Ring-opening polymerizations of trimethylene carbonate (TC) and 2,2-dimethyltrimethylene carbonate (DTC) are initiated from hydroxyl-terminated polyethylene glycol (PEG) and PEG-based surfactants (Triton X-100 or Triton X-405) in the absence of any catalysts. The metal- and solvent-free polymerizations proceed under melt at 150 degrees C, affording Triton X-100-block-poly(TC) with M-n of 1400-5200 and Triton X-100-block-poly(DTC) with M. of 1800-7100 in excellent yields. The molecular weights and the comonomer composition of the resulting copolymers are controlled by the feed ratios of the monomers to the initiators, confirmed by gel permeation chromatography and H-1 NMR spectroscopy. The solubilities of the block copolymers composed of hydrophilic PEG segment and hydrophobic poly(TC) or poly(DTC) segment depend on both the compositions and the components. For example, Triton X-100-block-poly (TC) (TC/EG = 9.5/9.5) and Triton X-405-block-poly(TC) (TC/EG 28/40, 46/40) milky suspend in water, while Triton X-405-block-poly(TC) (TC/EG 9.7/40) dissolves in water. A dynamic light scattering study reveals that the particle distribution of a copolymer, Triton X-405-block-poly(TC) (TC/EG = 9.7/40) in water, has a monodisperse unimodal pattern ranging from 92 to 368 nm. (c) 2006 Wiley Periodicals, Inc.