General methods of preparation and mechanism of polymerisation Questions in English

(B) The Ziegler-Natta catalyst is a mixture of triethylaluminium $(Al(C_2H_5)_3)$ and titanium tetrachloride $(TiCl_4)$.
It is widely used in the industrial polymerization of alkenes,such as the production of high-density polyethylene $(HDPE)$.

(B) Bakelite is a thermosetting polymer formed by the condensation polymerization of phenol and formaldehyde in the presence of an acid or base catalyst. The reaction is as follows: $n C_6H_5OH + n HCHO \rightarrow \text{Bakelite}$.

(A) The condensation reaction of phenol with formaldehyde $(HCHO)$ in the presence of an acid or base catalyst leads to the formation of the polymer Bakelite.

(C) Bakelite is obtained by the polymerization of phenol and formaldehyde $(HCHO)$ in the presence of an acid or base catalyst.
This is a condensation polymerization reaction.

(D) Caprolactum is the monomer of nylon $-6$.
When caprolactum is heated with water at high temperature,it undergoes ring-opening polymerization to form nylon $-6$.

(B) In addition polymerization,the simple addition of monomer units takes place without the loss of any small molecules. This is in contrast to condensation polymerization,where small molecules like $H_2O$,$HCl$,or $NH_3$ are typically eliminated.

(C) The hydrolysis of dimethyl dichlorosilane,$(CH_3)_2SiCl_2$,produces a dihydroxy derivative,$(CH_3)_2Si(OH)_2$.
This dihydroxy derivative undergoes condensation polymerisation to form a straight chain silicone polymer,as shown in the reaction:
$n(CH_3)_2SiCl_2 + 2nH_2O \rightarrow n(CH_3)_2Si(OH)_2 + 2nHCl$
$n(CH_3)_2Si(OH)_2 \rightarrow -[O-Si(CH_3)_2-O]_n- + nH_2O$

(D) Caprolactam is heated with water at high temperature to undergo ring-opening polymerization.
This process yields $6$-aminohexanoic acid,which upon further heating undergoes condensation polymerization to form the polymer known as nylon $6$.
Therefore,caprolactam is the monomer used for the manufacture of nylon $6$.

(A) Neoprene is a synthetic rubber produced by the polymerization of chloroprene.
The $IUPAC$ name of chloroprene is $2$-chloro-$1,3$-butadiene.
Its chemical structure is $CH_2=C(Cl)-CH=CH_2$.

(D) Condensation Polymerization: This is a process of polymer formation by the reaction of smaller molecules to form bigger ones,with the elimination of small molecules such as $H_{2}O$ or methanol.
For example: In the formation of $Nylon-6,6$,small molecules of hexamethylenediamine and adipic acid react,resulting in the removal of a water molecule for each condensation step between the two monomers.

(D) Bakelite is a thermosetting polymer formed by the condensation polymerization of phenol and formaldehyde $(HCHO)$.
In the presence of an acid or base catalyst,phenol reacts with formaldehyde to form $o$- and $p$-hydroxymethylphenol intermediates.
These intermediates undergo further polymerization to form a linear polymer called Novolac.
Upon heating with more formaldehyde,Novolac undergoes cross-linking to form the infusible,hard,and cross-linked polymer known as Bakelite.

(C) Cationic polymerization is initiated by electrophiles or Lewis acids.
Electron-deficient species (Lewis acids) such as $AlCl_3$,$BF_3$,and $SnCl_4$ are commonly used as initiators for cationic polymerization because they can generate carbocations from the monomer.
Among the given options,$AlCl_3$ is a well-known Lewis acid.

(A) Nylon-$6$ is prepared by heating $\varepsilon$-caprolactam with water at a high temperature $(533-543 \ K)$.
In this process,the cyclic amide ring of $\varepsilon$-caprolactam undergoes a hydrolysis reaction to form an amino acid,which then undergoes polymerization to form Nylon-$6$.

(C) $1$. The starting material is cyclohexanone.
$2$. Reaction with hydroxylamine $(NH_2OH)$ followed by acid-catalyzed rearrangement (Beckmann rearrangement) using $H_2SO_4$ and heat converts cyclohexanone into caprolactam (intermediate $P$).
$3$. Caprolactam,when heated with water at $533-543 \ K$,undergoes ring-opening polymerization to form Nylon $-6$ (polymer $Q$).
$4$. Therefore,the correct option is $C$.

(D) The given monomer unit is caprolactam.
Caprolactam,when heated with water at high temperature,undergoes ring-opening polymerization to form Nylon-$6$.
The reaction is:
Caprolactam $\xrightarrow{H_2O, \Delta}$ Nylon-$6$.

(A) The polymerization of $1,3$-butadiene $(CH_2=CH-CH=CH_2)$ via free radical mechanism involves $1,4$-addition.
This results in the formation of polybutadiene,which can exist in two geometric isomeric forms due to the double bond in the polymer chain:
$1$. $cis$-$1,4$-polybutadiene (represented by structure $(i)$).
$2$. $trans$-$1,4$-polybutadiene (represented by structure $(ii)$).
Structure $(iii)$ represents a saturated chain which is not formed by the $1,4$-polymerization of $1,3$-butadiene.
Therefore,the possible products contain repeating units $(i)$ and $(ii)$.

(B) $PVC$ stands for Polyvinyl chloride.
It is formed by the addition polymerization of vinyl chloride monomer,which has the chemical formula $CH_2=CHCl$.

(B) The Ziegler-Natta catalyst is a mixture of titanium tetrachloride $(TiCl_4)$ and an organoaluminium compound like triethylaluminium $((C_2H_5)_3Al)$.
In the reaction mechanism,$TiCl_4$ is reduced by the organoaluminium compound to form an active species containing $Ti(III)$,which is $TiCl_3$ (or an alkylated derivative thereof).
This $TiCl_3$ species acts as the active site where the monomer coordinates and undergoes insertion into the metal-carbon bond to propagate the polymer chain.

(C) Neoprene,also known as polychloroprene,is a synthetic rubber produced by the free-radical polymerization of the monomer $2-$chloro$-1, 3-$butadiene (also known as chloroprene).
The chemical reaction is:
$n \ CH_2=C(Cl)-CH=CH_2 \rightarrow -[CH_2-C(Cl)=CH-CH_2]_n-$

(A) $PHBV$ stands for Poly-$\beta$-hydroxybutyrate-co-$\beta$-hydroxyvalerate.
It is a copolymer obtained by the polymerization of $3-$hydroxybutanoic acid and $3-$hydroxypentanoic acid.
Therefore,the correct option is $A$.

(B) $Nylon$ $6,6$ is a polyamide fibre obtained by the condensation polymerization of hexamethylene diamine $(H_2N(CH_2)_6NH_2)$ and adipic acid $(HOOC(CH_2)_4COOH)$.

(A) Bakelite is a thermosetting polymer formed by the condensation polymerization of phenol $(C_6H_5OH)$ and formaldehyde $(HCHO)$.
Therefore,the monomeric units of Bakelite are phenol and formaldehyde.

(C) Orlon,also known as polyacrylonitrile $(PAN)$,is a synthetic polymer formed by the polymerization of acrylonitrile (also known as vinyl cyanide).
The chemical reaction is: $n CH_2=CH(CN) \rightarrow -[CH_2-CH(CN)]_n-$.
Therefore,the monomer of Orlon is vinyl cyanide.

(C) Bakelite is a thermosetting polymer formed by the condensation reaction of phenol and formaldehyde in the presence of an acid or base catalyst.
In the initial stage,the reaction produces a linear polymer known as $Novolac$.
$Novolac$ is a linear chain of phenol units linked by methylene bridges.
Upon further heating with more formaldehyde,$Novolac$ undergoes cross-linking to form the infusible,hard,and rigid solid known as Bakelite.

(A) The given polymer structure is a poly($1$-alkene). By examining the repeating unit,we can identify the monomer. The backbone consists of a $2$-carbon chain with a $4$-carbon side chain (butyl group) attached to every other carbon atom. This corresponds to the polymerization of $1$-hexene $(CH_2=CH-CH_2-CH_2-CH_2-CH_3)$. The radical polymerization of $1$-hexene involves the opening of the double bond to form the polymer chain.

(B) . Styrene $(CH_2=CH-C_6H_5)$ and acrylonitrile $(CH_2=CH-CN)$ undergo addition polymerization in the presence of peroxide to form a copolymer.
The monomers link in a head-to-tail fashion,resulting in the following structure:
$n CH_2=CH(C_6H_5) + n CH_2=CH(CN) \xrightarrow{\text{Peroxide}} [CH_2-CH(C_6H_5)-CH_2-CH(CN)]_n$

(D) Teflon (polytetrafluoroethene) is an addition polymer formed by the free radical polymerization of its monomer,tetrafluoroethene $(CF_2 = CF_2)$.
In contrast,Terylene,Melamine polymer,and Nylon-$6, 6$ are condensation polymers formed by the elimination of small molecules like water or alcohol.

(C) Bakelite is a thermosetting polymer formed by the condensation polymerization of phenol and formaldehyde $(HCHO)$ in the presence of an acid or base catalyst.
The reaction involves the formation of ortho- and para-hydroxybenzyl alcohol derivatives,which further undergo cross-linking to form the complex structure of Bakelite.

(B) Chain growth polymerization involves the addition of monomers to the active site of a growing polymer chain,typically through free radical,cationic,or anionic mechanisms.
$Polystyrene$ is formed by the addition polymerization of styrene monomers,which is a classic example of chain growth polymerization.
$Nucleic$ $acid$,$protein$,and $starch$ are natural polymers formed through step-growth (condensation) polymerization.

(C) Bakelite is a thermosetting phenol-formaldehyde resin.
It is obtained by the condensation polymerization of phenol and formaldehyde in the presence of an acid or base catalyst.

(A) Step $1$: Hydrolysis of the starting material. The starting material is $4$-methoxyphenyl acetate. Treatment with $dil. \ HCl$ and heat causes hydrolysis of the ester group,yielding $4$-methoxyphenol.
Step $2$: Polymerization. The $4$-methoxyphenol is then reacted with oxalic acid $(COOH)_2$. This is a condensation polymerization reaction where the phenolic $-OH$ groups react with the carboxylic acid groups of oxalic acid to form a polyester linkage. The resulting polymer contains the $4$-methoxyphenyl unit linked via ester bonds.

(C) The starting material is $6$-aminohexanoic acid $(H_2N-(CH_2)_5-COOH)$.
$(i)$ Treatment with $NaNO_2/H_3O^+$ converts the amino group to a hydroxyl group,forming $6$-hydroxyhexanoic acid $(HO-(CH_2)_5-COOH)$.
(ii) Polymerization of $6$-hydroxyhexanoic acid via self-esterification results in the polyester polycaprolactone,which has the repeating unit $[ -O-(CH_2)_5-C(=O)- ]_n$.

(D) $4-$hydroxybutanoic acid $(HO-CH_2-CH_2-CH_2-COOH)$ undergoes self-condensation polymerization to form a polyester.
During this process,a water molecule is eliminated from each monomer unit.
The resulting repeating unit is $-[C(=O)-(CH_2)_3-O]_n-$.

(A) Nylon $6, 6$ is a polyamide formed by the condensation polymerization of two monomers:
$1$. Adipic acid: $HOOC(CH_2)_4COOH$
$2$. Hexamethylene diamine: $H_2N(CH_2)_6NH_2$
Therefore,the correct option is $A$.

(B) Step $1$: Dehydrohalogenation of $1-(4-chlorophenyl)-2-chloropropane$ with alcoholic $KOH$ leads to the formation of $1-(4-chlorophenyl)prop-1-ene$ via an $E2$ elimination mechanism.
Step $2$: The resulting alkene,$1-(4-chlorophenyl)prop-1-ene$,undergoes free radical polymerization to form the corresponding polymer. The structure of the polymer is formed by the addition of the monomer units,resulting in a backbone with a methyl group and a $4-chlorophenyl$ substituent on adjacent carbons.

(A) Nylon $-6,6$ is a condensation polymer formed by the reaction between hexamethylene diamine and adipic acid with the elimination of water molecules.
Buna $-S$,Teflon,and Neoprene are examples of addition polymers.

(B) Glyptal is a polyester formed by the condensation polymerization of ethylene glycol $(HO-CH_2-CH_2-OH)$ and phthalic acid $(C_6H_4(COOH)_2)$.
The reaction is as follows:
$n \ HO-CH_2-CH_2-OH + n \ C_6H_4(COOH)_2 \rightarrow \text{Glyptal} + 2n \ H_2O$
Thus,phthalic acid is treated with ethylene glycol to obtain glyptal.

(B) Step-growth polymerization involves the reaction of bifunctional or multifunctional monomers to form polymers with the elimination of small molecules like $H_2O$ or $CH_3OH$.
Polyesters,such as $Terylene$ (Dacron),are formed by the condensation polymerization of ethylene glycol and terephthalic acid,which is a classic example of step-growth polymerization.
Polyethylene,polypropylene,and polystyrene are addition polymers formed by chain-growth polymerization.

(C) The hydrolysis of dialkyldichlorosilane $(R_2SiCl_2)$ produces dialkylsilanediol $(R_2Si(OH)_2)$.
These silanediol molecules undergo condensation polymerization to form linear chain silicone polymers.
For $(CH_3)_2SiCl_2$:
$n(CH_3)_2SiCl_2 + 2nH_2O \rightarrow n(CH_3)_2Si(OH)_2 + 2nHCl$
$n(CH_3)_2Si(OH)_2 \rightarrow -[O-Si(CH_3)_2-O]_n- + nH_2O$
Thus,$(CH_3)_2SiCl_2$ is the correct precursor for linear chain polymers.

(A) Silicones are synthetic organosilicon polymers with the general formula $(R_2SiO)_n$.
They are prepared by the hydrolysis of dialkyldichlorosilanes,$R_2SiCl_2$.
The hydrolysis of $R_2SiCl_2$ yields a dihydroxy derivative,$R_2Si(OH)_2$,which undergoes polymerization to form silicones.
Therefore,the monomer unit is $R_2SiCl_2$.

(D) Bakelite is a thermosetting polymer formed by the condensation polymerization of phenol and formaldehyde $(HCHO)$ in the presence of an acid or base catalyst.

(B) The Lederer-Manasse reaction involves the reaction of phenol with formaldehyde in the presence of an acid or base catalyst.
This reaction leads to the formation of ortho- and para-hydroxybenzyl alcohols.
These hydroxybenzyl alcohols serve as the monomeric units for the polymerization process that produces Bakelite.
Among the given options,the structure corresponding to o-hydroxybenzyl alcohol is the correct monomeric unit.

(A) The chemical structure of $2-$chloro$-1,3-$butadiene is $CH_2=C(Cl)-CH=CH_2$.
This compound is commonly known as Chloroprene.
It is the monomer used for the preparation of the synthetic rubber known as Neoprene.

(A) Teflon (polytetrafluoroethylene) is a polymer formed by the addition polymerization of tetrafluoroethene $(CF_2=CF_2)$ monomers.
It is an addition polymer.

(A) The condensation polymerization of ethylene glycol $(HO-CH_2-CH_2-OH)$ and phthalic acid $(C_6H_4(COOH)_2)$ results in the formation of a polyester known as Glyptal.
This is a cross-linked polymer used in the manufacture of paints and lacquers.

(B) Polymers are classified into two types based on the mode of polymerization: $Addition$ and $Condensation$ polymers.
$Condensation$ polymers are formed through a condensation reaction,where monomers join together and eliminate small molecules as by-products,such as $H_2O$ or $CH_3OH$.
An $Addition$ polymer is formed by the simple linking of monomers without the loss of any small molecules.
Therefore,monomers can be converted to polymers by a condensation reaction between monomers.

(C) The Ziegler-Natta catalyst is a combination of an organometallic compound of a Group $1-3$ element (typically an alkyl aluminum compound like $R_3Al$) and a transition metal compound (typically a titanium compound like $TiCl_4$).
Thus,the correct composition is $R_3Al + TiCl_4$.

(A) Step-growth polymerization involves the reaction of bifunctional or multifunctional monomers to form polymers with the loss of small molecules like $H_2O$ or $HCl$.
Bakelite is a condensation polymer formed by the reaction of phenol and formaldehyde,which is a classic example of step-growth polymerization.
Polyethylene,Teflon,and $PVC$ are addition polymers formed by chain-growth polymerization.

(B) Condensation polymers are formed by the repeated condensation reaction between two different bi-functional or tri-functional monomeric units,usually with the elimination of small molecules like $H_2O$,$HCl$,or $CH_3OH$.
$Terylene$ (also known as $Dacron$) is a condensation polymer formed by the polymerization of ethylene glycol and terephthalic acid.
$PVC$,$Polypropylene$,and $Polystyrene$ are all examples of addition polymers.