Abstract: A composition which is a blend of at least two different polyetheramide copolymers, one having predominantly hard polyamide segments and one having predominantly soft polyether segments. When formed into a film and attached to a textile fabric, forms a laminate which is suitable for the production of surgical gowns, and the like. Such films are strong, have good moisture barrier properties while allowing the transmission of air therethrough and have a softness to which provides a clothlike feel.

Abstract: A rigid, aromatic polyimide composition prepared using a solution imidization process from an aromatic tetracarboxylic dianhydride and a diamine which is greater than 60 mole % to about 85 mole % p-phenylene diamine and 15 mole % to less than 40 mole % m-phenylene diamine exhibits exceptional tensile properties and thermal oxidative stability.

Abstract: A method for synthesizing 1,4-bis(4-aminophenoxy)naphthalene and a series of polyamides, polyimides and copoly(amide-imide)s derived from the said compound is disclosed. These polymers possess excellent thermal stability and mechanical strength.

Abstract: Disclosed herein is a pattern forming process comprising the steps of coating a substrate with a photosensitive resin composition comprising a polyamic compound having, at each terminal thereof, an actinic ray-sensitive functional group which has substituent groups each having a photopolymerizable carbon-carbon double bond, a photosensitive auxiliary having a photopolymerizable functional group, a photopolymerization initiator, and a solvent to form a film; subjecting the film to pattering exposure; and then developing the thus-exposed film with an alkaline developer or alkaline aqueous solution.

Abstract: The invention relates to an integrated circuit device comprising (i) a substrate, (ii) metallic circuit lines positioned on the substrate, and (iii) a porous dielectric material positioned on the circuit lines. The dielectric material comprises the reaction product of an organic polysilica and polyamic ester preferably terminated with an alkoxysilyl alkyl group.

Abstract: Pyrrolidonyl-containing polyesters and polyamides I to III ##STR1## where R, X, A and Z are defined herein, are suitable as film formers and conditioners in hair-cosmetic formulations, for stabilizing hydrogen-peroxide in aqueous solution, for complexing iodine, as tablet binders and as a constituent of film coatings in pharmaceutical preparations, for enzyme and bleach stabilization in detergent formulations, as an auxiliary in the production and finishing of textiles, as a solubilizer and protective colloid in the preparation and stabilization of polymer dispersions, and as an adhesive raw material.

Abstract: A solvent-soluble siloxane polyimide comprising a copolymer obtained by reaction of a diamine compound mixture comprising a diaminopolysiloxane and an alicyclic diamine with an aromatic tetracarboxylic acid anhydride, followed by polyimidization reaction of the resulting polyamic acid forms a heat-resistant adhesive by adding an epoxy resin, a diamine-based curing agent and an organic solvent thereto, The formed adhesives show a distinguished heat-resistant adhesiveness when the resulting siloxane polyimide soluble in ordinary organic solvents is used as a main component of the adhesive for bonding between a base material and a copper foil of a flexible printed substrate. By further addition of a fluorinated resin to the heat-resistant adhesive, the adhesiveness can be more improved.

Abstract: An aromatic polycarbodiimide containing a siloxane bond in the polymer main chain thereof.The polycarbodiimide can adhere at a low temperature in a short time and has a high heat resistance. The polycarbodiimide has a good adhesive property to an adherend such as semiconductor elements, has a low hygroscopic property and is excellent in the storage stability. Therefore, the polycarbodiimide can be stored for a long period of time at normal temperature.

Abstract: A process for inducing pre-tilt in alignment of a liquid crystal medium comprising exposing at least one optical alignment layer, comprising anisotropically absorbing molecules and hydrophobic moieties, to polarized light; the polarized light having a wavelength within the absorption band of said anisotropically absorbing molecules; wherein the exposed anisotropically absorbing molecules induce alignment of the liquid crystal medium at an angle + and -.theta. with respect to the direction of the polarization of the incident light beam and along the surface of the optical alignment layer, and induce a pre-tilt at an angle .PHI. with respect to the surface of the optical alignment layer and applying a liquid crystal medium to said optical alignment layer, is described. The invention also is directed to liquid crystal display elements made by the process of the invention and to novel polyimide compositions that are useful as optical alignment layers in the invention.

Abstract: Macrocyclic polyether oligomers, preferably as mixtures of oligomers of different degrees of polymerization, are incorporated in a direct displacement reaction mixture for the formation of polyetherimides, said reaction mixture comprising at least one alkali metal salt of a dihydroxy-substituted aromatic hydrocarbon and at least one bis(halo- or nitrophthalimide). The macrocyclic oligomers can be isolated from an earlier-prepared linear polyetherimide composition. Their incorporation in the reaction mixture does not increase the proportion of oligomers in the polyetherimide product.

Abstract: This invention provides a polyimide precursor solution having high concentration and low viscosity and a production process thereof, and polyimide coatings and films having excellent physical properties obtained therefrom and a production process thereof. Particularly, it relates to a polyimide precursor solution which contains a salt of a specific diamine with a specific tetracarboxylic acid, as its solute; to a process for the production of the polyimide precursor solution, which comprises allowing 1 mole of a specified diamine to react with 0.3 to 0.9 mole of a specific tetracarboxylic acid dianhydride, thereby obtaining a diamine, and subsequently adding 0.95 to 1.

Abstract: Disclosed are polyesteramide resin compositions having amide units of formula (I): ##STR1## and the units of the formula (II): ##STR2## wherein the polyesteramide is substantially devoid of units derived from butane diol. The ratio of (I) to (II) in the polyesteramide is preferably less than 1:3. Preferred polyesteramides have at least 80% of units of formula (I) separated by at least one of the units of formula (II).

Abstract: A photosensitive resin composition comprising, as its main ingredient, a poly(amic acid) resin constituted of a diamino compound represented by formula: ##STR1## and optionally used other diamino compound and a tetracarboxylic acid dianhydride as its constituent monomers and/or a poly(amic acid) ester resin obtained by esterifying said poly(amic acid) resin and/or a polyimide resin obtained by a dehydrating or alcohol-eliminating ring-closure reaction of said poly(amic acid) resin or poly(amic acid) ester resin has an excellent developability and a high film strength and can form a relief patter of low thermal expansion.

Abstract: A new diamine, 2,2'-dimethyl-4,4'-bis(4-aminophenoxy)-biphenyl was synthesized and used to prepare high performance engineering plastics by polycondensation. The new diamine as shown in the following formula has a noncoplanar 2,2'-disubstituted biphenylene and a flexible aryl units: ##STR1## The engineering plastics disclosed in the present invention includes polyamides, polyimides and poly(amide-imide)s.

Abstract: A polyimide fiber having textile physical property characteristics and the process of melt extruding same from a polyimide powder. Polyimide powder formed as the reaction product of the monomers 3,4'-ODA and ODPA, and endcapped with phthalic anhydride to control the molecular weight thereof, is melt extruded in the temperature range of 340.degree. C. to 360.degree. C. and at heights of 100.5 inches, 209 inches and 364.5 inches. The fibers obtained have a diameter in the range of 0.0068 inch to 0.0147 inch; a mean tensile strength in the range of 15.6 to 23.1 ksi; a mean modulus of 406 to 465 ksi; and a mean elongation in the range of 14 to 103%.

Abstract: Polyimides satisfying the requirements (a), (b) and (c) among the requirements described below, polyimides satisfying the requirements (b), (c) and (d), and polyimides satisfying the requirements (a), (b), (c) and (d) are excellent in transparency, isotropy and resistance to cracking (no crack is formed in the formation of a multilayer film, so that the multilayer formation is easy, namely, the polyimides are good in processability) and can give optical parts excellent in optical characteristics:(a) the difference between the refractive index in TE mode and that in TM mode is 0.02 or less,(b) the glass transition temperature (Tg) is 250.degree. C or higher,(c) the optical transmission loss at a wavelength of 0.7 to 1.6 .mu.m is 1 dB/cm or less, and(d) the fluorine content is 22.6% by weight or less.

Abstract: A method of producing a polyamide resin by reacting 1 mol of linear polyester resin (as calculated in repeating unit of the linear polyester resin) consisting of at least one dicarboxylic acid component and at least one diol component and having an intrinsic viscosity of not less than 0.2 dl/g with 0.5-1.5 mol of at least one diamine compound in a reaction medium comprising at least one solvent which is selected from the group consisting of hydrocarbons, halogenated hydrocarbons, ethers and acetals, so that the diol component of the linear polyester resin is substituted by the diamine compound to provide the polyamide resin as a reaction product.

Abstract: The method for preparing a crosslinked polycarbodiimide according to the present invention comprises reacting a polydicarbodiimide compound with a compound, which has in a molecule thereof two or more hydroxy or mercapto groups, in the presence of an alcoholate of an alkali metal or of an alkaline earth metal. The crosslinked polycarbodiimide obtained according to the method is excellent in heat resistance and mechanical properties.

Abstract: A process for making polyimide-polyamic ester copolymer composition comprisingreacting at least one diamine, a pyromellitic diacid diester compound; at least one other tetracarboxylic diacid diester compound and a selected phosphoramide in the presence of a base catalyst to form a polyimide-polyamic acid ester copolymer.

Abstract: A polyamic acid is herein disclosed which contains a structural unit represented by the formula ?2a! ##STR1## wherein m is an integer of 1 to 20; n is an integer of 1 to 2; and R.sup.2 is an alkyl group or an alkoxy group having 1 to 20 carbon atoms. Furthermore, a polyamic acid composition is also disclosed which comprises the polyamic acid containing the structural unit represented by the formula ?2a! and another polyamic acid containing a structural unit other than mentioned above. By heating the polyamic acid or the polyamic acid composition at a low temperature for a short time, a liquid crystal alignment film can be obtained which comprises a polyimide or a polyimide composition.

Abstract: The invention relates to a mixture in powder form and comprising (i) at least one polyamide and (ii) at least one polymer (A) containing hydroxyl functional groups and compatible with the polyamide. The polymer (A) may be an ethylene/vinyl alcohol copolymer. The mixture may be used to coat metal substrates.

Abstract: Aromatic polyether polymers, illustrated by polyethersulfones, polyetherketones and polyetherimides, are prepared by a phase transfer catalyzed reaction between a salt of at least one dihydroxyaromatic compound and at least one substituted aromatic compound such as bis(4-chlorophenyl) sulfone, bis(4-chlorophenyl) ketone or 1,3-bis?N-(4-chlorophthalimido)!benzene, in a monoalkoxybenzene such as anisole as diluent and in the presence of a phase transfer catalyst, preferably a hexaalkylguanidinium salt.

Abstract: A process is disclosed for preparing a polyamide by polymerizing a diacid and a diamine, aminocarboxylic acid or lactam in the presence of excess of either acid or amine such that the ratio of acid to amine end groups or the ratio of amine end groups to acidend groups in the polymer is at least 2.0:1.0.

Abstract: A sliding material and a heat resistant filament which primarily comprises a liquid crystal polyimide, a liquid crystal polyamide or a liquid crystal polyamide-imide copolymer having at least one recurring structural unit selected from the formula (1) and the formula (2) and is excellent in heat resistance, mechanical characteristics and other fundamental properties of polyimides, and relates to significant improvement of heat-resistance by heat-treating the sliding material, the filament and the molded items. The liquid crystal polyamide-imide copolymer which comprises in a polymer molecule 0.05.about.0.95 mole ratio of the recurring structural units of the formula (1) and 0.95.about.0.

Abstract: A hydroxy- or mercapto-bearing organic compound is caused to react with a polycarbodiimide compound in the presence of an alcoholate of an alkali metal or of an alkaline earth metal. The carbodiimide linkage in the polymer which results from the above-described reaction is crosslinked.

Abstract: The physical properties of high performance composites can be tailored by using blends to make the composites. The resulting composites are relatively easy to make and have long-term, high performance capabilities even in harsh service conditions. The blends of the present invention include at least one oligomer having an aromatic, aliphatic, or mixed aromatic and aliphatic backbone from one chemical family and an unsaturated hydrocarbon end cap and at least one polymer from a different chemical family. Upon curing, the oligomer in the blend addition polymerize to form composites possessing advanced properties with respect to those exhibited by the pure oligomer or the pure polymer. Coreactive oligomer blends can be used instead of a pure oligomer to form composites that include addition polymers, block copolymers, and the compatible polymer, thereby further achieving a tailoring of properties in the cured composite. The blends can be prepregged and cured to form composites.

Abstract: A diamine which is useful in preparing a new flexible polyamide and polyimide with an aromatic dicarboxylic acid and a tetracarboxylic dianhydrides, respectively, has a general formula as follows: ##STR1## wherein R.sub.1 is a proton (--H) or methyl (--CH.sub.3) and n is an integer ranging from 1 to 4. These polyamide and polyimide exhibit good mechanical performance and processability.

Abstract: The morphology of multidimensional oligomers is combined with the inclusion of charge carrier linkages within the oligomer arms to produce oligomers that are useful for preparing conductive or semiconductive composites, if suitably doped. The Schiff base linkages are prepared by the condensation of aldehydes and amines. The oligomers can be blended, and either the oligomers or their blends can be prepregged.

Abstract: The present invention relates to a new polyesterimide of the type containing ester repeat functional groups E=--CO--O--, imide repeat functional groups I: ##STR1## and at least one chromophore, characterized in that it contains a quantity of recurrent amide functional groups capable of ring closure to imides which is smaller than or equal to 5 mol % relative to the sum of the imide functional groups and of the amide functional groups capable of ring closure to imides, which are present, and in that the polymerization functional groups consist essentially of E functional groups.This polyesterimide is preferably free from amide functional groups capable of ring closure to imides.One of the processes for obtaining this polyesterimide constitutes another subject-matter of the invention.Such a polymer is advantageously capable of behaving like a material that is transparent and/or active in nonlinear optics.

Abstract: This invention is directed to a polyimide film useful as use applications for electronic materials; a liquid crystal aligning film using the same; a liquid crystal display element provided with the liquid crystal aligning film; and a polyamic acid used as a raw material of the polyimide constituting the polyimide film.The polyimide used for preparing the above polyimide films, consists of a diamine component, the 50% by mol or more based upon the total diamine, of which is a diamine having a core structure having no polar group such as 1,2-bis(4-(4-aminobenzyl)phenyl)ethane, 1,6-bis(4-(4-aminobenzyl)phenyl)hexane, 1,1-bis(4-(4-aminobenzyl)phenyl)heptane, etc., and a tetracarboxylic acid dianhydride, and if necessary, an aminosilicon compound, is used as a liquid crystal aligning film.

Abstract: At least bis-imido 1,3,5-triazines and processes of preparing the same are disclosed. Also disclosed are prepolymers having at least bis-imido functionality and curable compositions comprising at least bis-imido 1,3,5-triazines or prepolymers thereof in combination with active hydrogen and/or epoxy functional materials. The at least bis-imido 1,3,5-triazines and prepolymers may be advantageously employed as crosslinking agents which crosslink by a ring opening reaction that eliminates the release of volatile organic compounds.

Abstract: In a process for the preparation of poly-o-hydroxyamides and poly-o-mercaptoamides, a bis-o-aminophenol or a bis-o-aminothiophenol is reacted with a dicarboxylic acid derivative with the following structure:M--CO--R*--CO--Mwhere M stands for the residue of an (optionally substituted) 2-hydroxybenzoxazole, 2-hydroxybenzothiazole, or 1-hydroxybenzotriazole or of corresponding mercapto compounds and R* is the parent body of the dicarboxylic acid.

Abstract: A polyamide resin composition comprising: (A) 100 parts by weight of at least one member selected from a polyamide-11 resin and a polyamide-12 resin; optionally (B) from 3 to 30 parts by weight of a modified polyolefin resin; and (C) from 3 to 25 parts by weight of a plasticizer mixture comprising a plasticizer (C1) and a plasticizer (C2). The modified polyolefin resin (B) is either a modified polyolefin (B1) which is a copolymer of an olefin comprising at least one of ethylene and propylene, with an .alpha.,.beta.-unsaturated carboxylic acid or a derivative thereof, or a modified polyolefin (B2) which is a graft polymer obtained by grafting an .alpha.,.beta.-unsaturated carboxylic acid or a derivative thereof onto a copolymer of an olefin comprising at least one of ethylene and propylene. The plasticizer (C1) has a solidifying point of -40.degree. C.

Abstract: Polyimide compositions can be substantially improved by incorporating in the composition an inorganic, low hardness, thermally stable, sheet silicate, such as muscovite mica, talc, and kaolinite, which results in improved wear resistance and reduced coefficient of friction.

Abstract: A process for making polyimide composition comprising reacting at least one diamine, at least one tetracarboxylic diacid diester, selected phosphoramide and at least one base catalyst to form at least one polyimide compound, said reaction carried out at a temperature from about 20.degree. C. to about 60.degree. C. and wherein the molar ratio of diamine:tetracarboxylic diacid diester:phosphoramide:base catalyst is in the range of 0.8-1.2:1:2.5-4.0:2.5-4.0.

Abstract: A process for producing a polyimide composition by reacting at least one polyamic acid or at least one polyamic ester or a mixture of at least one polyamic acid and at least one polyamic ester with a selected phosphoramide in the presence of at least one base catalyst to from a polyimide composition.

Abstract: In a process for the preparation of poly-o-hydroxyamides and poly-o-mercaptoamides, a bis-o-aminophenol or a bis-o-aminothiophenol is reacted with a dicarboxylic acid ester with the following structure:G--O--CO--R*--CO--O--G,where G is an (optionally substituted) succinimide or maleinimide group and R* is the parent body of the dicarboxylic acid.

Abstract: There are provided a polyamic acid obtainable by reacting a diamine compound of the formula (1) ##STR1## wherein R.sup.1 is an alkyl group having 1 to 12 carbon atoms, a haloalkyl group having 1 to 12 carbon atoms or a halogen atom, each of X and Y is independently a divalent linking group,with a tetracarboxylic acid dianhydride; a polyimide obtainable by dehydrating and ring-closing the above polyamic acid; and a liquid crystal aligning agent containing the above polyamic acid and/or the above polyimide.

Abstract: A method for producing poly-o-hydroxy amides by conversion of an activated dicarboxylic acid derivative with a bis-o-aminophenol. A solution of the activated dicarboxylic acid derivative is added to a solution of the bis-o-aminophenol in a lactone, and a tertiary amine is added to the resulting mixture, wherein the lactone has the following structure: ##STR1## where A is--(CR.sup.1 R.sup.2).sub.m --or--(CR.sup.3 R.sup.4).sub.n --NR.sup.5 --,R.sup.1 to R.sup.5 are independent of one anotherR.sup.1 and R.sup.2 are hydrogen, alkyl with 1 to 7 carbon atoms (linear or branched), --CO(CH.sub.2).sub.p CH.sub.3, or --COO(CH.sub.2).sub.p CH.sub.3, with p=0 or 1,R.sup.3 and R.sup.4 are hydrogen or alkyl with 1 to 3 carbon atoms (linear or branched),R.sup.5 is hydrogen or methyl,m is a whole number from 2 to 11, andn is a whole number from 1 to 3.

Abstract: Disclosed is a process which comprises reacting a polyimide precursor with borane. Also disclosed is a thermal ink jet printhead containing a layer comprising the product of this reaction.

Abstract: The present invention relates to a process of producing a polyimide-type copolymer, to a thin layer forming agent, to a liquid crystal alignment layer and to processes of producing thin layer formation agents and liquid crystal alignment layers. More specifically, this invention relates to a polyamic acid block copolymer, a polyimide block copolymer, a polyimide-polyamic acid block copolymer, a thin layer forming agent comprised of a polyimide-type block copolymer, and a liquid crystal alignment layer comprised of a polyimide-type block copolymer and processes of their production.

Abstract: The present invention relates generally to a new adhesive comprising a vinyl containing siloxane-containing polyimide for use in TSM capping of electronic package assemblies with adhesive capability of providing a seal band width of less than 4mm and even less than 2mm, solubility in non-toxic and environmentally safe solvents and durable adhesive properties and to a method for making the polyimides, a method for using the polyimides to make electronic packages and electronic packages made using the adhesive. The preferred vinyl-containing siloxane containing polyimide is a block type polymer containing blocks of a dianhydride-aromatic diamine oligomeric reaction product joined by non-vinyl/vinyl containing siloxane diamine forming links.

Abstract: In the process of the present invention, a non-polar, aprotic solvent is removed from an oligomer/polymer solution by freeze-drying in order to produce IPNs and semi-IPNs. By thermally quenching the solution to a solid in a short length of time, the size of the minor constituent-rich regions is greatly reduced as they are excluded along with the major constituent from the regions of crystallizing solvent. The use of this process sequence of controlling phase morphology provides IPNs and semi-IPNs with improved fracture toughness, microcracking resistance, and other physical-mechanical properties as compared to IPNs and semi-IPNs formed when the solvent is evaporated rather than sublimed.

Abstract: Disclosed herein are cyclic oligomers comprising substituted or unsubstituted m-phenylene isophthalamide, complexes of these oligomers with selected metal salts, novel methods for their preparation, and polymerization of the cyclic oligomers to linear aramids. The aramids are useful, for example, as fibers for fire resistant clothing. Amino-finctional cyclic oligomers may be reacted with polyfunctional acyl halides to produce polyamides.

Abstract: Controlled molecular weight phenylethynyl terminated imide oligomers (PETIs) have been prepared by the cyclodehydration of precursor phenylethynyl terminated amic acid oligomers. Amino terminated amic acid oligomers are prepared from the reaction of dianhydride(s) with an excess of diamine(s) and subsequently endcapped with phenylethynyl phthalic anhydride(s) (PEPA). The polymerizations are carried out in polar aprotic solvents such as N-methyl-2-pyrrolidinone or N,N-dimethylacetamide under nitrogen at room temperature. The amic acid oligomers are subsequently cyclodehydrated either thermally or chemically to the corresponding imide oligomers. Direct preparation of PETIs from the reaction of dianhydride(s) with an excess of diamine(s) and endcapped with phenylethynyl phthalic anhydride(s) has been performed in m-cresol. Phenylethynyl phthalic anhydrides are synthesized by the palladium catalyzed reaction of phenylacetylene with bromo substituted phthalic anhydrides in triethylamine.

Abstract: Thermomechanical and thermo-oxidative stabilities in resin composites across the range of aerospace "engineering thermoplastic" resins are improved by forming four crosslinks at each addition polymerization site in the backbone of the resin using crosslinking functionalities of the general formula: ##STR1## in the oligomers, wherein ##STR2## .beta.=the residue an organic radical selected from the group consisting of: ##STR3## R.sub.8 =a divalent organic radical; X=halogen;Me=methylT=allyl or methallyl,G=--CH.sub.2 --, --S--, --CO--, --SO--, --O--, --CHR.sub.3 --, or --C(R.sub.3).sub.2 --;i=1 or 2;R.sub.3 =hydrogen, lower alkyl, lower alkoxy, aryl, or aryloxy; and.THETA.=--C.tbd.N, --O--C.tbd.N, --S--C.tbd.N, or --CR.sub.3 .dbd.C(R.sub.3).sub.2.

Abstract: Photosensitive polyimides (Ps-PIM) materials have been synthesized that belong to three families of Ps-PIM materials. Through the use of precursors, various catalytic compositions with differing photosensitivities are provided. The results are Ps-PIM materials having increased photosensitivities at wavelengths longer than approximately 330 to 350 nm and an associated catalytic system that is insensitive to oxygen. A variety of applications, including use in holographic systems, are improved by the present invention.

Abstract: A polyimide precursor composition, which comprises, a polyamic acid having a repeating unit represented by the following general formula (PA), and at least one kinds of cure accelerator selected from the group consisting of a substituted or unsubstituted nitrogen-containing heterocyclic compound exhibiting an acid dissociation index "pKa" of a proton complex ranging from 0 to 8 in an aqueous solution thereof, or an N-oxide compound of said nitrogen-containing heterocyclic compound (AC1), a substituted or unsubstituted amino acid compound (AC2), and an aromatic hydrocarbon compound or an aromatic heterocyclic compound having a molecular weight of 1,000 or less and two or more hydroxyl groups (AC3): ##STR1## wherein .phi. is a quadrivalent organic group, .phi. is a bivalent organic group, R is a substituted or unsubstituted hydrocarbon group, organosilicic group or hydrogen atom.

Abstract: A dope for cast formation comprising a fluorine including polyimide resin and an organic solvent (P) as main components. The fluorine including polyimide resin has at least one --CF.sub.3 group in the repeating molecular unit. The organic solvent (P) is present during the resin polymerization of the fluorine including polyimide resin. The organic solvent (P) is diethylene glycol dimethyl ether.

Abstract: A method for producing poly-o-hydroxy amides by heating a dicarboxylic acid to a temperature .gtoreq.80.degree. C., together with a sulfonic acid chloride and a tertiary amine in a suitable solvent, to form a reaction mixture and reacting the mixture obtained with a bis-o-aminophenol solution at a temperature <80.degree. C.