TITLE OF THE INVENTION COMPOSITION AND METHOD FOR RECOVERING HYDROCARBON FLUIDS FROM A SUBTERRANEAN RESERVOIR STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT [0001] Not Applicable. INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC [0002] Not Applicable. FIELD OF THE INVENTION [0003] This invention relates to compositions and methods for the recovery of hydrocarbon fluids from a subten^nean reservoir and more particularly to an expandable polymeric microparticle composition that modifies the permeability of subterranean formations, thereby increasing the mobilization and/or recovery rate of hydrocarbon fluids present in the formations. BACKGROUND [0004] In the first stage of hydrocarbon recovery an energy source present in a reservoir is allowed to move to a producing wells(s) where the hydrocarbon can flow or be pumped to a surface handling facility. Typically a relatively small proportion of reservoir hydrocarbon can be recovered by this means. To increase production fluids are injected down adjacent wells to force an additional amount of hydrocarbon to the surface. This is commonly known as secondary recovery. The fluids nonnally used are water (such as aquifer water, river water, sea water, or produced water), or gas (such as produced gas, carbon dioxide, flue gas and various others). Additionally, if the fluid encourages movement of nonnally immobile residual oil or other hydrocarlsons, such a process is termed tertiary recovery. [0005] A prevalent problem with secondary and tertiary recovery projects relates to the heterogeneity of &)e reservoir rock strata. The mobility of the injected fluid typically is different from the hydrocarbon. For instance, when the fluid is more mobile various mobility control processes are required to make the sweep of the reservoir more uniform and the consequent hydrocarijon recovery more efficient. Unfortunately such processes have limited value wrtien high permeability zones, commonly called thief zones or streaks, exist within the reservoir rock. The injected fluid follows a low resistance route from the injection well to the production well. In such cases the injected fluid does not effectively sweep the hydrocarbon from adjacent, lower permeability zones. Further, when the produced fluid is re-used this can lead to fluid cycling through the thief zone with little resulting benefit and at great cost in terms of fuel and maintenance of the pumping system. 1 [0006] Numerous physical and chemical methods have been used to divert injected fluids out of the thief zones and into or near production and injection wells. When the treatment is applied to a producing well it is usually termed a water (or gas etc.) shut-off treatment. When it is applied to an injection well it Is termed a profile control or conformance control treatment. [0007] In cases where the thief zone(s) are isolated fi'om the lower permeability adjacent zones, mechanical seals or "plugs" can be set in the well to block the entrance of the injected fluid. If the fluid enters or leaves the formation from the bottom of the well, cement can also be used to fill the well bore to above the zone of ingress. [0008] When the completion of the well allows the injected fluid to enter both the thief and the adjacent zones, a cement squeeze is often a suitable means of isolating the watered out zone. Certain cases, however, are not amenable to such methods because communication exists between layers of the reservoir rock outside the reach of cement. Typical examples of this are when fractures or rubble zones or washed out caverns exist behind the casing. In such Instances chemical gels, capable of moving through pores in reservoir rock have been applied to seal the swept out zones. [0009] When such methods fail the only remaining alternatives are to produce the well with poor recovery rate, sidetrack the well away from the prematurely swept zone, or abandon tiie well. Occasionally the producing well is converted to a fluid injector to increase the field injection rate above the net hydrocarbon extraction rate and increase the pressure in the reservoir. This can lead to improved overall recovery, but It is worth noting that the injected fluid will mostly enter the thief zone at the new injector and is likely to cause similar problems in nearby wells. Further, all of these methods are expensive. [0010] Near wellbore conformance control methods always fail when the thief zone is in widespread contact with the adjacent, hydrocarbon containing, lower permeability zones. The reason for this is that the injected fluids can bypass the treatment and re-enter the thief zone having only contacted little or none of the remaining hydrocarbon. It Is commonly known amongst those skilled in the art, that such near wellbore treatments do not succeed in significantly improving recovery in reservoirs having crossflow of the injected fluids between zones. [0011] A few processes have been developed with the aim of reducing the penneability in a substantial proportion of the thief zone and, or at a significant distance from the injection and production wells. One example of this is the Deep Diverting Gel process patented by Morgan et al (1). This has been used in the field and suffered from sensitivity to unavoidable variations In quality of the reagents, which resulted in poor propagation. The gelant mixture is a twocomponent formulation and it is believed that this contributed to poor propagation of the treatment into the fomiatlon. [0012] The use of swellable cross linked superabsorbent polymer microparticles for modifying the permeability of subterranean formations is disclosed in U.S. Pat. Nos. 5,465,792 and 2 5,735,349. However, swelling of the superabsorbent microparticles described therein is induced by changes of the carrier fluid from hydrocarbon to aqueous or from water of high salinity to water of low salinity. [0013] Crosslinked, expandable polymeric microparticles and their use for modifying the permeability of subten^nean fonnations and increasing the mobilization and/or recovery rate of hydrocarbon fluids present in the fomriation are disclosed in U.S. Patent Nos. 6,454,003 B1, 6,709,402 B2, 6,984,705 B2 and 7,300,973 82 and in published U.S. Patent Application No. 2007/0204989 A1. SUMMARY [0014] We have discovered novel expandable polymeric microparticles comprising structured polymers with reversible (labile) crosslinlcs, or with labile core units and non-labile crosslinkers. The initial microparticle conformation and unexpended size are constrained by the physical limits imposed by the structured polymers. The structured polymers maintain the unexpanded size of the microparticle until the opccurence of a desired activating event degrades the labile crosslinks or labile core-units and allows for overall expansion of the microparticle. The unexpanded microparticle properties, such as average particle size distribution and density, allow for efflcient propagation through the pore structure of hydrocarbon reservoir matrix rock, such as sandstone. On exposing the microparticles to an activating event such as a change in temperature and/or at a predetermined pH, the reversible (labile) internal crosslinks, or the labile core units in the structured polymers begin to degrade, allowing the microparticle to expand by absorbing the injection fluid (normally water). [0015] The ability of the microparticle to expand from its original size (at the point of injection) depends on the presence of conditions that induce the breaking of the labile crosslinkers or labile core units in the structured polymers forming the microparticle. The particles of this invention can propagate through the porous structure of the reservoir without using a designated fluid or fluid with salinity higher than the reservoir fluid. [0016] The released, expanded primary polymeric mk:roparticle is engineered to have a particle size distribution and physical characteristics, for example, particle rheology, that allow it to impede the flow of injected fluid in the pore structure. In doing so it is capable of diverting chase fluid into less thoroughly swept zones of the reservoir. [0017] The rheology and expanded partk:le size of the particle can be designed to suit the reservoir target. For example, characteristics of a microparticle for use in a particular reservoir are influenced by selecting a particular backbone monomer or comonomer ratio in the structured polymer. Another way to influence the characteristics of the microparticle is the relative contribution of reversible (labile) and irreversible crosslinking introduced during manufacture of the structured polymers of the microparticle. 3 [0018] Accordingly, this invention can be directed to a composition comprising expandable polymeric microparticles comprising structured polymers having labile cross-linkers or a labile core, the microparticles having an unexpanded volume average particle size diameter of from about 0.05 to about 5,000 microns. The invention is further directed to a method of modifying the water permeability of a subteranean fonmation by injecting into the subtenanean fonnation a composition comprising expandable polymeric microparticles comprising structured polymers having labile cross-linl-2-methyl propanesulfonic acid sodium salt is more preferred. [0027] "Anionic polymeric microparticle" means a crosslinked polymeric microparticle containing a net negative charge. Representative anionic polymeric microparticles include copolymers of acrylamide and 2-acrylamido-2-methyl propane sulfonic acid, copolymers of acryiamide and sodium acrylate, terpolymers of acrylamide, 2-acrylamido-2-methyl propane sulfonic acid and sodium acrylate and homopolymers of 2-acrylamido-2-methyl propane sulfonic acid. Preferred anionic polymeric microparticles are prepared from about 95 to about 10 mole percent of nonionic monomers and from about 5 to about 90 mole percent anionic monomers. More preferred anionic polymeric microparticles are prepared from about 95 to about 10 mole percent acrylamide and from about 5 to about 90 mole percent 2-acrylamido-2-methyl propane sulfonic acid. [0028] Betaine-containing polymeric mbroparticte" means a crosslinked polymeric microparticle prepared by polymerizing a betaine monomer and one or more nonionic monomers. [0029] "Betaine monomer" means a monomer containing cationically and anionically charged functionality in equal proportions, such that the monomer is net neutral overall. Representative betaine monomers include N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine, N,N-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine, N,Ndimethyl- N-acrylamidopropyl-N-(2-cart)oxymethyl)-ammonium betaine, N,N-dimethyl-NacrylamKlopropyl- N-(2-carboxymethyl)-ammonium betaine, N,N-dimethyl-N-acryloxyethyl-N-{3- suIfopropyl)-ammonium betaine, N,N-dimethyl-N-acryIamidopropyl-N-(2-carboxymethyl)- ammonium betaine, N-3-suifopropylvinylpyridine ammonium betaine, 2-(methylthio)ethyl methacryloyi-S-(suffopropyl)-sulfonium betaine, 1-(3-sulfopropyl)-2-vinylpyridinium betaine, N-(4- sulfobutyl)-N-methyldiallylamine ammonium betaine (MDABS), N,N-diaIlyl-N-methyl-N-(2- sulfoethyl) ammonium betaine, and the like. A preferred betaine monomer is N,N-dimethyl-Nmethacryloyloxyethyl- N-(3-sulfopropyl)-ammonium betaine. [0030] "Cationic Monomer" means a monomer unit as defined herein which possesses a net positive charge. Representative cationic monomers include the quaternary or acid salts of dialkylaminoalkyi acrylates and methacrylates such as dimethylaminoethyiacrylate nnethyl chloride quaternary salt (DMAEAMCQ), dimethylaminoethylmethacrylate methyl chloride quaternary salt (DMAEM MCQ), dimethylaminoethyiacrylate hydrochloric acid salt, dimethylaminoethyiacrylate sulfuric acid salt, dimethylaminoethyl acrylate benzyl chloride quatemary salt (DMAEA BCQ) and dimethylaminoethyiacrylate methyl sulfate quaternary salt; the quatemary or acid salts of dialkylaminoalkylacrylamides and methacrylamides such as dimethylaminopropyl acrylamide hydrochloric acid salt, dimethylaminopropyl acrylamide sulfuric 5 acid salt, dimethylaminopropyl methacrylamide hydrochloric acid salt and dimethylaminopropyl methacrylamide sulfuric acid salt, methacr^amidopropyl trimethyl ammonium chloride and acrylamidopropyl trimethyl ammonium chloride; and N,N-diallyldiall(yl ammonium halides such as diallyldimethyl ammonium chloride (DADMAC). Prefenred cationic monomers include dimethylaminoethylacrylate metiiyl chloride quatemary salt, dimethylaminoeth^methacrylate methyl chloride quaternary salt and diallyldimethyl ammonium chloride. Diallyldimethyl ammonium chloride is more preferred. [0031] "Cross linking monomer" means an ethylenically unsaturated monomer containing at least two sites of ethylenic unsaturation which is added to constrain the microparticle conformation of the polymeric microparticles of this invention. The level of cross linking used in these polymer microparticles is high, compared to conventional super-absorbent polymers, to maintain a rigid non-expandable microparticle configuration. Cross linking monomers according to this invention include both labile cross linking monomers and non-labile cross linking monomers. [0032] "Structured polymers" means any non linear polymers such as star polymers, dendrimers, hyperbranched, short-chain and tong-chain branched polymers or a combination thereof. Polymer architectures can be controlled using controlled radical polymerizations or living cationic and anionic polymerizations. [0033] "Emulsion", "microemulsion" and "inverse emulsion" mean a water-in-oil polymer emulsion comprising a polymeric microparticle according to this invention in the aqueous phase, a hydrocarbon oil for the oil phase and one or more water-in-oil emulsifying agents. Emulsion polymers are hydrocarbon continuous with the water-soluble polymers dispersed within the hydrocarbon matrix. The emulsion polymer are optionally "inverted" or converted into watercontinuous form using shear, dilution, and, generally an inverting surfactant. See U.S. Pat. No. 3,734,873, incorporated herein by reference. [0034] "Fluid mobilit/' means a ratio that defines how readily a fluid moves through a porous medium. This ratio is known as the mobility and is expressed as the ratio of the permeability of the porous medium to the viscosity for a given fluid. [0035] 1. EQUATION 1 for a single fluid x flowing in a porous medium. [0036] When more than one fluid is flowing the end point relative pemieabilities must be substituted for the absolute permeability used in equation 1. [0037] 2. EQUATION 2 for a fluid X flowing in a porous medium in the presence of one or more other fluids. Ax = — Vx 6 [0038] When two or more fluids are flowing the fluid mobilities may be used to define a IVIobility ratio: [0039] 3. EQUATION 3 [0040] The mobility ratio is used in the study of fluid displacement, for example in water flooding of an oil reservoir where x is water and y is oil, because the efficiency of the displacement process can be related to it. As a general principle at a mobility ratio of 1 the fluid front moves almost in a "Plug flow" manner and the sweep of the reservoir is good. When the mobility of the water is ten times greater than the oil viscous instabilities, known as fingering, develop and the sweep of the reservoir is poor. When the mobility of the oil is ten times greater than the water the sweep of the reservoir is almost total. [0041] "Ion-pair polymeric microparticle" means a crosslinked polymeric microparticle prepared by polymerizing an ampholytic ion pair monomer and one more anionic or nonionic monomers. [0042] "Labile cross linking monomer" means a cross linking monomer which can be degraded by certain conditions of heat, pH or a combination thereof, after it has been incorporated into the polymer stmcture, to reduce the degree of crosslinking in the polymeric microparticle. The aforementioned conditions are such that they can cleave bonds in the "cross linking monomer" without substantially degrading the rest of the polymer backbone. Representative labile cross linking monomers include diacrylamkles and methacrylamides of diamines such as the diacrylamide of piperazine, acrylate or methacrylate esters of di, tri, tetra hydroxy compounds including ethyleneglycol diacrylate, polyethyleneglycol diacrylate, ^'metiiylopropane trimethacrylate, ethoxylated trimethylol triacrylate, ethoxylated pentaerythritol tetracrylate, and the like; divinyl or diallyl compounds separated by an azo such as the diallylamide of 2,2'- Azobis(isbutyric acid) and the vinyl or allyl esters of di or tri functional acids. Prefen-ed labile cross linking monomers include water soluble diacrylates such as PEG 200 diacrylate and PEG 400 diacrylate and polyfunctional vinyl derivatives of a polyalcohol such as ethoxylated (9-20) trimethylol triacrylate. The labile cross linker may be present in an amount of from about 100 to about 200,000 ppm. In alternative aspects, the labile cross linker is present in the amount of about 1,000 to about 200,000 ppm, about 9,000 to about 200,000 ppm, about 9,000 to about 100,000 ppm, about 20,000 to about 60,000 or about 1,000 to about 20,000 ppm, about 500 to about 50,000 ppm based on total moles of monomer. [0043] "Monomer" means a polymerizable allylic, vinylic or acrylic compound. The monomer may be anionic, cationic, nonionic or zwitterionic. Vinyl monomers are preferred, acrylic monomers are more preferred. 7 [0044] "Nonionic monomer" means a monomer as defined herein wiiich is electrically neutral. Representative nonionic monomers Include N-lsopropylacrylamide, N.N-dimethylacryiamide, N,N-dtethylacrylamide, dimethylaminopropyl acrylamlde, dimethylamlnopropyl methacrylamide, acryloyi morphollne, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, dimethylaminoethylacrylate (DMAEA), dimethylaminoethyl methacrylate (DMAEM), maleic anhydride, N-vinyl pyrrolidone, vinyl acetate and N-vinyl formamide. Preferred nonionic monomers include acrylamlde, N-methylacrylamide, N,Ndlmethylacrylamide and methacrylamide. Acrylamlde Is more preferred. [0045] "Non-labile cross linking monomer" means a cross linking monomer which is not degraded under the conditions of temperature and/or pH which would cause incorporated labile cross linking monomer to disintegrate. Non-labile cross linking monomer is added, in addition to the labile cross linking monomer, to control the expanded conformation of the polymeric micropartlcle. Representative non-labile cross linking monomers Include methylene bisacrylamide, diallylamine, triallylamine, divinyl sulfone, diethyleneglycol diallyl ether, and the like. A preferred non-labile cross linking monomer is methylene bisacrylamide. [0046] The structured polymer for making the microparlicles can be any non linear polymer such as star polymers, dendrimers, hyperbranched, short-chain and long-chain branched polymers or a combination thereof. Polymer architectures can be controlled using controlled radical polymerizations or living cationic and anionic polymerizations. As disclosed herein, such structured polymers are used to make crosslinked, expandable polymeric microparticles as otherwise described in U.S. Patent Nos. 6,454,003 B1, 6,709,402 B2, 6,984,705 B2 and 7,300.973 B2 and In published U.S. Patent Application No. 2007/0204989 A1. An advantage of using structured polymers in creating the crosslinked expandable mcroparticles of the present invention is that either the labile crosslinks or non-labile crosslinks can be eliminated while maintaining the expandability of the micropartlcle. For example, a star polymer with all labile crossllnkers wrill function very similarly to the crosslinked microparticles described in U.S. Patent Nos. 6.454,003 81, 6,709,402 B2.6,984,705 B2 and 7,300,973 B2, and in published U.S. Patent Application No. 2007/0204989 A1 without requiring non-labile crosslinks. Upon decomposition of all the labile crosslinks, the final polymer expands and the star core will act as a permanent crosslinker. Altematively, a labile core-unit having all non-labile crosslinkers also yieWs polymeric microparticles with properties to those previously described for crosslinked expandable microparticles having both labile and non-labile crosslinkers. [0047] Star polymers are produced either by polymerization from multifunctional cores or by post modification reactions. Polymerization from a multifunctional core Is desirable for very high molecular weight polymers. Star polymer synthesis by post modification reactions is well known, and described for example In B. Charleus and J. Nicolas, Polymer 48:5813 (2007); and in S. Abraham et al., J Poly Sci A: Poly Chem 45:5559 (2007). WO2008016371 describes flie preparation of degradable star polymers using Atom Transfer Radical Polymerization (ATRP). 8 Labile or degradable crosslinks that can be used include those that are photodegradable, ozonolyzabte, biodegradable, hydrolyzable. Nondegradable crosslinks may also be used. An example of a suitable degradable (thennolyzable) star polymer for the micnsparticfes described herein is described in C.S. Patrickios et al., J Poly Sci A: Poly Chem 45: 5811 (2007). Recent introduction of the tetrafunctional peroxide initiator JWEB5D, available from Arkema Inc. of Philadelphia, PA, now permits synthesis of star polymers by traditional radical polymerization as well. JWEB50 is a tetrafunctional initiator that yields a four-ami star polymer after polymerization. (M.J. Scorah et al., Macromol React Eng 1:209 (2007). [0048] Dendritic polymers are another structured polymer suitable for making the expandable microparticles. Dendrimers and hyperbranched polymers belong to the dendritic family of polymers and can be configured to provide low bulk viscosity products. A relatively simple approach is to start with ABz monomers, or ABC2 monomers from a chain-growth polymerization process involving the copolymerization of an AB monomer with a C monomer. The "2" subscript denotes dual functionality of the monomers. In an ABCjthe C monomer has dual functionality. The AB group is a polymerizable vinyl group that is able to react with an active moiety such as an anion, a cation, a radical or a conventional initiating or propagating moiety of the type well known in vinyl polymerization. The C monomer contains a polymerizable group that can be initiated by A*, B* or by another suitable initiator including alkyl aluminum halides, Lewis acids, bases, heat, light and radiation. Once the reaction of C with an A* or B* unit or other initiator has occurred, C becomes a new activated C* gnDup capable of further reaction with any Acontaining moiety present in the system, and also with any C monomer remaining in the system. The reactive moiety of the C monomer may be exactly the same as the AB monomer, or it may be another type of vinyl group having a reactivity or polymerizability similar to that of A with respect to B* or to A*. US Pat. No. 5,663,260 for example describes the method of synthesis of such hyperbranched polymers by an ABC2 system. U.S. Pat. No. 5,587,441 describes the synthesis of AB2 polymers where the B monomer is the polymerizable initiator molecule. For the expandable microparticles, such polymers are configured as labile molecules \mth dual functionality so that the molecule degrades or decomposes with changes in the environment such as a change in temperature, pH, ionic strength, pressure or stress to obtain expandable microparticles with properties like those described in U.S. Pat. Nos. 6,454,003 and 6,984,705. [0049] In one aspect, the polymers fonning the constrained expandable microparticle are crosslinked expandable structured polymers. The structured polymers can be made with labile and non-labile crosslinkers such as, but not limited to, those described in U.S. Pat. No. 6,454,003. For example, in one aspect the non-labile cross linker is present in the expandable microparticles in an amount of from 0 to about 300 ppm, in another aspect from about 2 to about 300 ppm, in another aspect from about 0 to about 200 ppm, in another aspect from about 0 to about 100 ppm, in another aspect from about 01 to about 300 ppm, in another aspect from about 2 to about 300 ppm and in another aspect from about 5 to about 300 ppm based on total 9 moles of monomer. However, an advantage of the structured polymers is the ability to eliminate the labile crosslinkers or the non-labile crosslinkers. In the absence of a non-labile cross linker, the polymer microparticle, upon complete scission of labile cross linker, is converted into a mixture of linear polymer strands. Similarly, in the absence of labile crosslinkers, but with a structured polymer having a labile core, the polymer microparticle upon complete scission of the labile core is converted into a mixture of linear polymer strands. In either case, the particle dispersion is thereby changed into a polymer solution. This polymer solution, due to its viscosity, changes the mobility of the fluid in a porous medium. In the presence of a small amount of non-labile cross linker, the conversion from particles to linear molecules is incomplete. The particles become a loosely linked netvi/ork but retain certain 'structure'. Such 'stnjctured' particles can block the pore throats of porous media and create a blockage of flow. [0050] Thus, in one aspect, the structured polymers forming the expandable polymeric microparticles are any crosslinked structured polymers with all labile crosslinks, and which are capable of fonning unexpanded polymeric particles of a size of about 5,000 microns or less. In another aspect, the structured polymers forming the expandable polymeric microparticles are any crosslinked structured polymers with all non-labile crosslinks and a labile core that are capable of fomiing unexpanded polymeric particles of a size of about 5,000 microns or less. [0051] When used with to reference to crosslinks or the polymer core, the tenri "labile" means degradable, for example, photodegradable ozonolyzable, biodegradable, hydrolyzable or thermolyzable. In another aspect of the present invention, structured polymers fonn a micropartk:le that may be used advantageously in recovery of hydrocarbon from the subterranean fonnation. [0052] In an exemplary embodiment, structured polymers are made using labile crosslinks that degrade upon exposure to an activating event or condition such as a change in temperature, pH, salinity or the like. In one aspect, the crosslinkers degrade at the higher temperatures encountered in the subterranean formation. Once the crosslinkers degrade, the microparticle configuration degrades and allows the microparticle to expand or swell. Examples of suitable labile crosslinkers for structured polymers include, but are not limited to, diester and other types of labile crosslinkers such as polyethyleneglycol diacrylate (e.g. PEG-200 diacrylate) as described in detail in U.S. 6,454,003. In addition, cationic ester monomers can be used as ionic crosslinkers for the structured polymers, because they form ionic bonds with any anionic polymers forming the underling unejqsanded polymeric microparticle. In the higher temperatures encountered in the formation, the cationic ester mer units will hydrolyze, eventually converting the initially cationic labile polymers to an anionic polymer that is no longer capable of forming an ionic interaction with the anionic polymers forming the underlying unexpanded polymeric microparticle. Examples of suitable cationic ester monomers include N,N-dimethylaminoethyl acyrylate and N,N-dimethylaminoethyI methacrylate. [0053] Structured polymers may be formed using labile crosslinks Uiat can be selected for 10 susceptibility to degradation upon exposure to any one of a number activating events. Temperature and pH changes are exemplary activating events, but other activating events for sufficient degradation of labile cross-linlts in the labile polymers are contemplated, including a change in pressure, saiinrty, shear, or dilution. The activating event may be for example exposure to an activating agent such as exposure to an oxidant, a reductant, an acid, a base, a biological agent, an organic or inorganic cross-linking agent, or a salt, or to a combination thereof. Upon exposure to the activating event and consequent degradation of the structrured polymers the expandable polymeric microparticles are free to expand to several times the original size of the microparticle while yet constrained by the initial configuration of the structured polymer [0054] Preferred Embodiments [0055] In one aspect, the polymeric microparticles are composed of expandable structured polymers that are prepared using an inverse emulsion or microemulsion process to assure certain particle size range. In an embodiment, the unexpanded volume average particle size diameter of the stmctured polymers is from about 0.05 to about 5,000 microns. In an embodiment, the unexpanded volume average particle size diameter of the structured polymers is about 0.1 to about 3 microns. In another embodiment, the unexpanded volume average particle size diameter of the structured polymers is about 0.1 to about 1 microns. In another embodiment, the unexpanded volume average particle size diameter of the structured polymers is about 0.05 to about 50 microns. [0056] Representative preparations of crosslinked expandable polymeric microparticles using a microemulsion process are described in U.S. Pat. Nos. 4,956,400, 4,968,435, 5,171,808, 5,465,792 and 5,737,349. [0057] In an inverse emulsion or microemulsion process, an aqueous solution of monomers and cross linkers is added to a hydrocarbon liquid containing an appropriate surfactant or surfactant mixture to forni an inverse monomer microemulsion consisting of small aqueous droplets dispersed in the continuous hydrocarbon liquid phase and subjecting the mon(»ner microemulsion to free radical polymerization. [0058] In addition to the monomers and cross linkers, the aqueous solution may also contain other conventional additives including chelating agents to remove polymerization inhibitors, pH adjusters, initiators and other conventional additives. [0059] The hydrocarbon liquid phase comprises a hydrocarbon liquid or mixture of hydrocarbon liquids. Safeirated hydrocarbons or mixtures thereof are preferred. Typically, the hydrocarbon liquid phase comprises benzene, toluene, fuel oil, kerosene, odorless mineral spirits and mixtures of any of the foregoing. [0080] Surfactants useful in the mk:roemulsion polymerization process described herein include sorbitan esters of fatty acids, ethoxylated sorbitan esters of fatty acids, and the like or 11 mixtures thereof. Preferred emulsifying agents include ethoxyfated sorbitol oleate and sorbitan sesquioleate. Additional details on these agents may be found in McCutcheon's Detergents and Emulsifiers, North American Edition, 1980. [0061] Polymerization of the emulsion may be carried out in any manner known to those skilled in the art. Initiation may be effected with a variety of thermal and redox free-radical initiators including azo compounds, such as azobisisobutyronitrile; peroxides, such as t-butyl peroxide; organic compounds, such as potassium persulfate and redox couples, such as sodium bisuifite/sodium bromate. Preparation of an aqueous product from the emulsion may be effected by inversion by adding it to water, which may contain an inverting surfactant. [0062] Alternatively, the structured polymers cross linked with labile cross links are prepared by internally cross linking polymer particles which contain polymers with pendant carboxylic acid and hydroxy! groups. The cross linking is achieved tiirough the ester fomiation between the carboxylic acid and hydroxy! groups. The esterification can be accomplished by azeotropic distillation (U.S. Pat. No. 4,599,379) or thin film evaporation technique (U.S. Pat. No. 5,589,525) for water removal. For example, a polymer microparticle prepared from inverse emulsion polymerization process using acrylic acid, 2-hydroxyethyiacrylate, acrylamide and 2-acrylamido- 2-methylpropanesulfonate sodium as monomer is converted into cross linked polymer particles by the dehydratbn processes described above. [0063] The polymeric microparticles are optionally prepared in dry form by adding the emulsion to a solvent which precipitates the polymer such as isopropanol, isopropanol/acetone or methanol/acetone or other solvents or solvent mixtures that are miscible with both hydrocarbon and water and filtering off and drying the resulting solid. [0064] An aqueous suspension of the polymeric microparticles is prepared by redispersing the dry polymer in water. [0065] In another embodiment, this invention is directed to a method of modifying the permeability to water of a subterranean formation by injecting into the subterranean fomiation a composition comprising expandable microparticles which comprise structured polymers. The microparticles have an unexpanded volume average particle size diameter of from about 0.05 to about 5,000 microns and have a smaller diameter ttian the pores of the subterranean fonnation. The labile crosslinks or labile core of the structured polymers degrade under a change in environmental conditions in the subterranean fomiation so that the expandable polymeric microparticles are free to expand. The composition then flows through a zone or zones of relatively high permeability in the subterranean formation under increasing temperature conditions, until the composition reaches a location where the temperature or pH is sulficiently high to promote degradation of the labile crosslinks or labile core in the labile polymers, triggering expansion of the microparticles. [0066] In one embodiment, about 100 ppm to about 10,000 ppm of the composition, more preferably 500 ppm to about 1500 ppm of the composition, and even more preferably about 500 12 ppm to about 1000 ppm, based on polymer actives, is added to the subterranean formation. The subterranean fomiation is for example a sandstone or cartionate hydrocarbon reservoir. In one embodiment, the composition is added to injection water as part of a secondary or tertiary process for the recovery of hydrocarbon from the subten-anean fomiation. The injection water is added to the subterranean formation, for example a producing well, at a temperature lower than the temperature of the subterranean fomiation. The higher temperature within the fomiation causes the labile crosslin)