Polymerization of Myrcene in Both Conventional and Renewable Solvents: Postpolymerization Modification via Regioselective Photoinduced Thiol-Ene Chemistry for Use as Carbon Renewable Dispersants.

Polymeric dispersants are useful materials used in many different industries and often derived from oil-based chemicals, for example, in automotive fluids so as to prevent particulates from precipitation and causing potential damage. These are very often polyisobutene derivatives, and there is a growing need to replace these using chemicals using renewable resources such as the use of naturally occurring myrcene. Polymyrcene (PMy), with an ordered microstructure, has been successfully synthesized via both anionic and radical polymerization in different solvents and subsequently subjected to functionalization via photoinduced thiol-ene click reactions with a number of thiols, methyl thioglycolate, 3-mercaptopropionic acid, 3-mercapto-1-hexanol, 2-mercaptoethanol, and 1-thioglycerol, using 2,2-dimethoxy-2-phenylacetophenone as a photoinitiator under UV irradiation (λ = 365 nm) at ambient temperature. The polarity of the solvent has an important impact on the microstructure of the produced polymyrcene and, in particular, 1,2-unit (∼4%), 3,4-unit (∼41%), and 1,4-unit (∼51%) PMy were obtained via anionic polymerization in a polar solvent (THF) at ambient temperature, while 3,4-unit (∼6%) and 1,4-unit (∼94%, including cis and trans) PMy were obtained with cyclohexane as the solvent. Subsequently, photochemical thiol-ene reactions were carried out on the resulting PMy with different isomers exhibiting different reactivities of the double bonds. This strategy allows for the introduction of functional/polar groups (-COOH, -OH) into hydrophobic PMy in a controlled process. Hydrogenation of PMy and derivatized PMy was carried out to investigate any effects on the stabilities of the products which are desirable for many applications.

Self-healing and mechanical performance of dynamic glycol chitosan hydrogel nanocomposites.

The application of functional self-healing and mechanically robust hydrogels in bioengineering, drug delivery, soft robotics, etc., is continuously growing. However, fabricating hydrogels that simultaneously possess good mechanical and self-healing properties remains a challenge. Developing robust hydrogel formulations for the encapsulation and release of hydrophobic substances is a major challenge especially in some pharmaceutical treatments where the many of drugs show incompatibility with the hydrophilic hydrogel matrices. Schiff base hydrogels have been developed using a benzaldehyde multifunctional amphiphilic polyacrylamide crosslinker in conjunction with glycol chitosan. The polymeric crosslinker was synthesized by a two-step reaction using aqueous Cu-RDRP to give an ABA telechelic copolymer of N,N-dimethyl acrylamide (DMAc) and N-hydroxyethyl acrylamide (HEAm) from a bifunctional PEG. The polymer was then modified by post functionalization leading to a multifunctional benzaldehyde crosslinker that was shown to be capable of self-assembly into aggregates in aqueous media serving as a possible candidate for the entrapment of hydrophobic substances. Aqueous solutions of the crosslinker spontaneously formed hydrogels when mixed with glycol chitosan due to the in situ formation of imine bonds. Hydrogels were characterized while additional comparisons were made with a commonly used bifunctional PEG crosslinker. The effect of introducing partially reduced graphene oxide (GO) nanosheets was also examined and led to enhancements in both mechanical properties (2.0 fold increase in modulus and 1.4 fold increase in strain) and self-healing efficiencies (>99% from 60% by rheology) relative to the pristine polymer hydrogels.

Synthesis and Functionalization of Periodic Copolymers.

For the copolymerization of non-conjugated olefins and maleimides, it is known that under certain conditions periodic ABA monomer sequences are formed. In this work, such a copolymerization is used to create polymers which have defined (periodic) monomer sequences and can be functionalized after polymerization. The copolymerization of pentafluorophenol (PFP) active esters of 4-pentenoic acid and perillic acid with N-phenyl maleimide (PhMI) was studied in 1,2-dichloroethane (DCE) and 1,1,1,3,3,3-hexafluoro-2-phenyl-2-propanol (HFPP). In DCE and for the copolymerization of the PFP ester of 4-pentenoic acid and PhMI in HFPP, polymers were formed where the active esters were separated by at least one PhMI unit. The average number of separating PhMI units can be controlled by varying the feed ratio of the monomers. For the copolymerization of the PFP ester of perillic acid in HFPP, a preference for the formation of periodic copolymers was observed, where active esters were preferably separated from each other by a maximum of two PhMI moieties. Therefore, the copolymerization of said active ester containing monomers with PhMI provides a platform to create polymers in which reactive moieties are distributed along the polymer chain in different fashions. The active esters in the non-conjugated vinyl monomers could be used in a post-polymerization functionalization step to create functionalized polymers with defined monomer sequences in a modular way.