Thousands of polymeric materials have been made into synthetic polymers, based on a linear structure, and used in commercial applications. The study of synthetic polymeric materials has focused on those derived from long chain linear molecules. Alternatively, cyclic polymers (also referred to as polymer rings or macrocycles) can be prepared, which not only can be branched or cross-linked, but can also form noncovalently linked structures based on their loop topology. Through a number of different approaches and advances in cyclization techniques, a wide range of novel cyclic polymers have been synthesized in good yields. This review will focus on a variety of synthetic methods and some properties of cyclic polymers using many polymerization mechanisms in various fields of polymer synthesis.

Synthesis and Properties of Cyclic Polymers

I. THE CHILING TEMPERATURE CONCEPT A. Thermodynamic Approach The Gibbs free energy of a system at temperature T is defined as were H is the enthalpy and S the entropy of the system. The free energy change for any polymerization will be, therefore, When the polymer has a lower free energy than the initial monomer, a polymerization can occur spontaneously, and the sign of ΔG is negative. A positive sign for ΔG signifies, therefore, that the polymerization is not spontaneous. When the system is in equilibrium at a certain critical temperature, there is no tendency for polymerization, and, hence, ΔG = 0 [1–3]. This temperature is known as the ceiling temperature. These three possible conditions for free energy change of polymerization may be summarized as follows: At the ceiling temperature, Tc, ΔG is zero, so that where ΔHp and ΔSp are the enthalpy and entropy changes per monomer unit.

Thermodynamics of Polymerization

Thermodynamic functions of linear high polymers: Part I—polyoxymethylene

The present review articulates the syntheses and properties of industrially important disulfide and tetrasulfide polymers. The diselenide and ditelluride polymers have also been reviewed, for the first time, so that a comprehensive view on the polymers containing group VIA elements can be obtained. The latter two polymers are gaining considerable current attention due to their semi-conducting properties. The emphasis has been made to sift through the developments in the last ten years or so to get the latest flavour in these rapidly developing polymers. We have also attempted to bring to the fore several contradicting results, like, for example, the crystallinity of ditelluride polymers, to clear the mist in such reports. We hope that this review will help those working in the field to assess the progress achieved in this area and that it may also provide useful orientation for those who wish to become involved.

Polymers containing disulfide, tetrasulfide, diselenide and ditelluride linkages in the main chain

Near ultraviolet photopredissociation of formaldehyde has been verified as a highly selective method for enrichment of the rare stable isotopes of oxygen, hydrogen, and carbon contained in this molecule High resolution absorption spectra of rare‐isotope‐substituted fomaldehyde show coincidences to within the Doppler profile with strong ion laser transitions in Xeiii at 345 nm and Neii at 332 and 338 nm By tuning each ion laser transition with an intracavity etalon, optimum enrichment of each isotope was selected by monitoring formaldehyde fluorescence Oxygen‐18 was enriched up to ninefold using natural neon lasing at 332374 nm, while substituting Ne‐22 permitted up to ninefold O‐17 enrichment and 33‐fold C‐13 enrichment at 332371 nm Use of D2CO instead of H2CO permitted 44‐fold O‐18 and 27‐fold O‐17 enrichment Hydrogen photoproducts showed 24‐fold HD enrichment at 337822 nm, 60‐fold HD enrichment at 345426 nm, and 180‐fold D2 enrichment at 332377 nm Single vibronic level photolysis of HDCO shows greater than 90% molecular photoproducts at wavelengths longer than 330 nm and a sudden rise to greater than 50% radical photoproducts below 320 nm Photopredissociation of D2CO at 332 nm yields less than 1% radical photoproducts Isotope scrambling in HDCO is about 40% at 325 nm, but drops to less than 6% at 338 nm Isotope scrambling is 24% for both C‐13 and O‐18 at 332 nm Enrichment of deuterium, carbon‐13, and oxygen‐18 was carried out using formaldehyde with initial isotope composition ranging from natural abundance to 50% to yield photoproduct with up to 88% isotopic purity

Isotope separation of oxygen-17, oxygen-18, carbon-13, and deuterium by ion laser induced formaldehyde photopredissociation

The heats of polymerization of some cyclic and ethylenic compounds

https://pubs.rsc.org/en/content/articlepdf/1959/tf/tf9595500061

D. A. G. Walmsley

Papers

The heats of polymerization of some cyclic and ethylenic compounds

The equilbrium between gaseous formaldehyde and solid polyoxymethylene