1. Introduction

Ring opening metathesis polymerization (ROMP) is a process of one or more cyclic olefins transformation to polymer catalyzed by metal carbene compounds. Indeed, the number of

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

double bonds both in polymer and in monomer is equal [1–4]. As well as in any other type of polymerization, ROMP can be divided into several stages (Scheme 1).

The initiation begins with the coordination of the cycloolefins' double bond with the metalcarbene complex. The next step is a formation of a metal-cyclobutane intermediate. This process occurs in each act of addition of the monomer during the chain growth. The intermediate decomposes to form a new metal-carbene complex, with the growing chain being a ligand attached to the metal via a double bond.

The polymerization continues until the monomer is completely reacted or an equilibrium state is reached or the reaction is terminated by the addition of a special reagent that blocks the catalyst.

Living polymerization with ring opening metathesis is terminated by removing the transition metal from the end of the growing chain and its further deactivation. Deactivation in this case involves the formation of a complex unable to initiate polymerization [5]. Ethyl vinyl ether is an effective stopper for most ruthenium catalysts. It forms a very stable complex of the [Ru]=CHOEt type and ensures the functionalization of the polymer end-group. Acrylate derivatives of 2-butene-1,4-diol, succinic anhydride or butyl acrylate can also stop the growth of the macromolecule [6].

ROMP, as well as most metathesis reactions, is reversible, so the described transformations can proceed both in the forward and backward directions. The direction of the reaction can be predicted using the Gibbs energy:

Scheme 1. Stages of ROMP.

$$
\Delta G = -RT \cdot \ln K\_{\text{pann}} = \Delta H - T \cdot \Delta S \tag{1}
$$

The enthalpy factor makes an essential contribution to ROMP's Gibbs energy. This fact is explained by a high strain energy of cyclic unsaturated compounds participating in the polymerization [7]. The cycle strain energy of most cycloalkenes is more than 20 kJ/mole. For example, norbornene has an energy of about 100 kJ/mole [8]. The strain energy of the cycle releasing during the decomposition of the metal-cyclobutane complex and maintaining the forward direction of the reaction. However, if the deformation energy of cycle is low, the contribution of the entropy factor into the Gibbs energy becomes more significant in comparison with a smaller enthalpy factor. In this case, the entropy factor must be properly reduced in order to implement the direct process by increasing the monomer concentration or decreasing the temperature of the process [9].

double bonds both in polymer and in monomer is equal [1–4]. As well as in any other type of

The initiation begins with the coordination of the cycloolefins' double bond with the metalcarbene complex. The next step is a formation of a metal-cyclobutane intermediate. This process occurs in each act of addition of the monomer during the chain growth. The intermediate decomposes to form a new metal-carbene complex, with the growing chain being a

The polymerization continues until the monomer is completely reacted or an equilibrium state is reached or the reaction is terminated by the addition of a special reagent that blocks the

Living polymerization with ring opening metathesis is terminated by removing the transition metal from the end of the growing chain and its further deactivation. Deactivation in this case involves the formation of a complex unable to initiate polymerization [5]. Ethyl vinyl ether is an effective stopper for most ruthenium catalysts. It forms a very stable complex of the [Ru]=CHOEt type and ensures the functionalization of the polymer end-group. Acrylate derivatives of 2-butene-1,4-diol, succinic anhydride or butyl acrylate can also stop the growth of the

ROMP, as well as most metathesis reactions, is reversible, so the described transformations can proceed both in the forward and backward directions. The direction of the reaction can be

polymerization, ROMP can be divided into several stages (Scheme 1).

ligand attached to the metal via a double bond.

catalyst.

macromolecule [6].

16 Recent Research in Polymerization

Scheme 1. Stages of ROMP.

predicted using the Gibbs energy:

Secondary metathesis reactions can occur in addition to the main described reactions during the polymerization process. Intermolecular and intramolecular chain transfers are two main side reactions of ROMP (Scheme 2).

During the intermolecular transferring, the active metal-carbene complex located at the end of one macromolecule interacts with the double bond of the adjoined macromolecule, which leads to fragment exchange process. The reaction proceeds simultaneously in two directions. One of them provides two polymer chains with the active ruthenium on both. The second leads to one inactive chain and one chain with two active centers.

At the intramolecular chain transferring, the active metal-carbene complex reacts with the double bond of the same macromolecule led to a cyclization of the polymer chain. The listed side reactions, eventually, lead to a broadening of the molecular mass distribution (MMD) and a decrease in a molecular weight of the polymer [10].

The chain transfer as well as the spontaneous termination of the growing chain is highly improbable, so ROMP is a living polymerization. ROMP polymers are characterized by high molecular weights and a narrow MMD, as well as for products of other living polymerizations [11].

Scheme 2. Intermolecular and intramolecular chain transfers in ROMP.
