Structure and Properties of Model Polybutadienes - Effect of Microstructure on the Dynamic Mechanical Properties of Rubber

Abstract

A series of controlled microstructure polybutadiene rubbers (PBs) was synthesized via anionic polymerization. Their structure and properties are analyzed by means of GPC, 13 C NMR, DSC, and DMA, and compared to the behavior of some commercial high cis rubbers. Thermal analyses results indicate the presence of crystalline domains of different nature in PBs with high cis-1,4 and high trans-1,4 isomers content, while rubbers with high content of vinyl-1,2 units do not show evidence of crystals. A shift in T g to higher temperatures as vinyl content increases is observed; an expression was found for predicting T g of rubber from microstructure data.

Thermal Conductivity of Polybutadiene Rubber from Molecular Dynamics Simulations and Measurements by the Heat Flow Meter Method

“…−73 • C, indicating a slight shift in T g, DMA towards higher temperatures at an increasing degree of crosslinking, as already known from the literature [32]. This is in agreement with the published data on the glass transition temperature of polybutadiene rubbers with a different microstructure [33]. In this context, it must be noted that the glass transition temperatures obtained by dynamic scanning calorimetry (DSC) are usually ∼20 K lower than those obtained from DMA method [34].…”

Synthesis of High cis-Polybutadiene in Styrene Solution with Neodymium-Based Catalysts: Towards the Preparation of HIPS and ABS via In Situ Bulk Polymerization

“…However, as the amount of PS decreases the material begins to exhibit two melting endotherms which are associated with polymorphism (capability of a rubber to crystallize in more than one crystallographic form). In this respect, it has been reported that the first melting endotherm is related to a solid-to-solid transition from a monoclinic form to a hexagonal form, while the second melting endotherm is part of the melting of a hexagonal form [25]. Nevertheless, this has not been published before for structures (copolymers) containing principally high cis-1,4 PB.…”

Structure and Properties of Model Polybutadienes and HIPS: Effect of Rubber Microstructure on HIPS Dynamic Mechanical Properties

“…Therefore, this small relaxation is probably associated with some molecular arrangement of rubber chains. On the other hand, for both H LCTA and H LCTB relaxation associated with the rubber glass transition appears around 50 C (Figure 4); this high temperature is a consequence of the use of rubbers with low 1,4 units content, because these rubbers exhibit a higher glass transition temperature (T g ) [1].…”

“…A series of PBs with different microstructures were synthesized anionically and characterized as reported elsewhere [1]. To name them, abbreviations according to the isomer content (mole) are used: HC for high cis (>96% of cis-1,4 units); HT for high trans (>82% of trans-1,4 units); MCT for medium cis and trans (>42% of each cis and trans), and LCT for low cis and trans (<10% of each cis and trans, but >80% of vinyl-1,2 units).…”

“…S EVERAL EXPERIMENTAL AND theoretical studies have been published about high impact polystyrenes (HIPS), studies that have allowed little-by-little, the understanding of existing relationships between the structures of polybutadiene (PB) impact modifiers, their properties and, also the properties of HIPS composite materials made from them. However, there are a few works that take into account PB microstructure effect (microstructure understood as mole percentage of cis-1,4, trans-1,4, and vinyl-1,2 units present in PB polymer chains) on their dynamic mechanical properties [1] and on the dynamic mechanical properties of modified polystyrenes. Existing works [2][3][4][5][6] do not consider the different tendency of PB isomers to promote grafting, cross-linking, and crystallization inside rubber particles and the way they affect dynamic mechanical properties of HIPS, but rather focus on examining the effect of other interesting factors, such as oscillating frequency [2], degree of graft [3], particles cavitation [4], block copolymer addition [5], and rubber phase volume fraction [6].…”