1. EPB 201 – POLYMER SYNTHESIS Jumatia Binti Abdul Kahar - 94028 Mohamad Izzaidi Bin Md Zain -105983 Muhamaad Alif Mohd Shariff - 105985 Nor Aisah Binti Roslan - 94048 Syed Muhammad Firdaus Syed Alwi -105995

2. INTRODUCTION Polyurethane are well known resins used in a wide variety of commercial and technical applications, due to their high tensile strength, chemical resistance, good processability and good mechanical properties. Thermoplastic, elastomer, linear and crosslinked polyurethane are well known. One of the particular disadvantages of PU-based materials is their extreme sensitivity to light (UV light). This is a major limitation which relates to their use as surface coatings in outdoor applications. It is known that PU undergo significant structural changes on exposure to UV radiation, which cause deterioration in their physical and mechanical properties. Polyurethane made with an aromatic isocyanate will yellow on exposure to UV light. The yellowing is caused by oxidation reaction in the backbone of the polymer. Irradiation modifies physical and chemical characteristics of PU surface and results in rapid color change and degradation.

3. AROMATIC versus ALIPHATIC ISOCYANATE Aromatic IsocyanateAliphatic Isocyanate Aromatically linked isocyanate group is much more reactive Less reactive More economical to useExpensive Prone to yellowing (not light stable) Light stable (non-yellowing) Majority global diisocyanates production Limited to only special end use product

4. Nucleophilic attack of N-methylaniline towards aliphatic and aromatic isocyanates

6. GENERAL REACTION OF POLYURETHANE

7. HOW YELLOWING OCCUR IN POLYURETHANE? Aromatic isocyanate OxidationAdditivesUV lightHeat Butylated hydroxyl toluene (BHT)

8. AROMATIC ISOCYANATE Polyurethane made by aromatic isocyanate will yellow if exposed to UV light. The yellowing is caused by an oxidation reaction in the backbone of the polymer. The urethane bridge oxidizes to the quinone-imide structure, the latter being a chromophore, resulting in the yellowing of PU. Coloured components which appeared as a consequence of the loss of the urethane structure. The photooxidation mechanism occur in aromatic PU, involving the scission of the urethane group and oxidation of the central methylene group with quinone (yellow) formation as a chromophoric reaction product. For example; Polyurethane foam are made by reacting a polyol, an aromatic isocynate and water. The isocyanate typically toluene diisocyanate, reacts with the polyol to form urethane polymer. If an amine forms on one of the isocyanate groups instead of a urethane lingkage, this resulting to aromatic amine is capable of being oxidised to a quinone. Quinones are yellow and their formation will make the foam appear more and more yellow as the oxidation proceeds over time. Since the quinone structure is part of the backbone of the polymer, the foam will appear discolored before there is any degradation of the foam.

9. Oxidation of the central methylene group Decomposition of the aromatic ester structures

10. DISCOLORATION FROM OXIDATION (GAS INDUCED) Polyurethane foams will discolor if oxidized. Oxides of nitrogen from tow motor emissions, gas fired furnaces or pollution can cause a foam to oxidize and become yellow. This phenomenon may be more observable in the winter when warehouses are closed up and gas furnaces are in operation. Ozone exposure can also oxidize foam and cause discoloration.

11. DISCOLORATION FROM BHT Polyurethane foams, carpets, fabrics and other material can exhibit yellowing induced by the presence of butylated hydroxy toluene (BHT). BHT is a commonly used antioxidant in many plastics and foods although its use in the production of polyols for making polyurethane foams is being phased out. BHT is volatile. It can deposit on the materials, whether or not direct contact exists. Under the right conditions, BHT will oxidize and form yellow chromophores, a colored chemical species.

12. CONT….. The formation of these chromophores causes the surface of the material containing the BHT to turn a bright yellow. Reaction with oxides of nitrogen from sources such as air pollution, tow motor emissions, and gas furnaces will convert BHT to the colored form. The reaction is promoted by alkaline conditions and retarded by acidic environments. The formation of the yellow colored chromophores is reversible. The BHT can revert to a colorless form if treated with an acidic rinse such as dilute acetic or citric acid.

13. DISCOLORATION FROM HEAT Polyurethane foams can also become discolored from exposure to heat. This can occur during the foaming process or if the foam is exposed to heat in end use. The foam making process is exothermic, that is, the reaction produces heat. If an elevated temperature is reached and sustained, the foam can scorch in the center. The cooling foam draws oxygen rich air inside and the foam oxidizes. Scorching is more common in the summer than in the winter.

14. DISCOLORATION FROM ADDITIVES Fire retardants can increase the risk of discoloration.

15. EXAMPLE OF ALIPHATIC & CYCLOALIPHATIC DIISOCYANATE  organic compound  produced in small quantities (only 3.4% of the global diisocyanate market in the year 2000)  use in enamel coatings which are resistant to abrasion and degradation from ultraviolet light  exterior paint applied to aircraft Hexamethylene diisocyanates (HDI) Isophorene diisocyanate (IPDI)

16. ADVANTAGES OF ALIPHATIC ISOCYANATES  Color stability  Durability ~ Because keep their excellent mechanical properties, unchanged color and transparency during a longer period of time  Superior adhesion on a wide variety of substrates  Transparency  Heat & humidity resistance  User-friendly

17. Color stability The lack of phenyl group It makes polyurethane products prepared from aliphatic less prone to oxidation than those prepared with an aromatic isocyanates The superior resistance of the urethane bone when exposed to UV light. Impact of the type of isocyanates on color retention

18. User Friendly Formulating polyurethane adhesive with aliphatic isocyanates will not release carcinogenic amines such as MDA (methylene bisphenyl amine) or TDA (toluene diamine) as it happens with aromatic isocyanates. Transparency Aliphatic isocyanates allows for the formulation of transparent adhesives and sealants. Addition to exceptional durability and color stability makes it stay transparent upon ageing

19. SYNTHESIS OF POLYURETHANE USING ALIPHATIC ISOCYANATE

20. POLYMERIZATION OF POLYURETHANE Synthesized in a 250mL jacket glass reactor equipped with a mechanical stirrer, a nitrogen inlet and a condenser. A water bath was employed to control the reaction temperature. Polyol which is poly(1,4-butylene adipate) end-capped diol (PBAD) and internal emulsifier, 2,2-bis(hydroxymethyl) propionic acid (DMPA ) were fed into the flask reactor together with the catalyst. The system was heated to 60 ◦ C and once PBAD was totally melted, acetone and the required amount of triethylamine, in order to completely neutralized DMPA acidic groups, were added. TEA was added at this point to increase DMPA solubility in acetone.

21. CONT….. When the reaction temperature reached 60 ◦ C, Isophorone diisocyanate (IPDI) was added dropwise at 1mL/min. The reaction was carried out for 4 h under nitrogen atmosphere and mechanical stirring (200 rpm). Afterwards, the required amount of chain extender 1,4-butanediol (BD) was introduced. A catalyst was needed to complete the reaction.

22. DISPERSION PROCESS After completion of the polymerization process, the reactor temperature was lowered to 25 ◦ C and mechanical stirring was raised to 400rpm to improve the dispersion process. Afterwards, water was added dropwise to the reactor at a low flow rate, keeping stirring for 30 min. Finally, acetone was removed using distillation equipment. The resulting dispersion had 30–35% of solids and particle sizes between 35 and 45 nm.

23. APPLICATION OF NON YELLOWING POLYURETHANE Transportation Polyurethane adhesion based on aliphatic isocyanates are the solution of first choice to answer the highly demanding requirements of the transportation industry. They provide a very strong and very long lasting adhesion on all kind of substrates, in harsh conditions (high humidity and temperature, presence of various detergents and chemicals). Flexible packing Show a good adhesion on various types of materials (plastic films, aluminium, cardboard,..etc..) and their low viscosity makes them suitable for roller applications. In addition, no hazardous amines are released when aliphatic isocyanates are used to.

24. CONT…. Footwear They are manufactured with wide range of materials and are submitted to numerous repetitive constraints under various climates during their service life. The performance that contributing to suitability footwear are their excellent adhesion, exceptional durability and very good flexibility. Others are because of transperancy, heat & humidity resistnance and easy-to-use waterborne solutions. Wood For example, adhesion used for wooden kitchen furniture and bathroom cabinets are highly demanding applications as they have to stick firmly, even in very hot and humid conditions. Besides, they should be invisible and remain transparent upon ageing to preserve a nice and aesthetic aspect to the furniture.