TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The composition (C1) comprises (wt.%): poly(arylene ether)-polysiloxane block copolymer reaction product (67-87); styrenic polymer (5-17); and flame retardant (8-15); or poly(arylene ether)-polysiloxane block reaction product (greater than 55 to 65), and resorcinol bis(diphenyl phosphate) as flame retardant; or poly(arylene ether)-polysiloxane block copolymer reaction product (65-95), and bisphenol A bis(diphenyl phosphate) as flame retardant. The composition consists of poly(arylene ether), hydrogenated block copolymer, flame retardant, and, optionally, at least one additive (0.1-10 wt.%) selected from stabilizers, mold release agents, processing aids, drip retardants, nucleating agents, UV blockers, dyes, pigments, antioxidants, anti-static agents, blowing agents, mineral oil, metal deactivators, antiblocking agents, nanoclays, and electrically conductive agents. Preferred Components: The styrenic polymer consists of hydrogenated block copolymer of alkenyl aromatic compound and conjugated diene; or consists of rubber-modified polystyrene and unhydrogenated block copolymer of alkenyl aromatic compound and conjugated diene. The poly(arylene ether) block comprises arylene ether repeating units having formula (I). The polysiloxane block comprises repeating units having formula -(O-Si(R1)(R2))- (II). The polysiloxane block further comprises a terminal unit having formula (III). The polysiloxane block has the formula (IV). The process for forming poly(arylene ether)-polysiloxane block copolymer reaction product further involves precipitating an oxidative copolymerization reaction mixture with an antisolvent comprising isopropanol to form the poly(arylene ether)-polysiloxane block copolymer reaction product, and the poly(arylene ether)-polysiloxane block copolymer reaction product comprises hydroxyaryl-terminated polysiloxane (less than 1.5 wt.%, based on the total weight of the poly(arylene ether)-polysiloxane block copolymer reaction product). The flame retardant comprises organophosphate ester (preferably resorcinol bis(diphenyl phosphate) and/or bisphenol A bis(diphenyl phosphate)). The poly(arylene ether)-polysiloxane block copolymer reaction product preferably comprises (wt.%): siloxane repeating units (1-8) and arylene ether repeating units (92-99). The poly(arylene ether)-polysiloxane block copolymer reaction product is the product of a process by oxidatively copolymerizing a monomer mixture comprising a monohydric phenol and a hydroxyaryl-terminated polysiloxane.Z1=halo, optionally substituted 1-12C hydrocarbyl, 1-12C hydrocarbylthio, 1-12C hydrocarbyloxy, or 2-12C halohydrocarbyloxy (where at least two carbon atoms separate the halogen and oxygen atoms) (preferably CH3);Z2=H or Z1 (preferably H);R1 and R2=H, 1-12C hydrocarbyl or 1-12C halohydrocarbyl;Y1=H, 1-12C hydrocarbyl, 1-12C hydrocarbyloxy, or halo;R3 and R4=H, 1-12C hydrocarbyl or 1-12C halohydrocarbyl;n=30-60.Provided that the hydrocarbyl group is not tertiary hydrocarbyl. EXAMPLE - A composition comprising (parts by weight): poly(2,6-dimethyl-1,4-phenylene ether)-co-poly(dimethylsiloxane) block copolymer reaction product (80.15), having an intrinsic viscosity of 0.39-0.45 deciliter per gram measured in chloroform at 25 degrees C; prepared from 2,6-xylenol (95 wt.%) and eugenol capped polysiloxane (5 wt.%); high molecular weight polystyrene-poly(ethylene/butylene)- polystyrene triblock copolymer, having a polystyrene content of 30-33.0 wt.% and a weight average molecular weight of 240000-301000 (6); bisphenol A bis(diphenyl phosphate)(13); poly(styrene-acrylonitrile)-encapsulated polytetrafluoroethylene, containing polytetrafluoroethylene (50 wt.%) (0.05); magnesium oxide (0.15), zinc sulfide (0.15); carbon black (pigment) (having pH 7.85, heating loss of 1.87 wt.%, sulfur content of 0.45 wt.%, iodine absorption of 230.8 g/kg, toluene discoloration number of 99.5% transmittance, solvent extractables of 0.01 wt.%, and volatile constituents of 1.85 wt.%) (0.5); and tris(2,4-di-tert-butylphenyl) phosphate (0.5) was prepared. The composition showed a melt mass-flow rate (MFR) (at 300 degrees C under a load of 5 kg with a dwell time of 375.0 seconds): heat deflection temperature (measured at a stress of 1.82 megapascals (MPa) and a sample thickness of 3.2 mm): flexural modulus of 23.9 g/10 minutes: 121 degrees C: 2550 MPa.