o Block copolymers have two or more homopolymer subunits linked by covalent

O block copolymers have two or more homopolymer

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o Block copolymers have two or more homopolymer subunits linked by covalent bonds [28] (4). Polymers with two or three blocks of two distinct chemical species (e.g., A and B) are called diblock copolymers and triblock copolymers, respectively. Polymers with three blocks, each of a different chemical species (e.g., A, B, and C) are termed triblock terpolymers. o Graft or grafted copolymers contain side chains that have a different composition or configuration than the main chain.(5)
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~ Page 57 of 73 ~ POLYMER BUILDING BLOCKS Polymeric materials are all built from carbon atoms in association with other elements such as oxygen, hydrogen, nitrogen, chlorine and fluorine. Carbon atoms have a valence of four. Hydrogen atoms have a valence of one. So if hydrogen and carbon are combined in the simplest way to give a molecule of methane (natural) gas, the molecule would appear as in Fig. 2 below: H H C H H Fig. 2 Thus four hydrogen atoms combine with one carbon atom to make one molecule of methane gas, CH 4 , which because it consist solely of hydrogen and carbon, is referred to as a hydrocarbon.
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~ Page 58 of 73 ~ Hydrocarbons are found in crude oil, coal and natural gas. Hydrocarbons can be classified into four main groups as follows: 1) ALKANES This series was previously known as paraffin series. These are the simplest of the four groups of hydrocarbons. They have a general formula of C n H 2n+2 . For example, in the methane molecule above, there is only one carbon so n = 1, and the number of hydrogen atoms is 2(1) + 2 = 4 hence the formula for methane is CH 4 which agrees with the one earlier indicated. One way of recognizing alkanes is the fact that their names always end in ‘ane’ (as in methane, propane, octane, etc.). Alkanes are saturated hydrocarbons and, as such, they contain the maximum number of hydrogen atoms in each case, as shown in Fig. 3 below, and this makes them rather inactive chemically. Alkanes are the most common group of hydrocarbons appearing in crude oil. H H C H Methane (CH 4 ) – natural gas H H H H C C H Ethane (C 2 H 6 ) – converted into plastics H H H H H H C C C H Propane (C 3 H 8 ) – heating fuel H H H H H H H H C C C C H Butane (C 4 H 10 ) – heating fuel or converted into Synthetic rubbers H H H H Fig. 3 2) OLEFINS These are unsaturated hydrocarbons or alkenes. In these additional hydrogen atoms have to be added to olefins in order to saturate them. This unsaturated condition makes them chemically reactive and olefins form the basis of many thermoplastic and elastomer materials. When their general formula is C n H 2n they are called mono-olefins and are given names ending in ‘ylene’ (as in ethylene, propylene, etc.). Olefins are usually produced in the course of oil refinery operations, but they are not abundant in crude oil. They are used as a feed stock for the polymer (“plastics”) industry where they are known as chemical intermediates.
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