Intrachain Cyclization via Postmodification of the Internal Alkenes of Periodic ADMET Copolymers: The Sequence Matters

Abstract

We demonstrate that monomer sequence is important to regulate the vinyl copolymer thermal properties by intrachain cyclization. This is exemplified by the spontaneous intrachain cyclization with the formation of γ-butyrolactone by dihydroxylation of the internal alkenes of a designed periodic copolymer. A structurally symmetric α,ω-diene monomer 1 containing two tail-to-tail connected ethyl acrylate units was synthesized via a two-step approach. The acyclic diene metathesis (ADMET) polymerization of monomer 1 was conducted with a Hoveyda–Grubbs second generation catalyst in the presence of p-benzoquinone to get well-defined polymer (P1) with high molecular weights as revealed by GPC, NMR, and MALDI-TOF-MS characterizations. Dihydroxylation of P1 using hydrogen peroxide as the oxidant was successfully conducted to afford HP1. Characterization of HP1 by NMR and IR spectra indicated that it contained γ-butyrolactone units in the polymer main chain. Control experiments with four different polymers indicated that the formation of this ring structure was the outcome of the specific sequence of vinyl alcohol–ethyl acrylate formed by dihydroxylation of P1. The cyclization efficiency of P1 was calculated to be 77%. The T gs of all the modified polymers were increased compared to those of the unsaturated samples; significantly, the T g of HP1 was drastically elevated by 160 °C as compared to that of P1.

A General Approach to Sequence-Controlled Polymers Using Macrocyclic Ring Opening Metathesis Polymerization

“… 2 This leads to highly controlled microstructures, but is unable to produce high molecular weights and is generally time intensive. Step-growth approaches, such as click polymerization 3 or ADMET, 4 can generate elaborate periodic polymers from preformed sequences, but lack control over polymer molecular weight and dispersity. In contrast, chain-growth strategies have controlled polymerization characteristics, but lack a high level of sequence precision when compared to the previous methods.…”

Electronically Governed ROMP: Expanding Sequence Control for Donor–Acceptor Conjugated Polymers

“…Much work has been done to engineer systems capable of sequence-controlled assembly and/or synthesis, 8,11,12 owing to macromolecular function being prescribed by monomer order. Stepwise iterative strategies are common to string together peptides, though in practice, the classical Merrifield-type approach used in peptide coupling dictates supreme control over sequence; 13,14 yet struggles to achieve high molecular weights, while not being able to realize both time and cost efficiency.…”

“…Step-growth methods (e.g., acyclic diene metathesis, ADMET) afford high-molecular-weight polymers and often control periodicity; 12 however, such strategies realize ill-defined (high-dispersity) polymers. Methods based on supramolecular tactics (e.g., metal-coordination or hydrogen-bonding strategies) have been realized, yet are limited in scope.…”

The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2014

“…Several α,ω-dienes possessing the following structural features were subjected to ADMET polymerization: (1) substitution by ester groups (e.g. 104) [407,408], including polymerization in a miniemulsion system [409]; (2) substitution by alcohol groups [410]; (3) linkage through ester groups [411]; (4) linkage through an itaconate system (e.g. 105) [412]; (4) linkage through an amide group [413]; (5) linkage through an inositol system (e.g.…”