Carbon-13 Nuclear Magnetic Resonance Spectroscopy of Polystyrene

Abstract

Carbon-13 nuclear magnetic resonance configurational assignments are made for a free-radical polystyrene sample examined at 25.033 MHz and 140°C. The spectra of the aromatic C 1 and methylene were examined. New assignments were established based strictly on a oneparameter Bernoullian fit that was in satisfactory agreement with the relative intensities of the peaks observed.

Free Volume and Tacticity in Polystyrenes

“…The high field value is associated with syndiotactic structures, the low field resonance is associated with isotactic structures, and intermediate values are resonances from fragments with varying degree of atacticity. − The range of the C 1 chemical shifts in 13 C NMR spectra of anionically prepared polystyrene and the poly( p -methylstyrene) together with the deconvoluted curves are collected in Figure . Values of the degree of syndiotacticity expressed as the probability of occurrence of racemic dyads, P r , calculated as described by Suparno et al are seen in Table . By varying the reaction conditions in the anionic polymerization, it is thus possible to vary the degree of syndiotacticity in polystyrene and its derivatives.…”

Author reply

“…The 13 C NMR signals of phenyl ipso carbons were used for the determination of the tacticity. The stereochemistry of the polymers was based partially on Bernoullian20 and Markovian21 statistics.…”

High-Resolution Comonomer Sequencing of Blocky Brominated Syndiotactic Polystyrene Copolymers Using 13C NMR Spectroscopy and Computer Simulations

“…To develop a deeper understanding of the relationship between the homopolymer/solvent gel morphology and the resulting copolymer microstructure of the gel-state functionalized copolymers, a high-resolution, quantitative measure of the copolymer sequence, as offered by 13 C NMR spectroscopy, is required. For pure polystyrene, the NMR signal of the phenyl ring quaternary (C(1)) carbon in atactic polystyrene (aPS) and its phenyl ring-substituted derivatives exhibits high sensitivity to monomer configuration (i.e., tacticity), − composition, , and comonomer sequence distribution. ,,, Nevertheless, due to complexities in the C(1) resonances that arise from stereoirregularity and the chemical similarity of para-substituted styrene monomers, attempts by others to evaluate the comonomer sequence distribution of atactic polystyrene (aPS)-based copolymers by NMR have been generally unsuccessful. ,− Fortunately, for stereoregular syndiotactic polystyrene with high tactic purity, the spectral complexity of the brominated syndiotactic polystyrene (sPS- co -sPS-Br) copolymers used in this study is greatly reduced. Thus, the quaternary carbon resonances for styrene (C(1)) and brominated styrene (Br-Sty, C(1′)) monomers in this stereoregular model system are now recognized to be sensitive to neighboring monomers, which permits precise copolymer sequencing. ,, …”

“…Assignment of the C(1) resonances to stereosequences, or, for some syndiotactic polystyrene copolymers, diad or triad comonomer sequences, has been achieved by comparing the relative peak areas of the C(1) resonances to either Bernoullian − (i.e., statistically random) or first- or second-order Markovian (i.e., random sequence distribution based on probability parameter) models. ,, For example, Cui et al were recently able to assign the C(1) resonances in a syndiotactic styrene- co -4-methylthiostyrene copolymer to triad combinations of monomers based on the conformity of the relative peak areas to first-order Markov statistics. These statistical models are particularly relevant for random copolymers prepared by direct polymerization methods, where the catalyst and monomer reactivity ratio often control the stereoregularity and composition of the growing polymer chain.…”