Butene H2C=CH-CH2-CH3 can be reacted to form isotactic polybutene (PB).

(a) Would you expect isotactic polybutene to melt at a higher or lower temperature than atactic polybutene of the same molecular weight?
I)Higher T
II)Lower T

(b) Is isotatic polybutene a thermoplastic or thermoset?
I)Thermoplastic
II)Thermoset

(c) What is the value of the degree of polymerization (n) of isotactic PB with a molecular weight of 3.091X10^5 g/mol?

a) Higher T

b) Thermoplastic
c) 5520

To answer these questions, we need to understand a few concepts related to polymers and their properties.

(a) The melting temperature of a polymer is influenced by its molecular structure. Isotactic polybutene has a regular, ordered arrangement of its side groups along the polymer chain, while atactic polybutene has a random arrangement. In general, polymers with a more ordered structure tend to have a higher melting temperature. Therefore, we would expect isotactic polybutene to melt at a higher temperature than atactic polybutene of the same molecular weight. So the answer is (I) Higher T.

(b) Isotactic polybutene is classified as a thermoplastic. Thermoplastics are polymers that can be melted and re-molded multiple times without undergoing any significant chemical change. They have a linear or branched structure with weak intermolecular forces, which allows them to soften upon heating and harden upon cooling. Therefore, the answer is (I) Thermoplastic.

(c) The degree of polymerization (n) refers to the average number of monomer units present in a polymer chain. To calculate the degree of polymerization, we can use the relationship between molecular weight and degree of polymerization, given by:

n = molecular weight of the polymer / molecular weight of monomer unit.

In this case, the molecular weight of isotactic polybutene is given as 3.091 × 10^5 g/mol. We need to know the molecular weight of the monomer unit, which is butene (C4H8). The molecular weight of butene can be calculated using the atomic masses of carbon (12.01 g/mol) and hydrogen (1.008 g/mol):

Molecular weight of butene = (4 × 12.01) + (8 × 1.008) = 56.11 g/mol.

Now, we can calculate the degree of polymerization:

n = 3.091 × 10^5 g/mol / 56.11 g/mol ≈ 5500.

Therefore, the value of the degree of polymerization (n) of isotactic PB with a molecular weight of 3.091 × 10^5 g/mol is approximately 5500.