MATSCIE 250-200 Fall 2025 Homework#8
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MATSCIE 250-200 Fall 2025 Homework#8
Due: Tuesday, December 2, 2025
Q1. Compare and discuss the molecular structures, bonding types, and mechanical characteristics of thermoplastics, thermosets, and elastomers.
9 points: (3 points each, plus 1 extra for clarity)
Q2. Which of the following polymers are recyclable (i.e., melted and remolded)? Briefly explain why for each one.
10 points: 2 points each (1for correct answer yes/no + 1for explanation)
a) linear polypropylene
b) vulcanized polydimethylsiloxane
c) polyethylene terephthalate (PET)
d) branched polyethylene
e) epoxy resin
Q3. Determine (if possible) which polymer is more likely to crystallize:
10 points: 2 points each (1for selecting correct polymer + 1for explanation)
a) branched atactic polypropylene vs. linear syndiotactic polypropylene
b) network melamine (pg. A36) vs. lightly-crosslinked (5%) polyethylene
c) linear polyethylene vs. linear polystyrene
d) graft poly(styrene-butadiene) vs. alternating poly(éhloroprene-isobutylene)
e) heavily-crosslinked polyethylene terephthalate (PET) vs. phenol-formaldehyde
Q4. For a set of polymers built from the monomers below (with monomer molecular weight M0) with degree of polymerization DP = 5,000, what is the total molecular weight of the polymer?
5 points (1 point each)
|
Polymer |
Structure |
M0 (g/mol) |
|
1,4-Polyisoprene (PI) |
-(CH2CH=CHCH(CH3))- |
120 |
|
Polypropylene (PP) |
-(CH2CH2(CH3))- |
183 |
|
Poly(dimethyl siloxane) (PDMS) |
-(OSi(CH3)2)- |
381 |
|
Polyethylene (PE) |
-(CH2CH2)- |
150 |
|
Poly(methyl methacrylate) (PMMA) |
-(CH2C(CH3)(COOCH3))- |
598 |
Q5. For each of the following pairs of polymers, plot and label schematic stress - strain curves on the same graph [i .e., make separate plots for parts (a) to (c)]. If different behavior between the pairs is expected, please illustrate it in the graphs.
9 points, plus 1 extra for clean drawings (general behavior is ok, but if behavior is different must be clearly shown)
(a) Polyisoprene having a number-average molecular weight of 100,000 g/mol and 10% of available sites crosslinked; polyisoprene having a number-average molecular weight of 100,000 g/mol and 20% of available sites crosslinked
(b) Syndiotactic polypropylene having a weight-average molecular weight of 100,000 g/mol; atactic polypropylene having a weight-average molecular weight of 75,000 g/mol
(c) Branched polyethylene having a number. average molecular weight of 90,000 g/mol; heavily crosslinked polyethylene having a number-average molecular weight of 90,000 g/mol
Q6. Explain on a structural basis the differences in the glass transition temperature of:
6 points: 2 points each, plus 1 extra is explanation is clear and concise
a) polyethylene (Tg = -1400C)
b) polyvinylchloride (Tg=500C)
c) polystyrene (Tg=1000C)
2025-12-05