MSE 2100 Module 5: Structure of Polymers

thermoplastic polymer

A semicrystalline polymeric material that softens when heated and hardens upon cooling. While in the softened state, articles may be formed by molding or extrusion. Has linear and branched structures recyclable materials

monomer

A stable molecule from which a polymer is synthesized.

isotactic configuration

A type of polymer chain configuration (stereoisomer) in which all side groups are positioned on the same side of the chain molecule.

atactic configuration

A type of polymer chain configuration (stereoisomer) in which side groups are randomly positioned on one side of the chain or the other.

syndiotactic configuration

A type of polymer chain configuration (stereoisomer) in which side groups regularly alternate positions on opposite sides of the chain.

spherulite

An aggregate of ribbon-like polymer crystallites (lamellae) radiating from a common central nucleation site; the crystallites are separated by amorphous regions.

Permeability coefficient

Pm=D*S permeability coefficient is the product of the diffusion coefficient and solubility in the polymer

stereoisomerism

Polymer isomerism in which side groups within repeat units are bonded along the molecular chain in the same order but in different spatial arrangements.

degree of polymerization

The average number of repeat units per polymer chain molecule.

repeat unit

The most fundamental structural unit in a polymer chain. A polymer molecule is composed of a large number of repeat units linked together.

functionality

The number of covalent bonds a monomer can form when reacting with other monomers.

isomerism

The phenomenon by which two or more polymer molecules or repeat units have the same composition but different structural arrangements and properties.

Molecular entanglements occur when chains assume the _______, __________, and _______ shapes or contours as a consequence of ________ _______ ______________

twisted, coiled, and kinked......chain bond rotations *these random coils and molecular entanglements are responsible for a number of characteristics such as elasticity

saturated

A carbon atom that participates in only single covalent bonds with four other atoms.

polymer

A compound of high molecular weight (normally organic), the structure of which is composed of chains of small repeat units.

graft copolymer

A copolymer in which homopolymer side branches of one monomer type are grafted to homopolymer main chains of a different monomer type.

alternating copolymer

A copolymer in which two different repeat units alternate positions along the molecular chain.

macromolecule

A huge molecule made up of thousands of atoms.

block copolymer

A linear copolymer in which identical repeat units are clustered in blocks along the molecular chain.

homopolymer

A polymer having a chain structure in which all repeat units are of the same type.

branched polymer

A polymer having a molecular structure of secondary chains that extend from the primary main chains.

crosslinked polymer

A polymer in which adjacent linear molecular chains are joined at various positions by covalent bonds.

random copolymer

A polymer in which two different repeat units are randomly distributed along the molecular chain.

linear polymer

A polymer produced from bifunctional monomers in which each polymer molecule consists of repeat units joined end to end in a single chain.

network polymer

A polymer produced from multifunctional monomers having three or more active covalent bonds, resulting in the formation of three-dimensional molecules.

copolymer

A polymer that consists of two or more dissimilar repeat units in combination along its molecular chains.

thermosetting polymer

A polymeric material that, once having been cured (or hardened) by a chemical reaction, will not soften or melt when subsequently heated. Has cross linked and network polymers

crystallite

A region within a crystalline polymer in which all the molecular chains are ordered and aligned.

degree of polymerization

DP= Mn/m Mn- number average molecular weight m- repeat unit molecular weight to find m: multiply number of each repeat unit by atomic weight ex. 2 C and 3 H and 1 Cl m=2(12.01)+3(1.01)+1(34.45)

unsaturated

Describes carbon atoms that participate in double or triple covalent bonds and, therefore, do not bond to a maximum of four other atoms.

bifunctional monomer

Designates monomers that may react to form two covalent bonds with other monomers to create a two-dimensional chainlike molecular structure.

trifunctional

Designating monomers that may react to form three covalent bonds with other monomers.

_________ and ______ geometrical isomers are possible when a repeat unit contains a double chain bond

cis and trans

crystallites

crystalline regions plate-shaped and have a chain folded structure chains within the platelet are aligned and fold back and forth on themselves, with folds occurring at the faces

percent crystallinity of a semi-crystalline polymer is dependent on its _______ as well as the densities of the _____ ________ and _______ __________ materials

density; totally crystalline and totally amorphous

percent crystallinity

(pc(ps-pa))/(ps(pc-pa))*100 ps-density of specimen for which the percent crystallinity is to be determined pa- density of totally amorphous polymer pc- density of perfectly crystalline polymer pc=nA/VcNa n-number of repeat units A-repeat unit molecular weight Vc-unit cell volume Na-avagadros number

chain-folded model

For crystalline polymers, a model that describes the structure of platelet crystallites. Molecular alignment is accomplished by chain folding that occurs at the crystallite faces.

cis (structure)

For polymers, a prefix denoting a type of molecular structure. For some unsaturated carbon chain atoms within a repeat unit, a side atom or group may be situated on one side of the double bond or directly opposite at a 180° rotation position. In a cis structure, two such side groups within the same repeat unit reside on the same side (e.g., cis-isoprene).

trans (structure)

For polymers, a prefix denoting a type of molecular structure. For some unsaturated carbon chain atoms within a repeat unit, a single side atom or group may be situated on one side of the double bond, or directly opposite at a 180° rotation position. In a trans structure, two such side groups within the same repeat unit reside on opposite sides (e.g., trans-isoprene).

crystallinity(polymer)

For polymers, the state in which a periodic and repeating atomic arrangement is achieved by molecular chain alignment.

For repeat units that have more than one side atom or groups of atoms bonded to the main chain:

Head-to-head and head-to-tail configurations are possible. Differences in spatial arrangements of these side atoms or groups of atoms lead to isotactic, syndiotactic, and atactic stereoisomers.

Fick's First Law

J = Pm(deltaP/deltax) Pm- permeability coefficient deltaP- difference in pressure of the gas across the membrane deltax- membrane thickness diffusion flux for steady-state diffusion through a polymer membrane

number average molecular weight

Mn=summation(xiMi) Mi- mean molecular weight of size range i xi- fraction of the total number of chains within the corresponding size range if given molecular weight range like xxx-yyy, find Mi by adding xxx&yyy & divide sum by 2 Mn>Mw

weight average molecular weight

Mw=summation(wiMi) Mi- mean molecular weight within a size range wi-weight fraction of molecules within the same size interval Mn>Mw

molecular weight

The sum of the atomic weights of all the atoms in a molecule.

molecular chemistry

With regard only to composition, not the structure of a repeat unit.

molecular structure

With regard to atomic arrangements within and interconnections between polymer molecules.

spherulites

formed by many semicrystalline polymers each spherulite consists of a collection of ribbon-like chain-folded lamellar crystallites that radiate outward from the center

semi-crystalline

in addition of being entirely amorphous, polymers may also exhibit varying degrees of crystallinity-- crystalline regions dispersed within amorphous areas

defects in polymers

include: vacancies, interstitial atoms, impurity atoms, chain ends, dangling and loose chains, an dislocations

amorphous polymers are possible when the chains are _____ and ______

misaligned and disordered

diffusion

permeation of gaseous species characterized in terms of permeability coefficient rates of diffusion are greater in amorphous than in crystalline smaller molecules diffuse faster than larger

__________ ____________ is diminished when double chain bonds are present and also when bulky side groups are part of the repeat unit

rotational flexibility

diffusion in polymers

small molecules of foreign substances diffuse between molecular chains by an interstitial-type mechanism from one void to an adjacent one