Week 6-7-8(polymers)

Question 1

techniques used to form polymers into desirable shapes :

Answer 1

1. solution casting
2. melt molding
3. machining

Question 2

Ho can we make Polymers more compatible?

Answer 2

Polymers can also be made reactive so that different chemical molecules can be attached to the surface of implants in order to make them more compatible with the surrounding environment in the body.

Question 3

Adjacent polymeric chains or the different segments of the same chain may bond together by:

Answer 3

1. intermolecular forces or Van der Waals bonds.
2. In some cases, ionic bonds may also occur.

Question 4

Covalent bonds in polymers

1. Characteristics
2. Properties determined by covalent bonds

Answer 4

1. Relatively high energy, fixed angle, short distances (0.11-0.16 nm).
2. Determine the mechanical, thermal, chemical, and photochemical properties of a polymer.

Question 5

What physical characteristics of a material (polymer ) Govern the Secondary bonds:

Answer 5

1. dissolution,
2. melting,
3. diffusion, and
4. flow properties –properties which involve the breaking and forming of these bonds and the movement of the molecules relative to each other.

Question 6

Polymers are classified according to:

Answer 6

1. Origin
2. Thermal properties
3. Skeletal organization or macromolecular structure
4. Chemical composition
5. Conformation and configuration

Question 7

Polymers classification according to Thermal properties

Answer 7

1. Thermoplastic polymers:
   
   • soft upon heating
   • reversible process
2. Elastomers:
   
   • flexible, elastic polymer upon heating/cooling
   • slightly cross-linked
3. Thermosets:
   
   • soft at room temperature and hard upon heating.
   • irreversible process –upon heating the chains cross-link –high density of cross-linking
4. Crystalline polymers:
   • have melting temperature (Tm) which will depend on chemical composition and molecular weight.
5. Amorphous polymers:
   
   • have glass transition temperature (Tg) –glassy to rubbery transition –onset of segmental motion of chains.

Question 8

Polymers classification according to Skeletal organization or macromolecular architecture

Answer 8

1. Linear polymer: single molecular backbone
   
   • random coil
   • rigid rod
   • ciclic
2. Branched polymer: Small side chain extending from it.
   
   • randomly branched
   • comb branched:
   • star branched
   • Dendrimer: Perfectly branched macromolecule. level of control of the reaction. becomes significant expensive
   • Hyperbranched: cheap alternative to dendrimers. at very high density of branching

the random orientation of side

chains and angles of covalent bonds

will force the molecule to a nearly

perfect branching.

3. Cross-linked polymer: Network polymer chains covalently bond to one another. called gels, they form highly swollen networks. used to make membranes
   
   • regular ladder:
   • regular spiro:
   • irregular structure

Question 9

Polymers classification according to chemical composition

Answer 9

1. Homopolymer: built of RU of the same composition and structure (only one type of monomer used to form polymer). -AAAAAAAAAAAAA-
2. Heteropolymer chain (heterochain): groups other than Carbon (C) present in backbone -(-C–O-)-_n
3. Copolymer: two types of monomers (A and B) are used in the polymerization reaction:
   
   • block: -AAABBBBAAABBBB- poly (A)-block-poly(B)
   • alternating: -ABABABABABAB- poly (A)-alt-poly(B)
   • random statistical: -AABABAABBABABAABBBAAB- poly (A)-rand-poly(B)

Question 10

Polymers classification according to conformation and configuration:

Answer 10

• If a single polymer chain has carbon atoms in the backbone that have the same substituents, then the polymer is symmetric; if the carbon atoms have different substituents, then the carbon is called asymmetric
  1. Geometric configurations:
  
  1. isotactic: pendant or side groups attached to the carbons in the backbone are all on the same side:
  2. syndiotactic: pendant or side groups are attached alternatively on the carbon backbone:
  3. atactic: pendant or side groups are attached randomly on the carbon backbone:
  4. Cis and trans
     
     2. Geometric conformation (geometric isomers )
        * Isoprene isomers

Question 11

where geometrical isomers are pressent?

Answer 11

Geometrical isomers are present in unsaturated hydrocarbons (C=C), which restrict rotation of C-C due to the double bond.

Since pi bond ( = ) between carbon restricst the free rotation of carbon-carbon sigma bond, i**t creates different configurations of molecules **

Question 12

DP (degree of polymerization)

Answer 12

DP = MW polymer chain / MW monomer unit

Question 13

Average MW =

Answer 13

Average MW = DP_average x MW_monomer

Question 14

M_n=

M_ndescribes

Answer 14

M_n = Σw_i / ΣN_i= ΣM_iN_i / ΣN_i

w_i = total weight of chains with length “i”

w_i = ΣM_iN_i

M_i= molecular weight of a chain with DP of “i”

N_i = total number of chains of length “i”

• M_n describes size only: BRITTLENESS-FLOW PROPERTIES

Question 15

M_w =

M_w describes

Answer 15

M_w = Σ(M_iw_i) / Σ(M_iN_i) = Σ(M_iw_i) / Σ(w_i)

M_w = Σ(M_i²N_i) / Σ(M_iN_i)

w_i = ΣM_i x N_i

• M_w describes size and weight: TENSILE STRENGTH HARDNESS

Question 16

Polydispersity index

PDI =

Answer 16

PDI = Mw/ M_n

Question 17

Relationship between MW and Viscosity of a polymer

Answer 17

[viscosity] = K M_v

Mv = viscosity average molecular weight (which lies between M_n and M_m)

Viscosity is proportional to MW

Viscosity increase by a factor of 3-4 with MW

Question 18

1. MW (CH₄) 16 to MW 58 =
2. MW 114 =
3. MW 450 =
4. MW 420,030 =

Answer 18

1. GASES
2. LIQUIDS
3. SEMI-solid ( chains start to entangle)
4. SOLID (high chain entanglement)

Question 19

There are two main types of polymerization reactions:

Answer 19

1. o Addition (chain polymerization or chain growth)
2. o Condensation (step polymerization or step growth)

Question 20

Addition polymerization:

Answer 20

1. monomers with double bonds sequentially attach to the growing end of a forming polymer chain.
2. the atoms in the monomer are directly added to the chain and thus the monomer and the repeat unit have the same number of atoms.
3. there is usually an initiator that reacts with a monomer to start the reaction. This will create a free radical that will react with the next monomer and so on.
4. in this type of polymerization, the molecular weight of the polymer increases quickly while the consumption of monomers occurs at a slow rate.
5. o products of chain growth exhibit **broad molecular weight distribution. **

Question 21

Condensation polymerization

Answer 21

1. elimination of some atoms as a by-product during the reaction between the monomer and the growing chain.
2. results in fewer atoms in the reacted repeat unit than in the monomer.
3. reactions take place throughout the monomer matrix, and any two reactive monomer molecules with the correct orientation and energy will react.
4. reactions take place in a multitude of sites, thus changes in molecular weight occur slowly while the monomer is consumed rapidly.
5. in general step growth polymerization yields polymers with a narrow range of molecular weight distributions.

Question 22

Free Radica polymerization steps:

Answer 22

PMMA (total joint replacement)

1. Initiation:
   
   • BPO (benzoil peroxide) = initiator.
   • Generates free radicals (RO•)
   • Accelerator can be 1) heat or 2) DMPT (N,N dimethyl-p-toluidine)
2. Propagation:
   
   • RO• + monomer unit (MMA) ⇒ breaks down the (C=C) → RO–CH_2–CH₂(COOCH₃)•
   • RO–CH2–CH2(COOCH3)• + monomer unit (MMA)
3. Termination: Radical Combination ((HEAD TO HEAD termination) or Disproportionation (Hydrogen transfer).

Question 23

Condensation polymerization steps:

Answer 23

• We require appropiate functional groups (functional group transformations of polyfunctional reactants.)
• These polymerizations often (but not always) occur with loss of a small byproduct, such as water, and generally (but not always) combine two different components in an alternating structure.
• Controlled MW and dispersion
• very controlled Temperature and Pressure
• Ex. Nylon, PET (polyethylene therphthalate)

Question 24

pendant groups influence on:

1. Crystalinity (amorphous)
2. and Tg

Answer 24

1. Amorphous polymers can be formed due to the presence of bulky side groups such as benzene in styrene (fish hook)
2. Tg decreases with the presence of larger side groups

Question 25

How can we increase the flexibility of a polymer

Answer 25

1. by inserting ether linkages into the backbone T_g decreases
2. by adding bulky side chains or pendant groups –> they act as plasticizers decreasing T_g –> increasing the free space.

• Execption is the Benzene group –> T_g increases

Question 26

What happen when we insert ether linkages into the backbone

Answer 26

ether groups can aid in flexibility in the backbone chain. –> Tg decreases

Question 27

Tg is affected by?

Answer 27

1. Flexibility of backbone
2. Pendant groups
3. MW
4. Plasticiezers

Question 28

Pendant group (Benzene ring) effect on Tg

Answer 28

1. Bulky pendant groups, such as a benzene ring, can catch on neighboring chains like a “fish hook” and restrict rotational freedom. This increases Tg.

Question 29

Temperatures for :

1. Amorphous polymer
2. semi-crystaline polymer
3. Crystaline polymer

Answer 29

1. Amorphous polymer: only Tg
2. semi-crystaline polymer: Tg and Tm
3. Crystaline polymer: only Tm