6.31. An experiment was conducted on a chemical process that produces a polymer. The four factors studied were temperature

(A), catalyst concentration (B), time (C), and pressure

(D). Two responses, molecular weight and viscosity, were observed. The design matrix and response data are shown in Table P6.8.

(a) Consider only the molecular weight response. Plot the effect estimates on a normal probability scale. What effects appear important?

(b) Use an analysis of variance to confirm the results from part (a). Is there indication of curvature?

(c) Write down a regression model to predict molecular weight as a function of the important variables.

(d) Analyze the residuals and comment on model adequacy.

(e) Repeat parts (a)–

(d) using the viscosity response.

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Run Actual Run Number Order Factor Levels Molecular A B C D Weight Viscosity Low (-) High (+) 1234 2 18 9 I - 2400 1400 A (C) 100 120 + 2410 1500 B (%) 4 8 3. 13 I 2315 1520 C (min) 20 30 4 8 5 3 1 + 618 11 + 7 14 + T + 2510 1630 D (psi) 60 75 8 17 + + + +++ 2615 1380 2625 1525 2400 1500 2750 1620 9 10 11 12 10 13 20 14 19 15 15 16 17 1 0 18 0 19 16 0 20 12 0 67204950 T + 2400 1400 2390 1525 + + + + 2300 1500 2520 1500 + ++ + 2625 1420 + 2630 1490 + + + 2500 1500 562 0000 0000 +0000 + 2710 1600 2515 1500 2500 1460 2400 1525 2475 1500