Chap 3. Bonding in Polymers Primary Covalent Bond CCCH Hydrogen Bond O H H O C OHN d d + dd + Dipole Interaction CN N C d d + Ionic Bond CO O Zn O CO +1 _ _ _ _

PE  m r Attraction Repulsion Van der Waals CH 2 2

Six crystal system Isometric ; 3 mutually perpendicular axes of equal length. Tetragonal ; 3 perpendicular axes are equal in length. Orthogonal ; 3 perpendicular all of different length. Monoclinic ; 3 axes of unequal length. Unit cell 2 are not  to each other both are  to the third Triclinic; all 3 axes of different length. Hexagonal; 4 axes, 3axes in the same plane & symmetrically spa and of equal length. Chap 4. Crystallinity

Polymer crystallinity Some are amorphous, some are partially crystalline (semi-crystalline). -Why is it difficult to have a 100% crystalline polymer? ρ s = density of specimen in question ρ a = density of totally amorphous polymer ρ c = density of totally crystalline polymer

What is f c ? Volume fraction of crystalline component. To get f c : Using definition of volume fractions:and Substituting in f c into the original definition: Polymer crystallinity

Conditions for crystallization 1.Packing is facilitated for polymer chains that have structural regularity and compactness. In addition, polymers having stereoregular structure have higher degree of crystallinity comparing to polymers having irregular structure. 2.In the crystal lattice, the strong secondary attaractive forces affect the thermodynamic and kinetic freatures of the polymer. biaxial stress(stretching) is stronger than uniaxial stretch ∵ different arrangement of chain.

Conditions for crystallization Degree of crystallinity depends on processing conditions (e.g. cooling rate) and chain configuration. Cooling rate: during crystallization upon cooling through MP, polymers become highly viscous. Requires sufficient time for random & entangled chains to become ordered in viscous liquid. Chemical groups and chain configuration: More Crystalline Smaller/simper side groups Linear Isotactic or syndiotactic Less Crystalline Larger/complex side groups Highly branched Crosslinked, network Random

Semicrystalline polymers 1. Fringed-Micelle Model Fringed-Micelle(or crystallites) spread within the amorphous matrix orientation

2. Folded-Chain Crystallites There is a formation of polymer crystal as the single crystal grows from the dilute solution. Also from cooling or solvent evaporation process there is the formation of thin, pyramidal, or platelike polymer crystal(lamellae). The thickness of these crystallites is about 100Å where the length is several tens of thousands Å.From X-ray result, the chain axis is arranged in perpendicular way on the flat surface.Furthermore, each chain contains the lengh more than 1000Å. Therefore, it is concluded that the chain can only be folded back and forth. It can be seen not only from dilute solution but also from molten state where same lamellae type model is formed. The chain-foided structure for a plate-shaped Polymer Crystallite.

3. Extended-Chain X-tal In molten state, fibrillar structure is formed as the extension (stress) increases and the degree of crystallinity begin to rise where the chain arrangement takes place in the direction of expansion. They are known as extended-chain crystals and arranged in parallel way where the chain folding is minium. “Shish-Kebab”

4. Spherulites Polymer chains are arranged to form crystallites, a huge aggregate called as spherulites. These spherulites grow from nucleation to rounded circular shape. There is a control in the number of nucleus existing in each spherulites, therefore, more nucleus means more smaller spherulites. The bigger spherulites are one of the causes for the brittleness of polymer. So, adding nucleating agent to polymer or shock cooling process is performed to reduce the brittleness.