Abstract The unique feature of polymers is the flexibility of their long chains, achieved by rotation about their many backbone bonds, which enable them to assume an extremely large number of different Conformations. This is the source of their unique material behaviors, such as rubber‐like elasticity and their time and processing dependencies. Polymer conformations and material properties depend upon their Configurations, among which are the mode of enchainment of diene monomers, regiosequences (directions of monomer insertion), the stereosequences (stereochemical arrangements of atoms in the polymer chain), co‐monomer sequences of vinyl polymers, branches, and cross‐links. Polymer configurations cannot be altered without breaking and reforming their covalent bonds. In this article, we describe how the conformational characteristics of polymers can be rigorously treated, with account explicitly taken of their configurations, and how various conformationally averaged chain properties can be connected to the behaviors of their materials to allow improved structure–property relations. As examples, because 13 C NMR resonances depend on local polymer microstructures, the average bond conformation probabilities calculated for each microstructure can be used to assign their resonances. The applied to its dilute solution (the Kerr‐Effect) is very sensitive to the Configuration/Macrostructure of the overall polymer chain. When compared to the molar Kerr constants (mK) calculated for chains possessing the microstructures determined by 13 C NMR, the Macrostructures or complete molecular architectures of polymer chains may be revealed.

The primary plasticizers for the world’s most plasticized polymer, poly(vinyl chloride) (PVC), are organic phthalates, this despite being categorized as probable human carcinogens by the EPA. Di-2-ethylhexyl phthalate (DEHP or DOP) is such a typical PVC plasticizer. We sought to find an alternative plasticizer that lowered the glass transition temperature (Tg) and softened PVC, but was not as harmful to the environment and for our health as the currently employed phthalate plasticizers. We recently discovered that urea (U) could complex with amorphous polymers, such as atactic poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc). Compared to neat samples, the Tgs of the PMMA-U and PVAc-U complexes were increased and decreased, respectively. However, when complexed with dimethylurea (DMU), the Tg of the PMMA-DMU complex was lowered. Since Tgs of PMMA and PVAc were lowered by either U or one of its derivatives, this prompted us to investigate whether they could interact and complex with another largely amorphous polymer PVC, that is often plasticized, to soften and lower its Tg. Shifts in the vibrational frequencies observed by Fourier-Transform Infrared spectroscopy and Differential Scanning Calorimetry thermograms indicated that U, its derivative tetramethylurea (TMU)], and the related compound Acetamide (AC) were complexing with PVC. All three complexes (PVC-U, -TMU, and –AC) showed significantly lowered Tgs. Preliminary mechanical property measurements of PVC-U and PVC-AC films showed they were softer and more pliable than PVC films. Consequently, we believe our preliminary results warrant further examination of U, AC, and TMU as potential effective and less harmful PVC plasticizers.

Nanofiber technology has attracted great attention in many research and applications area because of its unique physicochemical properties and characteristics such as high surface area compared to bulk material. This property provides better cell adhesion and drug and protein loading. In addition, their fabrication from a wide range of polymers with different properties makes them excellent candidates for smart delivery systems. In this chapter, first different external stimuli-responsive nanofibers such as thermo-, magnet-, pH-, electrically-, biomolecule-, and multi-responsive are explained. Then their biomedical applications such as wound dressings, drug delivery systems, cell scaffolds, and diagnosis are discussed.

This brief review addresses the source of the dependence of copolymer glass transition temperatures (Tgps) on their comonomer sequences. Here we show that a comparison of the conformational entropies obtained from the Rotational Isomeric State (RIS) conformational models of the poly-A and poly-B homopolymers and their resultant poly-A/B co-polymers, i.e., ΔSconf = (XASA + XBSB) - SA/B (X = comonomer fraction), can be used to predict/understand the Tgps of copolymers. For copolymers with ΔSconf ~ 0, we expect their Tgps to follow Fox behavior and to depend only on copolymer composition, because of the similar conformational flexibilities of the A and B homo- and A/B-copolymers. When the conformational entropy ΔSconf is negative the A/B copolymer is assumed more flexible than the weighted sum of polymer-A and polymer-B conformational entropies, resulting in Tgps that are lower than expected from the Fox equation. Conversely, a positive ΔSconf suggests the copolymer’s lower flexibility, resulting in higher Tgps than expected from the Fox relation. We use the successful comparison of the observed dependence of numerous copolymer Tgps to demonstrate the validity of using their calculated RIS conformational entropies to predict their comonomer sequence dependencies.

Due to the promising properties of chitosan for biomedical engineering applications like biodegradability, biocompatibility, and non-toxicity, it is one of the most interesting biopolymers in this field. Therefore, Chitosan and its derivatives have attracted great attention in vast variety of biomedical applications. In the current paper, different types of chitosan-based bioadhesives including passive and active and their different types of external stimuli response structure such as thermo, pH and Light responsive systems are discussed. Different bioadhesives mechanisms with chitosan as an adhesive agent or main polymer component and some examples were also presented. Chitosan based bioadhesives and their potential biomedical applications in drug delivery systems, suture less surgery, wound dressing and hemostatic are also discussed. The results confirmed wound healing, hemostatic and bioadhesion capabilities of the chitosan bioadhesives and its great potential for biomedical applications.

Cyclodextrins (CDs) are a unique class of molecules that are naturally available via degradation of starchy molecules. Their toroidal structure and abundant presence of hydroxyl groups have given scientists exceptional leverage resulting in synthesizing novel molecules for applications ranging from food packaging, controlled release of small molecules, antibacterial coating, agriculture, and air and water filtration. With the advent of nanotechnology, CDs have positioned itself in a variety of forms such as their ability to act as capping/reducing agents for metallic nanoparticles, or form stable nanofibers or nanoparticles or nano micelles, which can be subsequently utilized for sophisticated applications. In this review, we summarize researches on the presence of CDs in various aspects of nanotechnology ranging from nanoparticles, nanorods, nanomicelles, to nanofibers. In addition, through this review, we provide state-of-the-art applications that are being carried out using these nanostructures.

The healing of wounds is still a challenging clinical problem for which an efficient and fast treatment is needed. Therefore, recent studies have created a new generation of wound dressings that can accelerate the wound healing process with minimal side effects. Chitosan, a natural biopolymer, is an attractive candidate for preparing biocompatible dressings. The biodegradability, non-toxicity, and antibacterial activities of chitosan have made it a promising biopolymer for treating wounds. Graphene oxide has also been considered by researchers as a non-toxic, inexpensive, and biocompatible material for wound healing applications. This review paper discusses the potential use of chitosan/graphene oxide composite films and their application in wound dressing and drug delivery systems.

Chitosan-based hydrogels involving gamma-cyclodextrin inclusion compounds of thyme oil were prepared by freeze-thaw cycling method. Clinoptilolite as a natural zeolite was added to investigate its effects on the structural, mechanical, and drug release behaviors of the hydrogels. Zeolite compressed the structure and improved mechanical properties, which decreased swelling values. Release of thyme oil in prepared hydrogels were investigated by UV spectroscopy and drug release mechanism was evaluated by applying various mathematical methods. Rates of water vapor transmission of the samples were calculated as 2247-2998 g m(-2)day(-1)which are all in the range of an ideal wound dressing. Hydrogels with clinoptilolite had slower drug release (from 56% to 24% for hydrogels containing zeolite 1%) in comparison with that of without zeolite. Based on MTT assay, samples were low-toxic. Obtained results suggest that drug loaded hydrogels can be applied in biomedical field including drug delivery systems and wound dressings.

Over 20 years ago we demonstrated that it is possible to control the melt crystallization of polymers via self-nucleation. Non-covalently bonded inclusion compounds (ICs) can be formed with cyclodextrins (CDs) or urea (U) when these small host molecules crystallize around guest polymers and form narrow parallel host channels, where the isolated and stretched guest polymer chains are included. Careful removal of the host crystalline lattice yields a neat coalesced (c) guest polymer sample with less entangled chains that are packed to a higher density than bulk samples of the same polymer obtained from its melt or solutions. Consequently, the reorganized c-polymer samples behave distinctly, with higher glass-transition temperatures for amorphous polymers and enhanced crystallizabilities for semi-crystalline polymers. Remarkably, c-polymer samples retain their distinct reorganized structures and behaviors even after extended periods of melt annealing. When a small amount of the rapidly crystallizable c-polymer is homogeneously dispersed in a large quantity of the same as-received (asr) polymer, and it is melted and then cooled, the c-polymer chains crystallize first and nucleate the crystallization of the asr-polymer chains, so that the entire sample (nuc-polymer) crystallizes at nearly the same temperature as the neat nucleant (c-polymer), including slow melt-crystallizing polymers, such as PET and PLLA.

In honor of Prof. Thorsteinn Loftsson’s 70th birthday, we offer this personal review of our work using cyclodextrins (CDs) complexed with a variety of active ingredients, including pharmaceuticals, for the purpose of improving their delivery to polymer materials, e.g., fibers, films, hydrogels, etc. Using the affinity of CDs to host and form non-covalent inclusion complexes (ICs) with guest molecules, including a variety of high molecular weight polymers, it is possible to readily deliver these guest molecules into polymer materials via either melt or solution processing of their crystalline or soluble guest molecule-CD-ICs or -rotaxanes. This provides the following advantages: i. CDs are non-toxic, implantable, and biodegradable and have earned the GRAS rating from the FDA. ii. Guest molecules, even those that are neat liquids, can form solid crystalline CD-ICs that are thermally stable to ~ 200 °C and above. This approach permits facile melt-processing into polymer materials for delivery without migration, loss, or degradation of the active guest ingredient. iii. For guests harmful and toxic to their users and the environment, delivery in the form of crystalline CD-ICs can limit any contact with and release of the included toxic guests before they function and are used. iv. It has been demonstrated that, by simple precipitation methods, neat as-received CDs that adopt cage crystal structures can be readily transformed to their columnar crystal structures containing only water in their channels, which can be easily displaced by small molecule, as well as polymer guests. v. Guest-CD-rotaxanes are water soluble, they protect the threaded guest from sources of degradation, and the CD hydroxyl groups may be modified to direct the guest-CD-rotaxane to specific substrates. For these reasons, here we summarize our contributions to the study of CD inclusion and delivery of a variety of guest molecules, including antibacterials, spermicides, insecticides, flame retardants, and dyes, that can more usefully functionalize polymer materials.

In a series of papers beginning in the 1950s, Flory, and later Flory and Ronca, and Yoon, Ronca, Bruckner et al. theoretically derived and described the Statistical Mechanics of rodlike particles and semi-flexible chain molecules. Their work was based on a Lattice-Model whose free-energy was separable into independent terms:a mixing term depending on concentration and an athermal disorientation term depending on the equilibrium flexibility of the chain molecules. They eventually added energetic interactions between the rodlike particles to the disorientation partition function, and also considered aromatic polyesters with mesogenic phenyl rings and attached ester bonds separated by inherently flexible polymethylene segments. To treat the thermotropic aromatic polyesters, Yoon, Ronca, Bruckner et al. added an independent conformational partition function to account for the loss of conformations required for extension of the polymethylene segments to form liquid crystals. Though these treatments achieved various degrees of agreement with experimental observations of liquid crystalline polymers, in all cases the mesogenic backbone segments were assumed to be rigid with extended conformations. Their inherent flexibilities were never considered. Here we demonstrate that the mesogenic backbone segments may in fact not be inherently rigid, but instead conformationally flexible. As an example, we show that Kevlar® [poly-1,4-phenylene (terephthalamide)] remains extended enough and sufficiently anisotropic to be liquid crystalline even though its 1,4-linked backbone phenyl rings are conformationally flexible.

While spectroscopic probes sensitive only to local polymer structures, like NMR, can identify and quantify local short-range microstructural elements, they are unable to locate their positions along the polymer backbone. The complete molecular architectures of synthetic polymers, which may be called their macrostructures, consist of the types and amounts of short-range microstructural elements they contain, such as comonomer contents and sequences, regio- and stereosequences, branches, cross-links etc., as well as their locations along the polymer backbone. Consequently, the present situation regarding our ability to characterize the complete chemical structures of synthetic polymers would be analogous to that of proteins if it were only possible to determine their amino acid compositions or possibly the amounts of consecutive pairs or even triplets of constituent amino acids. Fortunately, the DNA genome that controls the syntheses of proteins generally enables us to know their complete macrostructures, i.e., their complete amino acid sequences or primary structures. We demonstrate here that the birefringence induced by application of an electric field to a dilute solution (Kerr Effect) that is contributed by the polymer solute is macrostructurally sensitive and can begin to characterize the complete overall architectures of synthetic polymers. With their complete macrostructures in hand, we believe that for the first time relevant structure-property relations can be developed for polymer materials.

The establishment of methodologies for encapsulating polymers in small molecular hosts is not only highly desirable to facilitate new material functions but also very important for the development of fundamental science. Herein a new strategy for encapsulating noncrystalline polymer chains with bulky side groups in thiourea (TU) crystals is disclosed. In the process, the noncrystalline polymer is first complexed with TU and 1,4-dioxane molecules, forming a crystalline metastable complex structure with melting temperature below 110 degrees C. Subsequent removal of 1,4-dioxane through heating the complex at 120 degrees C collapses the metastable complexes, but surprisingly affords a polymer-TU inclusion compound (IC) structure, as demonstrated by infrared radiation, differential scanning calorimetry, and X-ray powder diffraction. The strategy is applicable to both atactic-poly (methyl methacrylate) and -polystyrene, suggesting that it might be a universal method for encapsulating noncrystalline polymer chains in thiourea crystal canals.