May  12, 2005  7  US 2005/0100814 Al  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 