain shuttling copolymerization (CSP) of ethylene and 1-octene in a semibatch operation. To make a deeper understanding of kinetics and evolution of microstructure, the reversible transfer reaction is first investigated by applying each of the individual catalysts to the reaction media, and the competences and shortcomings of a qualified set of CSP catalysts are discussed based on coordinative chain transfer copolymerization (CCTP) requirements. A detailed simulation study is also provided, which reflects and compares the contributions of chain transfer reversibility and other chain breaking reactions in controlling distribution fashion of molecular weight and chemical composition. The developed computer code is executed to capture developments in dead chain concentration and time-driven composition drift during CCTP. Also, the effect of chain shuttling agent (CSA) on the copolymerization kinetics is theoretically studied by simultaneous activation of both catalysts. In this way, it is attempted to make control over comonomer incorporation in the course of copolymerization. The molecular-level criteria reflecting copolymer properties, i.e., ethylene sequence length distribution and longest ethylene sequence length, as the signature of CSA performance, are virtually simulated in the presence and absence of hydrogen to capture an image on gradient copolymers in CCTP and blocks with gradually changing composition in CSP.

Facile synthesis of tunable alkali soluble latexes

Highly hydrophobic and highly hydrophilic (meth)acrylic monomers were copolymerized in heterophase system via a miniemulsion analogous polymerization technique. The versatility of the approach was demonstrated by the direct synthesis of hydrophobically modified alkali soluble emulsions (HASE) without the use of otherwise commonly required specialty monomers. It was demonstrated that copolymer composition drift during the course of the free radical heterophase polymerization the can be effectively regulated by the initial monomer ratios. This feature was employed to achieve (1) a more even distribution of acid functionalities throughout the growing polymer chains and the corresponding latex particles, (2) improved dissolution behavior upon deprotonation of the acid groups and (3) the possibility to tailor rheological properties at elevated pH values. Highly soluble HASE systems with surprisingly low contents of ionogenic groups and strong thickening effect were synthesized, which can provide beneficial characteristics in the coatings and adhesive sector.

Precise Compositional Control and Systematic Preparation of Multimonomeric Statistical Copolymers.

A comprehensive approach to target exact molecular weights and chemical compositions for multimonomeric statistical copolymers using a new controlled statistics method with reversible addition-fragmentation chain transfer free-radical (RAFT) polymerization is presented. The system chosen to illustrate this procedure is an acrylic quarterpolymer consisting of methyl acrylate, 2-carboxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-propylacetyl acrylate, modeling a well-known macromolecule utilized to deliver poorly water-soluble drugs (hydroxypropyl methylcellulose acetate succinate, HPMCAS). The relative reactivities at 70 °C between monomer pairs were measured and employed to predict the feed ratio necessary for synthesizing well-defined compositions based on the Walling-Briggs model. Application of Skeist's equations addressed compositional drift and anticipated the general monomer incorporation distribution as a function of conversion, which was verified experimentally. This new and simple paradigm combining both predictive models provides complementary synthetic and predictive tools for designing macromolecular chemical architectures with hierarchical control over spatially dependent structure-property relationships for complex applications such as oral drug delivery.

Vaccine effectiveness against laboratory-confirmed influenza hospitalizations among elderly adults during the 2010-2011 season.

Although annual influenza immunization is recommended for adults aged ≥65 years due to the substantial burden of illness, the evidence base for this recommendation is weak. Prior observational studies that examined influenza vaccine effectiveness against nonspecific serious outcomes suffered from selection bias and the lack of laboratory confirmation for influenza infection. The objective of this study was to determine the effectiveness of the 2010-2011 seasonal influenza vaccine against laboratory-confirmed influenza hospitalizations among community-dwelling elderly adults, a serious and highly specific outcome. We conducted a test-negative study of community-dwelling adults aged >65 years in Ontario, Canada. Respiratory specimens collected between 1 December 2010 and 30 April 2011 from patients admitted to acute care hospitals were tested for influenza using nucleic acid amplification techniques. Influenza vaccination was ascertained from physician billing claims through linkage to health administrative datasets. Receipt of the 2010-2011 seasonal influenza vaccine was associated with a 42% (95% confidence interval, 29%-53%) reduction in laboratory-confirmed influenza hospitalizations. Vaccine effectiveness estimates were consistent across age groups, by sex, and regardless of outcome severity, timing of testing, and when considering individuals vaccinated <7 or <14 days prior to admission as unvaccinated. Results of this study will better inform decision making regarding influenza vaccination of elderly adults. Similar analyses are needed annually due to antigenic drift and frequent changes in influenza vaccine composition. The linkage of routinely collected laboratory testing and health administrative data represents an efficient method for estimating influenza vaccine effectiveness that complements prospective studies.

Functional Thin Films Resulting from Parylene–Vinyl Copolymerization

Quantum and kinetic studies of novel materials based on parylene polymers and variously substituted vinyl molecules are presented and discussed. It is demonstrated that the thin films which are the products of the copolymerization reactions can be prepared (i) within the parylene CVD process on active vinyl substrates or (ii) employing the same process but involving an additional source of vinyl molecules transported to the reaction chamber. Both methods lead to differently functionalized microstructures, primarily dominated by the parylene units, while the vinyl molecules appear relatively seldom (depending on the nature of the substituents used). The copolymerization is shown to be independent of penultimate monomers in linear chains and to undergo composition drift within certain scope. Namely, it is found that even a small amount of p-xylylene monomers in feed leads to the formation of long blocks of pure parylene while the substituted vinyl molecules are expected to appear occasionally in chains. Fin...

Copolymerization of methyl methacrylate and vinylbenzyl chloride towards alkaline anion exchange membrane for fuel cell applications

Our previous studies demonstrated great potential of methyl methacrylate and vinylbenzyl chloride based copolymer electrolytes for alkaline fuel cell applications. In this study, a number of factors including polymer composition drift, molecular weight, and polymer crosslinking is investigated to understand their effects and to precisely control the electrolyte properties including conductivity, mechanical strength, and water mass-uptake. This investigation demonstrated a controllable polymerization procedure of poly (methyl methacrylate-co-vinylbenzyl chloride) membrane with tunable and balanced properties, which is promising for the alkaline fuel cell technology.

Suspension Copolymerization of Vinyl Acetate and Methyl Methacrylate in the Presence of Amoxicillin

AbstractThe effects of amoxicillin on the course of vinyl acetate (VAc)/methyl methacrylate (MMA) suspension copolymerizations are analyzed. It is shown that the presence of the drug affects the morphology of the produced particles, although the interfacial tension is insensitive to modification of the drug concentration in the analyzed range (1–3 wt% of the aqueous phase). It is also shown that this drug interacts preferentially with VAc, causing an inhibitory effect on the rate of polymerization and enhancing the characteristic composition drift of VAc/MMA copolymerizations. Finally, it is shown that the presence of the drug leads to significant modifications of the molecular weight distributions of the final polymer material.magnified image

Composition control through pH and ionic strength during acrylic acid/acrylamide copolymerization

AbstractThe possibility of controlling the composition of acrylic acid/acrylamide copolymers by controlling the pH and the ionic strength of the reaction medium is investigated. The reactivity ratios of charged monomers depend on the pH of the medium, acrylic acid is the more reactive monomer below pH 3 and acrylamide above pH 4. The working pH was set at 3.6, a candidate for the crossover point, where no composition drift is expected. Copolymerization kinetics is investigated at this pH at various ionic strengths and a reaction without composition drift up to 80% conversion was achieved. All the chains produced in this reaction contain 30% ± 3% acrylic acid. Copolymer conversions, molecular weights, and composition distributions were measured through Automatic Continuous Online Monitoring of Polymerization (ACOMP) system. The copolymerization data were analyzed by a recent error in variables method (EVM) and reactivity ratios are calculated. The results show that in salt free conditions, the reactivity ratios depend on the ionic monomer concentration (ionic strength) in addition to the pH of the reaction medium. The effect of polyelectrolytic interactions on the reactivity ratios and the resulting composition drift during the reaction, sequence length distribution, and Stockmayer bivariate distribution are discussed in detail. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Cationic Copolyelectrolytes: Online Monitoring of the Synthesis and Subsequent Copolymer Characterization

AbstractKinetics of copolymerization reactions of diallyldimethylammonium chloride (DADMAC) and dimethyl acrylamide (DMA) in aqueous solvent is studied, with highlights on features that control many aspects of the polymeric materials behavior throughout and post‐synthesis. The aim of this study is twofold; first, to offer a method to study the impact of the incorporation of the cationic DADMAC on the composition drift, molecular mass of the copolyelectrolyte, and on the polyelectrolyte behavior by monitoring in real time the copolymerization reactions with a neutral monomer under different conditions. Additionally, it is meant to make the transition toward the next step, controlling the reaction kinetics during designed semi‐batch experiments designed to achieve the average mass and composition distributions desired.

Reactivity ratios, and mechanistic insight for anionic ring-opening copolymerization of epoxides.

Reactivity ratios were evaluated for anionic ring-opening copolymerizations of ethylene oxide (EO) with either allyl glycidyl ether (AGE) or ethylene glycol vinyl glycidyl ether (EGVGE) using a benzyl alkoxide initiator. The chemical shift for the benzylic protons of the initiator, as measured by (1)H NMR spectroscopy, were observed to be sensitive to the sequence of the first two monomers added to the initiator during polymer growth. Using a simple kinetic model for initiation and the first propagation step, reactivity ratios for the copolymerization of AGE and EGVGE with EO could be determined by analysis of the (1)H NMR spectroscopy for the resulting copolymer. For the copolymerization between EO and AGE, the reactivity ratios were determined to be r(AGE) = 1.31 ± 0.26 and r(EO) = 0.54 ± 0.03, while for EO and EGVGE, the reactivity ratios were r(EGVGE) = 3.50 ± 0.90 and r(EO) = 0.32 ± 0.10. These ratios were consistent with the compositional drift observed in the copolymerization between EO and EGVGE, with EGVGE being consumed early in the copolymerization. These experimental results, combined with density functional calculations, allowed a mechanism for oxyanionic ring-opening polymerization that begins with coordination of the Lewis-basic epoxide to the cation to be proposed. The calculated transition-state energies agree qualitatively with the observed relative rates for polymerization.

Water-Soluble “Poly(propylene oxide)” by Random Copolymerization of Propylene Oxide with a Protected Glycidol Monomer

Hydrophilic, functional poly(propylene oxide) (PPO) copolymers were prepared by anionic random copolymerization of propylene oxide with the protected glycidyl derivative ethoxy ethyl glycidyl ether (EEGE). The monobenzyl-protected ethylene glycol initiator 2-(benzyloxy)ethanol was used to initiate the polymerization because it allows for the introduction of hydroxyl groups at both ends of the polymer chain. Acidic deprotection permitted selective removal of the acetal protecting groups in the chain or alternatively orthogonal deprotection of the terminal hydroxyl group by catalytic hydrogenation. A series of narrowly distributed hydroxyl-functional PPO copolymers (Mw/Mn < 1.07–1.25 g mol–1) was obtained with varying composition between 2 and 75% glycerol units and molecular weights in the range of 3000 to 8000 g mol–1. Monomer consumption and compositional drift in monomer feed were studied via 1H NMR kinetics, revealing a slightly tapered structure, but confirmed a distribution of EEGE in the polar PPO-based copolymers. Cloud-point measurements showed temperature-dependent water solubility, with LCSTs in the range of 20 to 70 °C. The study demonstrates that an incorporation of 11% of the hydroxyl-functional, linear glycerol units suffices to obtain functional PPO copolymers that are water-soluble at room temperature.

Combinatorial complexity and compositional drift in protein interaction networks.

The assembly of molecular machines and transient signaling complexes does not typically occur under circumstances in which the appropriate proteins are isolated from all others present in the cell. Rather, assembly must proceed in the context of large-scale protein-protein interaction (PPI) networks that are characterized both by conflict and combinatorial complexity. Conflict refers to the fact that protein interfaces can often bind many different partners in a mutually exclusive way, while combinatorial complexity refers to the explosion in the number of distinct complexes that can be formed by a network of binding possibilities. Using computational models, we explore the consequences of these characteristics for the global dynamics of a PPI network based on highly curated yeast two-hybrid data. The limited molecular context represented in this data-type translates formally into an assumption of independent binding sites for each protein. The challenge of avoiding the explicit enumeration of the astronomically many possibilities for complex formation is met by a rule-based approach to kinetic modeling. Despite imposing global biophysical constraints, we find that initially identical simulations rapidly diverge in the space of molecular possibilities, eventually sampling disjoint sets of large complexes. We refer to this phenomenon as “compositional drift”. Since interaction data in PPI networks lack detailed information about geometric and biological constraints, our study does not represent a quantitative description of cellular dynamics. Rather, our work brings to light a fundamental problem (the control of compositional drift) that must be solved by mechanisms of assembly in the context of large networks. In cases where drift is not (or cannot be) completely controlled by the cell, this phenomenon could constitute a novel source of phenotypic heterogeneity in cell populations.

A New, Practical Formulation of the Multicomponent Copolymerization Equation

A general and rigorous new formulation of the multicomponent extension to the Mayo Lewis copolymerization equation is presented based in matrix notation. In contrast to the original Walling and Briggs formulation, which was based on determinants and difficult to apply in practice, this new formulation is explicit, easy to implement, and introduces a natural scaling to the problem. The approach is illustrated with calculation of instantaneous composition and compositional drift with conversion for 4 and 6 monomers.

Downstream changes in spring-fed stream invertebrate communities: the effect of increased temperature range?

Reduced thermal amplitude has been highlighted as a limiting factor for aquatic invertebrate diversity in springs. Moving downstream water temperature range increases and invertebrate richness is expected to change accordingly. In the present study temperature patterns were investigated in seven spring-fed streams, between April 2001 and November 2002, and compared to five run-off-fed streams to assess the degree of crenic temperature constancy. Temperature and physico-chemical characteristics of the water, and food resource levels were measured, and the invertebrate fauna collected at 4 distances (0, 100, 500 m and 1 km) from seven springs in the North and South Islands of New Zealand. Temperature variability was greater for run-off-fed streams than for springs, and increased in the spring-fed streams with distance from the source. Periphyton and physico-chemical characteristics of the water did not change markedly over the 1 km studied, with the exception of water velocity and organic matter biomass, which increased and decreased, respectively. The rate of increase in temperature amplitude differed greatly for the studied springs, probably being affected by flow, altitude, and the number and type of tributaries (i.e., spring- or run-off-fed) joining the spring-fed stream channel. Longitudinal changes in the number and evenness of invertebrate taxa were positively correlated to thermal amplitude (rs = 0.8). Moving downstream, invertebrate communities progressively incorporated taxa with higher mobility and taxa more common in nearby run-off-fed streams. Chironomids and non-insect taxa were denser at the sources. Chironomid larvae also numerically dominated communities 100 and 500 m downstream from the sources, together with Pycnocentria spp. and Zelolessica spp., while taxa such as Hydora sp. and Hydraenidae beetles, the mayflies Deleatidium spp. and Coloburiscus humeralis, and the Trichoptera Pycnocentrodes spp., all had greater abundances 1 km from the sources. In conclusion, water temperature range was highly correlated with number of taxa, although other factors, such as substratum composition, stability and invertebrate drift, may also play an important role in the determination of longitudinal changes in invertebrate community composition and structure along spring-fed streams.