Abstract: A process for producing water-soluble, cationic polyelectrolytes is described, wherein the polymerization of the water-soluble monomers is initiated at low temperatures using a combination of UV light, photoinitiator and a redox system, and is characterized in that the redox system is capable of initiating the polymerization only at temperatures higher than or equal to 20° C. The polymers have a high molecular weight and a low content of residual monomer.

Abstract: A method for rapid polymerization, curing or a combination thereof of a polymerizable or curable composition to yield polymers and composites based on these polymers through the utilization of short wavelength microwave energy is described. The inventive method is generally applicable to the chemical transformation of any organic material that can be processed by heating. This invention also relates to specially prepared particulate polymerization curing materials which, when dispersed and irradiated in a polymerizable or curable composition, will effect rapid polymerization, curing or a combination of polymerization and curing of that composition without exceeding the decomposition temperature of the polymerizable or curable composition when the composition is exposed to microwave radiation. The polymerization agent may also be encapsulated by a material which coats the polymerization agent to prevent its premature release into the polymerizable or curable composition.

Abstract: Provided is a photopolymerization initiator which has a high sensitivity and is inexpensive and which does not cause precipitation of crystals when kept in cold storage after diluted and dissolved in an organic solvent.

Abstract: The present invention provides a polymer that can be used as an anti-refelctive coating (ARC) polymer, an ARC composition comprising the same, methods for producing the same, and methods for using the same. The polymer of the present invention is particularly useful in a submicrolithographic process, for example, using KrF (248 nm), ArF (193 nm), or F2 (157 nm) laser as a light source. The polymer of the present invention comprises a chromophore that is capable of absorbing light at the wavelengths used in a submicrolithographic process. Thus, the ARC of the present invention significantly reduces or prevents back reflection of light and the problem of the CD alteration caused by the diffracted and/or reflected light. The ARC of the present invention also significantly reduces or eliminates the standing wave effect and reflective notching.

Abstract: A methyacryloyl or acryloyl derivative of an ester of cyanoacetic acid may be of the formula: CN—CH2—COOR2OCOCR1═CH2. R1 may be H or CH3, and R2 may be one of the group of moieties including alkyl, alkenyl, alkynyl, alkoxyalkyl, poly (oxyalkyl), aryl, cycloalkyl, and heterocyclyc radical, or substitited combinations thereof. Further, R2 may include between 1 and 16 carbon atoms or heteroatom ring members.

Abstract: The present invention relates to novel compositions and methods for preventing corrosion.

Abstract: This invention is of a resin composition including an additive of one or more organic peroxide thermal imitators to cationic photoinitiators, that are sensitized with alpha-hydroxy-ketones, which composition provides a self-propagating thermal curing reaction first activated by a short duration of surface ultraviolet radiation. The thermal reaction is non-directional, thus eliminating the line of sight limitation of current radiation curing processes. Complete curing can be achieved of the composition in a very short time; often after only a few minutes or less. The activation period can be provided by only a few seconds of ultraviolet light using a wide variety of commercial ultraviolet light sources.

Abstract: New modified polyester resin/organic peroxide systems for powder coatings which are applicable to temperature sensitive and metallic substrates include (a) a polyester resin which is a hydroxylated or carbonxylated polyester with unsaturation in its chain, and (b) an organic peroxide with a minimum curing temperature of between 140° and 190° C.; the relative proportions of resin and organic peroxides being 55-60% by weight of resin based on the final composition and 0.5-3.0 by weight of organic peroxide based on the final formulation. These systems find their main application in the manufacture of powder coatings for the coating of temperature sensitive substrates like plastics and metallic substrates, especially aluminum substrates, using the systems currently existing in industry.

Abstract: The invention concerns the use of monomer-free saturated or unsaturated polyester resins or mixtures of saturated and unsaturated polyester resins containing structural units of general formulae (I) and/or (II), in which n=1-10, as impregnation, sealing and coating compounds for electrical engineering and electronic components and for carrier substances for flat insulating materials.

Abstract: The present invention provides polyester/vinyl dioxolane based coating compositions containing no or essentially no volatile organic components. Oligomers for forming the coating compositions of the present invention are vinyl dioxolane end-capped polyester oligomers.

Abstract: In a battery in which a metallic battery case for accommodating electricity-generating elements also serves as an electrode, a visible-light or near-infrared-light curing resin is used for providing a coating to insulate an end face and a peripheral edge portion of an opening portion of the battery case or a gap between a positive electrode and a negative electrode. The visible-light or near-infrared-light curing resin excels in a depth-curing characteristic as compared with a conventional ultraviolet curing resin, and cures well even up to a portion such as an insulating seal of a battery where a light-receiving port is light and the light is difficult to reach. Hence, the visible-light or near-infrared-light curing resin is prevented from becoming peeled off and provides a reliable insulting characteristic.

Abstract: A reactive melt mixing process for the preparation of a low fix temperature toner resin, comprising:(a) mixing a reactive base resin, an initiator, and a polyester with amine functionality, and(b) crosslinking the resulting polymer melt under high shear to form a crosslinked toner resin.

Abstract: A photosensitive resin composition for photoresist which is highly sensitive and can directly form an image using a laser is disclosed. Said composition comprises (A) an unsaturated resin having carboxyl group(s) which is obtained by firstly reacting 0.8 to 1.3 moles of an ethylenic unsaturated monocarboxylic acid with 1 mole of an epoxy group of a homopolymer or copolymer of ethylenic unsaturated monomer having an epoxy group to obtain an unsaturated resin which is then reacted with a dibasic acid anhydride, (B) ethylenic unsaturated compound without epoxy group, and (C) photopolymerization initiator.

Abstract: The invention relates to a process for heating polymer material, including irradiation of said polymer material with infrared radiation. In accordance with the process according to the invention the infrared radiation has wave lengths which substantially are not equal to the absorption peaks of the polymer material in respect of infrared radiation.

Abstract: A process for co-polymerizing unsaturated vegetable oils or fatty acids utilizing the steps of mixing the unsaturated vegetable oil or fatty acid with maleic anhydride in a container. Simultaneously, inert gas is added to the container to provide an oxygen free environment within the container. A sufficient amount of initiator is added to the mixture in the container to produce free radicals for the co-polymerization of the vegetable oil with this fatty acid or the maleic anhydride.

Abstract: The invention relates to an adhesive system for fixing dental restorative materials to hard dental substance constitutingi) a component which contains at least one activator which is a constituent of a chemical initiator system, and contains at least one ethylenically unsaturated compound which is capable of polymerization,ii) a component which contains at least one ethylenically unsaturated compound which is capable of polymerization but otherwise contains no further activator, which is able to start chemical curing with the activator from component i), andiii) a dental restorative material which contains at least one activator which, together with the activator from i), is able to start a polymerization reaction, or a cement for fixing dental restorative materials that have already cured, which contains at least one activator which, together with the activator from component i), is able to start radical polymerization.

Abstract: A novel method for producing thick composite parts based upon photopolymerizable compositions is disclosed. Also disclosed are novel methods for encapsulation of microelectronic devices based upon novel photopolymerizable compositions. The constituents of the photopolymerizable mixture comprise a monomer or monomers capable of polymerizing by free radical or cationic mechanisms, and a photoinitiator system which possesses an absorbance characteristic which is effectively reduced, or self-eliminating, upon initiation of the polymerization reaction. Parts having thicknesses up to 2 cm and thicker for varying end use applications are made by photopolymerizing such compositions. In addition, using such compositions composite parts can be made using a reinforcement material such as a glass fiber mat present in an amount by weight of from about 5 to about 70%.

Abstract: Dental restoratives comprising BisEMA6 UDMA, BisGMA and optionally TEGDMA are described. These restoratives exhibit excellent properties, including high toughness, low shrinkage, appropriate viscosity, long shelf stability, hardness and high strength.

Abstract: Opaquely pigmented or thick filmed powder coatings for heat sensitive substrates, such as wood, wood composites, for example, medium density fiber board, and plastics, that can be fully cured, especially near the substrate, through the incorporation of a dual cure system in the powder comprising a thermal initiator, such as a peroxide, along with a UV initiator. The UV initiator cures the surface, while the thermal initiator cures at the substrate. Surprisingly, virtually no pregelation occurs during the heated melt and flow out step prior to UV curing. Consequently, the hardened film finish formed on the surface exhibits exceptional smoothness which is comparable to that of traditional UV curable powders. The hardened film finish is also fully cured throughout and exhibits exceptional adhesion to the substrate which cannot be achieved with traditional UV curable powders that have been pigmented.

Abstract: Opaquely pigmented or thick filmed powder coatings for heat sensitive substrates, such as wood, wood composites, for example, medium density fiber board, and plastics, that can be fully cured, especially near the substrate, through the incorporation of a dual cure system in the powder comprising a thermal initiator, such as a peroxide, along with a UV initiator. The UV initiator cures the surface, while the thermal initiator cures at the substrate. Surprisingly, virtually no pregelation occurs during the heated melt and flow out step prior to UV curing. Consequently, the hardened film finish formed on the surface exhibits exceptional smoothness which is comparable to that of traditional UV curable powders. The hardened film finish is also fully cured throughout and exhibits exceptional adhesion to the substrate which cannot be achieved with traditional UV curable powders that have been pigmented.

Abstract: A process for producing a hermetic electric compressor for a refrigerating or air-conditioning apparatus using a refrigerant having a hydrofluorocarbon base which comprises a motor unit, a compressing unit driven by the motor unit and a sealed housing enclosing the motor unit and the compressing unit and stores a refrigeration oil on the bottom of the sealed housing, wherein a solventless varnish comprising a thermosetting resin having at least two (meth)acryloyl groups in one molecule, a low-viscosity vinyl or 1-alkylvinyl monomer having an ether or ester linkage as a reactive diluent and an organic peroxide as a reaction initiator is used as an insulating varnish to insulate and fix the magnet wires of the stator of the motor unit, and the solventless varnish is cured by heating at a temperature of from 153 to 180.degree. C. for from 0.5 to 3.5 hours.

Abstract: The invention describes a dental composition, delivery system and method for making temporary crowns and bridges in which the composition comprises two free-radical polymerizable pastes, one a catalyst paste and the other a base paste, wherein the catalyst paste comprises at least one polymerizable monomer, at least one polymerization initiator which is a peroxide oxidizing agent, at least one first polymerization inhibitor and a filler, and wherein the base paste comprises at least one polymerizable monomer, at least one polymerization accelerator, at least one second polymerization inhibitor, at least one non-polymerizable plasticizer and a filler. These catalyst and base pastes are stored in a dual cartridge from which they can be dispensed with a dispenser, preferably in a 1:1 volume ratio, and can be mixed in a static mixer to form a moldable polymerizing material, which is then applied to a prepared area of one or more teeth in a patient's mouth to form a crown or a bridge.

Abstract: A visible radiation-curable solder resist composition which comprises a resin component, a component for promoting photo-polymerization or -crosslinking, and optionally a diluent and any other additives, the resion componebt comprising a novolak resin skeleton and a polyfunctional acrylic monomer and the component for promoting photo-polymerization or -crosslinking comprising a photo-reaction initiator, a sensitizing dye and a heterocyclic compound having at least two endocyclic nitrogen atoms.

Abstract: This invention relates to a method of curing unsaturated polyester resins or mixtures of such resins and a monomer copolymerizable therewith. More particularly, the invention relates to the curing of such resins and mixtures thereof with a composition comprising acetylacetone peroxide (AAP) in an amount of from about 30 to about 35 percent and a high temperature peroxide. Preferably, the high temperature peroxide is t-butyl peroxybenzoate (TBPB) and is present in an amount of from about 5 to about 10 percent of the composition.

Abstract: A light sensitive composition and a manufacturing method of a planographic printing plate employing the same are disclosed, the composition comprising a radical generating agent and a dye represented by the following formula (1), (2) or (3): ##STR1##

Abstract: Opaquely pigmented or thick filmed powder coatings for heat sensitive substrates, such as wood, wood composites, for example, medium density fiber board, and plastics, that can be fully cured, especially near the substrate, through the incorporation of a dual cure system in the powder comprising a thermal initiator, such as a peroxide, along with a UV initiator. The UV initiator cures the surface, while the thermal initiator cures at the substrate. Surprisingly, virtually no pregelation occurs during the heated melt and flow out step prior to UV curing. Consequently, the hardened film finish formed on the surface exhibits exceptional smoothness which is comparable to that of traditional UV curable powders. The hardened film finish is also fully cured throughout and exhibits exceptional adhesion to the substrate which cannot be achieved with traditional UV curable powders that have been pigmented.

Abstract: A photopolymerizable composition and a presensitized planographic printing plate employing the same are disclosed which comprise a compound having an ethylenically unsaturated bond and a dye represented by the following formula (1) or (2): ##STR1##

Abstract: An improved barrier or drug delivery system which is highly adherent to the surface to which it is applied is disclosed, along with methods for making the barrier. The barrier can be prepared by staining tissue with a photoinitiator, applying a solution containing a polymerizable barrier material solution and a photoinitiator to the tissue, and polymerizing the polymer solution on exposure to light. The resulting polymer adheres strongly to the tissue surface, and also forms a gel in the rest of the applied volume. The polymerizable barrier materials are highly useful for sealing tissue surfaces and junctions against leaks of fluids. The method can be used to adhere preformed barriers to tissue or other surfaces, or to adhere tissue surfaces to each other. Tissue surfaces can be adhered to each other to repair wounds. In addition to photochemical initiators, non-photochemical initiators and combinations of chemical initiators and photochemical initiators can be used.

Abstract: A photopolymerizable composition is disclosed, comprising the following components (i), (ii) and (iii):(i) a compound having at least one addition-polymerizable, ethylenically unsaturated bond;(ii) a compound represented by formula (I): ##STR1## wherein A=represents a substituted or unsubstituted 2(3H)-thiazolylidene or 2-thiazolidinylidene group; --X-- represents --O--, --S--, --NR.sup.2 -- or --CONR.sup.3 --, in which R.sub.1, R.sup.2 and R.sup.3 each independently represents a hydrogen atom, an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, an alkenyl group, a substituted alkenyl group, an alkynyl group or a substituted alkynyl group; and=E represents a substituted or unsubstituted 1,3-dihydro-1-oxo-2H-inden-2-ylidene group; and(iii) a compound which generates an active radical upon light irradiation in the co-presence of component (ii).

Abstract: A photopolymerizable composition comprising an addition-polymerizable compound having at least one ethylenic unsaturated double bond, a specific sensitizing dye represented by the following formula (I), and a titanocene compound: ##STR1## The substituents in formula (I) are defined in the specification.

Abstract: The present invention provides a photosensitive resin composition wherein a sensitiveness of polysilane to photodegradation is improved and a time required for photodegradation is short. The photosensitive resin composition comprises:(a) a polysilane having a structure of the formula: ##STR1## ?wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4, the same or different, are selected from the group consisting of a substituted or non-substituted aliphatic hydrocarbon group, an alicyclic hydrocarbon group and an aromatic hydrocarbon group, and m and n indicate an integer!,(b) a photoradical generator, and(c) an oxidizing agent. A method for forming a pattern using the photosensitive resin composition is also disclosed.

Abstract: A modified acrylic urethane prepolymer composition and an unsaturated polyester resin composition to which the prepolymer has been added. The prepolymer composition includes an acrylic urethane prepolymer prepared by the reaction of diisocyanate, like MDI, with an hydroxyl-containing acrylate monomer, such as a pentaerythritol triacrylate, which prepolymer composition may contain a styrene monomer and an inhibitor, such as benzoquinone, to retard the reaction of the prepolymer and styrene monomer prior to the addition of the prepolymer composition into the polyester resin composition. The employment of the modified urethane prepolymer composition provides for the reduction in the amount of styrene monomer used in the unsaturated resin composition and also provides for improved chemical and physical properties of the cured, unsaturated resin composition, such as a reduction in glass roll-out when the resin composition is employed with fiberglass.

Abstract: The present invention relates to a radiation curable silicone release coating composition comprising (A) an alicyclic epoxy-functional silicone graft copolymer, (B) an organic compound having at least 2 alicyclic epoxy groups, and (C) a photocuring catalyst. The compositions of this invention are highly adhesive to a variety of substrates, have excellent coatability, and the release resistance values of films having the composition of this invention cured thereon can be adjusted over a wide range of values.

Abstract: A photopolymerizable composition comprising an addition-polymerizable compound having at least one ethylenic unsaturated double bond, at least one specific sensitizing dye such as the following formula (I), and a titanocene compound: ##STR1## The substituents in formula (I) are defined in the specification.

Abstract: A free radical polymerization process for the preparation of polymer comprising:a first heating and photoinitiating with ultraviolet light of a mixture comprised of a stable free radical agent, and at least one polymerizable monomer compound;optionally cooling said mixture;a second heating of said mixture at a temperature of from about 100.degree. C. to about 160.degree. C.;isolating the polymer product formed; andoptionally washing and drying said polymer.

Abstract: A photopolymerizable composition is described, comprising components (i) a compound having at least one addition-polymerizable ethylenically unsaturated bond, (ii) a compound represented by the following formula (I): ##STR1## and (iii) an activating agent which generates an active radical upon light irradiation in the co-presence of component (ii). The substituents in formula (I) are defined in the specification.

Abstract: A photopolymerizable composition is disclosed, which comprises an addition-polymerizable compound having at least one ethylenically unsaturated double bond, a sensitizing dye represented by the following formula (I): ##STR1## wherein the all symbols are defined in the disclosure, and a titanocene compound.

Abstract: A peroxide-generating composition for use in curing an unsaturated polyester resin and to the cured unsaturated polyester resin composition so prepared, particularly unsaturated polyester resin compositions containing inert filler materials used prepare a cast or molded product. The peroxide-generating composition comprises an allyl alcohol alkanoate, such as allyl alcohol propoxylate, which in the presence of a metal salt promoter, such as cobalt carboxylate, either with the allyl alcohol alkanoate or separately as a prepromoter in the unsaturated polyester resin composition provides for the generation from the allyl alcohol alkanoate of a peroxide to effect the in situ cure of the unsaturated polyester resin composition.

Abstract: A composition for producing an unsaturated polyester is provided. The composition comprises an unsaturated polyester resin; cement; sand; bleaching agent; and curing agent.

Abstract: A photopolymerizable composition is disclosed, comprising an addition polymerizable compound having at least one ethylenically unsaturated double bond, a sensitizing dye represented by formula (I) and a titanocene compound. The photopolymerizable composition exhibits high sensitivity to active light rays over a wide region of from ultraviolet light to visible light.

Abstract: An electrical component comprising an electrical component having an exterior protective layer on at least a portion of a surface. The layer is a cured copolymer of a reaction between at least one oligomer having a terminal ethylenically unsaturated group and at least one monomer having a terminal ethylenically unsaturated group. Alternatively, the layer is a cured copolymer of a reaction between at least two oligomers having a terminal ethylenically unsaturated group. The copolymerization reaction is preferably in the presence of a free radical initiator curing agent and a transition metal catalyst.

Abstract: A novel and safe ethylenically unsaturated peroxyester composition derived from an ethylenically unsaturated dicarboxylic acid is provided, as well as processes for making and using the composition. The peroxyester composition comprises about 0.04 to about 0.70 mole fraction of a first component compound having a formula I: ##STR1## about 0.32 to about 0.50 mole fraction of a second component compound having a formula II: ##STR2## about 0.04 to about 0.70 mole fraction of a third component compound having a formula III: ##STR3## wherein Q is an unsaturated ethylene divalent radical and R.sup.1 and R.sup.2 are organic substituents. Polymeric-peroxides are prepared via polymerizing the peroxyester compositions. The peroxyester compositions are also used for curing unsaturated polyester resins and for initiating polymerization of ethylenically unsaturated monomers.

Abstract: A photopolymerizable composition comprising an addition polymerizable compound having at least one ethylenically unsaturated double bond and a photopolymerization initiator system, wherein the photopolymerization initiator system comprises:(a) a sensitizer of the formula (I) ##STR1## wherein -A is ##STR2## wherein each of R.sup.1 and R.sup.2 is a hydrogen atom, an alkyl group, an aryl group or a halogen atom, each of R.sup.3 and R.sup.4 is an alkyl group which may have substituents, each of R.sup.5 to R.sup.8 is a hydrogen atom, an alkyl group or an alkoxy group, or R.sup.3 and R.sup.4, R.sup.3 and R.sup.5 and/or R.sup.4 and R.sup.6 bond to each other to form a ring structure, and n is 0, 1 or 2; and each of X.sup.1 and X.sup.

Abstract: Peroxycarboxylic ester photoinitiators derived from aromatic nitrogen containing heterocyclic carboxylic acids are described. The heterocyclic aromatic ring may contain additional nitrogen atoms, be fused with another aromatic ring system, be substituted with an additional peroxycarboxylic ester group and/or be substituted with an electron group having a Hammett sigma value greater than 0.1. The peroxycarboxylic ester photoinitiators have been found to be useful in photopolymerizable compositions and photosensitive elements.

Abstract: Resin compositions useful for filament winding applications comprising an epoxy component including at least one polyepoxide resin curable by heat, an olefinicially unsaturated monomer component including at least one polyolefinically unsaturated monomer curable by actinic radiation, at least one photoinitiator, at least one organic peroxide, and a heat activated curing agent for epoxides. The compositions have a viscosity less than about 2000 centipoise (cps) and are capable of retaining this viscosity for at least about 2 hours at a temperature of from about ambient temperature to about 60.degree. C. The resins are capable of being immobilized by actinic radiation exposure and further heat cured without substantial resin drip. One or more organic peroxides are employed, selected from the group of organic peroxides having 10 hour decomposition half lives at temperatures of from about 50.degree. C. to less than about 104.degree. C.

Abstract: A one-component reactive resin system which is stable in storage but nevertheless can readily be cured completely comprises a mixture of commercially available epoxy resins and phosphorus-containing glycidyl esters, in particular phosphonic acid diglycidyl esters, as well as cationic photoinitiators. The low-viscosity reactive resin systems cannot be cured purely by means of heat and can be processed at high temperatures and in particular can have a high filler content. The reactive resin systems, which are stable to storage even after UV activation, can be cured to flame-resistant molded materials under moderate conditions.

Abstract: Resin compositions useful for filament winding applications comprising an epoxy component including at least one polyepoxide resin curable by heat, an olefinicially unsaturated monomer component including at least one polyolefinically unsaturated monomer curable by actinic radiation, at least one photoinitiator, at least one organic peroxide, and a heat activated curing agent for epoxides. The compositions have a viscosity less than about 2000 centipoise (cps) and are capable of retaining this viscosity for at least about 2 hours at a temperature of from about ambient temperature to about 60.degree. C. The resins are capable of being immobilized by actinic radiation exposure and further heat cured without substantial resin drip. One or more organic peroxides are employed, selected from the group of organic peroxides having 10 hour decomposition half lives at temperatures of from about 50.degree. C. to less than about 104.degree. C.

Abstract: A method of forming dental products, such as dentures, denture relines, dental crowns, dental bridges and dental restorative materials, temporary crown, temporary bridge, provisional crown or provisional bridge, from two polymerizable paste compositions each having a complimentary component of a free radical catalyst system and a polymerizable acrylic compound. One of these paste compositions includes an oxidizing agent and a stabilizer and the other includes a reducing agent as components of a redox catalyst system for free radical polymerization. These paste compositions are mixed in a static mixer to form a polymerizing paste composition, which is then shaped into a dental prosthesis. A handheld mixing dispenser useful in carrying out this method, includes a static mixing conduit, and two containers enclosing the polymerizable paste compositions. The static mixing conduit encloses a static mixing member. The containers are adapted to be connected in fluid flow communication with the static mixing conduit.

Abstract: Resin compositions useful for filament winding applications comprising an epoxy component including at least one polyepoxide resin curable by heat, an olefinicially unsaturated monomer component including at least one polyolefinically unsaturated monomer curable by actinic radiation, a cyanate ester component including at least one cyanate ester compound having at least two cyanate functional groups per molecule, at least one organic peroxide, at least one photoinitiator, and a heat activated curing agent for epoxides. The compositions have a viscosity less than about 2000 centipoise (cps) and are capable of retaining this viscosity for at least about 6 months at about ambient temperature. The resins are capable of being immobilized by actinic radiation exposure and further heat cured without substantial resin drip. One or more organic peroxides are employed, selected from the group of organic peroxides having 10 hour decomposition half-lives at temperatures of from about 50.degree. C. to less than about 104.

Abstract: Peroxycarboxylic ester photoinitiators derived from aromatic nitrogen containing heterocyclic carboxylic acids are described. The heterocyclic aromatic ring may contain additional nitrogen atoms, be fused with another aromatic ring system, be substituted with an additional peroxycarboxylic ester group and/or be substituted with an electron group having a Hammett sigma value greater than 0.1. The peroxycarboxylic ester photoinitiators have been found to be useful in photopolymerizable compositions and photosensitive elements.