Textile Raw Material - II

Ishtiaqe Abu Sayed

123-036-041

Section : E

Ques 01:

Oligomer : oligomer (oligo- "a few" , mer- "parts") is a molecular complex that consists of a few monomer units, in contrast to a polymer that, at least in principle, consists of a nearly unlimited number of monomers. Dimers, trimers, and tetramers are, for instance, oligomers respectively composed of two, three and four monomers.

Monomer residue : The unpolymerized monomer that remains incorporated in a polymer after the polymerization reaction is completed.

Living polymer : Polymer with stable, polymerization-active sites formed by a chain polymerization in which irreversible chain transfer and chain termination are absent. or, In polymer chemistry, living polymerization is a form of chain growth polymerization where the ability of a growing polymer chain to terminate has been removed.

Dead polymer : the polymer formed in a chain polimerization which no more contains any active centers. it is incapable of further growth after addition of a monomer except after a few polymer transfers.

Ques 02 :

Major uses of polymers in textiles are Elastomers, plastics, fibers,

Ques 03 :

Read page ( 2,3,22 ) "Natural fiber book of Bakr sir"

Ques 04 :

Functionality of a monomer : The functionality of a monomer is the number of binding sites that is/are present in that monomer.

For example, the functionality of monomers such as ethene and propene is one and that of 1, 3-butadiene and adipic acid is two.

Functionality of a polymer : The functionality of a molecule is simply its interlinking capacity or the number of sites it has available for bonding with other molecules under the specific polymerization conditions.

Ques 05 :

Fiber morphology includes all properties that are visible, including those that are visible under a microscope. Fiber morphology is generally fixed for natural fiber, but is easily changed for manufactured fibers. Therefore, fiber morphology will not be discussed for manufactured fibers. Surface contour, shape, fineness, luster, color, and length of fibers are included under morphology.

Surface Contour and Shape - A microscope is used to view the surface contour (longitudinal view) and shape (cross section) of fibers. The longitudinal view and cross section are used to identify fibers. The shape of manufactured fibers can be changed to influence performance. Surface contour and shape affect cohesiveness (the ability of fibers to hold together when spun into a yarn), luster, opacity, hand, texture, and apparent soiling.

Fineness - Direct and indirect systems are used to measure the fineness of fibers. The denier and tex are direct systems. In both systems, the lower the number, the finer the fibers. Fibers used for apparel typically range from less than 1 to about 7 denier, and carpet fibers are approximately 20 denier. Microfibers are less than 1 denier. Fiber fineness affects drape, hand, wrinkle resistance, and strength.

Luster and Color - Luster, the sheen or shine of fiber, is dependent on light reflected from the surface of the fiber. The color of a fiber is dependent on the fiber source. Luster and color affect the physical appearance, and color affects the bleaching and dyeing of fibers.

Crimp - Crimp refers to a fiber’s waviness. Wool has a natural crimp, and crimp can be added to manufactured fibers. Manufactured fibers cut into staple lengths have to be crimped to improve cohesiveness. Crimp affects resiliency, resistance to abrasion, stretch, cohesiveness, bulk, warmth, absorbency, luster, and skin comfort.

1 . Crystalline Regions: Crystalline Regions are the regions that cannot absorb water, humidity and dyestuff solutions but they are the part for fiber strength.

2 . Non-Crystalline Regions: Non-Crystalline Regions or Amorphous regions are the regions that can absorb water, humidity and dyestuff therefore they can be dyed but they are a very weak part of the fibers.

3 . Orientation of the Crystalline Regions alongside the fiber axis . This property is very important in that it will increase the tensile strength of the fiber if it presents in the optimal quantity.

Define :

Conformations: If two atoms are joined by a single bond then rotation about that bond is possible since, unlike a double bond, it does not require breaking the bond.

The ability of an atom to rotate this way relative to the atoms which it joins is known as an adjustment of the torsional angle. If the two atoms have other atoms or groups attached to them then configurations which vary in torsional angle are known as conformations. Since different conformations represent varying distances between the atoms or groups rotating about the bond, and these distances determine the amount and type of interaction between adjacent atoms or groups, different conformation may represent different potential energies of the molecule. There several possible generalized conformations: Anti (Trans), Eclipsed (Cis), and Gauche (+ or -).

Configuration : The two types of polymer configurations are cis and trans. These structures can not be changed by physical means (e.g. rotation). The cis configuration arises when substituent

groups are on the same side of a carbon-carbon double bond. Trans refers to the substituents on opposite sides of the double bond.

Stereoregularity is the term used to describe the configuration of polymer chains. Three distinct structures can be obtained. Isotactic is an arrangement where all substituents are on the same side of the polymer chain. A syndiotactic polymer chain is composed of alternating groups and atactic is a random combination of the groups. The following diagram shows two of the three stereoisomers of polymer chain.

Constitution:

Tacticity : Tacticity describes the relative stereochemistry of chiral centers in neighboring structural units within a macromolecule. There are three types: isotactic (all substituents on the same side), atactic (random placement of substituents), and syndiotactic (alternating placement of substituents).

Ques 06 : (-ch2-ch2-)

Ques 07 :

read 4th semester polymer science ques no 4 classification of polymer

a) Natural polymers - Polymers either obtained from plants or animal are called natural polymers. They are called plant and animal polymers. Example- Cellulose, Jute, Lihen, Silk, Wool, Leather, RNA, DNA, Natural rubber.

b) Semisynthetic polymers - The polymers obtained by simple chemical treatment of natural fibres to improve their physical properties like lastrus nature, tensite strength are called semisynthatic fibres. Example- Acetate rayon, cuprammonium silk, viscous rayon.

c) Synthetic fibres - The fibres obtained by polymerisation of simple chemical molecules in laboratory are synthetic fibres. Example- Nylon, terylene, polyethene, polystyrene, synthetic rubber, nylon, pvc, backlite, teflon, orion etc.

Ques 08 :

The differences between anionic and cationic polymerization is that cationic polymerization is faster than anionic and radical polymerization

In anionic vinyl polymerization, the electrons in the pi bond more together instead of separately. The initiator (or growing chain end) attacks with a pair of electrons, used to form the new bond. The pi-bond electron pair "flows" away from the attacking species, reproducing the anion at the chain end.

Cationic vinyl polymerization is exactly the same mechanism, except that the initiator (or chain end) lacks a pair of electrons. The electron "flow" is simply in the oposite direction, leaving behind a positive charge at the chain end to continue the process.

One important difference: ionic polymerizations necessarily carry along a counterion, and their rates are much more sensitive to reaction conditions (e.g., solvent polarity, temperature).

The mods of anionic polymerization are Initiation, Propagation .

The mods of cationic polymerization are Initiation, Propagation and Termination

Ques 09 :

thermal properties of polymer:

The glass transition temperature , Tg

The crystalline melting temperature , Tm

Difference between :

A thermoplastic polymer is a type of plastic that changes properties when heated and cooled. Thermoplastics become soft when heat is applied and have a smooth, hard finish when cooled. There are a wide range of available thermoplastic formulas that have been created for many different applications.

Thermosetting plastics are rigid polymer plastic materials, that are resistant to higher temperatures than the ordinary thermoplastics. These materials are normally made up of lines of molecules, which are heavily cross-linked.

Thermoplastic polymers: These are the linear or slightly branched long chain molecules capable of repeatedly softening on heating and hardening on cooling. These polymers possess intermolecular forces of attraction intermediate between elastomers and fibres. Some common thermoplastics are polythene, polystyrene, polyvinyls, etc.

Thermosetting Polymers: Thesepolymers are cross linked or heavily branched molecules, which on heating undergo extensive cross linking in moulds and again become infusible. These cannot be reused. Some common examples are bakelite,

Ques 10 :

Homopolymer: A polymer resulting from the polymerization of a single monomer; a polymer consisting substantially of a single type of repeating unit.

Copolymer: When a polymer is made by linking only one type of small molecule, or

monomer, together, it is called a homopolymer. When two different types of monomers

are joined in the same polymer chain, the polymer is called a copolymer. Let's imagine

now two monomers, which we'll call Aand B. Aand Bcan be made into a copolymer in

many different ways.

When the two monomers are arranged in an alternating fashion, the polymer is called, of

course, an alternating copolymer:

In a random copolymer, the two monomers may follow in any order:

In a block copolymer, all of one type of monomer are grouped together, and all of the

other are grouped together. A block copolymer can be thought of as two homopolymers

joined together at the ends.

Graft copolymers : A polymer comprising molecules in which the main backbone chain of atoms has attached to it at various points side chains containing different atoms or groups from those in the main chain. The main chain may be a copolymer or may be derived from a single monomer.

Polymers with branches at irregular intervals along the polymer chain are called branched polymers.

Ques 11 :

This process of formation of polymers from respective monomers is called polymerisation. The transformation of ethene to polythene and interaction of hexamethylene diamine and adipic acid leading to the formation of Nylon 6, 6 are examples of two different types of polymerization reactions. nCH2=CH2 → [-CH2-CH2-]n

There are 2 types of polymerization, Addition polymerization and Condensation polymerization.

i. Addition polymerization:- By binding great number from saturated small molecules to give big molecules like poly-ethylene.

ii. Condensation polymerization:- Between two different monomers by losing water to give co-polymer like Bakelite.

Ques 12 :

a) Chain growth polymerisation - This polymerisation process involves the addition of molecules at the reactive end of the growing chain across the double bond.

• Many alkenes and its derivatives undergo growth chain polymerisation. Ex. polyethene

b) Step growth polymerisation - This type of polymerisation involve the step wise intermolecular condensation through a series of indipendant reaction.

• This process involve loss of simple molecules like NH3, H20 and HC1.

• It is possible when the monomer have more than one functional groups.

• It proceds through the formation of dimer, trimer, tetramer, etc.

Free radical :One of the most common and useful reaction for making polymers is free radical polymerization. It is used to make polymers from vinyl monomers, that is, from small molecules containing carbon-carbon double bonds. Polymers made by free radical polymerization include polystyrene, poly(methyl methacrylate), poly(vinyl acetate) and branched polyethylene.

Ques 13 :

Polymer characterization is the analytical branch of polymer science.

The discipline is concerned with the characterization of polymeric materials on a variety of levels. The characterization typically has as a goal to improve the performance of the material. As such, many characterization techniques should ideally be linked to the desirable properties of the material such as strength, impermeability, thermal stability, and optical properties.

Characterization techniques are typically used to determine molecular mass, molecular structure, morphology, thermal properties, and mechanical properties.

Solubility : The ability or tendency of one substance to dissolve into another at a given temperature and pressure.

Plasticizer : Plasticizers (UK: plasticisers) or dispersants are additives that increase the plasticity or fluidity of a material. The dominant applications are for plastics, especially polyvinyl chloride (PVC). The properties of other materials are also improved when blended with plasticizers including concrete, clays, and related products.

Sweeling : Swelling (polymer science), the increase of volume of material due to absorption of a solvent, common for polymers.

Hydration :

Capillarity :

Ques 14 :

Ques 15 :

Degradation means uncontrolled reduction of molecular weight. It also means the rupture of chemical bond. And for this degradation the polymer looses its luster and stability.

Physical degradation:

Thermal degradation.

Mechanical degradation.

By ultrasonic waves degradation

Photo degradation.

By light energy radiation.

Degradation Agents :

Ques 16 :

Thermal degradation: It may be affected the groups joined to C-C bonds the aromatic branching and the presence of oxygen atom in the polymer chain which causes polymers to thermal degradation.

Photo degradation: Free radicals are formed during photo-degradation and the reaction of free radicals depends on the physical state of polymer.Photo stabilizer protects polymers from the deteriorating effect of light. The function of photo stabilizer is to absorb the ultra violate radiation.

Chemical : Chemically assisted degradation of polymers is a type of polymer degradation that involves a change of the polymer properties due to a chemical reaction with the polymer’s surroundings. There are many different types of possible chemical reactions causing degradation however most of these reactions result in the breaking of double bonds within the polymer structure.

Biological : Biodegradable plastics can be biologically degraded by microorganisms to give lower molecular weight molecules. To degrade properly biodegradable polymers need to be treated like compost and not just left in a landfill site where degradation is very difficult due to the lack of oxygen and moisture.

Ques 17 :

Chain-End Degradation: Firstly the degradation start from chain end and resulting successive release of monomer unit.This phenomenon is actually reverse of propagation steps. So this type of degradation called de-polymerization. The molecular weight of the polymer decrease slowly.

Random Degradation : This degradation occurs at any random point along the polymer chain and it the reverse of poly condensation process. Here the polymer degrades to lower to lower molecular weight fragments suddenly with little or no release of the monomer.

Mn → Mx + My

Ques 18 :

An ionic bond is a chemical link between two atoms caused by the electrostatic force between oppositely-charged ions in an ionic compound.Examples: There is an ionic bond between the sodium and chloride ions in table salt, NaCl.

A covalent bond is a chemical link between two atoms in which electrons are shared between them.Examples: There is a covalent bond between the oxygen and each hydrogen in a water molecule (H2O). Each of the covalent bonds contains two electrons - one from a hydrogen atom and one from the oxygen atom. Both atoms share the electrons.

London Dispersion Force Definition: London dispersion force is a weak intermolecular force between two atoms or molecules in close proximity of each other. The force is a quantum force generated by electron repulsion between the electron clouds of two atoms or molecules as they approach each other.The London dispersion force is the weakest of the van der Waals forces and is the force that causes nonpolar atoms or molecules to condense into liquids or solids as temperature is lowered.

Induced dipole forces result when an ion or a dipole induces a dipole in an atom or a molecule with no dipole. These are weak forces.

Ques 19 :

End groups are an important aspect of polymer synthesis and characterization. In polymer chemistry, end groups are functionalities or constitutional units that are at the extremity of a macromolecule or oligomer (IUPAC).[1] In polymer synthesis, like condensation polymerization and free-radical types of polymerization, end-groups are commonly used and can be analyzed for example by nuclear magnetic resonance (NMR) to determine the average length of the polymer. Other methods for characterization of polymers where end-groups are used are mass spectrometry and vibrational spectrometry, like infrared and Raman spectrometry. Not only are these groups important for the analysis of the polymer, but they are also useful for grafting to and from a polymer chain to create a new copolymer. One example of an end group is in the polymer poly(ethylene glycol) diacrylate where the end-groups are circled.

Ques 20 :

Crystallinity is indication of amount of crystalline region in polymer with respect to amorphous content.

Crystallinity influences many of the polymer properties some of there are - Hardness, Modulus, Tensile, Stiffness, Crease , Melting Point.

Ques 22 :

Antioxidants are chemicals (both naturally occurring and man-made) that can prevent or slow cell damage. An “antioxidant” is actually not a substance; it’s a behavior. Any compound that can donate electrons and counteract free radicals has antioxidant properties.

ANTIOXIDANTS used to prevent thermal degradation , inhibit ‘oxidation’ (i.e. degradation), are ‘cheap’ insurance for multiple pass materials.

Phenolic stabilizers are primary antioxidants that act as hydrogen donors.

Ques 23 :

Read page 22 "Natural fiber book of Bakr sir"

Polyvinyl chloride is produced by polymerization of the monomer vinyl chloride (VCM), as shown.

Ques 24 :

The functionality of a compound depends on the number of reactive sites it have. low molecular weight compounds having a functionality of two or more are called functionality..monomers polymerises to polymers. monomer functionalty determins whether the polymer is branched or linear...bifunctional monomers give linear polymers. trifunctional monomers give a cross linked polymer. if we take a mixture of both bifunctional and trifunctional monomers , their ratio decides wether the polymer is branched or cross linked.

Ques 25 :

Dependance of Polymer Properties on MW:

Many polymer properties of interest (Tg, modulus, tensile strength, etc.) follow a peculiar pattern with increasing MW. Small molecules have small values, then there is a sharp rise in properties as the chains grow to intermediate size (oligomers), and then the properties level off as the chains become long enough to be true polymers.

MW dependence of properties

However, a few properties important for polymer processing, like melt viscosity and solution viscosity, increase monotonically with MW. This means that the goal of polymer synthesis is not to make the largest possible molecules, but rather, to make molecules large enough to get onto the plateau region. Increasing the MW beyond this does not improve the physical properties much, but makes processing more difficult.

A few properties are dictated by the repeat units alone, and therefore these are not changed much by MW. Examples: color, dielectric constant, and refractive index.

Ques 26 :

A Ziegler-Natta catalyst is a catalyst used in the synthesis of polymers of 1-alkenes (α-olefins). Three types of Ziegler-Natta catalysts are currently employed:

Solid and supported catalysts based on titanium compounds. They are used in polymerization reactions in combination with cocatalysts, organoaluminum compounds such as triethylaluminium, Al(C2H5)3.

Metallocene catalysts, combination of various mono- and bis-metallocene complexes of Ti. Zr or Hf. They are usually used in polymerization reactions in combination with a different organoaluminum cocatalyst, methylaluminoxane (or methylalumoxane. MAO).

Post-metallocene catalysts based on complexes of various transition metals with multidentate oxygen- and nitrogen-based ligands. These complexes are also activated with MAO.

Ziegler-Natta catalysts are used to polymerize terminal 1-alkenes (ethylene and alkenes with the vinyl double bond):

n CH2=CHR → -[CH2-CHR]n

kinetic chain length : In polymer chemistry the kinetic chain length of a polymer, ν, is the average number of monomers during polymerization. During this process, a polymer chain is formed when units called monomers are bonded together to form longer chains known as polymers. Kinetic chain length is defined as the average number of monomer units consumed for each radical initiator that begins the polymerization of a chain and is a more general development of the average degree of polymerization. The kinetic chain length can be calculated several ways, and its value can describe certain characteristics of the material, including chain mobility, glass-transition temperature, and modulus of elasticity.

Dendrimes : Dendrimers are repetitively branched molecules. The name comes from the Greek word δένδρον (dendron), which translates to "tree". Synonymous terms for dendrimer include arborols and cascade molecules. However, dendrimer is currently the internationally accepted term. A dendrimer is typically symmetric around the core, and often adopts a spherical three-dimensional morphology. The word dendron is also encountered frequently. A dendron usually contains a single chemically addressable group called the focal point. The difference between dendrons and dendrimers is illustrated in figure one, but the terms are typically encountered interchangeably.

Ques 27 :

Step-growth polymerization refers to a type of polymerization mechanism in which bi-functional or multifunctional monomers react to form first dimers, then trimers, longer oligomers and eventually long chain polymers. Many naturally occurring and some synthetic polymers are produced by step-

growth polymerization, e.g. polyesters, polyamides, polyurethanes, etc. Due to the nature of the polymerization mechanism, a high extent of reaction is required to achieve high molecular weight. The easiest way to visualize the mechanism of a step-growth polymerization is a group of people reaching out to hold their hands to form a human chain — each person has two hands (= reactive sites). There also is the possibility to have more than two reactive sites on a monomer: In this case branched polymers are produced.

Self condensation:

In one type of polymerization reaction, a series of condensation steps take place whereby monomers or monomer chains add to each other to form longer chains. This is termed 'condensation polymerization' or 'step-growth polymerization', and occurs for example in the synthesis of polyesters or nylons. It may be either a homopolymerization of a single monomer A-B with two different end groups that condense or a copolymerization of two co-monomers A-A and B-B. Small molecules are usually liberated in these condensation steps, in contrast to polyaddition reactions with no liberation of small molecules.

In general, condensation polymers form more slowly than addition polymers, often requiring heat. They are generally lower in molecular weight. Monomers are consumed early in the reaction; the terminal functional groups remain active throughout and short chains combine to form longer chains. A high conversion rate is required to achieve high molecular weights as per Carothers' equation.

Bifunctional monomers lead to linear chains (and therefore thermoplastic polymers), but, when the monomer functionality exceeds two, the product is a branched chain that may yield a thermoset polymer.

or ,

Condensation polymers are formed by the combination of monomers with the elimination of simple molecules such as H2O or CH3OH.

There are two types of Condensation polymers:

1. Polyester.

2. Polyamide.

Examples: Nylon, terylene, Bakelite.

Ques 28:

Initiator: The substance or molecule (other than reactant) that initiates a chain reaction, as in polymerization; an example is acetyl peroxide.

initiator, a source of any chemical species that reacts with a monomer (single molecule that can form chemical bonds) to form an intermediate compound capable of linking successively with a large number of other monomers into a polymeric compound.

The most widely used initiators produce free radicals (reactive atoms or groups of atoms that contain odd numbers of electrons); examples include peroxides and aliphatic azo compounds used to polymerize vinyl chloride, methyl methacrylate, and other monomers.

Acid-forming systems such as boron trifluoride with traces of water react with a monomer to produce a positively charged (cationic) intermediate. Such initiation is used in the conversion of isobutylene to butyl rubber.

Reaction of metallic sodium and biphenyl produces an anionic initiator that causes formation of polymer chains with reactive sites at both ends; these may be further treated with a different monomer to yield block copolymers.

Polypropylene and high-density polyethylene are prepared by use of Ziegler catalysts, which are initiators composed of organometallic compounds and metallic halides, such as triethylaluminum and titanium tetrachloride.

Azobisisobutyronitrile (abbreviated AIBN) is an organic compound with the formula [(CH3)2C(CN)]2N2. This white powder is soluble in alcohols and common organic solvents but is insoluble in water. It is often used as a foamer in plastics and rubber and as a radical initiator.

Atom transfer radical polymerization (ATRP) is an example of a living polymerization or a controlled/living radical polymerization (CRP). Like its counterpart, ATRA or atom transfer radical addition, it is a means of forming a carbon-carbon bond through a transition metal catalyst. As the name implies, the atom transfer step is the key step in the reaction responsible for uniform polymer chain growth

A cross-link is a bond that links one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers (such as proteins). When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of cross-links to promote a difference in the polymers' physical properties. When "crosslinking" is used in the biological field, it refers to the use of a probe to link proteins together to check for protein–protein interactions, as well as other creative cross-linking methodologies.

Cross-linking is used in both synthetic polymer chemistry and in the biological sciences. Although the term is used to refer to the "linking of polymer chains" for both sciences, the extent of crosslinking and specificities of the crosslinking agents vary. Of course, with all science, there are overlaps, and the following delineations are a starting point to understanding the subtleties. When cross links are added to long rubber molecules, the flexibility decreases, the hardness increases and the melting point increases as well.

Ques 29 :

Why Polymer Modification?

Turn one polymer into another!

Fundamental premise: Reactivity is unaffected by polymeric state. Often true, but not always (especially for heterogeneous reactions).

Yield is really conversion.

If conversion < 100%, the product is a copolymer. You cannot separate and remove unreacted repeat units or attached by-products.

Common themes: Make an insoluble polymer from a soluble one, or vice-versa.

Often performed on natural polymers.

A polymer can be modified at the synthesis stage by adjusting the monomer types and ratios. When the polymer is finished it can be surface treated to improve adhesion. As an example, polypropylene can be corona discharge treated, to improve adhesion of printing ink. Another technique is to flame treat.

Ques 30:

Read page 22 "Natural fiber book of Bakr sir"

Ques 33:

Inhibitor :Addivant inhibitors are critical process aids in the manufacture of styrene & acrylic monomers such as styrene, divinylbenzene, acrylic acid, & methyl methacrylate among others. They work by interfering with the chain initiation &/or chain propagation steps of the polymerization during manufacture & purification, when the monomers are at elevated temperatures. Some monomers can undergo thermally initiated polymerization even at ambient temperatures, but higher temperatures accelerate the rate of reaction. The polymerization is exothermic, thus becoming autocatalytic with the potential for explosion.

The use of polymerization inhibitors prevents temperature excursions due to exothermic polymerization, “fouling” & the build-up of large amounts of polymer in the process enabling manufacture & purification to run smoothly, reducing unscheduled shutdowns & increasing output.

Styrene inhibitors are categorized by their inhibition efficiency & protection length. ‘Retarders’ have lower efficiency but are effective for an extended time period. ‘True inhibitors’ are more efficient but are effective for a shorter time period. Addivant™ offers both retarders & true inhibitors as well as their synergistic combinations.

Retarder : Retarders are used in applications where control or analysis of polarization states is required. A retarder (or waveplate) is an optical device that resolves a light wave into two orthogonal linear polarization components and produces a phase shift between them. The resulting light wave is generally of a different polarization form. Ideally, retarders do not polarize, nor do they induce an intensity change in the light beam, they simply change its polarization form.

Entropy : Change of entropy during polymerization. Large and negative due to ordering of monomer molecules into chains.

Ques 34 :

4th semester polymer science question

Ques 35 :

Isotactic - all chiral centers same

Syndiotactic - chiral centers alternate

Atactic - chiral centers random

Ques 36:

In polymer chemistry, ring-opening polymerization (ROP) is a form of chain-growth polymerization, in which the terminal end of a polymer chain acts as a reactive center where further cyclic monomers can react by opening its ring system and form a longer polymer chain (see figure). The propagating center can be radical, anionic or cationic. Some cyclic monomers such as norbornene or cyclooctadiene can be polymerized to high molecular weight polymers by using metal catalysts. ROP

continues to be the most versatile method of synthesis of major groups of biopolymers, particularly when they are required in quantity.

The driving force for the ring-opening of cyclic monomers is via the relief of bond-angle strain or steric repulsions between atoms at the center of a ring. Thus, as is the case for other types of polymerization, the enthalpy change in ring-opening is negative.[3]

Cyclic monomers that are polymerized using ROP encompass a variety of structures, such as:

alkanes, alkenes,

compounds containing heteroatoms in the ring:

i. oxygen: ethers, acetals, esters (lactones, lactides, and carbonates), and anhydrides,

ii. sulfur: polysulfur, sulfides and polysulfides,

iii. nitrogen: amines, amides (lactames), imides, N-carboxyanhydrides and 1,3-oxaza derivatives,

iv. phosphorus: phosphates, phosphonates, phosphites, phosphines and phosphazenes,

v. silicon: siloxanes, silathers, carbosilanes and silanes.

Intermolecular Force:

The intermolecular forces for polymers 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.

Dispersion Forces , Dipole-Dipole Forces , Hydrogen Bonds

Ques 37 :

Difference:

Originally, “rubber” referred to a naturally derived (organic) material. The term was first used by an English chemist (Joseph Priestley). Joseph was working with natural rubber and observed that it could “rub out” a pencil mark.

In the past, “rubber” was used to describe materials that occurred naturally in nature; and “elastomer” was used for materials that were produced synthetically ... silicone elastomers, for example.

An elastomer is a polymer that shows elastic properties. Since the terms rubber-like and elastomeric mean almost the same thing, the terms “rubber” and “elastomer” are often used interchangeably today to describe silicone elastomers.

Ques 38:

Covalant bonding and dispersion forces

Ques 39:

There is no relationship between the glass transition point and crystalline melt point for a given polymer. Tg is a function of the mobility of the polymer chains, Tm is a function of intermolecular interaction and repeat unit stereo regularity. The naphthalene group of PEN does indeed stiffen the polymer chain, but if you build a model of a couple repeat units, you will see that the naphthalene groups also interfere with the dipole-dipole interaction of the ester carbonyls, at least compared to the para-phenyl group of PET.

As for crystallinity, it does strengthen the polymer, but at the same time makes it more brittle. In any crystalline substance, a force applied in the direction of a lattice can produce a micro crack; but for an amorphous polymer, there is no lattice for a crack to propagate. The best way to study these effects is by Dynamic Mechanical Analysis (DMA); I would check out some literature on this subject. Highly theoretical.

Factors effecting Tg:

1. Measuremnt techniques for tg from diff. instruments

2. Detailed study of DSC

3. Molecular weight

4. plasticizers

5. melting point

Ques 40:

Crystallinity is indication of amount of crystalline region in polymer with respect to amorphous content.Crystallinity influences many of the polymer properties some of there are - Hardness, Modulus , Tensile, Stiffness , Crease , Melting Point

Degree of Crystallinity : Fraction of the ordered molecules in polymer is characterized by the degree of crystallinity, which typically ranges between 10% and 80%.[3]Higher values are only achieved in materials having small molecules, which are usually brittle, or in samples stored for long time at

temperatures just under the melting point. The latter procedure is costly and is applied only in special cases.

Most methods of evaluating the degree of crystallinity assume a mixture of perfect crystalline and totally disordered areas; the transition areas are expected to amount to several percent. These methods include density measurement, differential scanning calorimetry (DSC), X-ray diffraction (XRD), infrared spectroscopy and nuclear magnetic resonance (NMR). The measured value depends on the method used, which is therefore quoted together with the degree of crystallinity.

From Ques 41-50 use the Natural Fiber book's 1st Chapter and 4th semester note