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Problem Set #2 Attempt all five questions. All questions carry equal points. Question 1. (a) Describe all of the essential raw materials you would need to synthesize a typical vinyl polymer by aqueous emulsion polymerization. (b) Explain the role that each raw material plays in the polymerization reaction. (c) Describe the composition of the emulsion at the microscopic and molecular levels (d) Describe the various stages of an emulsion polymerization and explain the physical and chemical changes that take place as the reaction proceeds from o 100% conversion Question 2 (a) Explain the similarities and differences in polymer chain architectures of hyperbranched polymers and dendrimers. (b) Describe the differences between the divergent and convergent approaches to synthesizing dendrimers. (c) Describe the polymer architecture (linear, branched, hyperbranched or crosslinked) that is obtained by step growth polymerization of each of the monomer blends (i)-(vi) below. Assume a high extent of reaction in each case. (i) A2+B2 (ii) AB2 A2 (iii) A2 B2 AB (iv) AB2 + B3 (v) A2 B3 (vi) A3 AB Question 3 Pure poly(vinyl chloride) (PVC) is a rigid plastic with a glass transition temperature (Tg) of 87°C (360°K) The polymer is fully miscible with the low molecular weight plasticizer dioctylphthalate, which has a Tg value of -86°C (187°K). What weight fraction of phthalate must be blended with the PVC in order to lower the Tg to 40°C (Note: absolute temperature values must be used in this calculation) Question 4. The diagram below shows the DSC trace (heating rate was 10°C/minute) of a sample of the semicrystalline polymer poly(ethylene terephthalate) (PET) of a common water bottle. The thermogram shows three distinct transitions labeled A, each of the transitions and describe the physical changes in the morphology that occur during these transitions. (b) What are the approximate values of glass transition (Tg), crystallization (Tc) and melting (Tm) temperatures of the polymer. What process step could you take to increase the degree of crystallinity of the polymer? (c) If the enthalpy (AH) associated with transition B is -147 J/g and transition Cis 167 J/g, what is the approximate degree of crystallinity (% crystallinity) of the PET polymer in the water bottle? 56 54 52 50 48 48 44 42 40 50 100 150 200 250 Temperature / °C Question 5 (a) Describe the difference between thermoplastic and thermosetting polymers. (b) How are the stiffness, strength, elongation and toughness of polymers evaluated in a quantitative manner? (c) Compare and contrast the physical properties and mechanical behavior of typical polymers in the following classes of materials: (i) flexible plastics (ii) rigid plastics (iii) fibers (iv) elastomers

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Question 1
a) Emulsion polymerization is a free-radical polymerization and requires at least four different components. These four components are; initiator (water soluble), monomer (vinyl, insoluble in water, or with very low solubility), emulsifiers - surfactants (Anionic, nonionic, and cationic surfactants) or non-surfactant stabilizers (water-soluble polymer such as PVA) and a continuous phase (water).

b) Water is the dispersing medium, in which different components are dispersed, due to the presence of the emulsifiers.
Initiators are used to create free radicals and propagating monomers inside the water phase.
Emulsifier (surfactant) molecules aggregate in water to form micelles (if their concentration is high enough – CMC). Polymerization reaction (free-radical) takes place Inside of the micelles...

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