Synthesis, characterization, and structural investigations of poly(ethyl acrylate)-l-polyisobutylene bicomponent conetwork

A new bicomponent conetwork, poly(ethyl acrylate)-linked-polyisobutylene (PEtA-l-PIB), was synthesized by radical copolymerization of equal amounts of telechelic alpha,omega -dimethacrylic PIE (MA-PIE-MA, M-n/(kg/mol) = 11.2, M-w/M-n = 1.12, and MA/chain = 2.0) obtained via quasi-living carbocationic polymerization and ethyl acrylate in 10% solution for each component in a common solvent, tetrahydrofuran, followed by extraction and drying. Low amounts of extractables (2.5% in acetone and 4.6% in hexane) and nearly theoretical composition (51% PEtA and 49% PIE) of the resulting conetwork indicate efficient network formation; i.e., this new conetwork is composed of PIE chains connected at each end to two PEtA chains. DSC experiments gave dose to literature value T-g's (-68 degreesC for PIE and -22 degreesC for PEtA), indicating a segregated morphology in this conetwork. In contrast to reported results for similar conetworks containing PIB and other polymers with polar groups, surface analysis with XPS found no significant difference in surface and bulk compositions in PEtA-l-PIB. For the first time in the field of bicomponent segmented conetworks, the structure of a conetwork was investigated by small-angle neutron scattering (SANS) in both the relaxed and strained states. Two correlation peaks were observed at q*/ Angstrom (-1) = 0.035 and at 3q*. The measured value of q* is less by more than a factor of 2 than that predicted by de Gennes for random bicomponent ("grafted") networks. The macroscopically homogeneous conetwork is characterized by nanoscale local layered like segregation with a correlation length of 445 Angstrom and periodicity of 180 Angstrom. This structure does not deform affinely with the macroscopic deformation. The measured modulus is in excellent agreement with an affine network prediction assuming that each MA-PIE-MA chain gives rise to three elastic strands in the network.