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The newly formed nucleophile will then attack the atom X in another monomer molecule, and the sequence would repeat until the polymer is formed.
The initiation process involves the coordination of the cycloalkene monomer to the metal alkylidene complex, followed by a [2 2] type cycloaddition to form the metallacyclobutane intermediate that cycloreverts to form a new alkylidene species.(xy) and ΔSp(xy) are the corresponding enthalpy (SI unit: joule per kelvin) and entropy (SI unit: joule) of polymerization, and T is the absolute temperature (SI unit: kelvin).
The free enthalpy of polymerization (ΔG is the active monomer.
Ring opening metathesis polymerization (ROMP) is a versatile tool for preparing side chain liquid crystalline polymers (SCLCPs) with different mesogenic units.
The living character of ROMP allows us to design well-defined polymers and copolymers with controlled molecular weight and molecular weight distributions.
The mesophase type and the thermal transition temperatures are influenced not only by the attached mesogenic moiety but also by the stiffness of the polymer backbone, the spacer lengths between the main chain and the liquid crystalline entity, the isomerism, the tacticity, and so on.
In addition, the use of acyclic diene metathesis polymerization (ADMET) or alternating diene metathesis polycondensation (ALTMET) offer new possibilities for creating new main chain liquid crystalline polymers (MCLCPs).Examples of cyclic monomers that polymerize through this mechanism include lactones, lactams, amines, and ethers.The mechanism is affected by the stability of the resulting cationic species.A polymerization in which a cyclic monomer yields a monomeric unit which is acyclic or contains fewer cycles than the monomer.Note: If the monomer is polycyclic, the opening of a single ring is sufficient to classify the reaction as ring-opening polymerization.Monomers with a three-member ring structure - such as epoxide, aziridine, and episulfide - undergo anionic ROP.Cationic initiators and intermediates characterize cationic ring-opening polymerization (CROP).Polarized functional group is represented by X-Y, where the atom X (usually a carbon atom) becomes electron deficient due to the highly electron-withdrawing nature of Y (usually an oxygen, nitrogen, sulfur, etc.).The nucleophile will attack atom X, thus releasing Y-.Alkyl chain transfer is also possible, where the active end is quenched by transferring an alkyl chain to another polymer.The mechanism for ROMP follows similar pathways as olefin metathesis.