CHE 411 POLYMER TECHNOLOGY Prof. AbdulAziz A. M. Wazzan

CHAPTER ONE Polymer Chemistry

INTRODUCTION Polymer (Poly  many) & (meros  part) Polymer is a long molecule consisting of many small units (monomers) joined end to end (together).

where: n  number of ethylene monomers which join together to form a molecules. Usually of order 10 4 up to 10 6  1,  2  The end group at very small concentration, they have no effect on the mechanical properties of the polymer but it give a chemical stability. (Initiate a degradation process) (Unzips). Polyethylene  1 [ CH 2 - CH 2 ] n  2 Example:

There are two molecular factors that affect the mechanical properties of a polymer. 1.The length of the molecules which is  to n which is  to molecular size or relative molar mass 2.The shape of the molecules. (Branches), branching affected by the polymerization conditions. Branching can affect the toughness, creep resistance and the modulus.

CLASSIFICATION OF POLYMERS This classification based on the molecular structure of the polymers.

STRUCTURE *Polymer macromolecules have a linear structure which represented with a chain with two ends. linear Branching point branched network Junction point *or nonlinear structure such as branched and Network *Branched polymer have side chains or branches of significant length which are bonded to the main chain at branch point.

Example Heating ethylene gas at  200 o C and high pressure of  2000 atmosphere in the presence of suitable polymerization initiation will result in LDPE used for film & packaging. New site for branching [ C-C-C-C=C-C-C] Low pressure process give linear PE or HDPE Used for pipe, bottles. There is also LLDPE made with copolymerization of ethylene with suitable butane co-monomens using ziegler - Natta type catalysis.

CROSS LINKED POLYMERS A three dimensional structures in which each chain is connected to all others by a sequence of junction points. They are characterize by their crosslink density or degree of crosslinking.

THERMOPLASTICS: (Plastics) Linear or branched which can be melt upon the application of heat. They can be moulded in different shape using different techniques. Such as injection moulding and extrusion. Crystallization is not easily obtained upon cooling to the solid state because it required a considerable ordering of the highly coiled and entangled macromolecules. These which crystallize do not form perfectly crystalline materials but (sime-crystalline) with both crystalline and amorphous regions. Crystalline can be characterized by T m (melting temperature). where as T g (Glass Transition Temperature) characterize the amorphous required for both (amorphous polymer and sime crystalline) T g is the temperature at which the material transform from the glassy state (hard) to the rubbery state (soft). (On set of chain motion) below T g chain are not moving and frozen. Both T g and T m increases with increasing the chain stiffness and force of intermolecular attraction

ELASTOMERS * Crosslinked rubbery polymers which can be stretched easily to high extensions (3 to 10 times there original length) and rapidly recover to the original dimension when the applied stress is released.

THERMOSETS *Normally rigid materials and net-work polymer where chain motion is restricted by a high degree of crosslinking. example (eggs).

HOMOPOLYMERS Definition of a homopolymer is a polymer derived from one species of monomer (one type of Repeat Unit R.U.) ---- A-A-A-A-A-A---- or [ A ] n where: n is the number of R.U. linked together to form the macromolecule. See table 1.1 slight difference in chemical structure can lead to very significant difference in properties.

COPOLYMERS Definition is a polymer derived from more than one species of monomer (two or more type of repeat unit R.U.).

CATEGORIES OF COPOLYMERS 1.Statistical copolymer are copolymers which the sequential distribution of the R.U. obeys known statical laws. ----A-A-B-B-B-A-A-B-B-B-A-A-A Random copolymer it is one typed statistical copolymer in which the distribution of R.U is truly random. ----B-A-A-A- B-B-A-A-B-A-A-A Alternating copolymer have only two different types of R.U. and these are arranged alternately along the polymer chain A-B-A-B-A-B----- The above three have a properties which are intermediate to those of the desirable properties. Of the homopolymer in one single materials.

4.Block copolymers a linear copolymers in which the R.U. exist only in long sequences. Or blocks of the same type. Di block -----A-A-A-A-A-B-B-B-B-B-B-B-B---- Tri block ----A-A-A-A-B-B-B-B-B-A-A-AA Graft copolymers are branched polymers in which the branches have a different Chemical structure to that of the main chain. B-B-B-B-B A-A-A-A-A-A- A-A-A-A-A-A----- B-B-B-B-B-B-B Block & Graft properties characteristic of each of the constituent homopolymers. Example Rubber toughened particles

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