Complexation between poly(methacrylic) and poly(acrylic) acids and star-shaped poly(ethylene glycol) based on pyrogallol

Complex formation between polymethacrylic (PMAA) and polyacrylic acids, and star-shaped poly(ethylene glycol) prepared by ethoxylation of pyrogallol (Pyr–PEG) has been studied viscometrically and by potentiometric titration in water solution. The competitive ability of Pyr–PEG and of the derivatives of the ethoxylation of phenol and hydroquinone in complex formation with PMAA has been compared by UV spectroscopy. Pyr–PEG turns out to be the weakest competitor because of its chemical structure. © 1996 John Wiley & Sons, Inc.     

Association of copolymers of methacrylic acid and 4-vinylpyridine in comparison with an intermacromolecular complex of poly(methacrylic acid) with poly(4-vinylpyridine)

Solution properties of copolymers [C(MA-Py)x] of methacrylic acid and 4-vinylpyridine and intermacromolecular complexes of poly(methacrylic acid) (PMAA) and poly(4-vinylpyridine) (PVP) in the presence or absence of a proton-accepting water-soluble polymer such as poly(ethylene glycol) (PEG) in water/methanol mixed solvent are studied by potentiometric titration, turbidity and viscosity methods. These copolymers behave like polyampholytes and their solubilities are strongly dependent with pH changes. The pH regions where they are precipitated around their isoelectric points are narrower than those of the intermacromolecular complex of PMAA with PVP. The polyampholyte can form an intermacromolecular complex with PEG in acidic solution but this complex is soluble in the medium.     

Studies on interpolymer self-organisation behaviour of protoporphyrin IX bound poly(carboxylic acid)s with complimentary polymers by means of fluorescence techniques

Covalently bound protoporphyrin IX was used as a fluorophore to investigate the interpolymer complex formation between the poly(carboxylic acid)s, PMAA/PAA and poly(N-vinyl pyrrolidone), PVP, poly(ethylene oxide), PEO or poly(ethylene glycol), PEG. Absorption and emission spectral properties of protoporphyrin IX bound to PAA, PMAA and PVP have been studied. Protoporphyrin IX in poly(MAA-co-PPIX) was found to be present in the dimer or higher aggregated form at low pH due to the environmental restriction imposed by the polymer whereas in the case of poly(AA-co-PPIX) and poly(VP-co-PPIX), PPIX exists in monomeric form. The fluorescence intensity and lifetime of PPIX bound to poly(carboxylic acid)s increase on complexation through hydrogen bonding with PVP, PEO and PEG due to the displacement of water molecules in the vicinity of the PPIX. Poly(MAA-co-PPIX) shows longer fluorescence lifetime due to the more compact interpolymer complexation as compared to poly(AA-co-PPIX) due to the enhanced hydrophobicity of PMAA. Poly(VP-co-PPIX) shows a decrease in the fluorescence lifetime on complexation with PMAA or PAA due to the hydrophilic and microgel like environment of the fluorophore bound to PVP. The contrasting behaviour of the same polymer adduct with respect to the site of the fluorophore is interpreted to be due to the solvent structure which determines the environment of the fluorophore.     

Interpolymer complex between poly(ethylene oxide) and poly(carboxylic acid)

An interpolymer complex was prepared by mixing aqueous solutions of poly(ethylene oxide) (PEO) and of a poly(carboxylic acid), i.e., poly(acrylic acid)(PAA), poly(methacrylic acid)(PMAA), or styrene-maleic acid copolymer(PSMA). The complexation mechanism was discussed on the basis of results of such experimental methods as viscosity, potentiometric titration, and turbidimetry. The hydrogen bond is primarily involved in these complexations, but the influence of hydrophobic interaction on complexation can not be ignored. If the degree of dissociation α of carboxylic acid or the degree of polymerization P_n of PEO was perceptibly changed, a stable complex was obtained at about α 0.1 or P_n (PEO) = 40 for PMAA, 200 for PAA. This fact indicates that more than a definite number of binding sites are necessary for a stable interpolymer complex to be formed and that cooperative interaction among active sites plays an important role in complex formation.     

Molecular weight effect on the complexation of poly(methacrylic acid) and poly(ethylene oxide) as studied by high-resolution solid-state C NMR spectroscopy

Complexes of poly(methacrylic acid) (PMAA) and poly(ethylene oxide) (PEO) with different PEO molecular weight were studied by solid-state high-resolution ¹³C NMR spectroscopy, with the emphasis on the PEO molecular weight effect on inter-polymer interaction, morphology and molecular motion. It is found that the crystalline phase of PEO is completely destroyed in the complex. The results of ¹H transverse relaxation times and ¹³C spin-lattice relaxation times indicate that the chain mobility of both PEO and PMAA are greatly restricted by inter-molecular hydrogen-bonding interactions, especially when the molecular weight of PEO is 1500. The bulk structures of the complexes are found to be closely dependent on the molecular weight of PEO. The fraction of “free” PEO segments without forming hydrogen-bonds with PMAA increases with increasing PEO molecular weight.     

Interpolymer complex formation between helical poly(L-proline) and random-coil poly(methacrylic acid) through hydrogen bonding

Interpolymer complex formation between poly(L -proline) (PLP) with helical structure and poly(methacrylic acid) (PMAA) with random-coil structure through hydrogen bonding in aqueous medium has been studied by several experimental techniques, e.g., viscometry, turbidimetry, potentiometry, conductometry, scanning electron microscopy, and x-ray diffraction methods. The decreases in reduced viscosity of the solution on addition of an increasing quantity of PLP to a constant amount of PMAA reveals the formation of a complex between PLP and PMAA. The minimum in reduced viscosity at a unit-mole ratio [PLP]/[PMAA] = 1.0 suggests a 1 : 1 complex formation. A distinct change in the curves for turbidity, pH, and conductance versus [PLP]/[PMAA] supports this conclusion. A scanning electron micrograph for the 1 : 1 PLP–PMAA complexes shows that the PLP/PMAA complex has the shape of entangled long fibers. An x-ray diffraction pattern for the PLP/PMAA complexes gives no diffraction patterns which appear in pure PLP, indicating the destruction of the helical structure of PLP due to the interpolymer complexation. Mixtures of PMAA with poly(γ-hydroxy-L -proline) (PHLP) which has a similar conformation as PLP, but involves intra- or intermolecular hydrogen bonds, has also been investigated by vicometry measurements. The reduced viscosity of a solution of the mixed polymers increases with increasing [PHLP], indicating no complex formation. All the results reveal that the magnitude and the nature of the forces acting in the polymers play an important role in interpolymer complexation.     

Preparation and complexation of an A–B–A type triblock copolymer consisting of helical poly(L-proline) and random-coil poly(ethylene oxide)

By using L -proline N-carboxyanhydride (LPNCA) and amino-group terminated poly(ethylene oxide) (ATPEO), an A–B–A–type [A = poly(L -proline) (PLP), B = poly(ethylene oxide) (PEO)] triblock copolymer (POP) was prepared which is water-soluble. In the POP, A = PLP is helical, and B = PEO is random coil. From the observations of the NMR spectra, specific optical rotation, and x-ray diffraction of the POP, it was found that the PLP component of the POP exists nearly as Form II PLP with trans-configuration, and interferes the crystal growth of PEO component, in solid state. With the addition of PMAA into an aqueous POP solution, dramatic decreases of reduced viscosity and pH are observed until the unit-mole-concentration-ratio (UMCR) [PMAA]/[POP] reaches its value of unity, while a distinct increase in turbidity appears. This shows a 1 : 1 interpolymer complex formation between PMAA and POP in aqueous medium through hydrogen bonding. The curves of viscosity, pH, and turbidity versus UMCR [PMAA]/[POP] show breaks at [PMAA]/[POP] = 0.3, suggesting the selective complexation of PLP component (ca. 30 unit-mol %) of POP with PMAA. The x-ray diffraction curve of the complex POP/PMAA shows entirely no diffraction patterns, indicating that the ordered POP structure (mainly due to that of PLP component) is completely destroyed owing to the complexation between POP and PMAA.     

Interaction between poly(N-vinylpyrrolidone) and poly(acrylic acid)s: Influence of hydrogen and cupric ions on the adduct formation

Interpolymer adduct formation between poly(N-vinylpyrrolidone) (PVP) and poly(methacrylic acid) (PMAA) is mainly due to hydrogen bonding. It is found that the interpolymer adduct formation is enhanced in the presence of Cu(II). A simple turbidity measurement making use of a spectrophotofluorometer is described for the study of the interpolymer adduct formation. Enhanced adduct formation in the presence of Cu(II) is described by the empirical relation d[PAd]/D[PVP] = k × 10^4α[Cu(II)]^α, where PAd represents the interpolymer adduct and α and k are constants. Similar results have been obtained in the case of interpolymer adduct formation between poly(acrylic acid) (PAA) and PVP. In the above expression α signifies the influence of chelation on Cu(II)–PAA/PMAA–PVP-type complex formation and k is the extent of PVP–PAA/PMAA interaction. The enhancement of adduct formation in the presence of Cu(II) is more in PAA than in PMAA. Turbidity and viscosity measurements further indicate that the influence of Cu(II) on interpolymer adduct formation between PVP and PMAA or PAA is more in the case of PAA than PMAA, as PAA is a better chelating ligand. But the extent of adduct formation is more in the case of PMAA in the absence of Cu(II) ions due to hydrophobic interactions exerted by methyl groups.     

Fluorescence probe studies on the complexation between poly(methacrylic acid) and poly(N, N-diethylacrylamide)

The complexation between poly(methacrylic acid) (PMAA) and poly(N, N-diethylacrylamide) (PDEAM) in aqueous phase was studied by UV-vis and fluorescence probe techniques. It was demonstrated that the complexation of PMAA with PDEAM occurs within a pH range of 1-6.5 and along with the complexation, the conformation of PMAA changed from a hypercoiled to a loose coiled form. The complex ratio between the two polymers is 1:1 (PMAA:PDEAM, in monomer unit). Salt effect studies showed that the complexation occurred due to formation of hydrogen bonds between the two polymers. Based upon these conclusions and the "compact micelle-like structure" for PMAA at low pH, a "ladder" model was proposed for the structure of PMAA-PDEAM complex formed at low pH.     

Characterization of poly(carboxylic acid)/poly(ethylene oxide) blends formed through hydrogen bonding by spectroscopic and calorimetric analyses

The solid state of the complex between poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO), and that between poly(methacrylic acid) (PMAA) and PEO formed via hydrogen-bonding was studied by differential-scanning calorimetric (DSC) and by Fourier-transform infrared (FT–IR) spectroscopic measurements. Melting temperature T_m and the degree of the crystallinity X_c of PEO in the systems PAA (or PMAA)/PEO blends obtained from aqueous or dimethyl sulfoxide (DMSO) medium were measured in various unit mol % of PEO ([PEO]100/{[PAA(or PMAA)] + [PEO]}) where [ ] is the unit mole concentration. It was found that 50 unit mol % of PEO is a critical composition, which gives new evidence for the 1 : 1 complex formation between PAA (or PMAA) and PEO. From the FT–IR spectroscopic analysis in conjunction with DSC measurements we also found that the effects of solvent and of hydrophobic interaction (due to the α-methyl group of PMAA) are the important factors controlling the complexation in the solution and solid systems. These factors also affect the crystallization behavior and the microstructure of the PAA (or PMAA)/PEO blend in solid state.     

A Rocket‐Like Encapsulation and Delivery System with Two‐Stage Booster Layers: pH‐Responsive Poly(methacrylic acid)/Poly(ethylene glycol) Complex‐Coated Hollow Silica Vesicles

Rocket‐like vesicles formed are composed of poly(acrylic aicd) (PMAA )/poly(ethylene glycol) (PEG) complex coated hollow silica spheres, and the structure and composition of the vesicles are characterized using TGA, ¹H NMR, FTIR, and TEM. Although only one‐third of EG units of PEG brushes grafted to hollow silica spheres form the complex with PMAA via hydrogen bonding, the first “booster” layer composed of PMAA/PEG complex can provide secure encapsulation of model compound calcein blue under an acidic condition. The second “booster” layer composed of PEG brushes can be formed by changing acidic pH to 7.4 through the disassociation of the PMAA/PEG complex. A higher molecular weight PMAA exhibits a faster disassembly due to the formation of a looser PMAA/PEG complex on the surfaces of hollow silica spheres.

     

Preparation and aggregation behavior of mannose-terminated poly(ethylene glycol)-b-poly(L-leucine) in water

Amphiphilic diblock copolymers composed of poly(ethylene glycol) (PEG) and poly(l-leucine) (PLeu) with mannose at the chain end of PEG were synthesized by a combination of ring-opening polymerization (ROP) and click chemistry. First, an α-azido, ω-amino PEG (N(3)-PEG-NH(2)) was synthesized and converted to the corresponding amine hydrochloride (N(3)-PEG-NH(2)·HCl), which was used as a macroinitiator to initiate the ROP of L-leucine-N-carboxyanhydride (Leu-NCA), yielding three amphiphilic block copolymers with different chain lengths of PLeu (N(3)-PEG-b-PLeu). Then, click chemistry of the alkynyl mannose with N(3)-PEG-b-PLeu anchored a mannose moiety to the PEG chain end of the copolymer. The self-assembly behavior of these copolymers in water was investigated using transmission electron microscopy (TEM), laser light scattering (LLS) and circular dichroism (CD). Depending on the copolymer composition and the initial concentration of the copolymer in organic solvent, different morphologies (e.g. spherical micelle, wormlike micelle) were observed. The aggregation behavior was demonstrated to be controlled by secondary structure formation and the hydrophobic interactions of the PLeu segments. With mannose moieties on the surface of the aggregates, these aggregates could bind reversibly the lectin Concanavalin A (Con A).     

Thermogelling polymers composed of poly(cyclohexylenedimethylene adipate) and poly(ethylene glycol)

Block copolymers composed of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic biodegradable polyesters have been reported as thermogelling polymers, because they feature temperature-dependent sol-to-gel or gel-to-sol transitions in aqueous solutions. In this study, a series of thermogelling poly(ethylene glycol methyl ether)-block–poly(cyclohexylenedimethylene adipate)-block–poly(ethylene glycol methyl ether) triblock copolymers and PEG-block–poly(cyclohexylenedimethylene adipate) multiblock copolymers was synthesized by reacting hydroxyl-terminated poly(cyclohexylenedimethylene adipate) (PCA) with poly(ethylene glycol methyl ether) and PEG, respectively, using 1,6-diisocyanatohexane as the coupling agent. Two hydroxyl-terminated PCAs, i.e., poly(1,4-cyclohexylenedimethylene adipate) and poly(1,3/1,4-cyclohexylenedimethylene adipate), were synthesized by the condensation reaction of adipic acid (AA) with 1,4-cyclohexanedimethanol (CHDM) and 1,3/1,4-CHDM, respectively, and used as the hydrophobic polyester blocks of these thermogelling copolymers to compare the effect of crystallinity on the sol-to-gel transition behavior.The polymers were characterized using proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, gel permeation chromatography, differential scanning calorimetry, solubility testing, and rheological analysis. Experimental results revealed that the structure of the PCA block (crystalline vs. amorphous), the molecular weights of the hydrophobic PCA and hydrophilic PEG blocks, and the type of thermogelling polymer (triblock vs. multiblock) influenced the solubility, polymer micelle packing characteristics, maximum storage modulus, and sol-to-gel temperature of the polymers. Among all the samples at 40 wt.% aqueous solutions, triblock copolymer TB3 showed sol-to-gel temperature at 22 °C, and had the highest maximum storage modulus about 170 Pa.     

Aggregation properties of oligo(methacrylic acid)-shelled dendrimer and its microenvironment in aqueous solutions

A third-generation poly(amido amine) dendrimer having poly(methacrylic acid) segments on the periphery (G3-PMAA) was newly synthesized. A xanthate-modified dendrimer (G3-X) was first prepared by condensation of the terminal amino groups of the poly(amido amine) dendrimer with an activated-ester xanthate. G3-PMAA was then synthesized by polymerization of methacrylic acid initiated with G3-X. The number-average degree of polymerization of PMAA segment was estimated to be 10. The pK_a value for G3-PMAA was evaluated to be 7.3 that is somewhat higher than that (6.8) of the corresponding linear PMAA with the same segment length, indicating the interaction of PMAA segments caused by assembling them at the dendrimer surface. When the diameter of G3-PMAA in aqueous solution at various pHs was measured by a dynamic light scattering, G3-PMAA was found to self-aggregate in a pH region, where the PMAA segment took a hydrophobic, compact coil conformation. Subsequently, the interaction of a fluorescent probe (1-anilino-8-naphthalenesulfonic acid ammonium salt (ANS)) with G3-PMAA was examined by means of fluorescence spectroscopy. As a result, ANS was found to bind to the hydrophobic site of G3-PMAA aggregates at lower pH, and to be released into water phase at higher pH.     

Synthesis of poly(ethylene glycol)/polypeptide/poly(D,L‐lactide) copolymers and their nanoparticles

Core‐shell structured nanoparticles of poly(ethylene glycol) (PEG)/polypeptide/poly(D ,L ‐lactide) (PLA) copolymers were prepared and their properties were investigated. The copolymers had a poly(L ‐serine) or poly(L ‐phenylalanine) block as a linker between a hydrophilic PEG and a hydrophobic PLA unit. They formed core‐shell structured nanoparticles, where the polypeptide block resided at the interface between a hydrophilic PEG shell and a hydrophobic PLA core. In the synthesis, poly(ethylene glycol)‐b‐poly(L ‐serine) (PEG‐PSER) was prepared by ring opening polymerization of N‐carboxyanhydride of O‐(tert‐butyl)‐L ‐serine and subsequent removal of tert‐butyl groups. Poly(ethylene glycol)‐b‐poly(L ‐phenylalanine) (PEG‐PPA) was obtained by ring opening polymerization of N‐carboxyanhydride of L ‐phenylalanine. Methoxy‐poly(ethylene glycol)‐amine with a MW of 5000 was used as an initiator for both polymerizations. The polymerization of D ,L ‐lactide by initiation with PEG‐PSER and PEG‐PPA produced a comb‐like copolymer, poly(ethylene glycol)‐b‐[poly(L ‐serine)‐g‐poly(D ,L ‐lactide)] (PEG‐PSER‐PLA) and a linear copolymer, poly(ethylene glycol)‐b‐poly(L ‐phenylalanine)‐b‐poly(D ,L ‐lactide) (PEG‐PPA‐PLA), respectively. The nanoparticles obtained from PEG‐PPA‐PLA showed a negative zeta potential value of ?16.6 mV, while those of PEG‐PSER‐PLA exhibited a positive value of about 19.3 mV. In pH 7.0 phosphate buffer solution at 36 °C, the nanoparticles of PEG/polypeptide/PLA copolymers showed much better stability than those of a linear PEG‐PLA copolymer having a comparable molecular weight. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Effect of cyclodextrins on pH-induced conformational transition of poly(methacrylic acid)

A pH-induced conformational transition of atactic poly(2-methylprop-2-enoic acid) (poly(methacrylic acid), PMMA) from the contracted to expanded conformation was investigated by viscometry, potentiometric titration, and anthracene solubilisation in the presence of low-molecular-mass non-ionogenic co-solutes-glucose, α-cyclodextrin (αCD), and γ-cyclodextrin (γCD), respectively. No effect of glucose and αCD on the conformational transition was observed with either of the methods used. On the other hand, the characteristic features of the conformational transition were absent in the presence of γCD. The different effects of the co-solutes indicate that the interaction between PMAA and γCD corresponds to the partial inclusion of the PMAA chain into the γCD cavity. The viscometry and anthracene solubilisation imply that γCD promotes the expanded conformation of PMAA at low pH. The potentiometric titration does not support this conclusion. Even though there is no break on the Henderson-Hasselbalch plot, a characteristic of the conformational transition, the potentiometric behaviour corresponds to that of the contracted PMMA conformation. Thus the results suggest the hierarchical picture of the PMAA conformation at low pH in which the local arrangement of the PMAA chain is a prerequisite for clustering on a larger scale.     

Preparation, characterization and biocompatibility of poly(ethylene glycol)-poly(n-butyl cyanoacrylate) nanocapsules with oil core via miniemulsion polymerization

A new type of nanocapsules with an oil core, coated by poly(ethylene glycol) (PEG) was designed. The loading efficiency and the biocompatibility of the polymeric nanocapsules were evaluated when it was used as a carrier for hydrophobic agent paclitaxel. The nanocapsules were synthesized through miniemulsion polymerization of butylcyanoacrylate (BCA) with PEG as initiator. The particle size and zeta potential of nanocapsules were influenced by the PEG content in the polymerization system. Fourier transform infrared (FTIR) spectra and ¹H NMR demonstrated the chemical coupling between PEG and poly(butylcyanoacrylate) (PBCA). Thermal characteristics of the copolymer were investigated by differential scanning calorimetry (DSC). The encapsulation efficiency increased concurrently with the increase of the PEG content in the system. The hemolytic assay and the cytotoxicity measurement showed that the PEG coating could significantly reduce the hemolytic potential and cytotoxicity of the nanocapsules. The results showed that the PEG-PBCA nanocapsules could be an effective carrier for hydrophobic agents.     

Y‐shaped poly(ethylene glycol) and poly(trimethylene carbonate) amphiphilic copolymer: Synthesis and for drug delivery

New Y‐shaped (AB₂‐type) amphiphilic copolymers of poly(ethylene glycol) (PEG) with poly(trimethylene carbonate) (PTMC), PEG‐b‐(PTMC)₂, were successfully synthesized by the ring‐opening polymerization (ROP) of TMC with bishydroxy‐modified monomethoxy‐PEG (mPEG). First, a bishydroxy functional ROP initiator was synthesized by esterification of acryloyl bromide with mPEG, followed by Michael addition using excess diethanolamine. A series of Y‐shaped amphiphilic PEG‐(PTMC)₂ block copolymers were obtained via ROP of TMC using this PEG with bishydroxyl end groups as macroinitiator and ZnEt₂ as catalyst. The amphiphilic block copolymers with different compositions were characterized by gel permeation chromatography (GPC) and ¹H NMR, and their molecular weight was measured by GPC. The results showed that the molecular weight of Y‐shaped copolymers increased with the increase of the molar ratio of TMC to mPEG‐(OH)₂ initiator in feed while the PEG chain length was kept constant. The Y‐shaped copolymer mPEG‐(PTMC)₂ could self‐assemble into micelles in aqueous medium and the critical micelle concentration values of the micelles decrease with increase in hydrophobic PTMC block length of mPEG‐(PTMC)₂. The in vitro cytotoxicity and controlled drug release properties of the Y‐shaped amphiphilic block copolymers were also investigated. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8131–8140, 2008     

Some aspects on the polymerization of N-vinylpyrrolidone in the presence of poly(methacrylic acid) templates

N-Vinylpyrrolidone (NVP) was polymerized in dimethylformamide (DMF) at 60°C in the presence of poly(methacrylic acids) (PMAA) of different tacticities and molecular weights. The rate enhancement, which was ascribed to chain growth of the poly(vinylpyrrolidone) (PVP) radical along the polyacid template, became more pronounced with increasing chain length and syndiotacticity of the PMAA template. The results can be expressed by v_R = aP _vⁿ, where v_R is the polymerization rate relative to that of the blank experiment, P _v is the viscosity-average degree of polymerization of PMAA, and a and n are constants depending on the reaction conditions and tacticity of PMAA. In the presence of excess monomer the rate enhancement decreased when the quantity of PVP produced corresponded to a stoichiometric ratio of 1:1 with the available PMAA. It is proposed that the template effect is caused mainly by delay of the bimolecular termination step of growing PVP radicals associated with PMAA. Diffusion of polymer radicals, and consequently termination, will be more impaired if the attached PMAA has a greater length (size) and if the binding forces between PVP radical and PMAA template are stronger. The latter implies that PVP forms the strongest complexes with syndiotactic PMAA. This is supported by experiments concerning complex stability.     

The effect of pH on charge, swelling and desorption of the dispersant poly(methacrylic acid) from poly(methyl methacrylate) microcapsules

Poly(methyl methacrylate) microcapsules have been prepared using the solvent evaporation technique with poly(methacrylic acid) (PMAA) as dispersant. The charge, swelling and desorption of PMAA from the microcapsules after treating the suspension with base have been followed using microelectrophoresis, X-ray photoelectron spectroscopy and quartz crystal microbalance with dissipation monitoring on model PMMA surfaces. Basic treatment of the microcapsule suspension leads to temporary colloidal stability through the introduction of charges on the PMAA chain. However, the increase in charge causes a continuous desorption of PMAA from the microcapsule surface, eventually leading to aggregation. If instead poly(diallyldimethylammonium chloride) is added to the base treated microcapsule suspension, good colloidal stability is obtained.