Structure Of Polyisoprene Research Articles

Weak bases, an efficient accelerator for the RAFT of isoprene

The use of weak bases as accelerators for reversible addition-fragmentation chain transfer radical polymerization (RAFT) of isoprene is demonstrated. Adding weak bases to RAFT polymerization, the conversion of isoprene could be greatly improved and reach about 50%. The effects of weak base on the polymerization were investigated. The living and controlled character of the RAFT polymerization of isoprene was confirmed by the linear increase in molecular weight with monomer conversion, the narrow molecular weight distribution and synthesis of polyisoprene-block-polystyrene (PIP-b-PS) block copolymer. The results of 1HNMR spectroscopy show that the structure of polyisoprene (PIP) with weak bases as accelerators was the same to the structure of PIP without any accelerator. The data presented here prove that weak bases are an efficient accelerator to inhibit Diels-Alder reaction of isoprene in the RAFT polymerization.

A new approach to the study of the structure of polyisoprene obtained by cationic polymerization

The use of the T2 filter in NMR studies allowed us to separate carbon atoms by their mobility in different fragments of the macromolecular chain of polyisoprene synthesized by cationic polymerization. The NMR signals of terminal units with conjugated double bonds were identified for the first time for the “cationic” polyisoprene, which experimentally confirmed the transfer of the growing chain to the monomer in the process of cationic polymerization of isoprene.

The Effect of Sequence Structure of Polyisoprene on its Crystallization and Reinforcement

soprene can be polymerized into three types of isomeric units, cis-1, 4, trans-1, 4 and 3, 4-units. Dyad or triad sequences of these units were investigated by 13C-NMR, which the signals are assigned for the sequences as well as the special linkages, head-to-head and head-to-tail structures. The crystallization ability of polyisoprene was mainly dependent on these sequence structures and was studied in this paper, including cold crystallization and stress-induced crystallization. As a result, the samples with regular sequence structure had better crystallized ability which will be as the guidance for the polymerization.

Effects of Frequency and Sonication Time on Ultrasonic Degradation of Natural Rubber Latex

Ultrasonic degradation of fresh latex was investigated at frequencies of 20 and 25 kHz, at a constant temperature of 25o C (±1o C) to avoid temperature-related effects. The time-dependent evolution of the molecular weight of the natural rubber latex was determined using gel permeation chromatography, and its structure by means of the fourier transform infrared (FTIR) technique. A 10 minute period of sonication resulted in reduction in the molecular weight of both the 20 and 25 kHz treated samples, the lowest average molecular weight () being obtained in the case of the 25 kHz sample. The of the 25 kHz sample also decreased with increasing latex concentration. However, after 30 minutes, fluctuations had occurred in both samples with respect to the and and also the molecular weight distributions, an effect possibly explained by the competing processes of chain scission and radically-induced cross-linking of the polymer chains. The FTIR results also suggest that the structure of polyisoprene is unaltered by ultrasonic wave treatment at these frequencies.

Anisotropic Self-Assembly of Gold Nanoparticle Grafted with Polyisoprene and Polystyrene Having Symmetric Polymer Composition

Methodology to self-assemble metal nanoparticles into three-dimensional mesoscale patterns is a fundamental technique to construct functional materials. Here, we demonstrate that hybridizing an immiscible polymer pair with a metal nanoparticle allows the hybrid to self-assemble in the film, resulting in spontaneous alignment of the nanoparticles at the phase-separated interface formed by the constituent polymers. Organic-inorganic hybrids composed of polyisoprene, polystyrene, and gold nanoparticle were prepared by multistep "grafting-to" method coupled with alkyne-azide click reaction. The polymer composition can be controlled by the feed ratio of gold nanoparticle to azide ligands. The gold nanoparticle hybrid with symmetric polymer composition forms an "alternating lamellar" structure of polyisoprene and polystyrene, where the gold nanoparticles were forced into the phase-separated interfaces.

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) of polyisoprenes

Polyisoprenes (PIPs) with average molecular weights from 650 to 800,000 Da have been studied by time-of-flight secondary ion mass Spectrometry (TOF-SIMS) in the static mode. Polymer samples were bombarded by argon primary ions, and positive SIMS spectra were collected. Effects of branching and unsaturation in the polymer structure on ion formation were studied. The pendant methyl group showed little tendency to fracture as a cation. In the low mass region, CnH2n−1+ appeared to be more intense than CnH2n+1+, attributed to the double bond structure of polyisoprene. Additionally, ion formation varied as a function of polymer molecular weight. Cationized intact oligomers and fragments dominate the high mass region. Oligomer distributions were used to calculate average molecular weights for polyisoprenes. A statistical chain scission mechanism was used to qualitatively explain the formation of five clusters within a unique fragmentation pattern. Detailed studies of the cluster structure pointed out that each cluster contained several species having varied degrees of unsaturation. It is believed that double bond rearrangements occur.

Random coils of polyisoprene in solution—a small angle x-ray scattering study

We report a systematic investigation of the structure of polyisoprene in solution by means of small angle X-ray scattering (SAXS). The SAXS results show that in solution there is little long range interaction between the polyisoprene chains with the scattering function being well fitted by the random coil model.

Polymerization of isoprene in n‐heptane with triethylaluminum–titanium tetrachloride catalyst. I. Effect of Al/Ti ratio on stereoregularity, conversion, molecular weight, and molecular weight distribution

AbstractThe influence of the Al/Ti ratio of the heterogeneous Ziegler–Natta catalyst system AlEt3–TiCl4 on the isoprene polymerization in n‐heptane at 30°C in a bench scale reactor was investigated. Each batch run consisted of 50 mL isoprene, 200 mL n‐heptane with 0.45 and 0.5g catalyst. Conversion of isoprene and molecular weights of polyisoprene increased with increasing Al/Ti ratio, reaching their maxima values at 1.0 and 1.2, respectively. Conversion and molecular weights decreased remarkably at a higher ratio of Al/Ti. As this ratio decreases from the value of 1.2 to 0.4, the cis1,4 content in polyisoprene decreased from 97 to 25%. When the ratio of Al/Ti increased from 1.2 to 2.2 the cis‐1,4 structure of polyisoprene decreased from 97 to 85%.

Influence of tertiary aromatic diamines on the n‐buLi‐initiated polymerization of isoprene in hexane solution

AbstractThe influence of three aromatic tertiary diamines, bis(4‐dimethylamino phenyl) methane (DMAPM), N,N,N′,N′‐tetramethyl‐p‐phenylenediamine (p‐TMPDA), and N,N,N′,N′‐tetramethyl‐o‐phenylenediamine (o‐TMPDA), on the kinetics of polymerization of isoprene in hexane solution, with n‐BuLi as initiator, was studied for different values of ratio r = [amine]/[n‐BuLi]. It is shown that added amine increases initiation rate according to its complexing ability (DMAPM < p‐TMPDA « o‐TMPDA); this result is explained by the formation of complexes between amine A and n‐BuLi, (n‐BuLi, A)x, where x = 6, 4, and 1 for the three amines, respectively. The propagation rate and the structure of polyisoprene are modified with o‐TMPDA only; the decrease in propagation rate and the increase in 3,4 units in the polymer obtained when r increases are assigned to the formation of solvated ion pairs PI−Li+, o‐TMPDA.

Isoprene Polymerization by Catalyst Systems of Rhodium Complex and Allyl Alcohol

Abstract To prepare polyisoprene of controlled microstructure and molecular weight in emulsion systems, a series of polymerizations was carried out with catalyst systems of rhodium complexes and allyl alcohol, with variation of the type of rhodium salts, emulsifiers, and other conditions. A dramatic change in the structure of polyisoprene and also an increase of the polymer yield were brought about by the addition of sodium dodecyl sulfate and allyl alcohol, p-Toluene sulfonic acid and other strong acids exhibited an effect similar to that of the sulfate type emulsifiers on the isoprene polymerization. The degree of polymerization of polyisoprene was increased from 150 to 2000 when the amount of allyl alcohol in the system was decreased from 100 mole % to less than 10 mole % with respect to isoprene monomer. Most samples of polyisoprene prepared with above catalyst systems were found to have almost equi-binary 1,4-cis- and trans- enchainments. The effects of several phosphines and phosphites as additives on the microstructure of polyisoprene prepared with the rhodium complex systems were also examined.

Problems of the polymerization mechanism of diene hydrocarbons in the presence of cobalt catalysts

Studies were made of homogeneous polymerization of butadiene and isoprene under the effect of soluble catalytic systems prepared using Co(AlCl 4) 2. It was shown that the structure of polyisoprene formed in these processes is practically independent of both the type and concentration of the co-catalytic additive and the content of the monomer. A mechanism is proposed for the formation of various structures in the polydiene chain which is based on concepts of anti-syn-isomerization of the active centre of polymerization.

The infrared absorption spectra and structure of polyisoprene formed by polymerization on the surface of ?-TiCl3

The infrared absorption spectra and structure of polyisoprene formed by polymerization on the surface of ?-TiCl3

Radiation‐induced ionic polymerization of isoprene

AbstractThe γ‐ray‐induced polymerization of isoprene was investigated in the temperature range of ‐78° to 40°C. The following variables were studied: the dependence of polymerization rate on temperature; the effects of DPPH and pyridine on the polymerization at various temperatures; the dependence of the polymerization rate on dose rate at ‐78° and 20°C.; and the structure of the polyisoprenes obtained at various temperatures. the following results were obtained: (1) Although the Arrhenius plot of the polymerization rate did not yield a linear relation, the total polymerization rate was successfully separated into radical and ionic contributions. (2) The polymerization rate was proportional to the square root of dose rate at 20°C., whereas it was proportional to the first power of the dose rate at ‐78°C. (3) The structure of polyisoprene prepared at ‐78°C. is closely similar to that of cationically polymerized polyisoprene. The partially ionic mechanism of the radiation‐induced polymerization of isoprene was elucidated in this investigation. It was concluded that a cationic mechanism is operative at low temperatures whereas a radical mechanism predominates at higher temperatures.