Poly(glycerol sebacate) (PGS) is an elastomer with potential biomedical applications but it suffers from problems with irreproducible synthesis and the unacceptable toxicity of very soft PGS elastomers. To establish the reason for these problems, PGS was synthesized using different temperatures and reaction times, and the reaction was monitored by titration of the unreacted carboxylic groups and measurement of the mass loss during synthesis. It was found that evaporation of glycerol was a major cause of irreproducibility of the elastomer synthesis and this was more significant at higher reaction temperatures. The polymer microstructure was analysed using NMR spectroscopy and all twelve acylglyceride 13C‐signals as well as two small extra peaks of the residual glycerol were observed for the pre‐polymer. For the PGS gel, the glyceride moieties were characterized using NMR spectroscopy for the first time. The modulus and ultimate tensile strength of the gel increased with longer cure times and at higher cure temperatures while the elongation to break decreased and this was interpreted in terms of network theory. The cell viability of mouse fibroblasts was better for PGS samples with a higher conversion.© 2012 Society of Chemical Industry

The curing kinetics and morphology of an interpenetrating polymer network (IPN) formed from an epoxy resin (DGEBA) cured by an imidazole (1-MeI) and a dimethacrylate resin (bisGMA), cured by low-and hightemperature peroxide initiators (TBPEH and DHPB, respectively) have been studied by temperature-ramping DSC, isothermal near-infrared (NIR), DMTA and small-angle neutron scattering (SANS). bisGMA and DGEBA are polar and chemically similar thermosetting resins which should enhance the miscibility of their IPNs. The phase structure was controlled by varying the curing procedure: the order of gelation of the components is dependent on the choice of low-and high-temperature initiators for bisGMA and this affects the morphology formation. In the cure of the bisGMA/TBPEH:DGEBA/1-MeI system, the dimethacrylate cures first. For isothermal cure studies at 80 • C, the final conversion of the epoxy is reduced by high crosslinking of the methacrylate groups in the IPN causing vitrification before full cure. The dimethacrylate conversion is enhanced due to plasticisation with unreacted DGEBA, and its cure rate is increased due to accelerated decomposition of TBPEH initiator by 1-MeI. SANS revealed that phase separation occurs in these IPNs with domains on the scale of 6-7 nm. In the cure of the bisGMA/DHBP:DGEBA/1-MeI system, the epoxy cures at a similar rate to that of the methacrylate groups. For isothermal cure studies at 80 • C, similar final conversions of the epoxy have been observed except for the 75:25 IPN. The cure rate of the methacrylate groups in the IPN is increased also due to accelerated decomposition of DHBP initiator by 1-MeI, and the extent of accelerated decomposition for DHBP is stronger than that in the TBPEH-based systems. SANS studies revealed that this system is more homogeneous due to the rapid formation of the dimethacrylate gel in the presence of the preformed epoxy network which interlocks the networks at low degrees of methacrylate conversion.

A new diepoxide monomer (ADTDE) containing an allylic dithioether moiety has been synthesized to extend the suite of monomers that form networks exhibiting radical-mediated photoplasticity. These cross-linked polymers show permanent shape change under load and stress relax only when under the stimulus of visible or UV radiation. The Lewis base-catalyzed reaction of the epoxide groups in ADTDE with tri-and tetrafunctional thiols was monitored by differential scanning calorimetry and infrared spectroscopy. These curing systems were found to be more efficient than anionic, cationic, or anhydride polymerizations. The dynamic mechanical thermal analysis of ADTDE with the tetrathiol showed that the network was rubbery at room temperature which is considered ideal for the demonstration of photoplasticity. The photoinduced creep behavior was shown to be controlled by the presence of active free radicals in the matrixon cessation of irradiation, the creep was terminated. The stress relaxation of the stretched network specimens during UV irradiation was studied and was found to be similar to that shown previously for thiol− vinyl ether networks. As expected, the cross-link density of networks prepared from ADTDE with the trithiol was lower than that formed with the tetrathiol and this was found to have a significant influence on the rate and extent of photoplasticity observed the less highly cross-linked ADTDE/trithiol system exhibited more rapid and more extensive photoplasticity since it contained fewer network strands.

Atmospheric pressure chemical ionization (negative ion) and electrospray ionization (positive and negative ion) mass spectrometry and nuclear magnetic resonance ( 1 H NMR and 13 C NMR) were used to characterize the prepolymer (i.e. uncrosslinked) poly(xylitol sebacate) (PXS), prepared by condensation of xylitol [X] and sebacic acid [S], and this was compared with poly(glycerol sebacate) (PGS), prepared by condensation of glycerol [G] and [S]. The PXS prepolymer, prepared at 118 ∘ C/24 h, gave predominantly 1-acyl-[XS] and 1,5-diacyl-[SXS] species and smaller amounts of 2-acyl substitutions. At 130 ∘ C/24 h an increase of the amount of the 1-acyl and 1,5-diacyl substitutions in the [(SX) n ], [S(XS) n ] and [(XS) n X] series was identified, as was found for the analogous PGS prepolymer ([(SG) n ], [S(GS) n ] and [(GS) n G] series). Novel tetrahydrofuranyl species were found in the PXS prepolymer. Further polymerization of the PXS prepolymer gave a gel which when analysed using 13 C NMR was shown to mainly contain 1-acyl and 1,5-diacyl substitutions.

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