Atlas of Polymer Structures

Polymeric materials show a very broad variety in structure and morphology and possess very different specific properties. The production of the first polymers used as manufacturing materials started over 100 years ago with the realization of phenol resins by L.H. Baekeland. The first polymer plant in the world in Erkner near Berlin began in 1910 with the production of such resins well-known as Bakelite.

The main microscopic techniques to study the morphology of polymers make use of direct imaging with optical, electron, and atomic force microscopy.

As has already been shown, the method of preparation and the investigation technique for polymers can influence the appearance of morphology of the particular polymer. In addition, one must consider whether varying the preparation methods and microscopic techniques can improve or even deteriorate the visibility of structural details. Some examples of the practical importance of sample preparation and of microscopic technique that can strongly influence the visibility of structures in the micrographs are described in the following sections.

Polymers of this group have their “amorphous” structure in common. In contrast to the usual definition of amorphous, meaning structureless, many amorphous polymers reveal a more or less detectable microstructure, from weak domainlike or globular structures up to a pronounced morphology. Therefore, a second definition is often used that amorphous polymers do not exhibit any crystalline structure in X-ray or electron scattering experiments.

Semicrystalline polymers constitute an important group of polymers with a very broad range of applications. In particular, the family of polyolefins, including polyethylenes and polypropylenes, is one of the most prominent commodity plastics that make up a great part of the world’s plastic market. The rapid development of new catalysts has allowed for the tailored design of macromolecules with defined semicrystalline morphologies and thus defined properties.

In block copolymers, two or more homopolymer chains form blocks, which exist in single macromolecules. There is an enormous variety of type, size, and arrangement of the different blocks and of the morphology due to microphase separation. Some basic architectures of frequently studied block copolymers are sketched in Fig. 3.1. Depending on the molecular configuration, there are two kinds of block copolymers: linear and branched.

Polymer blends consist of a combination of two or more different polymers. They are called “blends,” “polymer mixtures,” or “polymer combinations” because they are mainly created using a process of mixing or blending. Mixing of two or more polymers can be performed either in the molten or the solution state or by in situ polymerization of a monomer in the presence of a dissolved polymer.

A special family of polymer blends, known as rubber-toughened or rubber-modified polymers, exhibit enhanced, high toughness. The original idea for producing polymers with enhanced toughness was to combine hard, brittle polymers with soft, rubbery ones, according to the equation “brittle + soft = tough.” However, the toughness of optimized rubber-modified polymers does not simply result from combining the properties of their components (as illustrated in the additivity curve (a) in Fig. 4.1 in Chapter 4), but arises because the polymer has a pronounced morphology with special toughening mechanisms, corresponding to the synergistic effect illustrated in curve (d) in Fig. 4.1.

Composites are combinations of two or more materials: a polymeric matrix and reinforcing elements, particles, or fibers. In this chapter, the combinations with particles are considered; the combinations with fibers are described in the following Chapter 7. Over the last few decades, composites have been rapidly developed to meet the demand for materials that provide higher standards of performance and in-service reliability.

The relatively low stiffness and strength values of most polymers can be enhanced by adding fibers. Fiber materials used as fillers may be inorganic, such as glass or metals, synthetic, such as carbon, or natural, such as wood or bamboo or other highly oriented polymers. Thermoplastics are usually modified with short, discontinuous fibers, while thermoset resins, such as epoxies, are filled with long, continuous fibers.

Over the last few decades, significant advances have been made in the development of biocompatible, biodegradable polymers and materials for medical applications. In general, polymers are called biopolymers if they are biodegradable, biobased, or are materials from renewable resources. However, both terms are not very specific: “biodegradability” needs a closer specification concerning surrounding medium and time, and “biobased” should be combined with a percentage of biomass content used.

There are some developments in polymer processing using special processing routes to manufacture polymers with higher level properties. In particular, microand nanostructured biomaterials such as bones, mollusk shells, fibers produced by different insects, and so on have received increasing interest from material scientists, who are aiming to develop new advanced functional materials that are based on the unique architectures of these natural composites [1, 2].