Part III.3: Transition in Polymers - Level of Movement in the Amorphous Part of Polymer Chains - Factors that influence T g and T m - Transition at Tg and T m - The metastable amorphous state - Changes in T g and T m of Copolymers - Changes in T g and T m of Crosslinked Polymers - Instrument for Thermal Analysis OUTLINE 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 carbon atoms -polymers become soft and rubbery -happen above Tg Step 4: -movement of the whole polymer chain - polymers flow as in viscous melt

Factors that influence T g

(con’t) (bulky groups)

Factors that influence T m

- Polyurethane: contains the -o- swivel  high  S m  most flexible  low T m - Three polymers have comparable magnitude of hydrogen bonding - Polyurea: with extra N-H  extra hydrogen bonding  extra  H m  high T m Example: Rank T m of different polymers

(Ref.: S.L. Rosen, John Wiley&Sons 1993) Transition at T g

(Ref.: S.L. Rosen, John Wiley&Sons 1993) Transition at T m

(Ref.: S.L. Rosen, John Wiley&Sons 1993) Low c p High c p Schematic of DSC curve

Example PET is cooled rapidly from (state 1) C to (state 2) room temp. Get perfectly transparent and rigid polymer Then heat up to (state 3) C and maintain at C then cool down to (state 5) room temp. get rigid, translucent polymer Question : 1. Sketch general specific volume (v) curve 2. Show DSC curve

T g = 69 0 C T m = C V (CC/g) Temp. Specific volume (v) curve DSC curve

General Observation about T g and T m Polymers with symetric repeat unit T g /T m ~ 1/2 (absolute temp) n Ex. Polyethylene Poly vinylidine chloride Ex. Polypropylene Polychlorotrifluoride Polymers with asymetric repeat unit T g /T m ~ 2/3 (absolute temp)

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 PET After annealing (Cold Crystallization) Pressed PET Bottle Resin

Effect of Heating Rate on Temperature of Cold Crystallization in PET Heating Rate After Quench Cooling TgTg melt Crystallization [kinetic event]

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 V (CC/g) T g = 69 0 C T m = C Temp. 5 2 Fig. 8.5 Specific volume – temperature relation for crystallizable polymer State 2 = metastable amorphous, State 5 = semi-crystalline

(Ref.: S.L. Rosen, John Wiley&Sons 1993) Changes in T g and T m of Copolymers

apparent T g reduce / cannot crystallize less mobility hinder alignment Effect of crosslink lightly crosslinked : same as before heavily crosslinked : crosslink Changes in T g and T m of Crosslinked Polymers 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. Differential Scanning Calorimeter Heat flow vs. temp. Heat flow vs. time

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

Main Parts of DSC DSC: Differential Scanning Calorimeter

DSC Thermogram

DSC: Differential Scanning Calorimeter Endo Exo

TGA: Thermogravimetric Analysis Use for analyzing weight changes of material when exposed to heat by using sensitive balances (thermobalance) รูปที่ 3 แสดงเครื่อง Thermogravimetric 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 o C, Tm = 120 o C 2.A blend of two incompatible crystalline polymers with Tm’s of 90 o C and 160 o C 3.A 50/50 blend of two compatible glassy polymers with individual Tg’s of 110 o C and 200 o C 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 o C, Tm = 250 o C) 5.Polyvinyl chloride plasticized 20% with dioctyl phthalate (DOP)? (Tg of pure PVC = 85 o C)