ABSTRACT
The interpolymer complex forms as a consequence of the cooperative effects of the secondary forces that manifest between the polymers and depend on their molecular weights [10]. Initially the complexation reaction among the functional groups of the partners occurs randomly. Once a bond among the functional groups on the polymer chains is made, the adjoining functional groups are brought closer, and the reaction rate of the following steps is increased. This process occurs successively driving the complexation forward. When the molecular weight of the partners is low, even if there is a local interaction between them, it is difficult to cause conformational changes in the polymer chains, as the cooperative
∗Corresponding author. bmgg@icmpp.ro
effect is small therefore the complex formation is limited. The cooperative effect and thus the efficiency of the complexation increase by increasing the polymer chain length. There are studies dealing with the influence of the molecular weight of the partners on their ability to form IPCs [3, 5, 11, 12]. It has been established that IPC can start forming when the molecular weights of the partners are equal or higher than a certain value, known as critical molecular weight. The value of the critical molecular weight is a characteristic parameter of a particular system and it depends on the chemical structure of the partners. Nikolaeva et al. [10] studied the influence of the molecular weight of the poly(acrylic acid), PAA, on its complexation ability to form IPC with methylcellulose, MC. The authors used a MC with a molecular weight of 2.30 × 105 g/mol and a degree of substitution of 1.6. They found that the critical molecular weight of PAA necessary to form an IPC with MC was one order of magnitude higher (Mw,PAA = 0.6 × 105 g/mol) than that needed to form IPC between flexible, spatially complementary polymers. The complexation of polyethylene oxide, PEO, started from a critical polyacid chain length of about 40 monomer units for poly(methacrylic acid) PMAA and about 200 units for PAA [3]. This difference in the critical chain length required to form IPC could be partially explained by the higher hydrophicity of PMMA, known as stabilizer factor of IPC. Bekturov et al. [5] also showed that the hydrophobic interactions lead to a more stable IPC between PMMA and shorter polyethylene glycol, PEG chains in comparison with PAA and PEG. It has been also reported that the stability of polyelectrolyte complexes of PMAA, with a molecular weight equal to 40,000 g/mol, and the positively charged electrolyte [(CH2)2-N+(CH2)2, I−]n , exponentially increased with the chain length of the cations, n, for n between 1 and 6 [3].
