¹³C NMR analysis of polystyrene by means of model compounds

Abstract

I3C Nh4R spectroscopy has been applied to determine the stereochemical configuration of polymers. In the case of polystyrene methylene and phenyl C1 carbon signals were found to split, reflecting the configurational sequences. These signals were assigned in terms of tetrad, pentad, and hexad configurations by Inoue et al.I), Matsuzaki et aL2), Randall3), Suparno et aL4), and Chen et aL5). However, the assignments of these investigators differ from each other, which may be due to the absence of various polymers of known tacticity; only isotactic polymer has been prepared with Ziegler catalyst, which is used to assign the signals due to mmm tetrad and mmmm pentad.Jasse et a1.Q tried to assign the phenyl C1 carbon signal of polystyrene on the basis of the signal assignment for the diastereomers of 2,4,6,8-tetraphenylnonane. However, they could not provide a decisive information on the signal assignment for the polymer, because the tetramer is insufficient for the analysis of the phenyl C1 carbon signal in view of the fact that it splits reflecting the pentad configuration.We have successfully separated the diastereomers of 4,6,8,10,1Zpentaphenylpentadecane, styrene pentamer with propyl end group, and assigned their "C NMR signals". In this report the phenyl C1 and the methylene carbon signals of polystyrene are assigned on the basis of the correlation of the spectra of these pentamers.Polystyrene.was prepared with benzoyl peroxide as a catalyst in benzene at 80°C. 13C NMR spectra were rekorded on a E O L FX-200 spectrometer (50,l MHz) at 150°C of a 1 ,2-dichlorobenzene solution containing sufficient amount of perdeuterobenzene for the signal lock. The chemical shifts were referred to the C4 signal of 1,2-dichlorobenzene (126,8 p.p.m.) and converted to the tetramethylsilane (TMS) scale.Tab. 1 shows the chemical shifts of the central methylene carbon of the styrene pentamers. The methylene carbon of the pentamer resonates from the lower magnetic field in the following order; rmr, rrr, mmr, rrm + mmm, and mrm. The signals due to the rmr, rrr, rrm, and mrm tetrads resonate in the wide chemicals shift range, while the chemical shift ranges of the signals due to mmr and mmm tetrads are narrow. This indicates that the methylene carbon of polystyrene is expected to resonate from the 01 73-2803/82/03 01 8 1 -05/$01 . OO

Dynamic Depolarized Light Scattering and Nuclear Magnetic Relaxation Studies of Oligo- and Polystyrenes in Dilute Solutions

“…As a typical example, Figure 8 shows 18C NMR spectra obtained by the inversionrecovery method for the sample OS3 in cyclohexane at 40 ®C at c -0.180 g/cm3 in the range of the chemical shift 5 from 32 to 45 ppm, in which there are the peaks associated with the aliphatic carbon atoms except for those in the initiating-end (n-butyl) group. We have identified each peak of the spectra by the use of the assignments obtained by Ray et al 28 and labeled it with the index xa (x = 1-6; a = m, r), where x is the carbon atom number and a indicates whether the diad in the sample is meso (m) or racemic (r). The carbon atoms have been numbered from the methylene carbon atom adjacent to the initiating-end (n-butyl) group to the terminating-end methylene carbon atom, as explicitly shown in the caption of Table 3.…”

Quantitative Correlation between Steric Defects and Thermal Behavior in Highly Syndiotactic Polystyrene: A Study Based on DSC and 13C NMR Spectroscopy

“…In particular, the CH 2 carbon region shows four peaks arising from hexads rrrrr, mrrrr, rmrrr, and rrmrr. The most intense peak is obviously assigned to the rrrrr hexad, whereas the other ones are attributed by a comparison of their chemical shifts with those belonging to the calculated and experimental sequences published by Sato [10] and Tonelli, [13] respectively ( Table 2).…”

“…Many papers report on the attribution of sequences up to hexads for methylene, [10,13,15] and heptads on quaternary aromatic carbons. [12,13] Recently, the methylene sequences containing only one m defect have been clearly individuated on the NMR spectra of highly syndiotactic sPS, [15] whereas the attribution of peaks to aromatic heptad sequences is still uncertain.…”

“…Thus, information on stereochemistry can be obtained from DSC experiments starting from as-prepared (not extracted) samples.Stereospecificity is commonly measured by means of nuclear magnetic resonance spectroscopy (NMR). [4,[7][8][9][10][11][12][13] Generally, syndiotactic polystyrene is not obtained as the exclusive reaction product. Indeed, the cocatalyst may initiate the nonstereospecific polymerization of styrene affording low-molecular weight atactic polystyrene (aPS).…”

“…The atactic fraction can be dissolved and separated from sPS with suitable solvents, leaving a solid fraction of truly syndiotactic polystyrene. Thus, the NMR spectroscopic method for the determination of stereoregularity is consistent only when performed on extracted samples.Many papers report on the attribution of sequences up to hexads for methylene, [10,13,15] and heptads on quaternary aromatic carbons. [12,13] Recently, the methylene sequences containing only one m defect have been clearly individuated on the NMR spectra of highly syndiotactic sPS, [15] whereas the attribution of peaks to aromatic heptad sequences is still uncertain.sPS exhibits a complex thermal behavior in differential scanning calorimetry (DSC) experiments.…”