This essay discusses some preliminary thoughts on the development of a rational and modular approach for molecular design in soft matter engineering and proposes ideas of structural and functional synthons for advanced functional materials. It echoes the Materials Genome Initiative by practicing a tentative retro-functional analysis (RFA) scheme. The importance of hierarchical structures in transferring and amplifying molecular functions into macroscopic properties is recognized and emphasized. According to the role of molecular segments in final materials, there are two types of building blocks: structural synthon and functional synthon. Guided by a specific structure for a desired function, these synthons can be modularly combined in various ways to construct molecular scaffolds. Detailed molecular structures are then deduced, designed and synthesized precisely and modularly. While the assembled structure and property may deviate from the original design, the study may allow further refinement of the molecular design toward the target function. The strategy has been used in the development of soft fullerene materials and other giant molecules. There are a few aspects that are not yet well addressed: (1) function and structure are not fully decoupled and (2) the assembled hierarchical structures are sensitive to secondary interactions and molecular geometries across different length scales. Nevertheless, the RFA approach provides a starting point and an alternative thinking pathway by provoking creativity with considerations from both chemistry and physics. This is particularly useful for engineering soft matters with supramolecular lattice formation, as in giant molecules, where the synthons are relatively independent of each other.

Two series of trans-1,4-poly(butadiene-co-isoprene) copolymers (TBIR) were prepared using the catalyst system TiCl₄/MgCl₂-Al(i-Bu)₃ at different reaction temperatures. All dyad and triads sequence distributions, the number-average sequence length and the sequence concentration of the copolymers were calculated according to ¹³C-NMR spectra. The influences of temperature and initial molar ratio of butadiene to isoprene (Bd to Ip) on the distribution of the chain segments in the TBIR copolymers were discussed. The correlation of copolymer compositions and thermal properties were also evaluated, which facilitated the understanding of controlling the degree of crystallinity and the transition temperature by changing Bd content and temperature.

The effects of PEA on the γ-phase PVDF crystal structure and the crystallization of PEA within the pre-existing γ-phase PVDF spherulites have been investigated by optical microscopy (OM), infrared spectroscopy (IR) and scanning electron microscopy (SEM). The results demonstrate that the γ-phase PVDF spherulites consist of the lamellae exhibiting a highly curved scroll-like morphology and develop preferentially in PEA-rich blend. With increasing PEA concentration, the scroll diameter increases and the scrolls are better separated from each other. PEA crystallizes first in the interspherulitic region and transcrystalline layer develops. Subsequently, the transcrystalline layer of PEA continues to grow within the γ-phase PVDF spherulites, e.g., in the region between the scrolls, until impinging on other PEA transcrystalline layers or spherulites. The crystallization kinetics results indicate that the growth rate of PEA crystals in the intraspherulitic region of γ-phase PVDF shows a positive correlation with content of PEA, but a negative one with the crystallization temperature of γ-phase PVDF.

Polyethylenimine-poly(L-lysine) (PEI-PLL) copolymer was synthesized via ring-opening polymerization of L-lysine N-carboxyanhydride (Lys(Z)-NCA) initiated by PEI. The complexation of PEI-PLL with siRNA was studied by particle size and zeta potential measurements. The flow cytometric analysis and confocal imaging showed its excellent intracellular trafficking ability. PEI-PLL displayed higher gene silencing efficiency and lower cytotoxicity than commercial PEI-25k in vitro. In the antitumor study, PEI-PLL was further combined with siVEGF and showed obviously tumor inhibition effect for the treatment of CT26 tumor model. Therefore, PEI-PLL is a promising siRNA carrier candidate for further antitumor treatment in vivo.

A carbon dioxide copolymer poly(urethane-amine) (PUA) was blended with poly(propylene carbonate) (PPC) in order to improve the toughness and flexibility of PPC without sacrificing other mechanical properties. Compared with pure PPC, the PPC/PUA blend with 5 wt% PUA loading showed a 400% increase in elongation at break, whilst the corresponding yielding strength remained as high as 33.5 MPa and Young’s modulus showed slightly decrease. The intermolecular hydrogen bonding interaction in PPC/PUA blends was comfirmed by FTIR, 2D IR and XPS spectra analysis, and finely dispersed particulate structure of PUA in PPC was observed in the SEM images, which provided good evidence for the toughening mechanism of PPC.

In this study, a novel three functional chain extender (TATATRIOL) was synthesized from the reaction of 1,3,5-tri(prop-2-en-1-yl)-1,3,5-triazinane-2,4,6-trione (TATA) with 2-sulfanylethanol. Then new thermoplastic polyurethanes (TPUs) were synthesized by a one-step bulk polymerization from the reaction of 1,1'-methanediylbis(4-isocyanatocyclohexane) (H₁₂MDI), a poly(ethylene adipate) based polyester polyol and a chain extender. Butane-1,4-diol (BD) and the newly synthesized monomer, TATATRIOL, were used as chain extenders. The effects of TATATRIOL on the properties of the TPU were investigated and compared to those of the TPU prepared with BD. The TPUs which derived from the sulfur containing chain extender displayed lower modulus and high elongation at break values than the analogous TPUs derived from BD. Moreover sulfur containing TPUs exhibited higher thermal stability.

Polymerizable ionic liquid copolymer P(MMA-co-BVIm-Br) was synthesized by radical polymerization technique, and characterized by Fourier transform infrared spectrometry (FTIR), ¹H Nuclear magnetic resonance (¹H-NMR) and gel permeation chromatography (GPC). The resulting copolymer was used to prepare poly(vinylidene fluoride) (PVDF) blend membranes via a phase inversion method. The effects of the copolymer on the polymorphism, surface wettability and zeta potential (ζ) of the blend membranes were investigated by ATR-FTIR, contact angle instrument and zeta potential analyzer. Scanning electron microscopy (SEM and SEM-EDS) was also applied to investigate the morphology and the surface element changes of the fabricated membranes. The results indicated that P(MMA-co-BVIm-Br) copolymer existed on the surface of the membrane which made the blend membrane have a positive surface during the experimental pH range. The copolymer was also in favor of the formation of β crystal phase in PVDF membranes. The contact angle experiment indicated that P(MMA-co-BVIm-Br) copolymer could switch the wettability of the blend membranes from hydrophilic to hydrophobic by exchanging Br^- anion with PF₆^-. Compared with pure PVDF membranes, the water flux and water recovery flux of the blend membranes were enhanced obviously. The results from the flux recovery ratio (FR) and total fouling ratio (R_t) all suggested that the blend membranes had good anti-fouling properties.

By preparing homogenous blend samples with different degrees of chain entanglement, we report an anomalous contribution of chain entanglement to phase separation temperature and rate of poly(methyl methacrylate)/poly(styrene-co-maleic anhydride) (PMMA/SMA) blends presenting a typical lower critical solution temperature (LCST) behavior. The meltmixed PMMA/SMA blends with a higher chain entanglement density present a lower cloud point (T_c) and shorter delay time, but lower phase separation rate at the given temperature than solution-cast ones, suggesting that for the polymer blends with different condensed state structure, thermodynamically more facilitation to phase separation (lower T_c) is not necessarily equivalent to faster kinetics (decomposition rate). The experimental results indicate that the lower T_c of melt-mixed sample is ascribed to smaller concentration fluctuation wavelength (Λ_m) induced by higher entanglement degree, while higher entanglement degree in melt-mixed sample leads to a confined segmental dynamics and consequently a slower kinetics (decomposition rate) dominated by macromolecular diffusion at a comparable quench depth. These results reveal that the chain packing in polymer blends can remarkably influence the liquid-liquid phase separation behavior, which is a significant difference from decomposition of small molecular mixtures.

A non-isocyanate route for synthesizing thermoplastic polyurethanes with excellent thermal and mechanical properties was described. Melt transurethane polycondensation of 1,6-bis(hydroxyethyloxy carbonyl amino)hexane with four poly(ethylene glycol)s (PEGs), i.e. PEG400, PEG600, PEG1000, or PEG1500, was conducted at different molar ratios. A series of thermoplastic poly(ether urethane)s (TPEUs) with long PEG sequences were prepared. The TPEUs were characterized via gel permeation chromatography, FTIR, ¹H-NMR, differential scanning calorimetry, thermogravimetric analysis, wide-angle X-ray scattering, and tensile tests. The TPEUs exhibit T_g between 12.4 °C and −40.4 °C, T_m of up to 149.8 °C, and initial decomposition temperature over 239.4 °C. The tensile strength of the TPEUs reaches 38.39 MPa with a strain at break of 852.92%.

Based on the combination of B21C7/dialkylammonium salt host-guest interactions and tetraphenylethylene (TPE)-based aggregation-induced emission (AIE) effect, a fluorescent supramolecular crosslinked polymer gel was successfully prepared. Compared with the solution of TPE-containing small molecules, this gel exhibited remarkable fluorescence enhancement due to the AIE effect of TPE units. The "gelation induced fluorescence emission" phenomenon can be explained by the hindered intramolecular rotation of phenyl rings of TPE. Because of the reversibility and stimuli-responsiveness of the B21C7/dialkylammonium salt host-guest interactions, the transition between the fluorescent supramolecular crosslinked polymer gel and the disassembled sol with very weak fluorescence can be realized by adding pH and thermal stimuli. This novel material contributes to the development of supramolecular chemistry, polymer science and fluorescent materials and offers a new method to construct functional supramolecular materials.

A novel asymmetric Ni/PVC film has been developed by solution casting method. The structure, electrical conductivity, electromagnetic interference (EMI) shielding, and impact resistance were investigated. The results showed that the Ni particles were asymmetrically distributed along the thickness direction in the film. The top surface resistivity increased with film thickness, while the bottom surface exhibited the different trend. EMI shielding effectiveness (SE) depended on formation of closed packed conductive Ni network, which was influenced by both Ni content and film thickness. A linear relationship was observed between EMI SE and film thickness. The films with lower Ni content showed the faster increasing rate of EMI SE with film thickness. Some of the films show appreciably high EMI SE (> 40 dB), indicating the promising application in EMI shielding field. Moreover, the films exhibit different impact performance under different impacting directions. All the experimental facts demonstrate that the asymmetric structure endows the film achieving high-performance EMI shielding function.

Guanidine was introduced to low molecular weight linear polyethyleneimine (LPEI) via amide groups, to explore the effect of both guanidine degree and pendant chain length on its transfection behavior. The resulting guanidinoamidized LPEIs (GLPEIs) could dramatically reduce LPEI’s toxicity, enhance its DNA-packaging capability, cellular uptake and therefore transfection efficiency. These polyplexes were taken up very efficiently via caveolae-mediated endocytosis and their transfection efficiencies in ovarian cancer cells were significantly improved compared to native LPEI_10k polyplexes. Among these GLPEIs, LPEI-C₃-G₁₀₀ showed higher DNA affinity even than LPEI_25k and the highest transfection efficiency, probably due to the optimization of polymer chain flexibility. Of notice, LPEI-C₃-G₁₀₀ polyplexes could more effectively accumulate into cytoplasm than LPEI_25k, although the transfection efficiency of LPEI-C₃-G₁₀₀ polyplexes was not superior to that of LPEI_25k polyplexes, which would be probably attributed to the more efficient release of LPEI_25k polyplexes than LPEI-C₃-G₁₀₀ polyplexes in the cytoplasm.

Hyperbranched polyamidoamines (HPAs) were directly employed as macroinitiators to initiate the Sn(Oct)₂ catalyzed ring-opening polymerization of ε-caprolactone (CL), resulting in multiarm star copolymers with poly(ε-caprolactone) (PCL) as shells and HPA as core (HPA-b-PCL). From ¹H-NMR characterization it was deduced that both the primary amines and the secondary amide groups of HPAs could initiate the CL polymerization, and the initiation efficiency increased when more CL monomers were fed. The average arm-numbers of the obtained stars were in the range of 115-353. Differential scanning calorimetry measurements demonstrated that the melting and crystallization temperatures, fusion and crystallization enthalpy and the degree of crystallinity of the star polymers increased as the PCL arm length increased. HPA-b-PCL stars could be used as nanocarriers to efficiently accommodate anionic dyes at acidic condition, while load cationic dyes at basic condition. Compared with the dye-loading behavior of multiarm star PCL with the neutral hyperbranched polyglycerol as core, it was deduced that HPA-b-PCL nanocarriers accommodated anionic dyes using the HPA core, while loaded cationic dyes using both the HPA core and the PCL shell. Dynamic light scattering analyses also supported such deduction. Furthermore, HPA-b-PCL nanocarriers could selectively load the anionic Eosin Y or the cationic methylene blue from their mixture at pH = 6 or 9, respectively, realizing their separation.