MatE exam 3 polymers

polymers

long-chain moleucles made of repeating monor units

what are the two types of polymers

homopolymers and copolymers

what are homopolymers?

polymers composed of identical monomers

what are copolymers?

polymers composed of two or more different monomers

how many types of copolymers are there?

4

3 multiple choice options

random copolymers?

monomers arranged randomly

3 multiple choice options

alternating copolymers?

monomers alternate regularly

3 multiple choice options

block copolymers?

blocks of monomers grouped together

3 multiple choice options

graft copolymers?

branches of one polymer grafted onto the main chain

3 multiple choice options

what are pros and cons of homopolymers?

pros: simpler in structure and processing

cons: less versatile than copolymers

what is one characteristic of copolymers?

allow for customization of properties through different arrangements of monomers

what is a characteristic of random copolymers?

they can disrupt crystallinity, often resulting in softer and more flexible materials

what is a characteristic of alternating copolymers?

enhances crystallinity making the material stronger and more heat-resistant compared to random copolymers

what is a characteristic of block copolymers?

exhibit phase-separated structures which can enhance properties like toughness and impact resistance

what is a characteristic of graft copolymers?

exhibit enhanced adhesion or compatibility with other substrates

linear polymers

single chains with strong intermolecular forces

branches polymers

side chains reduce packing efficiency and have lower density

cross-linked polymers

chains are linked by covalent bonds increasing their strength

network polymers

highly interconnected rigid structures

linear polymer relationship

more flexible and have good processing properties

branched polymer relationship

reduce crystallinity and density compared to linear forms

cross-linked polymer relationship

stiffer and less flexible but have higher mechanical strength

network polymers relationship

most rigid and resistant to deformation due to extensive covalent bonding

what are the two types of polymer crystallinity?

amorphous (disordered) and crystalline (ordered)

crystalline characteristic

enhance strength and modulus

percent crystallinity

affects mechanical properties and is influenced by molecular weight, chain structure, and processing

what does increased crystallinity lead to?

increased strength and thermal stability

amorphous polymer characteristic

more flexible and impact-resistant, lower strength and thermal stability compared to crystalline polymers

crystalline polymer characteristic

greater strength, higher melting points, and better resistance to solvents, and better resistance to solvents but more brittle than amorphous polymers

semi-crystalline polymer characteristics

balance between amorphous and crystalline

higher molecular weight and crystallinity

increase modulus and tensile strength

3 multiple choice options

cross-linking characteristic

reduces chain mobility, enhancing strength and heat resistance

how do polymers behave under low temperatures?

brittle behavior

how do polymers behave under high temperatures?

viscous, fluid-like behavior

how do polymers behave under intermediate temperatures?

viscoelastic, showing both characteristics

how do glassy polymers behave?

they exhibit elastic properties

2 multiple choice options

how do rubbery polymers behave?

exhibit high viscoelasticity

3 multiple choice options

how do thermoplastic elastomers behave?

they behave as both elastomers and plastics based on temperatures

glass transition temperature

point where amorphous regions become soft and rubbery

melting temperature

point where crystalline regions melt into viscous liquid

what is the relationship between crystallinity and melting temperature?

they have a proportional relationship

1 multiple choice option

what lowers the glass transition temperature?

plasticizers; they enhance flexibility

cross-linking characteristics

increases thermal stability and resistance to deformation

how many types of polymer forming techniques are there?

4

3 multiple choice options

injections molding

a method of forming polymers in a mold while they harden

pros of injection molding

ideal for complex geometries, high precision, fast cycle times

cons of injection molding

high initial tooling cost, not economical for low-volume production

extrusion

a method of forming polymers with constant cross-sections through a die while they solidify

pros of extrusion

continuous production, low cost per unit, excellent for long products

cons of extrusion

limited to uniform cross-sections, not suitable for complex internal geometries

blow molding

similar to blow molding of glass

pros of blow molding

efficient for hollow shapes (bottles), low material waste

cons of blow molding

limited to thin-walled objects, more difficult for multi-layer structures

casting

liquid polymer poured into a mold

pros of casting

low cost for small runs, versatile shapes, simple process

cons of casting

slower production rates, not suitable for very high-strength applications

bipolymers

derived from biological origins (polylactic acid, cellulose)

- medical sutures

- biodegradable packaging

conductive polymers

polymers with electrical conductivity (polyaniline, polyacetylene)

- flexible electronics

- sensors

high-performance polymers

engineered for extreme conditions (PEEK, PPS)

- aerospace

- automotive

- high temperature components

thermoplastic elastomers (TPE)

combines the properties of rubbers and plastics

- automotive parts

- seals

- flexible tubing

ultra-high molecular weight polyethylene (UHMWPE)

high crystallinity and density, excellent toughness, and wear resistance

- bulletproof vests

- medical implants

- skis

spider silk and kevlar

biological and synthetic fibers with high tensile strength

- protective gear

- ropes

- textiles