Ch4 -...

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Unformatted text preview: **TI89**##BOOKS#############################################R###Ch4#########@###¥Z# ####æBEB#bZx&#######H###¾######################ÿÿÿþ##ÿÿÿý##ÿÿÿü##ÿÿÿû##ÿÿÿú##0##### ÿÿÿú####ÿÿÿû###############Uÿÿÿý####ÿÿÿû###########U####ÿÿÿü####ÿÿÿû###########]### #ÿÿÿþ####ÿÿÿû###########e##¼CH 4- STRUCTURES OF POLYMERS # 2. (a) Compute the repeat unit molecular weight of polypropylene. (b) Compute the number-average molecular weight for a polypropylene for which the degree of polymerization is 15,000. d A) For polypropylene, from Table 4.3, each repeat unit has three carbons and six hydrogens. m = 3(A_C) + 6(A_H) h B) DP = M_n(m) so M_n = DP*m where m = 42.08 (m from A)) B ================ 3. Below, molecular weight data for a polytetrafluoroethylene material are tabulated. Compute (a) the number-average molecular weight, (b) the weight-average molecular weight, and (c) the degree of polymerization. m A) Find mean M_i (ie avg molec wt range, [10+20]/2, and compute x_i*M_i. then M_n=sum(x_i*M_i). B) M_W = sum(w_i*M_i) C) m = 2(A_C) + 4(A_F) and DP = M_n/m C ================ 5. Molecular Shape A linear polyethylene has a number-average molecular weight of 300,000 g/mol; compute average values of L and r for this material. c m = 2(A_C)+4(A_H) = 28.05 and DP = M_n/m = 300,000/28.05 = # repeat units along avg chain. a Since there are two carbon atoms per repeat unit, there are two C#C chain bonds per repeat unit, which means that the total number of chain bonds in the molecule, N = (2)(10,695) = 21,390 bonds. Furthermore, assume that for single carbon-carbon bonds, d = 0.154 nm and theta = 109. b so L = N*d*sin(th/2) and r = d*sqrt(N) =============== 7. Make comparisons of thermoplastic and thermosetting polymers (a) on the basis of mechanical characteristics upon heating, and (b) according to possible molecular structures. (a) Thermoplastic polymers soften when heated and harden when cooled, whereas thermosetting polymers, harden upon heating, while further heating will not lead to softening. (b) Thermoplastic polymers have linear and branched structures, while for thermosetting polymers, the structures will normally be network or crosslinked....
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This note was uploaded on 11/16/2009 for the course ENGIN 45 taught by Professor Devine during the Fall '07 term at Berkeley.

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Ch4 -...

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