Stereoselective synthesis of polylactic acid (PLA) was achieved using titanium(IV) complexes. The NO3 ligands prepared from 2,2′-dihydroxybenzophenone and salicylaldehyde derivatives were used to control the stereoselectivity of Ti(IV)-catalyzed polymerization of rac-lactide, in which a substituted ligand provided heterotactic PLA with high stereoselectivity. Density functional theory calculations revealed that the ligand structure is crucial for differentiating reaction pathways, and that the octahedral transition states are stabilized by the preorganized intermediates.

We report that an alternating semifluorinated copolymer of chlorotrifluoroethylene (CTFE) and vinyl ether (VE) is an attractive platform for the synthesis of heterograft copolymers consisting of two distinct side chains. The radical terpolymerization of CTFE with PLA-tethered vinyl ether (PLAVE) synthesized by ring-opening polymerization and isobutyl vinyl ether (IBVE) as a spacer produced PLA-grafted fluorinated copolymer via a “grafting-through” manner. Two PLAVEs with different molar masses (2 and 10 kg mol–1) were successfully incorporated, and the grafting density could be controlled by varying the [PLAVE]/[IBVE] initial molar ratio. From the chlorine atoms in the CTFE repeating units, atom transfer radical polymerization (ATRP) of styrene was further employed to grow PS side chains following a “grafting-from” mechanism per each (CTFE-alt-VE) repeating unit dyad. First-order kinetics was observed for the styrene polymerization and supported controlled growth of PS. The resulting heterograft copolymers possessed regularly spaced PS chains and statistically distributed PLA chains on the backbone, generating a nanoscopic disordered morphology via microphase separation driven by incompatibility between PLA and PS. By copolymerization of styrene and divinylbenzene (DVB) in neat ATRP condition, a cross-linked polymer monolith with the disordered bicontinuous morphology could be also prepared via polymerization-induced microphase separation. The cross-linked precursor was converted into a mesoporous polymer with pore size of 3.7–10.4 nm by removal of PLA. The mesopore size was tunable by adjusting the PLA molar mass and styrene/DVB molar ratio.

We report a route to synthesize polylactide-b-poly(ether sulfone)-b-polylactide (PLA-b-PES-b-PLA) containing PES and PLA, which provide a mechanically robust framework and a sacrificial template for pore formation, respectively. High-molar mass PES terminated with fluorine groups was synthesized by the step-growth nucleophilic aromatic substitution (SNAr) reaction, and the chain ends were transformed into benzylic hydroxyl groups by chain end modification. Growth of the PLA using the hydroxyl groups as initiating sites via chain-growth ring opening transesterification polymerization (ROTEP) produced the target triblock copolymer. Although the step-growth polymerization produced a PES middle block with high dispersity, small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) analyses indicated the formation of an ordered lamellar morphology. We further demonstrated that a nanoporous PES with slit-like pores could be obtained by selective removal of the PLA.

We investigated the microphase separation behavior of well-defined poly(arylene ether sulfone)-b-polylactide (PES-b-PLA) diblock copolymers. PES was synthesized by the nucleophilic aromatic substitution polymerization of 4-fluoro-4′-hydroxydiphenyl sulfone potassium salt in the presence of an allyl-functionalized initiator, which follows a chain growth condensation polymerization mechanism. A hydroxyl group installed via a thiol-ene reaction was utilized as the initiating site for the ring opening polymerization of d,l-lactide, producing the target polymer. The polymers were further purified by preparative size-exclusion chromatography and analyzed by small-angle X-ray scattering with temperature variations from room temperature to 150 °C. The PES block was glassy in the employed temperature range, but the PLA chains provided sufficient mobility for ordering of the block copolymer when PES was the minor fraction. An order-disorder transition (ODT) with changing temperature could not be located because PLA was not stable above 170 °C. From the degree of polymerization values of the polymers near the ODT, the Flory–Huggins interaction parameter, χ, could be roughly estimated as 0.12 at 150 °C. This high χ value suggests that engineering plastic-containing block copolymers could be useful in advanced lithographic and filtration applications.

Using a simultaneous block polymerization/in situ cross-linking from a heterofunctional initiator approach, we produced a nanostructured and cross-linked block polymer in a single step from a ternary mixture of monomers and used it as a precursor for a cross-linked nanoporous material. Using 2-(benzylsulfanylthiocarbonylsulfanyl)ethanol as a heterofunctional initiator, simultaneous ring-opening transesterification polymerization of d,l-lactide in the presence of tin 2-ethylhexanoate as a catalyst and reversible addition–fragmentation chain transfer polymerization of styrene at 120 °C produced a polylactide-b-polystyrene (PLA-b-PS) block polymer. Incorporation of divinylbenzene in the polymerization mixture allowed in situ cross-linking during the simultaneous block polymerization to result in the cross-linked block polymer precursor in one step. This material was converted into cross-linked nanoporous polymer by etching PLA in a basic solution.