The copolymerization of MMA (1) and methyl alpha-phenylacrylate (2) by GTP has been studied. While no homopolymer could be obtained from 2, alternating copolymers were formed from mixtures of 1 and 2. Monomer consumption as measured by gas chromatography proved equimolar incorporation even with 1 in excess as long as 2 was present in the reaction mixture. MALDI-TOF mass spectrometry showed that all polymer chains contained 2 incorporated as first and last monomer resulting in a homologous series Init.(2,1)(n)2. The propagation constants decrease in the order k(12) >> k(11) > k(21) >> k(22). In model reactions of catalyst, ketene acetal, and 2, 2-fold addition of 2 also occurred to a small extent. This is the origin of a second homologous series in the mass spectra of the alternating copolymers. Block copolymers with an alternating (1,2) block and a PMMA block are formed from a monomer feed having MMA in excess.