23 Stereocontrol of Lactide ROP 6164 231 Isotactic Polylactides 6164 232 Syndiotactic Polylactides 6166 233 Heterotactic Polylactides 6166 3 Anionic Polymerization 6166 4 Nucleophilic Polymerization 6168 41 Mechanistic Considerations 6168 42 Catalysts 6169 421 Enzymes 6169 422 Organocatalysts 6169 43 Stereocontrol of Lactide ROP 6170 44 Depolymerization 6170 5 Cationic Polymerization 6170 6 Conclusion and Perspectives 6171 7 Acknowledgments 6173 8 References and Notes 6173

Controlled ring-opening polymerization of lactide and glycolide.

Dynamic covalent chemistry relates to chemical reactions carried out reversibly under conditions of equilibrium control. The reversible nature of the reactions introduces the prospects of "error checking" and "proof-reading" into synthetic processes where dynamic covalent chemistry operates. Since the formation of products occurs under thermodynamic control, product distributions depend only on the relative stabilities of the final products. In kinetically controlled reactions, however, it is the free energy differences between the transition states leading to the products that determines their relative proportions. Supramolecular chemistry has had a huge impact on synthesis at two levels: one is noncovalent synthesis, or strict self-assembly, and the other is supramolecular assistance to molecular synthesis, also referred to as self-assembly followed by covalent modification. Noncovalent synthesis has given us access to finite supermolecules and infinite supramolecular arrays. Supramolecular assistance to covalent synthesis has been exploited in the construction of more-complex systems, such as interlocked molecular compounds (for example, catenanes and rotaxanes) as well as container molecules (molecular capsules). The appealing prospect of also synthesizing these types of compounds with complex molecular architectures using reversible covalent bond forming chemistry has led to the development of dynamic covalent chemistry. Historically, dynamic covalent chemistry has played a central role in the development of conformational analysis by opening up the possibility to be able to equilibrate configurational isomers, sometimes with base (for example, esters) and sometimes with acid (for example, acetals). These stereochemical "balancing acts" revealed another major advantage that dynamic covalent chemistry offers the chemist, which is not so easily accessible in the kinetically controlled regime: the ability to re-adjust the product distribution of a reaction, even once the initial products have been formed, by changing the reaction's environment (for example, concentration, temperature, presence or absence of a template). This highly transparent, yet tremendously subtle, characteristic of dynamic covalent chemistry has led to key discoveries in polymer chemistry. In this review, some recent examples where dynamic covalent chemistry has been demonstrated are shown to emphasise the basic concepts of this area of science.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/1521-3773%2820020503%2941%3A9%3C1460%3A%3AAID-ANIE11111460%3E3.0.CO%3B2-N

Dynamic covalent chemistry.

Lignocellulosic biomass: a sustainable platform for the production of bio-based chemicals and polymers

Polycaprolactone (PCL) is an important polymer due to its mechanical properties, miscibility with a large range of other polymers and biodegradability. Two main pathways to produce polycaprolactone have been described in the literature: the polycondensation of a hydroxycarboxylic acid: 6-hydroxyhexanoic acid, and the ring-opening polymerisation (ROP) of a lactone: e-caprolactone (e-CL). This critical review summarises the different conditions which have been described to synthesise PCL, and gives a broad overview of the different catalytic systems that were used (enzymatic, organic and metal catalyst systems). A surprising variety of catalytic systems have been studied, touching on virtually every section of the periodic table. A detailed list of reaction conditions and catalysts/initiators is given and reaction mechanisms are presented where known. Emphasis is put on the ROP pathway due to its prevalence in the literature and the superior polymer that is obtained. In addition, ineffective systems that have been tried to catalyse the production of PCL are included in the electronic supplementary information for completeness (141 references).

/pdf/synthesis-of-polycaprolactone-a-review-vlm9rxg878.pdf

Synthesis of polycaprolactone: a review

Modern synthetic methods have revolutionized polymer chemistry through the development of new and powerful strategies for the controlled synthesis of complex polymer architectures. 1-5 Many of these developments were spawned by new classes of transition metal catalysts for the synthesis of new polyolefin microstructures, 5 the design of highly efficient families of “living” polymerization strategies for the synthesis of block, graft, and star polymers, 6-12 controlled methods for the synthesis of dendritic macromolecules, 3,13,14

Organocatalytic ring-opening polymerization.

In this article, we review our studies concerning the design of novel functional polymers based on amino acids. Although an amino acid is the simplest optically active compound in the nature, its polymers, peptides, and proteins show a wide variety of functions such as electron transfer, information transfer, photo reactivity, and selective catalytic function, which cannot be imitated by synthetic compounds. It is expected to develop “artificial proteins” consisting of polymeric materials which show excellent functions, with exploring a precise molecular design based on amino acids.

Syntheses and functions of polymers based on amino acids

Activated monomer cationic ring-opening polymerization of e-caprolactone (e-CL) and δ-valerolactone (δ-VL) and the synthesis of di- and triblock copolymers of a seven-membered cyclic carbonate (7CC) and these lactones initiated with n-butyl alcohol/HCl·Et2O and H2O/HCl·Et2O were carried out to obtain the corresponding homopolymers and block copolymers with narrow polydispersity ratios in one pot quantitatively. The molecular weights of the obtained polymers could be controlled with the feed ratio of the monomer and initiator.

Activated Monomer Cationic Polymerization of Lactones and the Application to Well-Defined Block Copolymer Synthesis with Seven-Membered Cyclic Carbonate

This article focuses on the substituent effect on the reactivity and selectivity of the ring-opening direction in the reaction of five-membered cyclic carbonates with n-hexylamine. The reactivity of the cyclic carbonate and the formation selectivity of the adduct with a secondary hydroxyl group increased as a stronger electron-withdrawing group was introduced at the α-methylene of the cyclic carbonate. These results are discussed on the basis of the stability of intermediates, primary and secondary alcoholate anions, Mulliken charges on carbonyl carbon, and the bond lengths and orders of the OCO single bond. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3678–3685, 2001

Model reaction for the synthesis of polyhydroxyurethanes from cyclic carbonates with amines: Substituent effect on the reactivity and selectivity of ring‐opening direction in the reaction of five‐membered cyclic carbonates with amine

Anionic equilibrium polymerization behavior of several six-membered cyclic carbonates was examined. The conversions of the monomers reached a constant below 100%, and the final conversion decreased in the order of 1,3-dioxan-2-one (1) > 5,5-dimethyl-1,3-dioxan-2-one (2) > 5,5-diethyl-1,3-dioxan-2-one (3) ≥ 5-methyl-5-phenyl-1,3-dioxan-2-one (4) > 5-ethyl-5-phenyl-1,3-dioxan-2-one (5). The reactions of 2,2-disubstituted-1,3-propanediols were carried out with phosgene dimer to find that the cyclic carbonate (5) was formed quantitatively in the reaction of 2-ethyl-2-phenyl-1,3-propanediol, while the corresponding polycarbonate was formed in the reaction of 2,2-diethyl-1,3-propanediol in 24% yield besides 3. Thermodynamic parameters were estimated in the anionic ring-opening polymerizations of cyclic carbonates (1−5) by Dainton's equation. The obtained ΔHp value in the ring-opening polymerization of each cyclic carbonate reflected the polymerizability. Molecular orbital calculations of the model compounds of ...

Substituent Effect on the Anionic Equilibrium Polymerization of Six-Membered Cyclic Carbonates

Three- and four-armed star-shaped poly(e-caprolactone)s were synthesized from trimethylolpropane and pentaerythritol as initiators using fumaric acid as an activator of the monomer, respectively. Star-shaped poly(e-caprolactone)s could be satisfactorily obtained, which was confirmed by size exclusion chromatography equipped with low-angle laser light scattering and viscometer detectors. Comparing the melting points among the polymers with similar molecular weights, the order was as follows:  linear poly(e-caprolactone) > three-armed poly(e-caprolactone) > four-armed poly(e-caprolactone). On the other hand, poly(e-caprolactone)s with similar arm length showed similar melting points irrespective of the arm numbers. Thermal decomposition temperature of poly(e-caprolactone)s increased with the arm number.

Fumio Sanda

Papers

Syntheses and functions of polymers based on amino acids

Activated Monomer Cationic Polymerization of Lactones and the Application to Well-Defined Block Copolymer Synthesis with Seven-Membered Cyclic Carbonate

Model reaction for the synthesis of polyhydroxyurethanes from cyclic carbonates with amines: Substituent effect on the reactivity and selectivity of ring‐opening direction in the reaction of five‐membered cyclic carbonates with amine

Substituent Effect on the Anionic Equilibrium Polymerization of Six-Membered Cyclic Carbonates

Star polymer synthesis from ∈-caprolactone utilizing polyol/protonic acid initiator