[hockey101]

Hey everyone...I'm having a really hard time following on how to draw dimers of plastics.

Here is the situation:

My teacher gave us this yellow sheet with a bunch of boxes on them.  One box labels the plastic identification code all the way up to 6 (yes I know there is 7 but it's labeled as an other which means it's pretty much unknown).  Another box labels its complete name, the next box labels as a monomer, the next a dimer, and then the last box labels the type of polymerization required to form the polymer (Addition or Condensation).

So here is what I'm really not understanding:

For example:

Plastic Code: 3
Complete Name: Polyvinyl Chloride (PVC)
Monomer: H    H
              |    |
              C = C
              |    |
              Cl   H

Dimer:  H H H  H
          |  |  |  |
         -C-C-C-C-
          |  |  |  |
          H H  Cl H
Polymerization: Addition

When I'm drawing a dimer, how do I know where to put the chlorine?

[Borek]

On every second carbon. But I agree it is not 100% obvious.

[hockey101]

But its on the 3rd Carbon in this example....

[hockey101]

So I'm still not understanding...you say that it's always on the 2nd carbon...in this example its on the 3rd.


Here is another example that I don't understand:

Code: 6
Name: Polystyrene
Monomoer: H    H
                |    |
                C = C
                |    |
                Θ   H

Dimer:   H  H H H
            |  |  | |
          -C-C-C-C-
            |  |  | |
            Θ H  Θ H

Type of Polymerization: Addition


(The thetas in this example represent the Benzenes since you can't insert a benzene on here)

So for this problem there was only 1 benzene in the monomer, but then in the Dimer the benzenes showed up on the 1st and the 3rd carbon.  I don't understand how this happens.

[Big-Daddy]

Surely you either produce the dimer (e.g. ) or the addition polymer itself?

But from the examples you have given, basically:

Monomer:

Then the dimer is:

Monomer:

Where the bonds which aren't shown, which you would otherwise assume to be C-H, either actually are C-H (if this is a dimer, i.e. 2 combined monomers, you're drawing) or are C-C extending to outside the repeat unit.

Sorry for the slightly unclear diagram, it was the best I could get out of smiles.

[hockey101]

Ok....so then why on my first example is the chlorine on the 3rd carbon instead of the 1st?

[Big-Daddy]

Ok....so then why on my first example is the chlorine on the 3rd carbon instead of the 1st?

If I understand your meaning of "dimer", and you are referring to repeat units of a polymer but for some reason with the repeat unit drawn in twice, then the Cl should be on both the first and third C (as Borek said, every 2nd C, so if you drew a tetramer then the Cl would be on the first, third, fifth and seventh of your 8 C atoms).

[hockey101]

I have no idea what you are talking about....

[hockey101]

I really don't know how I am supposed to memorize all the identification codes, all the monomers and dimers of the polymers, then let alone draw them.  Most of this is not even in the chem book which really sucks because then I can't look at examples from the book that would give explanations.  I'm also supposed to memorize the natural polymers, discuss the characteristics of polyacrylate, including current and potential uses of this polymer (which I have no clue what that is and I can't find it anywhere that can explain it too me).  I'm also supposed to list all the characterisitcs of thermoset and thermoplastic polymers...like how on earth am I supposed to know all this?

[Borek]

You don't have to memorize dimers when you know what the monomer is.

Dimer is produced when two monomers combine, so its formula simply contains twice the monomer. There are some possible complications, but I have a feeling you are missing the basics ATM.

[DrCMS]

I really don't know how I am supposed to memorize all the identification codes, all the monomers and dimers of the polymers, then let alone draw them.  Most of this is not even in the chem book which really sucks because then I can't look at examples from the book that would give explanations.  I'm also supposed to memorize the natural polymers, discuss the characteristics of polyacrylate, including current and potential uses of this polymer (which I have no clue what that is and I can't find it anywhere that can explain it too me).  I'm also supposed to list all the characterisitcs of thermoset and thermoplastic polymers...like how on earth am I supposed to know all this?

Stop this whingfest and do so independent reseach google/wikipedia will give you loads of info on this and put some thought into your work; alternatively carry on whinging get nowhere drop out of school and end up in the gutter.

A monomer is the smallest unit that a polymer is made from  (the give away is in the name mono = one while poly = many). 
A dimer is just two monomers joined together (the give away is again in the name di = two).  So if the monomer contains 1 chlorine or phenyl group then the dimer will contain 2 of them.

Polyacrylate is a very wide range of polymers that have many many uses (an acrylate monomer could be acrylic acid, methyl acrylate, ethyl acrylate butyl acrylate etc.). 
Polyacrylic acid as a low molecular weight solution of its sodium salt is used as a dispersant/anti-scale but as a high molecular weight solid it is used as a superabsorbant polymer in nappies etc.

So go do some work our your own and then come back if you have specific questions; we're not here just to do all your howework for you while you learn nothing.

[Big-Daddy]

I have no idea what you are talking about....

I don't see how it's humanly possible to be clearer than I was.

The Cl is on the first and third C. Do you understand me? It is NOT only on the third C. The diagram is WRONG.

DrCMS, how does the chain end if the molecule is a dimer? Do you have 2 extra C-H bonds coming in to finish the chain (which otherwise is a polymer where n=2 repeat units)?

[DrCMS]

DrCMS, how does the chain end if the molecule is a dimer? Do you have 2 extra C-H bonds coming in to finish the chain (which otherwise is a polymer where n=2 repeat units)?

In reality what is at the ends of a polymer (dimer) chain depends on the conditions used in the polymerisation, it might be an initiator fragment and one end and a C-H via abstraction from the solvent or another polymer chain at the other end.  Or it might be and intiator fragment at one end and from a chain transfer agent, added to control the molecular weight distrubition, at the other end etc etc.  See this for extra info http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/polymers.htm

[hockey101]

I have no idea what you are talking about....

I don't see how it's humanly possible to be clearer than I was.

The Cl is on the first and third C. Do you understand me? It is NOT only on the third C. The diagram is WRONG.

DrCMS, how does the chain end if the molecule is a dimer? Do you have 2 extra C-H bonds coming in to finish the chain (which otherwise is a polymer where n=2 repeat units)?

So my teacher was wrong....and didn't have the right diagram....and to answer your question you end the dimer with brackets to show that it's repeating

[hockey101]

DrCMS, how does the chain end if the molecule is a dimer? Do you have 2 extra C-H bonds coming in to finish the chain (which otherwise is a polymer where n=2 repeat units)?

In reality what is at the ends of a polymer (dimer) chain depends on the conditions used in the polymerisation, it might be an initiator fragment and one end and a C-H via abstraction from the solvent or another polymer chain at the other end.  Or it might be and intiator fragment at one end and from a chain transfer agent, added to control the molecular weight distrubition, at the other end etc etc.  See this for extra info http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/polymers.htm

I love how when I try to look for a website like that...I can never find one...haha...thanks that helped...A LOT