Question

The correct statement among the following is -

1) linear polymers have high melting point than cross linked polymer with the same molecular mass.

2) linear polymer is less dense than branched polymer.

3) low density polyethylene is formed due to the high linearity of the structure .

4) All of the above. ​

Answer 1

Answer:

Prior to the early 1920's, chemists doubted the existence of as averages. Two experimentally determined values are common: Mn , the number average molecular weight, is calculated from the mole fraction distribution of different sized molecules in a sample, and Mw , the weight average molecular weight, is calculated from the weight fraction distribution of different sized molecules. These are defined below. Since larger molecules in a sample weigh more than smaller molecules, the weight average Mw is necessarily skewed to higher values, and is always greater than Mn. As the weight dispersion of molecules in a sample narrows, Mw approaches Mn, and in the unlikely case that all the polymer molecules have identical weights (a pure mono-disperse sample), the ratio Mw / Mn becomes unity.

The influence of different mass distributions on Mn and Mw may be examined with the aid of a simple mass calculator.

To use this device Click Here.

Many polymeric materials having chain-like structures similar to polyethylene are known. Polymers formed by a straightforward linking together of monomer units, with no loss or gain of material, are called addition polymers or chain-growth polymers. A listing of some important addition polymers and their monomer precursors is presented in the following table.

Some Common Addition Polymers

Name(s)

Formula

Monomer

Properties

Uses

Polyethylene

low density (LDPE) –(CH2-CH2)n– ethylene

CH2=CH2 soft, waxy solid film wrap, plastic bags

Polyethylene

high density (HDPE) –(CH2-CH2)n– ethylene

CH2=CH2 rigid, translucent solid electrical insulation

bottles, toys

Polypropylene

(PP) different grades –[CH2-CH(CH3)]n– propylene

CH2=CHCH3 atactic: soft, elastic solid

isotactic: hard, strong solid similar to LDPE

carpet, upholstery

Poly(vinyl chloride)

(PVC) –(CH2-CHCl)n– vinyl chloride

CH2=CHCl strong rigid solid pipes, siding, flooring

Poly(vinylidene chloride)

(Saran A) –(CH2-CCl2)n– vinylidene chloride

CH2=CCl2 dense, high-melting solid seat covers, films

Polystyrene

(PS) –[CH2-CH(C6H5)]n– styrene

CH2=CHC6H5 hard, rigid, clear solid

soluble in organic solvents toys, cabinets

packaging (foamed)

Polyacrylonitrile

(PAN, Orlon, Acrilan) –(CH2-CHCN)n– acrylonitrile

CH2=CHCN high-melting solid

soluble in organic solvents rugs, blankets

clothing

Polytetrafluoroethylene

(PTFE, Teflon) –(CF2-CF2)n– tetrafluoroethylene

CF2=CF2 resistant, smooth solid non-stick surfaces

electrical insulation

Poly(methyl methacrylate)

(PMMA, Lucite, Plexiglas) –[CH2-C(CH3)CO2CH3]n– methyl methacrylate

CH2=C(CH3)CO2CH3 hard, transparent solid lighting covers, signs

skylights

Poly(vinyl acetate)

(PVAc) –(CH2-CHOCOCH3)n– vinyl acetate

CH2=CHOCOCH3 soft, sticky solid latex paints, adhesives

cis-Polyisoprene

natural rubber –[CH2-CH=C(CH3)-CH2]n– isoprene

CH2=CH-C(CH3)=CH2 soft, sticky solid requires vulcanization

for practical use

Polychloroprene (cis + trans)

(Neoprene) –[CH2-CH=CCl-CH2]n– chloroprene

CH2=CH-CCl=CH2 tough, rubbery solid syntheti

Answer 2

★ Required AnSwer:★

• The correct statement among the following is :-

➔ linear polymers have high melting point than cross linkêd polymer with the same molecular mass.

Explanation:-

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The polymers in which the constituent monomeric units are joined to form long straight chainß are called linear polymers or straight chain polymers.

• In such polymers, the polymeric chaiñs stack over one another and form well packed structure .
• Due to this close packing , they have high density, high tensile strength and high melting point .
• If the polymēr chain has no branches, they pack close to each other and the material has high density.
• High density polythene (HDPE) is a linear polymer.

Hence ,Statement 'A' is correct.

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• Branched chāin polymer are those which have side chains attached to main chain, which is the linear chāin .
• Due to this branching , Compåct packing is not possible.
• Thus , they have low density, melting point and tensile strength.
• Low density polythene (LDPE) is a branched chain polymēr.
• If the polymēr chain have lot of branches, then the chaìns cannot pack together as closely. Thus, the material has low density.

Hence, Statement 'B' is incorrect.

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• In cross linkêd polymērs , adjacent polymeric chāins lìnk through side chain to form a three dimensional nētwōrk.
• This makes the whole structure more rigìd and less elāstic.
• Long chaìns get tangled up in each other and stick together far more than short chāins.
• This means that polymers made of long chāin molecules have higher melting points than those made of short chaìns.
• Shorter molecules can pa.ss over each other more easily so the materials made of these molecules are softer and more 'squishy'.

Hence, Statement 'C' is incorrect.

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Correct statement:

Linear polymers have high melting point

than cross linkēd polymer with the same molecular mass.

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