Viscoelastic properties and phase behavior of 12‐tert‐butyl ester dendrimer/poly(methyl methacrylate) blends

Abstract

This study used refractometry, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, and dielectric analysis to assess the viscoelastic properties and phase behavior of blends containing 0 -20% (w/w) 12-tert-butyl ester dendrimer in poly(methyl methacrylate) (PMMA). Dendritic blends were miscible up through 12%, exhibiting an intermediate glasstransition temperature (T g ; ␣) between those of the two pure components. Interactions of PMMA CAO groups and dendrimer NOH groups contributed to miscibility. T g decreased with increasing dendrimer content before phase separation. The dendrimer exhibited phase separation at 15%, as revealed by Rayleigh scattering in ultravioletvisible spectra and the emergence of a second T g in dielectric studies. Before phase separation, clear, secondary ␤ relaxations for PMMA were observed at low frequencies via dielectric analysis. Apparent activation energies were obtained through Arrhenius characterization. A merged ␣␤ process for PMMA occurred at higher frequencies and temperatures in the blends. Dielectric data for the phase-separated dendrimer relaxation (␣ D ) in the 20% blend conformed to Williams-Landel-Ferry behavior, which allowed the calculation of the apparent activation energy. The ␣ D relaxation data, analyzed both before and after treatment with the electric modulus, compared well with neat dendrimer data, which confirmed that this relaxation was due to an isolated dendrimer phase.

Enhanced biological stability of collagen with incorporation of PAMAM dendrimer

“…As a new class of polymeric materials, dendrimer has attracted much interest since its synthesis in the mid-1980s because of the unique nanoscopic architecture with a central core, surface functionalities, and branching unites linking the two. 1,2 Unlike the traditional linear polymer, dendrimer possesses special physical and structural characteristics of (1) the compact and well-defined structure, (2) the large number of end groups which are often reactive, and (3) the possibility to encapsulate guest molecules between the branches. The special structure of the dendritic interior and functional end groups make dendrimer suitable for a broad scale of applications.…”

Novel polyhedral oligomeric silsesquioxane‐substituted dendritic polyester tougheners for linear thermoplastic polyurethane

“…Within the PU‐POSS‐Boltorn blends, these hydrogen bonds can occur through the unreacted OH groups on Boltorn and CO groups on the polyester (soft segment) component of linear TPU, increasing mechanical and T g properties. Furthermore, the T g of Boltorn (31°C)45 is considerably higher than linear TPU (−47°C), allowing the dendrimer to remain solid‐like and interact with linear chains while they experience T g and eventually flow 48. The rigid structure of POSS is also widely known to impart restrictions on polymer chains and increase the T g of polyurethane 49–53.…”

2,3-Branching benzyl ether dendrimers for the enhancement of dental composites

“…For example Grinstaff has explored the use of methacrylated dendrimers for opthamalic repair [31,32]. Several studies exploring dendrimer/polymer blends revealed unpredictable effects on the resulting properties [33][34][35], including improvements in strength [36]. The incorporation of polymerizable, high-molecular weight dendrimers [37][38][39][40][41][42][43] to existing dental composite resins may improve physical properties due to the compact structure of dendritic components.…”