•Stepwise polymerization kinetics was studied by a new molecular simulation algorithm.•Scaling of polymerization kinetics in diffusion-controlled regime was proposed.•Transition from reaction-to diffusion-controlled kinetics was provided.The kinetics of stepwise polymerization in the diffusion-controlled regime was investigated using dynamic Monte Carlo simulation and scaling analysis. In analogy to Flory’s expression, a concise expression of reaction kinetics in diffusion controlled regime was proposed, where the number average degree of polymerization was related to the initial concentration and reaction time through a power law dependence. In addition, the transition of kinetics from the classical reaction-controlled to diffusion-controlled regime was predicted and examined via simulation. The results provided a good description of kinetics for the late stage of stepwise polymerizations, and demonstrated good agreements with the various experiments.

Recent works by Tansil et al. suggested a promising way to introduce functionalities into silk fibroin by simply feeding, which was expected to allow silk-based functional biomaterials to have scalable production and direct application. In this research, we aimed to obtain deeper understanding on such a smart strategy of selectively absorbing additives via molecular recognition and the impact of additives on the secondary structures of fibroin. We suggested that the partition ratio of the additive in fibroin and sericin was a critical parameter to evaluate the ability of the additive to enter fibroin, which showed a strong correlation with the isoelectric point (pI) of the additive. On the basis of the classical micelle model, we suggested that silk in vivo recognized additives with low pI and amphiphile chemical structure from other chemical similar additives and assembled them into fibroin. Fibroin-additive assemblies were rather stable that hindered the formation of β-sheet and also crystallites, as indicated by FTIR and WAXD.Keywords: functionalization; isoelectric point; silk fibroin

In this paper, we report a novel and facile method of pressure-induced-flow (PIF) processing that remarkably enhanced the mechanical properties of polylactic acid (PLLA)–PEG blends. The impact strength and bending strength increased by about 20 and 4 times, respectively. Meanwhile, the tensile strength and elongation at break were 3 and 7 times higher compared with raw samples. As indicated by DSC and polarizing microscopy, POM, oriented spherulites were present in the sample after PIF processing. The SEM results showed that the fracture surface of the PIF samples became oriented and much rougher. The cell culture results indicated that the PLLA–PEG blends after PIF processing still maintain as good biocompatibility as the original.

In this paper, firstly, we systematically explain the deformation mechanism of the high impact polystyrene (HIPS) via pressure-induced-flow (PIF) processing. As indicated by TEM, AFM and SAXS, we find that a single salami domain is intensively deformed into a disk-like shape, and rubber-disk domains form parallel and oriented structure. In addition, chains in the interphase are oriented and become stiffer as suggested by FTIR and DMA. Such structural variation gives rise to the improvement in both strength and toughness. Impact and tensile strength for high impact polystyrene (HIPS) with parallel and oriented structure increase by 100% and 30% respectively. Moreover, we studied the toughening mechanism. The post-impact fracture surface transits from normal smooth fish scale like morphology to aligned grooves with high roughness, as demonstrated by SEM. The craze of impact fracture surface of HIPS samples after PIF processing is characterized by TEM. Finally, a model for the confinement of crazing is proposed.

We demonstrate that without changing the filler content mechanical properties of commodity plastics with immiscible soft inclusions can be decisively enhanced, simply by pressure induced flow processing in the solid state. As an example, we have chosen acrylonitrile-butadiene-styrene (ABS), where shape and orientation of the soft fillers were changed by processing, resulting in an array of aligned and oriented nanosize deformed rubber domains. These deformed domains effectively controlled the propagation of cracks inside the solid matrix and were responsible for a multifold increase of tensile and impact toughness. Thus, appropriate processing allows manufacturing plastics with high impact resistance in accordance with engineering needs.