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This article deals with the characterization of high trans‐1,4‐poly(butadiene) (TPBD) prepared by means of an anionic polymerization using an initiator composed of alkyl aluminum, n‐butyl lithium, and barium alkoxide. By controlling both initiator composition and polymerization temperature, a set of TPBD was prepared with well‐known number of 1,4‐trans units, molecular weight distribution, and average molecular weight. Analyses by differential scanning calorimetry and diffraction of wide‐angle X‐rays showed a direct relationship between the microstructure of the polymer and its thermal properties. By increasing the number of 1,4‐trans units (70–90%), the crystallinity of the polymer was increased (10–30%); polymers with less than 65% of 1,4‐trans units were amorphous, whereas TPBD with a number of 1,4‐trans units greater than 80% were polymorphous and presented two endothermic transitions. Summing up, the results presented in this article indicate that cyclohexane solutions of alkyl aluminum, n‐butyl lithium, and barium alkoxide allow produce polybutadienes with enough amount of 1,4‐trans units to display a regular microstructure that makes them susceptible to experience‐induced crystallization, likewise at a reaction rate similar to that observed for the commercial production of poly(butadiene) with n‐butyl lithium. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers

the advantages of undemanding condition requirements and the ability to polymerize a large number of monomers. The disadvantage of this method is poor control in both molar mass and polymer microstructure of the product.Reversible deactivation radical polymerization (RDRP) or controlled radical polymerization (CRP) techniques have received a great deal of attention because of their ability to generate materials with well-defined molar mass and microstructures. Such products include a great variety of polymers synthesized from functional monomers, which could not be created by living anionic polymerization without stringent requirements. The main CRP techniques, nitroxide-mediated polymerization (NMP), [7] atom transfer radical polymerization (ATRP), [8] and reversible addition-fragmentation chain transfer (RAFT), [9] have provided access to functional polymers with targeted molar mass, narrow molar mass distributions, and defined molecular microstructures. These properties were once thought impossible to obtain via free-radical technology.The RAFT technique is probably the most versatile of those mentioned, because it can be used with a wide range of functional monomers bearing a reactive side group (hydroxyl, carboxyl, amino, etc.), and is tolerant of water and oxygen in the system. [10][11][12] The RAFT process has been applied to a range of monomers, including vinyl, styrene, acrylates, and methacrylates, under relatively mild conditions, to produce a variety of molecular microstructures, including block copolymers, [13] star-shaped molecules, [14] and comb structures. [15] CRP of GMA by ATRP [16,17] and RAFT, [18] as well as copolymerization of GMA with styrene using NMP, [19] are already reported in the literature. Little experimentation has been carried out on RAFT copolymerization of S with GMA, and there are no reports on the synthesis of functional S-GMA copolymers by RAFT polymerization at temperatures higher than 100 °C, which is the range of interest for acrylate-based copolymers.On the other hand, controlling polymer microstructural characteristics, such as copolymer composition, copolymer sequence distribution, and molar mass distribution, is of particular importance in copolymerization processes. The estimation of monomer reactivity ratios in copolymerization studies is essential for determining polymerization rates and copoly mer sequence distributions, which support the manufacture of copolymers with the desired properties. This information is very important for selection of the reaction conditions needed to produce a desired product. On the other hand, the industrial RAFT CopolymerizationThe bulk reversible addition-fragmentation chain transfer (RAFT) copolymerization of glycidyl methacrylate (GMA) and styrene (S) at several GMA molar feed fractions in the presence of 2-cyano isopropyl dodecyl trithiocarbonate as RAFT agent and 1,10-azobis(cyclohexane carbonitrile) as initiator is reported. The reaction conditions are similar to those used in the industrial production of crystal and high-impact ...

The aim of this contribution is to assess the use poly(styrene-co-glycidyl methacrylate-b-styrene) copolymers synthesized by nitroxide mediated polymerization (NMP) as chain extenders in the recycling of poly(lactic acid) biopolyester. Concisely, the addition of such block copolymers during the melt processing of recycled poly(lactic acid) (rPLA) leads to important increases in the viscosity average molecular weight of modified polymeric materials. Molar masses increase from 31,000 g/mol for rPLA to 48,000 g mol–1 for the resulting rPLA/copolymer blends (bPLA). Fortuitously, this last value is nearly the same as the one for pristine PLA, which constitutes a first piece of evidence of the molar mass increase of the recycled biopolymer. Thermograms of chain extended rPLA show significant decreases in cold crystallization temperature and higher crystallinity degrees due to the chain extension process using NMP-synthesized copolymers. It was found that increasing epoxide content in the NMP-synthesized copolymers leads to increased degrees of crystallinity and lower cold crystallization temperatures. The rheological appraisal has shown that the addition of NMP synthesized copolymers markedly increases complex viscosity and elastic modulus of rPLA. Our results indicate that P(S-co-GMA)-b-S) copolymers act as efficient chain extenders of rPLA, likely due to the reaction between the epoxy groups present in P(S-co-GMA)-b-PS and the carboxyl acid groups present in rPLA. This reaction positively affects viscometric molar mass of PLA and its performance.

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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.

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