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Questions and Answers

Explain how the degree of polymerization influences a polymer's physical properties, considering both low and high molecular weights.

Lower molecular weight polymers tend to be soft, gummy, and brittle, while higher molecular weight polymers are tougher and more resistant due to increased chain entanglement and intermolecular forces.

Describe the key difference between addition and condensation polymerization, giving an example of a polymer formed by each process.

Addition polymerization involves monomers adding directly to the polymer chain without the loss of any atoms (e.g., polyethylene from ethylene). Condensation polymerization involves the joining of monomers with the loss of small molecules like water (e.g., nylon from diamines and dicarboxylic acids).

How does the presence of polar groups in a polymer chain affect its strength and solubility?

Polar groups increase intermolecular forces (e.g., hydrogen bonding), leading to higher strength. They also enhance solubility in polar solvents like water or alcohols.

Explain how creating cross-linking in a thermoplastic material changes its properties, and what new type of material does it become?

Creating cross-linking converts a thermoplastic material into a thermosetting material. This process makes the material stronger and more resistant to heat, as well as insoluble. Signup and view all the answers

Contrast the arrangement of molecules in amorphous and crystalline states of a polymer and how these arrangements affect the polymer's properties.

In the amorphous state, molecules are randomly arranged, leading to flexibility. In the crystalline state, molecules are regularly arranged, increasing intermolecular forces, resulting in higher softening points, greater rigidity, brittleness, and strength. Signup and view all the answers

Describe the conditions under which a polymer with non-polar groups is likely to be soluble.

A polymer with non-polar groups is likely to be soluble in non-polar solvents, such as benzene, toluene, or carbon tetrachloride. Signup and view all the answers

Explain how the degree of cross-linking affects the solubility of a polymer in a solvent.

The greater the degree of cross-linking, the less soluble the polymer is in a solvent. Highly cross-linked polymers may become completely insoluble due to the strong network structure. Signup and view all the answers

Describe the molecular behavior that gives a very long-chain polymer its elastic character.

Very long-chain polymers exhibit elastic character due to free-rotating groups that irregularly coil and entangle. When stretched, these coils straighten out, and upon release, they return to their original coiled state. Signup and view all the answers

Explain the difference in molecular motion between a polymer in the glassy state versus the rubbery state.

In the glassy state, there is no segmental or molecular motion, resulting in a rigid solid. In the rubbery state, segmental motion is present, but molecular motion is not. Signup and view all the answers

Describe what happens to a polymer at the point of 'necking' when subjected to continuous strain.

At the necking point, the polymer chains begin to uncoil and fully stretch. After this point, the polymer reaches its breaking point and yields. Signup and view all the answers

How does the behavior of amorphous polymers differ from that of crystalline polymers when heated above their glass transition temperature (Tg)?

Amorphous polymers become rubbery and then gummy as they are heated above Tg, eventually liquefying, whereas crystalline polymers exhibit thermoplastic behavior before liquefying. Signup and view all the answers

Name three common additives used in plastics and briefly state their purpose.

Three common additives are: Resins (provide the base material), Fillers (add bulk or modify properties), and Plasticizers (increase flexibility). Signup and view all the answers

What is the key difference between processing thermoplastics and thermosetting plastics in compression moulding, and why does this difference exist?

Thermoplastics can be repeatedly softened and reshaped, while thermosetting plastics undergo an irreversible chemical change and cannot be remelted. This is due to the cross-linked structure formed in thermosetting plastics during curing. Signup and view all the answers

Explain how 'blow moulding' is used in the processing of plastics and what types of polymers are typically used in this process.

Blow moulding involves inflating a heated plastic parison inside a mold to create hollow objects. Thermoplastics are typically used in this process. Signup and view all the answers

Describe the 'calendaring' process in plastics processing. What kind of polymers is it best suited for?

Calendaring is a process where plastic is squeezed between rollers to produce thin sheets or films. It's best suited for thermoplastics. Signup and view all the answers

Explain the difference between 'film casting' and 'die casting' in the context of plastic processing.

Film casting involves pouring a liquid plastic solution onto a moving belt to create a thin film, while die casting involves injecting molten plastic into a mold under high pressure to form a solid object. Signup and view all the answers

How does the distribution ratio $\frac{M_w}{M_n}$ indicate the homogeneity of a polymer sample, and what does a value significantly greater than 1 suggest about its composition?

A distribution ratio $\frac{M_w}{M_n}$ of 1 indicates a homogeneous polymer sample where all polymer chains have the same length. A value significantly greater than 1 indicates that the polymer is heterogeneous, containing chains of varying lengths. Signup and view all the answers

Explain the relationship between the number-average molar mass ($M_n$), the degree of polymerization (DP), and the molar mass of the monomer in an addition polymer.

The number-average molar mass ($M_n$) is equal to the degree of polymerization (DP) multiplied by the molar mass of the monomer: $M_n = DP \times \text{molar mass of monomer}$. Signup and view all the answers

In free radical polymerization, what type of reaction is the decomposition of the initiator (R-R → 2R°), and why is this step crucial for the overall polymerization process?

The decomposition of the initiator (R-R → 2R°) is an endothermic reaction. This step is crucial because it generates the free radicals (R°) necessary to initiate the chain reaction. Signup and view all the answers

Describe in two sentences how the number average molar mass ($M_n$) is calculated.?

The number average molar mass ($M_n$) is calculated by summing the product of the number of molecules ($N_i$) and their respective molar mass ($M_i$), and dividing by the total number of molecules ($N_i$). This can be represented as: $M_n = \frac{\Sigma N_iM_i}{\Sigma N_i}$. Signup and view all the answers

Explain how the weight average molar mass ($M_w$) differs from the number average molar mass ($M_n$) in terms of how each is influenced by the molar mass of polymer chains?

The weight average molar mass ($M_w$) is more sensitive to the presence of high molar mass polymers than the number average molar mass ($M_n$). $M_w$ considers the mass fraction of each polymer size, giving more weight to larger molecules. Signup and view all the answers

What is the Degree of Polymerization (DP) and why is it considered an average value for most synthetic polymers?

The Degree of Polymerization (DP) represents the number of repeating units in a polymer molecule. It is considered an average value because synthetic polymers typically consist of chains with varying lengths, resulting in a distribution of molar masses. Signup and view all the answers

Describe the three major steps involved in the mechanism of free radical addition polymerization.

The three major steps are: 1) Initiation, where free radicals are formed. 2) Propagation, where monomers are added to the growing polymer chain. 3) Termination, where the chain growth is stopped, typically by combining two radicals. Signup and view all the answers

In the context of polymer molar mass, what do $N_i$ and $M_i$ represent when calculating the number average molar mass ($M_n$)?

$N_i$ represents the number of molecules with a specific molar mass, and $M_i$ represents that specific molar mass. Signup and view all the answers

Flashcards

Degree of Polymerization

The number of monomer units in a polymer chain.

Copolymerization

Polymerization involving two or more different monomers.