Abstract
The methods for one-pot synthesis of ‘soluble’ star-shaped polymers by sequential living ring-opening metathesis polymerization (ROMP) of norbornene (NBE) and cross-linking (CL) reagent using Mo(CHCMe2Ph)(N-2,6-iPr2C6H3)(OtBu)2 have been explored. The method (called the “in and out” or core-first approach) basically consists of (i) the living ROMP of NBE (formation of arm), (ii) reaction with CL (formation of core), (iii) additional living ROMP of NBE (propagating arms from the core, formation of star), (iv) end-modification via Wittig-type cleavage of metal–carbon double bonds containing polymer chain with aldehyde. Two different approaches in the core formation step (reaction with CL mixed with/without NBE) for synthesis of the high molecular weight star-shaped ROMP polymers with more branching, unimodal molecular weight distributions have been explored in detail. The method (reacting CL with NBE in the core formation step) under highly diluted conditions afforded the high molecular weight polymers with unimodal molecular weight distributions.
Highlights
Star-shaped polymers consisting of linear arms connected at a central branched core are one of the simplest nonlinear polymers, and study for the precise synthesis by living polymerization technique attracts considerable attention [1,2,3,4,5,6,7]
Under high dilution conditions, the resultant polymers became unimodal molecular weight distributions (Mw /Mn = 1.28, 1.39, runs 16, 20, gel–permeation chromatography (GPC) traces are shown in Figure 1c,f), and the Mn values increased with the increase of NBE in the 3rd reaction with rather low PDIs [21]
The results showed that the Mn values in the resultant ring-opening metathesis polymerization (ROMP) polymers increased over the reaction time in the core formation
Summary
Star-shaped polymers consisting of linear arms connected at a central branched core are one of the simplest nonlinear polymers, and study for the precise synthesis by living polymerization technique attracts considerable attention [1,2,3,4,5,6,7]. 2. Chemoselective hydrogen transfer reactions of ketones by efficient recyclable ruthenium catalyst supported by star–polymer ligand [20]. We reported an improved protocol for controlled synthesis of ‘soluble’ star-shaped polymers with more arms (branching) by the living ROMP technique using the Mo–alkylidene initiator by sequential additions of norbornene (NBE) and the cross-linker (CL), expressed as Method 1 in Schemes 1 and 3 (shown below), upon addition of CL (15 and 20 equivalent to Mo) [21]. Since most methods (controlled radical, ROMP, etc.) face a difficulty of preparation of the polymers with “unimodal” molecular weight distributions and require separation for the obtainment of the desired star-shaped polymers with relatively controlled molecular weights [12,29], the report should be helpful for precise synthesis under optimized conditions
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