segments of such a preferred branched polymer typically contain between 35% to 100% of the protected acid groups present. Such a branched polymer when completely unpro› tected ( all protected acid groups converted to free acid groups) has an acid number between about 20 and about 500, preferably between about 30 and about 330, and more preferably between about 30 and about 130, and analogously the ethylenically unsaturated macromer component prefer› ably has an acid number of about 20 and about 650, more preferably between about 90 and about 300 and the majority of the free acid groups are in the branch segments. 

[0073] Each photosensitive composition of this aspect of the invention contains a branched polymer, also known as a comb polymer, which contains protected acid groups. The branched polymer has branch segments, known as polymer arms, of limited molecular weight and limited weight ratio relative to a linear backbone segment. In a preferred embodi› ment, a majority of the protected acid groups are present in the branch segments. The composition also contains a com› ponent, such as a photoacid generator, which renders the composition reactive to radiant energy, especially to radiant energy in the ultraviolet region of the electromagnetic spec› trum and most especially in the far or extreme ultraviolet region. 

[0074] In a specific embodiment, the branched polymer comprises one or more branch segments chemically linked along a linear backbone segment wherein the branched polymers have a number average molecular weight (Mn) of about 500 to 40,000. The branched polymer contains at least 0.5% by weight of branch segments. The branch segments, also known as polymer arms, typically are randomly dis› tributed along the linear backbone segment. The "polymer arm" or branch segment is a polymer or oligomer of at least two repeating monomer units, which is attached to the linear backbone segment by a covalent bond. The branch segment, or polymer arm, can be incorporated into the branched polymer as a macromer component, during the addition polymerization process of a macromer and a comonomer. A "macromer" for the purpose of this invention, is a polymer, copolymer or oligomer of molecular weight ranging from several hundred to about 40,000 containing a terminal ethylenically unsaturated polymerizable group. Preferably the macromer is a linear polymer or copolymer end capped with an ethylenic group. Typically, the branched polymer is a copolymer bearing one or more polymer arms, and pref› erably at least two polymer arms, and is characterized in that between about 0.5 and about 80 weight %, preferably between about 5 and 50 weight % of the monomeric components used in the polymerization process is a mac› romer. Typically, comonomer components used along with the macro mer in the polymerization process likewise contain a single ethylenic group that can copolymerize with the ethylenically unsaturated macromer. 

[0075] The ethylenically unsaturated macromer and the resulting branch segment of the branched polymer, and/or the backbone of the branched polymer, can have bonded thereto one or more protected acid groups. For the purposes of this invention, a "protected acid group" means a func› tional group which, when deprotected, affords free acid functionality that enhances the solubility, swellability, or dispersibility in aqueous environments, of the macromer and/or the branched polymer to which it is bonded. The protected acid group may be incorporated into the ethyleni- 

cally unsaturated macromer and the resulting branch seg› ment of the branched polymer, and/or the backbone of the branched polymer, either during or after their formation. While addition polymerization using a macromer and at least one ethylenically unsaturated monomer is preferred for forming the branched polymer, all known methods of pre› paring branched polymers using either addition or conden› sation reactions can be utilized in this invention. Further› more, use of either preformed backbones and branch segments or in situ polymerized segments are also appli› cable to this invention. 

[0076] The branch segments attached to the linear back› bone segment can be derived from ethylenically unsaturated macromers prepared according to the general descriptions in U.S. Pat. No. 4,680,352 and U.S. Pat. No. 4,694,054. Macromers are prepared by free radical polymerization processes employing a cobalt compound as a catalytic chain transfer agent and particularly a cobalt(II) compound. The cobalt(II) compound may be a pentacyanocobalt(II) com› pound or a cobalt(II) chelate of a vicinal iminobydroxyimino compound, a dihydroxyimino compound, a diazadihydroxy› iminodialky ldecadiene, a diazadihydroxyimnino-dialky lun› decadiene, a tetraazatetraalkylcyclotetradecatetraene, a tet› raazatetraalkylcyclotedodecatetraene, a bis(difluoroboryl)diphenyl glyoximato, a bis( difluorobo› ryl)dimethyl glyoximato, a N,N’-bis(salicylidene )ethylene› diamine, a dialkyldiaza-dioxodialkyldodecadiene, or a dialkyldiazadioxodialkyl-tridecadiene. Low molecular weight methacrylate macromers may also be prepared with a pentacyanocobalt(II) catalytic chain transfer agent as dis› closed in U.S. Pat. No. 4,722,984. 

[0077] Illustrative macromers using this approach are methacrylate polymers with acrylates or other vinyl mono› mers wherein the polymers or copolymers have a terminal ethylenic group and a hydrophilic functional group. Pre› ferred monomer components for use in preparing macromers include: tertiary-butyl methacrylate (tBMA), tertiary-butyl acrylate (tBA), methyl methacrylate (MMA); ethyl meth› acrylate (EMA); butyl methacrylate (EMA); 2-ethylhexyl methacrylate; methyl acrylate (MA); ethyl acrylate (EA); butyl acrylate (BA); 2-ethylhexyl acrylate; 2-hydroxyethyl methacrylate (HEMA); 2-hydroxyethyl acrylate (HEA); methacrylic acid (MA); acrylic acid (AA); esters of acrylic and methacrylic acid wherein the ester group contains from 1 to 18 carbon atoms; nitriles and amides of acrylic and methacrylic acid ( e.g., acrylonitrile ); glycidyl methacrylate and acrylate; itaconic acid (IA) and itaconic acid anhydride (ITA), half ester and imide; maleic acid and maleic acid anhydride, half ester and imide; aminoethyl methacrylate; t-butyl aminoethyl methacrylate; dimethyl aminoethyl meth› acrylate; diethyl aminoethyl methacrylate; aminoethyl acry› late; dimethyl aminoethyl acrylate; diethyl aminoethyl acry› late; acrylamide; N-t-octyl acrylamide; vinyl methyl ether; styrene (STY); alpha-methyl styrene (AMS); vinyl acetate; vinyl chloride; and the like. 

[0078] Itaconic acid anhydride (ITA, 2-methylenesuccinic anhydride, CAS No.=2170-03-8) is a particularly advanta› geous comonomer for use in the branched polymer since it has two active functional groups in the anhydride form, which become three upon ring opening to afford, diacid. The ethylenically unsaturated moiety is a first functional group, which provides capability for this comonomer to be incor› porated into a copolymer by, for example, free radical 

