The synthesis of high molecular weight star-shaped polymers comprising poly(1,3-cyclohexadiene) arms coupled to a divinylbenzene (DVB) core is reported. In-situ FTIR spectroscopy was
used to verify first-order polymerization kinetics for 1,3-cyclohexadiene at 40 °C in cyclohexane with a
10 wt % monomer concentration using a tetramethylethylenediamine (TMEDA) to n-butyllithium (n-BuLi) ratio of 5/4. The propagation rate constant was determined to be 0.31 L mol-1 s-1. The degree of
1,2-addition (70%) vs 1,4-addition (30%) for 1,3-cyclohexadiene was determined using 1H NMR
spectroscopy. The molecular weights of the preformed arms were 10 000 and 5000 g/mol, and the ratio of
DVB to n-BuLi was systematically varied from 6:1 to 24:1. Gel permeation chromatography coupled with
light scattering detection was utilized to detect the formation of star-shaped polymers and the presence
of star−star coupling. In-situ spectroscopy and obvious color changes indicated that the addition of DVB
to poly(1,3-cyclohexadienyllithium) was rapid. The molecular weight distribution (M
w/M
n) of the star
polymers ranged from 1.4 to 1.9. The polymeric materials were thermally stable to 330 °C under a nitrogen
environment. The refractive indices of both the homopolymers and star polymers were 1.572 at 600 nm
and remained relatively constant from 1600 to 550 nm. The T
g of the high molecular weight star-shaped
polymers was 150 °C.
We present neutron spin echo and structural measurements on a perdeuterated miscible polymer blend: poly(ethylene oxide)[PEO]/poly(methyl methacrylate)[PMMA], characterized by a large difference in component glass transition temperatures and minimal interactions. The measurements cover the q range 0.35 to 1.66 A(-1) and the temperature range Tg -75 to Tg +89 K, where Tg is the blend glass transition. The spectra, obtained directly in the time domain, are very broad with stretching parameters beta approximately 0.30. The relaxation times vary considerably over the spatial range considered however at none of the q values do we see two distinct relaxation times. At small spatial scales relaxations are still detectable at temperatures far below Tg. The temperature dependence of these relaxation times strongly resembles the beta-relaxation process observed in pure PMMA.
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