Chemistry of polymers

Lecture note on DSE-4(Polymer chemistry) by Dr. Dulal Chandra Maiti, Associate Professor of Chemistry, Bajkul Milani Mahavidyalaya, West Bengal

1.1 Macromolecule:

The term “macromolecule” was coined by Nobel laureate Hermann Staudinger in the 1920s . Large molecules with diameter ranging from 100 to 10 000 angstroms that may or may not have large number of repeating units are called macro molecules. Lipids, proteins, nucleic acids, silk, polyethenes and resins are some examples of macro molecules. Lipids are composed of smaller sub units like glycerol and fatty acids joined by ester linkages: CH2OCOR-CHOCOR-CH2OCOR

1.2 Polymer:

The term "polymer" was coined in 1833 by Jöns Jakob Berzelius.The word polymer is acombination of two greek words poly means ‘many’ and meros means ‘parts or units’. A polymer is a type of macromolecules that is composed of a large number of repeating units or mers. Proteins, carbohydrates and nucleic acids are some examples of polymers as these are made of repeating units. Proteins (–NHCHRCO-)n are composed of large number of smaller sub units of same type, –NHCHRCO- , known as repeating unit derived from small molecules like amino acid NH2CHRCOOH, known as monomers.

Table-1. Difference between polymer and macromolecule

Polymers MacromoleculesPolymers refers to large molecules that are built from smaller subunits of same type

Macromolecules refers to large molecules that are built from smaller subunits

Polymers are composed of repeating units i.e. monomers

Macromolecules may or may not be composed of repeating units

Polymers are formed essentially from polymerization.

Macromolecules may form in different ways

Some polymers are soluble in organic solvents Most macromolecules are highly insoluble in water and other similar solvents.

All polymers are macromolecules All macromolecules may not be polymersProteins, nucleic acid etc are polymers Lipids, proteins, nucleic acid etc are

macromolecules

Some examples of polymers: i)DNA: the monomers are all nucleotides. ii) Proteins: the monomers are all amino acids iii) Carbohydrates: the monomers are all simple sugars

Example of macromolecule: Triglycerides (fat): made of glycerol backbone and several fatty acid chains.

1.3 Repeating unit and Monomer: Smallest structural unit which is repeated by covalent bond to form the polymer is called repeating unit. Simple reactive molecules from which repeating units are derived are called monomers. For example Ethylene,CH2=CH2 is the monomer and –CH2-CH2- is the repeating unit of polyethene–(-CH2-CH2- )-n

Table-1. Polymers and their repeating unit and monomers

Monomers Repeating unit Polymer structure PolymerEthene CH2=CH2 –CH2-CH2- –(-CH2-CH2- )-n PolyetheneVinyl chloride CH2=CHCl –CH2-CHCl- –(-CH2-CHCl- )-n Polyvinylchloride

(PVC)Cis-isoprene CH2=CMe- CH=CH2

-CH2-CMe=CH-CH2- -(CH2-CMe=CH-CH2)-n

Natural ruber

Amino acid NH2CHRCOOH

- NHCHRCO- -( NHCHRCO)-n Protein

Adipic acid CO2H-(CH2)4-CO2H;hexamethylene diamine NH2-(CH2)4-NH2

-CO-(CH2)4-CO- NH-(CH2)4NH-

(-CO-(CH2)4-CO- NH-(CH2)4NH-)n

Nylon 6,6

Teripthalic acid CO2H-(C6 H5)-CO2H; ethylene glycol HOCH2-CH2OH

-CO(C6 H5)CO2- CH2-CH2O-

[-CO(C6 H5)CO2- CH2-CH2O-]n

Terilene

1.4 Homopolymer and copolymer: Homopolymers(e.g. polyethenes) have identical monomers(e.g. ethylene). Hence repeating unit is identical with monomer. Copolymer(e.g. nylon 6,6) have different monomers(e.g. adipic acid and hexamethylene diamine). Here repeating unit is not identical with monomers. Two monomers are combined to give one repeating unit as shown in table-1.

1.5 Functionality(f) in polymer chemistry According to IUPAC, in polymer chemistry the functionality of a monomer is defined as the number of covalent bonds that a monomer's repeating unit forms in a polymer with other monomers. Thus in polymer chemistry, a double bond possesses a functionality of two (because two points of contact for further polymer chains are present, on each of the two adjacent carbon atoms), while in organic chemistry the double bond is a functional group and thus has a functionality of one. Significance of Functionality: a) Functionality of monomer determines structural aspects of polymer. Thus for a monomer with i) a functionality,f = 2 forms a linear polymer (a thermoplastic polymer) ii) a functionality f ≥ 3 lead to a branching point, which can lead to cross-linked polymers (a thermosetting polymer) iii) a functionality.f=1 do not form polymer as such molecules lead to a chain termination. Vinyl chloride with f=2 forms PVC, a linear chain polymer. Bakelite, a copolymer of phenol(f=3) and formaldehyde(f=2) is a cross linked polymer where 2,4,6 positions of phenol are involved in condensation with formaldehyde.

Table-1: Functionality and structure of polymer:

Monomers Structure Functionality PolymersOlefin CH2 = CHX 2 LinearFormaldehyde CH2 = O 2 LinearEthylene glycol HOCH2CH2OH 2 LinearTeripthalic acid CO2HC6H4CO2H 2 LinearAdipic acid CO2H(CH2)4CO2H 2 LinearHexamethylene diamine NH2(CH2)4NH2 2 LinearAmino acids NH2CHRCO2H 2 LinearGlycerol HOCH2CHOHCH2OH 3 Cross linkedCystin NH2CH(CH2SH) CO2H 3 Cross linkedPhenol C6H5OH 3 Cross linked

b) From the average functionality of the used monomers the reaching of the gel point can be calculated as a function of reaction progress. Side reactions may increase or decrease the functionality.

[In polymer chemistry, the gel point is an abrupt change in the viscosity of a solution containing a polymer. At the gel point, a solution undergoes gelation, leading to a gel formation, as reflected in a loss in fluidity and the formation of a 3D network. In rheology, the gel point is corresponding to the change of comportment.]

1.5  Functionality and functional unit of a polymer: Functionality of a repeating unit is the number of sites it has for bonding to other monomers under the given conditions of the polymerization reaction. Functionality determines the structural aspect of polymer. While functional unit is the functional group of the polymer chain back bone formed by combination of monomer functional groups. For example polymers formed from monomers containing amine and carboxyl group are called to have polyamide functional unit. Ester –COO-, amide -CONH-, urethane –OCONH-, phosphor ester –OPO2 O-, sulphide-SO2- etc are common functional unit of polymers. Functional units give specific properties to the polymers. Depending on the types of functional unit of main chain backbone, properties of polymers may vary. Thus protein having poly amide functional unit which may be degraded (hydrolysed) by dilute acids or bases or enzymes while PVC having no such functional unit does not degrade.

1.6 The degree of polymerization(DP): According to IUPAC degree of polymerisation is defined as the number of  monomeric units in a polymer molecule. This number does not reflect the variation in molecule size of the polymer that typically occurs, it only represents the mean number of monomer units. For a homopolymer, there is only one type of monomer unit and the number-average degree of polymerization is given by DP=Mn/Mo, where Mn is the number-average molecular weight and M0 is the molecular weight of the monomer unit. Thus for a polyethenes with average molecular weight(Mn) =

28000 and monomer mol.wt.(Mo) = 28; Hence DP = 28000/28 = 1000 Some authors, however, define DP as the number of repeating units, where for copolymers the repeating unit may not be identical to the monomeric unit For example, in nylon-6,6, the repeating unit contains the two monomeric units —NH(CH2)6NH— and —OC(CH2)4CO—, so that a chain of 1000 monomeric units corresponds to 500 repeat units. The degree of polymerization or chain length is then 1000 by the first (IUPAC) definition, but 500 by the second.

1.7 Classification of polymers: Polymers have been classified in several ways.

1. Based on monomer i) Homo polymer: These polymers consist of identical monomers and may be represented as -M-M-M-M-M-M. Examples –natural rubber, polyethenes, polypropylene, nylon 6 etc. ii) Copolymer: These polymers consist of different monomers and may be represented as –

i A + i B ---------> —(A-B)i—

i H2C=CHCl + i H2C=CCl2 -----> (-H2C-CHCl - H2C-CCl2- )n vinyl chloride vinylidene chloride poly(vinylchloride-co-vinylidene chloride)

Copolymers may be further classified according to relative arrangement of different monomer units as follows

a) Alternating copolymer —A-B-A-B-A-B—b) Random copolymer —A-A-A-A-B-A-B— .c) Block copolymers-two long sequences of repeat units

—A-A-A-A-A-A-A-B-B-B-B-B-B-B—

d) graft polymers- segmented copolymers with a linear backbone of one composite(A) and randomly distributed branches of another composite(B).

branch point

2. Based on source of availability

i) Natural polymers: Polymers obtained from nature, mostly plants and animal. Examples – Cellulose, starch, rubber, proteins, nucleic acids etc. ii) Synthetic polymers: Polymers prepared in laboratory. Examples – Teflon, Nylon 6,6 , Synthetic rubber (Buna – S) etc. iii) Semi synthetic polymers: Polymers derived from naturally occurring polymers by carrying out chemical modifications. Examples – Rayon (cellulose acetate), cellulose nitrate, etc.

3. Based on the structure of polymer

i)Linear polymers: Polymer consists of long and straight chains. Examples – High density polythene, polyvinyl chloride, teflon, nylon etc. ii)Branched chain polymers: Polymers contains linear chains having some branches. Examples – Low density polythene iii)Cross linked or network polymers: Polymers in which monomer units are cross linked together to form a 3 dimensional network polymers. Examples – Bakelite, melamine, etc.

4. Based on molecular structures i) Linear polymers These polymers consist of uninterrupted long and straight chains. The examples are high density polythene, polyvinyl chloride, etc. These are represented as

ii) Branched chain polymers: These polymers contain linear chains having some branches, e.g., low density polythene. These are depicted as follows

iii) Cross linked or Network polymers: These are usually formed from bi-functional and tri-functional monomers and contain strong covalent bonds between various linear polymer chains, e.g. Bakelite, melamine etc. These polymers are depicted as follows:

5. Based on molecular forces

i).Elastomers: Polymer chains are held together by weakest intermolecular forces. Polymers are rubber – like solids with elastic properties. Examples – Buna – S, Buna – N, Neoprene.

ii).Fibre: Polymers have strong intermolecular force like hydrogen bonding. Fibres are the thread forming solids which possess high tensile strength and high modulus. Examples – Nylon 6, 6, Polyesters.

iii).Thermoplastic polymers: Polymers are held by intermolecular forces which are in between those of elastomers and fibres. These polymers are capable of repeated softening on heating and hardening on cooling. Examples – Polythene, Polystyrene.

iv) Thermosetting polymers: Polymers are cross linked or heavily branched molecules, which on heating undergo extensive cross linking in moulds and eventually undergo a permanent change. Examples – Bakelite, Urea-formaldelyde resins

6. Based on tacticity:

Polymers with chiral centers at the chain may be classified according to tacticity i,e. the sterechemical deposition of side groups along chain in space as follows

i) Isotactic polymers: In these polymers identical side groups are deposited on the same side of the chain i.e. all chiral center have the same configuration. Polypropylene formed by Ziegler–Natta catalysis is an isotactic polymer Isotactic polymers are usually semicrystalline and often form a helix configuration.

ii) Syndiatactic polymers: Here identical side groups are deposited alternatively on the same side of the chain i.e. alternate chiral centers have same configuration. Crystaiiine Polystyrene, made by metallocene catalysis polymerization with melting point of 161 °C and Gutta percha are examples for syndiotactic polymer.

iii) Atactic Polymers: In atactic polymers identical side groups are deposited randomly around the chain. Polymers that are formed by free-radical mechanisms such as polyvinyl chloride are usually atactic. Due to their random nature atactic polymers are usually amorphous.

iv) Eutactic polymers: In eutactic macromolecules, substituents may occupy any specific (but potentially more complex) sequence of positions along the chain. Isotactic and syndiotactic polymers are instances of the general class of eutactic polymers, which also includes heterogeneous macromolecules in which the sequence consists of substituents of different kinds (for example, the side-chains in proteins and the bases in nucleic acids).

7. Based on mode of polymerization

a) Addition Polymers or Chain Growth Polymers:

These polymers are formed by addition of monomers repeatedly without removal of any byproduct. These polymer contain all atoms of monomers hence their molecular weight are integral multiple of monomers. Addition polymerization is called chain growth polymerization because it takes place through stages leading to increase in chain length and each stage produces reactive intermediates for use in next stage of the growth of chain. Usually olefins form addition polymers. Examples – Polythene, Polystyrene,Buna-S, Buna –N etc.

b) Condensation polymers or step growth polymers:

These polymers are formed by step wise combination of monomers by removal of small molecules like water, alcohol, ammonia etc, Their molecular mass is not integral multiple of monomers. Usually polymers with esters amide, ether, phosphoester etc. are condensation polymers. Examples – Nylon 6, 6; Nylon 6; Bakelite etc.

8. Based on crytalinity

1. Crystalline: In crystalline polymers the monomers arranged in ordered way, where the molecular chains are largely locked in place against one another. Apply a load and it will break rather than bend. On heating it suddenly melts at a given temperature known as melting temperature. Crystalline structures are generally opaque because the structure acts to reflect light.

2. Amorphous: In amorphous polymers the monomers arranged in random way. Rather than being rigid, the random molecular jumble lets the chains move across each other when the polymer is pushed or pulled(easily deformed). In short, amorphous polymers have flexibility and elasticity. Amorphous polymers have no clear melting point. Instead they have a glass transition temperature or Tg where the polymer transitions from rigid or solid to being soft and pliable. Amorphous polymers are usually transparent.

9. Based on biodegrability

1. Non- Biodegradable polymers are solid substances that are made up of long carbon chains with strong chemical bonds between the atoms and hence are harder to be broken down by microbes. Synthetic non biodegradable polymers- common examples are Polythene, Polyvinylchloride (PVC), Polystyrene and Teflon

2. A polymer that can be decomposed by microorganism into carbon dioxide, water vapor, and organic material, which isn't harmful to the environment is called a biodegradable polymer. The common examples of aliphatic biodegradable polymers are polyglycolic acid(PGA), Polyhydroxy butyrate (PHB), Polyhydroxy butyrates-co-beta hydroxyl valerate( PHBV), Polycaprolactone(pcl), Nylon-2-nylon-6.

2.1 Nominclature of polymers

2.2 Polymeristpation reactions

In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are two general types of polymerization reactions: addition polymerization and condensation polymerization.

In addition polymerization, the monomers add to one another in such a way that the polymer contains all the atoms of the starting monomers.The reaction involves chain initiation, chain propagation and chain termination. Reactions may be initiated by free radicals, cations or anions or by coordination. Hence the reactions are so classified as:

1. Free radical polymerization:

A variety of alkenes or dienes and their derivatives are polymerised in the presence of a free radical generating initiator (catalyst) like benzoyl peroxide, acetyl peroxide, tert-butyl peroxide, etc. For example, the polymerisation of ethene to polythene consists of heating or exposing to light a mixture of ethene with a small amount of benzoyl peroxide initiator. The process starts with the addition of phenyl free radical formed by the peroxide to the ethene double bond thus generating a new and larger free radical. This step is called chain initiating step. As this radical reacts with another molecule of ethene, another bigger sized radical is formed. The repetition of this sequence with new and bigger radicals carries the reaction forward and the step is termed as chain propagating step. Ultimately, at some stage the product radical thus formed reacts with another radical to form the polymerised product. This step is called the chain terminating step. The sequence of steps may be depicted as follows:

*Chain initiation

C6H5CO-O-COC6H5 ----> 2 C6H5CO. ---> C6H5.

CH2= CH2 + C6H5CO. -----> C6H5- CH2- CH2.

*Chain propagation

C6H5- CH2- CH2. + CH2=CH2 ----> C6H5- CH2- CH2- CH2- CH2. --->

C6H5-( CH2- CH2-)n CH2- CH2.

*Chain termination: It occur generally by coupling of radicals or rarely by dis proprtionation

Coupling

C6H5-( CH2- CH2)n- CH2- CH2. ---> C6H5-( CH2- CH2)n- CH2- CH2-( CH2- CH2)n- C6H5

Disproportionation

C6H5-( CH2- CH2)n- CH2- CH2. ---> C6H5-( CH2- CH2)n- CH2=CH2 +CH3(CH2- CH2)n- C6H5

2. Cationic polymerization:

Cationic polymerization is a type of chain growth polymerization in which a cationic initiator (usually protic acid with weaker anion, lewis acid or carbenium salts) transfers charge to a monomer( usually alkenes with electron donating group) which then becomes reactive carbenium ion. This reactive monomer goes on to react similarly with other monomers to form a polymer. Chain initiation

. CH2 = CH C6 H5 + HY -----> E-CH2 – CH+ C6 H5 + Y-

*Chain propagation

Ph- CH=CH2. + H-CH2 – CH+ Ph ----> H-CH2- CH(Ph)- CH2- CH+ (Ph). ---> H-[CH2- CH(Ph)]n- CH2- CH+ (Ph).

*Chain termination:

It generally occurs when an anionic fragment of the counterion combines with the propagating chain end

H-[CH2- CH(Ph)]n- CH2- CH+ (Ph) + Y-.----> H-[CH2- CH(Ph)]n- CH2- CH (Ph)Y.

Termination may also occur through chain transfer which can take place in two ways i) by hydrogen abstraction from the active chain end by the counterion.

H-[CH2- CH(Ph)]n- CH2- CH+ (Ph) + Y- ---->. H-[CH2- CH(Ph)]n- CH= CH (Ph) + HY

ii) by hydrogen abstraction from the active chain end by the monomer. This terminates the growing chain and also forms a new active carbenium ion-counterion complex which can continue to propagate, thus keeping the kinetic chain intact.

H-[CH2- CH(Ph)]n- CH2- CH+ (Ph) + Ph- CH=CH2 --->H-[CH2- CH(Ph)]n- CH= CH (Ph) + H-CH2 – CH+ Ph

3. Cationic ring-opening polymerization

Cationic ring-opening polymerization follows the same mechanistic steps of initiation, propagation, and termination. However, in this polymerization reaction, the monomer units are cyclic in comparison to the resulting polymer chains which are linear. The linear polymers produced can have low ceiling temperatures, hence end-capping of the polymer chains is often necessary to prevent depolymerization.

Cationic ring-opening polymerization of oxetane involving (a and b) initiation, (c) propagation, and (d) termination with methanol

4. Anionic polymerization: Anionic addition polymerization is a form of chain-growth polymerization or addition polymerization that involves the polymerization of monomers initiated with anions(usually alkyl lithium).

*Chain initiation:

CH2 = CH Ph + R- Li+ ----> RCH2 -HC- Ph

*Chain propagation:

RCH2 -HC- Ph + CH2 =HCPh --->RCH2 -HC- Ph- CH2 -HC- Ph ---> R(CH2 HC Ph)n- CH2HC- Ph

*Termination:

R(CH2 HCPh)n- CH2HC- Ph + H+ -----> R(CH2 HC Ph)n- CH2 CH2 Ph

5. Living anionic polymerization

Living anionic polymerization was demonstrated by Szwarc and co workers in 1956. Their initial work was based on the polymerization of styrene and dienes. One of the remarkable features of living anionic polymerization is that the mechanism involves no formal termination step. In the absence of impurities, the carbanion would still be active and capable of adding another monomer. The chains will remain active

indefinitely unless there is inadvertent or deliberate termination or chain transfer. This gave rise to two important consequences:

The number average molecular weight, Mn, of the polymer resulting from such a system could be calculated by the amount of consumed monomer and the initiator used for the polymerization, as the degree of polymerization would be the ratio of the moles of the monomer consumed to the moles of the initiator added. Mn= Mo/[M]o, where Mo = formula weight of the repeating unit, [M]o = initial concentration of the monomer, and [I] = concentration of the initiator

.ii) All the chains are initiated at roughly the same time. The final result is that the polymer synthesis can be done in a much more controlled manner in terms of the molecular weight and molecular weight distribution (Poisson distribution).

iii The following experimental criteria have been proposed as a tool for identifying a system as living polymerization system.

*Polymerization until the monomer is completely consumed and until further monomer is added.

*Constant number of active centers or propagating species.

*Poisson distribution of molecular weight

*Chain end functionalization can be carried out quantitatively.

6. Coordination polymerization:

Coordination polymerization started in the 1950s with heterogeneous Ziegler–Natta catalysts based on titanium tetrachloride and organoaluminium co-catalyst. The mixing of TiCl4 with trialkylaluminium complexes produces Ti(III)-containing solids that catalyze the polymerization of ethene and propene.

Homogeneous Ziegler–Natta polymerization

In some applications heterogeneous Ziegler–Natta polymerization has been superseded by homogeneous catalysts such as the Kaminsky catalyst discovered in the 1970s. The 1990s brought forward a new range of post-metallocene catalysts. Typical monomers are nonpolar ethene and propene. The development of coordination polymerization that enables copolymerization with polar monomers is more recent.[4] Examples of monomers that can be incorporated are methyl vinyl ketones[5] methyl acrylate[6] and acrylonitrile.

Illustrative metallocene-based coordination catalysts

Kaminsky catalysts are based on metallocenes of group 4 metals (Ti, Zr, Hf) activated with methylaluminoxane (MAO).[8][9] Polymerizations catalysed by metallocenes occur via the Cossee–Arlman mechanism. The active site is usually anionic but cationic coordination polymerization also exists.

Simplified mechanism for Zr-catalyzed for ethene polymerization

However many alkenes do not polymerize in the presence of Ziegler–Natta or Kaminsky catalysts. This problem applies to polar olefins such as vinyl chloride, vinyl ethers, and acrylate esters. Large scale production prcess of polybutadiene employs a neodymium-based homogeneous catalyst.

[N.B. Coordination polymerization has a great impact on the physical properties of vinyl polymers such as polyethylene and polypropylene compared to the same polymers prepared by other techniques such as free-radical polymerization. The polymers tend to be linear and not branched and have much higher molar mass. Coordination type polymers are also stereoregular and can be isotactic or syndiotactic instead of just atactic. This tacticity introduces crystallinity in otherwise amorphous polymers. From these differences in polymerization type the distinction originates between low-density polyethylene (LDPE), high-density polyethylene (HDPE) or even ultra-high-molecular-weight polyethylene (UHMWPE).]

Coordination polymerization of other substrates: Coordination polymerization can also be applied to non-alkene substrates. Dehydrogenative coupling of silanes of dihydro- and trihydrosilanes to polysilanes has been investigated, although the technology has not been commercialized. The process entails coordination and often oxidative addition of Si-H centers to metal complexes.

Lactides also polymerize in the presence of Lewis acidic catalysts to give polylactide:

2.3 Structure and bonding in polymers

A single polymer molecule may consist of hundreds to a million monomers covalently bonded to each other and may have a linear, branched, or network structure. Covalent bonds hold the atoms in the polymer molecules together and secondary bonds(intermolecular forces) then hold groups of polymer chains together to form the polymeric material. Intermolecular Forces The intermolecular forces for polymers are the forces between polymer chains, are the same as for small molecules. Because polymer molecules are so large, though, the magnitude of their intermolecular forces can vastly exceed those between small molecules. The presence of strong intermolecular forces is one of the main factors leading to the unique physical properties of polymers. Intermolecular forces are usually following types Dispersion ForcesDispersion forces are due to instantaneous dipoles that form as the charge clouds in the molecules fluctuate. Dispersion forces, the weakest of the intermolecular forces, are present in all polymers. They are the only forces possible for nonpolar polymers such as polyethylene.Dispersion forces depend on the polarizability of a molecule. Larger molecules generally are more polarizable, so large polymers with high molecular weights can have significant dispersion forces. Ultra high molecular weight polyethylene (UHMWPE), which has a molecular weight in excess of 3,000,000 g/mole, is used to make bulletproof vests.Dipole-Dipole ForcesDipole-dipole forces result from the attraction between polar groups, such as those in polyesters and vinyl polymers with chlorine pendant groups.Hydrogen BondingHydrogen bonding can take place when the polymer molecule contains -OH or -NH groups. Hydrogen bonding is the strongest of the intermolecular forces. Polymers such as poly(vinyl alcohol) and polyamides are hydrogen bonded.

Questions to be answered by students by one week

Q.1. Polymers are macromolecules, but not all macromolecules are polymers explain.

Q3.Protein is polymer but lipid is not –explain

Q2. Give some examples of biopolymers

Q4. What do you mean byrepeating unit and monomer? Indicate difference if any.

Q5. Define functionality. How it dictets polymer structure?

Q6. Differentiate between functionality and functional unit of polymer.

Q7 Why proteins are biodegradable but polyethenes are not?

Q8 What is degree of polymerization. How it can be calculated?

Q.9 Calculate the molecular weight of the polythene polymer given DP is 100.

Q10. Differentiate between copolymer and homopolymer with example

Q11.Classify polymers on structural basis with examples

Q12.write differences between thermo plastics and thermo setting plas tics with example

Q13. Write differences between chain growth polymer and step growth polymers with example

Q14. Write differences between glass transition temperature and melting temperature of polymer with example

Q15. Write differences between crystalline and amorphous polymers with example.

Q 16. What are inter molecular forces present in polymers? Which force present in polyethenes?

Q17. What do you mean by LDPE and HDPE? Write role of Ziggler Natta Catalyst for HDPE formation.

Q18. Explain why linear polymers are thermo plastics and cross linked polymers are thermosetting?

Q19. Anionic polymerization may be called living polymerization-explain.

Q20 Define crystalinity of polymer. How it is related totacticity

Q20. Write monomers and repeating units of following polymers : Nylon66; Dacron; melamine; Bakelite

Q21. Write IUPAC name of: polystyrene; polyethelene oxide; nylon6

Q22. Write structure of the polymers: poly(1-carboxylatoethylene); copoly(styrene /methylmethacrylate)

What are the 4 types of polymers?They can be classified into four main categories: thermoplastics, thermosets, elastomers, and synthetic fibers. They are commonly found in a variety of consumer products. Various main chains and side chains are used to make different synthetic organic polymers.Why are lipids not polymers?However lipids are not considered to be polymers, because lipids do not contain monomers and polymers are made up out of monomers. Moreover, the basic units of lipids are fatty acids and glycerol molecules, which do not form repetitive chains (thus lipids contain non-similar units).Why are proteins considered polymers but lipids not?Give some examples of biopolymersNatural polymers (also called biopolymers) include silk, rubber, cellulose, wool, amber, keratin, collagen, starch, DNA, and shellac]