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Chapter 3 Chapter 3 Molecular Weight Molecular Weight 1. Thermodynamics of Polymer Solution 2. Mol Wt Determination 1. Weight, shape, and size of polymers 1. Weight, shape, and size of polymers monomer – oligomer – polymer dimer, trimer, --- telomer ~ oligomer from telomerization (popcorn polymerization) telechelic polymer ~ with functional group macro(mono)mer ~ with polymerizable group [wrong definition p72] pleistomer ~ mol wt > 1E7 usual range of mol wt of polymers 25000 ~ 1E6 mol wt of chain polymers are higher molecular weight conformation Æ shape molecular size LS (solution) and SANS (bulk) determine size. DSV and GPC utilize this relation in solution. Ch 3-1 Slide 2 2. Solution 2. Solution ΔG = ΔH –T ΔS m m m m for mixing f for melting (fusion) ΔSm > 0 always ΔHm > 0 almost always “like dissolves like” ΔHm = 0 at best (when solute is the same to solvent) if not, ΔHm > 0 ΔHm < 0 only when specific interaction like H-bonding exists For solution, ΔH < T ΔS m m Ch 3-1 Slide 3 Solubility parameter Solubility parameter ½ ½ 2 : solvent ΔH = V [(ΔE /V ) –(ΔE /V ) ] v v 1 m m 1 1 2 2 1 2 : solute = V [δ – δ ]2 v v 2 m 1 2 1 2 ΔE ~ cohesive energy ~ energy change for vaporization ΔE = ΔH –PΔV ≈ ΔH –RT [J] vap vap ΔE/V ~ cohesive energy density [J/cm3 = MPa] ½ δ ~ solubility parameter [MPa ] ½ 6 2 ½ 3 ½ 3 ½ [MPa ] = [(10 N/m ) ] = [(J/cm ) ] ≈ [(1/2)(cal/cm ) ] Table 3.1 & 3.2 Ch 3-1 Slide 4
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