Novel carboxyl- and amino-functionalized copolyesters, based on poly(ε-caprolactone)-block-poly(butylene fumarate)-block-poly(ε-caprolactone), were efficiently synthesized via Michael-type thiol-ene click chemistry. The resulting amphiphilic copolyesters with controllable molecular weights and abundant positively or negatively charged groups could spontaneously form pH-sensitive micelles in aqueous solutions, as confirmed by transmission electron microscopy, dynamic light scattering, fluorescence probing technique, and zeta potential analyses. Importantly, charge-reversal hybrid micelles can be obtained by co-assembly of carboxyl- and amino-functionalized copolyesters. The surface charges of hybrid micelles reversed rapidly from negative to positive at isoelectric point via protonation of surface carboxyl and amino groups. Interestingly, the hybrid micelles showed apparent pH-triggered Nile red-release behavior in acidic condition resembling tumor intracellular environment, which is fairly desirable for drug delivery. Our work indicates that co-assembly is a facile but efficient way to prepare charge-reversal micelles, which have great potential to be used as intelligent drug delivery systems for cancer therapy. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1259–1267

A series of aliphatic–aromatic poly(carbonate-co-ester)s poly(butylene carbonate-co-terephthalate)s (PBCTs), with weight-average molecular weight of 113,000 to 146,000 g/mol, were synthesized from dimethyl carbonate, dimethyl terephthalate, and 1,4-butanediol via a two-step polycondensation process using tetrabutyl titanate as the catalyst. The PBCTs, being statistically random copolymers, show a single T_g over the entire composition range. The thermal stability of PBCTs strongly depends on the molar composition. Melting temperatures vary from 113 to 213°C for copolymers with butylene terephthalate (BT) unit content higher than 40 mol %. The copolymers have a eutectic melting point when about 10 mol % BT units are included. Crystal lattice structure shifts from the poly(butylene carbonate) to the poly(butylene terephthalate) type crystal phase with increasing BT unit content. DSC and WAXD results indicate that the PBCT copolymers show isodimorphic cocrystallization. The tensile modulus and strength decrease first and then increase according to copolymer composition. The enzymatic degradation of the PBCT copolymers was also studied. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41952.

A series of novel biodegradable poly(ester-carbonate) consisting of poly(L-lactic acid) (PLLA) and poly(butylene carbonate) (PBC) (PLLA-b-PBC) have been successfully synthesized by chain-extension reaction of dihydroxyl-terminated poly(L-lactic acid) prepolymer (PLLA-OH) and dihydroxyl-terminated poly(butylene carbonate) prepolymer (PBC-OH) using hexamethylene diisocyanate as a chain-extender. The chemical structures and molecular weights of copolymers are characterized by ¹H NMR and gel permeation chromatography. The thermal properties, morphology, and mechanical properties of PLLA-b-PBC are investigated by differential scanning calorimetry, thermogravimetric analysis, phase contrast optical microscopy, and mechanical testing. The results indicate that PBC soft segment slightly increases the thermal stabilities and effectively enhances the impact strength of the copolymers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 39158.

Poly(isosorbide carbonate) (PIC) was synthesized by melt polycondensation of dimethyl carbonate (DMC) and isosorbide using lithium acetylacetonate (LiAcac) as the catalyst. The reaction conditions were optimized to achieve PIC with relatively high number-average molecular weight (M_n) of 28,800 g/mol and isosorbide conversion of 95.2%. A series of poly(aliphatic diol-co-isosorbide carbonate)s (PAICs) were also synthesized by melt polycondensation of DMC with isosorbide and equimolar amounts of aliphatic diols (1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 1,4-cyclohexane dimethanol) in the presence of LiAcac and the TiO₂/SiO₂-based catalyst (TSP-44). PAICs with M_n values ranging from 18,700 to 34,400 g/mol and polydispersities between 1.64 and 1.69 were obtained. The ¹³C NMR analysis revealed the random microstructure of PAICs. The differential scanning calorimetry results demonstrated that all the PAICs were amorphous with a unique T_g ranging from 46 to 88 °C. The dynamic analysis results showed that the incorporation of linear or cyclohexane structure changed the dynamic mechanical properties of PIC drastically. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Block copolymers demonstrate excellent thermal and mechanical properties superior to their corresponding random copolymers and homopolymers. However, it is difficult to synthesize block copolymers comprising of different polyester segments by copolycondensation due to the serious transesterification reaction. In this study, multiblock copolymers comprising of two different polyester segments, i.e. crystallizable poly(butylene succinate) (PBS) and amorphous poly(1,2-propylene succinate) (PPSu), were synthesized by chain-extension with hexamethylene diisocyanate (HDI). Amorphous PPSu segment was incorporated to improve the impact strength of PBS. The copolymers were characterized by GPC, laser light scattering (LLS), NMR, DSC, and mechanical testing. The results of ¹³C NMR spectra suggest that multiblock copolymers with regular sequential structure have been successfully synthesized. The data of DSC and mechanical testing indicate that block copolymers possess excellent thermal and mechanical properties with satisfactory tensile strength and extraordinary impact strength achieving upto 1900% of pure PBS. The influence of PPSu ratio and chain length of both the segments on the thermal and mechanical properties was investigated. The incorporation of an amorphous soft segment PPSu imparts high-impact resistance to the copolymers without obviously decreasing the melting point (T_m). The favorable mechanical and thermal properties of the copolymers also depend on their regular sequential structure. At the same time, the introduction of amorphous PPSu segment enhances the enzymatic degradation rate of the multiblock copolymers. Copyright © 2009 John Wiley & Sons, Ltd.

Crosslinking is an effective way to improve polymer properties. This paper focuses on ultraviolet-induced crosslinking of poly(butylene succinate) (PBS) in the presence of a photoinitiator and a crosslinking agent at ambient temperature. The effects of the concentration of photoinitiator, the crosslinking agent content, and the irradiation time on the crosslink behavior were investigated. To obtain an appropriate gel fraction in different irradiation times, 3.0 wt% of photoinitiator and 10.0 wt% of crosslinking agent were proved to be the optimum choice. Furthermore, properties such as thermal properties, dynamic mechanical property, and enzymatic degradation of PBS before and after crosslinking were examined. Differential scanning calorimetry (DSC) analysis revealed that glass transition temperature (T_g) increased with increase in gel fraction, while melting temperature (T_m) and the degree of crystallinity decreased. This may be caused by the reduced molecular chain mobility and inhibited molecular motion for crystallization in crosslinked samples. The crosslinked polymer also showed improved thermal stability and dynamic mechanical property. In addition, the introduction of crosslinking retarded the enzymatic degradation rate of PBS, but it was still biodegradable. The improved properties of crosslinked PBS will extend the application of PBS. Copyright © 2009 John Wiley & Sons, Ltd.

In this exploration of novel biodegradable polyesters, multiblock copolymers based on poly(butylene succinate) (PBS) and poly(1,2-propylene terephthalate) (PPT) were successfully synthesized with hexamethylene diisocyanate as a chain extender. The amorphous and rigid PPT segment was chosen to modify PBS. The structures of the polymers were characterized using ¹H NMR and ¹³C NMR spectroscopy, gel permeation chromatography and wide-angle X-ray diffraction; the physical properties were investigated using thermogravimetric analysis, differential scanning calorimetry, mechanical testing and enzymatic degradation. The results indicate that the copolymers possess satisfactory mechanical and thermal properties, with impact strength 186% higher than that of PBS homopolymer, while tensile strength, flexural strength, thermal stability and melting point (T_m) are slightly decreased. Crystallization and biodegradation rates are still acceptable at 5 wt% PPT, although they are decreased by the introduction of PPT. The addition of appropriate amounts of PPT can improve the impact strength effectively without an obviously deleterious effect on tensile strength, flexural strength, thermal stability, T_m, crystallization rate and biodegradability. This study describes a convenient route to novel multiblock copolymers comprising crystallizable aliphatic and amorphous aromatic polyesters, which are promising for commercialization as biodegradable materials. Copyright © 2011 Society of Chemical Industry

In this article, isothermal crystallization, melting behaviors, and spherulitic morphologies of high-impact multiblock copolymers, comprising of PBS as hard segment and poly(1,2-propylene succinate) (PPSu) as soft segment with hexamethylene diisocyanate as a chain extender, were investigated. The results from differential scanning calorimetry (DSC) suggest that the two segments of multiblock copolymers are miscible in amorphous region. The crystallization kinetics were analyzed by the Avrami equation. The effect of PBS segment length as well as the introduction of PPSu segment on the crystallization kinetics and melting bebaviors of block copolymers was studied. Both crystallization rate (G) and spherulitic growth rate (g) are markedly increased with the increase of PBS segment length or decreased with the incorporation of PPSu segment. All the multiblock copolymers show the multiple melting behaviors, whose position and area depend on PBS segment length and the presence of PPSu segment. The melting peaks shift to higher temperature region with increasing PBS segment length. Spherulitic morphologies of the multiblock copolymers after being isothermally crystallized were examined by polarized optical microscopy. It is the first time to investigate the effect of one segment length on crystallization bebavior of block copolymers based on a fixed weight ratio systematically. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

A series of titanium dioxide/silicon dioxide based poly(ethylene terephthalate) (PET) polycondensation catalysts were synthesized with different Si/Ti molar ratios and various amounts of polyvinylpyrrolidone (PVP). The composition, structure, and catalytic activities of the catalysts and the properties of the PET samples catalyzed by these catalysts were characterized with thermogravimetric analysis, electron probe microanalysis, X-ray diffraction, X-ray photoelectron spectroscopy, and so forth. The results indicated that the Si/Ti molar ratios of the catalysts could be well controlled by the synthesis processes used in this study, whereas the content of PVP was influenced by the amount of titanium dioxide. The activities of the catalysts greatly depended on the Si/Ti molar ratios and coordinative effects between titanium and PVP. Some of the catalysts possessed ultrahigh activities, and the corresponding PET material had excellent properties.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

TiO₂/SiO₂ sol was intercalated into montmorillonite (MMT), which was pretreated with polyvinylpyrrolidone (PVP). A series of poly(ethylene terephthalate) (PET)/MMT hybrids were prepared using the obtained MMT as polycondensation catalysts. X-ray diffraction (XRD) results proved that MMT dispersion states could be controlled by the amount of TiO₂/SiO₂ sol that was incorporated into MMT, ranging from agglomeration to exfoliation. The crystallization behavior of PET/MMT composites synthesized in this study was characterized by differential scanning calorimeter (DSC), polarized optical microscope (POM) and scanning electron microscopy (SEM) to clarify the effects of clay treatment and its dispersion state on the crystallization behavior of the PET substrate. The results indicated that MMT treated with less PVP would retain relatively higher nucleation efficiency while when MMT containing more PVP, the nucleation effect of MMT became weaker. If MMT formed big grains within PET substrate, the disturbance of the growing crystals was negligible; but the exfoliation of MMT layers would greatly magnify the spatial constraint which would slow down the crystallization process of PET matrix. For certain exfoliated PET/MMT composites, the crystallization rate was even lower than that of pure PET though clay content was low. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

BACKGROUND: To obtain a biodegradable thermoplastic elastomer, a series of poly(ester-ether)s based on poly(butylene succinate) (PBS) and poly(propylene glycol) (PPG), with various mass fractions and molecular weights of PPG, were synthesized through melt polycondensation.

RESULTS: The copolyesters were characterized using ¹H NMR, gel permeation chromatography, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, mechanical testing and enzymatic degradation. The results indicated that poly(ester-ether)s with high molecular weights were successfully synthesized. The composition of the copolyesters agreed very well with the feed ratio. With increasing content of the soft PPG segment, the glass transition temperature decreased gradually while the melting temperature, the crystallization temperature and the relative degree of crystallinity decreased. Mechanical testing demonstrated that the toughness of PBS was improved significantly. The elongation at break of the copolyesters was 2–5 times that of the original PBS. Most of the poly(ester-ether) specimens were so flexible that they were not broken in Izod impact experiments. At the same time, the enzymatic degradation rate of PBS was enhanced. Also, the difference in molecular weight of PPG led to properties being changed to some extent among the copolyesters.

CONCLUSION: The synthesized poly(ester-ether)s having excellent flexibility and biodegradability extend the application of PBS into the areas where biodegradable thermoplastic elastomers are needed. Copyright © 2009 Society of Chemical Industry

A novel organic montmorillonite, which could act as both polycondensation catalyst of poly(ethylene terephthalate) (PET) and filler of PET/clay nanocomposites, was prepared. Original montmorillonite was first treated with different amounts of poly(vinylpyrrolidone) (PVP), and then intercalated by TiO₂/SiO₂ sol to gain polycondensation catalytic activity. The acquired clay possessed excellent thermal stability and would not degrade during the polycondensation step. PET/clay nanocomposites were prepared via in-situ polymerization using the organo-clay as polycondensation catalysts. The morphologies of the nanocomposites were characterized by X-ray diffraction and transmission electron microscope. The results indicated that the amount of PVP and TiO₂/SiO₂ sol strongly affected the dispersion state of the clay, and finally, partially exfoliated PET/clay nanocomposites were obtained. The nanocomposites had better properties than pure PET due to the incorporation of the delaminated clay layers. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers