Synthesis and Investigation of Surface Properties of Dendrimer-like Copolymers Based on Polystyrene and Poly(tert-butylacrylate)

Modification of nanocellulose via atom transfer radical polymerization and its reinforcing effect in waterborne UV-curable resin

Cellulose nanocrystals (CNCs) are green reinforcing materials, and their potential has been evaluated in the preparation of waterborne UV-curable resin composites with high-performance. Herein, we present a novel and scalable approach for preparing surface-modified CNCs with acrylic-based polymers to strengthen the compatibility and interaction between CNCs and UV-curable resins. Using tert-butyl acrylate as the monomer, the nanocellulose grafted copolymer CNC-g-PtBA was successfully synthesized via atom transfer radical polymerization (ATRP) in the presence of a macromolecular initiator. Then, the CNC-g-PtBA is blended into the acrylic resin as a nanofiller to prepare the UV-curable nanocomposite. The results indicated that the contact angle of the CNCs increased from 38.7° to approximately 74.8°, and their thermal stability was significantly improved after graft modification. This contributed to the effective alleviation of the agglomeration phenomenon of nanocomposites due to the high hydrophilicity of pure CNCs. Notably, not only was the UV curing efficiency of the nanocomposites greatly increased but the mechanical properties were also further enhanced. Specifically, with the addition of 0.5 wt% CNC-g-PtBA, the curing time of the nanocomposite was shortened from >30 mins down to approximately 6 mins, and the bending strength was increased from 10 MPa for the original resin and 5 MPa for the addition of pure CNCs to 14.3 MPa, and the bending modulus was also greatly increased (up to approximately 730 MPa). Compared to pure CNCs, they are compatible with the resin, exhibiting high mechanical strength and flexibility, and have virtually no effect on the light transmission of the nanocomposites. Additionally, dielectric analysis (DEA) was used to monitor the dielectric constant and conductivity of the UV-curable nanocomposites in real time to further characterize their curing kinetics. The permittivity of these nanocomposites increased by 125 % compared to pristine resin, which shows potential for applications in high dielectric composites or for improving electrical conductivity. This work provides a feasible method for preparing UV-curable nanocomposites with high curing efficiency and permittivity, realizing a wider application of this high-performance nanocomposite.

Unimolecular Micelles from Layered Amphiphilic Dendrimer-Like Block Copolymers

In this report, we synthesized layered amphiphilic dendrimer-like block copolymers containing a polystyrene core and poly(p-tert-butoxystyrene)/poly(p-hydroxylstyrene) shell (coded G4-PtBOS/G4-PHOS). The synthetic method is easy involving anionic polymerization, epoxidation, ring-opening reaction and hydrolysis reaction. The hydrolyzed G4-PtBOS was soluble in alkaline water and behaved as unimolecular micelle, as demonstrated by the results of DLS, cryo- and normal TEM, and pyrene entrapping experiment. The stability of the unimolecular micelles was investigated via ζ-potential measurements.

A Facile Strategy for Preparation of α-Heterobifunctional Polystyrenes with Well-Defined Molecular Weight

A facile strategy for synthesis of α-heterobifunctional polystyrenes is reported. The novel functional polystyrenes have been successfully synthesized via a combination of atom transfer radical polymerization (ATRP) and chemical modification of end-functional groups. First, ε-caprolactone end-capped polystyrenes with controlled molecular weight and low polydispersity were prepared by ATRP of styrene using α-bromo-ε-caprolactone (αBrCL) as an initiator. Then, removal of the terminal bromine atom was performed with iso-propylbenzene in the presence of CuBr/PMDETA. Finally, ring-opening modifications of the caprolactone group were carried out with amines, n-butanol and H(2) O to produce novel polystyrenes containing two different functional groups at one end.

Surface Grafting Modification of Silk Fibroin by Atom Transfer Radical Polymerization

In this work, surface modification of silk fibroin was conducted by grafting dimethylaminoethyl methacrylate (DMAEMA) via ATRP to produce well controlled grafting silk. First, the amino groups and hydroxyl groups on the side chains of the silk fibroin reacted with 2-bromoisobutyryl bromide (BriB-Br) to obtain efficient initiator for ATRP. Subsequently, the functional silk fibroin was used as macroinitiator of DMAEMA in 1,2-dichlorobenzene in conjunction with CuBr/N,N,N',N",N" -pentamethyldiethylenetriamine (PMDETA) as a catalyst system. FT-IR characterization of the modified silk substrate showed a peak corresponding to DMAEMA indicating that the polymer had been formed on the silk surface. Following the polymerization, the tertiary amino groups on the grafted silk fibroin were quaternized to produce a large concentration of quaternary ammonium groups, which endowed the silk substrate with potential antibacterial surface. The graft chains were cleaved by acid hydrolysis and analyzed by gel permeation chromatography (GPC). The GPC results indicated that the graft layer were well-controlled.