Structure and performance characteristics of hyperbranched polyester-Iota

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Service > Structure and performance characteristics of hyperbranched polyester

Structure and performance characteristics of hyperbranched polyester

2.2 hyperbranched polyester modified
Hyperbranched polyester having a large number of end groups and end groups can easily be chemically modified, the nature of the end groups in the largely determine the physical and chemical properties of hyperbranched polyester, so you can get a different degree of branching by modification and hyperbranched polyester with a large number of terminal groups can be realized in different areas of application.
Modification method there are two: (1) with a short chain or small organic molecules terminated; (2) by graft polymerization activity terminated.
2.2.1 capped modified
Capping modification has three main purposes: (1) eliminate the impact of a number of functional groups in the detection of molecular weight; the impact on the hyperbranched polymer properties (2) The end of the group; (3) synthesis of novel hyperbranched polymer.
By capping modification can change the glass transition temperature of the polymer (Tg), solubility and thermal decomposition temperature (Td), can also be introduced into other functional groups, such as the double bond group, a carboxyl group and an epoxy group.
2.2.2 The end of the graft modification
Multi-arm star polymers star polymer shell structure or hyper - a hyperbranched polymer having a core in the end of the graft polymerization can be obtained. By the end of the graft modification can change some of the properties of the polymer, such as polarity, solubility and the like. Polymerizing graft-modified in three main ways: anionic polymerization, cationic polymerization and radical living polymerization.
2.3 hyperbranched polyester structure and performance characteristics
Similar to the traditional linear polyesters, hyperbranched polyester molecular chain main link group also is an ester group, but compared with the traditional linear polyesters, hyperbranched polyester with a highly branched structure, a large number of terminal functional groups, molecular Memory structural features in the cavity.
2.3.1 Composition and Structure
(1) Composition
Hyperbranched polyester composition and synthesis method, and when the use of nuclear synthesized, the molecule consists of three parts: a, initial triggering a nuclear or central core; b, the initial trigger repeat branching units composed of nuclear radial connection The inner layer; c, surface functional groups area. If you do not have nuclear monomer, the molecular structure has only repeated branching structure and a large number of end groups.
(2) structural integrity
Hyperbranched polyester present, or quasi-step-by-step method for the synthesis, there are more defective molecules.
(3) geometric symmetry
Hyperbranched polyester in the presence of structural defects, and there are a lot of holes in the branch point. Hyperbranched polyester isomers, and the number of isomers increases with the complexity and increase the polymer molecular weight monomers.
(4) The terminal functional groups
Hyperbranched polyester having a large number of terminal functional groups, which is the basis for its modification and applications, but because it has many structural defects, that the end functional groups are not all located in the outermost layer of hyperbranched polyester.
(5) molecular weight controllability
Hyperbranched polyester-step synthesis method, the molecular weight of controllability is small, but has approved one-step synthesis method can be used, be controlled by controlling the amount of added monomers.
2.3.2 Features
(1) Good flowability
In general, small molecule liquids can be regarded as Newtonian fluids, but many fluids include linear polymer melts and concentrated solutions, including not obey Newton's laws. Hyperbranched polyester molecules compact and space-like three-dimensional structure having a spherical shape, often exhibit Newtonian fluid behavior, and therefore has potential applications in rheology-modifying polymer material aspects.
(2) low viscosity
Hyperbranched polymers, linear polymers, dendrimers three structural polymer intrinsic viscosity lg (η) in comparison with the variation of the molecular weight as shown in Fig.
Hyperbranched polyester with a similar molecular structure spherical, less chain entanglement between the molecular interactions between molecules mainly from the interaction between the terminal functional groups. Therefore, with respect to the linear polyester, hyperbranched polyester having a lower melt viscosity, especially hyperbranched polyester having a non-polar end groups, lower viscosity.
(3) Multifunction
Hyperbranched polyester having a hydroxyl, carboxyl and other large terminal functional groups can be modified by giving it a wide range of functional groups
Functions.
(4) crystallization behavior
Because of hyperbranched polyester of highly branched structure, reducing the regular arrangement of molecular chains, thereby significantly reducing the crystallization behavior, typically an amorphous structure without stereotypes. For higher transparency requirements for applications, this feature hyperbranched polyester is very important.
(5) film-forming property
Hyperbranched polyesters have good flowability, easy film formation.
(6) good weatherability
Traditional linear polyester there is often a strong water sensitivity, primarily due to the molecular chain of the ester group readily hydrolyzable easily due to direct exposure to air. Highly branched structure can hyperbranched polyester molecular chain ester formed embedded, effectively prevent the direct contact with the ester group of the moisture in the air, thereby reducing the probability of the ester group hydrolysis.
2.3.3 Characterization of the hyperbranched polyester
Hyperbranched polymer having a specific structure spherical, it is difficult to find a suitable standard substance in characterizing, traditional methods and means are often obtained with a deviation of actual results. People to a series of exploration and research in the characterization of hyperbranched polyester, gained some characterization methods suitable for hyperbranched polyester.
(1) the degree of branching
The degree of branching of hyperbranched polyester, refers to a fully branching units and terminal units in all the units occupied by mole fraction, is the characterization of hyperbranched polyester structural characteristics of key parameters (the higher the degree of branching, the molecular structure of the nearly the same chemical composition of the dendrimer, the corresponding lower melt viscosity).
Hyperbranched polyester containing three kinds of repeating units of different types: terminal units (T), branching unit (D), linear unit (L), Fréchet definition of hyperbranched polymers degree of branching
DB = (ΣD + ΣT) / (ΣD + ΣT + ΣL)
Determination of the degree of branching commonly used NMR techniques.
(2) Molecular weight and its distribution
Hyperbranched polyester having a molecular weight polydispersity characteristics, wide molecular weight distribution than conventional linear polyesters.
Hyperbranched polymer molecular weight and molecular weight distribution is more difficult to characterize, generally adopt a narrow distribution polystyrene standard gel permeation chromatography (GPC). But hyperbranched polyester spherical shape, its fluid mechanics by more than half with a low molecular weight linear polyesters, and therefore determined by GPC method is much lower than the actual value, and because of hyperbranched polyester chain end with a large number of functional groups, and the solvent solvation between the polyester can also affect the hydrodynamic radius.
Matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) is a new method for determination of hyperbranched polyester, the measured results with the theoretical molecular weight very close, can be more accurately reflected the actual molecular weight hyperbranched polyester, But because this is not a tester application, most people still use the GPC method for determining the molecular weight of the hyperbranched polyester.
(3) end group content
End groups have a greater impact on the performance of hyperbranched polyester, which often determines the size of the content and application of the modified hyperbranched polyester. Hyperbranched polyester end groups of the main types of hydroxy, carboxy two categories. In addition to NMR, elemental analysis, mass spectrometry and infrared and other quantitative methods, but also to characterize the hyperbranched polyester end group content using chemical methods.
Chemical methods hyperbranched polyester end group content measured, generally need to try to extend the time or appropriate to improve chemical reaction chemical reaction temperature, so terminal functional groups react sufficiently to obtain accurate measurement results.
In addition, other properties characterizing the hyperbranched polyester, as well as elemental analysis and IR characterization structures, characterization of thermal properties DSC, TG, DMA, TMA, etc. viscometer rheological characterization properties.

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