Vincent J. McBrierty

Understanding hydrated polymers: the perspective of NMR

Abstract This review examines the divergent views in the literature on the role of water in hydrated polymers, specifically the origin of non-freezable water. One approach, based largely on site-specific information furnished by NMR invokes binding sites in the host polymer matrix as a principal source of bound or non-freezable water; the second approach is based on the thermodynamics of metastable, non-equilibrium states in the hydrated polymer without the necessity of binding sites. There is merit in both approaches: and they are not mutually exclusive. The situation is further exacerbated with a proliferation of terminology that is both technique and temperature dependent. Despite these difficulties, the behaviour of water has several generic features that are common to a wide variety of hydrated polymeric and non-polymeric systems. The advantages of a multi-technique approach in unravelling the intricacies of polymer-water interactions cannot be over-emphasised.

Use of rotation operators in the general description of polymer properties

In this paper we are concerned with the formulation of a general mathematical scheme which may be used to describe many polymer properties of interest. The responses of polymers to the following experimental techniques have been analysed: infrared absorption, x‐ray diffraction, nuclear magnetic resonance absorption, fluorescence polarization, and elasticity measurements. A principal feature of the analysis is the use of matrix elements of the three‐dimensional rotation operator. This approach greatly facilitates the treatment of the various types of symmetry, both statistical and crystallographic, which are often an inherent feature of polymer structure. It is clearly demonstrated how measurements from different experiments can complement each other and lead to a more complete description of the polymer.

Campus companies and the emerging techno-academic paradigm: the Irish experience

Abstract The paper identifies ‘knowledge equity’ as the central resource on which the competitive advantage of industry and, increasingly, of countries is based. This new perception of knowledge — embedded in intellectual capital — as a form of equity is at the heart of what we believe to be a new and distinctive paradigm shift. This ‘techno-academic paradigm’ — reflected, for example, in the central role of campus companies in the development of the information technology sector in the United States — identifies the higher education (HE) sector both as a generator of knowledge equity and as an implicit risk-sharing framework within which the full potential of campus companies can be exploited. The paper provides the first systematic evidence of a new technological entrepreneurialism within the HE sector in Ireland, as manifest in the growth of campus companies. In effect, the paper argues that the culture and focus of the HE sector is being reshaped by its new catalytic role in the generation, application and diffusion of knowledge.

Hydration and plasticization effects in cellulose acetate: a solid-state NMR study

Abstract The conjoint effects of water and diethyl phthalate (DEP) plasticizer on molecular motion in cellulose acetate (CA) have been examined. 1 H, 13 C and cross polarization NMR data reveal a number of interesting features. As in other hydrated polymers, there are different types of water ranging from tightly bound to bulk-like water in CA. Both tightly and loosely bound water can act as a plasticizer. In CA which is devoid of DEP, water preferentially interacts with carbonyl groups in the side chains whereas in the plasticized and filled polymer, water associates with oxygen atoms in both main and side chains via weak hydrogen bonding. Hydration significantly enhances chain motions but, as expected, reduces the ability to cross-polarize carbons and protons. Information is obtained on the relaxation behaviour of CA and the manner in which it is affected by water and DEP plasticizer. From a practical point of view, it is significant that water and plasticizer act in concert to alter the properties of the material quite dramatically. That these property changes can be induced, for example, by climatic changes in humidity has important bearing on the processability of the material.

DYNAMICS OF WATER MOLECULES IN POLYMERS

Abstract When water is incorporated into a host matrix such as a polymer its behaviour is significantly different from the anticipated response of normal water. This brief review examines the complex, non-equilibrium character of water in a number of hydrated systems which find routine application in the commercial world. In relating the macroscopic properties of hydrated polymers to events at a molecular level, the major advantages to be gained from the use of a range of experimental approaches over a wide temperature range are clearly demonstrated.

Solid polymers: a challenge for NMR.

The sheer structural and motional complexity of polymers presents a formidable challenge to the power and versatility of NMR. This challenge is well met through exploitation of the plethora of experimental devices which have been developed over the past 50 years, among which the discovery of Magic Angle Spinning by Raymond Andrew features prominently. This paper presents a brief review of the subject in terms of a number of examples which illustrate the rich and detailed information which NMR provides.

An n.m.r. investigation of structure and motion in hydrated α,ω-dicarboxylatopolybutadiene☆

Abstract N.m.r. analysis of the hydration and temperature behaviour of resolved carboxyl carbon resonances in the acid and neutralized α,ω-dicarboxylatopolybutadiene telechelics reveal a complex interaction between water and chain end groups participating in the formation and subsequent stability of crosslinks. A multiplicity of environments are detected above the glass transition of the host polymer matrix arising from chemical and physical inequivalences. Reasonable interpretations are advanced to account for the observed carboxyl peaks. Analysis of the temperature dependence of 13C linewidths offers further insight into the manner in which end groups influence overall motion in the polymer. Extraction of meaningful activation energies from 13C linewidth data, however, must take correlation frequency distributions into account. The anomalous behaviour of water and its influence on structure and motion is explored.

General Description of the Mechanical Anisotropy in Drawn Polymers in Terms of Spherical Tensors

The paper presents a general theoretical description of the elastic behavior of oriented polycrystalline polymers in terms of the spherical components of the compliance tensor. The use of the spherical representation has a number of advantages. For example, the analysis of Roe and Kringbaum [J. Chem. Phys. 40, 2608 (1964)] which describes the crystallite orientation distributions in partially oriented systems in terms of experimental x‐ray data can be incorporated directly into the theory. A second advantage relates to the simple way in which different crystal symmetries can be treated. The analysis may be readily extended to include two‐phase systems.

The glass transition in an ionomer: Interpretation of Mössbauer data

The glass transition in α,ω‐dicarboxylatopolybutadiene (Mn=4600) neutralized with ferric iron has been studied by quasi‐static and high frequency techniques (shear modulus, differential scanning calorimetry, pulsed NMR and Mossbauer spectroscopy). The temperature dependence of the Mossbauer recoilless fraction f begins to deviate from Debye behavior at the quasi‐static glass transition at T=190 K due to softening of the long‐wavelength vibrational modes. f  becomes unmeasurably small above a higher temperature T0 which is identified as the glass transition on a time scale of 10−7 s.

Elasticity in Polymers. II. The Directional Properties of the Compliance Constants in Uniaxially and Biaxially Drawn Polymers

The theoretical analysis of elasticity in oriented polymers in terms of the spherical components of the compliance tensor presented earlier has been extended to include biaxial orientation and also the case of a segment cut at an arbitrary angle in a drawn polymer. The significance of the results is discussed.