Molecular weight PNIPAAm

Fig. 1 Calculated and measured ( ) swelling curves for PNIPAAm of different molecular weight-of the net chains in g/mol. The Flory-Huggins interaction parameter % was calculated using (12). The dashed curve was calculated considering only a temperature-dependent x (X2 = 0)-The sharp decrease of the volume degree of swelling with temperature is only observed for concentration-dependent interactions. The sharpness of the curve is influenced by Me...

PNIPAAm-containing materials, defined molecular weight and end-group but also low polydispersity index are highly desirable. 

To prove the versatility of this process, different molecular weights of PNIPAAm were synthesized. Figure 2 indicates that an increase of the ratio of monomer/initiator leads (at a comparable conversion) to a linear increase of the molecular weight. The SEC traces display unimodal and narrow peaks. Moreover a large range of molecular weights from rather low (DP=30) to rather high (DP=400) were achieved. In all cases the PDI remains below 1.2 at full conversion, without any trace of termination. All these criteria indicate the controlled fashion of the ATRP of NIPAAm in water. 

Figure 3. Molecular weight distribution for the chain extension of PNIPAAm by ATRP in water at 4°C. [M]o=0.5 M, [M]f[PNIPAAm,2o-Cl]o=300. (—) precursor, (- -) extension after 40% conversion.

Zhao, T., Chen, H., Zheng, J., Yu, Q., Wu, Z., Yuan, L. (2011). Inhibition of protein adsorption and ceU adhesion on PNIPAAm-grafted polyurethane surface effect of graft molecular weight. Colloids and Surfaces B, 85, 26-31. http //dx.doi.Org/10.1016/j.colsurfb.2010.10.047. 

Fig. 8 Change in the elution time of dextrin with various molecular weights in response to temperature changes from the PNIPAAm-treated column (pore size 23.7 nm, flow rate 0.6 ml/min).

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