A strategy for the modular ambient temperature synthesis of ABA and ABC triblock copolymers via a combination of photoinduced Diels-Alder reactions with thermal Diels-Alder reactions and azide-alkyne click chemistry is reported. Polystyrene (PS) and PMMA (PMMA) with alpha-2,5-dimethylbenzophenone and omega-cyclopentaclienyl or omega-azide end-functionality were prepared via atom transfer radical polymerization (ATRP) and subsequent transformation of the bromine end-group. The phototriggered conjugation reaction proceeds via an in situ formation of highly reactive o-quinodimethanes. Maleimide-capped poly(tert-butyl acrylate) obtained via ATRP was employed as dienophile. Alkyne and maleimide functionalized poly(ethylene glycol) (PEG) were synthesized by esterification of monomethoxy PEG. PtBA-b-PMMA-b-PtBA and PtBA-b-PS-b-PtBA were successfully prepared in a one-pot reaction at ambient temperature combining photoinduced and thermal Diels-Alder reactions. ABC triblock copolymers (PtBA-b-PS-b-PEG) with narrow polydispersities were obtained via the combination of photoinduced Diels-Alder reactions with thermal Diels Alder reactions as well as CuAAc chemistry. The polymers were characterized by size exclusion chromatography and H-1 NMR spectroscopy.