This paper reports the synthesis of alternating donor-acceptor copolymers (DA polymers) containing thiazole units via palladium-catalyzed direct arylation polymerization (DArP), which has recently emerged as a viable alternative to conventional cross-coupling polycondensations. While thiazole-based C-H monomers such as benzodithiazole and thiazolothiazole are poorly reactive toward DArP, thiazolothiazoles (TzTz) capped with 5-bromothienyl and thienyl groups at the 2,5-positions, 2,5-bis[5-bromo-3-(2-octyldodecyl)thiophene-2-yl]-thiazolo [5,4-d]thiazole (1-Br) and 2,5-bis[3-(2-octyldodecypthiophene2-yl] thiazolo [5,4-d] thiazole (1-H), successfully react with C-H and C-Br monomers, respectively. The reactions proceed in THF at 100 degrees C in the presence of Pd-2(dba)(3) and P(2-MeOC6H4)(3) (L1) as catalyst precursors and pivalic acid and Cs2CO3 as additives to afford TzTz-containing DA polymers with high molecular weight (M-n up to 88 100) and good solubility in almost quantitative yields. A high-temperature NMR analysis of the resulting polymers reveals well-controlled structures containing a small amount of homocoupling defects.