Average Copolymer Composition Research Articles

Modeling of the Copolymerization of Propylene with 1‐Hexene to Predict the Copolymer Molecular Weight and Composition

AbstractA detailed mathematical model of the propylene‐1‐hexene copolymerization based on the two‐dimensional probability generation function technique is developed. It calculates the joint molecular weight‐copolymer composition distribution (MWD‐CCD) of the copolymer, as well as the average copolymer composition distribution, the molecular weight distribution (MWD), the copolymer composition distribution (CCD), average molecular weights and composition, and yield. The parallelized execution of the model code allows for obtaining the different copolymer microstructure distributions efficiently. The model allows for reaching a thorough understanding of the copolymer microstructure under different operating conditions of a semibatch reactor. It also has the potential to become a powerful tool for selecting operating conditions to obtain a material with target molecular properties.

An automated recipe generator for semi-batch solution radical copolymerization via comprehensive stochastic modeling and derivative-free algorithms

• Comprehensive stochastic modeling of semibatch starved-feed radical copolymerization. • Model used to optimize system while maintaining starved-feed features. • Nonlinear dosing strategy developed for monomer, comonomer, and initiator feeds. • New strategy experimentally assessed by measuring evolution of copolymer properties. • Strategy scaled-up to produce a uniform product while greatly reducing reaction time. Knowledge of the average composition and molecular weights of copolymers containing functional groups is often not enough to ensure product quality, as the distribution of the reactive moieties among the chains affects performance. This work couples a kinetic Monte Carlo model, previously verified as providing an accurate description of the semi-batch radical solution copolymerization of butyl methacrylate with 2-hydroxyethyl methacrylate under constant-feed higher-temperature conditions, with an optimization procedure designed to maintain the robust features of starved-feed operation (with no on-line measurements of reactant concentrations or polymer properties) while reducing batch time and keeping product properties at target values. The optimizer calculated piece-wise time-varying dosing strategies for monomer, comonomer, and initiator feeds that reduced reaction time by 75% while improving the uniformity of the product molecular weight, composition, and non-functional fraction. The strategy was successfully tested in a 1 L lab-reactor, and then scaled to a larger test system of 5 L to demonstrate the feasibility of significantly reducing the total reaction time while simultaneously improving the quality of the resin.

Fractionation of microbial populations in a PHA accumulating mixed culture and associated PHA content and composition

The uniformity of PHA composition and content across groups of organisms in mixed cultures was considered. An activated sludge microbial community, with an average PHA content of 20wt%, was fractioned by Percoll assisted buoyant density separation. The microbial community in the two principal fractions was characterised using amplicon pyrosequencing. While organisms were common to both fractions, the relative abundances of species were found to be different between the two fractions. The average PHA content in one of the fractions was found to be higher (24wt%) than the other (16wt%); separation was considered to be in part driven by the density difference associated with PHA content, but also by other factors such as cell dimension and cellular morphology. But while differences in PHA content were observed, the PHA composition in both fractions was found to be approximately the same (43–44mol% HV), which shows that distinct groups of microbial populations within mixed cultures may generate PHA with similar average copolymer composition.

Improved kinetic Monte Carlo simulation of chemical composition-chain length distributions in polymerization processes

Composite binary trees are introduced for an improved kinetic Monte Carlo (kMC) calculation of chemical composition-chain length distributions (CC-CLDs) in polymerization processes, such as the bivariate copolymer composition-CLD (CoC-CLD). For the calculation of the CC-CLD, each leaf node of the main tree, which reflects the number of macromolecules with a given chain length, serves as a root node for a sub-tree containing information on the CC distribution for the macromolecules with the selected chain length. For low maximum chain lengths of 1000, the improvement consists already in a reduction of the kMC operations by a factor between 103 and 106. The approach is illustrated for the calculation of the CoC-CLD in free and atom transfer radical copolymerization of methyl methacrylate and styrene while accounting for potential diffusional limitations. Main focus is on the capability of the algorithm to ensure an accurate calculation of the average copolymer composition including high chain lengths.

A new general approach to determine more accurate comonomer reactivity ratios in controlled/living radical copolymerization systems

In controlled/living radical copolymerization (atom transfer radical copolymerization in this study) and in any other living chain-growth copolymerization, the possible preferential addition of one of the comonomers onto the (macro)initiator-derived (macro)radical can affect the copolymer composition, especially at low conversion; this results in inaccurate comonomer reactivity ratio estimation by the classic approach. A new general approach is introduced in this article, which allowed us to exclude the influence of the possible preferential addition of one of the comonomers onto the (macro)initiator-derived (macro)radical on the copolymer composition at any conversion. According to this approach, copolymer chain grown during time t (t ≠ 0) is considered to be, in fact, the macroinitiator terminated with one of the comonomers under study, which will further grow during the time interval Δt′ = t′ − t [where any reaction time t′ is considered to be grater than reaction time t, i.e. t′ > t] from a comonomer mixture with composition of f(t) [where f(t) is the molar ratio of comonomer i to comonomer j in the comonomer mixture] at time t. In such a situation, it is possible to obtain individual comonomer conversions [xi(Δt′) and xj(Δt′)], the overall comonomer conversion [xov(Δt′)], and the cumulative average copolymer composition for the copolymer formed during Δt′, from which more accurate comonomer reactivity ratios can be calculated by the various low- or high-conversion methods, depending on the overall comonomer conversion. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Composition effects on ethylene/propylene copolymers studied by GPC-MALS and GPC-IR

Copolymer composition and comonomer distribution along the polymer chains are important to determine the properties and the final usefulness of the polymer. There are several ways to study directly or not directly such comonomer distribution because it has a big effect on different kind of properties. GPC-MALS (multi-angle light scattering coupled to size exclusion chromatography), GPC-IR (size exclusion chromatography with an IR detector), CRYSTAF-TREF (crystallization analysis fractionation-temperature rising elution fractionation) or NMR are very common used techniques to obtain such kind of knowledge. In this work several ethylene/propylene copolymers in the whole composition range are characterized using NMR, GPC-IR and GPC-MALS. Average copolymer composition was obtained by 13C-NMR and by IR, and a linear correspondence between both results was found. GPC-IR allows to study the percentage of ethylene for each M w and to check that incorporation of ethylene is done uniformly over the entire range of molecular weights, while the incorporation of propylene presents heterogeneity in the incorporation. GPC-MALS characterization allows the q shape parameter determination and quantification of the effect that the second monomer introduces as impediment to adopt the random coil distribution.

Atom transfer radical homo‐ and copolymerization of styrene and methyl acrylate initiated with trichloromethyl‐ terminated poly(vinyl acetate) macroinitiator: A kinetic study

AbstractAtom transfer radical bulk copolymerization of styrene (St) and methyl acrylate (MA) initiated with trichloromethyl‐terminated poly(vinyl acetate) macroinitiator was performed in the presence of CuCl/PMDETA as a catalyst system at 90°C. Linear dependence of ln[M]0/[M] versus time data along with narrow polydispersity of molecular weight distribution revealed that all the homo‐ and copolymerization reactions proceed according to the controlled/living characteristic. To obtain more reliable monomer reactivity ratios, the cumulative average copolymer composition at moderate to high conversion was determined by 1H‐NMR spectroscopy. Reactivity ratios of St and MA were calculated by the extended Kelen‐Tudos (KT) and Mao‐Huglin (MH) methods to be rSt = 1.018 ± 0.060, rMA = 0.177 ± 0.025 and rSt = 1.016 ± 0.053, rMA = 0.179 ± 0.023, respectively, which are in a good agreement with those reported for the conventional free‐radical copolymerization of St and MA. Good agreement between the theoretical and experimental composition drifts in the comonomer mixture and copolymer as a function of the overall monomer conversion were observed, indicating that the reactivity ratios calculated by copolymer composition at the moderate to high conversion are accurate. Instantaneous copolymer composition curve and number‐average sequence length of comonomers in the copolymer indicated that the copolymerization system tends to produce a random copolymer. However, MA‐centered triad distribution results indicate that the spontaneous gradient copolymers can also be obtained when the mole fraction of MA in the initial comonomer mixture is high enough. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Effect of nanoclay and macroinitiator on the kinetics of atom transfer radical homo- and copolymerization of styrene and methyl methacrylate initiated with CCl 3-terminated poly (vinyl acetate) macroinitiator

Effect of nanoclay on the kinetics of atom transfer radical bulk homo- and copolymerization of styrene (St) and methyl methacrylate (MMA) initiated with CCl 3-terminated poly (vinyl acetate) macroinitiator at 90 °C was investigated. CuCl/PMDETA was used as a catalyst system. Results showed that nanoclay significantly enhances the homopolymerization rate of MMA. It was attributed to the activated conjugated C C bond of MMA monomer via interaction between the carbonyl group of MMA monomer and the hydroxyl moiety (Al O H) of nanoclay as well as to the effect of nanoclay on the dynamic equilibrium between the active (macro)radicals and dormant species. Homopolymerization rate of St (a noncoordinative monomer with nanoclay) decreased slightly in the presence of nanoclay. It could be explained by inserting of a portion of macroinitiator into the clay galleries, where no sufficient St monomer exists due to the low compatibility or interaction of St monomer with nanoclay to react with the macroinitiator. Controlled/living characteristic of all the reactions were confirmed by GPC results. More reliable reactivity ratios of the St and MMA in the presence of nanoclay were calculated by using the cumulative average copolymer composition at the moderate to high conversion to be r St = 0.290 ± 0.082, r MMA = 0.443 ± 0.093 (extended Kelen–Tudos method) and r St = 0.293 ± 0.071, r MMA = 0.447 ± 0.080 (Mao–Huglin method). Results indicated that the rate of incorporation of MMA comonomer into the copolymer increases in the presence of nanoclay, verifying the existence of interaction between the carbonyl group of MMA comonomer and the hydroxyl moiety of nanoclay. It was found that in the presence of nanoclay, tendency of the random copolymerization of St and MMA toward an alternating copolymerization increases.

Kinetic study of atom transfer radical homo- and copolymerization of styrene and methyl methacrylate initiated with trichloromethyl-terminated poly(vinyl acetate) macroinitiator

Atom transfer radical bulk copolymerization of styrene (St) and methyl methacrylate (MMA) was performed in the presence of CuCl/PMDETA as a catalyst system and trichloromethyl-terminated poly(vinyl acetate) telomer as a macroinitiator at 90°C. The overall monomer conversion was followed gravimetrically and the cumulative average copolymer composition at moderate to high conversion was determined by 1H NMR spectroscopy. Reactivity ratios of St and MMA were calculated by the extended Kelen–Tudos (KT) and Mao–Huglin (MH) methods to be rSt=0.605±0.058, rMMA=0.429±0.042 and rSt=0.602±0.043, rMMA=0.430±0.032, respectively, which are in good agreement with those reported for the conventional free-radical copolymerization of St and MMA. The 95% joint confidence limit was used to evaluate accuracy of the estimated reactivity ratios. Results showed that in the controlled/living radical polymerization systems such as ATRP, more reliable reactivity ratios are obtained when copolymer composition at moderate to high conversion is used. Good agreement between the theoretical and experimental composition drifts in the comonomer mixture and copolymer as a function of the overall monomer conversion was observed, indicating the accuracy of reactivity ratios calculated by copolymer composition at the moderate to high conversion. Instantaneous copolymer composition curve and number-average sequence length of comonomers in the copolymer indicated that the copolymerization system tends to produce a random copolymer.

Industrial SBR Process: Computer Simulation Study for Online Estimation of Steady‐State Variables Using Neural Networks

AbstractThis work investigates the industrial production of styrene‐butadiene rubber in a continuous reactor train, and proposes a soft sensor for online monitoring of several processes and polymer quality variables in each reactor. The soft sensor includes two independent artificial neural networks (ANN). The first ANN estimates monomer conversion, solid content, polymer production, average particle diameter, and average copolymer composition; the second ANN estimates average molecular weights and average branching degrees. The required ANN inputs are: (i) the reagent feed rates into the first reactor and (ii) the reaction heat rate in each reactor. The proposed ANN‐based soft sensor proved robust to several measurement errors, and is suitable for online estimation and closed‐loop control strategies.magnified image

Determining the composition and microstructure of ethylene–propylene copolymers by pyrolysis–gas chromatography

The average composition and detailed microstructure of copolymers of ethylene and propylene have been studied by pyrolysis–gas chromatography (Py–GC), using a statistical modeling approach to analyze the data. The trimer distribution obtained from Py–GC is used to infer monomer arrangement information, which is quantified in terms of a number-average sequence length for each monomer. These values are used to define the microstructure and to calculate the average composition. Compared with other available techniques, Py–GC provides a simple, quick and reliable approach to study the microstructure and composition of polyolefin copolymers. Details of this Py–GC method are discussed, including an examination of its advantages and disadvantages, and a summary of the qualitative and quantitative analysis aspects of this approach is presented. The combination of a statistical modeling approach with Py–GC to study copolymer composition and microstructure allows one to investigate the complex problem of monomer arrangement in copolymers using a widely available analytical technique. We expect that with further advances in separation technology, especially two-dimensional gas chromatography (GC × GC), research of this type will be become increasingly accurate and reproducible in the near future.

Continuous emulsion copolymerization of acrylonitrile and butadiene: Computer simulation study for improving the rubber quality and increasing production

This theoretical article investigates an industrial emulsion copolymerization of acrylonitrile (A) and butadiene (B), for the production of grades BJLT and AJLT of a nitrile rubber (NBR). The simulated process involves a train of eight continuous stirred-tank reactors operating at 10 °C. The product quality is determined by its molecular structure (average copolymer composition, average molecular weights, and average level of branching), and by its final latex characteristics (number particle concentration and number-average particle diameter). The mathematical model by Vega et al. [Vega, J. R., Gugliotta, L. M., Bielsa, R. O., Brandolini, M. C., & Meira, G. R. (1997). Emulsion copolymerization of acrylonitrile and butadiene, mathematical model of an industrial reactor. Industrial and Engineering Chemistry Research, 36, 1328] for the semibatch process was extended to investigate three alternative steady-state (SS) operations of a continuous reactor train. When all the reagents are fed into the first reactor (Normal SS), then a deteriorated quality compared with respect to the equivalent batch process is produced (with increased polydispersities and degrees of branching). This can be improved by admitting intermediate feeds of A and chain transfer agent (CTA) along the train. If in addition, constant B feeds are admitted, then it is possible to eliminate the compositional drift, to generate predetermined profiles of the average molecular weights, and to increase the rubber production by over 10% with respect to the Normal SS. The best improvements were observed for grade AJLT.

Graft Copolymers of Poly(methyl methacrylate) and Polyamide-6: Synthesis by Reactive Blending and Characterization

Reactive blending is used as a tool for the synthesis of graft copolymers of poly(methyl methacrylate) and polyamide-6 (PMMA-g-PA). The grafting reaction occurs between the amino end group of PA and glutaric anhydride units randomly distributed along the PMMA backbone. The anhydride units are formed by thermal treatment (typically above 180 °C) of a precursor PMMA bearing a low fraction of methacrylic acid units (5 or 10 mol %). With this method, it is possible to control the amount of anhydride units without degradation or cross-linking of the PMMA chains. The resulting blends with PA are characterized by size exclusion chromatography in benzyl alcohol at 130 °C and selective extraction of ungrafted PMMA chains. Combining these techniques, we were able to estimate the fraction and the average composition of the graft copolymers synthesized in situ during the blending process. High fractions of graft copolymer (35−75 wt %) are obtained in all the blends studied in this work. A higher amount of graft copolymer is obtained by increasing the amount of PA in the blend or the anhydride content on a functionalized PMMA. Optimum grafting is also influenced by the remaining acid groups on the PMMA chain. These groups are expected to contribute to the reversible interactions (hydrogen bonding) between PMMA and PA at the interface.

Copolymerization of N‐vinylcaprolactam and glycidyl methacrylate: Reactivity ratio and composition control

AbstractFree‐radical copolymerizations of N‐vinylcaprolactam (VCL) and glycidyl methacrylate (GMA) were investigated to synthesize temperature‐responsive reactive copolymers with minimized compositional heterogeneity. The average copolymer composition was determined by Fourier transform infrared and nuclear magnetic resonance techniques. The reactivity ratios for VCL and GMA were found to be 0.0365 ± 0.0009 and 6.44 ± 0.36 by the Fineman–Ross method and 0.039 ± 0.006 and 6.75 ± 0.29 by the Kelen–Tudos method, respectively. When prepared by batch polymerization, VCL–GMA copolymers had a highly heterogeneous composition and fractions of different solubilities in water. The use of a gradual feeding technique, which included the sequential addition of more reactive GMA monomer into the reaction, yielded copolymers with much more homogeneous composition. The produced copolymers with 0.9 and 0.11 fractional GMA contents preserved their temperature‐responsive properties and precipitated from aqueous solutions when the temperature exceeded 31 °C. The GMA units in the VCL–GMA copolymers were capable of reacting with amino end‐functionalized poly(ethylene oxide) at room temperature to produce poly(N‐vinylcaprolactam)–poly(ethylene oxide) graft copolymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 183–191, 2006

Analysis of molecular weight distributions of styrene‐methyl methacrylate copolymers using size exclusion chromatography data

AbstractSize exclusion chromatography (SEC) is a common method for the determination of molecular weight distributions (MWD) of polymers. Using appropriate normalization procedures, MWD data may be put in a form suitable for the description by different theoretical distribution functions. In this paper such a procedure is described and applied to a model system. Statistical copolymers of styrene and methyl methacrylate (SMMA) of different compositions were synthesized by radical copolymerization in a batch isothermal reactor with toluene as solvent and azobisisobutyronitrile as initiator. Copolymer MWDs were obtained by SEC and average copolymer composition by elemental analysis. MWDs of SMMA copolymers were correlated with the lognormal, Flory, Schulz, and Tung theoretical function. The best match between experimental and calculated data was obtained by the Schulz distribution. The α‐parameter of Schulz's function was related to the average molecular weight and showed its maximum at the midpoint of the copolymer composition range, in connection with the observed minimal copolymerization rate. The variation of the b‐parameter was found to be less pronounced; the parameter was related to the polydispersity index. This feature indicated that there was no significant change in the copolymerization reaction mechanism throughout the entire copolymer composition range.

Modeling of Ethylene‐Norbornene Copolymer Microstructure in Solution Polymerization with Homogeneous Metallocene Catalysts

AbstractSummary: The microstructure of ethylene‐norbornene copolymer produced in solution polymerization is analyzed through kinetic modeling and experiments using homogeneous rac‐Et(1‐indenyl)2ZrCl2/methylaluminoxane catalyst in toluene at 70 °C. The sequence distribution function and average chain length equations are derived for terminal model and penultimate model. The model simulations show that both models provide similar predictions of average copolymer composition, especially at low norbornene concentration in the copolymer. However, at higher norbornene concentrations the penultimate model yields much better predictions of norbornene sequence length distribution than the terminal model. The terminal model has been inadequate in describing the copolymerization rate, whereas the penultimate model yields excellent predictions of rate behavior. The model calculations also indicate that at norbornene concentration in the copolymer larger than about 10 mol‐%, the maximum ethylene block length is smaller than 70, prohibiting the formation of crystalline copolymer.Ethylene sequence distribution curves at different mol‐% of norbornene in copolymer.magnified imageEthylene sequence distribution curves at different mol‐% of norbornene in copolymer.

Association of cationic surfactants with maleic acid copolymers: Dependence of binding on the nature of the neutral comonomer unit

Isotherms of binding of dodecylpyridinium chloride (DPC) and cetylpyridinium chloride (CPC) by copolymers of maleic acid (MA; degree of neutralization=1) with methyl methacrylate (MMA), styrene (St), and vinyl acetate (VA) were determined at various salt concentrations by using the potentiometric technique. The average composition of copolymers corresponds to designations MA(MMA) 3, MASt, and MAVA. Very different binding behavior has been found. The cooperativity parameter, u, for binding to MA(MMA) 3 is the lowest and displays no dependence on ionic strength, which is a consequence of significant hydrophobic polymer–surfactant interactions. Isotherms for the DPC/MASt system display a two-step binding mechanism, which could not be clearly identified in the CPC/MASt case, presumably due to interference of surfactant micellization with the second step. It is proposed that the first step of binding in DPC/MA(MMA) 3 and in DPC/MASt solutions is of electrostatic origin, as is the second step in DPC/MASt. On the contrary, the second step in DPC/MA(MMA) 3 is mostly due to hydrophobic interactions of surfactant hydrocarbon tails with the predominantly uncharged DPC/MA(MMA) 3 complex. MAVA solutions display the highest critical aggregation concentration (cac) values, which show a slight decreasing trend with increasing ionic strength. The very compact form of the MAVA copolymer at high salt content was responsible for this.

The effect of chemical heterogeneity on the properties of statistical copolymers: the conductivity of poly(aniline‐co‐2‐bromoaniline)

AbstractChemical heterogeneity can influence the properties of statistical copolymers. It is shown that any integral property of a copolymer will depend on the chemical heterogeneity if such a property is a non‐linear function of copolymer composition. This is illustrated by means of the conductivity of copolymers of aniline and 2‐bromoaniline. The monomer reactivity ratios of this monomer pair are rA (aniline) = 0.94 and rB (2‐bromoaniline) = 0.31. The dependence of conductivity on the copolymer composition is non‐linear. Consequently, the conductivity depends on the compositional distribution, ie on the extent of chemical heterogeneity. Heterogeneous high‐conversion copolymers have lower conductivity than corresponding relatively homogeneous low‐conversion copolymers. The change in the average copolymer composition with increasing conversion is demonstrated for a copolymerization mixture containing 30 mol% aniline. The conductivity decreases at the same time as the chemical heterogeneity of the copolymer develops. The change in the average copolymer composition alone cannot explain the observed conductivity decrease. The conductivity is dependent not only on average composition but also on the chemical composition distribution. Copyright © 2004 Society of Chemical Industry

Surface micelle formation of polystyrene-b-poly(2-vinyl pyridine) diblock copolymer at air-water interface

We have studied the surface micelle formation of polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP) at the air-water interface. A series of four PS-b-P2VPs were synthesized by anionic polymerization, keeping the PS block length constant (28 kg/mol) and varying the P2VP block length (1, 11, 28, or 59 kg/mol). The surface pressure-area (π-A) isotherms were measured and the surface morphology was studied by atomic force microscopy (AFM) after Langmuir-Blodgett film deposition onto silicon wafers. At low surface pressure, the hydrophobic PS blocks aggregate to form pancake-like micelle cores and the hydrophilic P2VP block chains spread on the water surface to form a corona-like monolayer. The surface area occupied by a block copolymer is proportional to the molecular weight of the P2VP block and identical to the surface area occupied by a homo-P2VP. It indicates that the entire surface is covered by the P2VP monolayer and the PS micelle cores lie on the P2VP monolayer. As the surface pressure is increased, the π-A isotherm shows a transition region where the surface pressure does not change much with the film compression. In this transition region, which displays high compressibility, the P2VP blocks restructure from the monolayer and spread at the air-water interface. After the transition, the Langmuir film becomes much less compressible. In this high-surface-pressure regime, the PS cores cover practically the entire surface area, as observed by AFM and the limiting area of the film. All the diblock copolymers formed circular micelles, except for the block copolymer having a very short P2VP block (1 kg/mol), which formed large, non-uniform PS aggregates. By mixing with the block copolymer having a longer P2VP block (11 kg/mol), we observed rod-shaped micelles, which indicates that the morphology of the surfaces micelles can be controlled by adjusting the average composition of block copolymers.

Synthesis and characterization of hydrophobically modified polyacrylamides and some observations on rheological properties

Hydrophobically modified polyacrylamide (PAM) polymers were synthesized by means of an aqueous micellar copolymerization, the di-alkyl substituted acrylamides di- n-propylacrylamide (DPAM) and di- n-octylacrylamide (DOAM) being used as hydrophobic comonomers. The number of hydrophobic blocks was varied using three different comonomer contents ( f=1, 3 and 5 wt.%). The length of hydrophobic blocks, i.e. the number of hydrophobes per micelle, N H, was controlled by the sodium dodecyl sulphate surfactant concentration. The effect of the type of hydrophobic comonomer and the number and length of hydrophobic units on the composition of the copolymer and its solubility and rheological properties were studied. The results indicate that the average copolymer composition is independent of the degree of conversion and surfactant concentration. Solubility and rheological measurements lead to a number of conclusions. First, DPAM is a weak hydrophobic monomer, all DPAM/AM (AM=acrylamide) copolymers being water soluble. Second, there is no strong hydrophobic interaction between DPAM units, in particular for low polymer concentration and N H, and thus no strong associative thickening behaviour. Third, DOAM is a strong hydrophobic comonomer. Incorporation of a small amount of DOAM into PAM causes a dramatic enhancement in viscosity due to hydrophobic interactions. The properties of the copolymers are strongly dependent on the N H values, most DOAM/AM copolymers being insoluble in water.