Question

Which of the following polymers would be stronger or more rigid? Explain your choices. a. The copolymer of ethylene glycol and terephthalic acid or the copolymer of 1,2 -diaminoethane and terephthalic acid \((1,2-\) diaminoethane \(=\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\) ) b. The polymer of \(\mathrm{HO}-\left(\mathrm{CH}_{2}\right)_{6}-\mathrm{CO}_{2} \mathrm{H}\) or that of O=C(O)c1ccc(O)cc1 c. Polyacetylene or polyethylene (The monomer in polyacetylene is ethyne.)

Short answer

The copolymer of 1,2-diaminoethane and terephthalic acid is stronger and more rigid due to stronger hydrogen bond interactions. The polymer with the structural formula \( -[-O-C(-O)-C_6H_4-C(-O)-]- \) (derived from smiles notation) is stronger and more rigid due to the π-π stacking interactions between the aromatic rings in the backbone. Polyacetylene is stronger and more rigid than polyethylene due to the presence of conjugation and π-π stacking interactions in its structure.

Step-by-step solution

Write down the structural formulas

To compare the strength and rigidity, first write down the structural formulas of the cop polymers under consideration: 1. Copolymer of ethylene glycol and terephthalic acid \[ -[-O-CH_2-CH_2-O-C(-O)-C_6H_4-C(-O)-]- \] 2. Copolymer of 1,2-diaminoethane and terephthalic acid \[-[-NH-CH_2-CH_2-NH-C(-O)-C_6H_4-C(-O)-]- \]

Analyze the interactions

Next, analyze the interactions between the copolymer chains in the structural formulas: 1. In the copolymer of ethylene glycol and terephthalic acid, there are hydrogen bonds between the oxygen of ethylene glycol and the hydrogen of the neighboring -CH_2- group. This leads to a stronger interchain interaction. 2. In the copolymer of 1,2-diaminoethane and terephthalic acid, there are stronger hydrogen bonds between the nitrogen of 1,2-diaminoethane and the hydrogen of the neighboring -CH_2- group. Here, the interchain interaction is stronger compared to the first copolymer because nitrogen forms stronger hydrogen bonds than oxygen.

Conclusion

The copolymer of 1,2-diaminoethane and terephthalic acid is stronger and more rigid due to the stronger hydrogen bond interactions between the nitrogen and hydrogen of the neighboring -CH_2- group. #Part b: Comparison between the polymer of \(\mathrm{HO}-\left(\mathrm{CH}_{2}\right)_{6}-\mathrm{CO}_{2} \mathrm{H}\) and the polymer with smiles notation#

Convert the smiles notation

First, we need to convert the smiles notation to the structural formula: \[ -[-O-C(-O)-C_6H_4-C(-O)-]- \]

Analyze the interactions

Now, compare the interactions between the polymer chains in the structural formulas: 1. The polymer of \(\mathrm{HO}-\left(\mathrm{CH}_{2}\right)_{6}-\mathrm{CO}_{2} \mathrm{H}\) has van der Waals forces between the CH_2 groups in the long carbon chain. 2. The polymer with the structural formula \( -[-O-C(-O)-C_6H_4-C(-O)-]- \) has aromatic rings in the backbone that can exhibit π-π stacking, which leads to stronger interactions between the chains.

Conclusion

The polymer with the structural formula \( -[-O-C(-O)-C_6H_4-C(-O)-]- \) (derived from smiles notation) is stronger and more rigid due to the π-π stacking interactions between the aromatic rings in the backbone. #Part c: Comparison between polyacetylene and polyethylene#

Write down the structural formulas

Write down the structural formulas of polyacetylene and polyethylene: 1. Polyacetylene: \[ -[-C≡C-]- \] 2. Polyethylene: \[ -[-C-H-C-H-]- \]

Analyze the interactions

Compare the interactions between the polymer chains in the structural formulas: 1. Polyacetylene has alternate single and triple bonds, which can lead to stronger interactions through conjugation and π-π stacking. 2. Polyethylene has only single bonds and exhibits weaker van der Waals interactions between the chains.

Conclusion

Polyacetylene is stronger and more rigid than polyethylene due to the presence of conjugation and π-π stacking interactions in its structure.

Key concepts

Copolymer Interactions

Copolymers are polymers made from two or more different types of monomers, which, when coupled together, exhibit a range of physical properties that can be fine-tuned for specific applications. One key aspect affecting the strength and rigidity of copolymers is the interactions between their molecular chains.

For instance, in copolymers such as those formed from ethylene glycol and terephthalic acid or 1,2-diaminoethane and terephthalic acid, the interactions are significantly influenced by the functional groups present. In the first copolymer, oxygen atoms from the ethylene glycol groups can form hydrogen bonds with neighboring hydrogen atoms on the -CH₂- groups. However, the second copolymer exhibits stronger hydrogen bonding due to the nitrogen atoms' involvement, which have a higher electronegativity compared to oxygen.

This highlights the importance of functional group chemistry in copolymer interactions, which directly impacts the material's mechanical properties such as tensile strength and elasticity. Copolymers can be engineered with tailored strength and flexibility by carefully selecting monomer units that interact beneficially.

Hydrogen Bonding in Polymers

Hydrogen bonding is a significant factor in determining the strength of polymers. These bonds are a type of dipole-dipole interaction where a hydrogen atom covalently bonded to a highly electronegative atom, like nitrogen, oxygen, or fluorine, experiences an attractive force with another electronegative atom.

Within a polymer matrix, these hydrogen bonds can form 'cross-links' that help to hold the chains together, thereby increasing the tensile strength and rigidity of the material. For instance, the copolymer of 1,2-diaminoethane and terephthalic acid showcases stronger hydrogen bonding because of the nitrogen atoms in the amino group that form robust hydrogen bonds with the hydrogen of the neighboring -CH₂- groups. This enhances the polymer's mechanical properties and thermal stability, resulting in a material that is tougher and maintains its shape better under stress.

Van der Waals Forces in Polymers

Van der Waals forces are another type of intermolecular force that affect polymer characteristics, particularly in polymers without strong covalent or hydrogen bonding between chains. These forces include attractions and repulsions between atoms, molecules, and surfaces, as well as various other intermolecular forces such as dipole-dipole, dipole-induced dipole, and London dispersion forces.

The strength of van der Waals forces in polymers like polyethylene, which consists of long chains of -CH₂- groups, can significantly influence the flexibility and ductility of the material. Although weaker than covalent or hydrogen bonds, van der Waals forces are ubiquitous and help the polymer chains to pack closely, which can impart some level of tensile strength and impact resistance to the material.

However, in general, polymers that rely primarily on van der Waals forces for interchain interactions tend to be less rigid and have lower melting points compared to those with stronger bonding interactions.

π-π Stacking in Polymers

π-π Stacking is a particular type of non-covalent interaction that is important in polymers containing aromatic rings. It refers to the attractive, stack-like interaction between the electron clouds of these rings, which can significantly increase a polymer's strength and thermal stability.

In the case of polymers derived from benzene-based monomers, such as terephthalic acid, π-π stacking allows the stiff aromatic rings to align and interact through their π-electron systems. This interaction reinforces the rigidity of the polymer chain, creating a stronger and more rigid material compared to those without π-π stacking capability. As seen in the exercises, the presence of aromatic rings in a polymer's backbone, like the one derived from the given SMILES notation, enables this sort of stacking, translating into enhanced physical properties such as increased strength, stiffness, and resistance to solvents and heat.