Question

From problem 9.10 in the book. An initial experiment at an eyeglass manufacturer has produced poly(methyl methacrylate), whose monomer is (used in eyeglasses and hard contact lenses) with a number average molecular weight of 143,000, by carrying out the reaction at 65 °C for 45 minutes. Since the product design group has determined that a molecular weight of 100,000 is satisfactory, how fast can you speed up the production process and still achieve the desired MW? The activation energies for each reaction step are: propagation = 7 kcal/mol initiator decomposition = 27 kcal/mol termination = 3 kcal/mol.

Answer 1

Answer for first part:

The rate of reaction and activation energy are related according to the following equation.

activation energy rate constant ΕΑ kelvin temperature k = Ae RT -the gas consant frequency factor or pre-exponential factor mathematical quantity, e

The more is the Activation energy, the slower the chemical reaction is.

Also, in case of a free radical polymerisation reaction, the rate is given as,

Rp 11 = (4) V2 V2 [r] [M]

The rate is directly proportional to rate constant of propagation reaction and initiation reaction and inversely proportional to termination reaction. So, if the rate of initiation and propogation increases, it can be faster. Also, if rate of termination decreases,it can be acheived in lesser time. A catalyst can be used to speed up the reaction. The temperature can be alered to increase the rate of this reaction so as to acheive the desired mol wt in less duration.

Answer for 2nd part:

PMMA can be produced by emulsion ploymerization, bulk and solution polymerization. Generally, it is produced by Rasdical initiation but anionic polymerization of PMMA can also be performed. Mechanical and optical property degradtion is less in PMMA if caused by UV exposure. The reason being PMMA absorbs only trace amounts of light and UV radiation due to it's transparency.This small amount of absorbed radiation lacks the energy required to break the bonds of molecules in PMMA. Optical and Mechanical properties are directly influenced by the microstructure. It has great scratch resistance also.