โ Scribed by J.N. Hay; Sathi Roy
No coin nor oath required. For personal study only.
The sequence length and tacticity of methyl methacrylate polymers prepared at 303-363ยฐK in the presence of trichlorobromomethane as a transfer agent were measured from NMR spectra. The lengths did not change appreciably but there was an increase in syndiotacticity with increasing concentration of transfer agent. There is no marked change in tacticity with molecular weight. INTROD UCTION North and Richardson [1] have determined the mean sequence length distribution and the entropy of stereoregularity of finite molecular weight polymers by allowing for end-group concentration. They determined that the number fraction of sequences and the entropy of stereoregularity are molecular weight dependent for values below 105 .
Low molectilar weight polymers are more appropriate for NMR study of configuration because of their lower viscosities and potentially higher solubilities. Trichiorobromomethane transferred polymers were chosen for a study of end-group effects on the entropy of stereoregularity of free radical polymerization. Bovey and Tiers have made a comprehensive study of the NMR spectrum of polymethyl methacrylate, and their method of deconvoluting the spectra was adopted. EXPERIMENTAL Purified methyl methacrylate (B.D.H. Ltd.) was polymerized in vacuo to about 5% conversion with benzoyl peroxide as initiator at various temperatures from 303 to 363ยฐK. The reaction was followed dilatometrically. Molecular weights were controlled by varying initiator concentration, and by using a transfer agent (trichlorobromomethane) according to the Mayo equation,
๐ SIMILAR VOLUMES
## Abstract A Haakeยฎ viscometer with the NV cupโandโbob sensor is used to measure the viscosity, ฮท, of polymethyl methacrylate (PMMA) solutions in methyl methacrylate (MMA) at several polymer concentrations, weightโaverage molecular weights, and temperatures, and under nonreacting conditions. Six p
Strong thermal relaxation effects of low energy excitations have been studied in polymethyl methacrylate (PMMA) at low temperatures. These excitations are characteristic of the amorphous structure and their relaxation gives rise to large apparent heat leaks after temperature changes in low temperatu
## Abstract Although the general complication rate for vertebroplasty is low, neural compression and thermal damage have been related to the use of polymethylโmethacrylate cement. This study focuses on the risk of thermal tissue damage after vertebroplasty. In this study, cavities were created by a