This article reviews recent topics in the controlled synthesis of polycarbonates and polylactones with small polydispersity indices by activated monomer cationic ring-opening polymerizations, especially with new initiator systems, such as alcohol/ protonic acid and boron alkoxide/protonic acid.

Controlled ring‐opening polymerization of cyclic carbonates and lactones by an activated monomer mechanism

Chain transfer to macromolecules with chain scission is the most often observed side reaction in the polymerization of heterocyclics. In our previous works we analysed quantitatively the intramolecular chain transfer to the own macromolecule (back-biting). This paper gives a general treatment of the kinetics of polymerization with propagation and intermolecular chain transfer to macromolecules, accompanied with chain scission. The numerical solution developed allows determining the k p /k tr ratio from the dependence of M w /M n on monomer conversion. This treatment was applied to the polymerization of L,L-lactide and k p /k tr ratios were measured for covalent alcoholate active species bearing At, Fe, Ti, Sm, and La. In this way selectivities of active species (expressed with k p /k tr ) were for the first time measured and finally correlated with the atomic number of the corresponding metal atoms, related to the strength of the bond involved in the monomer addition.

Intra‐ and intermolecular chain transfer to macromolecules with chain scission. The case of cyclic esters

Background: House dust contains many organic contaminants that can compete with the thyroid hormone (TH) thyroxine (T4) for binding to transthyretin (TTR). How these contaminants work together at l...

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Transthyretin-Binding Activity of Complex Mixtures Representing the Composition of Thyroid-Hormone Disrupting Contaminants in House Dust and Human Serum

Advances in the major areas of the cationic ring-opening polymerizations are discussed. In the first part synthesis of new polymers is reviewed; this includes mainly novel block and graft copolymers based on the di- and multicationically ended living polyacetals and polyethers (polyTHF).



Recent data on thermodynamics of nonideal systems, giving dependence of [M]e on [M]o, are summarized with special emphasize of the differences between monomers due to variation of their nucleophilicities.



Discussion of kinetics and mechanisms of polymerization of cyclic acetals and ethers is focused on the macroring formation and reactivities of active centers.



The reactivity of covalent and various ionic growing species are compared in the polymerization of cyclic ethers (THF and oxepane) and oxazolines. Reasons for much lower reactivity of covalent than ionic species and reasons for similar reactivities of macroion-pairs and macroions are presented.



It is shown, that the kinetically controlled proportions of macrorings in the polymerization of these and other heterocyclic monomers depend on the structure of the end-groups, formed upon initiation. Initiation with acids, giving H-X∼ (where X=heteroatom) end-groups, leads to the kinetically enhanced proportion of macrorings. This is particularly important for the low degrees of polymerization.

T. K. Wu

Papers

Macrocyclic Tetrahydrofuran Oligomers. 2. Formation of Macrocycles in the Polymerization of Tetrahydrofuran with Triflic Acid