GROUP 14 ONG HUI JIN 152161SITI ZAHARAH BT SYED RAMLI 152197NORASHEILA BT MOHD SAAD 152167
INTRODUCTION •AKA isobutylene- isoprene rubber • synthetic rubber/ elastomer • a copolymer of isobutylene with isoprene •isoprene units: double bond that provides a site forcrosslinking during vulcanisation & located randomly inthe polymer chain •excellent impermeability& good flex properties -lowlevels of unsaturation between long polyisobutylenesegments
Produced by cationic copolymerization between ≈ 98% isobutylene&≈ 2% isopreneTypical method:Initiator: Friedel-Craft acids(e.gAlCl3)Medium: methyl chloride (reaction diluent)& boiling liquidethyleneWhy? To remove the heat of reaction and maintain the neededtemperature (Reaction is highly exothermic)Temperature: controlled at low temperatures (-90 to -100 °C)Why? To achieve high molecular weight butyl rubber for applicationas rubber)
Alternative method:Initiator: mixture of a major amount of diethylaluminum chloride& a minor amount of ethylaluminum dichloride( activated by minuteamounts of water / methylaluminoxane (MAO) )-modified initiators :higher molecular weights, higher degrees ofconversion & higher isoprene contents in the butyl rubberMedium: hexaneTemperature: -60 °C- Activation by MAO allow higher polymerization temperaturewhich does not require much heat removal from reaction mixture
PROPERTIES OF BUTYL RUBBERLow permeability to air, gases and moistureVibration damping converting the mechanical vibrational energy of solids into heat energy.Low glass transition temperatureLow modulus elastomer Elastomer: able to stretch a long distance and still bounce backLow compression set Compression set: percentage deflection from original shape of a rubber item having been subjected to a constant compressive load, then released.
PROPERTIES OF BUTYL RUBBER cont.Resistance to aging and to weathering from atmospheric exposureWide vulcanization versatility Vulcanization: chemical process for converting rubber into a compound material (polymer) with the addition of sulphurFast cure rates Cure rates: toughening or hardening of a polymer material by cross- linking of polymer chainsProcessing safety: no nitrosamines or nitrosamines precursors Nitrosamines: carcinogenic and can cause cancer
PROPERTIES OF BUTYL RUBBER cont.High extensibility Broad range of durometer and tensile strength properties Low filler content for specific gravity, cost-effective compounding Best sealant of all the known rubbers Sealant rubber -type of product seals and protects different materials using rubber-based substancesBlood compatible Allows this substance to be used in biomedical applications