Temporal Control over Two‐ and Three‐State Living Coordinative Chain Transfer Polymerization for Modulating the Molecular Weight Distribution Profile of Polyolefins

Abstract

A highly versatile new strategy for manipulating the molecular weight profiles, including breadth, asymmetry (skewness) and modal nature (mono‐, bi‐, and multimodal), of a variety of different polyolefins is reported. It involves temporal control over two‐ and three‐state living coordinative chain transfer polymerization (LCCTP) of olefins in a programmable way. By changing the identity of the R′ groups of the chain transfer agent, ER′n, with time, different populations of chains within a bi‐ or multimodal polyolefin product can be selectively tagged with different end‐groups. By changing the nature of the main‐group metal of the CTA, programmed manipulation of the relative magnitudes of the dispersities of the different maxima that make up the final MWD profile can be achieved. This strategy can be implemented with existing LCCTP materials and conventional reactor methods to provide access to scalable and practical quantities of an unlimited array of new polyolefin materials.

Tuning Ligand Concentration in Cu(0)-RDRP: A Simple Approach to Control Polymer Dispersity

“…One of the elegant approaches for tuning dispersity is the temporal regulation of initiation method developed by Fors and co-workers, where the initiator is fed in throughout a polymerization, so polymer chains start growing at different times. ,,− In addition, the groups of Boyer, Junkers, Frey, Leibfarth, Guironnet, and others have independently introduced a range of flow approaches, where dispersity can be carefully controlled by adjusting reaction parameters. − These methods are often associated with excellent mathematical modeling and the ability to be automated, allowing desired molecular weight distributions to be obtained. ,− ,, Furthermore, several batch methods have been recently developed to tune polymer dispersity. − These include reducing the catalyst concentration in atom transfer radical concentration (ATRP), ,,− mixing high and low activity chain transfer agents in reversible addition–fragmentation chain transfer (RAFT) polymerization, , adjusting the solvent polarity and concentration of azide in reversible complexation-mediated polymerization, and using photochromic initiators to control dispersity in cationic polymerization . Other reported methods involve the modification of CRPs by either addition of a comonomer or a termination agent ,, or blending prepurified polymers of either different molecular weight or dispersity. , Despite these excellent recent breakthroughs, there are only limited techniques that can give access to well-defined polymers with controlled dispersity, hindering the widespread use of these materials.…”

Multi-State Living Degenerative and Chain Transfer Coordinative Polymerization of α-Olefins via Sub-Stoichiometric Activation

“…19 In this regard, we have also recently demonstrated the ability to use temporal control over the addition of successive portions of CTAs during the two-and three-state LCCTP of a variety of α-olefins as a means by which to program different targeted MWD profiles for the polyolefin products, including variations in breadth, asymmetry, and modal nature (e.g., mono-, bi-, and multi-modal). 20 For MSD-LCCTP, we hypothesized that it might be possible to now modulate the breadth of the MWD using different AlEt 3 /ZnEt 2 ratios as a way to fine-tune the overall apparent rate constant of chain transfer, k app , relative to propagation via the relationship, D̵ ≈ 1 + k p /k app (see Scheme 1). Thus, runs 9−12 of Table 1 were additionally performed in order to probe this conjecture and gratifyingly, the yields and GPC data obtained and presented in the table and Figure 3 appear to validate the use of MSD-LCCTP for this purpose.…”