So far, the discussion has been confined to polymers with only a single type of repeat unit, but in reality, a large and growing number of commercial polymers are actually composed of different types of unit attached together by chemical covalent bonds. They are known as copolymers, and can comprise just two different units (binary copolymers) or three (ternary), and so on. It is one of the common strategies used by molecular engineers to manipulate the properties of polymers to gain just the right combination of properties for a specific application. One of the best known examples involves polystyrene. In its homopolymer form, it is a rigid, transparent thermoplastic which is also very brittle. It thus finds little application for stressed applications in its original state. It also shows a glass transition temperature of about 97 °C, so is useless for containers which could hold boiling water (like very hot coffee). The glass transition temperature ( T g) is the temperature at which an amorphous thermoplastic becomes flexible and rubbery ( Box 4).
Understand and construct condensed structural PROCESSING OF VARIOUS MATERIALS 4 PROCESSING OF VARIOUS MATERIALS CHAPTER CONTENTS 4. 1 Shaping Processes for Polymers Polymers Manufacturing Processes for Polymers 4.
The properties are different again to those of the random copolymer because each type of chain segregates together to form minute domains, as shown by the microstructure of Figure 24. Such materials retain thermoplastic behaviour yet behave as crosslinked rubbers, and the SBS block copolymer was the first commercial thermoplastic elastomer or TPE. Although most polymer chains are incompatible with one another, there are some exceptions to the rule. One in particular has gained commercial success, and is a blend of polystyrene and poly(phenylene oxide) (PPO). The T g is increased as is the toughness of the resulting physical mixture of different chains, and the polymer mixture is known by the trade name Noryl. It is used widely for enclosure of consumer products. Figure 24 Block copolymers are formed by sequential addition of monomer in polymerization: (a) SBS block copolymer; (b) microstructure with polystyrene and chains segregated to form 10–20 nm diameter domains Self assessment question 3 uPVC for window frames is too brittle to be acceptable in a product destined to last more than 50 years without damage.
About 96% of cytoplasm and its included structures are composed of the elements carbon, hydrogen, oxygen, Intermolecular Forces Intermolecular Forces: Introduction Intermolecular Forces Forces between separate molecules and dissolved ions (not bonds) Van der Waals Forces 15% as strong as covalent or ionic bonds Chapter 11 Intermolecular Molar Mass of Butane Cautions Butane is toxic and flammable. No OPEN Flames should be used in this experiment. Purpose The purpose of this experiment is to determine the molar mass of butane using Dalton s Law of Partial Pressures 1 Material Properties of Plastics j3 1 Material Properties of Plastics 1. 1 Formation and Structure The basic structure of plastics (or polymers) is given by macromolecule chains, formulated from monomer units by chemical reactions. Typical Chapter 10 Liquids & Solids 1 Chapter 10 Liquids & Solids * 10. 1 Polar Covalent Bonds & Dipole Moments - van der Waals constant for water (a = 5. 28 L 2 atm/mol 2) vs O 2 (a = 1. 36 L 2 atm/mol 2) -- water is polar (draw diagram) Chapter 13 - LIQUIDS AND SOLIDS Chapter 13 - LIQUIDS AND SOLIDS Problems to try at end of chapter: Answers in Appendix I: 1, 3, 5, 7b, 9b, 15, 17, 23, 25, 29, 31, 33, 45, 49, 51, 53, 61 13.