Method for predicting physical properties of polymers

A method for manufacturing a pipe comprising:

• polymerizing one or more olefin monomers in a presence of a catalyst,
• forming a polymer resin,
• measuring a molecular weight distribution curve of the polymer resin using a gel permeation chromatography (GPC) at a temperature of 160° C., wherein a log value of a molecular weight MW (log MW) is denoted by x-axis, and a molecular weight distribution to the log value (dwt/dlog MW) is denoted by y-axis;
• dividing a section between 3.0 and 7.0 on the x-axis of the molecular weight distribution curve into four equal parts to obtain an integral value of the molecular weight distribution curve at each section;
• and
• calculating a predicted value of a die swell ratio value from the integral value, and
• manufacturing the pipe using the polymer resin,
• wherein the calculating the predicted value of the die swell ratio is performed according to following Equation 1 using the integral value:
• Die swell ratio, PV=(−0.136)*A1+(−0.1152)*A2+(−0.1033)*A3+(−0.181)*A4+13.97 [Equation 1]
• A1 is an integral value of a molecular weight distribution curve in the section where log MW is 3.0 to 4.0,
• A2 is an integral value of a molecular weight distribution curve in the section where log MW is 4.0 to 5.0,
• A3 is an integral value of a molecular weight distribution curve in the section where log MW is 5.0 to 6.0,
• A4 is an integral value of a molecular weight distribution curve in the section where log MW is 6.0 to 7.0, and
• the integral value of A1 to A4 means relative values when an integral value of entire molecular weight distribution curve is 100.