ANALYSIS OF A SYMMETRICAL NEOPOLYOL ESTER .2. SOLID-STATE UC NMR AND X-RAY MEASUREMENTS

The symmetric neopolyol ester ethyleneoxycarbonyl(2,4,4-trimethyl)pent yl]methane (MOCPM) has been studied by variable-temperature solid-stat e C-13 NMR and X-ray powder diffraction and compared to molecular mech anics calculations of the molecular structure. Between melting and gla ss transition temperatures the material is semicrystalline, consisting of two conformationally and motionally distinguishable phases. The mo re mobile phase is liquid-like and is, thus attributed to an amorphous phase (approximate to 16%). The branches of the molecules in the crys tal exhibit two conformationally distinguishable behaviors. In one, th e branches are well ordered (approximate to 56%), in the other, the br anches are conformationally disordered (approximate to 28%). Different branches of the same molecule may show different conformational order . This unique character of the rigid phase is the reason for the defic it of the entropy of fusion observed earlier by DSC. In the melt, soli d state NMR can identify two bonds that are rotationally immobile, eve n though the molecules as a whole have liquid-like mobility. This part ial rigidity of the branches accounts quantitatively for the observed increase in heat capacity at the glass transition. The reason for this unique behavior of MOCPM, a small molecule, is the existence of one c hiral centers in each of the four arms of the molecule. A statistical model assuming that at least two of the chiral centers must fit into t he order of the crystal can explain the crystallization behavior and w ould require 12.5% amorphous phase, 28.1% conformational disorder, and 59.4% crystallinity, close to the observed maximum perfection.