To investigate the photoefficiency differences between the macrophotoinitiator and the polymerizable photoinitiator, a novel thio-containing macrophotoinitiator P(MTPBP-co-DMAEMA) bearing side-chain benzophenone and coinitiator amine was synthesized through free radical copolymerization of a polymerizable photoinitiator 4-[(4-maleimido)thiophenyl]benzophenone (MTPBP) and an unsaturated coinitiator amine N,N-dimethylaminoethyl methacrylate (DMAEMA). To determine the influences of coinitiator amine on photopolymerization, a macroamine P(DMAEMA) was also synthesized through homopolymerization of DMAEMA for comparison. FT-IR, H-1 NMR, and gel permeation chromatography (GPC) analyses confirmed the structures of the two polymers. The UV-vis spectra of macrophotoinitiator P(MTPBP-co-DMAEMA) and polymerizable photoinitiator MTPBP are similar, and both exhibit high red-shifted maximum of absorption compared with benzophenone. Photopolymerization of 1,6-hexanediol diacrylate (HDDA) and trimethylolpropane triacrylate (TMPTA), initiated by benzophenone/DMAEMA, MTPBP/DMAEMA, MTPBP/P(DMAEMA), and P(MTPBP-co-DMAEMA) systems, was studied by differential scanning photocalorimetry (photo-DSC). The results indicate that P(MTPBP-co-DMAEMA) is most efficient for the polymerization of both HDDA and TMPTA. As for the photopolymerization of HDDA, the final conversion runs LIP to 98%. However, the photoefficiency of the MTPBP/P(DMAEMA) system, with macroamine as coinitiator, is unsatisfactory.