Polymer Chemistry NMR question












2












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I am extremely new to both polymer chemistry and NMR.
I am struggling with the following question:
A proton NMR is used to attempt to quantify the molecular weight of a poly(ethylene oxide) molecule with methyoxy end groups at each terminus. If the integration of the methyl protons relative to the methylene protons gave a ratio of 1:20, what can you say about the molecular weight?



Thank you. All help is appreciate including resources for me to be able to read up on my lacking knowledge.










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    2












    $begingroup$


    I am extremely new to both polymer chemistry and NMR.
    I am struggling with the following question:
    A proton NMR is used to attempt to quantify the molecular weight of a poly(ethylene oxide) molecule with methyoxy end groups at each terminus. If the integration of the methyl protons relative to the methylene protons gave a ratio of 1:20, what can you say about the molecular weight?



    Thank you. All help is appreciate including resources for me to be able to read up on my lacking knowledge.










    share|improve this question







    New contributor




    Carl is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
    Check out our Code of Conduct.







    $endgroup$















      2












      2








      2





      $begingroup$


      I am extremely new to both polymer chemistry and NMR.
      I am struggling with the following question:
      A proton NMR is used to attempt to quantify the molecular weight of a poly(ethylene oxide) molecule with methyoxy end groups at each terminus. If the integration of the methyl protons relative to the methylene protons gave a ratio of 1:20, what can you say about the molecular weight?



      Thank you. All help is appreciate including resources for me to be able to read up on my lacking knowledge.










      share|improve this question







      New contributor




      Carl is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.







      $endgroup$




      I am extremely new to both polymer chemistry and NMR.
      I am struggling with the following question:
      A proton NMR is used to attempt to quantify the molecular weight of a poly(ethylene oxide) molecule with methyoxy end groups at each terminus. If the integration of the methyl protons relative to the methylene protons gave a ratio of 1:20, what can you say about the molecular weight?



      Thank you. All help is appreciate including resources for me to be able to read up on my lacking knowledge.







      polymers nmr-spectroscopy






      share|improve this question







      New contributor




      Carl is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.











      share|improve this question







      New contributor




      Carl is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.









      share|improve this question




      share|improve this question






      New contributor




      Carl is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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      asked 3 hours ago









      CarlCarl

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      112




      New contributor




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      New contributor





      Carl is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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          1 Answer
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          $begingroup$

          I hope this is not a home work question. Suppose your polymer has $n$ reapeating units and capped with methyl grops at the end as you described. Thus, it should looks like following figure:
          PEO



          Thus it has $n$ $ce{(-CH2CH2-)}$ units and $2$ $ce{(-CH3)}$ units. Thus your $ce{(-O-CH2)}$ signal is accounted for $4n$ protons while $ce{(-O-CH2)}$ signal accounted for only $6$ protons. Thus,
          $$frac{4n}{6} = frac{20}{1}$$
          You may find the value of $n$ from this equation and you can calculate the molecular weight of the polymer in hand.






          share|improve this answer









          $endgroup$









          • 2




            $begingroup$
            Importantly, almost all polymer samples are a mixture of molecules with different chain lengths, and quantification by NMR provides an average value for the whole sample, more specifically the number-average chain length/molecular weight.
            $endgroup$
            – Nicolau Saker Neto
            1 hour ago











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          1 Answer
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          1 Answer
          1






          active

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          active

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          active

          oldest

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          3












          $begingroup$

          I hope this is not a home work question. Suppose your polymer has $n$ reapeating units and capped with methyl grops at the end as you described. Thus, it should looks like following figure:
          PEO



          Thus it has $n$ $ce{(-CH2CH2-)}$ units and $2$ $ce{(-CH3)}$ units. Thus your $ce{(-O-CH2)}$ signal is accounted for $4n$ protons while $ce{(-O-CH2)}$ signal accounted for only $6$ protons. Thus,
          $$frac{4n}{6} = frac{20}{1}$$
          You may find the value of $n$ from this equation and you can calculate the molecular weight of the polymer in hand.






          share|improve this answer









          $endgroup$









          • 2




            $begingroup$
            Importantly, almost all polymer samples are a mixture of molecules with different chain lengths, and quantification by NMR provides an average value for the whole sample, more specifically the number-average chain length/molecular weight.
            $endgroup$
            – Nicolau Saker Neto
            1 hour ago
















          3












          $begingroup$

          I hope this is not a home work question. Suppose your polymer has $n$ reapeating units and capped with methyl grops at the end as you described. Thus, it should looks like following figure:
          PEO



          Thus it has $n$ $ce{(-CH2CH2-)}$ units and $2$ $ce{(-CH3)}$ units. Thus your $ce{(-O-CH2)}$ signal is accounted for $4n$ protons while $ce{(-O-CH2)}$ signal accounted for only $6$ protons. Thus,
          $$frac{4n}{6} = frac{20}{1}$$
          You may find the value of $n$ from this equation and you can calculate the molecular weight of the polymer in hand.






          share|improve this answer









          $endgroup$









          • 2




            $begingroup$
            Importantly, almost all polymer samples are a mixture of molecules with different chain lengths, and quantification by NMR provides an average value for the whole sample, more specifically the number-average chain length/molecular weight.
            $endgroup$
            – Nicolau Saker Neto
            1 hour ago














          3












          3








          3





          $begingroup$

          I hope this is not a home work question. Suppose your polymer has $n$ reapeating units and capped with methyl grops at the end as you described. Thus, it should looks like following figure:
          PEO



          Thus it has $n$ $ce{(-CH2CH2-)}$ units and $2$ $ce{(-CH3)}$ units. Thus your $ce{(-O-CH2)}$ signal is accounted for $4n$ protons while $ce{(-O-CH2)}$ signal accounted for only $6$ protons. Thus,
          $$frac{4n}{6} = frac{20}{1}$$
          You may find the value of $n$ from this equation and you can calculate the molecular weight of the polymer in hand.






          share|improve this answer









          $endgroup$



          I hope this is not a home work question. Suppose your polymer has $n$ reapeating units and capped with methyl grops at the end as you described. Thus, it should looks like following figure:
          PEO



          Thus it has $n$ $ce{(-CH2CH2-)}$ units and $2$ $ce{(-CH3)}$ units. Thus your $ce{(-O-CH2)}$ signal is accounted for $4n$ protons while $ce{(-O-CH2)}$ signal accounted for only $6$ protons. Thus,
          $$frac{4n}{6} = frac{20}{1}$$
          You may find the value of $n$ from this equation and you can calculate the molecular weight of the polymer in hand.







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered 2 hours ago









          Mathew MahindaratneMathew Mahindaratne

          4138




          4138








          • 2




            $begingroup$
            Importantly, almost all polymer samples are a mixture of molecules with different chain lengths, and quantification by NMR provides an average value for the whole sample, more specifically the number-average chain length/molecular weight.
            $endgroup$
            – Nicolau Saker Neto
            1 hour ago














          • 2




            $begingroup$
            Importantly, almost all polymer samples are a mixture of molecules with different chain lengths, and quantification by NMR provides an average value for the whole sample, more specifically the number-average chain length/molecular weight.
            $endgroup$
            – Nicolau Saker Neto
            1 hour ago








          2




          2




          $begingroup$
          Importantly, almost all polymer samples are a mixture of molecules with different chain lengths, and quantification by NMR provides an average value for the whole sample, more specifically the number-average chain length/molecular weight.
          $endgroup$
          – Nicolau Saker Neto
          1 hour ago




          $begingroup$
          Importantly, almost all polymer samples are a mixture of molecules with different chain lengths, and quantification by NMR provides an average value for the whole sample, more specifically the number-average chain length/molecular weight.
          $endgroup$
          – Nicolau Saker Neto
          1 hour ago










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