10th Class Chemistry Chapter 13 Notes

Definition

Addition polymerization joins many identical monomer molecules (each containing a double bond) together, one after another, with no other product formed — the double bonds simply open up and link the monomers into a long chain.

A catalyst in addition polymerization typically works by generating a reactive initiating species that opens the first monomer's double bond, starting a chain reaction that keeps adding one monomer after another without needing further catalyst input for every step — speeding up the reaction and controlling how it starts.

Two examples of addition polymers: poly(ethene) — from ethene monomers — and PVC (polyvinyl chloride) — from vinyl chloride monomers.

Definition

Structures of two common addition polymers: (a) polypropylene — ${\left[-C{H}_2-CH(C{H}_3)-\right]}_n$, from propene monomers; (b) polystyrene — ${\left[-C{H}_2-CH(C_6{H}_5)-\right]}_n$, from styrene (phenylethene) monomers.

Definition

Condensation polymerization joins monomer molecules together while also releasing a small molecule (usually water) at each linkage, unlike addition polymerization which releases nothing.

For condensation polymerization to occur, monomer molecules must have at least two reactive functional groups each (e.g. two $-OH$ groups, two $-COOH$ groups, or one of each, or an amine and a carboxylic acid group) — a functional group at each end is what lets each monomer link to two different neighbours, building a continuous chain rather than stopping after one connection.

Nylon (a polyamide) forms by condensation polymerization between a diamine and a dicarboxylic acid (or diacid chloride), with an amide linkage forming at each connection and water (or HCl) released each time. Polyester (like PET, polyethylene terephthalate) forms by condensation polymerization between a diol and a dicarboxylic acid, with an ester linkage forming at each connection and water released each time.

PET is formed from ethylene glycol (a diol) and terephthalic acid (a dicarboxylic acid) reacting by repeated esterification, releasing water at each linkage — PET can be recycled, and is one of the most commonly recycled plastics (used for drink bottles, then reprocessed into new products like fibres or new bottles).

Definition

Reaction conditions to prepare a polyamide (like nylon): a diamine reacts with a dicarboxylic acid (or its diacid chloride), typically at a controlled temperature, forming an amide linkage and releasing water (or HCl) at each step. To prepare a polyester: a diol reacts with a dicarboxylic acid, typically with heat and often a catalyst, forming an ester linkage and releasing water at each step.

Definition

The non-stick coating used on cooking pans is an example of PTFE (polytetrafluoroethylene, commonly known as Teflon) — an addition polymer made from tetrafluoroethene monomers, valued for its extremely low friction and chemical inertness.

Definition

Key differences: addition polymerization uses monomers with a double bond and releases no by-product, giving a polymer whose molecular mass is exactly the sum of its monomers' masses; condensation polymerization uses monomers with two reactive functional groups each and releases a small molecule (usually water) at every linkage, giving a polymer whose mass is less than the simple sum of its monomers' masses.

Definition

A synthetic polymer is one manufactured artificially in a lab/factory (e.g. nylon, polyester, PVC), as opposed to a natural polymer that occurs in living organisms (e.g. cellulose, natural rubber, proteins, DNA).

Natural polymers are generally not hazardous to the environment, because they're biodegradable — natural decomposer organisms (bacteria, fungi) have enzymes that can break their specific chemical structures down into simpler, harmless substances over a reasonable time.

Synthetic fibres differ from natural fibres in generally being more durable, resistant to shrinking/wrinkling, cheaper to mass-produce, and easily engineered to have specific desired properties — but they're usually not biodegradable, unlike most natural fibres (like cotton or wool).

Definition

Discarded plastic articles can take hundreds of years (commonly cited as up to $500$ years or more, depending on the specific plastic) to break down in the environment, since most common plastics aren't biodegradable and resist the natural decomposition processes that break down organic matter.

Plastics cause more severe environmental pollution than natural materials mainly because of this extreme persistence (they accumulate rather than decompose), combined with their tendency to fragment into microplastics that spread widely through soil, water, and even the food chain, rather than fully breaking down.

Definition

Not all synthetic polymers are equally harmful — some (like certain newer bioplastics) are specifically engineered to be biodegradable, and many common plastics (like PET and some polyethylenes) can be recycled, reducing (though not eliminating) their environmental impact when properly collected and processed.

Definition

Polymers are useful because their properties (strength, flexibility, resistance to chemicals/water, light weight, and low cost of production) can be tailored for an enormous range of applications — from packaging and construction to medicine and electronics.

Three properties that make synthetic fibres suitable for the textile industry: durability/strength, resistance to shrinking and wrinkling, and the ability to be engineered with specific desired characteristics (like water resistance, elasticity, or a particular texture).