Question

question 4 consider a random nitrile rubber poly(acrylonitrile - butadiene) copolymer in which the fraction by number of butadiene repeat units is 0.34. calculate the average molecular weight of the copolymer repeat unit in g/mol. hint: you calculated the molecular weights of acrylonitrile and butadiene in the previous two questions. $overline{m}=53.34$ g/mol (2 decimal places) question 5 this is the continuation of the previous question. calculate the number - average molecular weight of a random nitrile rubber poly(acrylonitrile - butadiene) copolymer in which the fraction by number of butadiene repeat units is 0.34; assume that this concentration corresponds to a degree of polymerization of 1000. $overline{m_n}=$ g/mol (nearest integer) 1 pts 1 pts

Explanation:

Step1: Recall molecular - weight formula for copolymers

The number - average molecular weight formula for a copolymer is $\overline{M_n}=\sum_{i}x_iM_i$, where $x_i$ is the mole fraction of the $i$ - th repeat unit and $M_i$ is the molecular weight of the $i$ - th repeat unit. Let the mole fraction of butadiene be $x_{BD}=0.34$, then the mole fraction of acrylonitrile is $x_{AN}=1 - 0.34=0.66$. Assume the molecular weight of butadiene repeat unit is $M_{BD}$ and acrylonitrile repeat unit is $M_{AN}$.

Step2: Calculate number - average molecular weight

We know that $\overline{M_n}=x_{BD}M_{BD}+x_{AN}M_{AN}$. But we are not given the molecular weights of the individual repeat units. However, if we assume we have already calculated the average molecular weight of the copolymer repeat unit $\overline{m} = 53.34$ g/mol.

For question 5, if we assume the degree of polymerization is $DP = 1000$. The number - average molecular weight $\overline{M_n}=DP\times\overline{m}$.
$\overline{M_n}=1000\times53.34$
$\overline{M_n}=53340$ g/mol

Answer:

53340