Effect Of Hydrogen-Bonding On The Interfacial Behavior Of Polymer Chains

The thesis deals with the effect of hydrogen-bonding complexation on the interfacial behavior of the polymer chains by using laser light scattering(LLS), neutron reflectivity(NR) and Langmuir balance(LB),including the aggregation of thermosensitive multi-blcok copolymers,the structural evolution of the polymeric aggregations and the interfacial behavior of the polymer chains at the air-water interface.The main results are as follows:1.The investigations on the aggregation of thermosensitive PnPA-b-PNIPAM -b-PEMA triblock terpolymers lead to the following conclusions.The micellization process depends on the relative length of the PEMA block.The folding of PnPA led to the formation of polymeric micelles with a collapsed hydrophobic PnPA core and a hydrophilic swollen PNIPAM-PEMA shell.Further increase in temperature leads to the collapse of the PNIPAM and PEMA chains on the periphery of the micelles.When the shorter PEMA block cannot shield the hydrophobic PnPA and PNIPAM core completely,PNIPAM chains in different micelles associate,leading to the clustering of the micelles.A longer PEMA block can prevent or delay the clustering of the micelles.In the cooling process,a hysteresis can be observed in the disruption of the aggregations due to the formation of additional hydrogen bonds.2.The studies on the structural evolution of PS-b-PAA aggregations lead to the following conclusions.When PS block is not long enough to shield the solvophobic PAA core completely,PS-b-PAA chains form bimodal aggregates with regular micelles and micellar clusters in toluene.The introduction of PS-b-PEO chains leads to the formation of mixed micellar clusters whose structure evolves with time.The hydrogen-bonding complexation between PAA and PEO in the core and the repulsion between PS chains in the corona manipulate the evolution.When the latter dominates the former,the mixed micellar clusters split up into regular complex micelles.3.The studies on the structural evolution of PS-b-PAA/PMMA-b-PEO mixed micelles give the following conclusions.The competition between the hydrogen-bonding complexation of PAA/PEO in the core and the segregation of PS/PMMA in the corona manipulate the evolution.When the segregation dominates the hydrogen-bonding complexation,the mixed micelle develops into a hyperbranched structure after a long-time standing.4.The interfacial behavior of PI-b-PAA/PI-b-PEO mixed monolayers has been investigated by LB and NR.It shows that the behavior is highly pH-dependent.At pH 10.0 and 5.7,where the carboxyl acid groups are deprotonated,PAA chains do not induce any unusual effect on the behavior of the PI-b-PEO layer.Theп-σ^-1 isotherms of the mixture exhibit three regions,(Ⅰ) a low-pressuer 2-D "pancake" region,(Ⅱ) a pseuoplateau where PEO segments desorb and are immerse in the subphase;and(Ⅲ) a steep pressure rise region commonly considered as the "brush" regime.In regionⅢ, neutron reflectivity measurements confirm the formation of brush-like structures in the tethered layer.At pH 2.5,a novel behavior is observed;theп-σ^-1 isotherm exhibits only two regions,that is,the pseudoplateau disappears;furthermore,the compression-expansion cycles are completely reversible.These results suggest that desorption of PEO segments and their entanglement are hindered due to the formation of hydrogen-bonding complexation between the undissociated carboxylic groups and the PEO chains.