Polymer, chemical physics analytical techniques

Scientists have used a wide arsenal of analytical techniques to monitor chemical and physical transformations of polymers following exposure to laser radiation, among which UV-Vis absorption, nuclear magnetic resonance (NMR) spectroscopy, electron spin resonance (ESR) spectroscopy for detection of free radicals, GC/MS analysis, FTIR for detection of various functional groups and bonds, X-ray photoelectron spectroscopy (XPS) for the chemical composition of surfaces, optical, and fluorescence microscopy, atomic force microscopy (AFM) for surface topography, quartz crystal microbalance (QCM) for in situ mass loss measurements, and so forth. 

The drawback to this approach is relating the time domain information to a chemical species or physical phenomena. Many broadline systems are used in an empirical fashion in which the results are correlated with a process control parameter or measured physical property. However, this approach alone does not indicate which chemical species is being measured. The signals could be due to water or fat content, bound water versus free water in a slurry or different phases of a polymer, crystalline, amorphous or interfacial regions. To ensure that these correlations are due to specific chemical species broadline NMR data must be related to some other primary analytical technique such as high resolution NMR. 

The surface properties of polymers are important in many applications and they are dependent on the structure and composition of the ontermost molecular layers. The surface layer thickness involved is typically of the order of a few nanometers. Understanding surface structure-property relationships therefore requires analytical techniques which have this degree of surface sensitivity (or specificity). Two techniques stand out X-ray photoelectron spectroscopy (XPS) (1), also known as ESCA (electron spectroscopy for chemical analysis), and secondary ion mass spectrometry (SIMS) (2). The information provided by these methods is highly complementary and they are frequently used in combination. This article describes the physical bases and anal5dical capabilities of XPS and SIMS and illustrates their application in polymer surface characterization (3). 

Infrared (IR) spectroscopy is a reliable, fast, and cost-effective analytic technique. It is one of the classic methods to determine the structure of small molecules or fimctional groups. IR is ideally suited for quahtative analysis of polymers and finished products as well as for quantification of components in polymer mixtures. Thermal analysis techniques include physical-chemical methods to study materials and processes under conditions of programmed changes in the surrounding temperature. Thermal volatihzation analysis (TVA) is a technique that analyzes the products formed when, for example, a polymer is heated. It analyzes the polymer itself as well as the volatile compounds released during this heating. In this chapter, we present the application of TVA to biodegradable polymers, especially polylactic acid (PLA), starch, and their mixtures. 

The decomposition of initiator can be followed by usual analytical methods and k can be determined. The efficiency factor/can be obtained by comparing the amount of initiator [I] decomposed with the number of polymer chain formed. The rate of polymerization can be determined by monitoring the change in a physical or chemical property of the system. Generally, dilatometry technique is used for determination of the rate of polymerization. Let the extent of polymerization be small and concentration of initiator be constant. Let r0, rt and r be the readings on dilatometer initially, at time t and at the completion of reaction, respectively. If reaction is first order in [M],... 

The size difference, however, is important enough to make polymers the fascinating and useful materials they are. As a consequence of their size, physical and chemical properties become a function of molecular weight. Analytical experimental techniques must be modified to incorporate the size factor, and theories must account, accordingly, for the types of interaction that occur in these large molecules. 

Fortunately, polymers have a range of properties as diverse as the applications for sensors. Sometimes, however, the multitude of choices of polymers makes selection of the proper polymer difficult, and one resorts to trial and error methods of selection—an inefficient and time-consuming technique. However, sufficient knowledge of the physical and chemical properties of the analyte, the potential interferences, and the environment in which the sensor will operate, combined with insight into the desired function of the polymer, can make selection of polymers for sensor fabrication a much less daunting task. 

Chemical heterogeneity in synthetic polymers offers a challenge to the analytical chemist to devise sensitive techniques for the characterization of these chemical distributions. It is well known that many synthetic copolymers consist of a collection of polymer chains that differ in their individual compositions. This distribution of repeat-unit composition from chain to chain can influence the physical properties of synthetic polymers significeuitly. Consequently, a thorough characterization of a copolymer sample would include a description of the average composition eUid its compositional distribution. 

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