Designing scaffolds with physical, mechanical, and biological properties like those of the extracellular matrix (ECM) of the target tissue, is the most critical challenge in tissue engineering. Ideally, proper cell proliferation can simultaneously occur with the degradation of the scaffold to finally restore and create the desired tissue within the scaffold. The use of biodegradable polymers or a combination of these polymers and ceramics, metals or carbon leads to the fabrication of scaffolds with the required properties. Thus far, different natural and synthetic polymers have been proposed for this purpose, of which aliphatic biodegradable and biocompatible polyesters as a result of their predictable and adjustable properties have been known as one of the best polymeric matrices in designing scaffolds used in tissue engineering. Due to the unique properties of these polymers, the number of research works performed on them for application in tissue engineering is increasing and therefore it is necessary to review the goals and challenges ahead. Accordingly, the present work has attempted to re-examine studies performed on widely used biodegradable aliphatic polyesters including poly(lactic acid)(PLA), poly(glycolic acid)(PGA), poly(lactic-co-glycolic acid) (PLGA), polycaprolactone (PCL), and the family of microbial polyesters of the polyhydroxyalkanoates (PHA), especially poly(hydroxybutyrate) (PHB) as well as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) copolymer. This article specially focuses on the synthetic techniques and structural, physical, mechanical, and biological properties of these polymers to overcome the challenging task of designing ECM-like scaffolds by evaluating the various physical and chemical modification methods reported in recent research papers. The present study also reviews and discusses the application of these polyesters in soft and hard tissue engineering, such as bone, cartilage, ligament, tendon, muscle, spleen, cornea, and skin.

In order to improve the toughness of glass fiber (GF) reinforced unsaturated polyester resin (UPR), low molecular weight polyisobutylene (LPIB) was selected as the toughening agent. Considering its poor thermal compatibility with UPR matrix, LPIB was first grafted by two small molecular compounds, named maleic anhydride (MAH) and glycidyl methacrylate (GMA) through the novel solvothermal method which was developed in our laboratory. And then, all of these three kinds of low modulus elastomers, including LPIB, MAH grafted polyisobutylene (LPIB-g-MAH) and GMA grafted polyisobutylene (LPIB-g-GMA) were selected to modify GF reinforced UPR (GFRUP) composites. According to the results, incorporation of small amounts of grafted LPIB contributed greatly to the improvement of the toughness of GFRUP composites because of the high flexibility of the molecular chain without obviously influencing other primary properties. Moreover, 4 wt% of elastomer was an optimal amount for promoting the mechanical properties of GFRUP composite. Compared to other liquid rubbers, LPIB-g-GMA had the best toughening effect due to its stronger effect of GMA on UPRGF system. In addition, the impact strength of the modified GFRUP composite was improved up to 2.3 order of that of the unmodified GFRUP composites when 4 wt% LPIB-g-GMA was added. Consequently, LPIB-g-GMA could be employed as an effective toughening agent to GFRUP system. The toughening mechanism, thermal behavior, thermal stability and morphology of GFRUP composite are also discussed. The morphology analysis further proved the increase in toughness through the addition of grafted LPIB.

Unsaturated polyesters because of their valuable applications and versatile preparation are the most interesting resins among the cross-linkable polymers and a huge volume of works is completed or currently running on this type of polymers. This work is of those kinds resembling the incorporation of new monomers into the ordinary unsaturated polyester resins and investigating the influence of this monomer on the resin properties. By this way the monomer, which is of interest in this work constitutes benzofuro[2,3-b] benzofuran-2,9-dicarboxylic acid. This monomer was synthesized by the authors in 1996 for first time. For polymerization, this molecule, maleic anhydride and several diols were reacted in a polycondensation reaction to yield the unsaturated resins. The produced resins were characterized subsequently by 1H NMR and IR spectra, measuring molecular weight, and inherent viscosity. On the other hand, thermal and environmental resistance (resistance to acidic and alkaline moiety) was investigated on the cured resins with styrene 30% (by weight), as are described in the paper. Their thermal and chemical stability show an acceptable range of properties.    

Nucleophilic substitution reaction of two moles of benzilic acid with terephthaloyl chloride in the presence of triethylamine hydrochloride yielded terephthalic acid bis-(carboxydiphenyl methyl) ester (TBE) as a new monomer for the preparation of polyesters. This diester-diacid (TBE) was converted to its acid chloride derivative, terephthalic acid bis-(chlorocarbonyldiphenyl methyl) ester (TBECl), using thionyl chloride. Polymerization reactions of TBECl with different aromatic diols including hydroquinone, 1,5-dihydroxy naphthalene, phenolphthalein, 1,4-dihydroxy anthraquinone, 1,8-dihydroxy anthraquinone, and bisphenol A in the presence of triethylamine hydrochloride using high temperature solution polycondensation method resulted in different polyesters. All the polymers were characterized and their physical and thermal properties such as thermal behaviour, thermal stability, solution viscosity, and solubility behaviour were studied. Polymers showed good thermal stability while the presence of bulky groups improved their solubility.

Introduction: Aromatic polyesters are certainly one of the most successful classes of high-temperature polymers. However these polymers encounter processing difficulty due to their infusibility and poor solubility in organic solvents. Therefore, more researches have been focused on maintaining considerable thermally stable and improving their solubility. These studies include: 1) Introducing rather soft segments on the main chain such as methylene and vinyl segments 2) Breaking its symmetry and regularity, thereby making crystallization impossible 3) Introducing the bulky side groups to be exempt from crystallization and 4) Destroying the hydrogen bonding by N-substitution with certain groups such as methyl.Aim: In this paper a series of novel polyesters were obtained by the solution polycondensation reaction of p-phenylene diacryloyl chloride (4) with six different of aromatic diols (5a-f) in DMAc solvent and in the presence of pyridine as a base. These polymers have a soft segment such as vinyl moiety in the main chain for improving the solubility in organic solvents in compare to aromatic polyesters. These polymers have been noticed because they can be used for preparing photosensitive liquid crystalline polymers. There are some reported papers about synthesis polyamides, polyimides, polyesters and poly (amid-co-imide) s containing p-phenylenediacrylic moiety in the main chain.Materials and Methods: All chemicals were purchased from Fluka and Merck Chemical Company. The 1H-NMR spectrum (300 MHz) was recorded on a Bruker Avance 300 spectrometer (Germany). Fourier transform infrared (FT-IR) spectra were recorded on a Galaxy series FTIR 5000 spectrophotometer (England).Results: p-Phenylenediacrylic acid (3) was prepared by the reaction of terephthal aldehyde (1) and malonic acid (2) in the presence of pyridine. The diacid (3) was then converted to p-phenylenediacryloyl chloride (4) by the reaction with thionyl chloride. Solution polycondensation reactions of diacid chloride (4) with hydroquinone (5a), 2, 7- dihydroxy naphtalene (5b), 4, 4΄-dihydroxy diphenyl sulfone (5c), bisphenol A (5d), 1, 4- dihydroxy antraquinone (5e) and phenol phethalein (5f) were carried out in DMAc solution and in the presence of pyridine as a base. The polycondensation reactions produce a series of new polyesters (6a-f) in high yields having inherent viscosity between 0.32-0.50 dL/g. The resulting polyesters were characterized by elemental analysis, viscosity measurements, thermal gravimetric analysis (TGA and DTG), differential scanning calorimetry (DSC), solubility test and FT-IR spectroscopy.Conclusion: Several new polyesters (6a-f) have been synthesized by the solution polycondensation reaction of the monomer (4) with six different of aromatic diols (5a-f) in DMAc in the presence of pyridine as a base. These new polyesters are soluble in various organic solvents and have good thermal stability. These properties can make these polyesters attractive for practical applications such as processable high-performance engineering plastics.