Periodic Vinyl Copolymers Containing γ-Butyrolactone via ADMET Polymerization of Designed Diene Monomers with Built-in Sequence

Abstract

The synthesis of a new family of periodic copolymers containing γ-butyrolactones by acyclic diene metathesis polymerization (ADMET) and their thermal properties are presented. Two symmetric diene monomers, M6 and M8, were designed. Both monomers contain two γ-butyrolactone units, but they are different in the length of methylene spacers between cyclic structures and terminal alkenes. The monomers have been prepared by a two-step approach; first, the atom transfer radical addition (ATRA) of diethyl meso-2,5-diiodohexanedioate with either 1,5-hexadiene or 1,7-octadiene was conducted to yield intermediates containing two γ-iodo ester sequences; subsequently, the specific sequence was transformed into γ-butyrolactone unit via intramolecular cyclization upon heating. The two monomers were polymerized using two Grubbs catalysts (Grubbs I and Grubbs II) to produce four polymers with moderate to high molecular weights (P6-1, P6-2, P8-1, and P8-2) and hydrogenation of which gave the final saturated polymers. The expected periodic copolymers have been obtained and were characterized with a variety of methods, indicating that the γ-butyrolactone units could endure the polymerization and hydrogenation. Polymers catalyzed by Grubbs II catalyst suffer from chain heterogeneity due to severe olefin isomerization. Thermal properties of the polymers were investigated via thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA measurements show that these polymers are stable up to 350 °C. DSC results demonstrate that the glass transition and melting behaviors of the polymers are not only affected by the rigidity of γ-butyrolactone units in polyethylene chains but also dependent on the methylene spacer length and chain homogeneity. Copolymerization of M6 or M8 with 1,9-decadiene resulted in random copolymers with lower γ-butyrolactone content and less regular chain structure. These copolymers exhibit lower T g or T m compared with the periodic copolymers.

Synthesis and characterization of precisely-defined ethylene-co-aryl ether polymers via ADMET polymerization

“…Typical polymerization strategies for the preparation of ether incorporated polyolefins could also include transition-metal-catalyzed coordination-insertion polymerization and free radical processes, but the oxophilicity of the transitionmetal polymerization catalysts which generally leads to poisoning by strong s-coordination of the Lewis basic moiety of a polar vinyl monomer or poor control over branching ratios, and distribution of the polar functional groups in the polymer chain. Alternatively, ring-opening metathesis polymerization (ROMP) of functionalized cyclooctenes [22e24] or acyclic diene metathesis (ADMET) of functionalized dienes [25e27] represents a potentially ideal method for the controlled synthesis of functional polyolefins in a single step, particularly, precisely control the identity and distribution of branches along the backbone of polyethylene, as well as functional groups incorporated in the main chain, including model copolymers of ethylene with acrylates [28], styrene [29], vinyl acetate [30], and vinyl halide [31], silicon-containing polymers [32] and chiral polymers [33] have been unprecedently achieved in the presence of Schrock' catalyst and Grubbs' series of catalysts.…”

Recent developments in the synthesis of sequence controlled polymers

“…Li and coworkers [69] designed a series of ,-dienes containing bifunctional carboxylates, -butyrolactone units, and acetoxy groups. After ADMET in the presence of Grubbs catalysts and subsequent hydrogenation, periodic model copolymers of ethylene and acrylates, -butyrolactone, or vinyl acetate, respectively, were obtained ( Figure 17).…”

Synthesis and Crystallization of Precision Polymers with Repetitive Folding Elements

“…known to enable a complete hydrogenation of poly/ oligo(olefi ns). [ 39,40,42 ] After 6 h, the reaction mixture was allowed to cool to room temperature and the hydrogenated polymer was obtained after removal of the solvent and subsequent dialysis from methanol.…”