A METHOD OF IMPROVING THE MELT PROCESSING OF THERMOPLASTIC POLYMERS AND COMPOSITIONS PRODUCED THEREBY

Abstract: A method of forming a thermoplastic melt blend including a segmental copolymer, wherein the melt blend displays improved processing characteristics, is disclosed. A method of forming a plastic article including a thermoplastic and a segmental copolymer is further disclosed, as is a plastic article formed thereby.

Description: A METHOD OF IMPROVING THE MELT PROCESSING OF THERMOPLASTIC POLYMERS AND COMPOSITIONS PRODUCED THEREBY This application is a continuation- in-p art of Serial No. 60/232,414, filed September 14, 2000. The present invention relates to a method of improving the melt processing of thermoplastics by forming blends with segmental polymers. The present invention further relates to articles produced thereby. Compositions of the thermoplastic polymer "poly(vinyl chloride)", "PNC", in the absence of a plasticizer or processing aid, are difficult to process into homogeneous, useful articles. The compositions are difficult to flux (i.e., to transition from a solids blend to a fused melt blend), and the resulting melts are heterogeneous and "cheesy" having poor melt strength and low elongation. Plasticizers eliminate many of these processing problems but with a resultant loss of physical properties, particularly rigidity, in the thermoplastic articles produced. Processing aids for PNC are polymeric additives that allow PNC to be processed to give good physical properties without loss of rigidity. It is known in the art that reducing the glass transition temperature, Tg, of processing aids for PNC allows those processing aids to disperse more completely into PNC (US 3833686, EP394659). This can be seen in improved clarity and reduced gel defects in clear PNC sheet and indirectly in how rapidly the PNC fuses from a solids blend into a thermoplastic melt blend during processing. This greater ease of fusion manifests itself in, for example, shorter fusion time at a given temperature, or the achievement of a given fusion time at a lower temperature. Unfortunately, there are limits to the extent to which the Tg of a processing aid can be lowered in that the processing aid, in the dry state, must be a free flowing solid, typically a powder, and it must remain so under typical storage conditions in order to be blended and formulated with PNC powder prior to melt processing. If the processing aid is an emulsion or suspension polymer it must not fuse or form a film during its isolation which is typically accomplished by such operations as spray drying at elevated temperature. Typically, if the Tg , of the processing aid drops below 50 °C, a free flowing, storage stable powder can not be obtained, nor can the clumps, or even "bricks" that form during storage be easily broken down during solids blending to form a uniform solids blend. One approach to reducing overall Tg of a processing aid is to use polymers prepared in two polymerization stages, wherein one component has a reduced Tg. US-A-3, 833,686 discloses two-stage sequentially produced, core-shell particles made by emulsion polymerization, wherein the lower Tg component is the core and a high Tg material, e.g., methyl methacrylate (MMA) is the shell. These core-shell particles contain substantially proportions of low Tg polymers having no high Tg segment, high Tg polymers having no low Tg segments, and polymers having both high and low Tg segments. Further, many of the chains are very long and have networked structure due to adventitious crosslinking. While one achieves a free flowing powder in this way even if the Tg of the core is near to, or below, room temperature, it is an unfortunate reality that such polymer particles are unable to break down fully during melt processing and, therefore, cannot realize their full potential as processing aid. We have, surprisingly, found that segmental copolymers may be produced as non-tacky powders, yet behave as processing aids for thermoplastics (e.g., PNC), providing short fusion times and low fusion temperatures consistent with those promoted by low Tg processing aids. These segmental copolymers can further be stored under typical conditions without compacting, clumping, or fusing. They can be transported to a processing hall, and combined with thermoplastics to make solids blends, again without clumping. Heating and mixing of these solids blends produces melt blends, having improved melt processing behavior, that can be shaped and cooled to produce homogeneous, useful thermoplastic articles. Such improved processing behavior is essential if articles of consistently high quality are to be produced at high output rates with minimal downtime in such processing operations as, for example, calendering, extrusion, blow molding, injection molding, expansion into foam, and making of bi-oriented materials. One aspect of the present invention relates to a method comprising the steps of- (a) forming a solids blend comprising a thermoplastic polymer and a segmental copolymer, ' and (b) mixing and heating said solids blend to form a melt blend. wherein said melt blend has a melt processing improvement term having a value of at least 10. A second aspect of the present invention relates to a method comprising the steps of (a) forming a solids blend comprising a thermoplastic polymer and a segmental copolymer; (b) mixing and heating said solids blend to form a melt blend. (c) shaping said melt blend to form an article, and (d) cooling said article to room temperature. wherein said melt blend has a melt processing improvement term having a value of at least 10. A third aspect of the present invention relates to an article, wherein said article comprises a thermoplastic polymer and a segmental copolymer. A fourth aspect of the present invention relates to a plastic article produced by the method of the second aspect of the present invention. In another aspect, the thermoplastic polymer of aspects one through four is a polymer selected from the group consisting of poly(vinyl halide) homopolymer, poly(vinyl halide) copolymer, chlorinated poly(vinyl chloride) "CPNC", and combinations thereof. A preferred thermoplastic polymer is poly(vinyl chloride). In a still further aspect, the segmental copolymer of aspects one through four is a copolymer selected from the group consisting of comb copolymer, block copolymer, and combinations thereof. It is preferred that the segmental copolymer is a comb copolymer. Used herein, the following terms have these definitions: The "backbone" of a polymer chain is a collection of polymerized monomer units attached to one another. The attachment is typically achieved by covalent bonding. "Non-terminal" monomer units are directly attached to at least two other monomer units. A "terminal" monomer unit resides at the end of the polymer chain and is directly attached to one other monomer unit. For example, the polymerized monomer units of the backbone may be derived from ethylenically unsaturated monomers. A "linear" polymer (homopolymer or copolymer) is a polymer having a backbone that is not branched. As used herein, the term "linear" is also meant to include polymers wherein a minor amount of branching has occurred. For example, hydrogen abstraction may lead to branching during free radical polymerizations. A "branched" polymer is a polymer having a first "backbone segment" that has other backbone segments (i.e., "branches") chemically attached to it through a "non-terminal" atom of the first backbone segment. Typically, this first backbone segment and all of the branches have the same, or similar, composition. A "pendant" group is a group that is attached to the backbone of a polymer. The term pendant may be used to describe a group that is actually part of a polymerized monomer unit. For example, the hydroxyethyl group of a polymerized unit of 2-hydroxyethyl methacrylate may be referred to as a "pendant hydroxyethyl group", or as "pendant hydroxy functionality". It is also common to refer to large groups attached to a polymer backbone as "pendant" when those large groups are compositionally distinct from the backbone polymer. These large groups may themselves be polymer chains. For example, when a macromonomer becomes incorporated into a polymer chain by reaction with other monomers, the two carbons of its reactive double bond become part of the backbone, while the polymeric chain originally attached to the double bond of the macromonomer becomes a "pendant group" that may, for example, have a molecular weight of 500 to 100,000. A "pendant" group may further be described as "pendant to" the backbone. A "terminal" group resides at the end of the polymer chain and is chemically attached to a terminal monomer unit. A terminal group may, for example, have a composition distinct from the composition of the backbone of the polymer. A "pendant" group may occur in a "terminal" position. As such, a "terminal" group is a special case of a "pendant" group. A "macromonomer" is any low molecular weight water-insoluble polymer or copolymer having at least one terminal ethylenically unsaturated group that is capable of being polymerized in a free radical polymerization process. By "water-insoluble" it is meant having a water solubility of no greater than 150 millimoles/liter at 25°C to 50°C. By "low molecular weight" it is meant that the macromonomer has a degree of polymerization preferably from 10 to 1,000, more preferably from 20 to 1,000, and most preferably from 20 to 200. By "degree of polymerization" it is meant the number of polymerized monomer units present in the macromonomer. A "macromonomer" is a low molecular weight polymer having at least one functional group at the end of the polymer chain that can further polymerize with others monomers to yield comb copolymers. See e.g., Kawakami in the "Encyclopedia of Polymer Science and Engineering", Vol. 9, pp. 195-204, John Wiley & Sons, New York, 1987. Typically, the macromonomer polymer chain contains ethylenically unsaturated monomers, as polymerized units. Preferably, the ethylenically unsaturated monomer is selected to impart low or no water solubility to the macromonomer as previously described herein. The term "macromonomer aqueous emulsion" is used herein to describe an aqueous emulsion containing macromonomer dispersed therein as water insoluble particles. A "graft segment" is a polymer chain occupying a pendant position along the polymer backbone. A graft segment may include, as polymerized units, one type of monomer or more than one type of monomer. The composition of a graft segment is different from the composition of the backbone polymer to which it is attached, in contrast to a "branch segment" of a branched backbone which has a composition which is the same as, or similar to, other portions the branched backbone of which it is a part. A "terminal graft segment" resides at an end of a backbone polymer chain and is chemically attached to that backbone polymer 5 chain. A "terminal graft segment" is a special case of a "pendant graft segment". The comb copolymer (i.e., graft copolymer) of the present invention includes one or more compositional types of graft segment. "Graft copolymers" are macromolecules formed when polymer or copolymer chains are chemically attached as side chains to a polymeric 10 backbone. Those side chains are the "graft segments" described herein above. Because graft copolymers often chemically combine unlike polymeric segments in one macromolecule, these copolymers have unique properties compared to the corresponding random copolymer analogues. These properties include, for example, mechanical fil properties resulting from thermodynamically driven 15 microphase separation of the copolymer, and decreased melt viscosities resulting in part from the segmental structure of the graft copolymer, and from separation of a soft (i.e., low Tg) phase. With respect to the latter, reduced melt viscosities can advantageously improve processability of the polymer. See e.g., Hong-Quan Xie and Shi-Biao Zhou, J. Macromol. Sci.-Chem., A27(4), 491-507 (1990); 20 Sebastian Roos, Axel H.E. Mύller, Marita Kaufmann, Werner Siol and Clenens Auschra, "Applications of Anionic Polymerization Research", R.P. Quirk, Ed., ACS Symp. Ser. 696, 208 (1998). The term "comb copolymer," as used herein, refers to the type of copolymer that is the "graft copolymer" of the present invention, wherein the polymeric 25 backbone of the graft copolymer is linear, or essentially linear, and each side chain (graft segment) of the graft copolymer is formed by a "macromonomer" that is grafted to the polymer backbone. The comb copolymers may, for example, be prepared by the free radical copolymerization of macromonomer with conventional monomer (e.g., second ethylenically unsaturated monomer). It is 30 . required that either the backbone, the graft segment, or both backbone and graft segment be miscible in the thermoplastic polymer of the present invention. The solubility parameters of the backbone and the thermoplastic polymer can be estimated and compared to predict miscibihty by methods such as that of Nan Krevelen, described herein below. Used herein, the terms "graft copolymer" and "comb copolymer" are interchangeable. A "block copolymer" is a copolymer having a backbone characterized by the presence of two or more "blocks". A "block" is a segment of copolymer backbone having a particular and distinct composition. See e.g., G. Odian "Principles of Polymerization", Third Edn., pp. 142-149, John Wiley & Sons, New York, 1991. For example, a block could be composed entirely of styrene monomer, present as polymerized units. At least two blocks differing in composition must be present in a block copolymer, however, more than one block of a given composition may be present. For example, a poly(styrene)-b- poly(butadiene)-b-poly(styrene) has two poly(styrene) blocks joined by a poly(butadiene) block. Blocks are typically at least 10 monomer units, preferably at least 50 monomer units, and more preferably at least 100 monomer units in length. A "copolymer segment" is a segment selected from the group including a "backbone" of a comb copolymer, a "graft segment" of a comb copolymer, and "block" of a block copolymer. It is required that at least one copolymer segment of the segmental copolymer (i.e., comb copolymer or block copolymer) of the present invention is miscible with the thermoplastic polymer. The solubility parameters a given copolymer segment and the thermoplastic polymer can be estimated and compared to predict miscibihty by methods such as that of Van Krevelen described herein below. The comb copolymer of the present invention comprises a first copolymer segment and at least one second copolymer segment. The first copolymer segment is the backbone of the comb copolymer, and the second copolymer segment is the graft segment of the comb copolymer. A "random copolymer" is a copolymer having monomers, as polymerized units, randomly distributed along its backbone. Used herein, the term "random" has its usual meaning in the art of polymerization. For example, the distribution of monomer units along a polymer chain prepared by emulsion polymerization is dictated not only by the relative amounts of each type of monomer present at any point during the polymerization, but also by such factors as, for example, the tendency of each monomer type to react with itself relative to its tendency to react with each of the other types of monomer present. These reactive tendencies are defined by reactivity ratios which are well know for many monomer combinations. See e.g., G. Odian "Principles of Polymerization", Third Edn., pp. 460-492, John Wiley & Sons, New York, 1991. A "segmental copolymer" is a copolymer selected from the group consisting of "block copolymer", "comb copolymer", and combinations thereof. A "aqueous dispersion of a segmental copolymer" is a aqueous medium in which are dispersed a plurality of particles of segmental copolymer. Used herein, an "aqueous dispersion of a segmental copolymer" is an "aqueous copolymer composition". "Tg" is the "glass transition temperature" of a polymeric phase. The glass transition temperature of a polymer is the temperature at which a polymer transitions from a rigid, glassy state at temperatures below Tg to a fluid or rubbery state at temperatures above Tg. The Tg of a polymer is typically measured by differential scanning calorimetry (DSC) using the mid-point in the heat flow versus temperature transition as the Tg value. A typical heating rate for the DSC measurement is 20 Centigrade degrees per minute. The Tg of various homopolymers may be found, for example, in Polymer Handbook, edited by J. Brandrup and E. H. Immergut, Interscience Publishers. The Tg of a polymer is estimated by using the Fox equation (T.G. Fox, Bull. Am. Physics Soc, Volume 1, Issue No. 3, page 123 (1956)). "Effective Tg". When a substance having some degree of solubility in a polymer is imbibed by that polymer, the softening temperature of the polymer decreases. This plasticization of the polymer can be characterized by measuring the "effective Tg" of the polymer, which typically bears an inverse relationship to the amount of solvent or other substance contained in the polymer. The "effective Tg" of a polymer containing a known amount of a substance dissolved within is measured just as described above for "Tg". Alternatively, the "effective Tg" may be estimated by using the Fox equation (supra), assuming a value for Tg (e.g., the freezing point) of the solvent or other substance contained in the polymer. Molecular Weight. Synthetic polymers are almost always a mixture of chains varying in molecular weight, i.e., there is a "molecular weight distribution", abbreviated "MWD". For a homopolymer, members of the distribution differ in the number of monomer units which they contain. This way of describing a distribution of polymer chains also extends to copolymers. Given that there is a distribution of molecular weights, the most complete characterization of the molecular weight of a given sample is the determination of the entire molecular weight distribution. This characterization is obtained by separating the members of the distribution and then quantitating the amount of each that is present. Once this distribution is in hand, there are several summary statistics, or moments, which can be generated from it to characterize the molecular weight of the polymer. The two most common moments of the distribution are the "weight average molecular weight", "M ", and the "number average molecular weight", "Mn". These are defined as follows: Mw = ∑(WiMi)/∑Wi = ∑(NiMi 2 )/∑NiMi M„ = ∑Wi/∑(Wi/Mi) = ∑(NiMi)/∑Ni where: Mi = molar mass of i th component of distribution Wi = weight of i th component of distribution Ni = number of chains of i th component and the summations are over all the components in the distribution. M w and M n are typically computed from the MWD as measured by Gel Permeation Chromatography (see the Experimental Section). "Particle size" is the diameter of a particle. The "average particle size" determined for a collection of particles (e.g., macromonomer particles, or particles of graft copolymer) the "weight average particle size", "d w ", as measured by Capillary Hydrodynamic Fractionation technique using a Matec CHDF 2000 particle size analyzer equipped with a HPLC type Ultra-violet detector. The term "particle size distribution" and the acronym "PSD" are used interchangeably. "Polydispersity" is used in the art as a measure of the breadth of the PSD. Used herein, "polydispersity" is a description of the distribution of particle sizes for a plurality of particles. As such, "polydispersity" and "PSD polydispersity" are used interchangeably. PSD polydispersity is calculated from the weight average particle size, d w , and the number average particle size, d n , according to the formulae: PSD Polydispersity = (d w )/(dn), where d n = ∑ di /∑ni d w = ∑nididi /∑nidi, and where ni is the number of particles having the particle size Estimation of whether a polymer and another component (i.e., another polymer or a solvent) will be miscible may be made according to the well-known methods delineated in D. W. Nan Krevelen, Properties of Polymers, 3 rd Edition, Elsevier, pp. 189-225, 1990. For example, Nan Krevelen defines the total solubility parameter (δt) for a substance by: δt 2 = δd 2 + δ P 2 + δh 2 , where δd, δ P , and δh are the dispersive, polar, and hydrogen bonding components of the solubility parameter, respectively. Values for δd, δ p , and δh have been determined for many solvents, polymers, and polymer segments, and can be estimated using the group contribution methods of Van Krevelen. For example, to estimate whether a polymer having a given composition will be miscible with a particular solvent, one calculates δt 2 for the polymer and δt 2 for the solvent. Typically, if the difference between the two, Δδt 2 , is greater than 25 (i.e., Δδt > 5), then the polymer and the solvent will not be miscible. If, instead, it is desired to determine whether two polymers, differing in composition, will be miscible, the same calculations may be carried out, but the predicted upper limit of Δδt 2 for miscibihty will decrease as the molecular weight of one or both of polymers under consideration increases. This decrease is thought to parallel the decrease in entropy of mixing which occurs as the molecular weight of the components being mixed increases. For example, two polymers, each having a degree of polymerization of 100, will likely be immiscible even if the value of Δδt 2 for their mixture is 9, or even 4 (i.e., Δδt = 3, or even 2). Still higher molecular weight polymers may be immiscible at even lower values of Δδt. To estimate whether a graft segment of the copolymer of the present invention, having a given composition, will be miscible with a backbone having another composition, one calculates δt 2 for the graft segment and δt 2 for the backbone. Typically, if the difference between the two, Δδt 2 , is greater than 9 (i.e., Δδt > 3), then the graft segment should be insoluble in the backbone polymer such that a film formed by the graft copolymer would have two distinct types of polymeric phase. Similar calculation can be performed to determine whether a film formed from a block copolymer will have more than one polymeric phase. Because it is desirable that the graft segment not be miscible with the backbone, the Nan Krevelen calculations of miscibihty provide useful estimates of whether a given pair of compositions of the graft segment and backbone will result in phase separation in, for example, films formed from the segmental copolymer. A "polymeric additive", "PA" is a polymer that is added to the thermoplastic polymer composition. A "processing aid" is a polymeric additive having a value of IMP ≥ 10 (defined below). A "solids blend" is any thermoplastic polymer composition that is substantially solid, and not a melt blend. Such solids blends include, for example, blends of thermoplastic polymer in powder or pellet form with other components that themselves may, or may not, be solids. Through heating and mixing, a solids blend may be transformed into a melt blend. A "melt blend" is any thermoplastic polymer composition that is substantially in melt form. Fusion of a sohds blend, through heating and mixing, creates a melt blend. "Fusion time" is the time interval between the initial loading (i.e., compaction) of the test sample in a melt flow instrument (e.g., Haake Rheocord 90 with a Haake Bowl attachment using counter rotating paddles) and the torque maximum which occurs on fusion. "Fusion temperature" is the temperature at which the solids blend becomes a melt blend, and is measured at the point at which the torque reaches its peak (i.e., maximum) value. Fusion temperature depends upon the settings chosen for the melt flow instrument as well as the characteristics of the solids blend. "Equilibrium Torque" is the torque value measured once the torque has become constant after peak torque (at fusion) has occurred. "Melt strength" is proportional to the torque of a given melt blend. High melt strength is associated with formation of uniform thermoplastic melt blends, consistent processing, and formation of uniform thermoplastic articles. Because performance properties such as fusion time, fusion temperature, and equilibrium torque are all indicative of the processing performance of a melt of a thermoplastic polymer, consideration of only one of these properties to the exclusion of the others may give an incomplete assessment of the extent to which a given polymeric additive imparts improved melt processing behavior to a thermoplastic polymer. In recognition of that problem, three dimensionless terms are herein defined that express the extent to which each of those three performance properties are improved by the addition of a particular polymeric additive ("PA") to a blend containing a thermoplastic polymer. The fusion time, fusion temperature, and equilibrium torque are measured under a well controlled set of processing conditions (e.g., type of melt blending apparatus, initial temperature, and RPM of mixing element) for a given thermoplastic polymer absent a particular polymeric additive, and then in the presence of that additive at a given level. The three dimensionless terms are then combined (i.e., summed) to give an overall term that more fully describes whether an improvement in melt processing performance has resulted from the presence of the polymeric additive and, if so, the extent of that improvement. All four of these "improvement terms" are defined herein below: The "fusion time improvement term", "IFTI" is defined as: IFTI = [((FTI without PA) - (FTI with PA))/(FTI without PA)] X 100, where "FTI" is the "fusion time" (e.g., in seconds) and "PA" is the "polymeric additive" being assessed. If, for example, a PNC masterbatch (see Table 6 below) had a fusion time of 150 seconds, whereas a blend of that PNC masterbatch with a polymeric additive displayed a fusion time of only 75 seconds, the fusion time improvement term would have a value of "50". A positive value of IFTI indicates a shorter fusion time in the presence of the polymeric additive, and shorter fusion times are associated with improved melt processing. Hence, a positive value of IFTI is one indicator that the melt processing of a thermoplastic polymer improves when the polymeric additive being assessed is present. The "fusion temperature improvement term", "IFTP" is defined as: IFTP = [((FTP without PA) - (FTP with PA))/(FTP without PA)] X 100, where "FTP" is the "fusion temperature" (in °C) and "PA" is the "polymeric additive". As with IFTI, a positive value of IFTP is an indicator that the melt processing of a thermoplastic polymer improves when a the polymeric additive being assessed is present. The "equilibrium torque improvement term", "IET" is defined as: IET = [((ET with PA)/(ET without PA)) - l] X 100, where "ET" is the "equilibrium torque" (e.g., in meter-grams) and "PA" is the "polymeric additive" being assessed. If, for example, a PNC masterbatch had an equilibrium torque of 750 m-g, whereas a blend of that PNC masterbatch with a polymeric additive displayed a value of 825 m-g under identical conditions, the equilibrium torque improvement term would have a value of "10". As with IFTI and IFTP, a positive value of IET is an indicator that the melt processing of a thermoplastic polymer improves when a the polymeric additive being assessed is present. Equilibrium torque correlates directly with melt viscosity which, in turn, is directly correlated with melt strength. Therefore, an increase in equilibrium torque upon addition of polymeric additive indicated increased melt strength, a processing characteristic desired in a thermoplastic melt. The "melt processing improvement term", "IMP", more fully describes the ability of a given polymeric additive to improve the melt processing of a thermoplastic polymer through a summation of the other three improvement terms as follows: The segmental copolymers of the present invention are typically included in melt blends with the thermoplastic polymer at concentrations of 0.5 to 10 PHR (parts per hundred parts, weight/weight), based on the weight of the thermoplastic polymer. Over that concentration range, the segmental copolymers of the present invention preferably have values for the melt processing improvement term, IMP, of greater than 10, more preferably 20 to 200, and most preferably 35 to 200. All ranges used herein are inclusive and combinable. A preferred method of preparing the graft copolymers of the present invention and their aqueous dispersions is by emulsion polymerization. A preferred process for this preparation includes (a) forming, by polymerization of at least one first ethylenically unsaturated monomer, a macromonomer aqueous emulsion containing one or more water-insoluble particles of macromonomer; (b) forming a monomer composition containing at least one second ethylenically unsaturated monomer; and (c) combining at least a portion of the macromonomer aqueous emulsion and at least a portion of the monomer composition to form a "polymerization reaction mixture". The macromonomer and second ethylenically unsaturated monomer are polymerized in the presence of an initiator to form graft copolymer particles. The graft copolymers prepared by this preferred process are comb copolymers. The macromonomer, present in the macromonomer aqueous emulsion as water insoluble particles, is any low molecular weight water-insoluble polymer 5 or copolymer having at least one terminal ethylenically unsaturated group that is capable of being polymerized in a free radical polymerization process. By "water-insoluble" it is meant having a water solubility of no greater than 150 millimoles/liter at 25°C to 50°C. By "low molecular weight" it is meant that the macromonomer has a degree of polymerization of preferably from 10 to 1,000, 10 more preferably from 20 to 1,000, and most preferably from 20 to 200. By "degree of polymerization" it is meant the number of polymerized monomer units present in the macromonomer. The macromonomer contains, as polymerized units, at least first ethylenically unsaturated monomer. Preferably, the first ethylenically 15 unsaturated monomer is selected to impart low or no water solubility to the macromonomer as previously described herein. If the macromonomer will be used to prepare the graft segment of a comb copolymer, the backbone of which is not miscible with the thermoplastic polymer of the present invention, it is required that the composition of the 20 macromonomer be chosen such that the graft segments of the comb copolymer formed therefrom will be miscible in the thermoplastic polymer. If the backbone is miscible with the thermoplastic polymer, the graft segment may, optionally, be miscible in the thermoplastic polymer. The solubility parameters of the macromonomer (and graft segment prepared therefrom) and the thermoplastic 25 polymer can be estimated and compared to predict miscibihty by methods such as that of Nan Krevelen, described herein above. The composition of the macromonomer should be chosen so that the Tg of the graft segment of the comb copolymer formed therefrom will be preferably from -65 °C to 180 °C, more preferably from -45 °C to 180 °C, and most 3.0 . preferably from -20 °C to 130 °C. . Suitable first ethylenically unsaturated monomers for use in preparing macromonomer include for example methacrylate esters, such as Ci to Cis normal or branched alkyl esters of methacrylic acid, including methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, lauryl methacrylate, stearyl methacrylate; acrylate esters, such as Ci to Cis normal or branched alkyl esters of acrylic acid, including methyl acrylate, ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate; styrene; substituted styrenes, such as methyl styrene, a-methyl styrene or t-butyl styrene; olefinically unsaturated nitriles, such as acrylonitrile or methacrylonitrile; olefinically unsaturated halides, such as vinyl chloride, vinylidene chloride or vinyl fluoride; vinyl esters of organic acids, such as vinyl acetate! N-vinyl compounds such as N-vinyl pyrrolidone! acrylamide, ' methacrylamide; substituted acrylamides, ' substituted methacrylamides, ' hydroxyalkylmethacrylates such as hydroxyethylmethacrylate; hydroxyalkylacrylatesJ basic substituted (meth) acrylates and (meth) acrylamides, such as amine-substituted methacrylates including dimethylaminoethyl methacrylate, tertiary-butylaminoethyl methacrylate and dimethylaminopropyl methacrylamide and the likes; dienes such as 1,3-butadiene and isoprene; vinyl ethers; or combinations thereof. The term "(meth)" as used herein means that the "meth" is optionally present. For example, "(meth)acrylate" means methacrylate or acrylate. The first ethylenically unsaturated monomer can also be a functional monomer including for example monomers containing hydroxy, amido, aldehyde, ureido, polyether, glycidylalkyl, keto functional groups or combinations thereof. These functional monomers are generally present in the macromonomer at a level of from 0.1 weight percent to 15 weight percent and more preferably from 0.5 weight percent to 10 weight percent, and most preferably from 1.0 to 3 weight percent, based on the total weight of the graft copolymer. Used herein, all ranges are inclusive and combinable. Examples of functional monomers include ketofunctional monomers such as the acetoacetoxy esters of hydroxyalkyl acrylates and methacrylates (e.g., acetoacetoxyethyl methacrylate) and keto- containing amides (e.g., diacetone acrylamide); allyl alkyl methacrylates or acrylates, ' glycidylalkyl methacrylates or acrylates; or combinations thereof. Such functional monomers can provide crosslinking if desired. The macromonomer typically also contains as polymerized units less than 10 weight percent, preferably less than 5 weight percent, more preferably less than 2 weight percent and most preferably less than 1 weight percent acid containing monomer, based on the total weight of the macromonomer. In a most preferred embodiment, the macromonomer contains no acid containing monomer. Used herein, "acid containing monomer" and "acid functional monomer" are used interchangeably. By "acid containing monomer" it is meant any ethylenically unsaturated monomer that contains one or more acid functional groups or functional groups that are capable of forming an acid (e.g., an anhydride such as methacrylic anhydride or tertiary butyl methacrylate). Examples of acid containing monomers include, for example, carboxylic acid bearing ethylenically unsaturated monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid and fumaric acid; acryloxypropionic acid and (meth) aery loxypropionic acid, " sulphonic acid-bearing monomers, such as styrene sulfonic acid, sodium vinyl sulfonate, sulfoethyl acrylate, sulfoethyl methacrylate, ethylmethacrylate- 2- sulphonic acid, or 2-acrylamido-2- methylpropane sulphonic acid; phosphoethylmethacrylate; the corresponding salts of the acid containing monomer; or combinations thereof. The macromonomer may also contains as polymerized units, mercapto- olefins. Used herein, "mercapto-olefin" and "mercaptan-olefin" are used interchangeably. These mercapto-olefin compounds are those as disclosed in US- A-5,247,000 to Amick. Further, the methods of US-A-5,247,000 may be utilized to prepare comb copolymers of the present invention. In a preferred embodiment of the present invention, the macromonomer is composed of 20 weight percent to 100 weight percent, more preferably from 50 to 100 weight percent, and most preferably from 70 to 100 weight percent, based on total weight of macromonomer, of at least one α-methyl vinyl monomer, a non α- methyl vinyl monomer terminated with an α-methyl vinyl monomer, or combinations thereof. In a most preferred embodiment of the present invention the macromonomer contains as polymerized units from 90 to 100 weight percent α-methyl vinyl monomers, non α-methyl vinyl monomers terminated with α- methyl vinyl monomers, or combinations thereof, based on the total weight of the macromonomer. The phrase "non α-methyl vinyl monomer terminated with an α-methyl vinyl monomer" means that, when a vinyl monomer bearing no α- methyl group is present, as polymerized units, in the macromonomer, the macromonomer must be terminated by a unit derived from an α-methyl vinyl monomer. For example, while styrene might be present, as polymerized units, in a macromonomer chain, that macromonomer chain would be terminated by α- methyl styrene, or some other α-methyl vinyl monomer. Suitable α-methyl vinyl monomers include, for example, methacrylate esters, such as Ci to Cis normal or branched alkyl esters of methacrylic acid, including methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, or stearyl methacrylate; hydroxyalkyl methacrylates such as hydroxyethyl methacrylate; glycidylmethacrylate; phenyl methacrylate; methacrylamide; methacrylonitrile, ' or combinations thereof. One skilled in the art will recognize that there are many ways to prepare the macromonomer useful in the present invention. For example, the macromonomer may be prepared by a high temperature (e.g., at least 150°C) continuous process such as disclosed in US-A-5,710,227 or EP-A-1,010,706, published June 21, 2000. In a preferred continuous process, a reaction mixture of first ethylenically unsaturated monomers is passed through a heated zone having a temperature of at least 150°C, and more preferably at least 275°C. The heated zone may also be maintained at a pressure above atmospheric pressure (e.g., greater than 3,000 kPa = greater than 30 bar). The reaction mixture of monomers may also optionally contain a solvent such as water, acetone, methanol, isopropanol, propionic acid, acetic acid, dimethylformamide, dimethylsulfoxide, methylethylketone, or combinations thereof. The macromonomer useful in the present invention may also be prepared by polymerizing first ethylenically unsaturated monomers in the presence of a free radical initiator and a catalytic metal chelate chain transfer agent (e.g., a transition metal chelate). Such a polymerization may be carried out by a solution, bulk, suspension, or emulsion polymerization process. Suitable methods for preparing the macromonomer using a catalytic metal chelate chain transfer agent are disclosed in for example U.S. Patent Nos. 4,526,945, 4,680,354, 4,886,861, 5,028,677, 5,362,826, 5,721,330, and 5,756,605; European publications EP-A-0199,436, and EP-A-0196783; and PCT publications WO 87/03605, WO 96/15158, and WO 97/34934. Preferably, the macromonomer useful in the present invention is prepared by an aqueous emulsion free radical polymerization process using a transition metal chelate complex. Preferably, the transition metal chelate complex is a cobalt (II) or (III) chelate complex such as, for example, dioxime complexes of cobalt (II), cobalt (II) porphyrin complexes, or cobalt (II) chelates of vicinal iminohydroxyimino compounds, dihydroxyimino compounds, diazadihydroxy- iminodialkyldecadienes, or diazadihydroxyiminodialkylundecadienes, or combinations thereof. These complexes may optionally include bridging groups such as BF 2 , and may also be optionally coordinated with ligands such as water, alcohols, ketones, and nitrogen bases such as pyridine. Additional suitable transition metal complexes are disclosed in for example U.S. Patent Nos. 4,694,054; 5,770,665; 5,962,609; and 5,602,220. A preferred cobalt chelate complex useful in the present invention is Co II (2,3-dioxyiminobutane-BF2)2, the Co III analogue of the aforementioned compound, or combinations thereof. The spatial arrangements of such complexes are disclosed in for example 199436 and U.S. Patent No. 5,756,605. In preparing macromonomer by an aqueous emulsion polymerization process using a transition metal chelate chain transfer agent, at least one first ethylenically unsaturated monomer is polymerized in the presence of a free radical initiator and the transition metal chelate according to conventional aqueous emulsion polymerization techniques. Preferably, the first ethylenically unsaturated monomer is an α-methyl vinyl monomer as previously described herein. The polymerization to form the macromonomer is preferably conducted at a temperature of from 20°C to 150°C, and more preferably from 40°C to 95°C. The solids level at the completion of the polymerization is typically from 5 weight percent to 70 weight percent, and more preferably from 30 weight percent to 60 weight percent, based on the total weight of the aqueous emulsion. The concentration of initiator and transition metal chelate chain transfer agent used during the polymerization process is preferably chosen to obtain the desired degree of polymerization of the macromonomer. Preferably, the concentration of initiator is from 0.2 weight percent to 3 weight percent, and more preferably from 0.5 weight percent to 1.5 weight percent, based on the total weight of monomer. Preferably, the concentration of transition metal chelate chain transfer agent is from 5 ppm to 200 ppm, and more preferably from 10 ppm to 100 ppm, based on the total monomers used to form the macromonomer. The first ethylenically unsaturated monomer, initiator, and transition metal chelate chain transfer agent may be added in any manner known to those skilled in the art to carry out the polymerization. For example, the monomer, initiator and transition metal chelate may all be present in the aqueous emulsion at the start of the polymerization process (i.e., a batch process). Alternatively, one or more of the components may be gradually fed to an aqueous solution (i.e., a continuous or semi-batch process). For example, it may be desired to gradually feed the entire or a portion of the initiator, monomer, and/or transition metal chelate to a solution containing water and surfactant. In a preferred embodiment, at least a portion of the monomer and transition metal chelate are gradually fed during the polymerization, with the remainder of the monomer and transition metal chelate being present in the aqueous emulsion at the start of the polymerization. In this embodiment, the monomer may be fed as is, or suspended or emulsified in an aqueous solution prior to being fed. Any suitable free radical initiator may be used to prepare the macromonomer. The initiator is preferably selected based on such parameters as its solubility in one or more of the other components (e.g., moηomers, water), ' half life at the desired polymerization temperature (preferably a half life within the range of from about 30 minutes to about 10 hours), and stability in the presence of the transition metal chelate. Suitable initiators include for example azo compounds such as 2,2'-azobis (isobutyronitrile), 4,4'-azobis(4-cyanovaleric acid), 2,2'- azobis [2- methyl- N- ( 1 , 1 -bis(hy droxy methyl) - 2 - (hydroxyethyl)] -propionamide , and 2,2'-azobis [2-methyl-N-(2-hydroxyethyl)] -propionamide, ' peroxides such as t- butyl hydroperoxide, benzoyl peroxide, ' sodium, potassium, or ammonium persulphate or combinations thereof. Redox initiator systems may also be used, such as for example persulphate or peroxide in combination with a reducing agent such as sodium metabisulphite, sodium bisulfite, sodium formaldehyde sulfoxylate, isoascorbic acid, or combinations thereof. Metal promoters, such as iron, may also optionally be used in such redox initiator systems. Also, buffers, such as sodium bicarbonate may be used as part of the initiator system. An emulsifier is also preferably present during the aqueous emulsion polymerization process to prepare the macromonomer. Any emulsifier may be used that is effective in emulsifying the monomers such as for example anionic, cationic, or nonionic emulsifiers. In a preferred embodiment, the emulsifier is anionic such as for example sodium, potassium, or ammonium salts of dialkylsulphosuccinates, ' sodium, potassium, or ammonium salts of sulphated oils,' sodium, potassium, or ammonium salts of alkyl sulphonic acids, such as sodium dodecyl benzene sulfonate; sodium, potassium, or ammonium salts of alkyl sulphates, such as sodium lauryl sulfate, ' ethoxylated alkyl ether sulfates; alkali metal salts of sulphonic acids; C12 to C24 fatty alcohols, ethoxylated fatty acids or fatty amides; sodium, potassium, or ammonium salts of fatty acids, such as Na stearate and Na oleate, ' or combinations thereof. The amount of emulsifier in the aqueous emulsion is preferably from 0.05 weight percent to 10 weight percent, and more preferably from 0.3 weight percent to 3 weight percent, based on the total weight of the monomers. The macromonomer thus prepared is emulsion polymerized with at least one second ethylenically unsaturated monomer to form a copolymer composition containing graft copolymer particles. The polymerization is carried out by providing the macromonomer as water insoluble particles in a macromonomer aqueous emulsion and the second ethylenically unsaturated monomer in a monomer composition. At least a portion of the macromonomer aqueous emulsion is combined with at least a portion of the monomer composition to form a polymerization reaction mixture that is polymerized in the presence of an initiator. Although in no way intending to be bound by theory, it is believed that by providing the macromonomer in the form of water insoluble macromonomer particles in an aqueous emulsion, and the second ethylenically unsaturated monomer in a separate monomer composition, upon combination, the second ethylenically unsaturated monomer diffuses through the aqueous phase and then into the macromonomer particles where the polymerization occurs. Preferably, the diffusion of the second ethylenically unsaturated monomer into the macromonomer particles is evidenced by swelling of the macromonomer particles. It is an essential feature of the invention that, prior to being combined with the monomer composition, the macromonomers are present in plural discrete particles dispersed in the aqueous phase. Preferably, these plural macromonomer particles have previously been formed by aqueous emulsion polymerization, and the resultant macromonomer aqueous emulsion is combined with the monomer composition and subsequently polymerized without being isolated. Addition of the monomer composition to the macromonomer aqueous emulsion results initially in the presence of plural monomer droplets in the aqueous emulsion as separate entities distributed among, but not in direct contact with, the plural macromonomer particles. That is, the monomer droplets are separated from the macromonomer particles, and from each other, by an aqueous phase. Individual monomer molecules must then exit the monomer droplet, dissolve in the aqueous phase, diffuse through that aqueous phase to a macromonomer particle, and enter that macromonomer particle where polymerization to form the graft copolymer (preferably, comb copolymer) occurs. Because the water insoluble macromonomers are unable to diffuse through the aqueous phase, it is essential that the monomer droplets not include water insoluble macromonomer if gel formation is to be avoided and if the number of particles initially established by the macromonomer particles is to be maintained during polymerization of monomers with macromonomers. The macromonomer aqueous emulsion useful in the present invention may be formed in any manner known to those skilled in the art. For example, the macromonomer, produced by any known method, may be isolated as a solid (e.g., spray dried) and emulsified in water. Also, for example, the macromonomer, if prepared via an emulsion or aqueous based polymerization process, may be used as is, or diluted with water or concentrated to a desired solids level. In a preferred embodiment of the present invention, the macromonomer aqueous emulsion is formed from the emulsion polymerization of at least one first ethylenically unsaturated monomer in the presence of a transition metal chelate chain transfer agent as described previously herein. This embodiment is preferred for numerous reasons. For example, the macromonomer polymerization can be readily controlled to produce a desired particle size distribution (preferably narrow, e.g., polydispersity less than 2). Also, for example, additional processing steps, such as isolating the macromonomer as a solid, can be avoided, leading to better process economics. In addition, the macromonomer, macromonomer aqueous emulsion, and the graft copolymer can be prepared by consecutive steps in a single reactor which is desirable in a commercial manufacturing facility because process parameters, such as manufacturing cost and particle size distribution, may be optimized. The "macromonomer aqueous emulsion" useful in the present invention contains from 20 weight percent to 60 weight percent, and more preferably from 30 weight percent to 50 weight percent of at least one water insoluble macromonomer, based on the total weight of macromonomer aqueous emulsion. The macromonomer aqueous emulsion may also contain mixtures of macromonomer. Preferably, the macromonomer aqueous emulsion contains less than 5 weight percent and more preferably less than 1 weight percent of ethylenically unsaturated monomer, based on the total weight of macromonomer aqueous emulsion. The water insoluble macromonomer particles have a particle size chosen such that, upon addition of monomers, particles of graft copolymer having a desired particle size will be formed. For example, the final graft copolymer particle size is directly proportional to the initial particle size of the macromonomer and the concentration of second ethylenically unsaturated monomer in the polymerization reaction mixture, assuming all the particles participate equally in the polymerization. Preferably, the macromonomer particles have a weight average particle size of from 50 nm to 500 nm, and more preferably from 80 nm to 200 nm as measured by Capillary Hydrodynamic Fractionation technique using a Matec CHDF 2000 particle size analyzer equipped with a HPLC type Ultra-violet detector. The macromonomer aqueous emulsion may also include one or more emulsifying agents. The type and amount of emulsifying agent is preferably selected in a manner to produce the desired particle size. Suitable emulsifying agents include those previously disclosed for use in preparing the macromonomer by an emulsion polymerization process. Preferred emulsifying agents are anionic surfactants such as, for example, sodium lauryl sulfate, sodium dodecylbenzene sulfonate, sulfated and ethoxylated derivatives of nonylphenols and fatty alcohols. The total level of emulsifying agent, based on the total weight of macromonomer is preferably from 0.2 weight percent to 5 weight percent and more preferably from 0.5 weight percent to 2 weight percent. The "monomer composition" useful in the present invention contains at least one kind of ethylenically unsaturated monomer. The monomer composition may contain all (i.e., 100%) monomer, or contain monomer dissolved or dispersed in an organic solvent and/or water. Preferably, the level of monomer in the monomer composition is from 50 weight percent to 100 weight percent, more preferably from 60 to 90 weight percent, and most preferably from 70 to 80 weight percent, based on the total weight of the monomer composition. Examples of organic solvents that may be present in the monomer composition include Cβ to Cι alkanes. The organic solvent in the monomer composition will be no more than 30 weight percent, and more preferably no more than 5 weight percent, based on the total weight of the monomer composition. In addition to water and/or organic solvent, the monomer composition may also optionally contain monomers containing functional groups, such as, for example, monomers containing hydroxy, amido, aldehyde, ureido, polyether, glycidylalkyl, keto groups or combinations thereof. These other monomers are generally present in the monomer composition at a level of from 0.5 weight percent to 15 weight percent, and more preferably from 1 weight percent to 3 weight percent based on the total weight of the graft copolymer. Examples of functional monomers include ketofunctional monomers such as the acetoacetoxy esters of hydroxyalkyl acrylates and methacrylates (e.g., acetoacetoxyethyl methacrylate) and keto-containing amides (e.g., diacetone acrylamide); allyl alkyl methacrylates or acrylates; glycidylalkyl methacrylates or acrylates! or combinations thereof. Such functional monomer can provide crosslinking if desired. In a preferred embodiment, the monomers in the monomer composition are pre-emulsified in water to form a "monomer aqueous emulsion". Preferably, the monomer aqueous emulsion contains monomer droplets having a droplet size from 1 micron to 100 microns, and more preferably from 5 micron to 50 microns. Any suitable emulsifying agent may be used, for example those previously described, to emulsify the monomer to the desired monomer droplet size. Preferably, the level of emulsifying agent, if present, will be from 0.2 weight percent to 2 weight percent based on the total weight of monomer in the monomer composition. The second ethylenically unsaturated monomer of the monomer composition is preferably selected to provide the desired properties in the resulting graft copolymer (i.e., copolymer) composition. Suitable ethylenically unsaturated monomers include for example methacrylate esters, such as Ci to Cis normal or branched alkyl esters of methacrylic acid, including methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate, isobornyl methacrylate, ' acrylate esters, such as Ci to Cis normal or branched alkyl esters of acrylic acid, including methyl acrylate, ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate; styrene; substituted styrenes, such as methyl styrene, a-methyl styrene or t-butyl styrene,' olefinically unsaturated nitriles, such as acrylonitrile or methacrylonitrile; olefinically unsaturated halides, such as vinyl chloride, vinylidene chloride or vinyl fluoride; vinyl esters of organic acids, such as vinyl acetate; N-vinyl compounds such as N-vinyl pyrrolidone, ' acrylamide; methacrylamide, ' substituted acrylamides; substituted methacrylamides; hy droxy alky lmethacry late s such as hy droxye thy lmethacry late; hydroxyalkylacrylates; dienes such as 1,3-butadiene and isoprene; vinyl ethers! or combinations thereof. The ethylenically unsaturated monomer can also be an acid containing monomer or a functional monomer, such as those previously described herein. Preferably, the ethylenically unsaturated monomer of the monomer composition does not contain amino groups. If the monomers (i.e., the second ethylenically unsaturated monomers) of the monomer composition will be used to prepare the backbone of a comb copolymer, the graft segment of which is not miscible with the thermoplastic polymer of the present invention, it is required that the composition of the those monomers be chosen such that the backbone of the comb copolymer formed therefrom will be miscible in the thermoplastic polymer. If the graft segment is miscible with the thermoplastic polymer, the backbone may, optionally, be miscible in the thermoplastic polymer. The composition of the monomers of the monomer composition further should be chosen so that the Tg of the backbone of the comb copolymer formed therefrom will be preferably from -65 °C to 180 °C, more preferably from -45 °C to 180 °C, and most preferably from -20 °C to 130 °C. In a preferred embodiment, the monomer composition includes one or more ethylenically unsaturated monomers selected from Ci to Cis normal or branched alkyl esters of acrylic acid, including methyl acrylate, ethyl acrylate, n- butyl acrylate and 2-ethylhexyl acrylate,' styrene, ' substituted styrenes, such as methyl styrene, α-methyl styrene or t-butyl styrene," butadiene or combinations thereof. As previously mentioned, the macromonomer aqueous emulsion and monomer composition are combined to form a "polymerization reaction mixture", and polymerized in the presence of a free radical initiator to form an "aqueous copolymer composition", also referred to herein as an "aqueous dispersion of a segmental copolymer". The term "polymerization reaction mixture," as used herein, refers to the resulting mixture formed when at least a portion of the macromonomer aqueous emulsion and at least a portion of the monomer composition are combined. The polymerization reaction mixture may also contain initiator or any other additive used during the polymerization. Thus, the polymerization reaction mixture is a mixture that changes in composition as the macromonomer and monomer in the monomer composition are reacted to form graft copolymer. The macromonomer aqueous emulsion and monomer composition may be combined in various ways to carry out the polymerization. For example, the macromonomer aqueous emulsion and the monomer composition may be combined prior to the start of the polymerization reaction to form the polymerization reaction mixture. Alternatively, the monomer composition could be gradually fed into the macromonomer aqueous emulsion, or the macromonomer aqueous emulsion could be gradually fed into the monomer composition. It is also possible that only a portion of the macromonomer aqueous emulsion and/or monomer composition be combined prior to the start of the polymerization with the remaining monomer composition and/or macromonomer aqueous emulsion being fed during the polymerization. The initiator can also be added in various ways. For example, the initiator may be added in "one shot" to the macromonomer aqueous emulsion, the monomer composition, or a mixture of the macromonomer aqueous emulsion and the monomer composition at the start of the polymerization. Alternatively, all or a portion of the initiator can be co-fed as a separate feed stream,. as part of the macromonomer aqueous emulsion, as part of the monomer composition, or any combination of these methods. The preferred method of combining the macromonomer aqueous emulsion, the monomer composition, and initiator will depend on such factors as the desired graft copolymer composition. For example, the distribution of the macromonomer as a graft along the backbone can be affected by the concentrations of both the macromonomer and the second ethylenically unsaturated monomers at the time of the polymerization. In this regard, a batch process will afford high concentration of both the macromonomer and the second ethylenically unsaturated monomers at the onset of the polymerization whereas a semi-continuous process will keep the second ethylenically unsaturated monomer concentration low during the polymerization. Thus, through the method by which the macromonomer aqueous emulsion and monomer composition are combined, it is possible to control, for example: the number of graft segments, derived from macromonomer, per polymer chain; the distribution of graft segments in each chain, and the length of the polymer backbone. Initiators useful in polymerizing the macromonomer and second ethylenically unsaturated monomer include any suitable initiator for emulsion polymerizations known to those skilled in the art. The selection of the initiator will depend on such factors as the initiator's solubility in one or more of the reaction components (e.g. monomer, macromonomer, water)," and half life at the desired polymerization temperature (preferably a half life within the range of from about 30 minutes to about 10 hours). Suitable initiators include those previously described herein in connection with forming the macromonomer, such as azo compounds such as 4,4'-azobis(4-cyanovaleric acid), peroxides such as t" butyl hydroperoxide,' sodium, potassium, or ammonium persulfate; redox initiator systems such as, for example, persulphate or peroxide in combination with a reducing agent such as sodium metabisulfite, sodium bisulfite, sodium formaldehyde sulfoxylate, isoascorbic acid; or combinations thereof. Metal promoters, such as iron, " and. buffers, such as sodium bicarbonate, may also be used in combination with the initiator. Additionally, Controlled Free Radical Polymerization (CFRP) methods such as Atom Transfer Radical Polymerization; or Nitroxide Mediated Radical Polymerization may be used. Preferred initiators include azo compounds such as 4,4'-azobis(4-cyanovaleric acid). The amount of initiator used will depend on such factors as the copolymer desired and the initiator selected. Preferably, from 0.1 weight percent to 1 weight percent initiator is used, based on the total weight of monomer and macromonomer. The polymerization temperature will depend on the type of initiator chosen and desired polymerization rates. Preferably, however, the macromonomer and second ethylenically unsaturated monomer are polymerized at a temperature of from 0°C to 150°C, and more preferably from 20°C to 95°C. The amount of macromonomer aqueous emulsion and monomer composition added to form the polymerization reaction mixture will depend on such factors as the concentrations of macromonomer and second ethylenically unsaturated monomer in the macromonomer aqueous emulsion and monomer composition, respectively, and the desired graft copolymer composition. Preferably, the macromonomer aqueous emulsion and monomer composition are added in amounts to provide a graft copolymer containing as polymerized units from 20 weight percent to 80 weight percent, more preferably from 30 weight percent to 70 weight percent, and most preferably from 40 weight percent to 60 weight percent macromonomer as polymerized graft segment, and from 20 weight percent to 80 weight percent, more preferably from 30 weight percent to 70 weight percent and most preferably from 40 weight percent to 60 weight percent second ethylenically unsaturated monomer as polymerized units of the backbone. One skilled in the art will recognize that other components used in conventional emulsion polymerizations may optionally be used in the method of the present invention. For example, to reduce the molecular weight of the resulting graft copolymer, the polymerization may optionally be conducted in the presence of one or more chain transfer agents, such as n-dodecyl mercaptan, thiophenol; halogen compounds such as bromotrichlorome thane, " or combinations thereof. Also, additional initiator and/or catalyst may be added to the polymerization reaction mixture at the completion of the polymerization reaction to reduce any residual monomer, (e.g., chasing agents). Suitable initiators or catalysts include those initiators previously described herein. In addition, the chain transfer capacity of a macromonomer through addition-fragmentation can be utilized in part to reduce molecular weight through appropriate ' design of monomer compositions and polymerization conditions. See e.g., E. Rizzardo, et. ah, Prog. Pacific Polym. Sci., 1991, 1, 77-88; G. Moad, et. ah, WO 96/15157^ Preferably, the process of the present invention does not require neutralization of the monomer, or resulting aqueous graft copolymer composition. These components preferably remain in unneutralized form (e.g., no neutralization with a base if acid functional groups are present). The resulting aqueous graft copolymer composition formed by polymerization of the macromonomer and the ethylenically unsaturated monomer in the monomer composition preferably has a solids level of from 30 weight percent to 70 weight percent and more preferably from 40 weight percent to 60 weight percent. The aqueous graft copolymer composition preferably contains graft copolymer particles that are water insoluble and have a particle size of from 60 nm to 500 nm, and more preferably from 80 nm to 350 nm. The graft copolymer formed preferably has a backbone containing, as polymerized units, the second ethylenically unsaturated monomer from the monomer composition, and one or more macromonomer units, as polymerized units, wherein a terminal ethylenically unsaturated group of the macromonomer is incorporated into the backbone and the remainder of the macromonomer becomes a graft segment pendant to the backbone (i.e., a side chain) upon polymerization. Preferably, each side chain is a graft segment derived from the grafting of one macromonomer to the backbone. The degree of polymerization of the graft segments derived from the macromonomer is preferably from 10 to 1,000, more preferably from 20 to 1,000, and most preferably from 20 to 200, where the degree of polymerization is expressed as the number of polymerized units of ethylenically unsaturated monomer used to form the macromonomer. The weight average molecular weight of the graft copolymer (e.g., of the comb copolymer) is preferably in the range of from 50,000 to 2,000,000, and more preferably from 100,000 to 1,000,000. . The number average molecular weight of a comb copolymer is typically less than the corresponding weight average molecular weight. The number average molecular weights of the comb copolymers of the present invention are at least 25,000, and typically range from 25,000 to 600,000. Molecular weights as used herein can be determined by size exclusion chromatography (SEC), also known as gel permeation chromatography (GPC). In a preferred embodiment of the present invention, the polymerization is conducted in two stages. In the first stage, the macromonomer is formed in an aqueous emulsion polymerization process, and in the second stage the macromonomer is polymerized with the second ethylenically unsaturated monomer in an emulsion. For efficiency, preferably these two stages are conducted in a single vessel. For example, in the first stage, the macromonomer aqueous emulsion may be formed by polymerizing in an aqueous emulsion at least one first ethylenically unsaturated monomer to form water insoluble macromonomer particles. This first stage polymerization is preferably conducted using a transition metal chelate chain transfer agent as previously described herein. After forming the macromonomer aqueous emulsion, a second emulsion polymerization is preferably performed in the same vessel to polymerize the macromonomer with at least one second ethylenically unsaturated monomer. This second stage may be conducted for example by directly adding (e.g., all at once or by a gradual feed) the monomer composition and initiator to the macromonomer aqueous emulsion. One main advantage of this embodiment is that the macromonomer does not have to be isolated, and the second polymerization can take place simply by adding the monomer composition and initiator to the macromonomer aqueous emulsion. In this preferred embodiment, the particle size and particle size distribution of the plural water insoluble macromonomer. particles may be precisely controlled, and later addition of more macromonomer aqueous emulsion would typically not be required, except when, for example, a second mode (particle size and/or composition) of graft copolymer is desired. In another preferred embodiment of the present invention, the polymerization of the macromonomer and second ethylenically unsaturated monomer is at least partially performed in the presence of an acid containing monomer, acid containing macromonomer, or combinations thereof. The acid containing monomer or acid containing macromonomer may be added in any manner to the polymerization reaction mixture. Preferably, the acid containing monomer or acid containing macromonomer is present in the monomer composition. The acid containing monomer or acid containing macromonomer may also be added as a separate stream to the polymerization reaction mixture. The amount of acid containing monomer or acid containing macromonomer added to the polymerization reaction mixture is preferably from 0.2 weight percent to 10 weight percent, more preferably from 0.5 weight percent to 5 weight percent, and most preferably from 1 weight percent to 2 weight percent, based on the total weight of monomer and macromonomer added to the polymerization reaction mixture. Acid containing monomers which may be used in this embodiment include ethylenically unsaturated monomers bearing acid functional or acid forming groups such as those previously described herein. The "acid containing macromonomer" useful in this embodiment is any low molecular weight polymer having at least one terminal ethylenically unsaturated group that is capable of being polymerized in a free radical polymerization process, and that is formed from at least one kind of acid containing monomer. Preferably, the amount of acid containing monomer present, as polymerized units, in the acid containing macromonomer is from 50 weight percent to 100 weight percent, more preferably from 90 weight percent to 100 weight percent, and most preferably from 95 weight percent to 100 weight percent. The acid containing macromonomer may be prepared according to any technique known to those skilled in the art such as those previously described herein. In a preferred embodiment of the present invention, the acid containing macromonomer is prepared by a solution polymerization process using a free radical initiator and transition metal chelate complex. Such a process is disclosed in, for example, US-A-5,721,330. Preferred acid containing monomers used to form the acid containing macromonomer are α-methyl vinyl monomers such as methacrylic acid. In another preferred embodiment of the present invention, a "macromolecular organic compound" having a hydrophobic cavity is present in the polymerization medium used to form the macromonomer and/or aqueous copolymer composition. Preferably, the macromolecular organic compound is used when copolymerizing ethylenically unsaturated monomers with very low water solubility such as lauryl or stearyl acrylates and/or methacrylates. By "very low water solubility" it is meant a water solubility at 25°C to 50°C of no greater than 50 millimoles/liter. For example, the macromolecular organic compound may be added to the monomer composition, the macromonomer aqueous emulsion, or the polymerization reaction mixture used to form the aqueous copolymer composition. Also, for example, the macromolecular organic compound may be added to an aqueous emulsion of ethylenically unsaturated monomer used to form the macromonomer. Suitable techniques for using a macromolecular organic compound having a hydrophobic cavity are disclosed in, for example, US-A-5,521,266. Preferably, the macromolecular organic compound having a hydrophobic cavity is added to the polymerization reaction mixture to provide a molar ratio of macromolecular organic compound to very low water solubility monomer or macromonomer of from 5:1 to 1:5000 and more preferably from 1:1 to 1:500. Macromolecular organic compounds having a hydrophobic cavity useful in the present invention include for example cyclodextrin or cyclodextrin derivatives, " cyclic oligosaccharides having a hydrophobic cavity such as cycloinulohexose, cycloinuloheptose, or cycloinuloctoseJ calyxarenes; cavitandsJ or combinations thereof. Preferably, the macromolecular organic compound is β- cyclodextrin, more preferably methyl-β-cyclodextrin. Monomers having low water solubility include for example primary alkenes; styrene and alkylsubstituted styrene; α-methyl styrene; vinyltoluene; vinyl esters of C to C30 carboxylic acids, such as vinyl 2-ethylhexanoate, vinyl neodecanoate; vinyl chloride," vinylidene chloride, " N-alkyl substituted (meth) acrylamide such as octyl acrylamide and maleic acid amide, ' vinyl alkyl or aryl ethers with (C3 -C30) alkyl groups such as stearyl vinyl ether; (Ci -C30) alkyl esters of (meth) acrylic acid, such as methyl methacrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, benzyl (meth) acrylate, lauryl (meth) acrylate, oleyl (meth) acrylate, palmityl (meth) acrylate, stearyl (meth)acrylate, " unsaturated vinyl esters of (meth) acrylic acid such as those derived from fatty acids and fatty alcohols, " multifunctional monomers such as pentaerythritol triacrylate; monomers derived from cholesterol or combinations thereof. The aqueous methods used to produce the comb copolymer of the present invention may produce an aqueous copolymer composition containing water insoluble particles of comb copolymer. The comb copolymer particles preferably have a weight average particle size of from 50 nm to 500 nm, and more preferably from 80 nm to 350 nm. Preferably, the particles of comb copolymer contain from 20 weight percent to 80 weight percent, more preferably from 30 to 70 weight percent, and most preferably from 40 to 60 weight percent polymerized units of a macromonomer, based on the total weight of the copolymer, where the macromonomer preferably has a composition as previously described herein for the water insoluble macromonomer present in the macromonomer aqueous emulsion. The comb copolymer particles also preferably contain from 20 weight percent to 80 weight percent, more preferably from 30 to 70 weight percent, and most preferably from 40 to 60 weight percent polymerized units of at least one second ethylenically unsaturated monomer, based on the total weight of the copolymer. The second ethylenically unsaturated monomer may be any ethylenically unsaturated monomer that provides desirable properties in the copolymer particles, such as those useful in the monomer composition as previously described herein. Although the backbone of the comb copolymer may be branched, with such branching including, for example, "star" structures, it is preferred that the backbone is linear. Compositionally, the backbone of the copolymer preferably contains polymerized units of the second ethylenically unsaturated monomer derived from the monomer composition. Preferably, the Tg of the backbone of the comb copolymer of the present invention is from -65°C to 180°C, more preferably from -45°C to 180°C, and most preferably from -20°C to 130°C. It is further required that, if the graft segment of the comb copolymer is not miscible with the thermoplastic polymer of the present invention, the backbone is miscible with that thermoplastic polymer. The pendant graft segments of the graft copolymer preferably contain polymerized units of the macromonomer. In a preferred embodiment of the present invention, each graft segment is derived from one macromonomer. Additionally, the pendant graft segments contain less than 5 weight percent and more preferably less than 1 weight percent of the polymerized second ethylenically unsaturated monomer derived from the monomer composition, based on the total weight of the pendant graft segments. Preferably, the Tg of the graft segment is from -65°C to 180°C, more preferably from -45°C to 180°C, and most preferably from -20°C to 130°C. It is further required that, if the backbone of the comb copolymer is not miscible with the thermoplastic polymer of the present invention, the graft segment is miscible with that thermoplastic polymer. Preferably, the overall weight average molecular weight of the comb copolymer is from 50,000 to 2,000,000, and more preferably from 100,000 to 1,000,000. In a preferred embodiment of the present invention, the water insoluble graft copolymer particles further contain from 0.2 weight percent to 10 weight percent, more preferably from 0.5 weight percent to 5 weight percent, and most preferably from 1 weight percent to 2 weight percent of an acid containing macromonomer, based on the total weight of the graft copolymer. The acid containing macromonomer preferably has a composition as previously described herein. Although in no way intending to be bound by theory, it is believed that the "acid containing macromonomer" is attached to the surface of the water insoluble graft copolymer particles and provides stability. By "attached," as used herein, it is believed that the acid containing macromonomer is bound in some manner (e.g., covalent, hydrogen bonding, ionic) to a polymer chain in the particle. Preferably, the acid containing macromonomer is covalently bound to a polymer chain in the particle. It has been found that the acid containing macromonomer provides stability to the particles such that the aqueous copolymer composition produced exhibits unexpected improved shear stability, " freeze thaw stability; and stability to additives in formulations, as well as reduction of coagulum during the polymerization. Although improved stability can be achieved using acid containing monomer, these benefits are most dramatic when an acid containing macromonomer is used. When the segmental copolymer of the present invention is a block copolymer, at least one block (i.e., copolymer segment) must be miscible with the thermoplastic polymer of the present invention. The segmental copolymers of the present invention may be isolated as powders, or other solid particles, from dispersions containing them (e.g., aqueous emulsions) by methods well known in the art. These methods include, for example, spray drying, coagulation and oven drying, and freeze drying. For purposes of isolation, handling, storage, shipping, and blending of the segmental copolymer, it is preferred that either the backbone or graft segment have a Tg of at least 30°C, more preferably from 50°C to 180°C, and most preferably from 70°C to 130°C. The segmental copolymer of the present invention are, for example, blended with the thermoplastic polymer to form a solids blend that is mixed and heated to form uniform melt blends containing the segmental copolymer at a level of, preferably, 0.5 to 10 PHR and more preferably 1 to 10 PHR. Used herein, "PHR" refers to parts by weigh per hundred part by weight of thermoplastic polymer. The melt blends are then shaped and cooled, typically to room temp, and preferably to below the desired use temperature of the article so formed. The melt blend is shaped to form the thermoplastic article of the present invention by any technique common to the art. Equipment used to shape the melt blend includes, for example, dies, presses, molds, and blow molds. The articles thus formed are typically cooled to room temperature. The articles of the present invention may further be laminated to other thermoplastic compositions or thermoset compositions by techniques know in the art, such as, for example, co-extrusion. The article of the present invention may also be affixed directly to other substrates, such as for example wood or metal, with or without the use of an adhesive. Any type of thermoplastic article common to the art may be made by the method of the present invention. A non-exhaustive list of these articles includes, for example: construction materials, such as siding, gutters, downspouts, pipe, pipe fittings, wallboard, wall-coverings, molding, fencing, decking, window frames and profiles; consumer goods such as bottles, jars, other containers, films, and laminates; appliance housing such as housings for computers, refrigerators, and air conditioners, as well as interior appliance parts," both interior and exterior automotive parts such as body side molding, and instrument and door panels, " packaging materials; rigid film and sheet such as credit cards and computer disks; toys! and plastic parts such as screws, gears, and wires. The preferred thermoplastic polymers, and the polymers which are most effectively modified by the segmental copolymers of the present invention, are the homopolymers of vinyl chloride and copolymers of vinyl chloride and vinyl acetate. More preferred are the homopolymers of vinyl chloride and copolymers of vinyl chloride and vinyl acetate. Poly(vinyl chloride) is the most preferred thermoplastic polymer. Solids blends of the segmental copolymer and the thermoplastic polymer can be accomplished by any convenient technique. Dry mixing techniques, as with a mechanical mixer-blender device, may be employed. The powder blends can, if desired, be processed in commercial extrusion equipment at conditions varying with the molecular weight of the polyvinyl halide used and the equipment employed for that purpose. Certain lubricants, stabilizers, and the like are often incorporated in the blends. The stabilizers serve to prevent the breakdown of the polyvinyl halide and are of several different types. Two varieties stabilize against thermal and ultraviolet light stimulated oxidative degradation, discoloration, and the like. Other additives to the blends prepared in accordance with the present invention may include, for example, colorants, including organic dyes, such as anthraquinone red! organic pigments and lakes such as phthalocyanine blue! inorganic pigments such as titanium dioxide, and cadmium sulfi.de,' fillers and particulate extenders such as carbon black, amorphous silica, asbestos, glass fibers, and magnesium carbonate; plasticizers such as dioctyl phthalate, dibenzyl phthalate, butyl benzyl phthalate, and hydrocarbon oils, ' and impact modifiers such as typical core-shell methacrylate/butadiene/styrene modifiers and core- shell acrylate/methacrylate modifiers. While only a few of such materials have been specifically recited, it is not intended to exclude others, ' the recitation is exemplary only, and each category of additives is common and well-known in the art. The inclusions can be made at any stage of preparation in. accordance with accepted techniques well-known to those ordinarily skilled in the art, in proportions which are commonly employed. Such additional materials are not of particular significance in the present invention. Experimental Molecular Weight Determination using Gel Permeation Chromatography (GPC) Gel Permeation Chromatography, otherwise known as size exclusion chromatography, actually separates the members of a distribution of polymer chains according to their hydrodynamic size in solution rather than their molar mass. The system is then calibrated with standards of known molecular weight and composition to correlate elution time with molecular weight. The techniques of GPC are discussed in detail in Modern Size Exclusion Chromatography, W. W. Yau, J. J Kirkland, D. D. Bly, ' Wiley-Interscience, 1979, and in A Guide to Materials Characterization and Chemical Analysis, J. P. Sibilia; NCH, 1988, p.81-84. For example, the molecular weight information for a low molecular weight sample (e.g., 10,000) may be determined as follows: The sample (an aqueous emulsion containing low molecular weight particles) is dissolved in THF at a concentration of approximately 0.1% weight sample per volume THF, and shaken for 6 hours, followed by filtration through a 0.45μm PTFE (polytetrafluoroethylene) membrane filter. The analysis is performed by injecting lOOμl of the above solution onto 3 columns, connected in sequence and held at 40°C. The three columns are: 0 ne each of PL Gel 5 100, PL Gel 5 1,000, and PL Gel 5 10,000, all available from Polymer Labs, Amherst, Massachusetts. The mobile phase used is THF flowing at 1 ml/min. Detection is via differential refractive index. The system was calibrated with narrow polystyrene standards. PMMA-equivalent molecular weights for the sample are calculated via Mark- Houwink correction using K=14.1xl0 '3 ml/g and a=0.70 for the polystyrene standards and K=10.4xl0 "3 ml/g and a=0.697 for the sample. Examples Some embodiments of the invention will now be described in detail in the following Examples. The following abbreviations shown in Table 1 are used in the examples: Table 1 " Abbreviations In the Examples, monomer conversion was determined by GC analysis of unreacted monomer using standard methods. Weight percent solids for the macromonomer and copolymer compositions were determined by gravimetric analysis. Particle size of the macromonomer and copolymer compositions were obtained using a Matec CHDF 2000 particle size analyzer equipped with a HPLC type Ultra-violet detector. Macromonomer was measured for number average molecular weight by SEC using a polystyrene standard from Polymer Laboratories (PS-l) having a peak average molecular weight ranging from 580 to 7,500,000 with narrow molecular weight distribution. Conversions from polystyrene to PMMA were made using Mark-Houwink constants. Copolymer compositions were evaluated for number average molecular weight and weight average molecular weight using SEC as described above. Examples 1.1 to 1.8 " Preparation of Macromonomers by Emulsion Polymerization Macromonomer (MM) was prepared by emulsion polymerization processes in Examples 1.1 to 1.8. The polymerization was conducted in a 5-liter, four neck round bottom reaction flask equipped with a mechanical stirrer, temperature control device, condenser, monomer feed line and a nitrogen inlet except for example 1.3 which was prepared in a 5 gallon reactor with similar attachments. The specific amounts of water, surfactant, monomers, chain transfer agent (CTA), and initiator used in Examples 1.1 to 1.8 are shown in Table 2. These ingredients were added according to the following procedure. In a different flask from the reaction flask, a monomer solution was prepared by dissolving the chain transfer agent in the monomer mixture consisting of all the monomers listed in Table 2 under a nitrogen purge. Deionized water and surfactant were introduced into the reaction flask at room temperature to form a water surfactant solution. The water surfactant solution was mixed and heated to 80 °C with stirring under a nitrogen purge. Upon reaching a temperature of 80 °C, and upon complete dissolution of the surfactant, the initiator (CNA) was added to the water surfactant solution with stirring for 2 minute to permit the initiator to dissolve. After dissolution of the initiator, MMA (350 g for example 1.3 and 63 g for examples 1.1, 1.2, 1.4 and 1.6 to 1.8, respectively) was introduced into the reaction flask and allowed to react for 10 minutes. An acrylic latex polymer was used as a seed for example 1.5 (206 g of a acrylic with particle size of 150 nm and solids at 30%). For example 1.7 and 1.8, 46.4 g of a methyl-b-cyclodextrin solution (50%) was added prior to the addition of the following monomer. At the end of 10 minutes, 20 percent by weight of the monomer solution was added to the reaction flask with stirring. Following this initial charge, the remaining monomer solution was fed over a period of 2 hours, with stirring, to form a reaction mixture. At the end of the feed period, the reaction mixture was maintained at 80°C for an additional 2 hours. The reaction mixture was then cooled to room temperature and passed through a filter cloth to remove any coagulum. Generally, the resulting macromonomer emulsion contained less than 5 weight percent coagulum based on the total weight of macromonomer, and the conversion of monomer was over 99 weight percent, based on the total weight of monomer added. The Mn, weight percent solids and particle size for each macromonomer are reported in Table 2. ® CNA, supplied by Aldrich as a 75 weight percent aqueous solution of initiator. (3 > A-16-22 ) ^ ) Lauryl Methacrylate W Zonyl®TM (Dupont) ® The values indicated for the ingredients of Examples 1.7 and 1.8 are the values that are would be expected to form the macromonomers of Examples 1.7 and 1.8 using the method of Example 1, and the values for Particle Size, Mn, and Wt% Solids are the values expected for those macromonomers. Example 2 Preparation of PMAA-MM By Solution Polymerization MAA macromonomer (PMAA-MM) was prepared by aqueous solution polymerization in a 2-liter baffled flange flask equipped with a mechanical stirrer, condenser, temperature control device, initiator feed lines and a nitrogen inlet. The apparatus was purged with nitrogen for 30 minutes after 0.018g of CoBF was added. Deionized water, 1080 g, was charged to the flask and heated to 55°C under a nitrogen purge. A monomer mixture containing 510 ml of MAA and 0.01 g of CoBF was prepared separately under nitrogen. When the deionized water reached a temperature of 55°C, 1.94 g of initiator (Wako VA-044) was added to the reaction flask. Following the addition of the initiator, the monomer mixture was added over a period of 60 minutes to the reaction flask with stirring. The temperature was then held at 55°C for 2 hours following completion of the monomer mixture feed. Upon cooling the reaction flask to room temperature, the MAA-MM (Example 2.1) was isolated as dried polymer by rotary evaporation. The number average molecular weight (Mn) of the MAA-MM was determined by proton nuclear magnetic resonance to be 4030 based on the integration of the vinyl end group with respect to the methyl and methylene groups of the polymer chain. Example 3 Preparation of Acrylic graft copolymers by Semi-continuous Process In Examples 3.1 to 3.9, graft copolymers were prepared by a semi-continuous emulsion polymerization process in a 5-liter round bottom flask with four neck equipped with a mechanical stirrer, temperature control device, initiator feed lines and a nitrogen inlet. The specific amounts of Macromonomer (MM, as emulsion), water, surfactant, monomers, acid containing monomers, and initiator used in Examples 3.1 to 3.9 are shown in Table 3. These ingredients were added according to the following procedure. A monomer emulsion of deionized water (H 2 O #2 in Table 3), surfactant, and monomers (as listed in Table 3) was prepared in a separate flask. Deionized water (H2O #1 in Table 3), MM from the example indicated in Table 1 and 20% of the monomer emulsion were introduced into the reaction flask at room temperature to form a reaction mixture. The reaction mixture was heated to 85°C while stirring under a nitrogen purge. Upon reaching 85°C, the initiator and buffer solutions were introduced into the reaction flask. The remaining monomer emulsion was added over a period of 30 minutes with the temperature maintained at 90°C. Upon completion of the feeds, the reaction mixture was maintained at the reaction temperature for a period of 1 hours. The resulting copolymer composition was analyzed for conversion and other properties as described in Example 5. The conversion of BA, determined by standard GC methods, was greater than 99 weight percent based on the total weight of BA charged. (1) Macromonomer emulsion prepared by method of Example 1. (2) Ethoxylated Cβ to Cis alkyl ether sulfate having from 1 to 40 ethylene oxide groups per molecule (30% active in water). Except for example 3.1. (4 ^ NaPS dissolved in lOg of water. (5) Sodium carbonate dissolved in 15g of water. (6) PMAA-MM (prepared by method of Example 2) W 190 g of EHA and 290 g of MMA ® Alpha methyl styrene (9) 5.8 g of Example 2.1 dissolved in 56 g of water was added to the monomer emulsion. (10) 28 g of Ethylene urea was added to the final latex on cooling to 50°C. (n) The values indicated for the ingredients of Examples 3.7 and 3.8 are the values that are would be expected to form the graft copolymer (i.e., comb copolymers) of Examples 1.7 and 1.8 using the method of Example 3.. Example 4 Preparation of comparative examples. In Examples C-4.1 to C-4.4, random copolymers were prepared by semi- continuous emulsion polymerization in a 5-liter round bottom flask with four neck equipped with a mechanical stirrer, temperature control device, initiator feed lines and a nitrogen inlet. The specific amounts of water, surfactant, monomers used in Examples C-4.1 to C-4.4 are shown in Table 4. These ingredients were added according to the following procedure. A monomer emulsion of deionized water (H2O #2 in Table 4), surfactant (Surf. #2), and monomers (as listed in Table 4) was prepared in a separate flask. Deionized water (H2O #1 in Table 4), and surfactant (for example C-4.2, 4.3, and 4.4, surf. #1) were introduced into the reaction flask at room temperature to form a reaction mixture. For example C-4.1, 7.5 g of an acrylic latex was used as seed polymer (90 nm at 30% solids). The reaction mixture was heated to the 85°C while stirring under a nitrogen purge. Upon reaching 85°C, an initiator solution (5.3 g of NaPS in 50 g of water) and buffer solution (for example C-4.3 only, 5.3 g of Na 2 CO3 in 30g of water) were introduced into the reaction flask with stirring. The monomer emulsion was fed to the reaction mixture over a period of 3 hours together with an initiator solution (0.8 g NaPS in 210g of water). Various amount of water was added to the reaction mixture during the polymerization to control the viscosity. Upon completion of the feeds, the reaction mixture was maintained at the reaction temperature for 20 minutes. Table A ' - Preparation of comparative examples groups per molecule (30% active in water). (2) An acrylic latex was used as seed polymer (90 nm at 30% solids) Characterization of Example 3 Copolymer Compositions (See Table 5) Graft and Random copolymer compositions prepared in the previous examples were characterized by various analytical techniques to determine wt% solids, particle size, weight average molecular weight, number average molecular weight, and percent incorporation of macromonomer. Determination of the amount of unreacted macromonomer was carried out by HPLC analysis using the following procedure. The copolymer compositions were dissolved in THF and analyzed by gradient elution on an LC-18 column supplied by Supelco, located in Bellefonte, PA such that a well-isolated peak was observed for the unreacted macromonomer. Quantification was carried out by caUbrating the detector response using known standards of the same macromonomer employed in the synthesis. The results of the characterization are reported in Table 5 below. (i) Based on the total weight of macromonomer added to reaction vessel. All samples were isolated to dry polymer by freezing the emulsion polymers to induce coagulation followed by drying at 40 °C in a vacuum oven until moisture content was less than 0.5% based on polymer. Measurement of fusion time and melt viscosity (See Table 7). Measurements were made on a Haake Rheocord 90 with a Haake Bowl attachment (available from Haake Buchler Instruments, Saddlebrook, N.J.) which uses counter rotating paddles. The paddle speed was set at 60 rpm and the starting temperature was 170 °C. Torque vs. time was measured for 6 minutes. Torque is proportional to melt viscosity. Fusion time was determined as the time difference between initial loading (i.e., compaction) of the test sample into the instrument and the torque maximum which occurs on fusion. Equilibration torque was measured as the torque value after the torque leveled off to a constant value. Final temperature due to frictional mixing was 195 to 199 °C for all samples. Table 6. Com onents of the master batch formulation. The components (Table 6) were blended in a Henschel blender (available from Henschel Mixers Americas, Houston, Texas) to make a master batch. After the PVC was charged and the blades begin turning, the blender temperature increased from frictional heating at approximately 3-5°C/min. After the PVC was charged, the remaining ingredients were added through the addition port when the temperature reached the temperatures listed below. Charge PVC to blender at 25 °C and close lid. Turn on mixing blades at about 1000 rpm. Monitor temperature. No cooling. Add Advastab™ TM-181 stabilizer at 52°C. Add Loxiol VPG-1304 and OP Wax lubricants at 55°C. Add lubricating processing aid, Paraloid™ K-175, at 77°C. At 100°C start cooling water flow. Reduce blade speed to near minimum (ca. 200 rpm). Cool to 45°C, turn off blades, and remove masterbatch powder from blender. Example processing aids were post added to the master batch at the desired levels - parts per hundred on PVC (PHR) levels and mixed by shaking in a bag to make example formulations. (a) Used herein, "PHR" is an abbreviation for parts of a given component per hundred parts of PVC, based on weight. (b) The "C" designation means "comparative", i.e., "C-8" in column 1. PVC does not on its own have high melt strength and benefits in processing from the addition of high MW polymers that are soluble in PVC to build melt strength. MW as measured by GPC of these materials is typically in the milhons (Plastic Additives Handbook 4 th ed., Editors R. Gachter, H. Muller, P.P. Klemchuk, Hanser Publishers , NY, 1996 ( p. 483)). Table 7 illustrates that the comb copolymers behave well as processing aids for PVC, providing reduced fusion time and reduced temperature at the time of fusion. Based on fusion time and fusion temperature, the comb copolymers displayed performance similar to that of the corresponding random copolymers. However, the random copolymer of Example 4.4, having a Tg of 13°C as calculated by the Fox equation, was extremely difficult to work with. During isolation and drying, it had become a tacky film which had to be cut up prior to combination with the PVC powder. Both the necessity for cutting, and the small, tacky pieces that result from that cutting, are unacceptable as part of a process in a large scale PVC processing facility. By contrast, the corresponding comb copolymer was isolated at a flowable powder that was easily combined and mixed with the PVC master batch to produce the formulation for melt processing. Table 8. Values of "improvement" terms for comb copolymers and random co ol mers used as rocessin aids for PVC. (a) Used herein, "PHR" is an abbreviation for parts of a given component per hundred parts of PVC, based on weight. (b) "Exmpl No." means "example number", " the "C" designation means "comparative", i.g., "C-8" in column 1.

Claims: We Claim: 1. A method comprising the steps of (a) forming a solids blend comprising a thermoplastic polymer and a segmental copolymer, " and (b) mixing and heating said solids blend to form a melt blend; wherein said melt blend has a melt processing improvement term having a value of at least 10. 2. The method of claim 1, wherein said thermoplastic polymer is a polymer selected from the group consisting of poly(vinyl halide) homopolymer, poly(vinyl hahde) copolymer, chlorinated poly(vinyl chloride), and combinations thereof. 3. The method of claim 1, wherein said thermoplastic polymer is poly(vinyl chloride). 4. The method of claim 1, wherein said segmental copolymer is a copolymer selected from the group consisting of comb copolymer, block copolymer, and combinations thereof. 5. The method of claim 1, " wherein said segmental copolymer is a comb copolymer comprising at least two copolymer segments; and wherein a first copolymer segment is a backbone and a second copolymer segment is a graft segment. 6. The method of claim 5, wherein at least one copolymer segment of said comb copolymer is miscible with said thermoplastic polymer. 7. The method of claim 5, wherein at least one copolymer segment of said comb copolymer has a glass transition temperature of at least 50°C. 8. The method of claim 5, wherein the degree of polymerization of said graft segment is 10 to 1,000. 9. The method of claim 5, wherein said comb copolymer has a weight average molecular weight of 50,000 to 2,000,000. 10. A method comprising the steps of (a) forming a solids blend comprising a thermoplastic polymer and a segmental copolymer; (b) mixing and heating said solids blend to form a melt blend, " (c) shaping said melt blend to form an article, " and (d) cooling said article to room temperature, " wherein said melt blend has a melt processing improvement term having a value of at least 10. 11. The method of claim 10, wherein said thermoplastic polymer is a polymer selected from the group consisting of poly(vinyl halide) homopolymer, poly(vinyl halide) copolymer, chlorinated poly (vinyl chloride), and combinations thereof. 12. An article, wherein said article comprises a thermoplastic polymer and a segmental copolymer. 13. An article produced by the method of claim 10.

Inventors: LAU WILLIE, VAN RHEENEN PAUL RALPH, LAU, WILLIE, VAN RHEENEN, PAUL, RALPH
Applicants: ROHM & HAAS, ROHM AND HAAS COMPANY
Application year: 2001
Main classification: C08J3
IPC codes: B32B27, C08F4, C08F257, C08F265, C08F290, C08F291, C08F293, C08J5, C08L23, C08L25, C08L27, C08L33, C08L51, C08L53, C08L55, C08L67, C08L69, C08L77, C08L101, C09D5, C09D133, C09D151, C09D153, C09D155, C09D157, C09J133, C09J151