H.A. Willis

The laser-Raman and infra-red spectra of poly(methyl methacrylate)

Abstract The laser-Raman spectrum of poly(methyl methacrylate) complete with depolarization data is reported. A spectrum of powdered poly(ethyl meth-acrylate) is also given for reference purposes. Infra-red data on these polymers are included. The spectral data are fully assigned on a group-vibrational basis.

An infra-red spectroscopic study of molecular orientation and conformational changes in poly(ethylene terephthalate)

Polarized infra-red (i.r.) spectroscopy has been used to study the changes in molecular orientation and conformation which occur on drawing poly(ethylene terephthalate) sheets. The i.r. data provided orientation functions 〈P2(θ)〉ir where θ is the angle between the molecular chain axis and the draw direction for these uniaxially oriented sheets. Excellent agreement was obtained between the i.r. orientation functions for absorption bands associated with benzene ring mode vibrations, and orientation functions obtained from optical birefringence. Infra-red orientation functions for absorption bands associated with the trans and gauche conformations of the glycol residue, were then combined with i.r. estimates of the trans/gauche concentrations to examine the changes occurring in drawing. For drawing at 80°C up to a draw ratio of about 3·5, there was good agreement with expectations based on the deformation of a rubberlike network.

The effect of cooling rate upon the morphology of quenched melts of isotactic polypropylenes

Abstract Experimental data are provided on the molecular structure of paracrystalline samples of quenched melts (glasses). We propose that rods of helical molecules are present in the ‘glasses’, their length being sensitive to the temperature of the melt from which the ‘glass’ is produced, the amount of time held in the melt and the rate of quenching. A comparison is made between samples crystallized from the melt and those crystallized via the glassy phase. By measuring the lamellar thickness, from Raman spectroscopy, and calculating the absorbance ratio A 998 A 973 from infra-red spectroscopy, longer helical sequences were shown to exist to a greater extent in the samples crystallized from the melt. Samples crystallized from the glassy phase contained shorter helical sequences. In investigating the effect of the surrounding temperature on solid polypropylenes, we have shown that the density of the material can be related to the temperature of storage. We comment on the relevance of this observation to dimensional stability in mouldings.

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 spectroscopic study of structural changes in isotactic polypropylene below the melting point

Abstract Some 30°C below the melting point in annealed samples of highly crystalline polypropylene, considerable changes occur in the coefficient of linear expansion and in a wide variety of temperature derivatives of spectroscopic features. It is shown that these changes are athermal and therefore are not attributable to premelting as has been suggested in the past.

The far infra-red spectrum of crystalline polytetrafluoroethylene

Abstract The far infra-red spectrum of highly crystalline polytetrafluoroethylene has been shown to contain a new band near 33cm−1, the band at 55cm−1 has been shown to be a close doublet and two further bands at 291 and 308cm−1 have been observed. These results strongly support the conclusions of Boerio and Koenig from Raman observations that the unit cell contains at least two molecular segments.

Temperature effects and the observation of the B2u lattice mode in the far infrared absorption spectrum of polyethylene

Abstract Using high precision radiometry in conjuction with a Michelson far infrared spectrometer the B 2u lattice mode of polyethylene has been observed at both room and liquid-nitrogen temperatures. The continuum absorption of polyethylene in the far infrared has been shown to be temperature dependent from whick it is concluded that difference type multiphonon bands make a considerable contribution.

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.

The far infra-red spectrum (400-10 cm−1) of isotactic polypropylene

Abstract Infra-red spectra of isotactic polypropylene samples having different crystallinity have been observed in the range 400 to 10cm−1. Eleven bands have been identified, whereas only eight internal modes are predicted for this region on the basis of line group symmetry. Experimental evidence, including dichroic behaviour of the bands, indicates that contrary to previous reports one of these additional features arises from a lattice mode and the others from the effect of crystal symmetry.

The observation of a band near 14 cm−1 in the raman and far infrared spectra of polytetrafluorethylene

A band has been observed near 14 cm−1 in the vibrational spectrum of PTFE. It is assigned to the E2 intersection of the ν9 branch, which was not previously known experimentally, and it therefore completes the vibrational assignment for polytetrafluorethylene.