General methods of preparation and mechanism of polymerisation Questions in English

(C) Condensation polymerization involves the repeated loss of small molecules like $H_2O$,$HCl$,or $NH_3$ during the formation of the polymer chain.
Bakelite is a thermosetting polymer formed by the condensation reaction between phenol and formaldehyde.
Polyethylene,Teflon,and natural rubber are formed via addition polymerization.

(C) Cationic polymerization is initiated by the formation of a carbocation intermediate.
Therefore,the alkene that forms the most stable carbocation will be the most reactive towards cationic polymerization.
In $CH_2 = CH - C_6H_5$ (styrene),the carbocation formed is $CH_3 - CH^+ - C_6H_5$,which is highly stabilized by resonance with the phenyl group.
In contrast,the other options contain electron-withdrawing groups (like $-Cl$ or $-COOCH_3$) or only weak electron-donating groups (like $-CH_3$),which do not stabilize the carbocation as effectively as the phenyl group.

(B) In vinyl polymerization,a chain transfer agent is a substance that reacts with the growing polymer chain to terminate it,while simultaneously initiating a new chain. $CCl_4$ (Carbon tetrachloride) is a well-known chain transfer agent because the $C-Cl$ bond is relatively weak,allowing the chlorine atom to be abstracted by the growing radical,thereby terminating the original chain and creating a new $CCl_3$ radical to start a new chain. Therefore,the correct option is $B$.

(A) Anionic polymerization is initiated by a nucleophile (anion) attacking the double bond of the monomer.
For this reaction to occur,the monomer must have electron-withdrawing groups $(EWG)$ attached to the double bond to stabilize the resulting carbanion intermediate.
$CH_2=CH-CN$ and $CH_2=CH-C_6H_5$ have strong electron-withdrawing groups ($-CN$ and $-C_6H_5$ respectively) that stabilize the negative charge.
$CF_2=CF_2$ is also susceptible to anionic polymerization due to the strong inductive effect of fluorine atoms.
$CH_2=CH-CH_3$ (propene) contains an electron-donating methyl group $(-CH_3)$,which destabilizes the carbanion intermediate,making it the least reactive towards anionic polymerization.

(A) Addition polymerization involves the repeated addition of monomers containing double or triple bonds without the loss of any small molecules.
$PVC$ (Polyvinyl chloride) is formed by the addition polymerization of vinyl chloride $(CH_2=CHCl)$.
$Nylon$,$Terylene$,and $Polyamide$ are formed through condensation polymerization,which involves the elimination of small molecules like $H_2O$ or $CH_3OH$.

(C) Anionic addition polymerization occurs when the monomer contains electron-withdrawing groups that stabilize the carbanion intermediate. $Styrene$ $(C_6H_5CH=CH_2)$ is a classic example of a monomer that undergoes anionic polymerization because the phenyl group stabilizes the negative charge through resonance. Therefore,$Polystyrene$ is formed by this mechanism.

(D) Free radical addition polymerization is initiated by the presence of a free radical initiator. $Acetyl \ peroxide$,$benzoyl \ peroxide$,or $tert-butyl \ peroxide$ are commonly used as initiators in this process. These compounds undergo homolytic fission to generate free radicals,which then initiate the polymerization of monomers like ethene or styrene.

(C) The Ziegler-Natta catalyst is a mixture of an organometallic compound of a Group $1-3$ element (typically an alkyl aluminum compound like $Al(C_2H_5)_3$) and a transition metal compound (typically a titanium compound like $TiCl_4$).
It is widely used in the polymerization of alkenes,such as the production of high-density polyethylene $(HDPE)$.
Therefore,the correct combination is $Al(C_2H_5)_3 + TiCl_4$.

(B) Polyvinyl alcohol cannot be prepared directly by the polymerization of vinyl alcohol because vinyl alcohol is unstable and tautomerizes to acetaldehyde.
It is commercially prepared by the alkaline hydrolysis (or alcoholysis) of polyvinyl acetate.
The reaction is: $(CH_2-CH(OCOCH_3))_n + nH_2O \xrightarrow{OH^-} (CH_2-CH(OH))_n + nCH_3COOH$.

(A) $PMMA$ stands for Polymethyl methacrylate. It is formed by the polymerization of the monomer methyl methacrylate $(CH_2=C(CH_3)COOCH_3)$.

(D) Glyptal is a polyester resin formed by the condensation polymerization of ethylene glycol $(HO-CH_2-CH_2-OH)$ and phthalic acid $(C_6H_4(COOH)_2)$.
The reaction involves the elimination of water molecules to form the polymer chain.

(C) $Nylon-66$ is a polyamide formed by the condensation polymerization of two monomers: $Hexamethylenediamine$ $(H_2N-(CH_2)_6-NH_2)$ and $Adipic \text{ } acid$ $(HOOC-(CH_2)_4-COOH)$.
Therefore,the correct option is $C$.

(D) Caprolactam is heated with water at high temperature $(533-543 \ K)$ to undergo ring-opening polymerization.
This process results in the formation of Nylon-$6$.

(A) The polymerization of olefins (like ethylene or propylene) to produce high-density polyethylene or polypropylene is carried out using the $Ziegler-Natta$ catalyst.
This catalyst is typically a mixture of a transition metal compound,such as $TiCl_4$,and an organometallic compound,such as $Al(C_2H_5)_3$ (triethylaluminium).

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

(A) Ethylene glycol $(HO-CH_2-CH_2-OH)$ is a monomer used in the synthesis of the polyester polymer known as $Dacron$ (also called $Terylene$).
It reacts with terephthalic acid through a condensation polymerization process to form the polymer.

(B) Teflon is a synthetic fluoropolymer of tetrafluoroethene. Its chemical formula is $(CF_2=CF_2)_n$. The monomer unit is tetrafluoroethene $(CF_2=CF_2)$.

(A) Terylene (also known as Dacron) is a polyester fiber. It is prepared by the condensation polymerization of terephthalic acid $(C_6H_4(COOH)_2)$ and ethylene glycol $(HO-CH_2-CH_2-OH)$.
The reaction is as follows:
$n \ HOOC-C_6H_4-COOH + n \ HO-CH_2-CH_2-OH \rightarrow [-CO-C_6H_4-CO-O-CH_2-CH_2-O-]_n + 2n \ H_2O$

(A) The reaction between phenol and formaldehyde to form Bakelite is a step-growth polymerization process. The initial step involves the electrophilic attack of formaldehyde (in the presence of an acid or base catalyst) on the ortho or para positions of the phenol ring. Since the phenol ring is electron-rich,it undergoes $Aromatic \ electrophilic \ substitution$ to form ortho-hydroxybenzyl alcohol or para-hydroxybenzyl alcohol.

(A) Neoprene is a synthetic rubber formed by the polymerization of chloroprene ($2$-chloro-$1,3$-butadiene). The chemical formula for chloroprene is $CH_2=C(Cl)-CH=CH_2$.

(B) Orlon,also known as polyacrylonitrile $(PAN)$,is a synthetic polymer.
It is prepared by the polymerization of acrylonitrile monomer.
The chemical formula for acrylonitrile is $CH_2 = CH-CN$.

(C) Teflon (polytetrafluoroethene) is prepared by the free radical polymerization of tetrafluoroethene $(CF_2=CF_2)$.
This reaction is carried out in the presence of a high pressure and a catalyst such as ammonium persulphate or a peroxide initiator.
Therefore,the correct catalyst used is persulphate.

(A) Chain transfer agents are substances that react with the growing polymer chain to terminate its growth,thereby initiating a new chain.
This process limits the average molecular mass of the polymer.
Among the given options,$CCl_4$ acts as a chain transfer agent in radical polymerization because the $C-Cl$ bond is relatively weak and can easily undergo homolytic cleavage to transfer a chlorine atom to the growing radical chain.

(B) Vinyl alcohol is unstable and tautomerizes to acetaldehyde. Therefore,it cannot be polymerized directly. Polyvinyl alcohol is prepared by the alkaline hydrolysis (or alcoholysis) of polyvinyl acetate. The reaction is: $-(CH_2-CH(OCOCH_3))_n- + nH_2O \xrightarrow{OH^-} -(CH_2-CH(OH))_n- + nCH_3COOH$.

(A) Nylon $-66$ is a polyamide formed by the condensation polymerization of adipic acid $(HOOC(CH_2)_4COOH)$ and hexamethylenediamine $(H_2N(CH_2)_6NH_2)$.
Therefore,the correct set of compounds is $HOOC(CH_2)_4COOH + H_2N(CH_2)_6NH_2$.

(C) The formation of Bakelite involves the reaction between phenol and formaldehyde.
Initially,formaldehyde undergoes electrophilic substitution on the benzene ring of phenol to form ortho- or para-hydroxybenzyl alcohol.
Subsequently,these intermediate molecules undergo condensation polymerization involving the loss of water molecules (dehydration) to form the cross-linked polymer known as Bakelite.

(N/A) Polymerisation is the process of forming high molecular mass $(10^{3} - 10^{7} \ u)$ macromolecules,which consist of repeating structural units derived from monomers. In a polymer,various monomer units are joined by strong covalent bonds.

(N/A) The polymerisation reaction in which a mixture of more than one monomeric species is allowed to polymerise and form a copolymer which contains units of both species is called copolymerisation. The process of forming polymer $Buna-S$ from $1,3-butadiene$ and $styrene$ is an example of copolymerisation.
$n CH_2=CH-CH=CH_2 + n C_6H_5CH=CH_2 \xrightarrow{\text{Copolymerisation}} [CH_2-CH=CH-CH_2-CH(C_6H_5)]_n$ $(Buna-S)$
$Nylon-6,6$ is also a copolymer formed by $hexamethylenediamine$ and $adipic acid$.
$n H_2N(CH_2)_6NH_2 + n HOOC(CH_2)_4COOH \to [NH(CH_2)_6NHCO(CH_2)_4CO]_n + 2n H_2O$ $(Nylon-6,6)$

(N/A) The polymerization of ethene to polythene involves a free radical mechanism initiated by benzoyl peroxide. The process occurs in three steps:
$1$. Chain Initiation Step:
Benzoyl peroxide decomposes to form phenyl radicals,which then react with ethene to form a new radical.
$(C_6H_5COO)_2 \to 2C_6H_5COO\cdot \to 2C_6H_5\cdot + 2CO_2$
$C_6H_5\cdot + CH_2=CH_2 \to C_6H_5-CH_2-\dot{C}H_2$
$2$. Chain Propagating Step:
The radical reacts with more ethene molecules to grow the chain.
$C_6H_5-CH_2-\dot{C}H_2 + n(CH_2=CH_2) \to C_6H_5-(CH_2-CH_2)_n-CH_2-\dot{C}H_2$
$3$. Chain Terminating Step:
Two long-chain radicals combine to form the final polymer.
$C_6H_5-(CH_2-CH_2)_n-CH_2-\dot{C}H_2 + \dot{C}H_2-CH_2-(CH_2-CH_2)_n-C_6H_5 \to C_6H_5-(CH_2-CH_2)_n-CH_2-CH_2-CH_2-CH_2-(CH_2-CH_2)_n-C_6H_5$

(N/A) One common initiator used in free radical addition polymerization is benzoyl peroxide. Its structure is as follows:
$C_6H_5-CO-O-O-CO-C_6H_5$

(N/A) Dacron (also known as Terylene) is obtained by the condensation polymerisation of ethylene glycol and terephthalic acid at high temperatures in the presence of a catalyst (zinc acetate-antimony trioxide).
The chemical reaction is as follows:
$n \ HOCH_2-CH_2OH + n \ HOOC-C_6H_4-COOH$ $\xrightarrow{\Delta, \text{catalyst}} -[OCH_2-CH_2-O-CO-C_6H_4-CO]_n- + 2n \ H_2O$

In this type of polymerization,molecules of the same or different monomers add together on a large scale to form a polymer.
The monomers used are unsaturated compounds,e.g.,alkenes,alkadienes,and their derivatives.
This mode of polymerization leads to an increase in chain length,and chain growth can occur through the formation of free radicals or ionic species.
Free radical mechanism: $A$ variety of alkenes or dienes and their derivatives are polymerized in the presence of a free radical generating initiator (catalyst) like benzoyl peroxide,acetyl peroxide,$tert-butyl$ peroxide,etc.
For example,the polymerization of ethene to polythene consists of heating or exposing to light a mixture of ethene with a small amount of benzoyl peroxide initiator.
$1$. Chain initiation step: The process starts with the addition of a phenyl free radical,formed by the peroxide,to the ethene double bond,generating a new and larger free radical.
$C_6H_5-CO-O-O-CO-C_6H_5$ $\rightarrow 2C_6H_5-CO-O^{\bullet}$ $\rightarrow 2C_6H_5^{\bullet} + 2CO_2$
$C_6H_5^{\bullet} + CH_2=CH_2 \rightarrow C_6H_5-CH_2-\dot{C}H_2$
$2$. Chain propagating step: As this radical reacts with another molecule of ethene,a larger radical is formed. The repetition of this sequence carries the reaction forward.
$C_6H_5-CH_2-\dot{C}H_2 + n(CH_2=CH_2) \rightarrow C_6H_5-(CH_2-CH_2)_n-CH_2-\dot{C}H_2$
$3$. Chain terminating step: At some stage,the product radical reacts with another radical to form the polymerized product.
$C_6H_5-(CH_2-CH_2)_n-CH_2-\dot{C}H_2 + C_6H_5-(CH_2-CH_2)_n-CH_2-\dot{C}H_2$ $\rightarrow C_6H_5-(CH_2-CH_2)_n-CH_2-CH_2-CH_2-CH_2-(CH_2-CH_2)_n-C_6H_5$

(N/A) Condensation polymerization involves repetitive condensation reactions between two different bi-functional or tri-functional monomeric units.
These polycondensation reactions often result in the elimination of small molecules such as $H_2O$,$ROH$,or $HCl$,leading to the formation of high molecular mass condensation polymers.
In these reactions,the product of each step is again a bi-functional species,and the condensation sequence continues.
Since each step produces a distinct functionalized species and is independent of others,this process is also called step-growth polymerization.
Example: The formation of Terylene (or Dacron) by the interaction of ethylene glycol and terephthalic acid.
$nHO-CH_2-CH_2-OH + nHOOC-C_6H_4-COOH \rightarrow -[O-CH_2-CH_2-O-CO-C_6H_4-CO]_n- + 2nH_2O$

(N/A) Step-growth polymerization generally involves a repetitive condensation reaction between two different bi-functional or tri-functional monomeric units.
These polycondensation reactions may result in the loss of simple molecules such as $H_2O$,$ROH$,$HCl$,etc.,and lead to the formation of high molecular mass condensation polymers.
In these reactions,the product of each step is again a bi-functional species,and the sequence of condensation continues.
Since each step produces a distinct functionalized species and is independent of others,this process is called step-growth polymerization.
The formation of Terylene or Dacron by the interaction of ethylene glycol and terephthalic acid is an example of this type of polymerization:
$nHO-CH_2-CH_2-OH + nHOOC-C_6H_4-COOH \rightarrow -[O-CH_2-CH_2-O-CO-C_6H_4-CO]_n- + 2nH_2O$

(N/A) Definition: Polymerisation is a process in which a large number of small monomer molecules combine together under high temperature,high pressure,and in the presence of a catalyst to form a large molecule called a polymer.
$(b)$ Examples:
$(i)$ Polymerisation of ethene $(nCH_2=CH_2)$ at $473-673 \ K$ under high pressure and catalyst forms polyethene $(-(CH_2-CH_2)-_n)$.
$(ii)$ Polymerisation of propene $(nCH_3-CH=CH_2)$ under high temperature and pressure yields polypropene $(-(CH(CH_3)-CH_2)-_n)$.
$(c)$ Uses: Polymers are used for the manufacture of plastic bags,squeeze bottles,refrigerator dishes,toys,pipes,radio and $T$.$V$. cabinets,etc. Polypropene is used for the manufacture of milk crates,plastic buckets,and other moulded articles.
Limitations: Though these materials have now become common,excessive use of polythene and polypropylene is a matter of great environmental concern.

(N/A) Definition: Polymerization is a process in which a large number of small monomer molecules combine to form a large macromolecule called a polymer under high temperature,high pressure,and in the presence of a catalyst.
$(b)$ Examples:
$(i)$ Polymerization of ethene: $nCH_2=CH_2 \xrightarrow[\text{High pressure, catalyst}]{473-673 \ K, O_2} (-CH_2-CH_2-)_n$ (Polythene)
$(ii)$ Polymerization of propene: $nCH_3-CH=CH_2 \xrightarrow[\text{High pressure, catalyst}]{\text{High temperature}} (-CH(CH_3)-CH_2-)_n$ (Polypropene)
$(c)$ Uses: Polymers are used for the manufacture of plastic bags,squeeze bottles,refrigerator dishes,toys,pipes,radio and $T$.$V$. cabinets,etc. Polypropene is used for the manufacture of milk crates,plastic buckets,and other moulded articles.
Limitations: Though these materials have now become common,excessive use of polythene and polypropylene is a matter of great concern for the environment.

(N/A) Nylon-$2$-nylon-$6$ is an alternating polyamide copolymer prepared by the condensation polymerization of glycine $(H_{2}N-CH_{2}-COOH)$ and amino caproic acid $(H_{2}N-(CH_{2})_{5}-COOH)$.
The reaction is as follows:
$n H_{2}N-CH_{2}-COOH + n H_{2}N-(CH_{2})_{5}-COOH \rightarrow -[NH-CH_{2}-CO-NH-(CH_{2})_{5}-CO]_{n}- + 2n H_{2}O$
It is a biodegradable polymer.

(A) The given reaction represents chain growth polymerization. In this process,the polymer chain grows by the addition of monomer units to the active site without the loss of any small molecules like $H_2O$ or $CH_3OH$. The reaction $-(A)_m + -(A)_n \to -(A)_{m+n}$ indicates the simple addition of two chains or units,which is characteristic of chain growth polymerization.

(N/A) The resin intermediate is prepared by the reaction of $Melamine$ with $Formaldehyde$ $(HCHO)$.
This reaction involves the nucleophilic addition of the amino group of $Melamine$ to the carbonyl group of $Formaldehyde$.
The resulting resin intermediate undergoes further polymerization to form the $Melamine-Formaldehyde$ polymer (also known as $Melamine$ resin).
The process is shown below:
$Melamine + HCHO$ $\rightarrow \text{Resin intermediate}$ $\xrightarrow{\text{Polymerization}} \text{Melamine polymer}$

(N/A) Benzoyl peroxide acts as a free radical initiator in the addition polymerization of alkenes. It undergoes homolytic fission to produce free radicals,which then initiate the polymerization process. The mechanism involves three steps:
$(i)$ Chain initiation step:
$C_6H_5-CO-O-O-CO-C_6H_5$ $\rightarrow 2C_6H_5-CO-O$ $\rightarrow 2C_6H_5^{\bullet} \text{ (Phenyl radical)}$
$(ii)$ Chain propagation step:
$C_6H_5^{\bullet} + CH_2=CH_2$ $\rightarrow C_6H_5-CH_2-CH_2^{\bullet}$ $\rightarrow C_6H_5-(CH_2-CH_2)_n-CH_2-CH_2^{\bullet}$
$(iii)$ Chain termination step:
$2C_6H_5-(CH_2-CH_2)_n-CH_2^{\bullet}$ $\rightarrow C_6H_5-(CH_2-CH_2)_n-CH_2-CH_2-CH_2-CH_2-(CH_2-CH_2)_n-C_6H_5 \text{ (Polythene)}$

(N/A) During free radical polymerization,monomers must be very pure because even trace amounts of impurities can act as chain inhibitors. These inhibitors react with the free radicals,terminating the chain growth prematurely,which leads to the formation of polymers with shorter chain lengths and lower molecular weights.

(A) . Nylon $-6, 6$ is formed by the condensation polymerization of hexamethylenediamine and adipic acid. Thus,$A-iv$.
$B$. $PVC$ (polyvinyl chloride) is formed by the free radical polymerization of vinyl chloride monomer. Thus,$B-i$.
$C$. $HDP$ (high-density polyethylene) is prepared using Ziegler-Natta catalyst (coordination polymerization). Thus,$C-ii$.
Therefore,the correct match is $A-iv, B-i, C-ii$.

(N/A) $(1)$ Conversion of $2-$bromopropane to $1-$bromopropane:
$CH_3CHBrCH_3$ $\xrightarrow{KOH(alc.)} CH_3CH=CH_2$ $\xrightarrow{HBr, \text{peroxide}} CH_3CH_2CH_2Br$
$(2)$ Conversion of calcium carbide to polythene:
$CaC_2 + 2H_2O \rightarrow HC \equiv CH + Ca(OH)_2$
$HC \equiv CH + H_2 \xrightarrow{Pd} CH_2=CH_2$
$n(CH_2=CH_2) \xrightarrow{\text{polymerisation}} (-CH_2-CH_2-)_n$

(A) 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 $H_2O$,$HCl$,etc.
Bakelite,Nylon $6$,and Nylon $6,6$ are all examples of condensation polymers.
Buna-$N$ is formed by the copolymerization of $1,3$-butadiene and acrylonitrile in the presence of a peroxide catalyst. It is an addition polymer,not a condensation polymer.

(B) The given reaction sequence represents the synthesis of $Nylon-6$.
Cyclohexanone oxime undergoes a Beckmann rearrangement in the presence of $H_2SO_4$ to form $Caprolactam$ $(X)$.
$Caprolactam$ is then heated at $540 \ K$ to undergo ring-opening polymerization to form $Nylon-6$.
Thus,$X$ is $Caprolactam$.

(A) The given polymer is polyisobutylene,which is formed by the polymerization of $2$-methylpropene (isobutylene).
The structure of the monomer is $CH_3-C(CH_3)=CH_2$.

(A) Novolac is a linear polymer of phenol and formaldehyde. On heating with formaldehyde,it undergoes cross-linking to form an infusible solid mass known as Bakelite.

(C) Novolac is a linear polymer formed by the condensation polymerization of phenol and formaldehyde.
In the initial step,the reaction between phenol and formaldehyde yields a mixture of $o-$ and $p-$hydroxymethylphenol derivatives.
These derivatives act as the monomers that undergo further condensation to form the linear polymer known as Novolac.
Therefore,$o-$hydroxymethylphenol is the monomeric unit involved in the formation of Novolac.

(A) Teflon is an addition polymer formed by the addition polymerisation of tetrafluoroethene $(CF_2=CF_2)$.
The reaction is as follows:
$n \ CF_2=CF_2 \xrightarrow{\text{Polymerisation}} [-CF_2-CF_2-]_n$
Nylon-$6,6$,Novolac,and Dacron are condensation polymers.

(A) Melamine polymer,also known as melamine-formaldehyde resin,is formed by the condensation polymerization of melamine and formaldehyde $(HCHO)$.
The reaction involves the formation of a resinous material through the elimination of water molecules.