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Materials Science C

Posted: February 8th, 2018, 6:31 am
by Tesel
I was surprised to see that there wasn't a forum for this, so I'll start us off.

Image

A. Give the common name of this compound.

B. Give the strict IUPAC system name of this compound. (Even though the common name is also generally accepted by the IUPAC.)

Re: Materials Science C

Posted: February 13th, 2018, 10:31 pm
by wethose
A) tert-butylcyclohexane
b) (1,1-dimethylethyl) cyclohexane


Speaking in terms of hybridization, why do alkanes lack isomers?

Re: Materials Science C

Posted: February 14th, 2018, 6:47 am
by Tesel
wethose wrote:A) tert-butylcyclohexane
b) (1,1-dimethylethyl) cyclohexane


Speaking in terms of hybridization, why do alkanes lack isomers?


Correct on both parts!

Alkanes have structural isomers, of course. However, they do not have geometric isomers. This is because they contain only sigma bonds, which are able to freely rotate between all possible geometric configurations. In terms of hybridization, their carbons form bonds with 4 sp3 hybrid orbitals. Geometric isomers occur when pi bonds (in double and triple bonds) restrict rotation around the sigma bond. To form such geometric isomers, carbon atoms must contain sp or sp2 hybrid orbitals for sigma bonds and p orbitals for pi bonds.

I assume this covers the question, but I will wait for you to verify before I post another question.

Re: Materials Science C

Posted: February 15th, 2018, 1:02 am
by wethose
Tesel wrote:
wethose wrote:A) tert-butylcyclohexane
b) (1,1-dimethylethyl) cyclohexane


Speaking in terms of hybridization, why do alkanes lack isomers?


Correct on both parts!

Alkanes have structural isomers, of course. However, they do not have geometric isomers. This is because they contain only sigma bonds, which are able to freely rotate between all possible geometric configurations. In terms of hybridization, their carbons form bonds with 4 sp3 hybrid orbitals. Geometric isomers occur when pi bonds (in double and triple bonds) restrict rotation around the sigma bond. To form such geometric isomers, carbon atoms must contain sp or sp2 hybrid orbitals for sigma bonds and p orbitals for pi bonds.

I assume this covers the question, but I will wait for you to verify before I post another question.


Yep! Thanks for catching the structural vs geometric thing.. I'm new to this event lol

Re: Materials Science C

Posted: February 15th, 2018, 4:52 am
by Tesel
wethose wrote:Yep! Thanks for catching the structural vs geometric thing.. I'm new to this event lol


Not a problem, it was still a good question!

Below is a stress-strain curve characteristic of thermoplastic polymers:

Image

Given that this graph uses engineering stress and strain values, why does the polymer show a rapid decrease in stress after the yield strength, then a plateau, then a gradual increase in stress before fracture?

Re: Materials Science C

Posted: February 25th, 2018, 10:04 am
by IcsTam
Tesel wrote:
wethose wrote:Yep! Thanks for catching the structural vs geometric thing.. I'm new to this event lol


Not a problem, it was still a good question!

Below is a stress-strain curve characteristic of thermoplastic polymers:

Image

Given that this graph uses engineering stress and strain values, why does the polymer show a rapid decrease in stress after the yield strength, then a plateau, then a gradual increase in stress before fracture?


The polymer chains become increasingly oriented with the tensile axis, increasing the strength of the polymer (strain hardening)

Re: Materials Science C

Posted: February 25th, 2018, 11:54 am
by Tesel
IcsTam wrote:The polymer chains become increasingly oriented with the tensile axis, increasing the strength of the polymer (strain hardening)


Correct!

Re: Materials Science C

Posted: February 25th, 2018, 4:27 pm
by IcsTam
What is the Ziegler-Natta catalyst and what is its function?

Re: Materials Science C

Posted: February 25th, 2018, 5:17 pm
by Name
IcsTam wrote:What is the Ziegler-Natta catalyst and what is its function?

Ziegler natta catalyst is used in addition polymerization in order to control tacicity and eliminate branching, allowing to produce certain types of polymers that couldn't have produced otherwise

Re: Materials Science C

Posted: February 25th, 2018, 5:52 pm
by IcsTam
Name wrote:
IcsTam wrote:What is the Ziegler-Natta catalyst and what is its function?

Ziegler natta catalyst is used in addition polymerization in order to control tacicity and eliminate branching, allowing to produce certain types of polymers that couldn't have produced otherwise


Correct! Your turn.

Re: Materials Science C

Posted: February 26th, 2018, 8:37 am
by Name
What is vulcanization? What effect does it have on rubber? How does vulcanization molecularly affect the rubber?

Re: Materials Science C

Posted: February 26th, 2018, 9:47 am
by Tesel
Name wrote:What is vulcanization? What effect does it have on rubber? How does vulcanization molecularly affect the rubber?


Vulcanization is a process where natural rubber is heated with sulfur. It causes the rubber to become less sticky, more durable, and more useful. It creates sulfur cross-links between the rubber chains, similar to the curing of thermoplastic polymers.

Re: Materials Science C

Posted: February 26th, 2018, 12:33 pm
by Name
Tesel wrote:
Name wrote:What is vulcanization? What effect does it have on rubber? How does vulcanization molecularly affect the rubber?


Vulcanization is a process where natural rubber is heated with sulfur. It causes the rubber to become less sticky, more durable, and more useful. It creates sulfur cross-links between the rubber chains, similar to the curing of thermoplastic polymers.

Yup your turn

Re: Materials Science C

Posted: March 3rd, 2018, 3:43 pm
by IcsTam
I'm just going to post a question, if that's alright.

1. What is a copolymer?
2. Describe and differentiate between a random, alternating, block, and graft copolymer.

Re: Materials Science C

Posted: March 3rd, 2018, 5:53 pm
by Tesel
IcsTam wrote:I'm just going to post a question, if that's alright.

1. What is a copolymer?
2. Describe and differentiate between a random, alternating, block, and graft copolymer.


Yep, my bad.

Answer
1. A copolymer contains multiple different monomer units.
2A. A random copolymer has monomers randomly ordered, e.g. ABAAABBAABABBBAAB.
2B. An alternating copolymer has regularly alternating monomer units, e.g. ABABABAB.
2C. A block copolymer consists of multiple "blocks" which each contain only one type of monomer, e.g. AAAABBBBAAAAABBB.
2D. A graft copolymer has one type of monomer on the main chain and a different type of monomer on the side chains. In other words, one chain is "grafted" onto the other.


Assuming I'm right, I'll just post the next question, to make sure I don't forget.

Describe the "melting process" for:
1. Amorphous thermoplastic polymers.
2. Crystalline thermoplastic polymers.
3. Thermoset polymers.