Part III.3: Transition in Polymers OUTLINE - Level of Movement in the Amorphous Part of Polymer Chains - Factors that influence Tg and Tm - Transition at Tg and Tm - The metastable amorphous state - Changes in Tg and Tm of Copolymers - Changes in Tg and Tm of Crosslinked Polymers - Instrument for Thermal Analysis AE 449 TEPE: Cattaleeya Pattamaprom Level of Movement in the Amorphous Part of Polymer Chains Step 1: -vibration of atoms at equilibrium -movement of 1-2 carbon atoms -happen below Tg of polymers Step 2: -movement of 5-6 carbon atoms or movement of side groups -happen at around Tg Step 3: -movement of 40-50 carbon atoms -polymers become soft and rubbery -happen above Tg Step 4: -movement of the whole polymer chain - polymers flow as in viscous melt Factorthat thatinfluence influencesTT Factors gg 1. The free volume of the polymer (vf) vf = v – vs vol. of solidly packed molecules free volume bulk specific vol. (ปริ มาตรจาเพาะของช่องว่าง) vf   more room to move around  Tg  2. The attractive forces between molecules   difficult to move around  Tg  (con’t) 3. Steric hindrance  more difficult  Tg  (bulky groups) to move around 4. The stiffness of chain  difficult to coil up and fold  Tg  5. The chain length Tg Tg length Factorsthat that influence Tm T Factors influence m Melting Point (Tm) or so called “Crystalline melting point” Thermodynamics of melting Gm = Hm - TSm energy needed to overcome crystalline bonding at eqn Gm  0  Tm = Hm Sm - short chain S  - long chain S  or stiff chain Example: Rank Tm of different polymers O [ -O-C-N-(CH2)n-]X H O [-C-N--(CH2)n-]x H polyurethane polyamides Tm < Tm O [-N-C-N--(CH2)n-]x H H polyureas < Tm - Polyurethane: contains the -o- swivel high Sm  most flexible low Tm - Three polymers have comparable magnitude of hydrogen bonding - Polyurea: with extra N-Hextra hydrogen bonding extra Hm high Tm Transition at Tg (Ref.: S.L. Rosen, John Wiley&Sons 1993) Transition at Tm (Ref.: S.L. Rosen, John Wiley&Sons 1993) Schematic of DSC curve Low cp High cp (Ref.: S.L. Rosen, John Wiley&Sons 1993) Example PET is cooled rapidly from (state 1) 3000C to (state 2) room temp. Get perfectly transparent and rigid polymer Then heat up to (state 3) 1000C and maintain at 1000C then cool down to (state 5) room temp. get rigid, translucent polymer Question : 1. Sketch general specific volume (v) curve 2. Show DSC curve Specific volume (v) curve 1 3 V (CC/g) 2 5 4 Tm = 2670 C Tg = 690 C Temp. DSC curve General Observation about Tg and Tm • Polymers with symetric repeat unit Tg/Tm ~ 1/2 (absolute temp) Ex. Polyethylene Poly vinylidine chloride n • Polymers with asymetric repeat unit Tg/Tm ~ 2/3 (absolute temp) Ex. Polypropylene Polychlorotrifluoride The metastable amorphous state • metastable amorphous state : – Occur when decreasing temperature of polymer melts quickly – Produce transparent polymers รูปที่ 1 Amorphous polymer structure The metastable amorphous state • An example of metastable amorphous application in polymer industries – PET (soda bottles) PET Bottle Resin – Before and After Annealing Pressed PET Bottle Resin PET After annealing (Cold Crystallization) Effect of Heating Rate on Temperature of Cold Crystallization in PET Heating Rate After Quench Cooling Crystallization [kinetic event] Tg melt Volume changes of the metastable amorphous state • Study the changes in temperature and specific volume of crystallizable polymer Ex. PET – Tm = 267 °C และ Tg = 69 °C – Molten PET at initial temp of 300 °C (state 1) The metastable amorphous state 1 V (CC/g) 3 2 5 4 Tm = 2670 C Tg = 690 C Temp. State 2 = metastable amorphous, State 5 = semi-crystalline Fig. 8.5 Specific volume – temperature relation for crystallizable polymer Changes in Tg and Tm of Copolymers (Ref.: S.L. Rosen, John Wiley&Sons 1993) Changes in Tg and Tm of Crosslinked Polymers Effect of crosslink lightly crosslinked : same as before heavily crosslinked : crosslink less mobility hinder alignment apparent Tg reduce / cannot crystallize Summary crosslinking in polymers : leads to (I) higher Tg (II) obstruct and reduce crystallization Instrument for Thermal Analysis • Two popular instruments in measuring temperature response of polymers - Differential Scanning Calorimeter (DSC) - Thermogravimetric Analysis System (TGA) DSC: Differential Scanning Calorimeter • This technique can analyze characteristic temperatures and heat flow from thermal transition of material with respect to temperature or time. Heat flow vs. temp. Heat flow vs. time Differential Scanning Calorimeter DSC: Differential Scanning Calorimeter • DSC used to analyze : – Temp and heat that makes polymers or ceramics melt, crystalize or change phases – Crytallinity of polymers – Glass transition temperature (Tg) of polymers – Heat capacity of materials DSC: Differential Scanning Calorimeter Main Parts of DSC DSC: Differential Scanning Calorimeter DSC Thermogram DSC: Differential Scanning Calorimeter Exo Endo TGA: Thermogravimetric Analysis • Use for analyzing weight changes of material when exposed to heat by using sensitive balances (thermobalance) รูปที่ 3 แสดงเครื่ องThermogravimetric Analysis TGA: Thermogravimetric Analysis • TGA can be used to analyze : – Additives in plastic products – Water or solvent in paints coatings adhesives or ceramics – Compositons of rubber products ex. Rubber content, organic fillers, and inorganic fillers TGA: Thermogravimetric Analysis Main Parts of TGA TGA: Thermogravimetric Analysis TGA Thermogram HW Chapter 8. Phase transition and Thermal properties of polymer • Sketch scanning calorimeter traces upon heating from room temperature for each of the following situations labelling temperatures and exothermic/endothermic directions on each. 1. A 50/50 glassy crystalline polymer, Tg = 50 oC, Tm = 120 oC 2. A blend of two incompatible crystalline polymers with Tm’s of 90 oC and 160 oC 3. A 50/50 blend of two compatible glassy polymers with individual Tg’s of 110 oC and 200 oC 4. A crystallizeable polymer which has been quenched from above it’s Tm rapidly enough so that crystalline does not occur upon cooling. (Tg = 100 oC, Tm = 250 oC) 5. Polyvinyl chloride plasticized 20% with dioctyl phthalate (DOP)? (Tg of pure PVC = 85 oC)