Polymer Structure and Chemistry (Структура и химия полимеров). Учебное пособие

3

4 3 3

3. & ' $(

' . to form polymer chains

to categorize

step polymerization

incorporating double chemical bonds to link up with other monomers

to bond together

the loss of a small molecule functional groups

4. '

1.

5. .

' .

. 3 — 3

4 ;3 3

3 4 3 , 4 3

4 . / 3 3

, 4 , ,

, 3 3 3,

.

. — 3

(4 ) ,

4 3 3

( , . .) 3

.

6. ' $(

'.

Condensation polymers are any class of polymers formed through a condensation reaction, releasing (or condensing) a small molecule by-

11

product such as water or methanol, as opposed to addition polymers which involve the reaction of unsaturated monomers. Types of condensation polymers include polyamides, polyacetals and polyesters.

Condensation polymerization, a form of step-growth polymerization, is a process by which two molecules join together, with the loss of a small molecule which is often water. The type of end product resulting from a condensation polymerization is dependent on the number of functional end groups of the monomer which can react.

Monomers with only one reactive group terminate a growing chain, and thus give end products with a lower molecular weight. Linear polymers are created using monomers with two reactive end groups and monomers with more than two end groups give three dimensional polymers which are crosslinked.

7. $

$( '.

In polymer chemistry, a series of condensation reactions take place whereby monomers or monomer chains add to each other to form longer chains. This may also be termed as “condensation polymerization” or “stepgrowth polymerization”. It occurs either as a homopolymerization of an A- B monomer or a polymerization of two co-monomers A-A and B-B. Small molecule condensates are usually liberated, unlike in addition polymerization where there is no liberation of small molecules.

A high conversion rate is required to achieve high molecular weights.

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.

8. '

$( .

1.In the synthesis of polymers, monomers react and become covalently bonded with one another through the loss of a water molecule.

2.A condensation reaction may be considered as the opposite of a hydrolysis reaction.

3.Most commonly known condensation polymers are proteins, and fabrics such as nylon, silk, or polyester.

12

4.Addition polymerization involves the breaking of double or triple bonds, which are used to link monomers into chains.

5.Chain growth polymers grow to high molecular weight at a very fast rate.

6.Condensation polymers, unlike addition polymers are bio-degradable.

7.The first useful addition polymer was made by accident in 1933 by chemists Reginald Gibson and Eric Fawcett.

8.Addition polymers are widely used today in the form of rubber.

9.Addition polymers are non-biodegradable and hard to recycle.

10.An addition polymer is a polymer which is formed by an addition reaction, where many monomers bond together via rearrangement of bonds without the loss of any atom or molecule.

9. '

$( .

1.' 3 3 3

3 3 3 3,

3 3, 4 .

2. . 3 ( , 2" ", ,

.) 3

3 4 3

3.

3. .3 3 3, 4

3 3 3

.

4.3 3,

3 3 3 3

, 4 3 3

3 .

5. .3 — : 3

4, 3 3 3 (3 3)

;3 3

3 4 (3 3) 3

4 .

6. .3 — : 3 3, 3

3 3 3 3 ( 3 3)

3

3 .

7. . — : 3 -

13

(3 3),

4 3 3

4 ( , , .).

8. .

, , .

9. . 4 3 3 3

3 3 ( 3 3)

3 ( ).

10.3 3 3/4 4 3

3, 3

, , ,

, 3

.

10. '

$( .

monomer molecules — 3 — step-growth polymerization

— 4 3 3 — triple chemical bond —

— to incorporate double chemical bonds —

— multiple bond — — byproduct — 3 — crosslinked polymer —

— synthetic rubber — — threedimensional networks — 3 — triple chemical bond — — non-saturated monomers — release of water — — 3 — conversion rate —

11. ) ' $

.

1.What is addition polymerization?

2.What is condensation polymerization?

3.What are the examples of addition polymers?

4.What are the examples of condensation polymers?

5.What kind of polymers is generally lower in molecular weight?

12.

'.

14

UNIT 3

SUPRAMOLECULAR STRUCTURE OF POLYMERS

1. .

Polymer molecules come in many shapes and sizes. A polymer may be a long chain of a single monomer repeated over and over again or a complex network containing dozens of different types of monomers. The identity, variety, and arrangement of monomers in a polymer molecule affect the chemical and physical properties of the polymer molecule. The arrangement of macromolecules defines bulk properties of the polymer material.

A synthetic polymer may be described as crystalline if it contains regions of three-dimensional ordering on atomic (rather than macromolecular) length scales, usually arising from intramolecular folding and/or stacking of adjacent chains. Synthetic polymers may consist of both crystalline and amorphous regions; the degree of crystallinity may be expressed in terms of a weight fraction or volume fraction of crystalline material. Few synthetic polymers are entirely crystalline.

Polymer crystals frequently do not display the perfection that is usual for low-molar-mass substances. A crystallite may have irregular boundaries and parts of its constituent macromolecules may extend beyond its boundaries. The smallest, regularly repeating material portion contained in a parallelepiped from which a crystal is formed by parallel displacements in three dimensions is called a unit cell.

Unlike in the case of low-molar-mass substances, the unit cell of polymer crystals usually comprises only parts of the polymer molecule and the regularity of the periodic repetition may be imperfect.

2. & '

$( ' .

4

3 3

3

3

15

3 3 3

3

3 3 3

3. & ' $(

' . unit cell

arrangement of molecules degree of crystallinity intramolecular folding crystallite

volume fraction crystalline region three-dimensional ordering constituent macromolecule imperfect regularity

macromolecular length scale stacking of adjacent chains repeating material portion parallel displacement complex network

4. '

1.

5. '

.

2 3

— ,

. .

3 3. '

3 3 3 4

16

3. )

3 , , ,

< 3

.

. 2" — :

. ' — : ,

; 3

. 2 2" 3

3 3 . & 3

3 2",

3 3 .

6. ' $(

':

The attractive forces between polymer chains play a large part in determining a polymer’s properties. Because polymer chains are so long, these interchain forces are amplified far beyond the attractions between conventional molecules. Different side groups on the polymer can lend the polymer to ionic bonding or hydrogen bonding between its own chains. These stronger forces typically result in higher tensile strength and melting points.

The attractive forces between polyethylene chains arise from weak Van der Waals forces. Molecules can be thought of as being surrounded by a cloud of negative electrons. As two polymer chains approach, their electron clouds repel one another. This has the effect of lowering the electron density on one side of a polymer chain, creating a slight positive dipole on this side. This charge is enough to actually attract the second polymer chain. Van der Waals forces are quite weak, however, so polyethylene can have a lower melting temperature compared to other polymers.

7. $

$( '.

Branching of polymer chains also affect the supramolecular properties of polymers. Long chain branches may increase polymer strength and toughness, due to an increase in the number of entanglements per chain.

Short side chains may likewise reduce crystallinity due to disruption of the crystal structure. Reduced crystallinity may also be associated with

17

increased transparency due to light scattering by small crystalline regions. A good example of this effect is related to the range of physical

attributes of polyethylene. High density polyethylene (HDPE) has a very low degree of branching, is quite stiff, and is used in applications such as milk jugs. Low density polyethylene (LDPE), on the other hand, has significant numbers of short branches, is quite flexible, and is used in applications such as plastic films.

The branching index of the polymer is a parameter that characterizes the effect of long-chain branches on the size of a branched macromolecule in solution.

8. '

$( :

1.Tie molecule: a molecule that connects at least two different crystals.

2.Stem: a crystallized, sticklike portion of a polymer chain connected to non-sticklike portions, or chain ends.

3.Chain folding: the conformational feature in which a loop connects two parallel stems belonging to the same crystal.

4.Globular-chain crystal: a type of crystal comprised of macromolecules having globular conformation.

5.Dendrite: a crystalline body produced by skeletal growth, leading to a ‘tree-like’ supramolecular structure.

6.Fibrous crystal: a type of crystal significantly longer in one dimension than in either of the other two.

7.Shish-kebab structure: a polycrystalline structure consisting of fibrous crystals surrounded by lamellar crystals, the stems of which are parallel to the fibre axis.

8.Spherulite: a polycrystalline, roughly spherical morphology consisting of lath, fibrous or lamellar crystals emanating from a common centre.

9.Lath crystal: a lamellar crystal prevailingly extended along one lateral dimension.

10.Extended-chain crystal: a polymer crystal in which the chains are in an essentially fully extended conformation.

9. '

$( .

1.2 4 4

, 4

, 4 3

3.

18

2.( 3 3 < 3 .

3.3 3

3 3 3.

4." 3 3

3 .

5. . , 3 3 3 3,

3 , ;

3 3.

6.3 3 3 3 3 3

, , 3

.

7.2" 3 3

— .

8.) 3

3, 3,

3 3 3 3 3.

9. .: 3

: 3

.

10.3 3 3

3 3 3 .

10. '

$(

crystallite — — intramolecular folding — 3 — constituent macromolecule — fourth order structure

—— parallel displacement — 3

— arrangement of molecules — 4 —

— macromolecular length scale —

— 3 3 — stacking of adjacent chains — volume fraction — 3 — crystalline region —

— imperfect regularity — 3 3 — three-dimensional ordering — 3 3 —

— unit cell — 3 — tertiary structure

—degree of crystallinity — repeating material portion —

3 — complex network — supramolecular level —

—

19

11. ) ' $

.

1.What scale of polymer structure and properties is called supramolecular?

2.Describe two main types of organization in supramolecular polymer aggregates.

3.What is a crystalline phase?

4.What is more amorphous: HDPE or LDPE?

5.Are polymer crystals more regular than the low molecular weight ones?

12.

'.

20