General methods of preparation and mechanism of polymerisation Questions in English

(C) Novolac is a linear polymer formed by the condensation polymerization of $Phenol$ and $Methanal$ (formaldehyde) in the presence of an acid catalyst.
The reaction involves the initial formation of $o$- or $p$-hydroxybenzyl alcohol derivatives,which then undergo condensation to form a linear chain structure known as Novolac.
Therefore,the correct monomers are $Phenol$ and $Methanal$.

(C) Dacron is manufactured by heating a mixture of ethylene glycol and terephthalic acid at $420-460 \ K$ in the presence of zinc acetate-antimony trioxide catalyst.

(C) Neoprene is a synthetic rubber formed by the free radical polymerization of chloroprene ($2$-chlorobuta-$1,3$-diene).
The chemical reaction is as follows:
$n \ CH_2=C(Cl)-CH=CH_2 \xrightarrow{\text{polymerization}} [-CH_2-C(Cl)=CH-CH_2-]_n$
Thus,chloroprene is the monomer used for the preparation of neoprene.

(A) Dextron (also known as Dexon) is a biodegradable polymer formed by the copolymerization of lactic acid $(CH_3CH(OH)COOH)$ and glycolic acid $(HOCH_2COOH)$.
This reaction involves the elimination of water molecules to form an ester linkage,resulting in a polyester copolymer.
The chemical reaction is:
$n \ CH_3-CH(OH)-COOH + n \ HO-CH_2-COOH \rightarrow -[O-CH(CH_3)-CO-O-CH_2-CO]_n- + 2n \ H_2O$
Thus,the correct monomers are lactic acid and glycolic acid.

(D) High density polythene (or plastic) is prepared by heating ethylene at about $330-350 \ K$,under a pressure of $1-2 \ atm$ and in the presence of Ziegler-Natta catalyst.
$n \ CH_2=CH_2 \xrightarrow[\text{Ziegler-Natta catalyst}]{330-350 \ K, 1-2 \ atm} (-CH_2-CH_2-)_n$
High density polythene.

(A) Terylene (also known as Dacron) is a condensation polymer formed by the reaction between ethylene glycol $(HO-CH_2-CH_2-OH)$ and terephthalic acid $(C_6H_4(COOH)_2)$.
The polymerization reaction is represented as:
$n \ HO-CH_2-CH_2-OH + n \ HOOC-C_6H_4-COOH \rightarrow -[O-CH_2-CH_2-O-CO-C_6H_4-CO]_n- + 2n \ H_2O$
From the stoichiometry of the reaction,$n$ moles of ethylene glycol react with $n$ moles of terephthalic acid.
Therefore,for $1$ mole of terephthalic acid,$1$ mole of ethylene glycol is required.

(C) $n HOCH_2-CH_2OH + n HOOC-C_6H_4-COOH \rightarrow HOCH_2CH_2O[OC-C_6H_4-CO-O-CH_2-CH_2-O]_{n-1} OC-C_6H_4-COOH + n H_2O$
Terylene (also known as $Dacron$ or $Terene$) is a condensation polymer formed by the reaction between ethylene glycol and terephthalic acid. It is widely used as a synthetic fibre.

(A) Novolac is a linear polymer formed by the condensation polymerization of phenol and formaldehyde in the presence of an acid or base catalyst.
The reaction involves the formation of $o-$ or $p-$hydroxymethylphenol intermediates,which then undergo further condensation to form the linear polymer Novolac.

(B) Condensation polymerisation occurs when monomers containing two or more functional groups (such as $-NH_2$ and $-COOH$) react,resulting in the loss of small molecules like $H_2O$,$HCl$,etc.
Glycine $(NH_2CH_2COOH)$ contains both an amino group $(-NH_2)$ and a carboxylic acid group $(-COOH)$. Therefore,it can undergo condensation polymerisation to form polyglycine.
Styrene,isoprene,and propene contain carbon-carbon double bonds and undergo addition polymerisation.

(C) Ziegler-Natta catalyst is a mixture of $TiCl_4$ and $Al(C_2H_5)_3$ (titanium tetrachloride and triethylaluminium).
It is specifically used in the polymerization of ethene to produce high-density polythene $(HDP)$.
This process occurs at a temperature of $333 \ K$ to $343 \ K$ under a pressure of $6-7 \ atm$.

(C) $Buna-S$ rubber is a copolymer of $1,3-butadiene$ and styrene.
It is prepared by the polymerization of $1,3-butadiene$ $(75 \%)$ and styrene $(25 \%)$ in the presence of sodium $(Na)$ as a catalyst.
Thus,the $s$-block element used is $Na$.

(D) The Ziegler-Natta catalyst,which is a mixture of $TiCl_4$ and $(C_2H_5)_3Al$,is specifically used in the production of $High \ density \ polythene$ $(HDPE)$.
This catalyst allows for the polymerization of ethene at low pressure and temperature,resulting in a linear polymer chain with high density and strength.

(B) The reaction $nClCH=CH_2 \xrightarrow{X} Y$ represents the polymerization of vinyl chloride to form polyvinyl chloride $(PVC)$.
$X$ is the initiator,which is benzoyl peroxide,represented as $(C_6H_5COO)_2$.
$Y$ is the polymer formed,which is polyvinyl chloride $(PVC)$.
Polyvinyl chloride is a thermoplastic polymer because it softens on heating and hardens on cooling.
Therefore,the correct pair is $X = (C_6H_5COO)_2$ and $Y = \text{thermoplastic polymer}$.

(A) In the anionic polymerisation of $C_6H_5-CH=CH_2$ initiated by $RLi$,the active species is a carbanion,$C_6H_5-CH^{-}-CH_2R$.
Since there is no mechanism for the termination of these carbanions (unlike free radical or cationic polymerisation where termination occurs via coupling,disproportionation,or chain transfer),the chain continues to grow until the monomer is consumed.
This is known as 'living polymerisation',where the chain termination step is effectively absent.

(B) Chain-growth polymerization is a process where unsaturated monomer molecules add to the active site of a growing polymer chain one at a time.
Growth of the polymer occurs only at one or more active ends.
Addition of each monomer unit regenerates the active site.
Examples include polyethylene,polypropylene,polyvinyl chloride $(PVC)$,and $Teflon$.
Bakelite,$Nylon$,and $Terylene$ are examples of step-growth polymers.
Hence,option $(B)$ is correct.

(D) Anionic polymerisation involves the formation of a carbanion as the active species.
Alkyl lithium compounds,such as $R^-Li^+$,act as effective chain initiators because they provide a nucleophilic carbanion $(R^-)$ that attacks the monomer to initiate the polymerisation process.
$BF_3$ is a Lewis acid used in cationic polymerisation,while $(CH_3CO)_2O_2$ is a peroxide used in free radical polymerisation.

(D) In ionic polymerisation,the chain initiation involves the formation of ions or ion pairs at the active center.
$NaNH_2$ acts as an initiator for anionic polymerisation,while $SnCl_2$ and $AlCl_3$ are Lewis acids that can act as initiators for cationic polymerisation.
$(C_6H_5CO)_2O_2$ (benzoyl peroxide) is a covalent compound that undergoes homolytic cleavage to produce free radicals.
Therefore,it is used as an initiator in free radical polymerisation,not in ionic polymerisation.

(B) Bakelite is a condensation polymer formed by the reaction of phenol and formaldehyde $(HCHO)$.
Melamine-formaldehyde polymer is formed by the condensation polymerization of melamine and formaldehyde $(HCHO)$.
Therefore,formaldehyde $(HCHO)$ is the common monomer for both Bakelite and Melamine-formaldehyde polymers.

(A) Novolac is a linear polymer of phenol and formaldehyde.
It is prepared by the condensation polymerization of phenol and formaldehyde in the presence of an acid or base catalyst.
The initial step involves the formation of ortho- or para-hydroxybenzyl alcohol as the monomer '$x$'.
Specifically,$o$-hydroxybenzyl alcohol is the primary monomer that undergoes linear polymerization to form Novolac.

(B) In the reaction forming $Y$,the catalyst used is Ziegler-Natta catalyst ($(C_2H_5)_3Al$ and $TiCl_4$) at low pressure and temperature,which produces High Density Polyethylene $(HDP)$.
In the reaction forming $X$,the initiator used is a peroxide $((C_6H_5COO)_2)$ at high pressure and temperature,which produces Low Density Polyethylene $(LDP)$.
Therefore,$X$ is $LDP$ and $Y$ is $HDP$.
$LDP$ is used in the insulation of electricity-carrying wires and in the manufacture of squeeze bottles.
$HDP$ is used in the manufacture of containers like buckets,dustbins,bottles,and pipes.
Thus,option $B$ is correct.

(C) Neoprene (polychloroprene) is prepared by the free radical polymerisation of chloroprene ($2$-chloro-buta-$1,3$-diene) in the presence of a peroxide initiator like benzoyl peroxide,$(C_6H_5CO)_2O_2$.
The reaction is:
$n CH_2=C(Cl)-CH=CH_2 \xrightarrow{(C_6H_5CO)_2O_2} [-CH_2-C(Cl)=CH-CH_2-]_n$
Thus,option $C$ represents the correct polymerisation reaction.

(A) High-density polyethylene $(HDPE)$ is prepared using the Ziegler-Natta catalyst,which consists of $TiCl_4$ and $Et_3Al$.
$HDPE$ has a linear structure with a low degree of branching,which allows for close packing and higher density.
It is chemically inert and is typically prepared at a temperature range of $333 \ K$ to $343 \ K$ under $6-7 \ atm$ pressure.

(C) The reaction between $ethane-1,2-diol$ and $benzene-1,4-dicarboxylic$ acid (terephthalic acid) in the presence of a catalyst mixture of $zinc$ acetate and $antimony$ trioxide leads to the formation of $Terylene$ (also known as $Dacron$).
This is a condensation polymerization reaction.

(D) High density polyethylene $(HDP)$ is produced by the addition polymerization of ethene in a hydrocarbon solvent in the presence of a Ziegler-Natta catalyst.
This catalyst is a mixture of trialkylaluminium,such as $Al(CH_3)_3$,and titanium tetrachloride,$TiCl_4$.
This process occurs at a temperature of $333 \ K$ to $343 \ K$ and a pressure of $6-7 \ \text{atmospheres}$.
The resulting polymer consists of linear molecules,which allows for close packing and high density.

(C) The reaction between ethylene glycol $(HO-CH_2-CH_2-OH)$ and phthalic acid $(C_6H_4(COOH)_2)$ is a condensation polymerisation reaction.
This reaction leads to the formation of a polyester known as Glyptal.
Step-growth polymerisation refers to a type of polymerisation mechanism in which bi-functional or multifunctional monomers react to form first dimers,then trimers,longer oligomers,and eventually long-chain polymers.
Hence,the correct option is $C$.

(A) chain transfer agent is a substance that reacts with the growing polymer chain to terminate its growth while simultaneously initiating a new chain.
$CCl_4$ (carbon tetrachloride) acts as an effective chain transfer agent in vinyl polymerization because the $C-Cl$ bond is relatively weak,allowing for the abstraction of a chlorine atom by the growing radical,which terminates the original chain and creates a new radical species to continue the polymerization process.
Therefore,the correct option is $A$.

(C) The Ziegler-Natta catalyst,which consists of $TiCl_4$ and $(C_2H_5)_3Al$,is used for the industrial manufacture of high-density polyethylene $(HDPE)$.

(C) The monomer that can undergo polymerisation by all three mechanisms (free radical,cationic,and anionic) is $Styrene$ $(C_6H_5CH=CH_2)$.
$1$. Free radical polymerisation: The phenyl group stabilizes the radical intermediate.
$2$. Cationic polymerisation: The phenyl group stabilizes the carbocation intermediate through resonance.
$3$. Anionic polymerisation: The phenyl group stabilizes the carbanion intermediate through resonance.
Therefore,$Styrene$ is the correct answer.

(D) Bakelite is a thermosetting polymer formed by the condensation polymerization of phenol and formaldehyde in the presence of an acid or base catalyst.
During this process,the phenol molecules are linked together by methylene $(-CH_2-)$ bridges to form a cross-linked structure.

(A) Nylon $6,6$ is made by using step growth polymerization (also known as condensation polymerization).
In step growth polymerization,bifunctional or multifunctional monomers react to form dimers,which then react to form longer chain polymers.
Specifically,for Nylon $6,6$,hexamethylene diamine $(H_2N(CH_2)_6NH_2)$ and adipic acid $(HOOC(CH_2)_4COOH)$ react with each other to form a dimer,which then polymerizes into long chains with the elimination of water molecules.

(A) Condensation polymerization occurs between two bifunctional monomers,which results in the formation of a high molecular mass condensation polymer.
$Dacron$ (or $Terylene$) is obtained by the condensation polymerization of ethylene glycol $(HO-CH_2-CH_2-OH)$ and terephthalic acid $(HOOC-C_6H_4-COOH)$.
During this process,small molecules like water $(H_2O)$ are eliminated.
It is an example of a polyester.

(C) condensation polymer is formed by the repeated condensation reaction between two different bi-functional or tri-functional monomeric units,usually with the elimination of small molecules like $H_2O$,$HCl$,etc.
$1$. Bakelite is a cross-linked condensation polymer formed from phenol and formaldehyde.
$2$. Terylene is a condensation copolymer formed from ethylene glycol and terephthalic acid.
$3$. Nylon-$6$ is a condensation homopolymer formed by the ring-opening polymerization of caprolactam,which involves the elimination of water during the initial step of hydrolysis,and it is a homopolymer because it is made from a single type of monomer (caprolactam).
$4$. Nylon-$6,6$ is a condensation copolymer formed from hexamethylenediamine and adipic acid.
Therefore,Nylon-$6$ is the correct condensation homopolymer.

(C) Caprolactam on heating with water at $533-543 \ K$ undergoes ring-opening polymerization to form Nylon-$6$.
The reaction is:
$Caprolactam \xrightarrow[H_2O]{533-543 \ K} [CO-(CH_2)_5-NH]_n$
This polymer is known as Nylon-$6$. The structure of the repeating unit is $[CO-(CH_2)_5-NH]_n$.

(C) Ziegler-Natta catalyst is a mixture of $TiCl_4$ and $Al(C_2H_5)_3$.
It is specifically used for the polymerization of ethene to produce $HDPE$ (High Density Polythene) under low pressure conditions.

(D) Anionic polymerisation involves an anionic initiator that generates a carbanionic intermediate.
In this process,the active centre of the propagating species carries a negative charge.
Therefore,polymerisation occurs most readily with monomers containing electron-withdrawing groups $(EWG)$ such as nitrile $(-CN)$,phenyl,or carbonyl groups,which stabilize the negative charge on the propagating species through inductive or resonance effects.
Among the given options,the nitrile group $(-C\equiv N)$ is a strong electron-withdrawing group.
Thus,$CH_2=CH-CN$ (acrylonitrile) is the most reactive towards anionic polymerisation.

(A) Bakelite is a thermosetting phenol-formaldehyde resin formed by the condensation reaction of phenol with formaldehyde.
In the initial step,the reaction between phenol and formaldehyde involves the attack of an electrophile (derived from formaldehyde in the presence of an acid or base catalyst) on the electron-rich aromatic ring of phenol.
This process is an electrophilic aromatic substitution reaction,where the hydroxymethyl group $(-CH_2OH)$ is introduced at the ortho or para positions of the phenol ring.

(A) Melamine polymer (melamine-formaldehyde resin) is formed by the condensation polymerization of melamine and formaldehyde $(CH_2O)$.
The structure of melamine is a $1,3,5$-triazine ring with three amino groups attached at positions $2, 4,$ and $6$.
The reaction involves the formation of a resin intermediate through the reaction of the amino groups of melamine with formaldehyde.

(D) The copolymerisation of $1,3-$butadiene and phenylethene (styrene) results in the formation of Buna-$S$ (also known as $SBR$).
The reaction is as follows:
$n CH_2=CH-CH=CH_2 + n CH_2=CH(C_6H_5) \rightarrow -[CH_2-CH=CH-CH_2-CH_2-CH(C_6H_5)]_n-$
Hence,option $(d)$ is the correct answer.

(C) Buna-$S$ is a synthetic copolymer formed by the polymerization of two monomers:
$(I)$ $1,3-$butadiene $(CH_2=CH-CH=CH_2)$
$(II)$ Styrene $(C_6H_5-CH=CH_2)$
Thus,the correct option is $C$.

(B) Neoprene is a synthetic rubber formed by the polymerization of chloroprene.
Chloroprene is chemically known as $2-$chlorobuta$-1,3-$diene.
The reaction is as follows:
$n \ CH_2=C(Cl)-CH=CH_2 \xrightarrow{\text{Polymerization}} [-CH_2-C(Cl)=CH-CH_2-]_n$

(A) The catalyst used for the polymerization of olefins (such as ethylene) is the Ziegler-Natta catalyst.
It is typically a mixture of titanium tetrachloride $(TiCl_4)$ or titanium trichloride $(TiCl_3)$ and an organoaluminum compound like triethylaluminum $((C_2H_5)_3Al)$.

(A, B, D) For a process to be spontaneous,the Gibbs free energy change,$\Delta G$,must be negative.
Polymerization involves the association of monomer units into a long chain,which leads to a decrease in the randomness of the system,meaning $\Delta S$ is negative.
According to the Gibbs-Helmholtz equation,$\Delta G = \Delta H - T\Delta S$.
Since $\Delta G < 0$ and $\Delta S < 0$,for the process to be spontaneous,$\Delta H$ must be negative and its magnitude must be greater than $T\Delta S$.

(A) $Nylon-6,6$ is a synthetic polymer formed by the condensation polymerization of two monomers: hexamethylenediamine $(H_2N(CH_2)_6NH_2)$ and adipic acid $(HOOC(CH_2)_4COOH)$.
These two monomers undergo a condensation reaction to form the polyamide chain,releasing water molecules as a byproduct.