Explain alkanoates. 2. State any three members of the alkanoate family. 3. Explain esterification. 4. Write a typical equation representing esterification. 5. Differentiate between polymerisation and condensation. What is the difference between alkalis and bases?

(1) Addition polymerization of alkenes

Addition polymerization of alkenes is a chain-growth process where multiple alkene molecules (monomers with C=C double bond) link together by opening the double bond, forming a long chain polymer without loss of any small molecule byproduct.

Typical mechanism: Free radical addition polymerization.

General reaction for ethene (a common alkene):

$$n \ \mathrm{CH_2=CH_2} \xrightarrow{\text{initiator}} \left[ -\mathrm{CH_2-CH_2}- \right]_n$$

Steps:

• Initiation: Peroxide initiator decomposes to radicals.

$$\mathrm{(R-O)_2} \rightarrow 2 \ \mathrm{R-O^\bullet}$$ $$\mathrm{R-O^\bullet + CH_2=CH_2 \rightarrow R-O-CH_2-CH_2^\bullet}$$

• Propagation: Radical adds to monomer repeatedly.

$$\mathrm{R-O-(CH_2-CH_2)_n ^\bullet + CH_2=CH_2 \rightarrow R-O-(CH_2-CH_2)_{n+1} ^\bullet}$$

• Termination: Radicals combine.

$$\mathrm{R-O-(CH_2-CH_2)_m ^\bullet + R-O-(CH_2-CH_2)_p ^\bullet \rightarrow R-O-(CH_2-CH_2)_{m+p}-O-R}$$

Three monomers (alkenes): Ethene ($\mathrm{CH_2=CH_2}$), propene ($\mathrm{CH_2=CH-CH_3}$), but-1-ene ($\mathrm{CH_2=CH-CH_2-CH_3}$).

(2) Chain reaction representing typical homopolymer situation

Homopolymer: Polymer formed from one type of monomer only.

Typical situation: Free radical addition polymerization of an alkene (e.g., ethene to polyethylene).

Chain reaction has three main steps:

Initiation:

Peroxide decomposes:

$$\mathrm{Bz_2O_2} \rightarrow 2 \ \mathrm{BzO^\bullet} \quad (\mathrm{Bz = C_6H_5CH_2})$$

Radical adds to monomer:

\mathrm{BzO^\bullet + CH_2=CH_2 \rightarrow \mathrm{BzO-CH_2-CH_2^\bullet}

Propagation:

\mathrm{BzO-CH_2-(CH_2-CH_2)_{n-1}-CH_2 ^\bullet + CH_2=CH_2 \rightarrow \mathrm{BzO-CH_2-(CH_2-CH_2)_n -CH_2 ^\bullet}

Termination (combination):

\mathrm{BzO-(CH_2-CH_2)_m ^\bullet + \mathrm{BzO-(CH_2-CH_2)_n ^\bullet \rightarrow BzO-(CH_2-CH_2)_{m+n}-OBz}

This represents homopolymerization as only one monomer (ethene) is used.

(3) Difference between polymerization and condensation

Polymerization (Addition)	Condensation
Monomers link by addition across multiple bond (e.g., C=C).	Monomers link by elimination of small molecule (e.g., H$_2$O).
No byproduct.	Byproduct formed.
Chain-growth, fast.	Step-growth, slower.
Example: $n \ \mathrm{CH_2=CH_2} \rightarrow [\mathrm{-CH_2-CH_2-}]_n$ (polyethene).	Example: HO-(CH$_2$)$_4$-OH + HOOC-(CH$_2$)$_4$-COOH $\rightarrow$ [-O-(CH$_2$)$_4$-OOC-(CH$_2$)$_4$-CO-]$_n$ + (2n-1) H$_2$O (nylon 6,6).

Difference between homopolymers and copolymers

Homopolymers: Formed from a single type of monomer. All repeating units identical.

Example: Polyethene $[\mathrm{-CH_2-CH_2-}]_n$ from ethene only.

Copolymers: Formed from two or more different monomers. Repeating units vary.

Example: Styrene-butadiene rubber (SBR): [-CH(CH$_3$)-CH$_2$-] from propene? Wait, styrene $\mathrm{C_6H_5CH=CH_2}$ and buta-1,3-diene $\mathrm{CH_2=CH-CH=CH_2}$.

Types of copolymers: Random, alternating, block, graft.

See above explanations