Michael E. A. Cudby

High resolution 13C n.m.r. spectra of solid isotactic polypropylene

Abstract The high-resolution 13 C n.m.r. spectra of three samples of solid isotactic polypropylene are reported. The spectra, obtained under conditions of proton dipolar-decoupling and fast magic-angle rotation and using cross-polarization, are of annealed and quenched samples of the α-crystalline form and of a sample of the β-crystalline form. Attention is drawn to the importance of knowing the proton relaxation characteristics in these experiments and some illustrative proton T 1 ϱ data are given. The 13 C n.m.r. spectrum of the annealed sample of the α-crystalline form shows well-resolved splittings of the methyl and methylene resonances in a 2:1 intensity ratio. These splittings are interpreted in terms of the crystal structure of the α-form as suggested by X-ray diffraction. Quenching the α-form causes significant changes in the spectrum including a loss of resolution of the splittings obtained from the annealed sample. The β-form shows broad symmetrical resonances for the methyl and methylene carbons. The chemical shifts and other spectral features are discussed in the light of the proposed crystal structures and the effects likely to be produced by quenching.

Discriminatory experiments in high-resolution13C NMR of solid polymers

SummaryCross-polarization spectra of solid polymers can be misleading when the material exhibits proton spinlattice relaxation in the rotating frame which cannot be represented by a single exponential. Quantitative and qualitative demonstrations of the problem are given. The use of two experimental procedures for alleviating the difficulties is suggested, and examples for polyalkenes and for polyethylene terephthalate are illustrated.

Some crystallization kinetics of isotactic polypropylene

Abstract Infra-red evidence is presented that the building of helices in the crystallization process from the glassy (or smectic) phase or from the melt are second order or zero-th order respectively. The observation coupled with data from density and X-ray diffraction measurements is interpreted in molecular structural terms.

A magic-angle rotor for NMR using a forced gas bearing

Abstract A new design for a rotor system to achieve spinning rates of the order of 3 kHz is presented. The design uses a simple cylindrical rotor, and involves a forced air bearing over the whole cylindrical surface. The jets of gas which make this bearing also cause the spinning. Powder-filled hollow rotors spin smoothly, and are convenient to make and use. The whole system is suitable for magic angle rotation, such as is needed to obtain high-resolution NMR spectra of solids. Examples of spectra obtained using the device are illustrated and discussed.

Chain branching in high pressure polymerized polyethylene

Abstract In a paper 6 years ago, we reported on the detailed molecular structure of lamellar crystalline high pressure polymerized polyethylenes rich in branching. We showed that the crystalline cores contained few ethyl and butyl side-branches but did contain long side chains. In this paper, we exploit recent developments in technique to refine our observations, improve their rigour and extend them to commercially significant high-pressure polymerized polyethylenes of modest side-branch content. We also study and report on some common ethylene olefin copolymers. We conclude that our earlier conclusions are correct, that the side-branches are bunched rather than being randomly situated along the backbones and that most of the branches, and in particular the branched branches, become concentrated in the inter-core regions on melt crystallization.

Vibrational spectra of crystalline polytetrafluoroethylene

Abstract Existing literature sources on the experimental vibrational spectroscopy of polytetrafluorethylene are reviewed and new detailed evidence in this field is presented. It has been proposed elsewhere on spectroscopic grounds that a structure exists involving two chains per unit cell at low temperatures, but X-ray support for this proposal is lacking. We explore this point in detail by referring to new spectroscopic data.

Laser-Raman spectrum of polyethylene: Part 1. Structure and analysis of the polymer

The Raman spectra of several different samples of polyethylene are reported. It appears that the spectra are sensitive to crystallinity and to the presence of impurities such as vinyl groups. The possible effect of the presence of gauche CH 2 groups are considered. There is definite evidence that Raman spectroscopy has value as an analytical technique for polyethylenes.

Fourier transform Raman spectroscopy in the analysis of polypeptides

The use of near-infrared Fourier transform Raman spectroscopy in the analysis of polypeptides is critically reviewed. A range of peptides and polypeptides are discussed and show promising results in the pure crystalline form. However, in aqueous solution analogous to in vitro conditions the results are disappointing and further developments in Fourier transform Raman techniques are required before the technique, applicable to these compounds, can be successful.

The vibrational analysis of polyperdeuteroethylene

Abstract The i.r. and Raman spectra of polyperdeuteroethylene (recorded at room temperature and at 77 K) are presented and discussed. The presence of lattice modes and a longitudinal acoustic mode were observed. The spectrum is assigned to the fundamental modes of vibration.

Solid-state high-resolution 13C n.m.r. spectra of polypropene

The high-resolution 13C n.m.r. spectra of solid isotactic and syndiotactic polypropene are reported and a novel confirmation of the specific helical nature of syndiotactic polypropene previously deduced from X-ray diffraction studies is given.