questions for part 1(3) PDF

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Questions for part 1 (3) of course for preparing final exam...

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Questions Part 1 (3) 1. The tensile strength and number-average molecular weight for two polyethylene materials are as follows: Tensile strength (MPa) 85 150

Number Average Molecular Weight (g/mol) 12,700 28,500

Estimate the number-average molecular weight that is required to give a tensile strength of 195 MPa. 2. List the two molecular characteristics that are essential for elastomers. 3. Which of following would you expect to be elastomers and which thermosetting polymer at room temperature: a) Linear and crystalline polyethylene b) Phenol-formaldehyde c) Heavily cross-linked polyisoprene having a glass-transition temperature of 55oC (122oF) d) Lightly cross-linked polyisoprene having a glass-transition temperature of -60oC (-76oF) e) Linear and partly amorphous polyvinyl chloride 4. Briefly explain the difference in molecular chemistry between silicone polymers and other polymeric materials. 5. Silicone polymers may be prepared to exist as liquids at room temperature. Cite differences in molecular structure between them and silicone elastomers. 6.

List two important characteristics for polymers that are to be used in fiber application

7. Why must fiber materials that are melt spun and then drawn be thermoplastics. Cite two reasons. In which cased there is a need to use electrospinning? 8. a) List several advantages and disadvantages of using transparent polymeric materials for eyeglass lenses b) Cite four properties (in addition to be transparent) that are important for this application c) Note three polymers that may be candidates for eyeglass lenses, and the tabulate values of the properties noted in part (b) for these three materials

9. Polymer containing chemical bonds similar to those found in the body, e.g., amide and ester groups are less biodegradable then polymer containing C-C and C-F bonds. Is this statement true? 10. Which kind of materials should be chose for temporary orthopedic fixation application? Why? 11. What are hydrogels? Name three important hydrogels and their applications? Are hydrogels the highly cross-linked materials? 12. Which materials are suitable for tendon and ligaments implants? Why?...