Polymer Chemistry and Colloidal Dispersions Lecture Notes

Flashcards covering vocabulary and definitions from the lecture on polymer chemistry, synthesis methods, physical properties, and colloid behavior.

Polymers

A large class of materials consisting of many small molecules (called monomers) that can be linked together to form long chains known as macromolecules.

Monomers

Small molecules that serve as the building blocks for polymers.

Degree of Polymerisation (DP)

The number of monomer units in a macromolecule, defined as $DP = \frac{M}{M_0}$ where $M$ is the molecular weight of the macromolecule and $M_0$ is the molar mass of the repeating unit.

Biobased

Materials composed in part or entirely of substances of renewable origin, whether plant, animal, algal, or residual.

Biodegradable

The ability of a material to decompose naturally under the action of micro-organisms or a favorable environment (humidity, temperature, light, oxygen, etc.), emitting water, $CO_2$, and/or $CH_4$.

Thermoplastic

Polymers with no covalent bonds between chains, featuring weak bonds that can be broken by heating, allowing for reshaping.

Thermosetting

Polymers characterized by covalent bonds between chains (crosslinked), preventing movement between chains and making the material rigid and fragile.

Elastomers

Compounds of linear chains with a molar mass of ~$10^5\,g/mol$ and very weak interchain interactions (low $T_g$), crosslinked with a low density of crosslinker (1 crosslinking / 100 units).

Homopolymer

A polymer formed from a single type of monomer.

Copolymer

Polymers that incorporate more than one kind of monomer into their chain during the synthesis reaction.

Random Copolymer

A copolymer containing a random arrangement of multiple monomers.

Block Copolymer

A copolymer containing blocks of monomers of the same type.

Graft Copolymer

A copolymer with a main chain consisting of one type of monomer and branches made up of other monomers.

Stereoregularity (Tacticity)

The term used to describe the configuration of polymer chains, categorized as isotactic, syndiotactic, or atactic.

Isotactic

A polymer arrangement where all substituents are on the same side of the polymer chain.

Syndiotactic

A polymer chain composed of alternating groups of substituents.

Atactic

A polymer chain with a random combination of substituent groups.

Number Average Molecular Weight ($M_n$)

The statistical average molecular weight of all the polymer chains in the sample, defined as $M_n = \frac{\sum N_i M_i}{\sum N_i}$ where $M_i$ is the molecular weight of a chain and $N_i$ is the number of chains of that molecular weight.

Weight Average Molecular Weight ($M_w$)

An average that takes into account the molecular weight of a chain in determining contributions; more massive chains contribute more to $M_w$. ($M_w = \frac{\sum N_i M_i^2}{\sum N_i M_i}$).

Polydispersity

Defined as Weight average molecular weight ($M_w$) divided by Number average molecular weight ($M_n$), giving an indication of the width of the distribution.

Glass Transition Temperature ($T_g$)

The temperature at which the mechanical properties of a polymer radically change due to internal chain movement; below $T_g$, the polymer is brittle (glassy), and above it, it is rubber-like.

Semi-crystalline

Polymers that form mixtures of small crystals and amorphous material, melting over a range of temperature instead of at a single melting point.

Initiator Half-life ($t_{1/2}$)

The time required for the concentration of the initiator ($I$) to decrease to one half its original value ($t_{1/2} = \frac{\ln(2)}{k_d}$).

Combination (Coupling)

A termination mechanism in free radical polymerization where two radicals at the chain ends join to form a single bond, doubling the weight average molecular weight ($M_w$).

Disproportionation

A termination mechanism where the radical at the end of one chain attacks a hydrogen atom on a second chain, resulting in two terminated chains with different end groups.

Chain Transfer Agents

Compounds added to a reaction mixture (like mercaptans/thiols) that react with a radical species to terminate one chain and initiate a new one, thereby decreasing molecular weight without changing the rate of conversion.

Inhibitor

An agent responsible for a termination reaction where the new radical formed is incapable of reinitiation (e.g., Many phenols or molecular oxygen).

Living Polymerization

Anionic polymerization where termination reactions do not occur, allowing the propagating species to remain unchanged at the chain end when the monomer is consumed.

Mayo's Equation

The copolymer composition equation: $\frac{d[M_1]}{d[M_2]} = \frac{[M_1](r_1[M_1]+[M_2])}{[M_2]([M_1]+r_2[M_2])}$ where $r_1$ and $r_2$ are monomer reactivity ratios.

Azeotropic Copolymerization

A condition where the composition of the copolymer is equal to the concentration of the monomer feed ($F_1 = f_1$).

Gel Point

The point at which one first observes the visible formation of a gel or insoluble polymer fraction, corresponding to the formation of an infinite crosslinked network.

Carothers Equation

The relationship between the extent of reaction at the gel point ($p_c$) and the average functionality ($f_{avg}$): $p_c = \frac{2}{f_{avg}}$.

Bulk Polymerization

Polymerization of undiluted monomer carried out by adding a soluble initiator to pure monomer in a liquid state.

Latex

A colloidal dispersion of polymer particles in an aqueous medium, typically containing 40-60% spherical solid polymer particles within the size range of $10\,nm$ to $1000\,nm$.

Disperse System

A system in which one substance (dispersed phase) is distributed in discrete units throughout a second substance (continuous phase or vehicle).

Colloid Dispersion

A microheterogeneous system with particle sizes between $1$ and $1000\,nm$, which is intermediate between true solutions and suspensions.

Tyndall Effect

The ability of a colloidal solution to scatter light, causing the appearance of turbidity; shorter (blue) wavelengths are scattered more strongly.

Brownian Movement

The zig-zag random continuous movement of colloidal particles caused by the impact of the dispersion medium's molecules.

Hydrophilic-Lipophilic Balance (HLB)

A measure of the degree to which a surfactant is hydrophilic or lipophilic; high values indicate water solubility and low values indicate oil solubility.