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The hydrogen‐bonding strength of poly(ϵ‐caprolactone) (PCL) blends with three different well‐known hydrogen‐bonding donor polymers [i.e., phenolic, poly(vinyl‐phenol) (PVPh), and phenoxy] was investigated with differential scanning calorimetry and Fourier transform infrared spectroscopy. All blends exhibited a single glass‐transition temperature with differential scanning calorimetry, which is characteristic of a miscible system. The strength of interassociation depended on the hydrogen‐bonding donor group in the order phenolic/PCL > PVPh/PCL > phenoxy/PCL, which corresponds to the q value of the Kwei equation. In addition, the interaction energy density parameter calculated from the melting depression of PCL with the Nishi–Wang equation resulted in a similar trend in terms of the hydrogen‐bonding strength. Quantitative analyses on the fraction of hydrogen‐bonded carbonyl groups in the molten state were made with Fourier transform infrared spectroscopy for all systems, and good correlations between thermal behaviors and infrared results were observed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1348–1359, 2001

How low can you go? Polybenzoxazines can display surface free energies which are even lower than that of pure poly(tetrafluoroethylene). The contact angles and surface free energies were monitored during the polymerizations (see graph for an example). These materials are cheaper to prepare and easier to process than fluoropolymers.

We have synthesized a new polyhedral oligomeric silsesquioxane (POSS) containing eight phenol functional groups and copolymerized it with phenol and formaldehyde to form novolac-type phenolic/POSS nanocomposites exhibiting high thermal stabilities and low surface energies. Our DSC results indicate that the glass transition temperature of these nanocomposites increased initially upon increasing their POSS content, but then decreased at POSS content above 10 wt.-%, presumably because of the formation of relatively low molecular weight species and POSS aggregation as evidenced from MALDI-TOF mass analyses. Our TGA analyses indicated that the 5-wt.-%-mass-loss temperatures (T d ) increased significantly upon increasing the POSS content because the incorporation of the POSS led to the formation of an inorganic protection layer on the nanocomposite's surface. XPS and contact angle data provided positive evidence to back up this hypothesis. In addition, contact angle measurements indicated a significant enhancement in surface hydrophobicity after increasing the POSS content.Syntheses procedures of phenolic/OP-POSS nanocomposites.

Difunctional haloxanthate inifers were used for successive reversible addition-fragmentation transfer (RAFT) polymerization of N-vinylpyrrolidone (NVP) and atom transfer radical polymerization (ATRP) of styrene (St), methyl acrylate (MA), and methyl methacrylate (MMA). Since a quantitative dimerization of NVP in the presence of bromoxanthate inifers occurred, two chloroxanthate inifers, S-[1-methyl-4-(6-chloropropionate)ethyl acetate] O-ethyl dithiocarbonate (CPX) and S-[1-methyl-4-(6-chloroisobutyrate)ethyl acetate] O-ethyl dithiocarbonate (CiBX), were synthesized. These two difunctional chloroxanthate inifers were used to prepare PNVP-b-PSt, PNVP-b-PMMA, and PNVP-b-PMA block copolymers, where each block was synthesized by different polymerization procedures (either RAFT or ATRP). In the RAFT-first approach, well-controlled polymerization of NVP was observed. Well-defined PNVP-b-PSt (M n,GPC = 15,000 g/mol and M w /M n < 1.4) and PNVP-b-PMMA (M n,GPC = 50,600 g/mol and M w /M n < 1.3) were successfully synthesized through a subsequent chain extension by ATRP. A reshuffling reaction between propagating acrylate radicals and the xanthate moiety next to the NVP unit occurred for the preparation of PNVP-b-PMA, resulting in poor control of the MA chain extension. In the ATRP-first approach, a well-controlled polymerization was observed only for the ATRP of MMA with the CiBX initiator (M n = 13,000 and M w /M n < 1.3). Significant reshuffling reactions between the xanthate moiety and styryl/acrylate propagating radicals were observed with the CPX initiator. This resulted in poor control and broad molecular weight distribution for the subsequent RAFT chain extension of NVP. Thus, the chloroxanthate inifers provide synthetic access to well-defined PNVP-b-PSt and PNVP-b-PMMA, but not to PNVP-b-PMA block copolymers.

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Biodegradable self-healing hydrogels are attractive materials for tissue repair; however, the impact of the self-healing abilities of hydrogels on tissue repair is not clear. In this study, we prepared novel chitosan-cellulose nanofiber (CS-CNF) composite self-healing hydrogels with the same modulus (approximately 2 kPa) but tunable self-healing properties. By adding a low amount of CNFs (0.06-0.15 wt%) in the pristine chitosan (CS) self-healing hydrogel, the reversible dynamic Schiff bonding, strain sensitivity, and self-healing of the hydrogel are obviously affected. Neural stem cells embedded in the CS-CNF hydrogel with better self-healing properties reveal significantly enhanced oxygen metabolism as well as neural differentiation. The differentiation of neural stem cells is highly correlated with their metabolic change in the self-healing hydrogel. Moreover, the neural regeneration effect of the optimized CS-CNF hydrogel with 0.09 wt% CNFs and the best self-healing properties show a 50% improvement over the pristine CS hydrogel in the zebrafish brain injury model. A mechanism is proposed to interpret the tunable self-healing properties of CS-CNF hydrogels with stiffness maintained in a similar range. The new self-healing hydrogels help to clarify the role of self-healing in the biological performance of hydrogels as well as provide design rationale for hydrogels with better injectability and tissue regeneration potential.