Urea monomer, block copolymers

Polymer characterization is an important use of NIR spectrometry. Polymers can be made either from a single monomer, as is polyethylene, or from mixtures of monomers, as are styrene-butadiene rubber from styrene and butadiene and nylon 6-6, made from hexamethylenediamine and adipic acid. An important parameter of such copolymers is the relative amount of each present. This can be determined by NIR for polymers with the appropriate functional groups. Styrene content in a styrene-butadiene copolymer can be measured using the aromatic and aliphatic C—H bands. Nylon can be characterized by the NH band from the amine monomer and the C=0 band from the carboxylic acid monomer. Nitrogen-containing polymers such as nylons, polyurethanes, and urea formaldehyde resins can be measured by using the NH bands. Block copolymers, which are typically made of a soft block of polyester and a hard block containing aromatics, for example, polystyrene, have been analyzed by NIR. These analyses have utilized the... 

Another way to obtain shape memory polyurethanes is by joining block copolymers (Lendlein et aL, 2009 Xue et al., 2010) with urea bonds. Lendlein (2009) investigated different polyurethanes from copolymers formed by lactic acid with other monomers. He obtained SMPs with tuneable transition temperature between 14°C and 56°C, depending on the monomers used and on their concentrations. Kim (1998) and co-workers have synthesized PCL polyurethanes with ionomers, monomers joined to ionic centres. In this manner, cohesion in the fixity phase is improved thanks to the Coulombic interaction between ionomers, enhancing the mechanical properties. Y. Zhu (2006, 2008) and co-workers have performed an exhaustive study on the influence of ionomers. Moreover, ionomers have also been used to obtain SMPs with copolymers (Han et al., 2007). 

Ring-opening polymerisation is receiving much interest presently probably due to the range of monomers that can be polymerised with this procedure. A number of recent reviews have appeared on aspects of ROP including polymerisation of lactones, lactides, and cyclic esters [138], cyclic carbonates and block copolymers with ureas and PTHE [139], and the use of a wide range of macroinitiators in ROP [140]. 

As PHTP is a chiral compound, polymerization of l,3-//-a 5-pentadiene in optically active PHTP gave an isotactic polymer [67]. Inclusion polymerization may be a living polymerization, in which termination and chain-transfer reactions are suppressed or reduced. Farina et al. [68] succeeded in preparing block copolymers by adding different monomers into the previously irradiated PHTP. Inclusion polymerization proceeds by a radical process, which has been studied by ESR spectroscopy [69]. Crystal structures of urea-monomer and urea-polymer inclusion compounds were studied by Chatani et al. [70-73] and those of PHTP complexes were studied by Colombo and Allegra [74]. 

Polyurethanes can also be prepared in inverse miniemulsion, if the monomers or prepolymers are suffidently hydrophilic. As polymerizations in non-aqueous inverse miniemulsions are possible (as shown previously) [119], polyurethanes that are free from the urea group could be produced in non-aqueous inverse emulsions, via a one-pot process [120]. In this case, emulsions ofdimethylformamide in hexane were stabiHzed by a copolymer surfactant with polyisoprene and PMMA blocks. An additional shell of PMMA could then be added after the polyaddition [121]. 

---