Organic polymers have had a great impact on our daily lives. Millions of tons of different kinds of — Organic Chemistry Chemistry Question
Spectroscopy and Polymer Chemistry
Organic polymers have had a great impact on our daily lives. Millions of tons of different kinds of polymers are produced every year. Synthetic organic polymers have a variety of uses, from textiles to computer chips, and to the life saving artificial heart valve. They are widely used as plastics, adhesives, engineering materials, biodegradable plastics, and paints. Poly(vinyl alcohol) (PVA) is an important example of a water–soluble polymer. One synthetic route to PVA is summarized in Scheme 1.
Scheme 1:
[Monomer A] --polymerization--> [Polymer B] --transformation--> [Poly(vinyl alcohol) PVA]
Polymer B shown above is also a major component in chewing gum. Elemental analysis of A suggests a ratio of C : H : O = 56 : 7 : 37. In addition, elemental analysis of B gives an almost identical composition of C, H, and O. The following IR and 1 H NMR spectra were recorded for monomer A.
[VISUAL]
What is the molecular formula of A?
Model Answer
C4H6O2
Which functional group would give an IR absorption band at 1761 cm–1?
Model Answer
C=O group
What is the chemical structure of A?
Model Answer
Vinyl acetate: CH3COOCH=CH2
Draw a portion of polymer B. Show at least three repeat units.
Model Answer
Poly(vinyl acetate). The structure consists of a polyethylenic backbone with acetate groups: -[CH2-CH(OCOCH3)]-n.
Provide a method for the transformation of B to PVA.
Model Answer
Organic reactions that could transform acetate to alcohol such as acid or base hydrolysis, alcoholysis, or LiAlH4 reduction.
How many pairs of enantiomers would be obtained from polymer B with a molecular mass of 8600, assuming that the polymer is terminated by hydrogen abstraction and the mass of the terminal groups can be ignored?
Model Answer
There are 100 units/molecule. However, the last one does not contain chiral center, therefore, there are 99 chiral centers and each of which would have R or S configuration. Totally there will be 2^99 stereoisomers, including enantiomers and diastereomers. Therefore, the number of pairs of enantiomers is 2^99/2 = 2^98.
Compound C, an isomer of A, is also an important monomer for the synthesis of polymers. On the basis of its 1 H NMR and IR spectra provided below [VISUAL], deduce the chemical structure of C.
Model Answer
Methyl acrylate: CH2=CHCOOCH3
Polymer D is an acid sensitive macromolecule. On treatment of D with a protic acid, gases E and F are released, and a new polymer G is formed. Gas E turns an aqueous solution of Ca(OH)2 into a turbid solution while gas F reacts with bromine to give a colorless solution of H.
[VISUAL]
Draw the chemical structures of E, F, G and H?
Model Answer
E: CO2
F: (CH3)2C=CH2 (isobutene)
G: Poly(vinyl alcohol) (PVA)
H: (CH3)2CBr-CH2Br (1,2-dibromo-2-methylpropane)
Polymer D has been used to formulate a photo–imaging material by mixing it with a photo acid–generator (PAG). After being coated onto a substrate and exposed to light, protons are generated from the PAG, catalyzing a chemical reaction within the polymer matrix. Sometimes baking after exposure is necessary to accelerate the acid catalyzed reaction. If light is applied through a mask (Figure 1 [VISUAL]), a latent image of the mask is formed in the polymer matrix. After baking and using an aqueous basic developer to wash away the acidic materials, a patterned substrate I is obtained.
Which of the following diagrams best illustrates the patterned structure of substrate I?
(a) [VISUAL]
(b) [VISUAL]
(c) [VISUAL]
(d) [VISUAL]
The dark areas represent a polymeric coating that is structurally different from the original one.
Model Answer
(d)