Molecular Weight Distribution in Ring‐Opening Polymerization of Propylene Oxide Catalyzed by Double Metal Complex: A Model Simulation

Abstract

easy to calculate. Even though this method cannot show out the full MWD curves, it gathers the most important information such as monomer conversion (x), molecular weight (MW), and polydispersity index (PDI). [28] PDI quantifies the width of MWD.The ring-opening polymerization (ROP) of propylene oxide (PO) catalyzed by double metal complex (DMC) is generally considered to have the characteristics of living polymerization. For example, the MW increases with x, and block copolymers with ethylene oxide can be prepared. However, our recent experimental study shows that the MWD of products is not easy to keep very narrow even if the polymerization is carried out in batch or plug flow reactor. [34] According to the polymerization mechanism proposed by Huang et al., [35][36][37] it is generally believed that the chain transfer reaction between active chains and dormant chains is the key to narrow MWD. However, up to now, no one has quantitatively investigated the effect of this chain transfer reaction on the MWD.In this work, a kinetic model involving chain propagation and chain transfer is established; the method of moments is used to simulate PDI as well as x and number-average polymerization degree (Xn) under various reaction conditions. We hope that this work can facilitate the understanding of the polymerization mechanism behind various complex phenomena in the ROP catalyzed by DMC. Modeling Section Polymerization MechanismAs Huang et al. [35][36][37] and Kim et al. [38,39] have reported, ROP of PO catalyzed by DMC consists of induction, chain propagation, and transfer reaction. Herein, only the chain propagation and transfer reaction are considered since they are the main reactions that affect MWD. As shown in Scheme 1, chains with active center can be propagated; meanwhile, the active center can be transferred to dormant chains so that they are activated and propagated. It is the chain transfer between the active chain and dormant chain that results in the more uniform chain growth. Obviously, it can be thought that the instant rate In the present work, method of moments is used to model the molecular weight distribution (MWD) of polypropylene glycol (PPG) produced with ring-opening polymerization of propylene oxide catalyzed by double metal complex (DMC), and an explicit expression about the polydispersity index (PDI) of PPG is obtained. The simulated results indicate that decreasing the initial concentration ratio of monomer to total chains (K 1 ) or increasing the rate constant ratio of chain transfer to propagation (K 2 ) leads to smaller PDI. Reducing the concentration of DMC can induce larger PDI. When the PPG's initial PDI (i.e., PDI of initiator) increases, PDI of the final PPG grows up linearly. However, with the increase of monomer conversion, PDI increases first and then decreases, that is, there is a critical conversion. The possible lack of chain transfer at the beginning of polymerization and the insufficient chain transfer caused by increased K 1 , decreased concentration of catalyst, and decreased...

DMC-Mediated Propoxylation in Semibatch with an External Loop: Insights into the Catalytic Action

“…Nonideal mixing thus significantly contributes to the broadening of the distribution, which is superimposed over the inherent catalysis that needs to be described in terms of macro- and microkinetics. ,, The vertical mixing efficiency of an anchor stirrer is limited, and a lower reaction rate set by a lower PO feeding rate in setup 1 gives more time for mixing, a converging reaction rate, and mixing times . This results in smaller gradients in the reaction mixture, exposing more volume elements of PPGs to PO at the inlet, but obviously decreases space–time yields.…”

Borinane Boosted Bifunctional Organocatalysts for Ultrafast Ring-Opening Polymerization of Cyclic Ethers

“…The above results revealed the remarkable advantages provided by the bifunctional ammonium salt B4 for the preparation of polyols, allowing one to perfectly control the molar mass of the polyether samples synthesized using B4 as a catalyst at low loading. Compared to the industrial scale production of PPO diols relying on the use of DMC as the catalyst, and necessitating oligomers or noncomplexing alcohols 42 as CTAs which tend to generate higher molar mass chains, 43,44 the process catalyzed by B4 not only affords sample free of any high molar mass contaminant but it can also be carried out under much milder conditions, using standard protic CTAs to generate well-defined PPO diols. Low Catalyst Loading for Polyol Preparation with Broad Monomer Scope.…”

Borinane Boosted Bifunctional Organocatalysts for Ultrafast Ring-Opening Polymerization of Cyclic Ethers

“…The above results revealed the remarkable advantages provided by the bifunctional ammonium salt B4 for the preparation of polyols, allowing one to perfectly control the molar mass of the polyether samples synthesized using B4 as a catalyst at ultralow loading. Compared to the industrial scale production of PPO diols relying on the use of DMC as catalyst, and necessitating oligomers or noncomplexing alcohols 39 as CTAs which tend to generate higher molar mass chains, 40,41 the process catalyzed by B4 not only affords sample free of any high molar mass contaminant, but it can also be carried out under much milder conditions, using standard protic CTAs to generate well-de ned PPO diols.…”