Abstract: The present disclosure is directed to using a blend of sorbitan esters as a surfactant to produce a stable water-in-oil high internal phase emulsion in the preparation of a low density porous crosslinked polymeric material. This process produces low density, high capacity, porous, crosslinked, polymeric materials with improved absorption capacity and foam properties.

Abstract: Disclosed is a process for the continuous preparation of high internal phase emulsions which are suitable for subsequent polymerization into polymeric foam materials that, upon dewatering, act as absorbents for aqueous body fluids. The process involves continuous introduction of a certain type of monomer-containing oil phase and a certain type of electrolyte-containing water phase into a dynamic mixing zone at relatively low water to oil phase ratios. Flow rates are then steadily adjusted to increase the water to oil ratio of the streams fed to the dynamic mixing zone while subjecting the dynamic mixing zone contents to shear agitation which is sufficient to thereby form a high internal phase emulsion that, upon subsequent polymerization, provides a foam having an average cell size of from about 5 to 100 microns. The formation of such a stable high internal phase emulsion is completed by feeding the contents of the dynamic mixing zone to and through a static mixing zone.

Abstract: A process for producing hollow particles of crosslinked melamine resin having a uniform particles diameter, said process comprising subjecting a water-soluble methyl-etherified-melamine resin precondensate to condensation reaction in the presence of a curing catalyst in an aqueous solution containing a water-soluble polymer with carboxyl groups or water-soluble copolymer of ethylenically unsaturated carboxylic acid monomer, when the reaction liquid becomes turbid, adding to the reaction mixture a substance which dissolves or swells the melamine resin, and continuing the condensation reaction, if necessary.

Abstract: In a process for the preparation of a low density porous crosslinked polymeric material by polymerizing a water-in-oil high internal phase emulsion, curing time of the monomers in the emulsion can be reduced without adversely affecting polymer properties or substantially affecting the emulsion by carrying out the curing in multiple-stages. The emulsion is first pre-cured at a temperature less than about 65.degree. C. until the emulsion reaches a Rheometrics dymanic shear modulus of at least about 500 and subsequently curing at a temperature above about 70.degree. C.

Abstract: A composite or asymmetric membrane for separating and concentrating a particular component from a mixture of gases. The asymmetric membrane is of a fluorine-containing aromatic polyimide resin of the 6FDA type. The composite membrane has a thin film of an elastomeric polymer formed on a supporting film of a fluorine-containing aromatic polyimide resin of the 6FDA type.

Abstract: A method for altering a macroporous cross-linked hydrophobic copolymeric lattice produced by precipitation polymerization in a solvent of at least one monounsaturated ester monomer and at least one polyunsaturated ester monomer soluble therein, in order to render the hydrophobic copolymeric lattice hydrophilic. The method involves saponifying the hydrophobic copolymeric lattice by reacting the surface of the hydrophobic copolymeric lattice with an aqueous alkali. The surface can also be rendered hydrophilic by polymerizing an acrylate monomer onto the lattice in order to form a surface containing carboxylic acid sites. The carboxylic acid sites formed on the surface of the lattice are converted to carboxylate anions.

Abstract: A process for forming polymer powders by dissolving one or more polymers in a suitable solvent, followed by atomizing the solution into a droplet atmosphere of a non-solvent to precipitate polymer particles. The particles are separated from the non-solvent, washed and dried to produce a powder with a rounded particle morphology, high internal porosity and surface area, and high apparent density.Polymer powders with these properties can be pressed to dense shaped articles suitable for sintering in automated presses because the powders have good low and compressibility characteristics. The process if particularly useful when applied to soluble polymers that are not readily shaped by melt processing means.

Abstract: A method to prepare uniform populations of macroscopic beads containing pores of at least 0.1 microns diameter is described. The beads consist essentially of a copolymer of a monoethylenically unsaturated monomer and a crosslinking polyethylenically unsaturated monomer, said resulting copolymer optionally being derivatized with functional groups, linking moieties, and/or affinity ligands. The macroporous beads are obtained by utilizing, as porogen in the polymerization reaction, porous inorganic particles which have been preabsorbed with a blowing agent. The blowing agent is not activated until after the polymerization takes place; when the blowing agent is activated, the organic polymer which isolates the inorganic porogen particles from each other in the bead is destroyed. Upon subsequent dissolution of the inorganic porogen, a network of pores throughout the organic copolymer-formed particle is formed. The resulting beads are useful in a variety of chromatographic, analytical and biomedical techniques.

Abstract: A porous membrane is formed from an interpenetrating polymer network of a hydrophobic polymer and a polymerized and crosslinked hydrophilic monomeric composition. A solution of the polymer and monomeric composition is cast, exposed to ultraviolet radiation, coagulated and dried. The resulting dried membrane is annealed in order to render its surface hydrophilic.

Abstract: A microporous, polymeric film is prepared by dissolving methylene-chloride-soluble, film-forming polymers completely in methylene chloride. Then an aqueous phase is prepared containing non-methylene-chloride-soluble, water-soluble thickeners and, if desired, additives, and brought to a viscosity of about 0.07 to 0.5 Pa s. The aqueous phase is then dispersed in the polymer solution and the resultant paste is spread onto a support material or intermediate support, the methylene chloride is evaporated, the resultant membrane is transferred to the actual support, and finally the water is removed by drying.

Abstract: A microporous sheet comprising a polymeric matrix having a liquid insoluble, particulate, activated polysaccharide media dispersed therein; use of the sheet in affinity chromatography or ion-exchange chromatography or as a biochemical reactor or battery separator; processes for manufacturing the sheet; apparatus containing the microporous sheet as its active element; and methods for using such sheet.

Abstract: Disclosed is a process for the continuous preparation of high internal phase emulsions which are suitable for subsequent polymerization into polymeric foam materials that, upon dewatering, act as absorbents for aqueous body fluids. The process involves continuous introduction of a certain type of monomer-containing oil phase and a certain type of electrolyte-containing water phase into a dynamic mixing zone at relatively low water to oil phase ratios. Flow rates are then steadily adjusted to increase the water to oil ratio of the streams fed to the dynamic mixing zone while subjecting the dynamic mixing zone contents to shear agitation which is sufficient to thereby form a high internal phase emulsion that, upon subsequent polymerization, provides a foam having an average cell size of from about 5 to 100 microns. The formation of such a stable high internal phase emulsion is completed by feeding the contents of the dynamic mixing zone to and through a static mixing zone.

Abstract: A process for forming polymer powders by dissolving one or more polymers in a suitable solvent, followed by atomizing the solution into a droplet atmosphere of a non-solvent to precipitate polymer particles. The particles are separated from the non-solvent, washed and dried to produce a powder with a rounded particle morphology, high internal porosity and surface area, and high apparent density.Polymer powders with these properties can be pressed to dense shaped articles suitable for sintering in automated presses because the powders have good low and compressibility characteristics. The process if particularly useful when applied to soluble polymners that are not readily shaped by melt processing means.

Abstract: The invention relates to ultrasonic contrast agents composed of microparticles which contain a gas and polyamino-dicarboxylic acid-co-imide derivatives, to processes for their preparation and to their use as diagnostic and therapeutic agents.

Abstract: A microporous particulate-filled thermoplastic polymeric article is provided. The article can be in the form of a film, a fiber, or a tube. The article has a thermoplastic polymeric structure having a plurality of interconnected passageways to provide a network of communicating pores. The microporous structure contains discrete submicron or low micron-sized particulate filler, the particulate filler being substantially non-agglomerated.

Abstract: Supercritical drying has distinct advantages in generating microcellular materials. The dimensional stability of the polymer is not affected on drying because the supercritical process does not go through the two phase path and therefore the effect of capillary forces is absent. This helps in maintaining the morphology of the final polymer structure and better control over cell size.Organic microcellular foams were prepared by polymerizing directly in a near-critical fluid and pursuing the supercritical drying in the same reactor. The critical variables are the choice of a diluent with a strong enough solvent power to stabilize the polymer matrix, but with a low enough critical temperature to permit critical point drying without damage to the polymer matrix.

Abstract: A microporous polyolefin shaped article is provided. The article comprises a polyolefin substrate of substantially uniform thickness having a patterned surface, the patterned surface providing substantially skinless areas having high microporosity and skinned areas of reduced microporosity. A method for preparing the article is also provided.

Abstract: An improved superabsorbent polymer having increased rate of water absorption is obtained by the addition, preferably prior to polymerization, of a carbonate blowing agent to a monomer solution of the monomers used to form the superabsorbent polymer. Preferred monomers include (meth)acrylic acids, preferably partially neutralized prior to polymerization and appropriate cross-linking agents. The carbonate cross-linking agents are any carbonate salt soluble or dispersible in the monomer solution, prior to polymerization. The multi-valent cationic salts of carbonate are preferred, especially the complex carbonates, for example, of magnesium.

Abstract: Disclosed is a process of producing microcellular from which comprises the steps of:(a) selecting a multifunctional epoxy oligomer resin;(b) mixing said epoxy resin with a non-reactive diluent to form a resin-diluent mixture;(c) forming a diluent containing cross-linked epoxy gel from said resin-diluent mixture;(d) replacing said diluent with a solvent therefore;(e) replacing said solvent with liquid carbon dioxide; and(f) vaporizing off said liquid carbon dioxide under supercritical conditions, whereby a foam having a density in the range of 35-150 mg/cc and cell diameters less than about 1 .mu.m is produced.Also disclosed are the foams produced by the process.

Abstract: A polymer solution contains a sulphonated polyarylethersulphone in a solvent mixture containing at least three components, where the solvent mixture has a delta-H in the range from 3 to 8.5; a delta-P in the range from 4 to 8 and a delta-D in the range 7.2 to 9.5 and each component of the solvent mixture is a liquid or low melting solid which is a non-solvent or poor solvent for the sulphonated polyarylethersulphone, and at least one of the components satisfies at least one of the conditions:a) said component has a delta-D of less than 8 when the value of delta-P is not more than 3; andb) said component has a delta-H of greater than 3 when the value of delta-P is at least 8.5; andc) said component has a delta-H of less than 8 when it contains at least one hydroxylic group; andd) said component is free of hydroxylic groups and has a delta-P which is greater than 3 and less than 8.5.The solution can be used for the production of membranes suitable for use in reverse osmosis applications.

Abstract: A method of preparing synthetic enzymes and synthetic antibodies in which method use is made of the so called molecular imprinting method, is described. As imprinting molecules use is made of transition state analogues, substrate-like compounds and antigen-like molecules, respectively. There is also described the use of the so prepared enzymes and antibodies.

Abstract: Solutions of segmented polyurethanes are coagulated to form shaped structures comprising a substantially continuous pore-free sheath surrounding a cellular core.

Abstract: Organic aerogels that are transparent and essentially colorless are prepa from the aqueous, sol-gel polymerization of melamine with formaldehyde. The melamine-formaldehyde (MF) aerogels have low densities, high surface areas, continuous porsity, ultrafine cell/pore sizes, and optical clarity.

Abstract: A porous membrane is formed from an interpenetrating polymer network of a hydrophobic polymer and a polymerized and crosslinked hydrophilic monomeric composition. A solution of the polymer and monomeric composition is cast, exposed to ultraviolet radiation, coagulated and dried. The resulting dried membrane is annealed in order to render its surface hydrophilic.

Abstract: An active agent delivery device comprises (a) microporous material comprising a matrix consisting essentially of linear ultrahigh molecular weight polyolefin, a large proportion of finely divided water-insoluble filler of which at least about 50 percent by weight is siliceous, and interconnecting pores; and (b) a releasable active agent or precursor thereof associated with at least a portion of the filler.

Abstract: A substrate comprises a porous polymeric material having a porosity of at least 75% and comprising pores having a diameter within the range 1 to 100 .mu.m and being interconnected by a plurality of holes, and a gel or material adapted in use to form a gel which gel or pre-gel materials is contained and retained within the pores of the polymeric material and is adapted in use to interact with a reactive species and can be made by depositing and retaining the gel or a material adapted in use to form the gel within the pores of the porous polymeric material. The high porosity of the porous polymeric material in combination with the retention of the gel within the pores permit high loading capacities, particularly in the area of peptide synthesis to be achieved. The substrate can be employed in chemical synthesis, chromatography techniques, ion exchange and separation techniques.

Abstract: Disclosed is a process of producing microcellular foam which comprises the steps of:(a) selecting a multifunctional epoxy oligomer resin;(b) mixing said epoxy resin with a non-reactive diluent to form a resin-diluent mixture;(c) forming a diluent containing cross-linked epoxy gel from said resin-diluent mixture;(d) replacing said diluent with a solvent therefore;(e) replacing said solvent with liquid carbon dioxide; and(f) vaporizing off said liquid carbon dioxide under supercritical conditions, whereby a foam having a density in the range of 35-150 mg/cc and cell diameters less than about 1 .mu.m is produced.Also disclosed are the foams produced by the process.

Abstract: Hollow, polymeric, acrylate, infusible, inherently tacky, solvent-insoluble, solvent-dispersible, elastomeric pressure-sensitive adhesive microspheres having an average diameter of at least about 1 micrometer. Preferred microspheres are those wherein a majority of the hollow microspheres contain at least one of interior void having a diameter of at least 10% of the diameter of the microsphere.These hollow microspheres are useful as repositionable pressure-sensitive adhesives. The invention also provides pressure-sensitive adhesives consisting essentially of such hollow microspheres. Aqueous suspensions of these microspheres, processes for their preparation, spray repositionable pressure-sensitive adhesive compositions, and microsphere-coated sheet materials are also provided. Surprisingly, hollow microspheres of the invention show reduced or even eliminated adhesive transfer, in comparison with prior art repositionable pressure-sensitive adhesives which are based on solid microspheres.

Abstract: A carbonized composite foam having a density less than about 50 mg/cm.sup.3 and individual cell sizes no greater than about 1 .mu.m in diameter is described, and the process of making it.

Abstract: Isotropic porous polymer beads having a high surface porosity and large pore diameters from about 0.002 to about 5 microns are produced from solutions of an acrylonitrile polymer or a copolymer by a thermally-induced phase separation process. The use of mixed solvent-non-solvent combinations as solvents for the polymers, produces high pore content, substantially spherical beads having a morphology ideally suited to the chromatography of large molecules, such as proteins, and for enzyme-binding.

Abstract: Hollow, polymeric, acrylate, infusible, inherently tacky, solvent-insoluble, solvent-dispersible, elastomeric pressure-sensitive adhesive microspheres having an average diameter of at least about 1 micrometer. Preferred microspheres are those wherein a majority of the hollow microspheres contain at least one of interior void having a diamter of at least 10% of the diameter of the microsphere.These hollow microspheres are useful as repositionable pressure-sensitive adhesives. The invention also provides pressure-sensitive adhesives consisting essentially of such hollow microspheres. Aqueous suspensions of these microspheres, processes for their preparation, spray repositionable pressure-sensitive adhesive compositions, and microsphere-coated sheet materials are also provided. Surprisingly, hollow microspheres of the invention show reduced or even eliminated adhesive transfer, in comparison with prior art repositionable pressure-sensitive adhesives which are based on solid microspheres.

Abstract: A process for preparing polymer emulsion particles having pores therein, an outside diameter D of 0.1 to 5.0[ , an inside diameter d of 0.05 to 4.0.mu. , and a ratio (d/D) of 0.1 to 0.9 in dry condition, comprising the steps of forming core-shell emulsion particles from specific monomers by two-emulsion polymerizations, and swelling the core of the particles with water by hydrolyzing the vinyl acetate part of polymer (A), thereby inducing the hydroxyl groups therein, e.g., using an acidic material or a basic material at 50.degree. to 100.degree. C. The particles when use as a pigment in coating compositions provide excellent converage rate, brightness, gloss and water resistance.

Abstract: An active agent delivery device comprises (a) microporous material comprising a matrix consisting essentially of linear ultrahigh molecular weight polyolefin, a large proportion of finely divided water-insoluble filler of which at least about 50 percent by weight is siliceous, and interconnecting pores; and (b) a releasable active agent or precursor thereof associated with at least a portion of the filler.

Abstract: Polymer particles or beads for use as opacifiers in paints are described in which a core is provided with a hard sheath and the particle has one or more voids produced by reaction with a non-volatile permanent or fixed base. The sheath is a coploymer of an ethylenically unsaturated aliphatic monomer free of acid groups and at least 2 percent by weight of a soft ester-containing monomer and optionally styrene in an amount of up to 25 mole percent. The core is formed from an ethylenically unsaturated monomer with acid functionality.The sheath polymer has a glass transition temperature of at least 40.degree. C. The particles have a size of up to 40000 nanometers before swelling the core by some 150 to 2000 percent.

Abstract: Microporous or open ultrafiltration poly (tetrafluoroethylene-co-perfluoro-(alkyl vinyl ether)) (PFA) or poly (tetrafluoroethylene-co-hexafluoropropylene) (FEP) film membrane or hollow fibers having open pores are formed from a melt blend of 10 to 35 weight percent of the PFA or FEP and a chlorotrifluoroethylene oligomer solvent. The melt blend is shaped and one or more surfaces of the shaped melt blend are coated with the solvent prior to phase separation of the melt blend. Coating the membrane with solvent during shaping results in membrane having larger pores on that membrane surface as compared to membranes not coated with solvent. The shaped melt blend is cooled to effect phase separation and crystallization of the PFA or FEP from the blend. The solvent is separated from the PFA or FEP by extraction and the porous PFA or FEP is heat set under restraint to prevent shrinkage.

Abstract: A porous polymeric material has cell sizes within the range 100 to 0.5 .mu.m and total pore volume with respect to the overall volume of the material in the range 75 to 98% and includes cross-linked polycondensation polymeric material. The material can be made from a high internal phase emulsion in which the cross-linked polycondensation polymer is formed in the continuous phase. The materials are preferably open interconnected cellular structures. They can be made of a wide range of polycondensation materials. The materials are thus highly porous and light weight and have a range of properties depending primarily on their constituent polycondensation materials.

Abstract: A dope for forming membranes and the resulting asymmetric gas separation membranes are disclosed, the membranes having graded density skins which exhibit improved permeability characteristics and increased failure pressure strength. The membranes are produced from a process utilizing membrane forming dopes of complexing solvent systems formulated from two non-solvents and one or more solvents. The non-solvents are chosen one each, from non-solvents grouped according to non-solvent strength, i.e., one strong non-solvent and one weak non-solvent which are combined with one or more solvents in an acid:base complex solvent system for dissolving high weight percent total solids of membrane forming polymers. The process for forming the membranes is also disclosed.

Abstract: The polycondensation of resorcinol with formaldehyde under alkaline conditions results in the formation of surface functionalized polymer "Clusters". The covalent crosslinking of these "clusters" produces gels which when processed under supercritical conditions, produce low density, organic aerogels (density.ltoreq.100 mg/cc; cell size .ltoreq.0.1 microns). The aerogels are transparent, dark red in color and consist of interconnected colloidal-like particles with diameters of about 100.circle.. These aerogels may be further carbonized to form low density carbon foams with cell size of about 0.1 micron.TABLE I ______________________________________ Theo- [Form- retical Actual Formu- % alde- [Resor- density Density lation Solids hyde] cinol] Na.sub.2 CO.sub.3 (g/cc) (g/cc) ______________________________________ A 5.0% 0.29M 0.58M 0.0029M 0.050 0.079 B 5.0% 0.29M 0.58M 0.0019M 0.050 0.073 C 5.0% 0.29M 0.58M 0.0015M 0.050 0.070 D 4.0% 0.24M 0.47M 0.0012M 0.040 0.054 E 3.5% 0.21M 0.41M 0.0010M 0.035 0.044 F 2.

Abstract: A repositionable pressure-sensitive adhesive comprising from about 70% to about 99% hollow, polymeric, acrylate, inherently tacky, infusible, solvent-insoluble, solvent-dispersible, elastomeric microspheres comprising at least one alkyl acrylate or alkyl methacrylate ester, a majority of the microspheres having one or more interior voids having a diameter of at least about 10% of the diameter of the microsphere, and correspondingly, from about 30% to about 1% of a binder copolymer comprising an elastomeric polymeric backbone having pendant therefrom high Tg polymeric moieties.

Abstract: Microporous or open ultrafiltration poly (tetrafluoroethylene-co-perfluoro-(alkyl vinyl ether)) (PFA) or poly (tetrafluoroethylene-co-hexafluoropropylene) (FEP) film membrane or hollow fibers having open pores are formed from a melt blend of 10 to 35 weight percent of the PFA or FEP and a chlorotrifluoroethylene oligomer solvent. The melt blend is shaped and one or more surfaces of the shaped melt blend are coated with the solvent prior to phase separation of the melt blend. Coating the membrane with solvent during shaping results in membrane having larger pores on that membrane surface as compared to membranes not coated with solvent. The shaped melt blend is cooled to effect phase separation and crystallization of the PFA or FEP from the blend. The solvent is separated from the PFA or FEP by extraction and the porous PFA or FEP is heat set under restraint to prevent shrinkage.

Abstract: Hollow, polymeric, acrylate, infusible, inherently tacky, solvent-insoluble, solvent-dispersible, elastomeric, nitrogen-containing, acid-free pressure-sensitive adhesive microspheres having an average diameter of at least about 1 micrometer wherein a majority of the microspheres contain multiple interior voids, a majority of the voids having a diameter of less than about 10% of the diameter of the microsphere, the total of the diameters of the voids being at least about 10% of the diameter of the microsphere.These hollow microspheres are useful as repositionable pressure-sensitive adhesives. The invention also provides pressure-sensitive adhesives consisting essentially of such acid-free hollow microspheres. Aqueous suspensions of these microspheres, processes for their preparation, spray repositionable pressure-sensitive adhesive compositions, and pressure-sensitive adhesive coated sheet materials are also provided.

Abstract: Organic resins with high surface areas and porosities, which are insoluble in organic solvents and contain few or no flexible groups in the resin structure, are disclosed. Also disclosed is a process for making such resins from polyfunctional aryl alkali metal compounds and a second polyfunctional monomer. Such resins are useful as absorbants.

Abstract: Polymer particles or beads for use as opacifiers in paints are described in which a core is provided with a hard sheath and the particle has one or more voids produced by reaction with a nonvolatile permanent or fixed base. The sheath is a copolymer of an ethylenically unsaturated aliphatic monomer free of acid groups and at least 2 percent by weight of a soft ester-containing monomer and optionally styrene in an amount of up to 25 mole percent. The core is formed from an ethylenically unsaturated monomer with acid functionality.The sheath polymer has a glass transition temperature of at least 40.degree. C. The particles have a size of up to 40000 nanometers before swelling the core by some 150 to 2000 percent.

Abstract: A porous polymeric material has cell sizes within the range 100 to 0.5 .mu.m and total pore volume with respect to the overall volume of the material in the range 75 to 98% and includes cross-linked polycondensation polymeric material. The material can be made from a high internal phase emulsion in which the cross-linked polycondensation polymer is formed in the continuous phase. The materials are preferably open interconnected cellular structures. They can be made of a wide range of polycondensation materials. The materials are thus highly porous and light weight and have a range of properties depending primarily on their constituent polycondensation materials.

Abstract: A membrane filter material formed from a solvent resistant bismaleimide polymer which is formed by polymerizing a bismaleimide compound with a perhydrodiaza-type heterocyclic compound and has a main structural skeleton represented by the following formula: ##STR1## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 represents a lower carbon chain which is linear or contains a methyl group or ethyl group on the side chain, R.sub.5 represents a divalent group containing an aromatic ring, Y is >R< or >N--R--N< in which R is a lower carbon chain, and m is 0 or 1.This bismaleimide polymer can be a membrane filter material having an excellent organic solvent resistance. When this polymer is formed into a hollow fiber or plain film, a high separating and filtering capacity and an excellent organic resistance can be attained.

Abstract: The semipermeable membrane contains a polyarylate resin and a polysulfone resin as a major membrane material and has a fibrilliform structure with a high mechanical strength and has a water permeability of 1,500 ml/m.sup.2.hr.mmHg or lower as well as an inhibitory rate against bovine serum albumin of 80% or higher and against cytochrome C of 40% or lower. The membrane is prepared by discharging a stock solution containing the polyarylate resin and the polysulfone resin in the total amount of 10% to 25% by weight and a core solution of an organic solvent containing water in the amount of 25% to 80% by volume into a coagulating solution.

Abstract: This invention relates to semi-permeable anisotropic syndiotatic polystyrene microporous membranes and a process for preparing such membranes.

Abstract: Sulfonated hexafluoro bis-A-polysulfone membranes of polymers and copolymers having the repeat unit of the structure; ##STR1## in the polymer molecule that exhibit improved permeation and separation characteristics and processes for the use thereof for separation of a component from a fluid mixture of said component in admixture with other components.

Abstract: Multi-stage polymer particles containing one or more void space(s) therein are produced by sequential emulsion polymerization of an essentially low-acid earlier polymer stage, encapsulation of said low-acid polymer stage with at least a final polymer stage, contacting said polymer particles with a non-polymeric carboxylic acid or anhydride to permit the acid or anhydride to be absorbed into said low-acid polymer stage and swelling the polymer particles by contacting the particles with an aqueous base. The low-acid polymer stage is formed by emulsion polymerizing a monomer system comprising ethylenically unsaturated monomer(s) and containing less than 5% by weight of monomer(s) containing acid functionality. The low-acid polymer stage is swubsequently encapsulated by one or more polymer stages by emulsion polymerizing ethylenically unsaturated monomer(s) in the presence of the low-acid polymer stage. The final stage has a glass transition temperature (Tg) of about 50.degree. C.

Abstract: Hollow, polymeric, acrylate, infusible, inherently tacky, solvent-insoluble, solvent-dispersible, elastomeric, nitrogen-containing, acid-free pressure-sensitive adhesive microspheres having an average diameter of at least about 1 micrometer wherein a majority of the microspheres contain multiple interior voids, a majority of the voids having a diameter of less than about 10% of the diameter of the microspheres, the total of the diameters of the voids being at least about 10% of the diameter of the microsphere.These hollow microspheres are useful as repositionable pressure-sensitive adhesives. The invention also provides pressure-sensitive adhesives consisting essentially of such acid-free hollow microspheres. Aqueous suspensions of these microspheres, processes for their preparation, spray repositionable pressure-sensitive adhesive compositions, and pressure-sensitive adhesive coated sheet materials are also provided.