emac 270 final review questions

T/F:

Hermann Staudinger is regarded as the father of polymer science for his discovery of the concept of the polymer. Initially he had great difficulty in convincing fellow scientists because he used colligative properties to demonstrate the constancy of molecular weight before and after the chemical modification of a polymer called polyindene. Unfortunately, colligative property measurements were useful only for large molecular weight polymers, but of limited value for small oligomers. This is the reason why he faced difficulty in proving the concept.

false, colligative property measurements are useful for small molecular weight polymers, including oligomers, but not sensitive for large molecular weight polymers

T/F:

The Fringed-Micelle Model is a model to describe the molecular arrangement of a semicrystalline polymer. In this model, well aligned molecular chains are forming local order (micelles) representing the crystalline portion of the polymer. Connecting the crystalline portion of the polymer with a more randomly coiled molecular chain is the amorphous portion of the polymer. The degree of crystallinity is the fraction of the crystalline portion of the polymer.

true

T/F:

Polydispersity Index (PDI) is the measure of the breadth of disturbance of the molecular weights in a polymer and is defined as the number average molecular weight divided by the weight average molecular weight. A monodisperse polymer is one with PDI = 1. No polymer is able to achieve precisely PDI = 1.

false; PDI is the measure of the breadth of distributions of the molecular weights in a polymer and is defined as the weight average molecular weight divided by the number average molecular weight.

T/F:

Head-to-head sequence isomers are more favorable that head-to-tail sequence isomers because there is less steric hindrance in the head-to-head sequence

false; the least steric hindrance occurs in head-to-tail sequence

T/F:

Crystalline polymers melt and amorphous polymers liquify

true

T/F:

syndiotactic and isotactic polymers tend to be crystalline

true

X-Y diblock polymer

polymer that shows properties of both homopolymer X and homopolymer Y. This polymer can be used to make two immiscible polymers of X and Y

which of the following measurement methods does not determine absolute molecular weight

chromotography

which macromolecular structure exhibits cross-linking

network

T/F:

thermosets will become permanently solid upon heating

true

branching molecule can be synthesized when the number of functionality is

3

which copolymer exhibits average properties of monomers A and B

random copolymer

which of the following stereoisomers tend to be amorphous

atactic

chain transfer:

reaction where a free radical is handed to the partner molecule and free radical reaction start from this new molecule

Trommsdorff-Norrish effect

it is caused by the immobilization of the polymer free radical due to the increased viscosity while maintaining the mobility of the monomer

backbiting

is an example of intramolecular chain transfer

intermolecular chain transfer

the concentration of free radicals does not change

what happens when the concentration of monomers increases

the degree of polymerization increases

retarders

increases the stability of the free radical

Carother's equation

the number average molecular weight can easily be determined

T/F:

I am a chemical engineer whose task is to design a large polymerization reactor using free radical polymerization. My chemist friend told me that the rate of reaction increased when the concentration of the monomer or initiator increased. I am told that my company is interested in producing a polymer with maximum molecular weight possible. I decided to design the reactor with maximum cooling facility since a large molecular weight polymer is favored when increased concentration of the initiator and monomer and charged and such a condition generates high temperature

false; increasing the initiator concentration would decrease the molecular weight, while increasing the monomer concentration would increase the molecular weight

T/F:

A chemical plant, which makes polystyrene, is having problems because they are making their polymer too rapidly for their equipment to handle. Therefore, the plant is starting to investigate inhibitors and retarders to help manage the process. The lead engineer presents his results and says that inhibitors work by converting the radical to a non-radical species and introduces an induction time to the process. This means that the reaction is just delayed for a portion of time until all of the inhibitor is consumed. A retarder works by slowing radical polymerization by decreasing the concentration of monomers in the system

false, inhibitors prevent polymerization from taking place by consuming the free radical species, whereas a retarder slows the polymerization process by converting the free radical into a more stable (less reactive) free radical

T/F:

step polymerization requires an initiator

false

T/F:

coupling is a termination mechanism

false???

T/F: DMA

it measures viscoelastic properties

true

T/F: FT-IR

Jacquinot's advantage is also known as the energy throughput advantage

true

T/F: FT-IR

Fellgett's advantage Multiplex advantage

true

T/F: DSC

the conversion of a thermosetting polymer, such as epoxy, can be studied

true

T/F:

NMR is ideal in determining detailed chemical structure of liquid samples. Using chemical shift concept, one can readily determine the chemical structure of the component in the unknown sample. Despite the fact that each nucleus, such as a proton, has a single Larmar frequency, the surrounding minute difference in electronic environment allow the observed, apparent Larmar frequency to be varies slightly, allowing the observation of chemical shift difference for protons in different chemical groups. NMR can also be used to study molecular mobility using relaxation times, such as T1 and T2 relaxation

false

T/F:

FT-IR has three intrinsic advantages, Conn's advantage, Jocquinnot's advantage, and the computer. Conn's advantage is a frequency accuracy advantage, Jocquinnot's advantage is the energy throughput advantage, and the computer is essentail in FT-IR

false

T/F:

DSC is a technique to study the thermal transitions of a polymer. It measures the heat required to maintain the same temperature, versus an appropriate reference material that does not undergo transitions in the temperature range being investigated. Every polymer will show a melting peak and glass transition temperature indication

false

T/F:

DMA can measure the viscoelastic properties of a polymer. It can be used to determine the cross-link density based on the rubber elasticity theory. The region above the Tg is sensitive to the material flow. The G' spectrum of a polymer shows the glassy region, glass transition region, and rubbery region.

true

T/F:

HPLC works by having a silica gel surface that differentiates between molecules based on their structure. The molecules will interact differently with the gel which causes the separation. This is an example of a purification technique

true

T/F:

TGA is a technique to determine the Mn, Mw, and Mz of a polymer. It heats the sample to 800C and measures the weight as a function of temperature

false

in HPLC, molecules with different chemical structure can be separated due to the interaction of these molecules with the silica gel surface. For example, a compound with a carboxylic acid group with molecular weight of 243 exhibits a peak later than a primary amine with molecular weight of 260

false

processing technique?

construction helmet (low performance product)

compression

processing technique?

nuclear submarine (100m long, 15m wide)

filament winding

processing technique?

PVC pipe (3cm diameter, 500m long)

extrusion

processing technique?

snowmobile

reaction injection molding

processing technique?

golf shaft

filament winding

processing technique?

jet fighter's wing (needs to be high strength)

hand lay-up molding

processing technique?

rocket's body (constant cross section)

pultrusion?

processing technique?

a very small gear used in a miniature, mobile Pokemon toy. Dimensions and precision of the gear is very important as the size of the toy is on the order of a quarter coin

injection molding

processing technique?

fishing boat that is 10m long with great strength to withstand the waves of the rough sea

transfer molding

processing technique?

processing technique for a product requiring a short cycle time

reaction injection molding

processing technique?

a product requiring a closed mold composite that allows the manufacturing of a very large object

transfer molding

processing technique?

processing technique suitable for processing a very intricate shaped object for many thermoplastic polymers

injection molding

processing technique?

processing technique that is the most versatile design flexibility for the mold shape of a product using continuous fiber reinforcement

hand lay-up molding

processing technique?

A roof of a very lightweight hybrid car. the size is approximately 2m (wide) x 3m (long) x 0.5cm (thick). It is basically a rectangular with somewhat concave shape. Monthly production rate is 5000. The matrix to be chosen is polypropylene

compression molding

processing technique?

a patrol boat that is used in a rough sea (15m long, 3m wide). In order to avoid failure at the connection point, the entire boat is to be made with a single part

VARTM

Flory-Huggins chi parameter

radius of gyration

is the average distance from the center of gravity to the chain segment

Flory-Huggins equation

assumes that the change in volume due to mixing is zero

the chi parameter for the theta solvent

0.5

the Tg of polymer A is 50C and the Tg of polymer B is 250C. What is the Tg of a 50/50 weight ratio mixture of both polymers if they are thermodynamically miscible

(use Fox equation) between 70 and 100C

the free volume fraction at Tg

0.025

chi parameter indicates the two polymers are immiscible

0.78

the molecular weight dependence on the viscosity on a log-log plot above the entanglement molecular weight

3.4

material A has a Young's Modulus of 5 GPa and Material B has a Young's Modulus of 10 GPa, so....

material B is stiffer

end to end distance

it is difficult to measure

Mark-Houwink-Sakurada equation

relates the molecular weight and the internal viscosity

melting temperature

is a first order transition

glass transition temperature

has a dependence on molecular weight

Gordon-Taylor equation

takes the thermal expansion coefficients of both polymers into account

asymmetric molecules

Tg = 2/3 Tm

Voigt model

has a dashpot and spring in parallel

G''

is the dynamic loss modulus

time temperature superposition

is based off of a shift factor

T/F:

A hypothetical chain polymer is considered. The distance between the starting atom and the ending atom is defined as the end-to-end distance. This distance can be theoretically calculated assuming no restriction in the chain movement. When a restriction is added based on the bond angle, the end-to-end distance of the same molecule changes. Under the restriction, the end-to-end distance is smaller than the restriction-free molecule

false, the end-to-end distance for the restricted bond angle is sqrt(2) times larger than the unrestricted bond angle case