How is lactide formed?

Lactide is prepared by a two-step process: first, the lactic acid is converted into oligo(lactic acid) by a polycondensation reaction; second, the oligo(lactic acid) is thermally depolymerized to form the cyclic lactide via an unzipping mechanism.

How do you polymerize lactic acid?

The polymerization process of lactic acid is initiated by dehydration of the monomer, which generates a prepolymer chains consisting of oligomers and low molecular weight PLA. This process, starting from lactic acid involves three distinct stages: polycondensation, obtaining lactide and ring-opening polymerization.

Can cationic polymerization be living?

Living cationic polymerization depends on an equilibrium between a reactive, growing phase and an unreactive, dormant phase. There is an inherent trade-off here. The concentration of reactive cationic chain ends is lowered because a large fraction of the chains are always dormant.

What is cationic polymerization example?

Several classes of molecules can undergo polymerization initiated by an acid species (cationic polymerization). Examples of these molecules include epoxies, vinyl ethers, oxetanes, etc.

What type of alkenes prefer under cationic polymerization?

q Cationic polymerization of simple alkenes is especially efficient for alkenes which form relatively stable carbocations (note the tertiary carbocation intermediate) and which have one double bond terminus of the alkene unsubstituted, so as to minimize steric effects in the TS for the addition reaction.

Is polylactic acid condensation polymerization?

Poly(lactic acids) with high molecular weights have been synthesized by direct condensation polymerization of lactic acid. These polymers have good mechanical properties and can be processed into products such as cups, film, and fiber, which can be used as compostable materials.

What is L lactide?

Lactide is the lactone cyclic ester derived by multiple esterification between two (usually) or more molecules from lactic acid (2-hydroxypropionic acid) or other hydroxy carboxylic acid.

Why does living polymerization occur?

Living polymerization is a popular method for synthesizing block copolymers since the polymer can be synthesized in stages, each stage containing a different monomer. Additional advantages are predetermined molar mass and control over end-groups.

Which of the following does not undergo the chain polymerization?

polyester
Which of the following do not undergo the chain polymerisation? Explanation: The polyester do not undergo the chain polymerisation. The compounds having the double bond undergo chain polymerisation. Olefins, vinyl, allyl and dienes undergo chain polymerisation.

What is the difference between anionic and cationic polymerization?

Anionic polymerization reactions are initiated by an active anionic species, whereas the cationic polymerization reactions are initiated by an active cationic species. This is the key difference between anionic and cationic polymerization. Both these polymerization reactions are sensitive to the solvent used.

What is the catalyst in cationic polymerization?

Suitable catalysts for cationic polymerization may be conveniently classified into three groups. The classic protonic mineral acids, such as H2SO4, HClO4, and H3PO4, are often useful. Effective catalysis is obtained if the acid selected has high acid strength, and an anion of low nucleophilicity (Eq. 22.9).

Which of the following can undergo cationic addition polymerisation?

Cationic addition polymerisation is applicable to vinyl monomers having e− rich double bond and is an important technique for the preparation of butyl rubbers, for eg:- polyisobutylene (PIB).

What type of polymer is polylactic acid?

Polylactic acid (PLA) is biodegradable hydrolyzable aliphatic semicrystalline polyester produced through the direct condensation reaction of its monomer, lactic acid, as the oligomer, and followed by a ring-opening polymerization of the cyclic lactide dimer.

What is the mechanism of polymerization of lactide?

Polymerization rate of lactide initiated by primary amines increases upon acid addition. Polymerization proceeds by cationic activated monomer mechanism. Amine (amino acid) end group is bound to PLA chain by stable amide linkage. Obtained products are free from metal contaminants.

Do primary amines polymerize lactide by cationic mechanisms?

On the basis of results presented in this contribution, we have concluded that the polymerization of lactide initiated by primary amines in the presence of a protic acid essentially proceeded via the same route as the cationic polymerization of lactide initiated by alcohols, i.e., by activated monomer cationic mechanism.

Does triflic acid influence the polymerization rate of lactide?

Polymerizations of lactide were performed in bulk with a primary amine as an initiator and in the presence of a protic acid as a catalyst. Triflic acid was used in different amounts to determine its influence on the polymer yield and polymerization rate. Polymerization without catalyst was also performed for comparison.

Is lactide anionic or pseudoanionic?

Lactide, as well as other lactones (e.g., ε-caprolactone), can polymerize by both anionic or pseudoanionic (coordination), as well as cationic, mechanisms [26], [27], [28], [29]. Amines are rather strong bases, and the polymerization that occurs in their presence can intuitively be associated with an anionic mechanism.